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Metamorphism and deformation on the northeast margin of the Shuswap metamorphic complex, Azure Lake,… Pigage, Lee Case 1979

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METAMORPHISM AND DEFORMATION ON THE NORTHEAST MARGIN OF THE SHUSWAP METAMORPHIC COMPLEX AZURE LAKE, BRITISH COLUMBIA by LEE CASE PIGAGE B . S c , U n i v e r s i t y of Wyoming, 1970 M.Sc, U n i v e r s i t y of B r i t i s h Columbia, 1973 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept t h i s t h e s i s as conforming to the req u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1978 © Lee Case Pigage, 1978 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Geological Sciences The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date January 15, 1979 i i ABSTRACT D e t a i l e d s t r u c t u r a l and p e t r o l o g i c mapping near Azure Lake, B r i t i s h Columbia provides an overview of geologic r e l a t i o n s along the northeast margin of the Shuswap Metamorphic Complex. Four phases of deformation have been recognized i n the Shuswap Complex and the adjacent lower grade metasediments of the cover sequence. The f i r s t deformation c o n s i s t s of west-verging i s o c l i n a l f o l d s plunging north and northwest. The second phase r e s u l t e d i n l a r g e upright f o l d s w i t h a shallow northwest or southeast plunge. The t h i r d and f o u r t h phases are only l o c a l l y developed as f a u l t s , f r a c t u r e s , and b r i t t l e f o l d s t rending n o r t h and n o r t h e a s t , r e s p e c t i v e l y . M i n e r a l assemblages range from g a r n e t - b i o t i t e through f i r s t s i l l i m a n i t e zones of the Barrovian f a c i e s s e r i e s . Metamorphic grade increases toward the southwest. Regional metamorphism i s a s s o c i a t e d w i t h the f i r s t phase of deformation. The Complex i s separated from the adjacent cover sequence by a f i r s t phase t e c t o n i c s l i d e . S t r u c t u r a l and metamorphic d i s c o n t i n u i t i e s across t h i s s l i d e probably r e s u l t e d from r e a c t i v a t i o n of the s l i d e surface during the second phase of deformation. Microprobe analyses have been combined w i t h l i n e a r r e g r e s s i o n techniques to o u t l i n e probable 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 i n p e l i t e s of the Complex. The regressions show that r e a c t i o n textures are p a r t l y preserved because of the exhaustion of r u t i l e as a reactant phase. Metamorphic c o n d i t i o n s i n the Complex are estimated from the mutual i n t e r s e c t i o n of experimentally s t u d i e d mineral e q u i l i b r i a . These con d i t i o n s are: P=7600 + 400 bars, T=705 + 40°C, A=0.5 + ^ . i i i Carbonate mineral assemblages i n i t i a l l y b u f f e r e d f l u i d phase compositions to high X _ values near 0.75 during metamorphism. Therefore the f l u i d CO 2 phase was not homogeneous i n composition throughout a l l rock types during metamorphism. Whole rock Rb-Sr dates of 138 + 12 Ma ( a l l f i v e samples) and 163 + 7 Ma were obtained f o r g r a n o d i o r i t e stocks i n the Azure Lake area. Two b i o t i t e - w h o l e rock + hornblende dates of 119 + 11 Ma and 77 + 20 Ma 87 86 i n d i c a t e i s o t o p i c r e s e t t i n g . I n i t i a l Sr -Sr r a t i o s vary from 0.7061 + 0.0001 to 0.7103 + 0.0002 f o r rock and m i n e r a l dates. These dated stocks cross-cut s t r u c t u r a l trends f o r the f i r s t two deformations and impose a h o r n f e l s i c contact aureole on r e g i o n a l metamorphic assemblages. Therefore r e g i o n a l metamorphism and deformation were completed by Late J u r a s s i c time. i v TABLE OF CONTENTS GENERAL INTRODUCTION 1 PAPER 1 - Metamorphic and S t r u c t u r a l R e l a t i o n s on the Northeast 3 Margin of the Shuswap Metamorphic Complex, Azure Lake, B r i t i s h Columbia A b s t r a c t 4 I n t r o d u c t i o n 6 Geologic S e t t i n g 11 St r a t i g r a p h y 14 Kaza Group 14 Isaac Formation 16 Cunningham Formation 18 Yankee B e l l e Formation 18 I n t r u s i o n s 18 Deformation/Metamorphism 19 Shuswap Deformation (P1,P2,P3) 20 Shuswap Metamorphism 33 Shuswap Summary 39 Cover Deformation (Fl,F2,F3,F4) 40 Cover Metamorphism 59 Cover Metamorphic Conditions 68 Cover Summary 71 Cover-Complex C o r r e l a t i o n 73 Regional Tectonics 77 Conclusions and Summary 79 Acknowledgments 80 Selected References 81 PAPER 2 - Metamorphic Conditions i n the Shuswap Metamorphic 105 Complex, Azure Lake, B r i t i s h Columbia A b s t r a c t 106 I n t r o d u c t i o n 108 Method of Study 110 P e l i t i c M i n e r a l Assemblages 112 Tests of E q u i l i b r i u m 113 Mi n e r a l Textures 124 Metamorphic Reactions 131 Li n e a r Regression (Table 2-19) 132 V I n t e r p r e t a t i o n 150 Metamorphic Conditions 152 K y a n i t e - S i l l i m a n i t e 157 S t a u r b l i t e - Q u a r t z-Garne t - A l 2 S i 0 5 *5 8 Mus c o v i t e - Q u a r t z - P l a g i o c l a s e - A ^ S i O ^ 160 P l a g i o c l a s e - G a r n e t - Q u a r t z - A l ^ i O ^ 169 Summary 173 Calcareous Assemblages 174 C a l c i t e - Q u a r t z - C a l c i c amphibole-Calcic pyroxene 186 Ca l c i t e - Q u a r t z - M u s c o v i t e - P l a g i o c l a s e - K - f e l d s p a r 189 C a l c i t e - Z o i s i t e - P l a g i o c l a s e 191 Summary 195 F l u i d Compositions 196 Summary 199 Acknowledgments 202 Selected References 203 Appendix 2-1 Modes and E l e c t r o n Microprobe Analyses 212 Appendix 2-2 Thermodynamic Equations 237 Fe-staurolite-Quartz-Almandine-A^SiO^ 246 Muscovite A c t i v i t y Model 248 Grossular-Kyanite-Quartz-Anorthite 252 Appendix 2-3 Standards used f o r Microprobe Analyses 256 PAPER 3 - Rb-Sr Dates f o r Gr a n o d i o r i t e I n t r u s i o n s on the 274 Northeast Margin of the Shuswap Metamorphic Complex, Cariboo Mountains, B r i t i s h Columbia A b s t r a c t 275 I n t r o d u c t i o n 276 Scope of Study 276 Results and I n t e r p r e t a t i o n 279 Conclusions 284 Acknowledgments 285 Selected References 286 Appendix 3-1 288 A n a l y t i c a l Methods 288 Petrographic D e s c r i p t i o n s 288 v i LIST OF TABLES Table 1-1 S t r a t i g r a p h y f o r the Azure Lake and McBride areas 15 1-2 R e l a t i o n of mineral growth to phases of deformation 37 i n the Shuswap Metamorphic Complex, Azure Lake, B r i t i s h Columbia 1-3 Metamorphic mineral assemblages i n the cover sequence, 62 Azure Lake, B r i t i s h Columbia 1-4 R e l a t i o n of mineral growth to phases of deformation 66 i n the cover sequence, Azure Lake, B r i t i s h Columbia 1- 5 C o r r e l a t i o n of deformation and metamorphism between the 74 Shuswap Complex and the cover sequence, Azure Lake, B r i t i s h Columbia Table 2-1 Assemblages and modes f o r p e l i t e microprobe samples 213 2- 2 Assemblages and modes f o r carbonate micrporobe samples 214 2-3 Garnet analyses from p e l i t i c samples 215 2-4 Muscovite analyses from p e l i t i c samples 218 2-5 B i o t i t e analyses from p e l i t i c samples 220 2-6 S t a u r o l i t e analyses from p e l i t i c samples 222 2-7 P l a g i o c l a s e analyses from p e l i t i c samples 223 2-8 K-feldspar analyses from p e l i t i c samples 225 2-9 I l m e n i t e analyses from p e l i t i c samples 226 2-10 C a l c i t e analyses from carbonate samples 228 2-11 P l a g i o c l a s e analyses from carbonate samples 229 2-12 K-feldspar analyses from carbonate samples 230 2-13 Muscovite and b i o t i t e analyses from carbonate samples 231 2-14 C a l c i c amphibole analyses from carbonate samples 232 2-15 C a l c i c pyroxene analyses from carbonate samples 233 2-16 Z o i s i t e analyses from carbonate samples 234 v i i Table 2-17 Sphene analyses from carbonate samples 235 2-18 S c a p o l i t e a n a l y s i s from carbonate samples 236 2-19 Regression equations f o r p e l i t i c mineral assemblages, 135 Shuswap Metamorphic Complex, Azure Lake, B r i t i s h Columbia 2-20 C a l c u l a t e d a(H 20) required f o r e q u i l i b r i a (E8,E9) to 168 pass through the estimated metamorphic c o n d i t i o n s : P_ „ , = 7600 bars, T = 705°C T o t a l 2-21 Thermodynamic parameters f o r s e l e c t e d mineral e q u i l i b r i a 243 2-22 Volume and heat ca p a c i t y data f o r s e l e c t e d m i n e rals 244 2-23 Experimental u n c e r t a i n t i e s f o r s e l e c t e d experimental 254 r e a c t i o n s t u d i e s 2-24 Standards used f o r e l e c t r o n microprobe a n a l y s i s 257 2-25 Standards used f o r garnet analyses 258 2-26 Standards used f o r muscovite and b i o t i t e analyses 259 2-27 Standards used f o r s t a u r o l i t e analyses 259 2-28 Standards used f o r p l a g i o c l a s e analyses 260 2-29 Standards used f o r K-feldspar analyses 260 2-30 Standards used f o r i l m e n i t e analyses 261 2-31 Standards used f o r c a l c i t e analyses 261 2-32 Standards used f o r c a l c i c amphibole analyses 262 2-33 Standards used f o r c a l c i c pyroxene analyses 262 2-34 Standards used f o r z o i s i t e analyses 263 2-35 Standards used f o r sphene analyses 263 2- 36 Standards used f o r s c a p o l i t e analyses 263 Table 3-1 Rb-Sr data f o r a l l analyzed samples 280 3- 2 I n t e r c e p t s and apparent ages f o r whole rock and 281 mineral separate data l i s t e d i n Table 3-1 v i i i LIST OF FIGURES Figure 1-1 Major s t r u c t u r a l elements of the Canadian C o r d i l l e r a 7 1-2 Regional geology of the Cariboo Mountains, 9 B r i t i s h Columbia 1-3 D i s t r i b u t i o n of metamorphic isograds i n the Cariboo 10 Mountains, B r i t i s h Columbia 1-4 D i s t r i b u t i o n of the d i f f e r e n t s t r u c t u r a l domains 12 i n the Azure Lake area 1-5 D i s t r i b u t i o n of metamorphic zones i n the Azure Lake area 13 1-6 I s o c l i n a l PI minor f o l d i n the Shuswap Complex near 21 Azure Lake 1-7 Large PI i s o c l i n a l f o l d i n i n t e r l a y e r e d s c h i s t and 22 q u a r t z i t e 1-8 Equal area stereographic p r o j e c t i o n s of poles to P0 25 compositional l a y e r i n g and PI a x i a l plane s c h i s t o s i t y i n the Shuswap Complex (Azure Lake area) 1-9 Equal area stereographic p r o j e c t i o n s of PI minor f o l d 27 s t r u c t u r e s i n the Shuswap Complex (Azure Lake area) 1-10 P2 minor f o l d i n i n t e r l a y e r e d s c h i s t and q u a r t z i t e 29 1-11 I s o c l i n a l PI minor f o l d r e f o l d e d around a P2 minor f o l d 30 1-12 Equal area stereographic p r o j e c t i o n s of P2 minor f o l d 32 s t r u c t u r e s i n the Shuswap Complex (Azure Lake area) 1-13 D i s t r i b u t i o n of p e l i t i c metamorphic m i n e r a l assemblages 35 c o n s t r a i n i n g the l o c a t i o n of the i s o g r a d between the k y a n i t e - s i l l i m a n i t e and the s i l l i m a n i t e metamorphic zones 1-14 Large F l f o l d hinge i n i n t e r l a y e r e d p h y l l i t e and q u a r t z i t e 42 1-15 I s o c l i n a l F l minor f o l d s i n i n t e r l a y e r e d s c h i s t and 43 q u a r t z i t e 1-16 Equal area stereographic p r o j e c t i o n s of poles to F0 46 compositional l a y e r i n g i n the cover sequence (Azure Lake area) 1-17 Equal area stereographic p r o j e c t i o n s of poles to F l a x i a l 48 plane s c h i s t o s i t y i n the cover sequence (Azure Lake area) i x F igure 1-18 Equal area stereographic p r o j e c t i o n s of F l minor 51 f o l d s t r u c t u r e s i n the cover sequence (Azure Lake area) 1-19 F2 minor f o l d s i n i n t e r l a y e r e d p h y l l i t e and marble 52 1-20 Equal area stereographic p r o j e c t i o n s of F2 minor 54 s t r u c t u r e s i n the cover sequence (Azure Lake area) 1-21 I s o c l i n a l F l f o l d s i n s c h i s t and q u a r t z i t e are 56 c o a x i a l l y r e f o l d e d around F2 f o l d s 1-22 Equal area stereographic p r o j e c t i o n s of s t r u c t u r a l 58 elements i n the cover sequence (Azure Lake area) 1-23 F4 minor f o l d s developed i n slabby q u a r t z i t e s of 60 the Yankee B e l l e Formation 1-24 Schematic AFM p r o j e c t i o n s of p e l i t i c m i n e r a l 64 assemblages i n the Kaza Group f o r the d i f f e r e n t metamorphic zones i n the cover sequence, Azure Lake, B r i t i s h Columbia 1-25 Experimental r e a c t i o n s d e f i n i n g pressure-temperature 70 c o n d i t i o n s i n the cover sequence during r e g i o n a l metamorphism (Azure Lake area) Figure 2-1 Major s t r u c t u r a l elements of the Canadian C o r d i l l e r a 109 2-2 Metamorphic zones i n the Shuswap Complex, Azure Lake, 111 B r i t i s h Columbia 2-3 Stereoscopic p r o j e c t i o n s of analyzed p e l i t i c 116 assemblages c o n t a i n i n g k y a n i t e 2-4 Stereoscopic p r o j e c t i o n s of analyzed p e l i t i c 118 assemblages c o n t a i n i n g k y a n i t e and s i l l i m a n i t e 2-5 Stereoscopic p r o j e c t i o n s of analyzed p e l i t i c 120 assemblages c o n t a i n i n g s i l l i m a n i t e 2-6 Fe-Mg d i s t r i b u t i o n diagram f o r garnet and b i o t i t e 121 2-7 P l o t of (X.. )„ vs. (X„ )_, . T 122 TJa Muscovite Ca P l a g i o c l a s e 2-8 Chemical zoning pa t t e r n s of s e l e c t e d garnets 127 2-9 Displaced e q u i l i b r i u m curves E4, E5 f o r p e l i t e 159 assemblages, Azure Lake, B r i t i s h Columbia Figure 2-10 Displaced e q u i l i b r i u m curves (E9) f o r the assemblage 162 m u s c o v i t e - q u a r t z - p l a g i o c l a s e - s i l l i m a n i t e w i t h a(H 20) =1.0 2-11 I n t e r s e c t i o n of e q u i l i b r i a E4 and E8 f o r s e v e r a l 163 d i f f e r e n t reduced R^O a c t i v i t i e s 2-12 V a r i a t i o n s i n the P-T-a(H 20) p o s i t i o n of the 165 i n t e r s e c t i o n of e q u i l i b r i a E4 and E8 2-13 I n t e r s e c t i o n of e q u i l i b r i a ( E l ) , (E4,E5), and 167 (E8,E9) f o r the f i v e samples c o n t a i n i n g the assemblage mu s c o v i t e - q u a r t z - p l a g i o c l a s e -s t a u r o l i t e - g a r n e t - A ^ S i O ^ 2-14 Displaced p o s i t i o n of e q u i l i b r i u m E10 f o r sample 82 171 2-15 Displaced e q u i l i b r i u m curves E10 f o r a l l 12 172 analyzed p e l i t e samples 2-16 Calcareous reactant and product assemblages f o r 177 carbonate mineral e q u i l i b r i a 2-17 I s o b a r i c T-X(C0 2) diagram f o r the system CaO-MgO- 182 A l 2 0 3 - S i 0 2 - H 2 0 - C 0 2 2-18 Displaced e q u i l i b r i u m curves E17 i n an i s o b a r i c 188 T-X(C0 2) diagram f o r samples 20, 224, and 2-312 2-19 Displaced e q u i l i b r i u m curves E14 f o r samples 387 and 69 190 2-20 P o l y b a r i c Temperature-X(C0 2) diagram f o r the 193 assemblage c a l c i t e - z o i s i t e - p l a g i o c l a s e -t s c h e r m a k i t i c amphibole-calcic pyroxene-quartz 2-21 P o l y b a r i c Temperature-X(C0 2) diagram f o r the assemblage c a l c i t e - m u s c o v i t e - q u a r t z - K - f e l d s p a r -p l a g i o c l a s e - z p o s i t e i n sample 387 194 2-22 Compositions of metamorphic f l u i d phase c o e x i s t i n g 198 w i t h graphite i n the sytem C-O-H at P„ „ , = 7600 bars, T - 727 °C T ° t a l 2-23 Experimental r e v e r s a l s and c a l c u l a t e d e q u i l i b r i a 247 curves f o r E4 and E5 2-24 White mica composition i n terms of four end-member 250 components 2-25 Experimental r e v e r s a l s f o r e q u i l i b r i u m E10 253 (Hariya and Kennedy 1968) x i Figure 3-1 Index map of s o u t h - c e n t r a l B r i t i s h Columbia 277 3-2 Geologic sketch map of study area, Wells Gray 278 P r o v i n c i a l Park, B r i t i s h Columbia 3-3 Isochron diagram f o r b i o t i t e - w h o l e rock + 282 hornblende isochrons l i s t e d i n Table 3-2 3-4 D e t a i l of area shown i n Figure 3-3 283 x i i LIST OF PLATES P l a t e 1-1 86 A) S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex B) S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex P l a t e 1-2 88 A) S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex B) S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex P l a t e 1-3 90 S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex P l a t e 1-4 92 A) S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex B) S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex P l a t e 1-5 94 S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex P l a t e 1-6 96 A) S c h i s t from the s t a u r o l i t e - k y a n i t e zone, cover sequence B) P h y l l i t e from the g a r n e t - b i o t i t e zone, cover sequence P l a t e 1-7 98 A) P h y l l i t e from the g a r n e t - b i o t i t e zone, cover sequence B) P h y l l i t e from the g a r n e t - b i o t i t e zone, cover sequence P l a t e 1-8 100 P h y l l i t e from the g a r n e t - b i o t i t e zone, cover sequence P l a t e 1-9 102 A) PI minor f o l d s i n i n t e r l a y e r e d s c h i s t and q u a r t z i t e , Shuswap Complex (Azure Lake area) B) F3 minor f o l d hinge i n p h y l l i t e P l a t e 1-10 104 A) F3 minor f o l d hinges i n p h y l l i t e B) Graded bedding i n f e l d s p a t h i c ' g r i t s ' of the Kaza Group P l a t e 2-1 265 A) S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex B) S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex P l a t e 2-2 267 A) S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex B) S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex x i i i P l a t e 2-3 S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex P l a t e 2-4 S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex P l a t e 2-5 A) C o e x i s t i n g c a l c i c amphibole, c a l c i c pyroxene, q u a r t z , and c a l c i t e from a discontinuous marble u n i t i n the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex B) C o e x i s t i n g muscovite, quartz, and c a l c i t e from a small marble u n i t i n the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex P l a t e 4-1 Geology, Azure Lake, B.C. P l a t e 4-2 S t r u c t u r a l geology, Azure Lake, B.C. P l a t e 4-3 Geology, Azure Lake, B.C. 269 271 273 pocket pocket pocket P l a t e 4-4 S t r u c t u r a l geology, Azure Lake, B.C. pocket xiv ACKNOWLEDGMENTS This study has benefited from the support and comments of numerous people. Although space doesn't permit recognition of a l l contributors, several people have made my years here most enjoyable. I am indebted to Dr. H.J. Greenwood for his consistent interest and enthusiasm while supervising the study. His patience during times of slow progress was also helpful. Discussions with Dr. T.H. Brown were useful i n debugging problems associated with the electron microprobe and the thermodynamics of fluids and solids. The structural interpretation was improved by discussions with Dr. J.V. Ross. Other interested contributors were Dr. R.L. Armstrong, Dr. P.B. Read, Dr. R.B. Campbell, and Dr. B. Ryan. B. Hall, P. Marcello, and N. Duncan were able f i e l d assistants during the three summer seasons. G.E. Montgomery and basement crew provided technical advice both i n work and recreation. K. Scott helped with the maze of act i v i t i e s in the geochronology lab. J. Nelson provided much needed moral support and helped me survive through the perils of convoluted geologic arguments. Field and laboratory expenses were covered by NRCC 67-4222 to Dr. H.J. Greenwood. Lab expenses for the Rb-Sr geochronology were partly supported by NRCC 67-8841 to Dr. R.L. Armstrong. During the course of this study I was supported by graduate research fellowships sponsored by the National Science Foundation and the International Nickel Company. 1 GENERAL INTRODUCTION The Shuswap Metamorphic Complex forms a metamorphic core complex w i t h i n the Omineca C r y s t a l l i n e B e l t i n southeastern B r i t i s h Columbia. I t i s c h a r a c t e r i z e d by s i l l i m a n i t e - b e a r i n g p e l i t e s and polyphase defor-mation. Near Azure Lake, B r i t i s h Columbia the margins of the Complex contain a r a p i d metamorphic t r a n s i t i o n from g a r n e t - b i o t i t e zone to s i l l i m a n i t e zone i n the Ba r r o v i a n f a c i e s s e r i e s . This study presents the r e s u l t s of a d e t a i l e d p e t r o l o g i c - s t r u c t u r a l i n v e s t i g a t i o n of the northeast margin of the Shuswap Complex near Azure Lake, B r i t i s h Columbia. I t provides a "window" on the deformation and metamorphic marginal r e l a t i o n s of a high grade metamorphic core complex. The r e s u l t s of t h i s study are presented i n three complementary papers. These papers discuss r e l a t e d facets of the marginal r e l a t i o n s . The lar g e s c a l e maps contained i n the pocket (plates 4-1 through 4-4) should be used when reading each of the three papers. The f i r s t paper provides a general overview of metamorphism and deformation of the Shuswap Complex and the adjacent lower grade metasediments. Deformation s t y l e s and trends, metamorphic assemblages, and the r e l a t i o n of metamorphism to deformation are presented. This paper a l s o discusses the nature of the contact s e p a r a t i n g the Complex from the lower grade metasediments. The metamorphic and t e c t o n i c patterns are then r e l a t e d to the r e g i o n a l t e c t o n i c framework. The second paper presents a d e t a i l e d d i s c u s s i o n of metamorphic c o n d i t i o n s w i t h i n the Shuswap Complex near Azure Lake, B r i t i s h Columbia. E l e c t r o n microprobe analyses are combined w i t h l i n e a r r e g r e s s i o n techniques to o u t l i n e probable 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 i n the p e l i t i c 2 assemblages. Pressure-temperature-a conditions f o r the p e l i t e s during H 2 ° metamorphism are estimated by a d j u s t i n g published experimental mineral e q u i l i b r i a s t u d i e s f o r the e f f e c t s of s o l i d s o l u t i o n . These estimated c o n d i t i o n s are then used to study b u f f e r i n g of f l u i d phase compositions during metamorphism by mineral assemblages i n p e l i t e and carbonate u n i t s . The t h i r d paper presents the r e s u l t s of Rb-Sr r a d i o m e t r i c d a t i n g of g r a n o d i o r i t i c i n t r u s i o n s i n the Azure Lake area. These i n t r u s i o n s postdate r e g i o n a l s t r u c t u r a l and metamorphic patterns i n the surrounding metasediments. A Rb-Sr date of 163 + 7 Ma i n d i c a t e s that the deformation and metamorphism described i n the two e a r l i e r papers was completed by Late J u r a s s i c time. 3 Metamorphic and S t r u c t u r a l R e l a t i o n s on the Northeast Margin of the Shuswap Metamorphic Complex, Azure Lake, B r i t i s h Columbia Lee C. Pigage Department of G e o l o g i c a l Sciences U n i v e r s i t y of B r i t i s h Columbia Vancouver, B r i t i s h Columbia V6T 1W5 Canada 4 ABSTRACT Four phases of deformation have been recognized i n the Shuswap Complex and adjacent lower grade metasediments of the cover sequence. The e a r l i e s t deformation ( P l - F l ) c o n s i s t s of west-verging i s o c l i n a l f o l d s plunging north and northwest. These f o l d s are accompanied by a pervasive a x i a l plane s c h i s t o s i t y . The second phase of deformation (P2-F2) r e s u l t e d i n l a r g e u p r i g h t f o l d s w i t h a shallow northwest or southeast plunge. The t h i r d and f o u r t h phases of deformation c o n s i s t of l a t e f a u l t s , f r a c t u r e s , and b r i t t l e f o l d s which trend north and n o r t h e a s t , r e s p e c t i v e l y . M i n e r a l assemblages on the northeast margin of the Complex range from g a r n e t - b i o t i t e through f i r s t s i l l i m a n i t e zones of the B a r r o v i a n f a c i e s s e r i e s . Metamorphic grade increases toward the southwest. Regional metamorphism i s a s s o c i a t e d w i t h the P l - F l phase of deformation. M i n e r a l tex t u r e s and i n c l u s i o n t r a i l p atterns i n d i c a t e that metamorphic r e c r y s t a l l i z a t i o n o u t l a s t e d the P l - F l deformation. The Shuswap Complex i s separated from the cover sequence by a t e c t o n i c s l i d e r e l a t e d to the geometry of major P l - F l i s o c l i n a l f o l d s . Estimated metamorphic c o n d i t i o n s on e i t h e r side of the s l i d e zone i n d i c a t e the presence of a 100°C temperature d i s c o n t i n u i t y across the s l i d e . S i m i l a r l y , o r i e n t a t i o n s of P l - F l minor s t r u c t u r e s are discordant across t h i s s l i d e . S t r u c t u r a l discordance and the temperature d i s c o n t i n u i t y are r e l a t e d to complex movement along the s l i d e w i t h at l e a s t part of the movement being r o t a t i o n a l . R o t a t i o n probably r e s u l t e d from r e a c t i v a t i o n of the s l i d e s u rface during the second phase (P2-F2) f o l d i n g . Late J u r a s s i c plutons cross-cut minor s t r u c t u r e s a s s o c i a t e d w i t h the P l - F l and P2-F2 deformations and impose a contact h o r n f e l s i c aureole on the 5 r e g i o n a l metamorphic assemblages. Regional deformation and metamorphism were ther e f o r e completed by Late J u r a s s i c time. The l a r g e s c a l e a n t i c l i n o r i a and s y n c l i n o r i a i n the Cariboo Mountains are c o r r e l a t e d w i t h the P2-F2 deformation. 6 INTRODUCTION The Shuswap Metamorphic Complex forms the core of the Omineca C r y s t a l l i n e B e l t i n southeastern B r i t i s h Columbia, Canada ( f i g u r e 1-1). I t i s defined by the s i l l i m a n i t e i sograd and i s c h a r a c t e r i z e d by polyphase deformation (R.B. Campbell 1977). Metasediments ranging i n age from Hadrynian (Windermere) to l a t e T r i a s s i c are i n v o l v e d i n the deformation and metamorphism (K.V. Campbell 1971; R.B. Campbell and Tipper 1971). Gneiss domes cored by r e a c t i v a t e d Hudsonian basement are r e g u l a r l y spaced along the eastern margin of the Complex (Ross 1968; Wanless and Reesor 1975). This paper presents the r e s u l t s of a d e t a i l e d s t r u c t u r a l - p e t r o l o g i c study of the northeast margin of the Shuswap Complex near Azure Lake, B r i t i s h Columbia. I t provides an overview of marginal r e l a t i o n s of a metamorphic core complex. Deformation s t y l e s and t r e n d s , metamorphic assemblages, and the r e l a t i o n of deformation to metamorphism are presented f o r the Complex and f o r the adjacent lower grade metasediments. I t i s shown that there i s no d i s c e r n i b l e d i f f e r e n c e i n metamorphic and t e c t o n i c p a t t e r n s across the marginal boundary although the Complex i s separated from the lower grade rocks by a syn t e c t o n i c f a u l t zone. A d e t a i l e d d i s c u s s i o n of metamorphic c o n d i t i o n s w i t h i n the Shuswap Complex near Azure Lake i s presented elsewhere (Pigage 1978, t h i s volume). The Azure Lake area i s o u t l i n e d i n f i g u r e s 1-2 and 1-3. I t i s l o c a t e d i n the Cariboo Mountains north of Clearwater, B r i t i s h Columbia. T o t a l r e l i e f i n the area i s approximately 1800 m (6000 f t ) . D e t a i l e d geologic mapping (1 i n = 1000 f t ) was completed during the summers of 1972 and 1973. In 1975 mapping (1 i n = 0.5 mi) was extended to the northwest to c o r r e l a t e the d e t a i l e d area w i t h r e g i o n a l s t r a t i g r a p h y and s t r u c t u r e . 7 Figure 1-1. Major s t r u c t u r a l elements of the Canadian C o r d i l l e r a . Figures 2 and 3 are i n d i c a t e d by the pa r a l l e l o g r a m . Shuswap Metamorphic Complex corresponds to the r u l e d area. M o d i f i e d from Wheeler and G a b r i e l s e (1972). Figure 1-2. Regional geology of the Cariboo Mountains, B r i t i s h Columbia. The area of study i s j u s t north of Azure Lake. M o d i f i e d from Wheeler, R.B. Campbell, Reesor, and Mountjoy (1972). LEGEND JURASSIC r + + +, + + + f r+ + + + + t + GRANODIONTE TO QUARTZ DIORITE UPPER TRIASSIC to MIDDLE JURASSIC DOMINANTLY VOLCANIC-CLASTIC ROCKS UPPER TRIASSIC UTS s I " Unnamed unit-BLACK PHYLLITE, ARGILLITE, MINOR LIMESTONE DEVONIAN (?) and MISSISSIPPIAN . D . M . S . ' | Slide Mountain Group-PILLOW BASALT, ARGILLITE, CHERT, CONGLOMERATE, LIMESTONE PRECAMBRIAN and CAMBRIAN " P € - E C Cariboo Group-INTERBEDDED PHYLLITE, QUARTZITE, MARBLE PRECAMBRIAN P € K | Kaza Group - INTERBEDDED PHYLLITE, QUARTZITE,'GRIT', MINOR MARBLE UNKNOWN GRANITIC GNEISS OF UNKNOWN AGE 9 121" W I20 " W SILLIMANITE STAUROLITE-KYANITE GARNET BIOTITE and CHLORITE Figure 1-3. D i s t r i b u t i o n of metamorphic isograds i n the Cariboo Mountains, B r i t i s h Columbia. M o d i f i e d from Wheeler, Campbell, Reesor, and Mountjoy (1972). o 11 In t o t a l , f i v e months were spent i n the Azure Lake area. Previous work c o n s i s t s of the four-mile r e g i o n a l c o m p i l a t i o n by R.B. Campbell (1963, 1968). D e t a i l e d s t u d i e s on po r t i o n s of the Complex to the west have been completed by K.V. Campbell (1971) and F l e t c h e r (1972). GEOLOGIC SETTING Figures 1-2 and 1-3 i l l u s t r a t e the r e g i o n a l geology along the northern margin of the Shuswap Complex. Northwest-plunging a n t i c l i n o r i a and s y n c l i n o r i a o u t l i n e a general t r a n s i t i o n to higher s t r u c t u r a l and s t r a t i g r a p h i c l e v e l s "down plunge" to the northwest (R.B. Campbell 1970). S t r u c t u r a l l y t h i s t r a n s i t i o n i s marked by the successive replacement of i s o c l i n a l polyphase f o l d s f i r s t by a t r a n s i t i o n zone of up r i g h t f o l d s and then by a b r i t t l e zone of t i l t e d f a u l t e d b l o c k s w i t h l o c a l f o l d s . Concomitantly metamorphic grade decreases r a p i d l y from s i l l i m a n i t e zone to c h l o r i t e zone ( f i g u r e 1-3). Generally metamorphic grade i s higher i n a n t i c l i n o r i a r e l a t i v e to adjacent s y n c l i n o r i a . The Azure Lake area c o n s i s t s of two structural-metamorphic provinces separated by a composite f a u l t zone which g e n e r a l l y d i p s at moderate angles to the north or northeast ( f i g u r e 1-4). I n d i v i d u a l f a u l t s i n t h i s zone formed together w i t h or l a t e r than the r e g i o n a l metamorphism and p e n e t r a t i v e deformation w i t h i n the area. The provinces d i f f e r i n both s t r u c t u r a l trend and metamorphic grade. Metamorphic grade i n the Azure Lake area ranges from g a r n e t - b i o t i t e to f i r s t s i l l i m a n i t e zones i n the Barrovian f a c i e s s e r i e s (Miyashiro 1961). Both metamorphic grade and g r a i n s i z e increase toward the southwest ( f i g u r e 1-5). Since the s i l l i m a n i t e i sograd i s g e n e r a l l y c o i n c i d e n t w i t h Figure 1-4. D i s t r i b u t i o n of the d i f f e r e n t s t r u c t u r a l domains i n the Azure Lake area. Province 1 corresponds to the Shuswap Metamorphic Complex, and province 2 i s the adjacent lower grade cover sequence. Figure 1-5. D i s t r i b u t i o n of metamorphic zones i n the Azure Lake area. The d e t a i l e d area shown i n Figure 1-13 i s c i r c l e d . 1 4 the fault zone separating the two provinces, the Shuswap Complex corresponds to province 1. Province 2 consists of the adjacent lower grade metasediments; in the following discussion province 2 i s referred to as the cover sequence. STRATIGRAPHY The stratigraphic framework and correlations for the Azure Lake area are based on studies by Holland (1954), Sutherland Brown (1957, 1963), and R.B. Campbell (1963, 1968). Recent work in the McBride area (see figure 1-2) by R.B. Campbell, Mountjoy, and Young (1973) has c l a r i f i e d stratigraphic problems resulting from poor exposure and complex structural relations in the other areas. The stratigraphic column presented in table 1-1 is based upon type sections from the McBride area. Units mapped informally near Azure Lake are included in the table for comparison. The detailed area of study contains Hadrynian metasediments of the Kaza and Cariboo Groups. The sequence represents miogeoclinal shelf deposits in a shallow to deep marine environment (R.B. Campbell, Mountjoy, and Young 1973). Textural relations and facies changes in the McBride area suggest a northeastern cratonic source for the sediments. Original stratigraphic thicknesses in the Azure Lake area cannot be readily estimated because of intense folding and flattening during deformation. Kaza Group The Kaza Group (Sutherland Brown 1963) i s the oldest unit exposed in the Cariboo Mountains. It consists largely of feldspathic grits with intercalated quartzites, gray to green phyllites, and minor marble. Its Table 1-1. S t r a t i g r a p h y f o r the Azure Lake and McBride areas. M c B R I D E A R E A A Z U R E L A K E A R E A C a m p b e l l , Mountjoy, Young (1973) P i g a g e (this s t u d y ) Y A N K E E B E L L E F M Y A N K E E B E L L E FM interbedded shale, s i l tstone, i n t e r l a y e r e d q u a r t z i t e and and l imestone -, m inor p h y l i i t e ; minor l imestone sandstone and dolostone CUNNINGHAM F M CUNNINGHAM FM LU dno l i m e s t o n e , d o l o s t o n e , s h a l e , s i l t s t o n e , and sandstone OUP l imestone with minor dolostone and phy l i i t e rr or or m a r k e r - s i l v e r y phyl i i te + LU e> mass ive white l imestone DERI Upper dark gray phyl l i t i c shale Upper a l t e r n a t i n g phyl i i te and (WINI BOO with minor arg i l laceous l imestone BOO l imestone - t rans i t iona l to Cunningham Fm (WINI or < WIATIOI ARI TIOls Middle res is tant , rus t -weather ing , o WIATIOI o <i dark gray phy l i i te < O M i d d l e or o Lower u. l e n s o i d , m a s s i v e u. s i l v e r y g reen phy l i i te > ISAAC l imestone cong lomerate i n t e r l a y e r e d wi th DR ISAAC l imes tone ; minor q u a r t z i t e DR ISAAC Lower gray to black phy l i i te AAC < ISAAC with minor s i l t s tone , X sandstone, and l imestone K A Z A GROUP K A Z A GROUP al ternat ing fe ldspath i c 'gr i ts ' and inter layered fe ldspath i c ' g r i t s ' , gray phyl i i te or sch is t minor phyl i i te or s c h i s t , a n d m a s s i v e l imestone and cong lomera te q u a r t z i t e j m i n o r l imestone and c a l c a r e o u s q u a r t z i t e 16 thickness has been estimated to exceed 3700 m (12000 f t ) w i t h the base unexposed (Sutherland Brown 1963). In the Azure Lake area the Kaza Group i s the only u n i t to occur i n both s t r u c t u r a l p r o v i n c e s . In the Shuswap Complex (province 1) i t c o n s i s t s of i n t e r c a l a t e d massive q u a r t z i t e s and coarse s c h i s t s . I n d i v i d u a l u n i t s range from 2 cm to more than 15 m i n thi c k n e s s . G r i t s are uncommon although q u a r t z i t e s commonly conta i n s c a t t e r e d white f e l d s p a r porphyroblasts. Discontinuous marble u n i t s up to 30 m t h i c k are s p a r s e l y d i s t r i b u t e d throughout the sequence. Thin c a l c - s i l i c a t e bands c o n t a i n i n g hornblende and garnet s c a t t e r e d i n a q u a r t z - p l a g i o c l a s e m a t r i x are common. Amphibolite bands occur only r a r e l y . Southwest of Ovis Creek the sequence has been d i s t u r b e d by numerous pegmatite i n t r u s i o n s . In the cover sequence the Kaza Group c o n s i s t s of i n t e r l a y e r e d pale green q u a r t z i t e and s i l v e r y green p h y l l i t e . I n d i v i d u a l u n i t s range from a few cm to greater than 5 m i n thicknes s . F e l d s p a t h i c g r i t s are common; c l a s t s i n c l u d e c l e a r quartz, blue opalescent quartz, p l a g i o c l a s e , and r a r e m i c r o c l i n e . Many of the g r i t horizons are graded and provide i n d i c a t o r s of s t r a t i g r a p h i c "tops" ( p l a t e 1-10B). Minor amounts of micaceous marble occur throughout the sequence. Thicknesses of marble u n i t s are h i g h l y v a r i a b l e . Thin (5 cm) c a l c - s i l i c a t e bands c o n s i s t i n g of hornblende and garnet i n a q u a r t z - p l a g i o c l a s e m a t r i x are common. Rare t h i n amphibolite bands are a l s o present. Isaac Formation The Isaac Formation (Sutherland Brown 1963) conformably o v e r l i e s the Kaza Group. With a measured thickness greater than 1200 m (4000 f t ) i n the McBride area, t h i s u n i t c o n s i s t s dominantly of calcareous gray p h y l l i t e i n t e r c a l a t e d w i t h s i l v e r y p h y l l i t e , micaceous gray limestone, and minor 17 q u a r t z i t e (R.B. Campbell, Mountjoy, and Young 1973). In the Azure Lake area the Isaac Formation has been i n f o r m a l l y d i v i d e d i n t o three l i t h o l o g i c a l l y d i s t i n c t members. The three u n i t s i n the eas t e r n part of the area are estimated to have the f o l l o w i n g t h i c k n e s s e s : lower member (610-700 m), middle member (30-180 m), upper member (30-150 m) . Although not i n d i c a t i v e of o r i g i n a l t h i c k n e s s , these estimates i n d i c a t e that the lower u n i t i s s u b s t a n t i a l l y t h i c k e r than the other two. The lower member c o n s i s t s dominantly of f i n e - g r a i n e d s i l v e r y green p h y l i i t e which i s c o l o r banded on a sc a l e of 1-2 cm. The lower contact has been defined as the top of the l a s t massive, pale green q u a r t z i t e of the Kaza Group. Minor l i g h t tan q u a r t z i t e s occur i n the lower p o r t i o n of t h i s u n i t . I n t e r l a y e r e d w i t h the p h y l i i t e are brown nodular marble, pale white to gray marble c o n t a i n i n g white c a l c i t e s t r i n g e r s , micaceous gray to brown marble, and f i n e l y interbanded p h y l i i t e and sandy r e d d i s h marble. I n d i v i d u a l u n i t s are up to 25 m t h i c k w i t h l a r g e v a r i a t i o n s i n t h i c k n e s s o c c u r r i n g along s t r i k e . These calcareous l i t h o l o g i e s occur mainly i n the lower p o r t i o n of t h i s member. The middle member c o n s i s t s of a f i n e - g r a i n e d gray to b l a c k p h y l i i t e which weathers to a deep r u s t y - r e d c o l o r . This u n i t i s r e s i s t a n t and commonly forms sharp angular r i d g e s . P y r i t e and p y r r h o t i t e are the only macroscopic m i n e r a l s . The upper member i s t r a n s i t i o n a l to the o v e r l y i n g Cunningham Formation. I t c o n s i s t s of t h i n l y banded s i l v e r y p h y l i i t e a l t e r n a t i n g w i t h pink-weathering sandy marble. I n d i v i d u a l l a y e r s are 0.2-1.0 cm t h i c k . The upper contact w i t h the Cunningham Formation has been defined as the base of the f i r s t massive, gray marble u n i t . 18 Cunningham Formation The Cunningham Formation (Holland 1954) i s over 550 m (1800 ft) thick at the type section. It consists dominantly of limestone with lesser amounts of dolostone, shale, siltstone, and sandstone (R.B. Campbell, Mountjoy, and Young 1973). In the Azure Lake region the middle portion of the formation consists of gray, massive to slabby marble with minor discontinuous micaceous partings. Lower and upper parts contain slabby, brown-weathering marble interlayered with abundant phyllite bands. Individual phyllite layers are from 0.5 to 15 cm thick. Boudinaged dolomitic layers are common throughout the formation. Dolomitic layers are up to 3 m thick; they are typically highly fractured with coarse white calcite f i l l i n g fractures. The marker horizon indicated in the maps (plates 4-3 and 4-4) consists of a silvery phyllite (5 cm - 6 m) overlain by a distinctive massive creamy white marble (6 m). Yankee Belle Formation Conformably overlying the Cunningham Formation i s the Yankee Belle Formation (Holland 1954). In the McBride area the Yankee Belle is more than 900 m (2900 ft) thick. The unit consists mainly of alternating beds of siltstone, quartzite, limestone, and shale (R.B. Campbell, Mountjoy, and Young 1973). In the Azure Lake area i t contains interlayered silvery phyllite, slabby creamy-colored quartzite, and gray to brown micaceous marble. Quartzite units are more common near the base of the formation. Intrusions Two sets of intrusions have been recognized in the cover sequence. The earliest occur only as s i l l s and dykes. These early intrusions have undergone a l l of the deformation and contain the same foliations as surrounding metasediments. Rock types range from fine-grained f e l s i c 19 a p l i t e s to h o r n b l e n d e - b i o t i t e metabasic i n t r u s i o n s . The second set of i n t r u s i o n s occurs as h o r n b l e n d e - b i o t i t e quartz d i o r i t e to g r a n o d i o r i t e stocks on the northern edge of the Azure Lake area. Abundant p l a g i o c l a s e phenocrysts i n an u n f o l i a t e d , medium-grained m a t r i x give a d i s t i n c t i v e appearance to these s t o c k s . Lesser amounts of hornblendite and f i n e - g r a i n e d white a p l i t e are t y p i c a l l y a s s o c i a t e d w i t h the i n t r u s i o n s . These stocks have imposed a h o r n f e l s i c contact metamorphic aureole on r e g i o n a l metamorphic assemblages i n the metasediments. E a r l y s t r u c t u r e s are cross-cut by the s t o c k s ; the e a r l i e s t recognized s t r u c t u r e s i n the stocks are F3 f r a c t u r e s (see s e c t i o n on deformation). Rb-Sr (Pigage 1977) and K-Ar (Wanless e_t a l . 1965) rad i o m e t r i c d a t i n g give c o n s i s t e n t Late J u r a s s i c dates f o r emplacement. Within the Shuswap Complex the only recognized i n t r u s i o n s are coarse, u n f o l i a t e d q u a r t z - m i c r o c l i n e - p l a g i o c l a s e ± muscovite pegmatites. These pegmatite bodies are e s p e c i a l l y abundant i n the area southwest of Ovis Creek. Modal amounts of the d i f f e r e n t minerals are h i g h l y v a r i a b l e w i t h i n the same pegmatite i n t r u s i o n . DEFORMATION/METAMORPHISM Both provinces are polydeformed w i t h metamorphism c o n t i n u i n g through more than one deformation phase. The f o l l o w i n g s e c t i o n s d i s c u s s deformation and metamorphic episodes f o r each of the provinces s e p a r a t e l y . The geometries of the deformation episodes are presented, and the phases of deformation are then r e l a t e d to metamorphic c o n d i t i o n s . C o e x i s t i n g mineral assemblages are used to estimate pressure-temperature c o n d i t i o n s during metamorphism. Through t h i s d e t a i l e d a n a l y s i s i t i s shown that deformation and metamorphic patt e r n s i n the two provinces are s i m i l a r . 20 Furthermore, estimated metamorphic c o n d i t i o n s a l l o w d i s c u s s i o n of r e l a t i v e displacement along the f a u l t zone separating the two p r o v i n c e s . Deformation and metamorphic c o n d i t i o n s f o r the Shuswap Complex are discussed f i r s t . D i f f e r e n t deformation episodes i n the Complex are designated as P1-P3 i n order to d i s t i n g u i s h them from recognized phases of deformat i o n i n the cover sequence ( F l — F 4 ) . Shuswap Deformation ( P I , P2, P3) Three phases of deformation have been recognized i n the Shuswap Complex near Azure Lake. Minor s t r u c t u r e s a s s o c i a t e d w i t h each deformation phase were d i s t i n g u i s h e d by s t y l e and o r i e n t a t i o n of minor f o l d s , r e l a t i o n of cleavages to minor f o l d s , and r e f o l d i n g of e a r l i e r minor s t r u c t u r e s by l a t e r f o l d s . Minor s t r u c t u r e s a s s o c i a t e d w i t h the two e a r l i e r deformation phases (PI and P2) are present over the e n t i r e area and c o a x i a l l y plunge gently northwest and southeast. A l a t e , b r i t t l e f o l d and f r a c t u r e p a t t e r n (P3) trending north to northeast i s only l o c a l l y present. The e a r l i e s t recognized minor s t r u c t u r e s are PI i s o c l i n a l recumbent f o l d s i n the compositional l a y e r i n g PO. PI minor f o l d s are preserved only i n q u a r t z i t e and c a l c - s i l i c a t e u n i t s . They are commonly r o o t l e s s w i t h thickened hinge zones and g r e a t l y attenuated limbs ( f i g u r e 1-6). These f o l d s are accompanied by a pervasive PI a x i a l plane s c h i s t o s i t y which forms the dominant f o l i a t i o n i n the Complex. The s u b p a r a l l e l o r i e n t a t i o n of PI and PO and the absence of PI minor f o l d s i n the s c h i s t s i n d i c a t e that PO i s a c t u a l l y transposed primary bedding. Figure 1-7 i l l u s t r a t e s the problems inherent i n using minor f o l d vergences to d e l i n e a t e macroscopic f o l d patterns i n the Shuswap Complex. The c l i f f exposure contains an i s o l a t e d f o l d nose w i t h a h a l f - a m p l i t u d e greater than 15 m and a haIf-wavelength of only 3m. A sequence of f o l d s F i g u r e 1-6. I s o c l i n a l P i m i n o r f o l d i n t he Shuswap Complex n e a r A z u r e L a k e . F o l d i s o u t l i n e d by q u a r t z i t e i n s c h i s t . The l i n e d r a w i n g i s t r a c e d f r o m a p h o t o g r a p h . 22 Figure 1-7. Large P I i s o c l i n a l f o l d i n i n t e r l a y e r e d s c h i s t and q u a r t z i t e . The l i n e drawing i s traced from a photograph. 23 on this scale is not commonly seen in outcrop. Consequently minor fold vergences may not be consistent even when considering a small area. Repetition of interlayered schist and quartzite units by large PI iso c l i n a l folds in the Azure Lake area could not be unravelled because of the absence of suitable continuous marker horizons. Just north of Azure River the PO compositional layering along the northeast margin of the Complex consistently dips toward the southwest. This discordance with the northeast-dipping PI schistosity suggests a large PI synform. The northern limb of this synform has been cut off by the fault bounding the Complex. The calculated orientation of the fault plane as determined from the surface trace is 142/36E. This orientation is subparallel to the PI schistosity in this area and suggests that the fault represents a major tectonic slide (Fleuty 1964) formed either during PI deformation or with tightening of PI structures during the P2 deformation. The slide and adjacent synform are offset by the later north-trending fault which truncates the metamorphic isograds and structural trends in the Complex and cover sequence. Other slides may be present within the Complex but were not detected. The Shuswap Complex in the Azure Lake area was divided into three homogeneous structural domains (la,lb,lc) based upon the orientation of the PI schistosity (figure 1-4). The domains are bounded by near-vertical faults which do not v i s i b l y offset regional metamorphic assemblages. Domain lb appears to be transitional between l a and l c . Figure 1-8 contains stereographic projections of poles to PO compositional layering and PI schistosity for each of the three domains. The different projections a l l show the general northwest strike for PO and PI planar structures. Planar structures in domains l a and l c dip predominantly northeast and southwest, respectively. The composite Figure 1-8 Equal area stereographic p r o j e c t i o n s of poles to PO compositional l a y e r i n g and PI a x i a l plane s c h i s t o s i t y i n the Shuswap Complex (Azure Lake area). Top row: Poles to PO compositional l a y e r i n g Domain l a - 250 p o i n t s , 0.4-2-4-8-12% per 1% area; maximum 13% Domain l b - 70 p o i n t s Domain l c - 280 p o i n t s , 0.4-2-4-8% per 1% area; maximum 8% Bottom row: Poles to PI a x i a l plane s c h i s t o s i t y Domain l a - 316 p o i n t s , 0.3-2-4-8-12% per 1% area; maximum 18% Domain l b - 46 p o i n t s Domain l c - 105 p o i n t s , 0.9-2-4-8-12% per 1% area; maximum 15% P , - a x i a l p l a n e s c h i s t o s i t y Figure 1-9 Equal area stereographic p r o j e c t i o n s of PI minor f o l d s t r u c t u r e s i n the Shuswap Complex (Azure Lake area). Top row: Domain l a - poles to PI minor f o l d a x i a l planes 115 p o i n t s , 0.9-4-8-12-16% per 1% area; maximum 20% Domain l b - PI minor f o l d s t r u c t u r e s dots - poles to a x i a l planes, 17 p o i n t s t r i a n g l e s - f o l d axes, 27 p o i n t s Domain l c - poles to PI minor f o l d a x i a l planes 77 p o i n t s , 1.3-4-8-12-16% per 1% area; maximum 17% Bottom row: Domain l a - PI minor f o l d axes and l i n e a t i o n s 160 p o i n t s , dashed l i n e i n d i c a t e s average PI a x i a l plane Domain l c - PI minor f o l d axes and l i n e a t i o n s 112 p o i n t s , dashed l i n e i n d i c a t e s average PI a x i a l plane Composite diagram of PO and PI poles to planar s t r u c t u r e s 12% per 1% area to PO compositional l a y e r i n g (8% per 1% area f o r domain l c ) 12% per 1% area f o r PI minor f o l d a x i a l planes 12% per 1% area f o r PI a x i a l plane s c h i s t o s i t y 28 p r o j e c t i o n i n f i g u r e 1-9 shows the overlap of PO and PI planar s t r u c t u r e s and demonstrates the i s o c l i n a l nature of the f o l d i n g . Figure 1-9 i l l u s t r a t e s p r o j e c t i o n s of PI minor f o l d elements. Most PI minor f o l d axes plunge gently to the northwest and southeast. In domains l a and l c the dashed l i n e s correspond to the mean PI a x i a l plane o r i e n t a t i o n . PI minor f o l d axes have v a r i a b l e plunge w i t h i n t h i s PI a x i a l surface. S i m i l a r plunge v a r i a t i o n s i n other t e r r a i n s have been a t t r i b u t e d to d i f f e r e n t i a l f l a t t e n i n g of f o l d s during deformation (Ramsay 1962a). In the Azure Lake area t h i s inhomogeneous s t r a i n i s a l s o evident on the nesoscopic s c a l e ( p l a t e 1-9A). The f l a t t e n i n g probably occurred e i t h e r during l a t e PI f o l d i n g or w i t h t i g h t e n i n g of PI f o l d s during the P2 deformation. The P2 deformation i s de l i n e a t e d by up r i g h t t i g h t to open minor f o l d s . Minor f o l d s are common both i n s c h i s t s and q u a r t z i t e s . A perv a s i v e P2 c r e n u l a t i o n cleavage i s a x i a l p lanar to P2 minor f o l d s . In s c h i s t s t h i s P2 cleavage forms a strong c r i n k l e l i n e a t i o n of PI s c h i s t o s i t y s u r f a c e s . F i g u r e 1-10 i l l u s t r a t e s a t y p i c a l P2 minor f o l d . In some instances PI minor f o l d s are r e f o l d e d around P2 f o l d s . The r e s u l t i n g i n t e r f e r e n c e p a t t e r n corresponds to Ramsay's type 3 (Ramsay 1967) f o r c o a x i a l deformation. Figure 1-11 i l l u s t r a t e s the t y p i c a l i n t e r f e r e n c e p a t t e r n f o r the Complex i n the Azure Lake area. Stereographic p r o j e c t i o n s of P2 minor s t r u c t u r e s f o r the three domains are presented i n f i g u r e 1-12. A x i a l planes are n e a r l y v e r t i c a l and l i n e a t i o n s ( f o l d axes and i n t e r s e c t i o n s of P2 and PI s c h i s t o s i t i e s ) plunge gently northwest and southeast. P2 minor f o l d s from domains l a and l c have opposing vergences and de f i n e a l a r g e P2 a n t i f o r m w i t h a hinge zone centered i n domain l b (see Figure 1-10. P2 minor f o l d i n i n t e r l a y e r e d s c h i s t and q u a r t z i t e . S t i p p l e d area i s q u a r t z i t e . I r r e g u l a r pods i n s c h i s t are coarse, milky white quartz lenses. The l i n e drawing i s traced from a photograph. 30 Figure 1-11. I s o c l i n a l PI minor f o l d r e f o l d e d around a P2 minor f o l d . Hammer handle i s p a r a l l e l to the a x i a l plane of the P2 f o l d . The l i n e drawing i s traced from a photograph. Figure 1-12 Equal area stereographic p r o j e c t i o n s of P2 minor f o l d s t r u c t u r e s i n the Shuswap Complex (Azure Lake area). Top row: P2 minor f o l d axes and l i n e a t i o n s Domain l a - 212 p o i n t s , 0.5-4-8-12% per 1% area; maximum 20% Domain l b - 33 p o i n t s Domain l c - 117 p o i n t s , 0.9-4-8% per 1% area; maximum 11% Bottom row: poles to P2 minor f o l d a x i a l planes and c r e n u l a t i o n cleavage Domain l a - 191 p o i n t s , 0.5-4-8-12% per 1% area; maximum 12% Domain l b - 60 p o i n t s Domain l c - 109 p o i n t s , 0.9-4-8-12% per 1% area; maximum 15% average o r i e n t a t i o n 140/50 SW 33 p l a t e 4-4). The s l i g h t d i f f e r e n c e s i n o r i e n t a t i o n of P2 s c h i s t o s i t i e s from domains l a and l c i n d i c a t e that the P2 a n t i f o r m i s a convergent fan s t r u c t u r e . The c l o s e a s s o c i a t i o n of the v e r t i c a l f a u l t s i s o l a t i n g domain l b w i t h the hinge zone of the P2 an t i f o r m suggests that the f a u l t s are l a t e f r a c t u r e s formed during the P2 deformation. Displacement across these f a u l t s appears to be minimal si n c e l i t h o l o g i e s are s i m i l a r and metamorphic grade does not vary across them. L o c a l l y a minor P3 deformation has produced f r a c t u r e s and angular f o l d s w i t h ruptured hinge zones. Fractures and f o l d s trend n o r t h to northeast. Pegmatite i n t r u s i o n s a l s o contain these P3 minor s t r u c t u r e s . Shuswap Metamorphism The Shuswap Complex near Azure Lake contains m i n e r a l assemblages ranging from k y a n i t e through f i r s t s i l l i m a n i t e zones i n the Barro v i a n f a c i e s s e r i e s . Three d i s t i n c t metamorphic zones may be d i s t i n g u i s h e d using the p e l i t i c m i n eral assemblages ( f i g u r e 1-5). These zones d e f i n e a general increase i n metamorphic grade toward the southwest. M i n e r a l assemblages f o r these zones are: Kyanite zone k y a n i t e - g a r n e t - b i o t i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e - i l m e n i t e ± s t a u r o l i t e K y a n i t e - S i l l i m a n i t e zone s i l l i m a n i t e - g a r n e t - b i o t i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e - i l m e n i t e ± 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 zone s i l l i m a n i t e - g a r n e t - b i o t i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e - i l m e n i t e ± s t a u r o l i t e Minor amounts of tourmaline, a p a t i t e , z i r c o n , and opaque dust (graphite?) 34 are accessory minerals i n each of the assemblages. The i s o g r a d surface s e p a r a t i n g the k y a n i t e - s i l l i m a n i t e and s i l l i m a n i t e zones has a V-shaped p r o f i l e on the r i d g e j u s t northeast of Ovis Creek ( f i g u r e 1-5). The "V" marks a steep v a l l e y which i n t e r r u p t s the ridge at that p o i n t . The v a l l e y therefore provides a cross s e c t i o n of the isograd s u r f a c e . Figure 1-13 shows that the p o s i t i o n of the i s o g r a d i n the v a l l e y i s f a i r l y t i g h t l y constrained by the d i s t r i b u t i o n of the p e l i t i c assemblages. The a t t i t u d e of the i s o g r a d c a l c u l a t e d from t h i s surface t r a c e i s 132/20NE. This o r i e n t a t i o n i s s u b p a r a l l e l to both the PO compositional l a y e r i n g and the PI s c h i s t o s i t y i n the same area. A d e t a i l e d d i s c u s s i o n of probable metamorphic r e a c t i o n s and estimated pressure-temperature c o n d i t i o n s during metamorphism i s presented elsewhere (Pigage 1978, t h i s volume). B r i e f l y , t e x t u r a l r e l a t i o n s demonstrate that aggregates of f i b r o l i t e - b i o t i t e - m u s c o v i t e - i l m e n i t e have formed at the expense of garnet, s t a u r o l i t e , and k y a n i t e . Estimated metamorphic con d i t i o n s f o r the Complex i n the Azure Lake area are: P = 7600 + 400 bars, T = 705 + 40°C, a^ Q = 0.5 + Q * ^ • These estimates were de r i v e d from the mutual i n t e r s e c t i o n of s e v e r a l d i s p l a c e d e q u i l i b r i a i n v o l v i n g s t a u r o l i t e , garnet, p l a g i o c l a s e , muscovite, quartz, and A ^ S i O ^ ( k y a n i t e , s i l l i m a n i t e ) . The metamorphic gradient n o t i c e d i n the f i e l d mapping i s not observed i n the c a l c u l a t e d pressure-temperature p o s i t i o n s of the d i s p l a c e d e q u i l i b r i u m curves. Apparently t h i s gradient i s s m a l l and i s masked by a n a l y t i c a l e r r o r and l o c a l d i s e q u i l i b r i u m . Metamorphism may be r e l a t e d i n time to the PI and P2 deformations through the use of m i n e r a l r e a c t i o n textures and i n c l u s i o n t r a i l p a t t e r n s . The d i f f e r e n t textures o u t l i n e a sequence of r e a c t i o n s that have been p a r t i a l l y preserved by growth patterns i n minerals. Table 1-2 summarizes Figure 1-13. D i s t r i b u t i o n of p e l i t i c metamorphic mineral assemblages c o n s t r a i n i n g the l o c a t i o n of the is o g r a d between the k y a n i t e - s i l l i m a n i t e and the s i l l i m a n i t e metamorphic zones. 36 the observations concerning mineral growth and deformation. T e x t u r a l r e l a t i o n s l e a d i n g to t h i s t a b l e are discussed i n the f o l l o w i n g s e c t i o n s . Garnet porphyroblasts from a l l three metamorphic zones i n the Complex o u t l i n e two stages of growth. F i r s t stage garnets form l a r g e ragged g r a i n s w i t h abundant i n c l u s i o n s . I t i s these garnets which are breaking down to form f i b r o l i t e - b i o t i t e - m u s c o v i t e - i l m e n i t e aggregates. Since replacement of stage one garnets i s more extensive w i t h i n c r e a s i n g metamorphic grade, these garnets are not commonly preserved southwest of Ovis Creek. I n c l u s i o n t r a i l s i n f i r s t generation garnets provide a means of r e l a t i n g garnet growth to the P1-P2 deformation phases. U s u a l l y the i n c l u s i o n s d e f i n e s t r a i g h t ( p l a t e 1-1A) or S-shaped ( p l a t e 1-lB) t r a i l s . In both cases i n c l u s i o n s t r a i l s are r o t a t e d r e l a t i v e to the e x t e r n a l PI s c h i s t o s i t y although continuous w i t h i t . O c c a s i o n a l l y the t r a i l s preserve a c r e n u l a t i o n cleavage ( p l a t e 1-2A). Since the c r e n u l a t i o n planes w i t h i n the garnet are continuous w i t h the e x t e r n a l PI s c h i s t o s i t y , the e a r l i e r c renulated surfaces represent PO compositional l a y e r i n g . These i n c l u s i o n p a t t e r n s i n d i c a t e n u c l e a t i o n and growth of stage one garnets during and a f t e r the PI deformation (Zwart 1960a, 1960b). R e l a t i v e r o t a t i o n of garnet porphyroblasts i n the s c h i s t s probably r e s u l t e d from f l a t t e n i n g e i t h e r during l a t e PI f o l d i n g or during P2 deformation (Ramsay 1962a; Powell and Treagus 1970). Second stage garnets t y p i c a l l y form c l e a r , i d i o b l a s t i c rims around ragged stage one garnet cores ( p l a t e 1-lB). Where f i r s t stage garnets are uncommon, the second generation garnets occur as s m a l l i d i o b l a s t i c g r a i n s ( p l a t e 1-2B). Commonly f i b r o l i t e and i l m e n i t e g r a i n s are p a r t l y to completely enclosed by second stage garnets ( p l a t e 1-3). Second stage garnets a l s o form euhedral o u t l i n e s against the f i b r o l i t e aggregates Table 1-2. R e l a t i o n of mineral growth to phases of deformation i n the Shuswap Metamorphic Complex, Azure Lake, B r i t i s h Columbia. P| P2 SYN- POST-TECTONIC SYN- POST-TECTONIC BIOTITE MUSCOVITE PLAGIOCLASE ™^ — • — ^ ™ ^ ™ GARNET M M m^m ™™ KYANITE STAUROLITE SILLIMANITE ILMENITE 38 (plate 1-3). Therefore second generation garnet growth occurred after the i n i t i a l formation of the fi b r o l i t e aggregates. A paucity of inclusions in second stage garnets makes i t d i f f i c u l t to relate their growth to the deformations. Inclusion t r a i l s in kyanite and staurolite are similar to those for garnet (plate 1-4A). Relic staurolite and kyanite grains are enclosed by muscovite or f i b r o l i t e aggregates. Kyanite forms large poikiloblastic grains partly enclosing garnet. In some instances kyanite grains are warped or kinked by P2 microfolds. Kyanite and staurolite growth occurred after i n i t i a l nucleation of stage one garnets but before the formation of fi b r o l i t e aggregates. Fibrolite-biotite-muscovite-ilmenite aggregates partly to completely enclose garnet, staurolite, and kyanite. Individual f i b r o l i t e needles are randomly oriented although aggregates are elongate in the PI and P2 schistosities. In some instances the aggregates are folded and warped by P2 microfolds (plate 1-4B). These different textures indicate growth of the major metamorphic minerals during and after the PI deformation and before or during the P2 deformation. The formation of f i b r o l i t e aggregates apparently was initiated after PI but before the P2 deformation phase. Since second stage garnets formed after the i n i t i a l growth of f i b r o l i t e aggregates, garnet growth may have continued during the P2 deformation. Narrow elongate grains of biotite and muscovite define both the PI and P2 schistosities. Grains are recrystallized to form polygonal arcs around P2 microfolds and crenulations. In the sillimanite-bearing zones randomly oriented biotite i s intimately intergrown with f i b r o l i t e aggregates. Muscovite also occurs as coarse, equant flakes which are randomly 39 o r i e n t e d . Commonly these f l a k e s contain r e l i c k y a n i t e and s t a u r o l i t e g rains ( p l a t e 1-5). When ass o c i a t e d w i t h f i b r o l i t e aggregates, i n d i v i d u a l muscovite grains are i n t e r l o c k i n g w i t h ragged margins. At higher metamorphic grades b i o t i t e - f i b r o l i t e aggregates form attenuated t r a i l s through the coarse muscovite f l a k e s ( p l a t e 1-5). The mica t e x t u r e s i n d i c a t e a long p e r i o d of continued growth and r e c r y s t a l l i z a t i o n . Polygonal arc t e x t u r e s r e q u i r e continued growth through the PI and P2 deformations. Muscovite growth continued a f t e r the formation of f i b r o l i t e aggregates, judging from the replacement t e x t u r e s v i s i b l e at higher metamorphic grades. Shuswap Summary The Shuswap Complex near Azure Lake contains two r e g i o n a l l y developed c o a x i a l phases of deformation. Minor s t r u c t u r e s a s s o c i a t e d w i t h both deformations plunge g e n t l y northwest and southeast. Folds a s s o c i a t e d w i t h the e a r l i e r PI deformation are i s o c l i n a l w i t h s h a l l o w l y d i p p i n g a x i a l s u rfaces. P2 minor f o l d s are u p r i g h t w i t h s t e e p l y d i p p i n g a x i a l s u r f a c e s . A l a r g e P2 a n t i f o r m i s present i n the western p a r t of the mapped area. A l o c a l l y developed l a t e f r a c t u r i n g and b r i t t l e f o l d i n g event w i t h north to northeast trends was a l s o recognized. T e x t u r a l r e l a t i o n s and i n c l u s i o n t r a i l p a t t e r n s i n d i c a t e t h a t r e g i o n a l metamorphism began during the P I deformation and probably extended i n t o the P2 deformation. The s u b p a r a l l e l o r i e n t a t i o n of mapped isograds and the PI s c h i s t o s i t y s u b s t a n t i a t e s a s s o c i a t i o n of metamorphism w i t h the P I deformation. P e l i t i c metamorphic assemblages range from k y a n i t e through f i r s t s i l l i m a n i t e zones of the Barrovian f a c i e s s e r i e s . Metamorphic c o n d i t i o n s are estimated to be P = 7600 bars, T = 705°C, a„ n = 0.5. Garnet i n c l u s i o n p a t t e r n s i n d i c a t e two stages of growth. In a more 40 detailed study of mineral zoning patterns and textural relations (Pigage 1978, this volume), i t i s shown that the two growth periods may be related to a sequence of continuous and discontinuous reactions during a single prograde metamorphism. Qualitatively removing the folding effects of the P2 antiform in the Azure Lake area shows that the PI schistosity and metamorphic isograds were originally subhorizontal. The increase in metamorphic grade is therefore at least partly related to increasing depth of burial, but not necessarily to the stratigraphy. It is suggested that the fault zone separating the Shuswap Complex from the adjacent cover sequence is a tectonic slide related to the PI fold geometry. Formation of the fault zone is probably related to tightening of PI folds either late during the PI deformation or with P2 folding. Two coaxial deformation phases followed by a locally developed fracturing event were also described for portions of the Shuswap Complex to the west (K.V. Campbell 1971; Fletcher 1972). Fletcher considered the regional metamorphism to have culminated after the second deformation. This i s later than the time interval suggested in this paper. This discrepancy i s partly related to the fact that he considered f i b r o l i t e aggregates to have formed after the growth of second stage garnets. Cover Deformation (Fl, F2, F3, F4) Four phases of deformation (Fl to F4) were recognized in the cover sequence near Azure Lake. Relative ages of the deformation phases have been determined from refolded minor structures and cross-cutting cleavages. Minor structures associated with each of the four phases are present in varying intensity over the entire Azure Lake area. 41 Overturned i s o c l i n a l F l f o l d s are the e a r l i e s t recognized s t r u c t u r e s i n the cover sequence. Major and minor f o l d s are accompanied by a pervasive F l a x i a l plane s c h i s t o s i t y which forms the major metamorphic f o l i a t i o n i n the cover sequence. Minor f o l d s g e n e r a l l y plunge moderately (30°) to the north. F o l d s t y l e s of F l minor f o l d s change s i g n i f i c a n t l y as the Shuswap Complex i s approached along a north-south t r a v e r s e . In the northern p a r t of the Azure Lake area F l minor f o l d s i n q u a r t z i t e u n i t s have l a r g e c o n c e n t r i c hinge zones w i t h no n o t i c e a b l e t h i c k e n i n g of i n d i v i d u a l u n i t s ( f i g u r e 1-14). FO primary bedding ( c o l o r banding) i s r e a d i l y v i s i b l e i n p h y l l i t e s and i s commonly at an acute angle to the F l s c h i s t o s i t y . Near the Shuswap Complex F l minor f o l d s i n the q u a r t z i t e u n i t s are i s o c l i n a l w i t h thickened, V-shaped hinge zones ( f i g u r e 1-15). Fold limbs are thinned to the extent that r o o t l e s s f o l d couplets are common. FO primary bedding i s no longer v i s i b l e i n the p h y l l i t e s ; F l minor f o l d s i n the p h y l l i t e s have been destroyed by extreme f l a t t e n i n g w i t h d i s r u p t i o n of the hinge zones. The FO compositional l a y e r i n g i n the d i f f e r e n t u n i t s now represents transposed primary bedding. This change i n F l f o l d s t y l e i s accompanied by an i n c r e a s e i n metamorphic grade along the same north-south t r a v e r s e . The metamorphic t r a n s i t i o n ranges from b i o t i t e - g a r n e t zone to s t a u r o l i t e - k y a n i t e zone i n the Barrovian f a c i e s s e r i e s (Miyashiro 1961). Isograds are not e a s i l y d e fined because bulk compositions of the Isaac and Cunningham Formations preclude development of the c l a s s i c a l p e l i t e m i n e r a l assemblages. Metamorphic assemblages marking t h i s t r a n s i t i o n are presented i n a subsequent s e c t i o n . Several macroscopic F l f o l d s are defined by the d i s t r i b u t i o n of Figure 1-14. Large F l f o l d hinge i n i n t e r l a y e r e d p h y l l i t e and q u a r t z i t e . F o l d i s l o c a t e d i n the northern part of the Azure Lake area (cover sequence). Dark u n i t s are p h y l l i t e s . F l a x i a l plane s c h i s t o s i t y i s s u b h o r i z o n t a l . The l i n e drawing i s traced from a photograph. Figure 1-15. I s o c l i n a l F l minor f o l d s i n i n t e r l a y e r e d s c h i s t and q u a r t z i t e . S t i p p l e d u n i t i s q u a r t z i t e . Hammer on r i g h t s i d e of outcrop i s f o r s c a l e . Folds are l o c a t e d i n the cover sequence near the Shuswap Complex, Azure Lake, B r i t i s h Columbia. The l i n e drawing i s traced from a photograph. 44 l i t h o l o g i e s i n the Azure Lake area. P l a t e 4-2 ( i n pocket) i n d i c a t e s a x i a l t r a c e s of the F l f o l d s . The major f o l d s are complicated by numerous p a r a s i t i c f o l d s on limbs and i n hinge areas of the l a r g e r s t r u c t u r e s . The most n o t i c e a b l e f o l d s are the l a r g e s y n c l i n e cored by the Cunningham Formation and the a n t i c l i n e o u t l i n e d by the Kaza-Isaac contact i n the northern part of the area. Both the s t r a t i g r a p h i c succession and graded bedding w i t h i n f e l d s p a t h i c g r i t s of the Kaza Group j u s t i f y the use of the d e s c r i p t i v e terms s y n c l i n e and a n t i c l i n e f o r these macroscopic f o l d s . Since the F l f o l d s plunge moderately to the n o r t h , the l i t h o l o g i c map p a t t e r n represents a general c r o s s - s e c t i o n of the f o l d s t r u c t u r e when viewed down-plunge. D i s t r i b u t i o n of the f o l d s i n d i c a t e s that the F l s t r u c t u r e s are west-verging. The s y n c l i n e and a n t i c l i n e are both o f f s e t some 6 km along a l a r g e r i g h t - l a t e r a l F3 f a u l t which runs through the c e n t r a l part of the Azure Lake area. The cover sequence contains f i v e s t r u c t u r a l l y homogeneous domains ( f i g u r e 1-4). Domain 2e i s i s o l a t e d from the others by the l a r g e F3 f a u l t mentioned above. Domain 2d i s separated from the others because intense F3 f o l d i n g a p p r e c i a b l y s c a t t e r s s t r u c t u r a l i n f o r m a t i o n f o r that area. Boundaries separating the other domains correspond to a x i a l t r a c e s of macroscopic F l f o l d s . Figures 1-16 and 1-17 present stereographic p r o j e c t i o n s of poles to FO compositional l a y e r i n g and F l a x i a l plane s c h i s t o s i t y i n the d i f f e r e n t domains. Both FO and F l planar s t r u c t u r e s trend east-west and dip moderately to the n o r t h . The summary p r o j e c t i o n comparing the o r i e n t a t i o n s f o r the d i f f e r e n t domains ( f i g u r e 1-22) i l l u s t r a t e s the s u b p a r a l l e l o r i e n t a t i o n s of FO and F l . Stereographic p r o j e c t i o n s of poles to F l a x i a l planes and F l minor fold axes are i l l u s t r a t e d i n f i g u r e 1-18. F l minor f o l d axes have Figure 1-16 Equal area stereographic p r o j e c t i o n s of poles to FO compositi l a y e r i n g i n the cover sequence (Azure Lake area). Domain 2a - 51 p o i n t s Domain 2b - 374 p o i n t s , 0.3-5-10-15-20% per 1% area; maximum average 90/32 N Domain 2c - 163 p o i n t s , 0.6-5-10-15-20% per 1% area; maximum average 72/26 N Domain 2d - 80 p o i n t s Domain 2e - 30 p o i n t s Figure 1-17 Equal area stereographic p r o j e c t i o n s of poles to F l a x i a l plane s c h i s t o s i t y i n the cover sequence (Azure Lake a r e a ) . Domain 2a - 78 p o i n t s , 1.2-5-10-15-20% per 1% area; maximum 23% average 76/43 N Domain 2b - 446 p o i n t s , 0.2-5-10-15-20% per 1% area; maximum 29% average 86/33 N Domain 2c - 167 p o i n t s , 0.6-5-10-15-20% per 1% area; maximum 30% average 64/28 N Domain 2d - 28 p o i n t s Domain 2e - 32 p o i n t s a x i a l p l a n e s c h i s t o s i t y 49 v a r i a b l e plunge w i t h i n the F l a x i a l plane. This p a t t e r n probably r e s u l t s from inhomogeneous f l a t t e n i n g of F l minor f o l d s (Ramsay 1962a) which occurred e i t h e r l a t e i n the F l deformation or w i t h t i g h t e n i n g of F l f o l d s during the F2 deformation. Since domain 2a contains the l e a s t f l a t t e n e d F l f o l d s (see above d i s c u s s i o n on f o l d s t y l e s ) , the n o r t h to northwest plunge of F l minor s t r u c t u r e s i n t h i s domain represents the l e a s t d i s t u r b e d plunge d i r e c t i o n of F l f o l d s t r u c t u r e s i n the Azure Lake area. The F2 deformation i s c h a r a c t e r i z e d by l o c a l l y developed mesoscopic f o l d s . In micaceous u n i t s F2 minor f o l d s are accompanied by an a x i a l plane c r e n u l a t i o n cleavage. R e f o l d i n g of F l minor s t r u c t u r e s around F2 f o l d s and d i s r u p t i o n of the F l s c h i s t o s i t y by the F2 c r e n u l a t i o n cleavage both denote the younger r e l a t i v e age of the F2 deformation phase. Fol d s t y l e s vary depending on l i t h o l o g y . In marble and p h y l l i t e u n i t s F2 f o l d s are t y p i c a l l y V-shaped w i t h s l i g h t l y thickened hinge zones ( f i g u r e 1-19). Minor f o l d s are not w e l l developed i n q u a r t z i t e s ; they are c o n c e n t r i c w i t h e xtensive f r a c t u r i n g i n the hinge zone. Opaque pe g m a t i t i c white quartz s t r i n g e r s are abundant i n areas of intense F2 f o l d i n g . These s t r i n g e r s are p a r a l l e l to F2 a x i a l planes. F2 minor f o l d s c o n s i s t e n t l y have southwest vergence. Figure 1-20 presents stereographic p r o j e c t i o n s of F2 minor s t r u c t u r e s . S t r u c t u r a l o r i e n t a t i o n s i n domain 2e are d i s t i n c t and w i l l be discussed s e p a r a t e l y . In a l l other domains F2 a x i a l planes tre n d approximately east-west and dip s t e e p l y to the n o r t h . L i n e a t i o n s and minor f o l d axes plunge moderately northwest. These f o l d o r i e n t a t i o n s are not c o a x i a l w i t h e a r l i e r F l s t r u c t u r e s . F2 minor f o l d s i n domain 2e are c o a x i a l w i t h the e a r l i e r F l Figure 1-18 Equal area stereographic p r o j e c t i o n s of F l minor f o l d s t r u c t u r e s i n the cover sequence (Azure Lake area). A l l domains - s o l i d c i r c l e s : poles to F l a x i a l planes - open t r i a n g l e s : F l minor f o l d axes Domain 2a - f o l d axes 26 p o i n t s - a x i a l planes 15 p o i n t s Domain 2b - f o l d axes 92 p o i n t s - a x i a l planes 73 p o i n t s great c i r c l e : 86/33 N - maximum f o r F l s c h i s t o s i t y Domain 2c - f o l d axes 38 p o i n t s - a x i a l planes 39 p o i n t s great c i r c l e : 74/26 N - maximum f o r F l s c h i s t o s i t y Domain 2d - f o l d axes 7 p o i n t s - a x i a l planes 8 po i n t s Domain 2e - f o l d axes 19 p o i n t s - a x i a l planes 18 p o i n t s F | - m i n o r f o l d s t r u c t u r e s 52 Figure 1-19. F2 minor f o l d s i n i n t e r l a y e r e d p h y l i i t e and marble. Hinge areas of these f o l d s c o n t a i n an F2 a x i a l plane c r e n u l a t i o n cleavage. The l i n e drawing i s traced from a photograph. Figure 1-20 Equal area stereographic p r o j e c t i o n s of F2 minor s t r u c t u r e s i n the cover sequence (Azure Lake area). A l l domains 2a - 2d 2e Domain 2a Domain 2b - s o l i d c i r c l e s : poles to minor f o l d a x i a l planes and c r e n u l a t i o n cleavage - open t r i a n g l e : F2 l i n e a t i o n s , F2 minor f o l d axes - s o l i d t r i a n g l e : F2 l i n e a t i o n s , F2 minor f o l d axes - open t r i a n g l e : poles to F2 c r e n u l a t i o n cleavage - f o l d axes 30 p o i n t s (300/40) - a x i a l planes 50 p o i n t s (97/85 N) - f o l d axes 172 p o i n t s (302/22) - a x i a l planes 180 p o i n t s (114/85 N) Domain 2c - f o l d axes 96 p o i n t s (296/22) - a x i a l planes 91 p o i n t s (98/56 N) Domain 2d - f o l d axes - a x i a l planes Domain 2e - f o l d axes 30 p o i n t s - a x i a l planes 34 p o i n t s 55 s t r u c t u r e s . F2 minor f o l d s plunge gently north and have east vergence. Figure 1-21 i l l u s t r a t e s the i n t e r f e r e n c e p a t t e r n f o r F l and F2 f o l d s f o r t h i s domain. F3 minor s t r u c t u r e s are only l o c a l l y developed i n the Azure Lake area. North-plunging minor f o l d s are accompanied by an a x i a l plane c r e n u l a t i o n cleavage or f r a c t u r e cleavage. Some f o l d s a l s o have tension gashes f i l l e d by quartz ( q u a r t z i t e u n i t s ) or c a l c i t e (marble u n i t s ) . F3 f o l d s are most e x t e n s i v e l y developed i n p h y l l i t e s . They are g e n e r a l l y c o n c e n t r i c and have west vergence. P l a t e 1-9B i l l u s t r a t e s an F2 c r e n u l a t i o n cleavage warped around an F3 minor f o l d ; t h i s gives a r e l a t i v e age f o r the F3 deformation. F3 minor f o l d s c o n s i s t e n t l y occur near s t e e p l y d i p p i n g , n o r t h -trending f a u l t s . R i g h t - l a t e r a l displacement along the f a u l t s i s g e n e r a l l y small (up to 200 m). S l i c k e n s i d e s on f a u l t surfaces i n d i c a t e near-v e r t i c a l movement. The s p a t i a l p r o x i m i t y of F3 minor f o l d s to these f a u l t s , the s u b p a r a l l e l o r i e n t a t i o n of both s t r u c t u r e s , and the opposing sense of movement f o r f o l d s and f a u l t s a l l suggest that the F3 deformation phase i s c h a r a c t e r i z e d by a conjugate f o l d - f a u l t system. As mentioned p r e v i o u s l y , the l a r g e f a u l t o f f s e t t i n g F l macroscopic f o l d s appears to be an F3 s t r u c t u r e . Measured a t t i t u d e s of t h i s surface are 158/27E and 96/60N. This f a u l t a l s o truncates metamorphic isograds and s t r u c t u r a l trends i n the Shuswap Complex j u s t northeast of Ovis Creek. Apparent r i g h t - l a t e r a l displacement along t h i s f a u l t i s a maximum of 6 1/2 km. Figure 1-22 presents the stereographic p r o j e c t i o n of F3 minor s t r u c t u r e s from a l l domains of the cover sequence. Measured f a u l t surfaces are s u b p a r a l l e l w i t h F3 minor f o l d a x i a l planes. F3 minor f o l d s i n domain 56 Figure 1-21. I s o c l i n a l F l f o l d s i n s c h i s t and q u a r t z i t e are c o a x i a l l y r e f o l d e d around F2 f o l d s . Outcrop i s l o c a t e d i n domain 2e i n the cover sequence. P h y l i i t e u n i t s are s t i p p l e d . Note hammer f o r s c a l e . The l i n e drawing i s traced from a photograph. Figure 1-22, Equal area stereographic p r o j e c t i o n s of s t r u c t u r a l elements i n the cover sequence (Azure Lake area). Top row: L e f t - F3 minor f o l d s t r u c t u r a l elements, a l l domains - open t r i a n g l e : F3 l i n e a t i o n s , F3 minor f o l d axes 90 p o i n t s - open square: poles to F3 f a u l t surfaces 3 p o i n t s - s o l i d c i r c l e : poles to F3 a x i a l planar surfaces 142 p o i n t s Right - F4 minor f o l d s t r u c t u r a l elements, a l l domains - open t r i a n g l e : F4 l i n e a t i o n s , F4 minor f o l d axes 20 p o i n t s - s o l i d c i r c l e : poles to F4 planar surfaces 28 p o i n t s Bottom row: L e f t - Composite diagram of F0 and F l poles to p l a n a r surfaces from domains 2a, 2b, and 2c. - h o r i z o n t a l r u l i n g : F l a x i a l plane s c h i s t o s i t y (20% contour) - v e r t i c a l r u l i n g : F0 compositional l a y e r i n g (20% contour) Right - Stress a n a l y s i s f o r box f o l d near Twin S p i r e s . a b b r e v i a t i o n s : °i > a 2 > CT3 c o m P r e s s i v e s t r e s s axes, f l - F l a x i a l plane s c h i s t o s i t y , a p l , ap2 - a x i a l plane o r i e n t a t i o n s of the box f o l d . cn oo 59 2d verge e a s t ; i n t h i s r e g i o n f o l d i n g r a t h e r than f a u l t i n g has been the dominant F3 deformation s t y l e . Since F3 f a u l t displacement i s l a r g e r than F3 f o l d movement i n the Azure Lake area, the net e f f e c t of the F3 deformation i s to counteract the northwest plunge of F2 s t r u c t u r e s . In most of the Azure Lake area F4 minor s t r u c t u r e s c o n s i s t of near-v e r t i c a l n o r t h e a s t - t r e n d i n g f r a c t u r e s . Near Twin S p i r e s these f r a c t u r e s are a x i a l planar to angular, V-shaped f o l d s w i t h ruptured hinge zones. Conjugate box f o l d s are common i n slabby q u a r t z i t e u n i t s of the Yankee B e l l e Formation ( f i g u r e 1-23). Figure 1-22 d e p i c t s a s t r e s s a n a l y s i s f o r one of the box f o l d s t r u c t u r e s near Twin Spires (Ramsay 1962b). As expected from the b r i t t l e f o l d p a t t e r n , the major compressive s t r e s s (a^) l i e s i n the F0-F1 s u r f a c e . Cover Metamorphism P e l i t i c mineral assemblages i n the cover sequence o u t l i n e a metamorphic t r a n s i t i o n from g a r n e t - b i o t i t e through s t a u r o l i t e - k y a n i t e zones i n the B a r r o v i a n f a c i e s s e r i e s . Metamorphic grade and g r a i n s i z e i n c r e a s e toward the south. Paragonite, margarite, and muscovite were d i s t i n g u i s h e d u s i n g x^ray d i f f r a c t i o n peaks suggested by Chatterjee (1971). In carbonate assemblages x-ray traces were run on i n s o l u b l e r e s i d u e s . A l l metamorphic assemblages i n the cover sequence have been subjected to a l a t e retrograde metamorphism. Porphyroblasts of garnet, b i o t i t e , and c h l o r i t o i d are p a r t i a l l y to completely a l t e r e d to a f i n e - g r a i n e d , i n t e r l o c k i n g matte of s e r i c i t e and c h l o r i t e . Kyanite and s t a u r o l i t e are rimmed by f i n e - g r a i n e d s e r i c i t e . The random o r i e n t a t i o n of these Figure 1-23. F4 minor f o l d s developed i n slabby q u a r t z i t e s of the Yankee B e l l e Formation. Folds are l o c a t e d i n the cover sequence near Twin S p i r e s . The l i n e drawing i s traced from a photograph. 61 a l t e r a t i o n rims i n d i c a t e s that the r e t r o g r a d i n g occurred a f t e r the main t e c t o n i c a c t i v i t y f o r the Azure Lake area; r e t r o g r a d i n g was d e f i n i t e l y l a t e r than the F2 and probably l a t e r than the F3 deformation phase. Isograds f o r the r e g i o n a l metamorphic t r a n s i t i o n are not e a s i l y d e fined because the Isaac and Cunningham Formations have b u l k compositions which preclude development of the c l a s s i c a l p e l i t e assemblages. The Isaac Formation t y p i c a l l y contains paragonite-bearing assemblages. B i o t i t e i s notably absent from the p h y l l i t e s . G u i d o t t i (1968) has shown tha t paragonite t y p i c a l l y occurs i n h i g h l y aluminous rocks which only r a r e l y contain b i o t i t e and p l a g i o c l a s e . Calcareous compositions i n the Cunningham Formation a l s o l i m i t development of p e l i t e mineralogy. In the subsequent d i s c u s s i o n of metamorphic zones, m i n e r a l assemblages from the Kaza Group are presented f i r s t s i n c e t h i s u n i t does c o n t a i n the p e l i t e index minerals t y p i c a l of Barrovian metamorphism. Table 1-3 contains mineral assemblages i n the Kaza Group f o r the d i f f e r e n t metamorphic zones. Figure 1-4 shows the approximate l o c a t i o n s of the zones i n the Azure Lake area. Schematic AFM p r o j e c t i o n s (J.B. Thompson 1957) of the d i f f e r e n t assemblages are shown i n f i g u r e 1-24. The g a r n e t - b i o t i t e zone has d i f f e r e n t c h a r a c t e r i s t i c s i n the northern and southern p o r t i o n s of the cover sequence. In the north only the q u a r t z i t e u n i t s c o n t a i n the three phase assemblage c h l o r i t e - b i o t i t e -garnet (muscovite-quartz). P h y l l i t e s t y p i c a l l y c o n t a i n only b i o t i t e -c h l o r i t e . This d i f f e r e n c e i s r e l a t e d to bulk composition as shown sc h e m a t i c a l l y i n f i g u r e 1-24. The p l a g i o c l a s e f e l d s p a r c o e x i s t i n g w i t h these assemblages i s a l b i t e . In the g r i t s the l a r g e f e l d s p a r porphyroclasts are a l b i t e , and the m a t r i x p l a g i o c l a s e r e t a i n s an o r i g i n a l composition of An^^-An^^. 62 Table 1-3. Metamorphic mineral assemblages in the cover sequence, Azure Lake, British Columbia. Kaza Group Garnet-Biotite zone (North) chlorite-muscovite-quartz ± biotite ± garnet ± albite Garnet-Biotite zone (South) chlorite-biotite-garnet-muscovite-quartz-plagioclase calcite-muscovite-quartz-plagioclase-carbon-pyrite/pyrrhotite ± chlorite Staurolite-Kyanite zone chlorite-biotite-garnet-muscovite-quartz-plagioclase ± staurolite ± kyanite calcite-muscovite-quartz-carbon-pyrite/pyrrhotite ± plagioclase ± chlorite Isaac Formation Garnet-Biotite zone chlorite-muscovite-quartz ± paragonite chlorite-muscovite-quartz ± garnet ± chloritoid ± paragonite calcite-muscovite-quartz ± paragonite ± margarite calcite-muscovite-quartz-chlorite-plagioclase ± biotite ± hornblende ± garnet ± clinozoisite Cunningham Formation Garnet-Biotite zone calcite-muscovite-quartz ± plagioclase ± paragonite ± margarite calcite-muscovite-quartz-dolomite iplagioclase calcite-muscovite-quartz-biotite ± garnet ± hornblende ± plagioclase ± clinozoisite ± chlorite 63 In the south both p h y l l i t e and q u a r t z i t e u n i t s w i t h i n the Kaza Group co n t a i n l a r g e garnets c o e x i s t i n g w i t h b i o t i t e and c h l o r i t e . Figure 1-24 shows that t h i s r e s u l t s from the systematic change of c h l o r i t e and b i o t i t e to more magnesian compositions during prograde metamorphism. This same trend has a l s o been noted by Atherton (1968). This t r a n s i t i o n i s not considered an i s o g r a d s i n c e the topology of the AFM p r o j e c t i o n has not changed (J.B. Thompson 1957). P l a g i o c l a s e i n the s c h i s t s and q u a r t z i t e s has compositions ranging from An2^-An^Q. The t r a n s i t i o n to the s t a u r o l i t e - k y a n i t e zone i s marked by the l o c a l appearance of s t a u r o l i t e and/or k y a n i t e w i t h the above assemblage. The f u l l assemblage i s shown i n f i g u r e 1-24. Carbonate u n i t s i n the Kaza Group occur only i n the higher temperature p a r t of the g a r n e t - b i o t i t e zone and i n the s t a u r o l i t e - k y a n i t e zone. The metamorphic assemblage i s the same i n both zones and i s i n d i c a t e d i n Table 1-3. Both the Isaac and Cunningham Formations occur e n t i r e l y w i t h i n the g a r n e t - b i o t i t e zone. Metamorphic assemblages f o r these two formations are presented i n Table 1-3. Common accessory minerals f o r p h y l l i t e assemblages are a p a t i t e , tourmaline, z i r c o n , and p y r i t e / p y r r h o t i t e . R u t i l e , carbon, and p y r i t e / p y r r h o t i t e are accessory minerals i n the calcareous assemblages. The carbon phase i s not c a l l e d graphite because i t s c r y s t a l l i n e form has not been v e r i f i e d . P y r i t e and/or p y r r h o t i t e are both present i n the d i f f e r e n t assemblages. The f o l l o w i n g s e c t i o n contains s e v e r a l comments on the d i f f e r e n t assemblages. P e l i t i c assemblages i n the Isaac Formation i n d i c a t e A l - r i c h b u l k compositions ( G u i d o t t i 1968). C h l o r i t o i d porphyroblasts occur only i n one s t r a t i g r a p h i c i n t e r v a l i n the lower member of the Isaac Formation: i t s 64 GARNET-BIOTITE GARNET-BIOTITE Bio Figure 1-24. Schematic AFM p r o j e c t i o n s of p e l i t i c m i n e r a l assemblages i n the Kaza Group f o r the d i f f e r e n t metamorphic zones i n the cover sequence, Azure Lake, B r i t i s h Columbia. T r i a n g l e corresponds to p h y l l i t e / s c h i s t , and c i r c l e represents q u a r t z i t e . 65 r e s t r i c t e d occurrence i s r e l a t e d to h i g h - A l , high-Fe bulk compositions (Hoschek 1967). Margarite i s r e s t r i c t e d to calcareous assemblages i n both formations. Within calcareous u n i t s margarite i s u s u a l l y subordinate to paragonite. Green hornblende garbenschiefer are common i n calcareous p h y l l i t e s . Hornblende has t y p i c a l l y been a l t e r e d to aggregates of c h l o r i t e , q u a rtz, c a l c i t e , opaques, and c l i n o z o i s i t e . Marginal zones between calcareous and p e l i t i c assemblages have sharp boundaries w i t h no apparent r e a c t i o n . Because of the numerous deformation phases present i n the cover sequence, i t i s important to r e l a t e the n u c l e a t i o n and growth of metamorphic minerals t o the d i f f e r e n t deformation episodes. Table 1-4 summarizes the va r i o u s observations on mineral t e x t u r e s and i n c l u s i o n t r a i l p a tterns i n the cover sequence. These textures are discussed i n the f o l l o w i n g s e c t i o n s . Porphyroblasts of garnet, c h l o r i t o i d , b i o t i t e , hornblende, s t a u r o l i t e , and k y a n i t e a l l have s i m i l a r i n c l u s i o n patterns and t e x t u r e s . I n c l u s i o n t r a i l s are planar or s l i g h t l y S-shaped (see p l a t e s 1-6A, 1-6B, 1-7A). These t r a i l s are continuous w i t h the e x t e r n a l F l s c h i s t o s i t y although r o t a t e d r e l a t i v e to i t . Q u a r t z - r i c h pressure shadows w i t h i n the F l s c h i s t o s i t y are common around these porphyroblasts. In one ins t a n c e a k y a n i t e g r a i n i s f r a c t u r e d by the F3 c r e n u l a t i o n cleavage. These d i f f e r e n t t e x t u r e s p l a c e mineral growth during and a f t e r the F l deformation phase (Zwart 1960a, 1960b). Rota t i o n of the i n c l u s i o n t r a i l s r e l a t i v e to the e x t e r n a l F l s c h i s t o s i t y r e s u l t e d from f l a t t e n i n g (Ramsay 1962a; Powell and Treagus 1970). F l a t t e n i n g probably occurred w i t h t i g h t e n i n g of F l f o l d s e i t h e r l a t e during F l deformation or w i t h F2 f o l d i n g . With increased f l a t t e n i n g toward the south (see s e c t i o n on deformation) 66 Table 1 - 4 . R e l a t i o n of mineral growth to phases of deformation i n the cover sequence, Azure Lake, B r i t i s h Columbia. B i o t i t e ( p ) r e f e r s to p o r p h y r o b l a s t i c b i o t i t e , and b i o t i t e ( m ) to matri x b i o t i t e . F l S Y N - POST-F 2 S Y N - POST-F 3 S Y N - POST-F 4 SYN- POST-CHLORITE MUSCOVITE BIOTITE (p) BIOTITE (m) GARNET CHLORITOID STAUROLITE KYANITE 67 b i o t i t e porphyroblasts form elongate augen w i t h i n the F l s c h i s t o s i t y ( p l a t e 1-7B). B i o t i t e a l s o occurs as narrow, elongate g r a i n s intermixed w i t h muscovite and c h l o r i t e i n the matrix of s c h i s t s and q u a r t z i t e s . This form occurs only i n the higher grade zones near the Complex. B i o t i t e g r a i n s are r e c r y s t a l l i z e d to form polygonal arcs around F2 m i c r o f o l d s and c r e n u l a t i o n s . Muscovite and c h l o r i t e t y p i c a l l y occur as narrow elongate f l a k e s i n the matrix. These g r a i n s define the F l , F2, and F3 s c h i s t o s i t i e s . R e c r y s t a l l i z e d g r a i n s form polygonal arcs around F2 and F3 m i c r o f o l d s and c r e n u l a t i o n s ( p l a t e 1-8). Occasionally f i n e - g r a i n e d narrow muscovite f l a k e s form s t r o n g l y crenulated polygonal arcs around F l m i c r o f o l d s . In some instances these f i n e micas have been transposed u n t i l concordant w i t h the dominant F l s c h i s t o s i t y . These muscovites predate the F l s c h i s t o s i t y and may be s u b p a r a l l e l to the o r i g i n a l bedding FO. E l e c t r o n microprobe x-ray scans f o r Na show that paragonite i s i n t i m a t e l y intergrown w i t h muscovite along the 001 d i r e c t i o n . T y p i c a l l y paragonite g r a i n s are up to 10 micrometres t h i c k . I t i s assumed that the few calcareous u n i t s c o n t a i n i n g muscovite and margarite have a s i m i l a r intergrowth t e x t u r e . C h l o r i t e a l s o occurs as la r g e equant to elongate f l a k e s w i t h l a m e l l a r twinning. These l a r g e g r a i n s define the F2-F3 s c h i s t o s i t i e s or are randomly o r i e n t e d . In many instances the randomly o r i e n t e d g r a i n s c o n t a i n sparse to abundant k i n k bands. The mica t e x t u r e s o u t l i n e a continued sequence of growth and r e c r y s t a l l i z a t i o n extending from the F l through the F3 deformations. Muscovite and c h l o r i t e were s t a b l e through a l l three deformations. B i o t i t e was s t a b l e only during the F l and F2 deformations. Textures i n the po r p h y r o b l a s t i c minerals i n d i c a t e that the r e g i o n a l metamorphism 68 culminated during and a f t e r the F l deformation. Cover Metamorphic Conditions M i n e r a l assemblages i n the cover sequence s t r a d d l e the t r a n s i t i o n from c h l o r i t o i d - b e a r i n g assemblages to s t a u r o l i t e - b e a r i n g assemblages. Broad l i m i t s on metamorphic c o n d i t i o n s are provided by p u b l i s h e d experimental s t u d i e s and oxygen isotope thermometry. F i g u r e 1-25 i l l u s t r a t e s the experimental r e a c t i o n s p e r t i n e n t to t h i s d i s c u s s i o n . Q i s assumed equal to Prr-otal" Where a p p l i c a b l e f ^ was b u f f e r e d by FMQ or NNO s o l i d b u f f e r s . The A l 2 S i 0 5 diagram by Holdaway (1971) was s e l e c t e d because i t i s most compatible w i t h recent c a l o r i m e t r y (Anderson, Newton, and Kleppa 1977). Ganguly (1969) has shown that the d i f f e r e n t r e a c t i o n s marking the breakdown of c h l o r i t o i d to form s t a u r o l i t e a l l occur w i t h i n a narrow temperature i n t e r v a l . This i s confirmed i n f i g u r e 1-25 by the narrow temperature range f o r the three r e a c t i o n s i n v o l v i n g c h l o r i t o i d and/or s t a u r o l i t e . Reaction (1) was reversed u s i n g n a t u r a l minerals (with compositions which are probably s i m i l a r to those from the Azure Lake area) (Hoschek 1969). The other two r e a c t i o n s used Fe-endmember compositions. Since Fe-Mg p a r t i t i o n i n g between c h l o r i t o i d and s t a u r o l i t e i s almost 1.0 (Albee 1972), s o l i d s o l u t i o n would not appreciably d i s p l a c e these two experimentally determined curves. Estimated metamorphic temperatures based on these r e a c t i o n s range from 540° to 580° C. Experimental curves f o r the s t a b i l i t y l i m i t s of margarite-quartz and paragonite-quartz are both g e n e r a l l y compatible w i t h these temperatures. More d e t a i l e d a n a l y s i s w i l l not be p o s s i b l e u n t i l compositions of c o e x i s t i n g m a rgarite, p a r a g o n i t e , and p l a g i o c l a s e are known. The coexistence of k y a n i t e w i t h s t a u r o l i t e i n the Kaza Group provides Figure 1-25. Experimental r e a c t i o n s d e f i n i n g pressure-temperature conditions i n the cover sequence during r e g i o n a l metamorphism (Azure Lake area). P„ n = P m ^ n • Reactions are from the f o l l o w i n g r e f e r e n c e s : H^ O T o t a l A l 2 S i 0 5 system (Holdaway 1971) Margarite r e a c t i o n s ( C h a t t e r j e e 1976) Paragonite + Quartz = H i g h - a l b i t e + A^SiO,. + Vapor (Chatterjee 1972) 1) C h l o r i t o i d + S i l l i m a n i t e = S t a u r o l i t e + Quartz + Vapor (Richardson 1968) 2) C h l o r i t e + Muscovite = S t a u r o l i t e + B i o t i t e + Quartz + Vapor (Hoschek 1969) 3) C h l o r i t o i d + Quartz = S t a u r o l i t e + Almandine + Vapor (Ganguly 1969) P a r a l l e l o g r a m o u t l i n e s estimated metamorphic c o n d i t i o n s f o r the Shuswap Metamorphic Complex i n the Azure Lake area (Pigage 1978, t h i s volume). A b b r e v i a t i o n s : Ab-high a l b i t e , A n -anorthite, And-andalusite, Ky-kyanite, S i l l - s i l l i m a n i t e , Laws-lawsonite, Ma-margarite, Pa-paragonite, Qtz-quartz, Z o - z o i s i t e , Als-A^SiO,-, V-vapor(t^O) . 7 0 71 a minimum pressure limit of 4.5 kilobars for the cover sequence. An upper pressure limit i s much less tightly controlled. Chatterjee (1976) has calculated an upper s t a b i l i t y limit of 7 to 8.6 kilobars for the assemblage margarite-quartz (see figure 1-25). This upper limit would shift to higher pressures with margarite solid solution and lower pressures with reduced E^O a c t i v i t i e s . An upper limit of 9 kilobars seems reasonable especially when considering possible effects of reduced H^ O activities in calcareous assemblages. O'Neil and Ghent (1975) have completed oxygen isotope analysis of similar metamorphic assemblages from the Esplanade Range, British Columbia. Mineral assemblages in the Esplanades range from chloritoid-biotite through staurolite-biotite zones. Using the calibration by Bottinga and Javoy (1973), they arrived at consistent temperatures of 490° C for the garnet zone and 540° C for the staurolite-biotite zone. These temperatures are similar to the estimates presented i n figure 1-25. Cover Summary The cover sequence near Azure Lake contains evidence of four phases of deformation (F1-F4). Isoclinal, west-verging F l macroscopic folds plunge moderately northward. These earliest structures are accompanied by a pervasive axial plane schistosity. F2 minor folds plunge gently northwest and consistently have southwest vergence. The F2 folds are accompanied by a steeply dipping axial plane crenulation cleavage. F3 and F4 structures are only locally developed. F3 structures consist of a north-trending conjugate fold-fault system. Minor F3 structures are near-vertical. F3 faults offset metamorphic isograds in both the cover sequence and the Shuswap Complex. F4 structures consist of fractures and angular folds with ruptured hinge zones. These structures consistently trend northeast. 72 Mineral assemblages in the different units outline a transition from garnet-biotite zone into the staurolite-kyanite zone in the Barrovian facies series. Classical pelite mineralogy is developed largely within the Kaza Group. The Isaac Formation is highly aluminous and commonly develops paragonite-bearing assemblages. The calcareous composition of the Cunningham Formation also precludes development of pelite mineralogy. Oxygen isotope thermometry of other similar rocks and published experimental studies place broad limits on metamorphic conditions within the cover sequence. Estimated temperatures range from 490° C (garnet-biotite zone) to 580° C (staurolite-kyanite zone). Pressure limits are less constrained; they range from 4.5 to 9 kilobars. Textural relations and inclusion t r a i l patterns indicate that the regional metamorphism began during the F l deformation. Biotite was stable into the F2 deformation. Recrystallization of muscovite and chlorite during the F3 deformation indicates that lower greenschist facies conditions prevailed during that deformation. A l l assemblages have been affected by a late retrograde metamorphism. The major v i s i b l e effect of retrograding i s partial to complete alteration rims of fine chlorite and/ or sericite around porphyroblastic minerals. These structural and metamorphic transitions outline a large scale asymmetry associated with the F l deformation. F l folds have undergone more extensive flattening closer to the Shuswap Complex. Increasing metamorphic temperatures near the Complex allowed the various rock units to behave in a more ductile fashion, resulting in increased flattening and intensity of deformation. This asymmetry i s substantiated by the 5 to 1 thickness ratio for the Isaac Formation on the north and south limbs of the F l syncline containing the Cunningham Formation. COVER-COMPLEX CORRELATION 73 Lack of s t r a t i g r a p h i c c o n t i n u i t y between the cover sequence and the Shuswap Complex means that e a r l y metamorphic and deformation events i n each province cannot be d i r e c t l y c o r r e l a t e d . In the f o l l o w i n g d i s c u s s i o n the two provinces are c o r r e l a t e d through s i m i l a r i t i e s i n the metamorphic-deformation r e l a t i o n s w i t h i n each province. I t i s shown that there i s no d i s c e r n i b l e d i f f e r e n c e i n the metamorphic and deformation patterns across the f a u l t zone s e p a r a t i n g the provinces. C o r r e l a t i o n of metamorphic and deformation events does not imply s t r i c t time-equivalence f o r these events i n both provinces. I t i s recognized that deformation and metamorphism are diachronous when developed over a l a r g e area. However, i t i s assumed that metamorphic and t e c t o n i c events are approximately time-equivalent w i t h i n a f a i r l y r e s t r i c t e d area. Table 1-5 l i s t s the d i f f e r e n t metamorphic and deformation events i n the Shuswap Complex and the cover sequence. The two provinces must have assumed t h e i r present geometric c o n f i g u r a t i o n before the F3 deformation phase because the l a r g e F3 f a u l t i n the c e n t r a l part of the area continues undisturbed through both the Complex and the cover sequence. S i m i l a r deformation s t y l e s and s t r u c t u r a l trends i n d i c a t e that F3 and F4 i n the cover sequence must both c o r r e l a t e w i t h the P3 deformation phase i n the Complex. In both provinces these deformation phases c o n s i s t of l a t e f r a c t u r e s and b r i t t l e f o l d s w i t h north and northeast trends. F3 and F4 could be d i f f e r e n t i a t e d i n the cover sequence but were combined when mapping i n the Shuswap Complex. Comparison of the e a r l i e r metamorphic and deformation events i n Table 1-5 shows s t r i k i n g s i m i l a r i t i e s between the two provinces. The r e g i o n a l metamorphism i n both domains i s a s s o c i a t e d l a r g e l y w i t h the e a r l i e s t phase 74 T a b l e 1-5. C o r r e l a t i o n o f d e f o r m a t i o n and metamorph ism b e t w e e n t he Shuswap Complex and t h e c o v e r s e q u e n c e , A z u r e L a k e , B r i t i s h C o l u m b i a . SHUSWAP P3 DEFORMATION P 2 DEFORMATION REGIONAL METAMORPHISM P| DEFORMATION COVER F4 DEFORMATION F 3 DEFORMATION LATE JURASSIC INTRUSIONS F 2 DEFORMATION REGIONAL METAMORPHISM F| DEFORMATION 75 of deformation. In both cases metamorphic r e c r y s t a l l i z a t i o n appeared to o u t l a s t the f i r s t deformation. Metamorphic grade i n both provinces ' • increases i n the same general d i r e c t i o n , and metamorphic assemblages across the f a u l t zone separating the provinces are roughly e q u i v a l e n t . The second deformation phase i n both provinces have s i m i l a r trends and f o l d i n g s t y l e s . In both provinces the minor f o l d s are upright w i t h n e a r - v e r t i c a l a x i a l plane s u r f a c e s . Furthermore vergences of minor f o l d s a s s o c i a t e d w i t h the second deformation have the same o r i e n t a t i o n across the f a u l t zone separating the two provinces. Because of these s i m i l a r i t i e s I consider the s t r u c t u r a l and metamorphic patterns to be continuous across the f a u l t zone separating the two provinces. Therefore the PI and P2 deformations i n the Complex are c o r r e l a t e d w i t h the F l and F2 deformations i n the cover sequence. Regional metamorphic assemblages i n each province are a s s o c i a t e d w i t h the same metamorphic event. The f a u l t zone separating the two provinces i s considered to be a t e c t o n i c s l i d e r e l a t e d to the PI f o l d geometry. The c o n s i s t e n t vergence of F2-P2 minor f o l d s across the f a u l t zone suggests that i n i t i a l formation of the s l i d e preceded the F2 deformation. Comparison of estimated metamorphic c o n d i t i o n s i n each province near the s l i d e shows a temperature discrepancy of roughly 100° C across the f a u l t zone. An estimated s e p a r a t i o n across ; t h i s slide..may.be c a l c u l a t e d from t h i s temperature gap ;using estimated metamorphic temperature gradients f o r the Azure Lake area. A rough estimate of the metamorphic temperature gradient was c a l c u l a t e d by measuring the thickness of the g a r n e t - b i o t i t e zone. Isograds were assumed to be p a r a l l e l to the F l s c h i s t o s i t y . The r e s u l t i n g Estimate i s a maximum value because the northern boundary of the garnet-b i o t i t e zone may be l o c a t e d north of the mapped area. The g a r n e t - b i o t i t e zone was assumed to encompass the temperature range between 490° C and 580° C. The c a l c u l a t e d gradient i s 15° C/km; t h i s gradient i s comparable to the r e c e n t l y c a l c u l a t e d metamorphic temperature gradient f o r the Alps (P. Thompson 1976). Using t h i s gradient the separation recorded along the t e c t o n i c s l i d e i s on the order of 7 km; i t i s reasonable to consider the separation as being 10 km or l e s s . A c t u a l displacement along the s l i d e i s probably much l a r g e r because the s l i d e surface i s approximately p a r a l l e l to the metamorphic isograds. Although the F l (cover sequence) and PI (Shuswap Complex) deformation phases have been c o r r e l a t e d , the o r i e n t a t i o n s of planar and l i n e a r s t r u c t u r e s associated w i t h t h i s deformation i n each province are dis c o r d a n t . This discordance may be r e l a t e d to movement along the t e c t o n i c s l i d e separating the two domains. I n i t i a l development of the s l i d e surface during the P l - F l deformation would juxtapose two provinces w i t h s l i g h t angular discordance. As a zone of weakness the s l i d e would be r e a c t i v a t e d during r e f o l d i n g a s s o c i a t e d w i t h the P2-F2 deformation. D i f f e r e n t i a l response of the s l i g h t l y discordant provinces to the P2-F2 deformation would cause r o t a t i o n along the r e a c t i v a t e d s l i d e surface. The discordance of P l - F l minor s t r u c t u r e s across the s l i d e i s ther e f o r e r e l a t e d to complex movement during both the P l - F l and P2-F2 phases of deformation. The 100° C temperature d i s c o n t i n u i t y across the t e c t o n i c s l i d e measures only the displacement and r o t a t i o n that has occurred a f t e r the metamorphic culmination. Since r e g i o n a l metamorphism i s as s o c i a t e d mainly w i t h the P l - F l deformation, the temperature d i s c o n t i n u i t y i s r e l a t e d 77 l a r g e l y to displacement during the P2-F2 r e a c t i v a t i o n of the s l i d e s u r f ace. This displacement has been estimated as being greater than 10 km based on the metamorphic temperature gradient c a l c u l a t e d from the g a r n e t - b i o t i t e zone i n the Azure Lake area. Recently F l e t c h e r and Greenwood (1978) have described marginal r e l a t i o n s f o r the Shuswap Complex j u s t west of the Azure Lake area. They noted a mylonite zone between the garnet and s t a u r o l i t e - k y a n i t e metamorphic zones but considered the metamorphism to postdate movement along the mylonite. C a l c u l a t e d temperature gradients f o r t h e i r metamorphic zones vary from 25° C/km ( b i o t i t e zone) to 120° C/km ( s t a u r o l i t e -k y a n i t e zone). Yet t h e i r d e t a i l e d e q u i l i b r i u m s t u d i e s detected no evidence f o r a temperature gradient w i t h i n the s t a u r o l i t e - k y a n i t e and s i l l i m a n i t e zones. Based on the geologic r e l a t i o n s i n the Azure Lake area, t h i s v a r i a t i o n i n temperature gradients might e q u a l l y w e l l r e s u l t from post-metamorphic displacement along the mylonite zone. REGIONAL TECTONICS In the previous s e c t i o n i t was shown that metamorphism and deformation are continuous across the margin of the Shuswap Complex. In t h i s s e c t i o n the r e l a t i o n of Azure Lake deformation s t r u c t u r e s to the r e g i o n a l metamorphic-deformation framework i s discussed. The predominant r e g i o n a l s t r u c t u r e s i n the Cariboo Mountains are l a r g e northwest-plunging a n t i c l i n o r i a and s y n c l i n o r i a . These l a r g e s t r u c t u r e s f o l d an e a r l i e r s c h i s t o s i t y that i s s u b p a r a l l e l to compositional l a y e r i n g (Sutherland Brown 1963; R.B. Campbell, Mountjoy, and Young 1973). This feature together w i t h the northwest trend of these l a r g e s t r u c t u r e s suggests that the a n t i c l i n o r i a and s y n c l i n o r i a c o r r e l a t e w i t h the P2-F2 phase of deformation i n the Azure Lake area. The n e a r - v e r t i c a l f a u l t s which bound many of the a n t i c l i n o r i a and s y n c l i n o r i a probably represent movement along the s t e e p l y d i p p i n g P2-F2 a x i a l plane surfaces. Within the Azure Lake area quartz d i o r i t e to g r a n o d i o r i t e i n t r u s i o n s cross-cut F l and F2 s t r u c t u r e s and impose a contact aureole on the r e g i o n a l metamorphic assemblages. An Rb-Sr date of 163 ± 7 Ma (Pigage 1977) f o r these i n t r u s i o n s i s c o n s i s t e n t w i t h an e a r l i e r K-Ar date of 148 ± 14 Ma completed by the G e o l o g i c a l Survey of Canada (Wanless et a l . 1965; r e c a l c u l a t e d from the reported date using new decay constant f o r 40.K (Beckinsale and Gale 1969)). Therefore r e g i o n a l metamorphism and deformation f o r both the Shuswap Complex and the cover sequence i n the Azure Lake area occurred before the Late J u r a s s i c emplacement of the st o c k s . Younger b i o t i t e - w h o l e rock ± hornblende Rb/Sr dates f o r these stocks i n d i c a t e s p o s t - i n t r u s i o n i s o t o p i c r e s e t t i n g (Pigage 1977). This r e s e t t i n g was t e n t a t i v e l y a s c r i b e d to the Eocene thermal event noted f o r p o r t i o n s of the Shuswap Complex f u r t h e r south (Medford 1975). Ross (1974) has shown that t h i s thermal event i s c o n s i s t e n t l y a s s o c i a t e d w i t h north-to n o r t h e a s t -trending b r i t t l e f o l d and f r a c t u r e s t r u c t u r e s . Since n o r t h - t r e n d i n g F3 f r a c t u r e s are the e a r l i e s t s t r u c t u r e s recognized i n the stocks from the Azure Lake area, the F3 and F4 deformations are 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 t h i s Eocene thermal event. Estimated metamorphic pressures f o r the Shuswap Complex i n the Azure Lake area r e q u i r e some 25 km of o v e r l y i n g m a t e r i a l . Yet the pre-Cretaceous s t r a t i g r a p h y i n the area accounts f o r a maximum of only about 12 km of o v e r l y i n g sediments. Extensive t e c t o n i c t h i c k e n i n g i s re q u i r e d to o b t a i n the necessary metamorphic pressures. 79 CONCLUSIONS AND SUMMARY Both low and high grade metasediments along the northeast margin of the Shuswap Complex near Azure Lake cont a i n four recognized phases of deformation. The e a r l i e s t deformation phase c o n s i s t s of west-verging i s o c l i n a l f o l d s plunging north to northwest. Regional metamorphism i n the Azure Lake area i s ass o c i a t e d w i t h t h i s e a r l i e s t deformation. M i n e r a l t e x t u r e s i n d i c a t e that r e c r y s t a l l i z a t i o n o u t l a s t e d deformation. The second phase of deformation r e s u l t e d i n l a r g e upright f o l d s w i t h a shallow northwest plunge. Major a n t i c l i n o r i a and s y n c l i n o r i a i n the Cariboo Mountains are as s o c i a t e d w i t h t h i s deformation phase. Late J u r a s s i c plutons cross-cut minor s t r u c t u r e s a s s o c i a t e d w i t h these f i r s t two phases of deformation. Deformation and metamorphism were th e r e f o r e completed by Late J u r a s s i c . The t h i r d and f o u r t h phases of deformation c o n s i s t of f r a c t u r e s and b r i t t l e f o l d s which trend north and northeast, r e s p e c t i v e l y . These deformations are t e n t a t i v e l y considered to be T e r t i a r y based on t h e i r o r i e n t a t i o n and i s o t o p i c r e s e t t i n g of minerals from the Late J u r a s s i c p l u tons. M i n e r a l assemblages on the margin of the Shuswap Complex range from g a r n e t - b i o t i t e through f i r s t s i l l i m a n i t e zones w i t h metamorphic grade i n c r e a s i n g towards the southwest. The margin of the Complex i s a t e c t o n i c s l i d e which i s r e l a t e d to t i g h t e n i n g of major f o l d s from the e a r l i e s t deformation phase. Metamorphic mineral assemblages i n d i c a t e the presence of a 100° C temperature gap between the Complex and adjacent lower grade metasediments across t h i s s l i d e . This temperature gap i s r e l a t e d to movement i n v o l v i n g r o t a t i o n w i t h r e a c t i v a t i o n of the t e c t o n i c s l i d e during the second deformation phase. Discordance i n e a r l i e s t deformation minor 80 s t r u c t u r e s between the Complex and adjacent metasediments i s a l s o caused by complex movement along t h i s f a u l t zone during the f i r s t two deformation episodes. ACKNOWLEDGEMENTS This paper represents part of a Ph.D. t h e s i s completed at the U n i v e r s i t y of B r i t i s h Columbia. Dr. H.J. Greenwood provided continued i n t e r e s t and enthusiasm w h i l e s u p e r v i s i n g the study. B r i a n H a l l , Pat M a r c e l l o , and Norm Duncan were able f i e l d a s s i s t a n t s during the summer seasons. The s t r u c t u r a l p r e s e n t a t i o n has been improved through d i s c u s s i o n s w i t h Dr. J.V. Ross, Dr. P.B. Read, and Dr. R.B. Campbell. J . Nelson provided much needed moral support and l i s t e n e d p a t i e n t l y to convoluted geologic argument. F i e l d and l a b o r a t o r y expenses were covered by NRRC 67-4222 to Dr. H.J. Greenwood. During the course of t h i s study I was supported by graduate research f e l l o w s h i p s from the N a t i o n a l Science Foundation (NSF) and the I n t e r n a t i o n a l N i c k e l Company (INCO). 81 SELECTED REFERENCES ALBEE, A.L. 1972. Metamorphism of p e l i t i c s c h i s t s : r e a c t i o n r e l a t i o n s of c h l o r i t o i d and s t a u r o l i t e . G e o l o g i c a l S o c i e t y of America B u l l e t i n , 83, pp. 3249-3268. ANDERSON, P.M., NEWTON, R.C., and KLEPPA, O.J. 1977. The enthalpy change of the a n d a l u s i t e - s i l l i m a n i t e r e a c t i o n and the A ^ S i O ^ diagram. American J o u r n a l of Science, 277, pp. 585-593. ATHERTON, M.P. 1968. The v a r i a t i o n i n garnet, b i o t i t e , and c h l o r i t e composition i n medium grade p e l i t i c rocks from the D a l r a d i a n , Scotland, w i t h p a r t i c u l a r reference to the zonation i n garnet. Contributions to Mineralogy and P e t r o l o g y , 18, pp. 347-371. BECKINSALE, R.D. and GALE, N.H. 1969. ^ A r e a p p r a i s a l of the decay constants and branching r a t i o of K. Earth and Pl a n e t a r y Science L e t t e r s , 6, pp. 289-294. BOTTINGA, Y. and JAVOY, M. 1973. Comments on oxygen isotope geothermometry. Earth and Planetary Science L e t t e r s , 20, pp. 250-265. CAMPBELL, K.V. 1971. Metamorphic petrology and s t r u c t u r a l geology of the Crooked Lake area, Cariboo Mountains, B r i t i s h Columbia. PhD t h e s i s , U n i v e r s i t y of Washington, S e a t t l e , WA, 192p. CAMPBELL, R.B. 1963. Quesnel Lake (east h a l f ) B r i t i s h Columbia. G e o l o g i c a l Survey of Canada, Map 1-1963. •_. 1968. Canoe R i v e r , B r i t i s h Columbia. G e o l o g i c a l Survey of Canada, Map 15-1967. . 1970. S t r u c t u r a l and metamorphic t r a n s i t i o n s from i n f r a s t r u c t u r e to s u p r a s t r u c t u r e , Cariboo Mountains, B r i t i s h Columbia. In St r u c t u r e of the southern Canadian C o r d i l l e r a . E d i t e d by J.O. Wheeler. G e o l o g i c a l A s s o c i a t i o n of Canada, S p e c i a l Paper 6, pp. 67-72. . 1977. The Shuswap Metamorphic Complex, B r i t i s h Columbia. G e o l o g i c a l Society of America, A b s t r a c t s w i t h Programs, 9, pp. 920. CAMPBELL, R.B., MOUNTJOY, E.W., and YOUNG, F.G. 1973. Geology of McBride map-area, B r i t i s h Columbia. G e o l o g i c a l Survey of Canada, Paper 72-35, 104 p. CAMPBELL, R.B. and TIPPER, H.W. 1971. Geology of Bonaparte Lake map-area, B r i t i s h Columbia. G e o l o g i c a l Survey of Canada, Memoir 363, lOOp. 82 CHATTERJEE, N.D. 1971. Phase e q u i l i b r i a i n the a l p i n e metamorphic rocks of the environs of the Dora-Maria-Massif, Western I t a l i a n A l p s . P a r t s I and I I . Neues Jahrbuch fuer M i n e r a l o g i e . Abhandlungen, 114, pp. 181-245. . 1972. The upper s t a b i l i t y l i m i t of the assemblage paragonite + quartz and i t s n a t u r a l occurrences. Contributions to Mineralogy and Pe t r o l o g y , 34, pp. 288-303. . 1976. Margarite s t a b i l i t y and c o m p a t i b i l i t y r e l a t i o n s i n the system CaO-Al 20^-2102-^0 as a pressure-temperature i n d i c a t o r . American M i n e r a l o g i s t , 61, pp. 699-709. FLETCHER, C.J. 1972. Metamorphism and s t r u c t u r e of Pe n f o l d Creek area, near Quesnel Lake, B r i t i s h Columbia. PhD t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, Vancouver, BC, 123 p. FLETCHER, C.J. and GREENWOOD, H.J. 1978. 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Untersuchungen zum S t a b i l i t a t s b e r e i c h von C h l o r i t o i d und S t a u r o l i t h . C o n t r i b u t i o n s to Mineralogy and Pe t r o l o g y , 14, pp. 123-162. . 1969. The s t a b i l i t y of s t a u r o l i t e and c h l o r i t o i d and t h e i r s i g n i f i c a n c e i n metamorphism of p e l i t i c rocks. C o n t r i b u t i o n s to Mineralogy and Pe t r o l o g y , 22, pp. 208-232. MEDFORD, G.A. 1975. K-Ar and f i s s i o n t rack geochronometry of an Eocene thermal event i n the K e t t l e R i v e r (west h a l f ) map area, southern B r i t i s h Columbia. Canadian J o u r n a l of Earth Sciences, 12, pp. 836-843. MIYASHIRO, A. 1961. E v o l u t i o n of metamorphic b e l t s . J o u r n a l of Petr o l o g y , 2, pp. 277-311. 83 O'NEIL, J.R. and GHENT, E.D. 1975. Stable Isotope study of c o e x i s t i n g metamorphic minerals from the Esplanade Range, B r i t i s h Columbia. G e o l o g i c a l S o c i e t y of America B u l l e t i n , 86, pp. 1708-1712. PIGAGE, L.C. 1977. Rb-Sr dates f r o g r a n o d i o r i t e i n t r u s i o n s on the northeast margin of the Shuswap Metamorphic Complex, Cariboo Mountains, B r i t i s h Columbia. Canadian J o u r n a l of Earth Sciences, 14, pp. 1690-1695. . 1978. Metamorphic conditions i n the Shuswap Metamorphic Complex, Azure Lake, B r i t i s h Columbia. PhD t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, Vancouver, BC, pp. 105-273. POWELL, D. and TREAGUS, J.E. 1970. R o t a t i o n a l f a b r i c s i n metamorphic minerals. M i n e r a l o g i c a l Magazine, 37, pp. 801-814. RAMSAY, J.G. 1962a. The geometry and mechanics of formation of " s i m i l a r " type f o l d s . J o u r n a l of Geology, 70, pp. 309-327. . 1962b. The geometry of conjugate f o l d systems. G e o l o g i c a l Magazine, 99, pp. 516-526. . 1967. F o l d i n g and f r a c t u r i n g of rocks. McGraw-Hill Book Company, New York, NY. 568 p. RICHARDSON, S.W. 1968. S t a u r o l i t e s t a b i l i t y i n a par t of the system Fe-Al-Si-O-H. J o u r n a l of P e t r o l o g y , 9, pp. 467-488. ROSS, J.V. 1968. S t r u c t u r a l r e l a t i o n s at the eastern margin of the Shuswap Complex, near Revelstoke, southeastern B r i t i s h Columbia. Canadian J o u r n a l of Earth Sciences, 5, pp. 831-849. . 1974. A T e r t i a r y thermal event i n s o u t h - c e n t r a l B r i t i s h Columbia. Canadian J o u r n a l of Earth Sciences, 11, pp. 1116-1122. SUTHERLAND BROWN, A. 1957. Geology of the A n t l e r Creek area, Cariboo D i s t r i c t , B r i t i s h Columbia. B r i t i s h Columbia Department of Mines and Petroleum Resources, B u l l e t i n 38, 105 p. . '. 1963. Geology of the Cariboo R i v e r area, B r i t i s h Columbia. B r i t i s h Columbia Department of Mines and Petroleum Resources, B u l l e t i n 47, 60 p. THOMPSON, J.B., JR. 1957. The g r a p h i c a l a n a l y s i s of mineral assemblages i n p e l i t i c s c h i s t s . American M i n e r a l o g i s t , 42, pp. 842-858. THOMPSON, P.H. 1976. Isograd patterns and pressure-temperature d i s t r i b u t i o n s during r e g i o n a l metamorphism. Co n t r i b u t i o n s to Mineralogy and P e t r o l o g y , 57, pp. 277-295. 84 WANLESS, R.K. and REESOR, J.E. 1975. Precambrian z i r c o n age of orthogneiss i n the Shuswap Metamorphic Complex, B r i t i s h Columbia. Canadian Journal of Earth Sciences, 12, pp. 326-332. WANLESS, R.K., STEVENS, R.D., LACHANCE, G.R., and RIMSAITE, R.Y.H. 1965. Age determinations and g e o l o g i c a l s t u d i e s . G e o l o g i c a l Survey of Canada, Paper 64-17, Pa r t 1, pp. 15-16. WHEELER, J.O., CAMPBELL, R.B., REESOR, J.E., and MOUNTJOY, E.W. 1972. S t r u c t u r a l s t y l e of the southern Canadian C o r d i l l e r a . In Guidebook f o r Excursion A-01 - X-01. 24th I n t e r n a t i o n a l G e o l o g i c a l Congress, Montreal, Quebec, 118 p. WHEELER, J.O. and GABRIELSE, H. 1972. The C o r d i l l e r a n s t r u c t u r a l province. In V a r i a t i o n s i n t e c t o n i c s t y l e s i n Canada. Edit e d by R.A. P r i c e and R.J.W. Douglas. G e o l o g i c a l A s s o c i a t i o n of Canada, S p e c i a l Paper 11, pp. 1-81. ZWART, H.J. 1960a. Ch r o n o l o g i c a l succession of f o l d i n g and metamorphism i n the c e n t r a l Pyrenees. Geologische Rundschau, 50, pp. 203-218. . 1960b. R e l a t i o n s between f o l d i n g and metamorphism i n the c e n t r a l Pyrenees. Geologie en Mijnbouw, 39e, pp. 163-180. PLATE 1-1 A) S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex. S t a u r o l i t e ( s ) and garnet(G) are surrounded by equant, p o r p h y r o b l a s t i c muscovite w i t h f i b r o l i t e ( m + f ) . I n c l u s i o n t r a i l s i n garnet are s t r a i g h t , ( x - n i c o l s ) B) S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex. F i r s t stage garnet contains S-shaped i n c l u s i o n t r a i l s . Second stage garnet rim (outer margin) contains only a few s c a t t e r e d i n c l u s i o n s . Garnet i s p a r t l y surrounded by p o r p h y r o b l a s t i c m u s c o v i t e - f i b r o l i t e aggregate(M + F ) . Kyanite(K) i s common i n the s c h i s t matrix, ( x - n i c o l s ) PLATE 1-2 A) S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex. Quartz i n c l u s i o n s o u t l i n e a r e l i c c r e n u l a t i o n cleavage i n t h i s l a r g e stage one garnet. Opaque i n c l u s i o n s are continuous w i t h the e x t e r n a l PI s c h i s t o s i t y although r o t a t e d r e l a t i v e to i t . F i b r o l i t e aggregates occur i n the lower p o r t i o n of. the photomicrograph, (plane l i g h t ) B) S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex. I d i o b l a s t i c second stage garnets(g) are enclosed by p o r p h y r o b l a s t i c muscovite w i t h minor f i b r o l i t e ( m + f ) . The large muscovite grains have a random o r i e n t a t i o n and i n t e r l o c k i n g g r a i n margins, ( x - n i c o l s ) PLATE 1-3 S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex. Garnet and s t a u r o l i t e ( s ) are p a r t l y enclosed by f i b r o l i t e - m u s c o v i t e - i l m e n i t e aggregates. Kyanite(k) i s abundant i n the s c h i s t m atrix. Arrow p o i n t s to area where f i b r o l i t e i s p a r t l y enclosed by second stage garnet. Second stage garnet rims are euhedral against the f i b r o l i t e aggregates. A) (plane l i g h t ) B) ( x - n i c o l s ) I m m PLATE 1-4 A) S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex. S t r a i g h t i n c l u s i o n t r a i l s i n k y a n i t e ( k ) and s t a u r o l i t e ( s ) are r o t a t e d r e l a t i v e to the e x t e r n a l PI s c h i s t o s i t y . Minor garnet i s a l s o present i n the photomicrograph. (plane l i g h t ) B) S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex. Photomicrograph shows a la r g e f i b r o l i t e - b i o t i t e - m u s c o v i t e - i l m e n i t e aggregate i n the s c h i s t matrix. F i b r o l i t e i s warped and folded by the P2 c r e n u l a t i o n cleavage. ( x - n i c o l s ) I m m i I m m PLATE 1-5 S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex. P o r p h y r o b l a s t i c muscovite(M) i s randomly o r i e n t e d i n the s c h i s t matrix. F i b r o l i t e -b i o t i t e aggregates form attenuated wispy t r a i l s through the muscovite (arrows). R e l i c s t a u r o l i t e ( s ) i s enclosed by f i b r o l i t e or muscovite. Arrow i n second generation garnet shows where f i b r o l i t e has been enclosed by the garnet. A) (plane l i g h t ) B) ( x - n i c o l s ) 94 B I m m PLATE 1-6 A) S c h i s t from the s t a u r o l i t e - k y a n i t e zone, cover sequence. S k e l e t a l garnet(g) contains S-shaped i n c l u s i o n t r a i l s which are r o t a t e d r e l a t i v e to the e x t e r n a l F l s c h i s t o s i t y . Kyanite(k) i s present i n the s c h i s t matrix. Sample i s from the Kaza Group, (plane l i g h t ) B) P h y l i i t e from the g a r n e t - b i o t i t e zone, cover sequence. S l i g h t l y S-shaped i n c l u s i o n t r a i l s i n i d i o b l a s t i c garnets are -rotated r e l a t i v e to the e x t e r n a l F l s c h i s t o s i t y . Quartz pressure shadows occur near the garnets. The s l i g h t warping of the F l s c h i s t o s i t y i s due to the F2 c r e n u l a t i o n cleavage. The arrow p o i n t s to a s m a l l retrograde rim of s e r i c i t e + c h l o r i t e around the garnet. Sample i s from the lower member of the Isaac Formation, (plane l i g h t ) 96 B i i I mm PLATE 1-7 A) P h y l l i t e from the g a r n e t - b i o t i t e zone, cover sequence. B i o t i t e porphyroblasts contain s t r a i g h t i n c l u s i o n t r a i l s which are s l i g h t l y r o t a t e d r e l a t i v e to the e x t e r n a l F l s c h i s t o s i t y . Warping of the F l s c h i s t o s i t y i s due to the F2 deformation. Sample i s from the Kaza Group i n the northern p a r t of the Azure Lake area, (plane l i g h t ) B) P h y l l i t e from the g a r n e t - b i o t i t e zone, cover sequence. B i o t i t e forms p o r p h y r o b l a s t i c augen concordant w i t h the F l s c h i s t o s i t y . Warping of the F l s c h i s t o s i t y i s caused by the F2 deformation. Sample i s from a p h y l l i t e u n i t w i t h i n the Cunningham Formation, (plane l i g h t ) I m m i i I m m PLATE 1-8 P h y l i i t e from the g a r n e t - b i o t i t e zone, cover sequence. F2 c r e n u l a t i o n cleavage r e f o l d s the e a r l i e r F l s c h i s t o s i t y . Sample i s from the Isaac Formation. (plane l i g h t ) 100 I m m PLATE 1-9 A) PI minor f o l d s i n i n t e r l a y e r e d s c h i s t and q u a r t z i t e , Shuswap Complex (Azure Lake area). Fold a x i s f o r a s i n g l e f o l d has a v a r i a b l e plunge although the a x i a l plane has a constant o r i e n t a t i o n . This i s r e l a t e d to d i f f e r e n t i a l f l a t t e n i n g of the PI minor f o l d s . B) F3 minor f o l d hinge i n p h y l l i t e . P e n c i l i s p a r a l l e l to the o r i e n t a t i o n of the F2 c r e n u l a t i o n cleavage which i s warped around the F3 f o l d hinge. P e n c i l and hammer are f o r s c a l e . PLATE 1-10 A) F3 minor f o l d hinges i n p h y l i i t e . Hinge areas are accompanied by a s u b v e r t i c a l F3 a x i a l plane c r e n u l a t i o n cleavage. B) Graded bedding i n f e l d s p a t h i c ' g r i t s ' of the Kaza Group. Fractures running from lower l e f t to upper r i g h t aire p a r a l l e l to the F l a x i a l plane s c h i s t o s i t y . These beds are overturned and form the lower limb of a l a r g e F l a n t i c l i n e . 104 Metamorphic Conditions i n the Shuswap Metamorphic Complex, Azure Lake, B r i t i s h Columbia Lee C. Pigage Department of G e o l o g i c a l Sciences U n i v e r s i t y of B r i t i s h Columbia Vancouver, B r i t i s h Columbia V6T 1W5 Canada 106 ABSTRACT P e l i t i c m i n eral assemblages i n the Shuswap Metamorphic Complex near Azure Lake, B r i t i s h Columbia are c h a r a c t e r i s t i c of the k y a n i t e through f i r s t s i l l i m a n i t e zones of the Barrovian f a c i e s s e r i e s . M i n e r a l t e x t u r e s p a r t i a l l y preserve a sequence of r e a c t i o n s i n v o l v i n g the breakdown of garnet, s t a u r o l i t e , and k y a n i t e to form aggregates of f i b r o l i t e - b i o t i t e -m uscovite-ilmenite. Microprobe analyses have been combined w i t h l i n e a r r e g r e s s i o n techniques to o u t l i n e probable 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 . The r e g r e s s i o n s show th a t r e a c t i o n t e x t u r e s are probably preserved because of the exhaustion of r u t i l e as a reactant phase. Several experimentally s t u d i e d mineral e q u i l i b r i a are adjusted f o r s o l i d s o l u t i o n e f f e c t s and used to estimate metamorphic c o n d i t i o n s f o r the p e l i t e assemblages. Mutual i n t e r s e c t i o n of these e q u i l i b r i a r e s u l t i n the c o n s i s t e n t estimated c o n d i t i o n s : P = 7600 ± 400 b a r s , T = 705 ± 40°C, a = 0.5. a i s very s e n s i t i v e to thermochemical u n c e r t a i n t i e s , a n a l y t i c a l e r r o r s , and the choice of s o l i d s o l u t i o n models f o r d i f f e r e n t m inerals; i t v a r i e s between 0.25 and 1.0 depending upon the s e l e c t e d parameters. Comparison of published experimental e q u i l i b r i a s t u d i e s w i t h carbonate mineral assemblages from the Azure Lake area shows that the carbonate assemblages i n i t i a l l y b u f f e r e d f l u i d phase compositions to high X values cu 2 near 0.75 during metamorphism. The f l u i d phase t h e r e f o r e was not homogeneous i n composition throughout a l l rock types during metamorphism. L o c a l occurrences of z o i s i t e r e p l a c i n g p l a g i o c l a s e i n carbonate assemblages i s i n t e r p r e t e d to r e s u l t from the l a t e i n f l u x of IL^O-rich f l u i d s to the carbonates from the e n c l o s i n g p e l i t e s and q u a r t z i t e s . 107 C a l c u l a t i o n s of the composition of the f l u i d phase c o e x i s t i n g w i t h graphite show that CH^, CO^, and JL^ O are the major species present at the estimated metamorphic c o n d i t i o n s . Oxygen f u g a c i t i e s f o r both carbonate and p e l i t e assemblages were buffered to values near FMQ oxygen b u f f e r . 108 INTRODUCTION The Shuswap Complex i n southeastern B r i t i s h Columbia i s a metamorphic core complex w i t h i n the Omineca C r y s t a l l i n e B e l t ( f i g u r e 2-1) . I t i s ch a r a c t e r i z e d by upper amphibolite f a c i e s metamorphism and polyphase deformation (R.B. Campbell 1977). Near Azure Lake, B r i t i s h Columbia the northeast margin of the Complex contains the t r a n s i t i o n from k y a n i t e through f i r s t s i l l i m a n i t e metamorphic zones of the Barrovian f a c i e s s e r i e s (Miyashiro 1961). This study presents the r e s u l t s of a d e t a i l e d i n v e s t i g a t i o n of metamorphic co n d i t i o n s w i t h i n the Complex i n the Azure Lake area. Mass-balance c a l c u l a t i o n s using l i n e a r r e g r e s s i o n techniques have been used to t e s t probable 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 i n the p e l i t i c u n i t s . Published experimental r e a c t i o n s t u d i e s were adjusted f o r s o l i d s o l u t i o n e f f e c t s and used to estimate p r e s s u r e - t e m p e r a t u r e - a c t i v i t y (H^O) c o n d i t i o n s f o r the p e l i t e s during metamorphism. These c o n d i t i o n s were then a p p l i e d to carbonate-bearing assemblages to study the b u f f e r i n g of f l u i d phase compositions by mineral assemblages during metamorphism. The Azure Lake study area i s i n d i c a t e d i n f i g u r e s 2-1 and 2-2. R.B. Campbell (1963, 1968) compiled the r e g i o n a l geologic map. D e t a i l e d s t u d i e s on p o r t i o n s of the Complex to the west have been completed by K.V. Campbell (1971) and F l e t c h e r (1972). I conducted the f i e l d work f o r t h i s study during the summers of 1972, 1973 and 1975. D e t a i l e d geologic r e l a t i o n s between the Complex and surrounding low grade rocks are discussed elsewhere (Pigage 1978, t h i s volume). B r i e f l y , the Complex c o n s i s t s of i n t e r l a y e r e d s c h i s t s and q u a r t z i t e s belonging to the Hadrynian (Windermere) Kaza Group (Sutherland Brown 1963). Minor marble and rar e amphibolite u n i t s are s c a t t e r e d throughout the Kaza Group i n the 109 Figure 2-1. Major s t r u c t u r a l elements of the Canadian C o r d i l l e r a . The Shuswap Complex i s i n d i c a t e d by the r u l e d area. The l o c a t i o n of f i g u r e 2-2 i s c i r c l e d . M o dified from Wheeler and G a b r i e l s e (1972). 110 study area. The Complex i s separated from lower grade rocks to the n o r t h -east by a composite f a u l t zone. Metamorphic grade adjacent to the Complex decreases r a p i d l y to g a r n e t - b i o t i t e zone i n the greenschist f a c i e s . The Complex i t s e l f contains two recognized c o a x i a l phases of deformation; minor and major s t r u c t u r e s plunge g e n t l y northwest and southeast. Regional metamorphism was synchronous w i t h both phases of deformation. Deformation and metamorphism are r e s t r i c t e d to the time i n t e r v a l between Late T r i a s s i c and Late J u r a s s i c (K.V. Campbell 1971; Pigage 1977). METHOD OF STUDY Figure 2-2 i l l u s t r a t e s the l o c a t i o n s of 20 samples (12 p e l i t e s and 8 carbonates) s e l e c t e d f o r a n a l y s i s of major mine r a l s . Estimated modes of these samples are given i n Tables 2-1 and 2-2. Analyses (Tables 2-3 through 2-18) were accomplished using a three-channel, automated ARL SEMQ e l e c t r o n microprobe at the U n i v e r s i t y of B r i t i s h Columbia. A c c e l e r a t i n g p o t e n t i a l was constant at 15 kV. Beam diameter (2-35 micrometers) and specimen current (0.02-0.05 microamperes) were v a r i e d to provide maximum counts w i t h minimum specimen damage. Count readings f o r a f i x e d time i n t e r v a l were normalized t o an averaged beam c u r r e n t . For most elements a 20 second counting i n t e r v a l was used. With f l u o r i n e and carbonate analyses, counting times of 120 and 40 seconds, r e s p e c t i v e l y , improved the counting s t a t i s t i c s . Analyzed s y n t h e t i c and n a t u r a l minerals from the U n i v e r s i t y of B r i t i s h c o l l e c t i o n were used as standards (see Appendix 2-3). A l l readings were corrected f o r dead time, d r i f t , and background. F l u o r i n e and carbonate analyses were computed using a l e a s t squares l i n e a r r e g r e s s i o n curve f i t to Figure 2-2. Metamorphic zones i n the Shuswap Complex, Azure Lake, B r i t i s h Columbia. Samples s e l e c t e d f o r e l e c t r o n microprobe a n a l y s i s of c o e x i s t i n g minerals are shown. 112 the standards. For a l l other elements count readings were correct e d f o r matrix e f f e c t s using the computer program EMFADR V I I (Rucklidge and G a s p a r r i n i 1969). Several g r a i n s of each mineral i n a probe mount were analyzed w i t h repeated counts on each g r a i n . D i f f e r e n t minerals were i n v e s t i g a t e d i n c l o s e c l u s t e r s to take i n t o account p o s s i b l e l o c a l d i f f e r e n c e s i n composition. A l l minerals were checked f o r c o n c e n t r i c and s e c t o r zoning; where zoning was present ( p l a g i o c l a s e , garnet, c a l c i c amphibole) the g r a i n edges were considered to represent the composition i n e q u i l i b r i u m w i t h the r e s t of the mineral assemblage. Mean compositions and sample variances f o r each g r a i n were c a l c u l a t e d from the spot analyses. In most instances separate g r a i n s i n the same s l i d e had mean compositions that were not s i g n i f i c a n t l y d i f f e r e n t ; these mean analyses were then combined to form an o v e r a l l mean and standard e r r o r . Sample variances a s s o c i a t e d w i t h the mean compositions f o r each g r a i n were used to weight the l a t t e r c a l c u l a t i o n (Bevington 1969). F e r r o u s - f e r r i c r a t i o s and water content cannot be determined w i t h the e l e c t r o n microprobe. Iron was computed as FeO or Fe^O^ depending on the mineral being considered. Water content i n hydrous minerals was c a l c u l a t e d from s t o i c h i o m e t r i c constraints i n the s t r u c t u r a l formulae. Standard e r r o r s f o r R^O were computed by a Monte Carlo approach assuming normally d i s t r i b u t e d random e r r o r s i n the other analyzed oxides (Anderson 1976) . PELITIC MINERAL ASSEMBLAGES P e l i t i c mineral assemblages i n the Azure Lake area may be d i v i d e d i n t o three d i s t i n c t metamorphic zones ( f i g u r e 2-2). D i s t r i b u t i o n of these zones i n d i c a t e s a general increase i n metamorphic grade toward the southwest. 113 M i n e r a l assemblages f o r each of these zones are: Kyanite Zone k y a n i t e - g a r n e t - b i o t i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e - i l m e n i t e ± s t a u r o l i t e K y a n i t e - S i l l i m a n i t e Zone S i l l i m a n i t e - g a r n e t - b i o t i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e - i l m e n i t e ± 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 Zone s i l l i m a n i t e - g a r n e t - b i o t i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e - i l m e n i t e ± s t a u r o l i t e Minor amounts of tourmaline, a p a t i t e , z i r c o n , and f i n e opaque dust (graphite?) are present i n each of the assemblages. These assemblages are i l l u s t r a t e d i n the p r o j e c t i o n s of f i g u r e s 2-3 through 2-5. A l l p r o j e c t i o n s were c a l c u l a t e d f o l l o w i n g the approach o u t l i n e d by Greenwood (1975b). TESTS OF EQUILIBRIUM I n v e s t i g a t i o n of r e g i o n a l metamorphic assemblages usi n g e q u i l i b r i u m constants n e c e s s a r i l y assumes e q u i l i b r i u m c o n d i t i o n s during metamorphism. D i f f e r e n t c r i t e r i a f o r e q u i l i b r i u m i n c l u d e homogeneity of mineral compositions, n o n - v i o l a t i o n of the Gibbs phase r u l e , systematic p a r t i t i o n i n g of elements between c o e x i s t i n g minerals, and e q u i l i b r i u m t e x t u r a l r e l a t i o n s (Zen 1963). P r o j e c t i o n ( f i g u r e s 2-3 through 2-5) and element d i s t r i b u t i o n diagrams ( f i g u r e s 2-6 and 2-7) f o r p e l i t i c assemblages from the Azure Lake area are u s e f u l i n d i s c u s s i n g these v a r i o u s e q u i l i b r i u m t e s t s . E l e c t r o n microprobe spot analyses of s e v e r a l g r a i n s f o r each mi n e r a l w i t h i n the same s l i d e i n d i c a t e that minerals are g e n e r a l l y homogeneous. P l a g i o c l a s e grains show the most v a r i a b i l i t y (see Table 2-7). This small 114 s c a l e v a r i a t i o n i n a n o r t h i t e content has a l s o been noted i n other r e g i o n a l l y metamorphosed t e r r a i n s (Evans and G u i d o t t i 1966; F l e t c h e r and Greenwood 1978). P e l i t i c assemblages from the Azure Lake area may be described by the ten component system K 20-Na 20-CaO-Al 20 3-Si0 2-MgO-FeO-MnO-Ti0 2-H 20. Two a l t e r n a t i v e t e t r a h e d r a l p r o j e c t i o n s are used to i l l u s t r a t e phase r e l a t i o n s and Mg-Fe-Mn p a r t i t i o n i n g f o r c o e x i s t i n g minerals i n the d i f f e r e n t metamorphic zones. Figures 2-3a, 2-4a, 2-5a are the AFM p r o j e c t i o n (J.B. Thompson 1957) w i t h MnO as the f o u r t h corner of the tetrahedron. This p a r t i c u l a r p r o j e c t i o n assumes that q u a r t z , muscovite, H 20, i l m e n i t e , a l b i t e , and a n o r t h i t e are present i n excess or behave as species w i t h f i x e d chemical p o t e n t i a l s . A l t e r n a t i v e l y Rumble (1974) suggested that H 20 should be included i n the p r o j e c t i o n s i n c e i t may not have a uniform chemical p o t e n t i a l f o r a l l samples. This has been incorporated i n f i g u r e s 2-3b, 2-4b, 2-5b by p r o j e c t i n g from the appropriate A l 2 S i O ^ polymorph rather than from H-20. In both p r o j e c t i o n s garnet i s the only mineral which p l o t s away from the (A,H)FM plane of the tetrahedron. T i e - l i n e s between c o e x i s t i n g minerals are g e n e r a l l y s u b p a r a l l e l i n d i c a t i n g systematic p a r t i t i o n i n g of Mg-Fe-Mn between phases. Assemblages i n the kyanit e and s i l l i m a n i t e zones are at l e a s t b i v a r i a n t i n both p r o j e c t i o n s . Coexistence of k y a n i t e and s i l l i m a n i t e i n the intermediate zone r e q u i r e s univariance i f e q u i l i b r i u m was a t t a i n e d . C o e x i s t i n g minerals i n the HFM diagram do not contai n c r o s s i n g t i e - l i n e r e l a t i o n s and i n d i c a t e that a^ ^  may have been uniform f o r a l l p e l i t e samples. Figure 2-6 a l s o i l l u s t r a t e s the re g u l a r p a r t i t i o n i n g of Mg-Fe between c o e x i s t i n g garnet and b i o t i t e . P a r t i t i o n i n g c o e f f i c i e n t s f o r each of the Figure 2-3. Stereoscopic p r o j e c t i o n s of analyzed p e l i t i c assemblages c o n t a i n i n g k y a n i t e . A) M o d i f i e d AFM p r o j e c t i o n w i t h MnO as the f o u r t h corner of the tetrahedron. B) P r o j e c t i o n onto the components MnO-FeO-MgO-H20. C) P r o j e c t e d phase r e l a t i o n s between Al 2SiC> 5, muscovite, p l a g i o c l a s e , and K - f e l d s p a r i n the subsystem K 20-Na 20-CaO-Al 20 3-Si0 2-H 20. Ab b r e v i a t i o n s : A b - a l b i t e , An-anorthite, B t - b i o t i t e , C e l - c e l a d o n i t e , I l m - i l m e n i t e , Gt-garnet, Ky-kyanite, Ma-margarite, Ms-muscovite, Or-or t h o c l a s e , Pa-paragonite, S i l - s i l l i m a n i t e , S t - s t a u r o l i t e . 116 An Ab Figure 2-4. Stereoscopic p r o j e c t i o n s of analyzed p e l i t i c assemblages c o n t a i n i n g k y a n i t e and s i l l i m a n i t e . A ) , B ) , C) and ab b r e v i a t i o n s are the same as i n f i g u r e 2-3. 118 Samples 8 2 , 2 2 3 , 3 6 7 , 4 9 2 , 2 - 3 7 6 MnO -> MgO Samples 8 2 , 2 2 3 , 3 6 7 , 4 9 2 , 2 - 3 7 6 An Ab MgO MnO FeO MgO FeO Samples 8 2 , 2 2 3 , 3 6 7 , 4 9 2 , 2 - 3 7 6 Cel.Or S i " A K y Projected from Qtz H , 0 Cel.Or Figure 2-5. Stereoscopic p r o j e c t i o n s of analyzed p e l i t i c assemblages con t a i n i n g s i l l i m a n i t e . A ) , B ) , C) and abbreviations are the same as i n f i g u r e 2-3. 120 1.20 1.10 A 0) o m 1.00 A 0.90 ^ 2 H 3 • . 398 A 373 ^ • 74 _ q 2-376 J * 9 2 " l 2 l • 82 Y = 0.293 + 0.115 X (X = 0.0073) 6.00 6.50 7.00 (Fe/Mg) Garnet 7.50 8.00 F i g u r e 2-6. Fe-Mg d i s t r i b u t i o n diagram garnet and b i o t i t e . "Best f i t " l i n e a r equation was c a l c u l a t e d r e c o g n i z i n g that both v a r i a b l e s are subject to e r r o r (Mark and Church 1977). A = (sample variance of y)/(sample variance of x) t r i a n g l e - k y a n i t e zone; c i r c l e - k y a n i t e - s i l l i m a n i t e zone; square - s i l l i m a n i t e zone. 1 2 2 .gure 2-7. P l o t of (£ T )„ . vs. (X„ )„, . , . "Best f i t " 5 TJa' Muscovite v Ca'Plagioclase l i n e a r equation was c a l c u l a t e d r e c o g n i z i n g that both v a r i a b l e s are subject to e r r o r (Mark and Church 1977). X = (variance of y ) / ( v a r i a n c e of x) t r i a n g l e - k y a n i t e zone; c i r c l e - k y a n i t e - s i l l i m a n i t e zone; square - s i l l i m a n i t e zone. 123 three metamorphic zones overlap on the diagram; temperature gradients cannot be d i s t i n g u i s h e d . Figures 2-3c, 2-4c, 2-5c d e p i c t phase r e l a t i o n s between A1 2S10 5-mus c o v i t e - p l a g i o c l a s e - ( K - f e l d s p a r ) i n the subsystem K20-Na20-Al 202-Si02-H 20. T i e - l i n e s between K-feldspar (samples 2-376, 398, 2-13) and other minerals are dotted because phase r e l a t i o n s are p r o b l e m a t i c a l . K-feldspar occurs only as t h i n selvages (approximately 20 micrometers t h i c k ) p a r t l y e n c l o s i n g some of the p l a g i o c l a s e g r a i n s . Microprobe analyses show that i t i s more p o t a s s i c than muscovite i n the same s l i d e (see Tables 2-4, 2-8). This p o t a s s i c composition c o n t r a s t s s h a r p l y w i t h K-feldspar compositions reported i n s t u d i e s on the prograde development of K-feldspar by subsolidus r e a c t i o n s or by p a r t i a l m e l t i n g (Evans and G u i d o t t i 1966; Lundgren 1966; G u i d o t t i , Herd, and T u t t l e 1973; Tracy 1978). In these s t u d i e s prograde K-feldspar was c o n s i s t e n t l y more sodic than the c o e x i s t i n g muscovite. G u i d o t t i , Herd, and T u t t l e (1973) noted that p o t a s s i c K-feldspar occurred only i n retrograde v e i n l e t s t r a n s e c t i n g the r e g i o n a l K-feldspar + s i l l i m a n i t e assemblages. Because of these c o n s i d e r a t i o n s , I conclude that the K - f e l d s p a r selvages i n the Azure Lake area are a retrograde a l t e r a t i o n of p l a g i o c l a s e and are not part of the assemblage formed during prograde r e g i o n a l metamorphism. Figures 2-3c, 2-4c, 2-5c and 2-7 i l l u s t r a t e the systematic p a r t i t i o n i n g of Na between p l a g i o c l a s e and muscovite. The diagrams i n d i c a t e the i n v e r s e r e l a t i o n between a n o r t h i t e content of p l a g i o c l a s e and paragonite content of c o e x i s t i n g muscovite. Again the d i f f e r e n t metamorphic zones do not have d i s t i n g u i s h a b l e element p a r t i t i o n i n g ( f i g u r e 2-7). The above compositional r e l a t i o n s a l l support the assumption of chemical e q u i l i b r i u m during r e g i o n a l metamorphism. M i n e r a l grains are 124 homogeneous on the s c a l e of a probe s e c t i o n . . D i f f e r e n t p r o j e c t i o n s i n d i c a t e that the Gibbs phase r u l e has not been v i o l a t e d . P r o j e c t i o n s and p a r t i t i o n i n g diagrams show a systematic p a r t i t i o n i n g of elements between c o e x i s t i n g m i n e r a l s . I n c o n t r a s t , t h i n selvages of K-feldspar p a r t l y e n c l o s i n g p l a g i o c l a s e probably represent a retrograde a l t e r a t i o n of the e a r l i e r r e g i o n a l metamorphic assemblage. MINERAL TEXTURES Te x t u r a l r e l a t i o n s w i t h i n the p e l i t e s deomonstrate that some of the c o e x i s t i n g minerals are not i n t e x t u r a l e q u i l i b r i u m . Aggregates of f i b r o l i t i c s i l l i m a n i t e - i l m e n i t e - b i o t i t e - m u s c o v i t e appear to have formed at the expense of garnet, s t a u r o l i t e , and k y a n i t e . These textures o u t l i n e a sequence of r e a c t i o n s that have been p a r t i a l l y preserved by growth patterns i n v a r i o u s m i n e r a l s . Garnet porphyroblasts i n a l l three metamorphic zones o u t l i n e two stages of growth ( f i g u r e 2-8 and p l a t e 2-18). F i r s t stage garnets form l a r g e , ragged grains w i t h abundant quartz, p l a g i o c l a s e , mica, and opaque i n c l u s i o n s . T y p i c a l l y they c o n t a i n an even, sparse, opaque d u s t i n g . I n d i v i d u a l porphyroblasts are p a r t l y to completely enclosed by aggregates of intergrown f i b r o l i t e , coarse muscovite, x e n o b l a s t i c i l m e n i t e , and b i o t i t e ( p l a t e s 2-1, 2-3). Breakdown of garnet to form these aggregates i s more extensive w i t h i n c r e a s i n g metamorphic grade. F i r s t stage garnets are not commonly preserved southwest of Ovis Creek ( f i g u r e 2-2) . S t a u r o l i t e and k y a n i t e porphyroblasts form s i m i l a r r e l i c t g rains w i t h i n aggregates of muscovite of f i b r o l i t e - m u s c o v i t e . F i b r o l i t e coarsens to form s i l l i m a n i t e prisms w i t h i n c r e a s i n g metamorphic grade. Second stage garnets form c l e a r , i d i o b l a s t i c rims around ragged, f i r s t 125 stage garnet cores. These rims c o n t a i n only minor i n c l u s i o n s ( f i g u r e 2-8, p l a t e 2-1B). Where f i r s t stage garnets are uncommon, second generation garnets form small i d i o b l a s t i c porphyroblasts. F i b r o l i t e , b i o t i t e , and i l m e n i t e are p a r t l y to completely enclosed by second stage rims ( f i g u r e 2-8, p l a t e 2-3). Second stage garnet growth succeeded formation of the f i b r o l i t e aggregates. Chemical zoning p a t t e r n s i n garnet a l s o r e f l e c t two stages of growth. Traverses across s e l e c t e d garnets are shown i n f i g u r e 2-8. F i r s t stage garnet cores are c o m p o s i t i o n a l l y homogeneous. Second generation rims are c o n c e n t r i c a l l y zoned w i t h s p e s s a r t i n e content decreasing outward. Almandine content v a r i e s i n v e r s e l y w i t h s p e s s a r t i n e . In most samples pyrope and g r o s s u l a r content remain f a i r l y constant. In sample 367 g r o s s u l a r and pyrope are a l s o c o n c e n t r i c a l l y zoned. Zoning patterns i n small second stage garnets at higher metamorphic grades are s i m i l a r but are l i m i t e d ... i n range. This zoning i s s i m i l a r to the "normal" zoning p a t t e r n described f o r metamorphic garnets from p e l i t i c s c h i s t s (Harte and Henley 1966; and many o t h e r s ) . H o l l i s t e r (1966) suggested a f r a c t i o n a t i o n - d e p l e t i o n model to e x p l a i n the d i s t i n c t i v e c o n c e n t r i c Mn-zoning. Recently i t has been suggested that the zoning r e s u l t s from continuous garnet-forming r e a c t i o n s during prograde metamorphism (Tracy, Robinson, and A.B. Thompson 1976; T r z c i e n s k i 1977) . In k y a n i t e - and s i l l i m a n i t e - b e a r i n g s c h i s t s d i f f u s i o n assumes increased importance i n modifying the o r i g i n a l growth zoning p a t t e r n (Anderson and Olimpio 1977; Woodsworth 1977). A.B. Thompson, Tracy, L y t t l e , and J.B. Thompson (1977) have f u r t h e r argued that i n t e r n a l chemical and i n c l u s i o n d i s c o n t i n u i t i e s i n garnets from Vermont r e s u l t e d from r e s o r p t i o n of garnet through a discontinuous r e a c t i o n i n v o l v i n g garnet Figure 2-8. Chemical zoning patterns of s e l e c t e d garnets. Spot analyses were determined w i t h the e l e c t r o n microprobe. B r i e f d e s c r i p t i o n s of the garnets are given below: A) Sample 74. F i r s t generation garnet w i t h numerous i n c l u s i o n s enclosed by a second generation rim c o n t a i n i n g f i b r o l i t e i n c l u s i o n s , B) Sample 2-376. Small f i r s t generation garnet core c o n t a i n i n g opaque dust surrounded by l a r g e second generation garnet rim. 127 mol % GARNET 74 Figure 2-8 (continued). C) Sample 367. Large f i r s t generation garnet w i t h narrow second generation garnet rim. Chemical zoning i n v o l v e s g r o s s u l a r pyrope as w e l l as almandine and s p e s s a r t i n e . D) Sample 40. Small second generation garnet from southwest of Ovis Creek. GARNET 40 mol 130 as a reactant phase. Since garnet was a product phase i n prograde continuous r e a c t i o n s at both higher and lower temperatures, the d i s c o n t i n u i t i e s may have formed during a s i n g l e prograde metamorphic episode. The sharp change i n i n c l u s i o n d e n s i t y between stage 1 and stage 2 garnets from the Azure Lake area suggests that each generation of growth was formed through a separate metamorphic r e a c t i o n . The o v e r a l l zoning p a t t e r n i s compatible w i t h homogenization of f i r s t generation garnets concomitant w i t h the formation of f i b r o l i t e aggregates. Concentric zoning i n second generation garnets r e s u l t e d from subsequent growth according to a continuous garnet-forming r e a c t i o n during prograde metamorphism. The suggested sequence of r e a c t i o n s may be due to a s i n g l e prograde metamorphic episode. Muscovite i n the f i b r o l i t e aggregates t y p i c a l l y forms coarse, equant, randomly o r i e n t e d f l a k e s . I n d i v i d u a l grains are i n t e r l o c k i n g w i t h ragged margins ( p l a t e s 2-1, 2-2, 2-3, 2-4). F i b r o l i t e content i n aggregates v a r i e s i n v e r s e l y w i t h the modal amount of muscovite; aggregates i n q u a r t z i t i c p e l i t e s commonly conta i n mainly muscovite. At higher metamorphic grades b i o t i t e - f i b r o l i t e aggregates form attenuated t r a i l s through coarse muscovite.grains ( p l a t e 2-4). P l a g i o c l a s e commonly forms elongate augen conformable w i t h the r e g i o n a l s c h i s t o s i t y . Grains are r a r e l y twinned. In many instances g r a i n s are c o n c e n t r i c a l l y zoned w i t h a narrow r im of more c a l c i c composition. Since p l a g i o c l a s e i s the only major Ca-bearing phase besides garnet i n the p e l i t e s , zoning i s probably r e l a t e d to garnet breakdown. These tex t u r e s describe the i n i t i a l breakdown of garnet, s t a u r o l i t e , and k y a n i t e to form aggregates of f i b r o l i t e - m u s c o v i t e - b i o t i t e - i l m e n l t e . 131 Second stage garnet growth occurred at the expense of p r e v i o u s l y formed f i b r o l i t e aggregates. Replacement tex t u r e s w i t h i n aggregates at higher metamorphic grades a l s o imply that muscovite growth continued beyond formation of the f i b r o l i t e . METAMORPHIC REACTIONS Described t e x t u r a l r e l a t i o n s support the f o l l o w i n g s i l l i m a n i t e -forming r e a c t i o n s : 8 gar + 9 mus = 14 s i l l •+ 3 b i o +13 q t z , 12 stau + 9 mus + 7 qtz = 58 s i l l +' 3 b i o +' 12 H 20, . (2) 1 ky = 1 s i l l . (3) These r e a c t i o n s are balanced f o r t y p i c a l metamorphic mineral compositions i n the system K^O-FeO-MgO-Al^-SK^-^O (KFMASH) (A.B. Thompson 1976a). Quartz, muscovite, and ^ 0 have been added where necessary. Reactions (1) and (2) are continuous i n the system KFMASH; they occur over an i s o b a r i c temperature i n t e r v a l because of Mg-Fe p a r t i t i o n i n g . These r e a c t i o n s do not account f o r g r o s s u l a r content i n garnet, paragonite content i n muscovite, or T l content i n b i o t i t e . A d d i t i o n a l phases needed to inco r p o r a t e these elements are p l a g i o c l a s e and i l m e n i t e . Muscovite i s re q u i r e d as a reactant phase i n r e a c t i o n s (1) and (2). Textures i n d i c a t e that coarse muscovite i s a product phase w i t h i n the f i b r o l i t e aggregates and i s r e p l a c i n g k y a n i t e and s t a u r o l i t e . This apparent discrepancy may be explained by l o c a l c a t i o n exchange r e a c t i o n s and/or changes i n composition, of the f l u i d phase. Both p o s s i b i l i t i e s are discussed l a t e r . 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 described from other r e g i o n a l l y metamorphosed t e r r a i n s (Chakraborty and Sen 1967; Yar d l y 1977). T e x t u r a l d e s c r i p t i o n s f o r garnet breakdown i n p e l i t e s from Connemara, 132 I r e l a n d are s i n g u l a r l y comparable (Yardley 1977). Reactions (1) and (2) c o n t r a s t w i t h the commonly observed r e a c t i o n i n v o l v i n g the breakdown of s t a u r o l i t e and muscovite to form garnet, b i o t i t e , and s i l l i m a n i t e (A.B. Thompson 1976a; Carmichael 1970). LINEAR REGRESSION (Table 2-19) The use of l i n e a r r e g r e s s i o n techniques to s o l v e the mass-balance c o n s t r a i n t s i m p l i e d by p o s s i b l e metamorphic r e a c t i o n s has been p r e v i o u s l y o u t l i n e d (Greenwood 1968; Reid, Gancarz, and Albee 1973; Gray 1973; Pigage 1976). B r i e f l y , the method uses a l e a s t squares approach to t e s t f o r l i n e a r dependencies among sets of minerals (vectors) i n one or more assemblages. T e x t u r a l r e l a t i o n s and other c o n s t r a i n t s are needed to s e l e c t probable r e a c t i o n s from among the d i f f e r e n t p o s s i b l e mass-balance r e g r e s s i o n equations. A p a r t i c u l a r mass-balance equation i s considered s i g n i f i c a n t i f the r e s i d u a l d i f f e r e n c e between the observed and modelled compositions i s smaller than the combined p r e c i s i o n estimates f o r the mineral and the model. In an e a r l i e r study using l i n e a r r e g r e s s i o n (Pigage 1976), small e r r o r l i m i t s were shown to be e s s e n t i a l to assess the r e l i a b i l i t y of a l e a s t squares model. Elements o c c u r r i n g i n small amounts commonly f a l l w i t h i n e r r o r l i m i t s r a t h e r than p r o v i d i n g a d d i t i o n a l c o n s t r a i n t s on the r e g r e s s i o n c o e f f i c i e n t s . I have minimized t h i s problem by weighting each mass-balance equation according to the i n v e r s e of the variance of the mean f o r a p a r t i c u l a r set of analyses (Reid, Gancarz, and Albee 1973). Inter-element covariances were considered n e g l i g i b l e . In t h i s way minor elements assumed increased importance i n the r e g r e s s i o n model. 133 The standard weighted l e a s t squares approach assumes that the independent v a r i a b l e s i n the r e g r e s s i o n equation are e n t i r e l y f r e e of e r r o r . This approach i s v a l i d when analyzed minerals are being modelled i n terms of end-member compositions. In modelling metamorphic r e a c t i o n s , however, mineral analyses among the independent v a r i a b l e s u s u a l l y have e r r o r s of -about the same magnitude as the dependent v a r i a b l e . In t h i s s i t u a t i o n the problem becomes no n l i n e a r and must be solved i t e r a t i v e l y . Albarede and Provost (1977) have described an al g o r i t h m f o r s o l v i n g weighted l e a s t squares problems which recognizes e r r o r s i n both the dependent and independent v a r i a b l e s . This a l g o r i t h m was used to t e s t f o r p o s s i b l e metamorphic re a c t i o n s , among the Azure Lake p e l i t e assemblages. Examination of r e g r e s s i o n c o e f f i c i e n t s and r e s i d u a l s from t h i s approach i n d i c a t e s that i t gives r e s u l t s s i m i l a r to those r e s u l t i n g from standard weighted l i n e a r r e g r e s s i o n techniques. A r e g r e s s i o n model was considered s i g n i f i c a n t , i f the modelled composition f o r each analyzed mineral i n the r e g r e s s i o n equation was w i t h i n the two-sided confidence i n t e r v a l c a l c u l a t e d from the estimated standard e r r o r s f o r that m i n e r a l . A l l confidence i n t e r v a l s were constructed at the 95% p r o b a b i l i t y l e v e l ( a = 0.05). Appropriate t - f a c t o r s were s e l e c t e d from s t a t i s t i c a l t a b l e s (Guenther 1965, p. 294). Te x t u r a l r e l a t i o n s i n p e l i t i c u n i t s of the Shuswap Complex 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 - m u s c o v i t e -i l m e n i t e - f i b r o l i t i c s i l l i m a n i t e aggregates. The r e g r e s s i o n approach was used to model s t a u r o l i t e and garnet i n terms of the other minerals c o e x i s t i n g w i t h them. Zn was excluded from the mass-balance equations because other metamorphic s t u d i e s i n d i c a t e that Zn remains i n r e l i c s t a u r o l i t e i n i n c r e a s i n g concentrations w i t h the progressive breakdown of mat r i x s t a u r o l i t e ( G u i d o t t i 1970; Woodsworth 1977). A f l u i d phase 134 c o n s i s t i n g of R^O was assumed to be present. Quartz, H^O, and s i l l i m a n i t e were considered to be s t o i c h i o m e t r i c and f r e e of e r r o r (Albee and Chodos 1969; Ghinner, Smith, and Knowles 1969; Kwak 1971). The r e g r e s s i o n models of s t a u r o l i t e and garnet should i d e a l l y use compositions of c o e x i s t i n g minerals at the time of i n i t i a l f i b r o l i t e formation. Based on the t e x t u r a l i n t e r p r e t a t i o n presented e a r l i e r , t h i s would correspond to mineral compositions i n e q u i l i b r i u m w i t h f i r s t genera-t i o n garnet rims. Systematic p a r t i t i o n i n g of Mg and Fe between second generation garnet rims and b i o t i t e ( f i g u r e 2-6)indicates that the various homogeneous minerals have adjusted t h e i r compositions to remain i n near e q u i l i b r i u m w i t h the l a t e r stage two garnet r i m compositions. Consequently compositions i n e q u i l i b r i u m w i t h f i r s t generation garnets have not surv i v e d and cannot be used f o r the r e g r e s s i o n s t u d i e s . While r e c o g n i z i n g t h i s problem, I have chosen to model s t a u r o l i t e and garnet breakdown using r i m compositions f o r a l l m i n e r a l s . Major p r i o r i t y has t h e r e f o r e been placed on using e q u i l i b r i u m compositions f o r c o e x i s t i n g m i n e r a l s . The. s i g n i f i c a n c e of t h i s choice cannot be f u l l y assessed. Garnet compositions d i f f e r mainly i n Fe and Mn content. The b i o t i t e i n c l u s i o n w i t h i n garnet from sample 74, however, has a composition very s i m i l a r to matrix b i o t i t e i n the same sample (see Table 2-5). Regression equations must be regarded as i n t e r p r e t i v e r a t h e r than s t r i c t l y q u a n t i t a t i v e . Several d i f f e r e n t p o s s i b l e r e g r e s s i o n models aire l i s t e d i n Table 2 —19 • Equati ons R—1 through R—9 use the same mineral compositions f o r comparative purposes (sample 82). A l l the models i n v o l v e the 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 . Reactions R - l and R-2 model garnet and s t a u r o l i t e i n terms of edge compositions of c o e x i s t i n g phases. Residuals are much l a r g e r than permitted 135 Table 2-19. Regression equations f o r p e l i t i c mineral assemblages, Shuswap Metamorphic Complex, Azure Lake, B r i t i s h Columbia. Equation R - l . Sample 82 - r e g r e s s i o n model of garnet. REGRESSION COEFFICIENTS SILL QTZ H20 BOS BIO PLAG ILH 17.321 18.557 11.100 -6.712 1.153 0.711 0.123 SIGMA 0.401 0.470 0. 277 0. 1*49 0.012 0.008 0. 005 GAR 1. 000 INFORMATION PERTAINING TO THIS PIT: RESIDUALS (X - X*) ELEMENT MUS BIO PLAG ILH GAR SI + 4 -0.000 0. 000 0.000 0.0 -0.000 A L O -0.000 0.000 0. 000 0. 000 -0.000 FE + 2 0. 040 -0.035 0.0 -0.002 0.02 0 HN*2 0.0 -0.006 0.0 -0.001 0.061 HG*2 -0.144 0. 128 0.0 0.002 -0.127 CA +2 0.0 0.0 0. 009 0. 0 -0.010 NA+ 1 0. 209 -0.012 -0.006 0. 0 0.0 K* 1 1.217 -0.423 -0.000 0.0 0.0 H + 1 -0.000 0. 000 0.0 0.0 0.0 TI*4 -0.009 0.008 0.0 0. 003 -0.000 BA + 2 0.0 19 -0.000 0.0 0.0 0.0 P*0 0.005 -0.001 0.0 0.0 0.0 ERROR RATIO (RESIDUAL / PERMITTED ERROR ) ELEMENT MUS BIO PLAG ILH GAS SI*4 0. 000 0.000 0.000 0.0 0. 000 AL*3 0. 000 0. 000 0.000 0. 000 0.000 FE + 2 8. 296 3. 170 0.0 0.223 2.364 HN*2 0. 0 6.561 0.0 0. 685 21.758 MG + 2 33.998 12.992 0.0 0. 406 12.917 CA*2 0. 0 0.0 2. 157 0.0 2.710 NA* 1 18.932 1.808 1.073 0.0 0.0 K* 1 83.676 19 .980 0. 237 0. 0 0.0 H + 1 0. 000 0. 000 0.0 0.0 0.0 TI*4 4. 230 1.616 0.0 0. 278 0. 16 1 BA + 2 16.987 0.651 0.0 0.0 0.0 F*0 1. 974 0.251 0.0 0.0 0.0 CORRELATION COEFFICIENTS SILL 1.000 QTZ 0. 977 1.000 H20 0. 995 0.984 1.000 MUS -0.996 -0.984 -0.998 1.000 BIO 0. 848 0.827 0.841 -0.864 1.000 PLAG -0.177 -0.199 -0. 164 0. 165 -0.153 ILH 0.662 0.66 1 0.668 -0.6 56 0.392 SILL QTZ H20 HUS BIO 1.000 -0.100 PL AS 1.000 ILH 136 Table 2-19 ( c o n t . ) . Equation R-2. Sample 82 - re g r e s s i o n model of s t a u r o l i t e . DEGRESSION COEFFICIENTS SILL QTZ H20 NUS BIO PLAG 10.383 -1. 316 2. 337 1. 254 1. 109 0.069 SIGBA 0.014 0. 056 0. 019 0.012 0. 007 0. 004 NPOHH AT ION PERTAINING TO T BIS FIT: RESIDUALS (X - X*) ELEMENT BUS BIO PL AG ILB STAU SI*4 -0.000 0.000 0.000 0.0 -0.000 AL*3 -0.000 0.000 0.000 0.000 -0.000 FE+2 0.014 -0.065 0.0 -0.004 0.322 BN + 2 0.0 -0.001 0.0 -0.000 0.008 BG + 2 -0.012 0.055 0.0 0.001 -1 .567 CA + 2 0. 0 0.0 0.003 0.0 -0.016 NA*1 0. 140 -0.040 -0.002 0. 0 0.0 K* 1 0. 046 -0.083 -0.000 0.0 0.0 H* 1 -0.000 0. 000 0.0 0.0 -0.000 TI*4 -0.003 0.013 0.0 0.005 -0.26 2 BA*2 0.010 -0.000 0.0 0.0 0.0 F*0 -0.052 0.026 0.0 0.0 0.0 EB ROB RATIO (RESIDUAL / PERBITTED ERROR ) ELEBENT BUS BIO PLAG ILB STAO SI + 4 0.000 0.000 0.000 0.0 0.000 AL»3 0.000 0.000 0.000 0.000 0.000 FE*2 2.981 5.867 0.0 0. 416 10.745 BB*2 0.0 1.606 0.0 0. 169 3.138 HG + 2 2. 823 5.557 0.0 0. 175 24.426 CA*2 0.0 0.0 0.712 0.0 5.264 NA* 1 12.641 6.220 0. 370 0.0 0.0 K*1 3. 182 3.913 0.005 0.0 0.0 H* 1 0. 000 0.000 0.0 0. 0 0.000 TI*4 1. 348 2.652 0.0 0. 460 9.714 BA»2 9. 201 1.815 0.0 0.0 0.0 F + 0 19.153 12.563 0.0 0.0 0.0 CORRELATION COEFFICIENTS SILL 1. 000 QTZ -0.209 1.000 U20 0. 527 0.469 1.000 nos -0.570 -0.405 -0.764 1.000 BIO 0. 272 0.061 0. 181 -0.705 1 .000 PL AG -0.118 -0.182 -0.066 0. 130 -0.138 1.000 ILB -0.144 -0.007 -0.061 0.414 -0.652 0.085 SILL QTZ H20 nos BIO PLAG IL (1 0. 119 0. 006 STAU •1. 000 1 .000 ILH 137 Table 2-19 (continued). Equation R-3. Sample 82 - Regression model of s t a u r o l i t e : garnet included i n model. REGRESSION COEFFICIEHTS SILL QTZ H20 MUS BIO PLUG IL H GAR STAU 9.915 -1. 583 2. 272 -1. 031 0.914 -0.045 0.095 0.248 -1.000 SIGMA 0.045 0.054 0.016 0. 012 0.009 0.005 0. 006 0. 009 INFORMATION PERTAINING TO THIS FIT: RESIDUALS (X - X«) ELEMENT MUS BIO PLAG ILN GAR STAU SI*4 0.000 -0.000 0.000 0.0 -0.000 0.000 AL*3 0.000 -0.000 0.000 -0.000 -0.000 0.000 FE»2 0.009 -0.041 0.0 -0.002 -0.007 0.246 MN»2 0.0 0.001 0.0 0.000 0.00 3 -0.006 NG»2 -0.008 0.037 0.0 0.000 0.011 -1.288 CA*2 0.0 0.0 -0.003 0.0 0.013 -0.027 NA*1 0. 196 -0.056 0.002 0.0 0.0 0.0 K*1 0.045 -0.080 0.000 0.0 0.0 0.0 H* 1 0.000 -0.000 0.0 0.0 0.0 0. 000 TI*4 -0.002 0.008 0.0 0. 003 0.000 -0.192 BA*2 0.010 -0.000 0.0 0.0 0.0 0.0 F»0 -0.052 0.026 0.0 0.0 0.0 0. 0 EBBOR BATIO (BESIOUAL / PEBHITTED EBROB ) ELEMENT HQS BIO PLAG ILH GAR STAU SI + 4 0. 000 0.000 0.000 0. 0 0.000 0.000 AL*3 0.000 0.000 0.000 0.000 0.000 0.000 FE»2 1. 869 3.690 0.0 0. 254 0. 860 8. 196 HN*2 0.0 1.059 0.0 0. 108 1 .098 2.510 HG*2 1. 908 3.766 0.0 0. 115 1. 170 20. 0 76 CA*2 0.0 0.0 0. 768 0.0 3.824 8.751 NA* 1 17.746 8.757 0.410 0. 0 0.0 0.0 K* 1 3.068 3.784 0.004 0.0 0.0 0.0 H»1 0.000 0.000 0.0 0.0 0.0 0. 000 TI»4 0.810 1.598 0.0 0.269 0.050 7. 101 BA»2 9. 173 1.815 0.0 0.0 0.0 0.0 P»0 19.192 12.626 0.0 0.0 0.0 0.0 CORRELATION COEFFICIENTS SILL 1.000 QTZ -0.215 1 .000 H20 0. 45* 0.425 1.000 H0S -0.590 -0.413 -0.638 1.000 BIO 0.412 0. 189 0. 163 -0.818 1.000 PLAG -0.011 -0.104 -0.152 0.002 0.138 1.000 ILH -0.070 0.016 -0.065 0.266 -0.314 0.299 1.000 GAB -0.316 -0.187 -0.032 0.493 -0.664 -0.530 -0.240 SILL QTZ B20 H0S BIO PLAG ILH 138 Table 2-19 (continued) Equation R-4. Sample 82 - Regression model of garnet: a n o r t h i t e included i n model. REGRESSION COEFFICIENTS SILL ANOR QTZ 19.948 -0. 733 17.945 SIGH* 0.470 0.028 0.450 INFORHATION PERTAINING TO THIS FIT: RESIDUALS (X - X*) U2 0 13.515 0. 343 BUS •8.020 0. 185 BIO 1.24 8 0.015 PLAG 3.252 0. 097 I L I 0. 1«8 0.006 GAB -1.000 ELEBENT DOS BIO SI»4 0.000 -0.000 AL*3 0.000 -0.000 FE*2 0.024 -0.019 HN*2 0.0 -0.006 HG»2 -0.130 0. 105 CA*2 0.0 0.0 NA*1 -0.004 0.000 K»1 1.254 -0.394 H«1 0.000 -0.000 TI*4 -0.006 0.005 BA*2 0.019 -0.000 F+0 0.007 -0.001 PLAG ILH GAR -0.000 0.0 0.000 -0.000 -0.000 0.000 0.0 -0.001 0.010 0.0 -0.001 0.059 0.0 0. 001 -0.096 0.000 0.0 -0.000 0.000 0.0 0.0 -0.000 0.0 0.0 0.0 0.0 0.0 0.0 0.002 -0.000 0.0 0.0 0.0 0.0 0.0 0.0 ERROR RATIO (RESIDUAL / PERMITTED ERROR ) ELEHENT SI*4 AL*3 FE+2 MN»2 NG + 2 CA*2 NA + 1 K*1 H»1 Tim BA»2 F»0 MUS 0.000 0.000 4.979 0.0 30.629 0.0 0.386 86.181 0.000 2. 864 17.160 2.646 BIO 0.000 0.000 1.723 6.943 10.603 0.0 0.033 18.643 0.000 0.991 0.595 0.305 PLAG ILH GAR 0.000 0.0 0.000 0.000 0.000 0.000 0.0 0.135 1.187 0.0 0. 808 21.272 0.0 0. 370 9.739 0.000 0.0 0.000 0.084 0.0 0.0 0.935 0.0 0.0 0.0 0.0 0.0 0.0 0. 190 0.091 0.0 0.0 0.0 0.0 0.0 0.0 CORRELATION COEFFICIENTS SILL AN0B QTZ H20 HUS BIO PLAG ILB 1.000 -0.757 0. 949 0.994 -0.995 0.875 0.775 0.656 SILL 1.000 -0.610 -0.781 0.782 -0.691 -0.973 -0.513 ANOR 1.000 0.948 1.000 •0. 948 -0.998 1.000 0.820 0.870 -0.889 1.000 0.624 0.802 -0.803 0.710 1.000 0.636 0.663 -0.651 0.420 0.527 QTZ H20 BUS BIO PLAG 1.000 ILH 139 Table 2-19 (continued). E l a t i o n R-5. Sa^l e 82 - Regression B „ d e l of staurolite: anorthite Included i n model. REGRESSION COEFFICIENTS SILL ANOR QTZ 10.446 -0.109 -1.726 SIGMA 0.04* 0.003 0.056 INFORMATION PERTAINING TO THIS FIT: RESIDUALS (X - X * l H20 2.443 0.019 MUS -1.318 0.012 BIO 1. 120 0. 00 7 PLAG 0.396 O.OU ILM 0.115 0.006 STAU -1.000 ELEMENT MUS BIO S I +4 0.000 -0.000 AL*3 0.000 -0.000 FE*2 0.014 -0.063 MN+2 0.0 -0.001 MG*2 -0.013 0.056 CA+2 0.0 0.0 NA»1 -0.000 0.000 K * l 0.071 -0. 122 H+l 0.000 -0.000 TI*4 -0.003 0.013 BA»2 0.011 -0.000 F*0 -0.050 0.025 PLAG -0.000 -0.000 0.0 0.0 0.0 0.000 0.000 -0.000 0.0 0.0 0.0 0.0 ILM 0.0 -0.000 -0.004 -0.000 0.001 0.0 0.0 0.0 0.0 0.005 0.0 0.0 ERROR RATIO (RESIDUAL / PERMITTEO ERROR . ELEMENT SI*4 AL*3 FE»2 MN*2 MG+2 CA»2 NA*1 K * l H*l TI*4 8A»2 F»0 MUS 0.000 0.000 3.027 0.0 2.990 0.0 0.02 0 4.900 0.000 1.369 9.577 18.598 BIO 0.000 0.000 5.725 1.621 5.656 0.0 0.010 5.791 0.000 2.588 1.816 11.722 CORRELATION COEFFICIENTS SILL ANOR OTZ H20 MUS BIO PLAG ILM 1 .000 0.158 0.286 0.520 0.554 0.260 0.159 0. 133 SILL 1 .000 0.158 -0.312 0.365 -0.215 -0.914 0. 119 ANOR PLAG 0.000 0.000 0.0 0.0 0.0 0.000 0.003 0.039 0.0 0.0 0.0 0.0 1.000 0.351 -0.26* -0.029 -0.184 0.045 OTZ ILM 0.0 0.000 0. 390 0.164 0.171 0.0 0.0 0.0 0.0 0.431 0.0 0.0 1.300 -0.781 0.204 0.342 -0.072 H20 STAU 0.000 0.000 0.311 0.008 -1.579 -0.000 0.0 0.0 0.000 -0.253 0.0 0.0 STAU 0.000 0.000 10.381 3.136 24.612 0.000 0.0 0.0 0.000 9.387 0.0 0.0 1 .000 -0.701 -0. J99 0.404 MUS 1.000 0.235 -0.642 BIO 1.000 -0.130 PLAG 1.000 ILM 140 Table 2-19 (continued) Equation R-6. Sample 82 - Regression model of staurolite: anorthite and garnet included in model. REGRESSION COEFFICIENTS SILL ABOB QTZ 8.330 -0.206 -3. 116 s i a m o.osi 0.003 o.osi INFORHATION PERTAINING TO THIS FIT: R20 2.085 0.010 BOS -0.273 0.022 BIO 0. 23 5 0.019 PLAG 0.082 0. 007 ILH 0.063 0.005 GAR 1.002 0.019 STA0 -1.000 RESIDUALS (X - X*) ELEHEHT H0S BIO PL AG SI HI 0.000 -0.000 -0.000 AL»3 0.000 -0.000 -0.000 Tt*2 0.000 -0.002 0.0 a»*2 0.0 0.001 0.0 NG»2 -0.000 0.002 0.0 CA«2 0.0 0.0 -0.000 NAM -0.000 0.000 0.000 N«1 0.062 -0.107 -0.000 H*1 0.0 0.0 0.0 T I M -0.000 0.000 0.0 BA»2 0.011 -0.000 0.0 T*0 -0.051 0.025 0.0 ILH GAB STAU 0.0 -0.000 0.000 -0.000 -0.000 0.000 -0.000 -0.005 0.043 0.000 0.0*0 -0.019 0.000 0.007 -0.205 0.0 -0.000 0.000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.000 0.000 -0.022 0.0 0.0 0.0 0.0 0.0 0.0 EBBON BATIO (BESID0AL / PEBHITTED EBBOB ) ELEHENT SI M AL»3 FE»2 NN»2 HG«2 CJ.2 NA«1 K»1 HO T I M BA»2 F»0 BOS 000 ,000 ,088 0 080 0 018 233 0 025 »37 810 BIO 0.000 0.000 0.168 0.870 0. 15* 0.0 0.008 5.078 0.0 0.0«7 1.816 12.03* COBBELATION COEFFICIENTS SILL 1.000 ANON 0.«02 1.000 0TI -0.060 0.317 B20 0.5*0 0.318 NOS -0.762 -0.50* BIO 0.757 0.511 FLAG 0.720 0.*11 ILI -0.002 0.236 CAN -0.7M -0.63* SILL ANOI PL AG ILI GAB STAU 0.000 0.0 0.000 0.000 0.000 0.000 0.000 0.000 0.0 0.030 0.615 1.450 0.0 0.227 1*.161 8. 007 0.0 0.012 0.75* 3.198 0.000 0.0 0.000 0.000 0.003 0.0 0.0 0.0 0.034 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.020 0.023 0. 816 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.000 0.332 1.000 0.453 -0.699 1.000 0.4*7 0.673 -0.997 1.000 0.*08 0.67* -0.950 0.9«* 1.000 0.120 -0.059 0.092 -0.09* -0.087 1.000 0.506 -0.627 0.930 -0.933 -0.880 -0.1*7 1.000 QT» H20 •as BIO PLA8 ILH HAN 141 Table 2-19 (continued). Equation R-7. Sample 82 - Regression model of garnet: a n o r t h i t e and r u t i l e i n c luded i n model. REGRESSION COEFFICIENTS SILL ANOR OTZ H20 RUT MUS BIO 1.0*2 0. 170 1.722 0.057 -2.120 -0.185 0.159 SIGMA 0.005 0.002 0.007 0.00 3 0.009 0.003 0.003 INFORMATION PERTAINING TO THIS FIT: PLAG 0 . 0 5 5 0 . 0 0 2 ILN 1 . 0 * 5 0 . 0 0 4 -I GAR . 0 0 0 RESIDUALS (X ELEMENT MUS BIO PL AG ILM GAR SI»* 0.000 -0.000 -0.000 0.0 0.000 AL*3 0.000 -0.000 -0.000 -0.000 0.000 FE*2 -0.000 0.001 0.0 0.00* -0.00* MN»2 0.0 -0.001 0.0 -0.006 0.053 MG*2 0.000 -0.001 0.0 -0.001 0.005 CA-»2 0.0 0.0 0.0 0.0 0.0 NA*1 -0.000 0.000 0.000 0.0 0.0 K*l 0.061 -0.107 -0.000 0.0 0.0 H-l 0. 000 -0.000 0.0 0.0 0.0 TI»* 0.000 -0.000 0.0 -0.300 0.000 BA*2 0.011 -0.000 0.0 0.0 0.0 F»0 -0.051 0.025 0.0 0.0 0.0 ERROR RATIO (RESIDUAL / PERMITTED ERROR 1 ELEMENT MUS BIO PL AG ILM GAR SI** 0.000 0.000 0.000 0.0 0.000 AL«3 0.000 0.000 0.000 0.000 0.000 FE*2 0.0*5 0.086 0.0 0.3 73 0.*63 MN»2 0.0 0.787 0.0 5.061 18.863 MG*2 0.039 0.075 0.0 0.1*5 0.5*0 C««2 0.0 0.0 0.0 0.0 0.0 NAU 0.018 0.008 0.003 0.0 0.0 K»l *.22* 5.069 0.03* 0.0 0.0 H»l 0.000 0.000 0.0 0.0 0.0 Tl»* 0.000 0.000 0.0 0.000 0.000 BA-2 "».*35 1.816 0.0 0.0 0.0 F»0 18.812 12.039 0.0 0.0 0.0 CORRELATION COEFFICIENTS SILL ANOR OT I H20 RUT MUS BIO PLAG ILM 1.000 0.*19 1 .000 0.158 -0.160 1 .000 0.771 -0.126 0.335 1.000 0.387 -0.082 -0 . 1 11 0.211 1.000 0.835 0.162 0. 000 -0.485 -0.5*1 1.000 0.667 -0.1*1 -0.180 0.3T3 0.588 -0.927 1.000 0.*26 -0.282 -0.275 0.**7 0.292 -0.573 0.501 1.000 0.*56 0.097 0.136 -0.2*3 -0.873 0.6*1 -0.700 -0.3*3 SILL ANOR OTZ M20 RUT MUS BIO PL AG . 0 0 0 ILN 142 Table 2-19 (continued). Equation R-8. Sample 82 - Regression model of s t a u r o l i t e : a n o r t h i t e and r u t i l e i n c l u d e d i n model. REGRESSION COEFFICIENTS SILL ANOR QTZ H20 RUT BUS BIO PLAG ILH STAU 9.232 -0.026 -1. 336 2. 106 -2. 397 -0.341 0.295 0. 102 1.213 -1.000 SIGflA 0.039 0.002 0.01K 0.009 0.031 0.015 0.012 0.005 0.015 | INFOBHATION PERTAINING TO THIS FIT: RESIDUALS (X - X*) ELEHENT BUS BIO PL AG ILH STAU SI*» 0.000 -0.000 -0.000 o . d 0.000 AL»3 0.000 -0.000 -0.000 -0.000 0.000 FE»2 0.000 -0.000 0.0 -0.000 0.001 HN»2 0.0 0.000 0.0 0.000 -0.001 no*2 -0.000 0.000 0.0 0.000 -0.005 C»»2 0.0 0.0 -0.000 0.0 0.000 NA»1 -0.000 0.000 0.000 0.0 0.0 K»1 0.061 -0.107 -0.000 0. 0 0.0 H«1 0.0 0.0 0.0 0.0 0.0 TI»4 -0.000 0.000 0.0 0.000 -0.000 BA*2 0.011 -0.000 0.0 0.0 0.0 P*0 -0.051 0.025 0.0 0.0 0.0 ERROR RATIO (RESIDUAL / PERMITTED ERROR ) ELEMENT HUS BIO PLAG ILH STAU sim 0.000 0.000 0.000 0.0 0.000 AL»3 0.000 0.000 0.000 0.000 0.000 PE»2 0.003 0.005 0.0 0.015 0.037 HR»2 0.0 0.078 0.0 0.322 0.572 MG»2 0.002 0.005 0.0 0.006 0.078 CA»2 0.0 0.0 0.000 0.0 0.000 NA»1 0.018 0.008 0.003 0.0 0.0 K»1 V. 229 5.069 0.034 0.0 0.0 B«1 0.0 0.0 0.0 0.0 3.0 TI»» 0.000 0.000 0.0 0.000 0.000 Bi»2 9.U35 1.816 0.0 0.0 0.0 r»o 18.812 12.039 0.0 0.0 0.0 CORRELATION COEFFICIENTS SILL 1.000 ANOR -0.31B 1.000 QTX -0.73* 0. 100 1.000 B20 0.293 -0.386 -0.011 1. o o o ROT 0. 370 -0.532 -0.123 0.408 1.000 BUS -0.46* 0.656 0. 127 -0.563 -0.81B 1.000 BIO 0. *«7 -0.692 -O.1»8 0.H95 0.829 -0.988 1.000 PLAG 0. 388 -0.769 -0.158 0.502 0.691 -0.853 0.835 1.000 ILH -o. * o a 0.582 0. 136 -0.9*5 -0.926 0.895 -0.907 -0.756 SILL ANOB QTI H20 BOT aos BIO PLAG I 143 Table 2-19 (continued). Equation R-9. Sample 82 - Regression model of s t a u r o l i t e : a n o r t h i t e , r u t i l e , and garnet i n c l u d e d i n model. 8EGBESSI0H COEFFICIEHTS SILL A HOB 9.262 -0. 020 SIGHA 0.043 0 . 0 0 1 QTZ H20 BUT -1.280 2. 107 -2.471 0.055 0.009 0.054 GAB BOS BtO 0.032 -0.315 0. 297 0.019 0.015 0.012 PLAS ILH STA0 0. 103 1. 280 -1. 000 0.005 0. 027 INPOBHATION PEBTAIHIHG TO TBIS FIT: BESIDUALS (I - !•) ELEMENT GAB BOS BIO PLAG ILB STAU SI.1 0. 000 0.000 -0.000 -0.000 0.0 0.000 AL*3 0.000 0.000 -0.000 -0.000 -0.000 0.000 FE»2 0.000 0.000 -0.000 0.0 -0.000 0.000 BN»2 -0.000 0.0 0.000 0.0 o . o o o -0.000 HG»2 0.000 0.000 -0.000 0.0 -0.000 0.000 C»»2 -0.000 0.0 0.0 0.000 0.0 -0.000 HAH 0.0 -0.000 o . o o o 0.000 0.0 0.0 K.I 0.0 0.061 -0.107 -0.000 0.0 0.0 HO 0.0 0.000 -0.000 0.0 0.0 0.000 TI»1 0.000 0.000 -0.000 0.0 -0.000 0.000 BA*2 0.0 0.011 -0.000 0.0 0.0 0.0 F»0 0.0 -0.051 0.025 0.0 0.0 0.0 ER BOB BATIO (BESIDUAL / PEBBITTED EBBOB ) ELEOEST GAB BUS BIO PLAG ILK STAU SI»4 0. 000 0.000 0.000 0.000 0.0 0.000 »L.3 0.000 0.000 0.000 0.000 0.000 0.000 FE«2 0.000 0.000 0.000 0.0 0.000 0.000 n»»2 0. 000 0.0 0.000 0.0 0.000 0.000 «Ci2 0.000 0.000 0.000 0.0 0.000 0.000 CA»2 0.000 0.0 0.0 0.000 0.0 0.000 »AO 0.0 0.018 0.008 0.003 0.0 0.0 HO 0.0 1. 221 5.069 0.031 0.0 0.0 HO 0.0 0.000 0.000 0.0 0.0 0.000 TI.U 0.000 0.000 0.000 0.0 0.000 0.000 BA»2 0.0 9.135 1. 816 0.0 0.0 0.0 P.O 0.0 18.812 12.039 0.0 0.0 0.0 COBBELATIoa COEPFICIEHTS SILL 1.000 ANOB 0.215 1 .000 QTZ -0.286 0.565 1.000 H20 0.292 -0.136 0. 029 1.000 B0T -0.1»0 -0.860 -0.518 0.185 1.000 GAB - o . m o -0.870 -0.602 -0.061 0.815 1.000 BOS -0.470 0.212 0.026 -0.565 -0.369 0.123 1.000 BIO 0.155 -0.201 -0.012 0.197 0.373 -0.125 -0.988 PLAG 0. 391 -0.286 -0.062 0.S03 0.311 -0. 104 -0.853 ILH 0.121 0.876 0.555 -0. 204 -0.975 -0.818 0.410 SILL ABOB QTZ B20 BUT GAB BUS 1.000 0. 835 -0.4 15 BIO 1.000 -0.346 PLAG 1.000 ILH 144 Table 2-19 (continued). Equation R-10. Sample 2-376 - Regression model of garnet: a n o r t h i t e and r u t i l e i n c luded i n model. 8E5RESSION COEFFICIENTS SILL ANOB QTZ 1. 003 0. 197 1.716 SIGN* 0. 007 0.003 0. 007 INPORHATION PERTAINING TO THIS PIT: RESIDDALS (X - X«) ELEMENT NOS BIO PLA3 ILH GAR sim 0.000 -0.000 -0.000 0.0 0.000 AL»3 0. 000 -0.000 -0.000 -0.000 0.000 FE*2 -0.000 0.00 1 0.0 0. 077 -o.ooi MN*2 0.0 -0.000 0.0 -0.023 0.014 HG*2 0. 000 -0.002 0.0 -0.000 0.003 CA»2 0.0 -0.000 -0.000 -0.ooo 0.000 Ni»1 -0.000 0.000 0.000 0.0 0.0 K • 1 0.058 -0.065 -0.000 0.0 0.0 H*1 0.0 0.0 0.0 0.0 0.0 TI*1 -0.000 0.000 0.0 0.000 -0.000 BA*2 0. 006 -0.001 0.0 0.0 0.0 F-tO -0.020 0.088 0.0 0.0 0.0 H20 RUT HUS BIO PLAG ILH SAR 0. 063 -2. 1 37 -0. 199 0. 172 0. 06 1 1. 053 -1 .000 0. 002 0. 5 16 0. 002 0. 001 0. 001 0. 007 ERROR RATIO (RESIDUAL / PERHITTED ERROR ) ELEMENT MUS BIO PLAG ILN GAR SI*4 0.000 0.000 0.000 0.0 0.000 AL + 3 0. 000 0.000 0.000 0.0 00 0.000 PE*2 0.060 0. 177 0.0 2. 9 06 0.690 MN»2 0.0 0.642 0.0 11.732 9.395 na*2 0.111 0. 218 0.0 0.060 0.637 CA*2 0.0 0.000 0.000 0.000 0.000 NA+ 1 0. 005 0.005 0.005 0.0. 0.0 K*1 5.579 5.453 0.055 0.0 0.0 H+1 0.0 0.0 0.0 0.0 0.0 T i n t 0.000 0.000 0.0 0. 000 0.000 BA*2 11.152 4. 37 2 0.0 0.0 0.0 P*0 22.667 14.329 0.0 0.0 0.0 CORRELATION COEPPICIENTS SILL 1.000 ANOR -0.535 1.000 QTZ -0.086 -0.175 1.000 H20 0. 159 -0.041 0.318 1.000 RUT 0.019 -0.005 -0.018 0. 039 1.000 HUS -0.162 0.049 -0.141 -0.755 -0.131 1.000 BIO 0. 280 -0.037 -0.074 0.260 0. 166 -0.822 1.000 PLAG 0. 399 -0.058 0. 108 0.710 0.102 -0.845 0.629 1.000 ILH -0.059 0.006 0.021 -0.045 -0.851 0.166 -0.209 -0.126 SILL ANOB QTZ H20 RUT HUS BIO PLAS 145 Table 2-19 (continued). Equation R - l l . Sample 40 - Regression model of garnet: a n o r t h i t e and r u t i l e i n c l u d e d i n model. B EGB ESSION COEFFICIENTS SILL ABOB OTZ H20 BUT BOS BIO PLAG ILB 1.044 0.130 1.671 0.025 -2..148 -0. 166 0. 158 0.052 1.063 SIGHA 0.004 0.003 0.005 0.002 0.310 0.002 0.001 0.001 0.003 GAB •1. 000 IHPOBHATION PERTAINING TO THIS FIT: BESIDUALS (X - X*) ELEHENT BUS BIO PLAG ILB GAB sim 0.000 -0.000 -0.000 0.0 0.000 »L»3 0.000 -0.000 -0.000 -0.000 0.000 FE»2 -0.000 0.000 0.0 0.000 -0.000 »B»2 0.0 -0.000 0.0 -0.000 0.062 HG»2 0.000 -0.000 0.0 -0.000 0.000 CA»2 0.0 0.0 0.0 0.0 0.0 NAtl -0.000 0.000 0.000 0.0 0.0 N»1 0. 000 -0.001 -0.000 0.0 0.0 H*1 0.0 0.0 0.0 0.0 0.0 TI*4 -0.000 0. 000 0.0 0.000 -0.000 BA»2 0.001 -0.005 -o.ooo 0.0 0.0 F*0 -0.010 0.113 0.0 0.0 0.0 ERROE RATIO (BESIDUAL / PEBBITTED ERBOB ) ELEHENT BUS BIO PL AG ILH GAB SI*4 0. 000 0.000 0.000 0.0 0.000 AL*3 0.000 0.000 0.000 0.000 0.000 rz*2 0.002 0.014 0.0 0.041 0.033 BN + 2 0.0 0. 104 0.0 0.413 8.203 HG»2 0.001 0.017 0.0 0.013 0.011 CA*2 0.0 0.0 0.0 0.0 0.0 NAU 0. 005 0.005 0.000 0.0 0.0 K»1 0. 062 0.099 0.001 0.0 0.0 H*1 0.0 0.0 0.0 0.0 0.0 TI»» 0.000 0.000 0.0 0.000 0.000 BA»2 1.503 4 .005 0.077 0.0 0.0 F»0 3. 861 12.356 0.0 0.0 0.0 COBRELATION COEFFICIENTS SILL 1.000 ABOB -0.719 1.000 QTZ 0. 388 -0.469 1.000 H20 0.531 -0.034 0.266 1.009 BUT 0. 110 -0.011 -0.059 0.042 1.000 BUS -0.585 0.049 0.034 -0.56S -0.248 BIO 0. 399 -0.040 -0.204 0. 164 0.280 PLAG 0.264 -0.092 -0.244 0.364 0.122 ILH -0.181 0.019 0. 101 -0.064 -0.629 SILL ANOB QTX H20 BOT 1.000 -0.890 -0.535 0.412 HOS 1.000 0.439 -0.470 BIO 1.000 -0.202 PL AS .000 ILB 146 Table 2-19 (continued). Equation R-12. Sample 40.- Regression model of s t a u r o l i t e : a n o r t h i t e and r u t i l e i n c l u d e d i n model. REGRESSION COEFFICIENTS SILL ANOR QTZ H20 ROT NOS BIO Pl»G ILN STAU 9. 1 93 - 0 . 0 2 2 -1. 5 7 8 2. 037 -2.127 -0.287 0. 275 0.090 1. 299 -1.000 SIGN* 0.019 0. 000 0 . 0 1 6 0.003 0.0 16 0.003 0.003 0. 002 0.006 INFOBHATION PERTAINING TO THIS PIT: R E S I D U A L S ( X - X») E L E M E N T HQS B I O SI*0 - 0 . 0 0 0 0. 000 A L » 3 -0. 000 0.000 F E » 2 0. 000 -0.000 «N »2 0. 0 0.000 NG»2 0. 000 -0.008 C A » 2 0. 0 0.0 NA* 1 -0. 000 0.000 K« 1 - 0 . 001 0.003 H» 1 0. 000 -0.000 T I » 9 0. 000 -0.000 B A « 2 0. 001 -0.005 P»0 -0. 002 0. 028 PLAG ILH STAO 0.000 0. 0 -0.000 0.000 0. 000 -0.000 0.0 -0. 000 0.000 0.0 0. 000 -0.000 0.0 -0. 001 0.004 0.000 0. 0 0.0 0.000 0. 0 0.0 0.000 0. 0 0.0 0.0 0. 0 0.000 0.0 -0. 000 0.000 0.000 0. 0 0.0 0.0 0. 0 -3.017 ERROR RATIO (RESIDUAL / PERBITTED ERROR ) ELEMENT HUS BIO PLAG ILH STAU SI »U 0.000 0.000 0.000 0. 0 0.000 AL»3 0. 000 0.000 0.000 0.000 0.000 PE*2 0. 001 0.006 0.0 0.011 0.023 fl««2 0.0 0.069 0.0 0. 185 0.979 HG»2 0.019 0. 345 0.0 0. 185 0. 477 CA»2 0.0 0.0 o.ooo 0.0 0.0 NA * 1 0. 009 0.009 0.000 0.0 0.0 K» 1 0. 156 0.250 0.002 0.0 0.0 H« 1 0. 000 0.000 0.0 0.0 0.000 Tl »9 0. 000 0.000 0.0 0.000 0.000 3 A » 2 1. 985 3.972 0.076 0.0 0.0 r*o 0. 957 3.072 0.0 0.0 9.72 9 CORRELATION COEFFICIENTS SILL 1.000 AMOR -0.199 1 .000 QTZ -0.737 0. 195 1.000 H20 0. 206 -0.297 0.119 1.000 BUT 0.079 -0.179 -0.051 0.051 1 .000 BOS -0.299 0.565 0.053 -0.435 -0.339 1.000 BIO 0. 219 -0.986 -0.135 0. 197 0.371 -0.917 PL AG 0.195 -0.980 -0.199 0. 302 0. 183 -0. 577 iLn -0.103 0.237 0.069 -0.063 -0.789 0.999 SILL ANOR QTZ H20 BUT HUS 1.000 0.496 -0.495 BIO 1.000 -0.242 PLAG .000 ILN 147 Table 2-19 (continued). Equation R-13. Sample 223 - Regression model of garnet: a n o r t h i t e and r u t i l e i n c l u d e d i n model. REGRESSION COEFFICIENTS SILL ANOR QTZ H20 BUT HUS BIO PLAG 23IL GAR 0. 972 0.181 1.685 0.028 -2.065 -0. 165 0. 156 0.053 1. 023 -1. 000 SIGMA 0.004 0. 003 0.006 0. 00 1 0.0 10 0. 001 0. 00 1 0. 00 1 0.004 INFOBHATION PERTAINING TO THIS FIT: RESIDUALS (I - X») ELEHENT HUS BIO PLAG ILH GAB SItU 0.0 0.0 0.0 0.0 0.0 AL*3 0.0 0.0 0.0 0.0 0.0 FE»2 -0.000 0.001 0.0 0.020 -9.001 H»»2 0.0 -0.000 0.0 -0.003 0.082 HG»2 0. 001 -0.002 0.0 -0.001 0.000 CA*2 0.000 -0.000 -0.000 0.0 0.000 NA»1 -0.000 0.000 0.000 0.0 0.0 K»1 0.0*5 -0.006 -o.ooo 0.0 0.0 a»i 0.000 -0.000 0.0 0. 0 0.0 TI»4 0. 000 -0.000 0.0 -0.000 0.0 B» »2 o.ooi -0.001 -0.000 0. 0 3.0 F*0 -0. 056 0.067 0.0 0.0 0.0 ERROR RATIO (RESIDUAL / PERHITTED EBROR ) ELEHENT HUS BIO SI»4 0.0 0.0 AL»3 0.0 0.0 FE»2 0.032 0.112 HN»2 0.0 0.851 nG»2 0.098 0.161 CA»2 0.000 0.000 NA* 1 0. 042 0.007 K»1 1.018 1.498 H»1 0. 000 0.000 TI*4 0.000 0.000 BA»2 3.187 1.416 P»0 20.317 22.566 PL AG ILH GAR 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.245 0.589 0.0 5.286 28.288 0.0 0.226 9. 182 0.000 0.0 o.ooo 0.011 0.0 0.0 0.043 0.0 0.0 0.0 0. 0 0.0 0.0 0.000 0.0 0. 134 0.0 0.0 0.0 O. 0 0.0 COBBELATION COEFFICIENTS SILL 1.000 ANOR -0.641 1 .000 QTZ 0. 140 -0.337 1.000 H20 0.391 -0.039 0.175 1.003 BUT 0.081 -0.012 -0.033 0. 042 1 .000 nus -0.156 0.059 0.008 -0.548 -0.230 1.000 BIO 0. 318 •0.018 -0.121 0. 177 0.259 -0.895 1.000 PLAG 0.059 -0.181 -0.313 0.214 0.068 -0.323 0. 265 1.000 ILH -0.093 0.014 0.039 -0.04S -0.899 0. 267 -0. 303 -0.079 SILL ANOR QTZ H20 RUT HUS BIO PL AG 148 e r r o r l i m i t s f o r s e v e r a l major elements. Large e r r o r s i n the b a l a n c i n g of Mg, Fe, Na, and K are e s p e c i a l l y n o t i c e a b l e . The l a r g e c o r r e l a t i o n c o e f f i c i e n t s between va r i o u s minerals i s r e f l e c t e d i n the l a r g e standard d e v i a t i o n s i n the r e g r e s s i o n c o e f f i c i e n t s . These l a r g e values are r e l a t e d to the occurrence of s p e c i f i c elements i n only a few m i n e r a l s . E r r o r s f o r the muscovite c o e f f i c i e n t , f o r example, are mirrored by e r r o r s i n the b i o t i t e c o e f f i c i e n t s i n c e these two minerals balance the r e g r e s s i o n equation f o r potassium. Equation R-3 i n c l u d e s garnet i n the s t a u r o l i t e model. Residuals are s t i l l q u i t e l a r g e . Garnet appears as a product phase which i s i n general agreement w i t h the commonly reported s t a u r o l i t e - o u t r e a c t i o n (A.B. Thompson 1976a). However, t h i s ^ e q u a t i o n c o n f l i c t s w i t h observed garnet breakdown textu r e s i n the Azure Lake p e l i t e s . Many of the p l a g i o c l a s e grains i n Azure Lake p e l i t e s e x h i b i t reverse c o n c e n t r i c zoning. In equations R-4, R-5, and R-6 a n o r t h i t e has been inc l u d e d i n the r e g r e s s i o n models to accommodate a, changing f e l d s p a r composition during r e a c t i o n . Residuals f o r Na and Ca become n e g l i g i b l e w i t h t h i s a d d i t i o n . The garnet r e g r e s s i o n model (R-4) improves considerably because i n c l u s i o n of a n o r t h i t e allows f o r b a l a n c i n g the g r o s s u l a r content of the garnet. A n o r t h i t e i s a reactant phase i n R-4, R-5, and R-6. This c o n t r a d i c t s the observed compositional zoning i n p l a g i o c l a s e . Mg, Mn, and K r e s i d u a l s s t i l l denote l a r g e imbalances f o r some of the major c o n s t i t u e n t s . Equation R-6 i s s i m i l a r to R-3 although i n c l u s i o n of a n o r t h i t e reduces the r e s i d u a l s . Garnet remains as a product phase i n c o n t r a d i c t i o n to the t e x t u r e s . Equations R-7, R-8, and R-9 show that r e s i d u a l s f o r both garnet and s t a u r o l i t e r e g r e s s i o n models are reduced s i g n i f i c a n t l y by the a d d i t i o n of 149 r u t i l e as a p a r t i c i p a t i n g phase. Major element r e s i d u a l s are w i t h i n or only s l i g h t l y above permitted e r r o r l i m i t s . Mn i n modelled garnet compositions i s c o n s i s t e n t l y lower than analyzed Mn-content. This i s at l e a s t p a r t l y r e l a t e d to the d i f f i c u l t y of a n a l y z i n g garnet rim compositions because of the c o n c e n t r i c zoning. Balance i s s t i l l poor f o r l e s s e r c o n s t i t u e n t s l i k e Ba and F. Because these elements are present i n small amounts, they could be r e a d i l y balanced by small concentrations i n unanalyzed phases (tourmaline or f l u i d phase). Continued K imbalance may i n d i c a t e increased m o b i l i t y of K r e l a t i v e to the other elements being considered or continued adjustment of mica compositions to lower temperatures d u r i n g c o o l i n g . A n o r t h i t e i s a product phase i n equation R-7. This equation i s c o n s i s t e n t w i t h both tex t u r e s and p l a g i o c l a s e zoning i n the Azure Lake p e l i t e s . I n c l u d i n g r u t i l e i n equation R-9 has caused garnet to appear as a reactant phase. Again t h i s i s c o n s i s t e n t w i t h the t e x t u r a l i n t e r p r e t a t i o n . A n o r t h i t e i s a reactant phase i n equations R-8 and R-9, but p a r t i c i p a t e s i n the suggested r e a c t i o n s only to a minor extent. The considerable improvement i n r e s i d u a l s f o r equations R-7, R-8, and R-9 suggests that r u t i l e must be included as a p a r t i c i p a t i n g reactant phase. This i s a l s o supported by the correspondence between r e g r e s s i o n equations and the observed tex t u r e s and p l a g i o c l a s e zoning. Problems w i t h b a l a n c i n g of minor elements may be r e l a t e d to unanalyzed phases or to increased m o b i l i t y . The r e g r e s s i o n equations are dehydration r e a c t i o n s and are c o n s i s t e n t w i t h an o v e r a l l i n c r e a s i n g metamorphic grade toward the southwest. R u t i l e occurs only as s c a t t e r e d i n c l u s i o n s i n p o r p h y r o b l a s t i c k y a n i t e and garnet i n the Azure Lake s c h i s t s . Lack of r u t i l e i n the s c h i s t matrix suggests that r e a c t i o n t e x t u r e s are p a r t l y preserved because of the 150 exhaustion of a v a i l a b l e r u t i l e . Reactions R-10 through R-13 show that s i m i l a r r e a c t i o n r e l a t i o n s are revealed when r e g r e s s i o n models are c a l c u l a t e d f o r other samples c o n t a i n i n g s t a u r o l i t e and/or garnet w i t h s i l l i m a n i t e . INTERPRETATION The zoning and i n c l u s i o n patterns i n garnets imply two periods of growth w i t h the second o c c u r r i n g a f t e r i n i t i a l formation of f i b r o l i t e aggregates. Second stage growth r e s u l t e d from a continuous garnet-forming r e a c t i o n during prograde metamorphism. Any growth zoning p a t t e r n s i n stage one garnets have been destroyed by homogenization through d i f f u s i o n . The h i a t u s between f i r s t and second generation garnets may be explained by r e s o r p t i o n of garnet through a discontinuous garnet breakdown r e a c t i o n . This garnet breakdown r e a c t i o n has been modelled f o r Azure Lake mineral compositions using l i n e a r r e g r e s s i o n techniques. Regression modelling of garnet and s t a u r o l i t e breakdown r e a c t i o n s i n d i c a t e s that r u t i l e i s re q u i r e d as a reactant phase i n the 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 . Reaction te x t u r e s i n the s c h i s t s . a r e p a r t l y preserved because of exhaustion of matri x r u t i l e . This sequence of r e a c t i o n s may be explained by a s i n g l e prograde metamorphism. Muscovite i s required as a reactant i n a l l of the above r e g r e s s i o n equations. Textures i n d i c a t e that coarse, equant muscovite i s a product phase w i t h i n the f i b r o l i t e aggregates and that i t replaces k y a n i t e and s t a u r o l i t e . Carmichael (1969) has suggested that t e x t u r a l r e l a t i o n s between minerals are c o n t r o l l e d by l o c a l c a t i o n exchange r e a c t i o n s ( i o n i c r e a c t i o n s ) . The "general" metamorphic r e a c t i o n r e s u l t s from the summation of two or more d i f f e r e n t l o c a l r e a c t i o n s . The l o c a l r e a c t i o n s are coupled by i o n i c 151 d i f f u s i o n so that the system i s closed to mass t r a n s f e r on the s c a l e of a t h i n s e c t i o n . His example of the l o c a l replacement of k y a n i t e by muscovite concomitant w i t h the formation of s i l l i m a n i t e i n nearby muscovite grains i s d i r e c t l y a p p l i c a b l e to s c h i s t s from the Azure Lake area. In t h i s case an o v e r a l l , decrease i n modal muscovite due to s t a u r o l i t e or garnet breakdown may be accompanied by the l o c a l formation of coarse muscovite around k y a n i t e . S i m i l a r i o n i c r e a c t i o n s would account f o r the replacement of other phases by muscovite. A l t e r n a t i v e l y , coarse muscovite may r e s u l t from a change i n metamorphic c o n d i t i o n s at some indeterminate time a f t e r the formation of the f i b r o l i t e aggregates. Eugster (1970) and Kwak (1971) have shown that i o n i c r e a c t i o n s r e l a t i n g muscovite and the a l u m i n o s i l i c a t e polymorphs are very s e n s i t i v e to s l i g h t changes i n concentrations of i o n i c species (K+ and H+) d i s s o l v e d i n the f l u i d phase. A small change i n f l u i d composition during metamorphism would cause muscovite to l o c a l l y r eplace k y a n i t e and/or s i l l i m a n i t e . Any such muscovite-forming r e a c t i o n could not be a simple r e t r o g r a d i n g according to the probable r e a c t i o n s o u t l i n e d by the r e g r e s s i o n equations s i n c e newly formed r u t i l e was not observed. With regard to t h i s l a t t e r model i t i s i n t e r e s t i n g to note that imbalance of K i n the r e g r e s s i o n equations may be r e l a t e d to increased m o b i l i t y of K r e l a t i v e to the other major elements considered. Observed tex t u r e s s u b s t a n t i a t e the l a t e r replacement of other metamorphic minerals by coarse muscovite i n d i c a t i n g that at l e a s t part of the muscovite t e x t u r e s may be r e l a t e d to t h i s model. F l e t c h e r and Greenwood (1978) have discussed metamorphic text u r e s i n s c h i s t s from the Shuswap Complex j u s t northwest of the Azure Lake area. They argue that two metamorphic episodes are r e q u i r e d to e x p l a i n the observed t e x t u r a l and zoning p a t t e r n s . In t h e i r suggested sequence of 152 r e a c t i o n s s i l l i m a n i t e i s the l a s t metamorphic m i n e r a l to c r y s t a l l i z e . In contrast I have attempted to show that s i m i l a r t e x t u r e s i n the Azure Lake area may be explained by a sequence of r e a c t i o n s during a s i n g l e prograde metamorphism. With t h i s i n t e r p r e t a t i o n the formation of f i b r o l i t e aggregates preceded growth of second generation garnets. Muscovite te x t u r e s are probably p a r t l y r e l a t e d to changes i n f l u i d composition d u r i n g l a t e stages of the same metamorphism. METAMORPHIC CONDITIONS The d i s c u s s i o n i n the s e c t i o n on e q u i l i b r i u m t e s t s has shown that mineral assemblages i n the Azure Lake area appear to have reached chemical e q u i l i b r i u m during metamorphism. I t i s therefore reasonable to estimate metamorphic c o n d i t i o n s by comparing Azure Lake p e l i t i c assemblages to published experimental s t u d i e s on mineral e q u i l i b r i u m . The thermodynamic parameters AG^, AS^, and AV^ _ have been used to describe the l o c a t i o n of each experimental e q u i l i b r i u m curve i n p r e s s u r e -temperature space. A l l thermodynamic parameters f o r the d i f f e r e n t e q u i l i b r i a have been reduced to a common reference s t a t e of 298.15 K and 1 bar t o t a l pressure to f a c i l i t a t e c a l c u l a t i o n s . Appendix 2-2 contains a d i s c u s s i o n of the assumptions and equations used i n reducing e q u i l i b r i a t o the reference s t a t e . I n t e r n a l consistency of thermodynamic parameters f o r each experimental e q u i l i b r i u m was confirmed using l i n e a r i n e q u a l i t i e s (Gordon 1973). Where p o s s i b l e , entropies of r e a c t i o n ( AS^) were s e l e c t e d to be c o n s i s t e n t w i t h p r e v i o u s l y tabulated values (Robie and Waldbaum 1968) . Approximate e r r o r l i m i t s on each c a l c u l a t e d e q u i l i b r i u m were de r i v e d from the permitted range i n AG values at the s e l e c t e d As . The permitted AG r r r range was estimated from the simplex of c o n s i s t e n t AG and AS values c a l c u l a t e d using l i n e a r i n e q u a l i t i e s (Gordon 1973). 1 5 3 At l e a s t three independent experimental e q u i l i b r i a are required to solve f o r pressure, temperature, and a c t i v i t y of H^O. I have used the f o l l o w i n g four e q u i l i b r i a to estimate metamorphic c o n d i t i o n s f o r the Shuswap Complex i n the Azure Lake area: 1 Kyanite = 1 S i l l i m a n i t e ( E l ) 6 F e - s t a u r o l i t e + 11 Quartz = 23 Kyanite + 4 Almandine + 3 H 20 (E4) 1 Paragonite + 1 Quartz = 1 A n d a l u s i t e + 1 H i g h - A l b i t e + 1 H 20 (E7) 1 Grossular + 2 Kyanite + 1 Quartz = 3 A n o r t h i t e (E10) E q u i l i b r i u m constants were used to consider s o l i d s o l u t i o n e f f e c t s and v a r i a t i o n s i n H 20 a c t i v i t y when c a l c u l a t i n g the d i s p l a c e d p o s i t i o n s of the e q u i l i b r i u m curves. The d i f f e r e n t e q u i l i b r i u m constants are. defined as: KE4 = ( aAlmandine ) ^ ^ ( P (a )6 F e - s t a u r o l i t e KE7 a A l b i t e aH 20 a_ Paragonite 3 K E 1 0 = ( a A n o r t h i t e ) a G r o s s u l a r Other phases i n these r e a c t i o n s were considered to be pure and s t o i c h i o m e t r i c ( a c t i v i t y = 1). Expressions r e l a t i n g composition to a c t i v i t y are needed f o r each of the above components i n order to use the e q u i l i b r i u m constants to d i s p l a c e the experimental e q u i l i b r i u m curves. The f o l l o w i n g s e c t i o n discusses the a c t i v i t y models f o r these d i f f e r e n t components. 154 Garnet: An i o n i c mixing model f o r almandine and g r o s s u l a r a c t i v i t i e s r e s u l t s i n the expressions (Greenwood 1977) : 3 a = ( v A 1 *x„ ) (A) Almandine v r Almandine "Fe ^ , = ( Y r i * X P > 3 C5) Grossular ' Grossular Ca where the X's are the mole f r a c t i o n s of the atoms on the e i g h t - f o l d s i t e s . This model assumes that A l i s the only t r i v a l e n t c a t i o n i n the octahedral s i t e (see Table 2-3). Recently Ganguly and Kennedy (1974) proposed a p r e l i m i n a r y model f o r nonid e a l garnet s o l i d s o l u t i o n i n v o l v i n g the four components almandine, g r o s s u l a r , pyrope, and s p e s s a r t i n e . More d e t a i l e d s t u d i e s along the grossular-pyrope b i n a r y j o i n are i n general agreement w i t h t h e i r model (Hensen, Schmid, and Wood 1975; Wood 1977). C a l c u l a t e d v _ n values ' ' ' Grossular f o r Azure Lake garnet compositions using t h i s model range from 1.5 to 1.7 ( f o r 500-700° C). The c a l c u l a t e d y ... ,. f o r the same temperature 1 Almandine range i s approximately 1.02. S t a u r o l i t e : Thermodynamic parameters f o r equations (E4 and E5) have been derived u s i n g the formula F e ^ l g S i ^ O ^ O H ) f o r F e - s t a u r o l i t e (Ganguly 1972). N a t u r a l s t a u r o l i t e s c o n s i s t e n t l y c o n t a i n twice as much hydroxyl content as t h i s formula ( G r i f f e n and Ribbe 1976). This compositional d i f f e r e n c e can be accounted f o r through the coupled s u b s t i t u t i o n s : A l ( V I ) + H + = S i ( I V ) , Fe(IV) = • (IV) + 2H +, and A l ( V I ) = • ( V I ) + 3H + where D denotes a vacancy i n the s i t e . The Roman numerals r e f e r to the c o o r d i n a t i o n of the s i t e being considered. F o l l o w i n g K e r r i c k and Darken (1975), the a c t i v i t y of F e - s t a u r o l i t e i s defined by the r e l a t i o n : 155 a F e - s t a u r o l i t e = ( X F e ) * ( XA1> * ( S S i ) ( 6 ) where , X.n, and X.,. r e f e r to the mole f r a c t i o n s of each of these Te A l S i elements i n the s t r u c t u r a l formula (note that i n t h i s model vacancies are included i n the t o t a l s i t e p o p u l a t i o n ) . This model assumes i d e a l mixing on the d i f f e r e n t s i t e s . Hydroxyl i s i m p l i c i t l y i n c luded through the d i f f e r e n t coupled s u b s t i t u t i o n s . The model i s admittedly s i m p l i f i e d s i n c e n a t u r a l s t a u r o l i t e s have A l and Fe d i s t r i b u t e d over both t e t r a h e d r a l and octahedral s i t e s ( G r i f f e n and Ribbe 1976). Expression (6) c o n t r a s t s w i t h e a r l i e r published models where the a c t i v i t y of F e - s t a u r o l i t e i s equal to the mole f r a c t i o n of Fe r a i s e d to the second power (Ganguly 1972; F l e t c h e r and Greenwood 1978). I n c l u d i n g the terms f o r A l and S i has the general e f f e c t of lowering the c a l c u l a t e d F e - s t a u r o l i t e a c t i v i t y . This i s o b a r i c a l l y d i s p l a c e s the c a l c u l a t e d e q u i l i b r i u m to higher temperatures. Comparison of d i s p l a c e d e q u i l i b r i u m curves (E4, E5) f o r Azure Lake s t a u r o l i t e compositions i n d i c a t e s that i n c l u d i n g the terms f o r A l and S i i s o b a r i c a l l y increases the e q u i l i b r i u m temperature by about 30° C. P l a g i o c l a s e : A c t i v i t i e s f o r a l b i t e and a n o r t h i t e i n p l a g i o c l a s e have been considered as, being equal to the mole f r a c t i o n s of NaAISi 0 o and 3 8 CaAl2Si20g. A c t i v i t y c o e f f i c i e n t s were taken from the study by O r v i l l e (1972). The r e s u l t i n g expressions f o r p l a g i o c l a s e compositions from the Azure Lake area are: a..,,..t = 1.0 * X A 1, . (7) A l b i t e A l b i t e v ' a. = 1-276 * X. (8) A n o r t h i t e A n o r t h i t e 156 Muscovite: Binary s o l i d s o l u t i o n between muscovite and paragonite i s n o n i d e a l . (Eugster et a l 1972). The asymmetric b i n a r y s o l u t i o n model (Eugster et a l . 1972) i s f u r t h e r complicated by the ubiquitous presence of c e l a d o n i t e component i n metamorphic white micas. F l e t c h e r and Greenwood (1978) have handled t h i s problem by assuming a quaternary nonideal mixing model w i t h muscovite, paragonite, K c e l a d o n i t e , and Na c e l a d o n i t e as components. A l l Margules W-parameters were considered zero except f o r the two parameters d e s c r i b i n g the muscovite-paragonite b i n a r y j o i n . A l t e r n a t i v e l y the quaternary mixing model may be constructed assuming that the excess W-parameters f o r Na-K i n t e r a c t i o n are i d e n t i c a l f o r the muscovite-paragonite and K celadonite-Na c e l a d o n i t e b i n a r y j o i n s . S o l i d s o l u t i o n toward the c e l a d o n i t e component along each b i n a r y j o i n from muscovite or paragonite i s considered i d e a l (W-terms = 0). F u l l expressions f o r G .and Y„ . using the l a t t e r s o l u t i o n model are presented i n excess Paragonite Appendix 2-2. Three d i f f e r e n t sets of Margules W-parameters have been suggested f o r the muscovite-paragonite j o i n (Eugster et: a l . 1972; Chatterjee and Froese 1975; Blencoe 1977). C a l c u l a t e d e q u i l i b r i u m curves (E8) f o r sample 82 . using the d i f f e r e n t parameters d i f f e r by a maximum of only 15° C. A l l subsequent computations use the 8 kbar volume data f o r s y n t h e t i c 2M^ polymorphs from Blencoe (1977). Paragonite a c t i v i t y i s r e l a t e d to mole f r a c t i o n by the equation ( K e r r i c k and Darken 1975) : 2 2 a P a r a g o n i t e = ^Paragonite * ^ a * ^ A l ^ * ( 8 ) This corresponds to the formula NaAl 3Si 3C> 1 0(OH) 2 f o r s t o i c h i o m e t r i c paragonite. Mixing on the S i s i t e i s accounted f o r by coupled s u b s t i t u t i o n s 157 f o r A l i n the octahedral s i t e . y . . i s c a l c u l a t e d by the scheme Paragonite presented above (also see Appendix 2-2). The above a c t i v i t y expressions have been used i n the e q u i l i b r i u m constants to d i s p l a c e e q u i l i b r i u m curves E4, E5, E8, E9, E10, and E l l . The d i s p l a c e d curves correspond to the e q u i l i b r i a f o r c o e x i s t i n g mineral compositions i n the Azure Lake area. The method of c a l c u l a t i o n i s discussed i n Appendix 2-2. Thermodynamic parameters used to the c a l c u l a t i o n s are presented i n Tables 2-21 and 2-22. The f o l l o w i n g s e c t i o n s discu s s the r e s u l t s f o r the d i f f e r e n t e q u i l i b r i a . K y a n i t e - S i l l i m a n i t e This t r a n s i t i o n i s independent of the a c t i v i t y of H^O, and therefore provides an important r e s t r i c t i o n on the p o s s i b l e pressure-temperature c o n d i t i o n s during metamorphism. Since both k y a n i t e and s i l l i m a n i t e c o n t a i n only minor i m p u r i t i e s , s o l i d s o l u t i o n displacement of the t r a n s i t i o n i s n e g l i g i b l e (Albee and Chodos 1969; Chinner, Smith, and Knowles 1969). Two d i f f e r e n t petrogenetic g r i d s f o r the A l ^ S i O ^ polymorphs are c u r r e n t l y i n the l i t e r a t u r e . Experimental s t u d i e s by Richardson, G i l b e r t , and B e l l (1969) place the i n v a r i a n t t r i p l e p o i n t at a higher pressure and temperature than the g r i d presented by Holdaway (1971). The major d i f f e r e n c e i n the two s t u d i e s i s the p o s i t i o n of the a n d a l u s i t e - s i l l i m a n i t e t r a n s i t i o n . Recent c a l o r i m e t r i c s t u d i e s are c o n s i s t e n t w i t h the Holdaway i n t e r p r e t a t i o n (Anderson, Newton, and Kleppa 1977). According to Holdaway (1971), the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n does not appear to be s i g n i f i c a n t l y a f f e c t e d by the presence of f i b r o l i t e i n place of sillimanite... I have used i n t e r n a l l y c o n s i s t e n t thermodynamic parameters f o r the 158 d i f f e r e n t A l ^ S i O ^ t r a n s i t i o n s from.the co m p i l a t i o n by Helgeson ejc a l . (1978). These parameters are c o n s i s t e n t w i t h the Holdaway petrogenetic g r i d . E r r o r l i m i t s f o r each t r a n s i t i o n are based on experimental s t u d i e s by Newton (1966a, 1966b), Richardson, B e l l , and G i l b e r t (1968), Richardson, G i l b e r t , and B e l l (1969), and Holdaway (1971). St a u r o l i t e - Q u a r t z - G a r n e t - A l ^ S i O ^ The upper s t a b i l i t y l i m i t of s t a u r o l i t e + quartz i s defined by r e a c t i o n (E4). This e q u i l i b r i u m has been experimentally c a l i b r a t e d by Ganguly (1972). Richardson (1968) has a l s o s t u d i e d t h i s r e a c t i o n using s i l l i m a n i t e i n s t e a d of k y a n i t e . His suggested r e a c t i o n c o e f f i c i e n t s are s l i g h t l y d i f f e r e n t because he assumed a d i f f e r e n t composition f o r F e - s t a u r o l i t e . C a l c u l a t e d thermodynamic parameters that are co n s i s t e n t w i t h experimental brackets from both s t u d i e s r e q u i r e the r e a c t i o n c o e f f i c i e n t s and s t a u r o l i t e composition presented by Ganguly (see Appendix 2-2). Ca l c u l a t e d p o s i t i o n s of the assemblage s t a u r o l i t e - g a r n e t - q u a r t z -Al„SiCv (k y a n i t e , s i l l i m a n i t e ) f o r P T T _ = P m _^ ., are i n d i c a t e d i n 2 5 H 20 T o t a l f i g u r e 2-9. The d i f f e r e n t curves, have a l l been d i s p l a c e d to correspond to mine r a l compositions from the Azure Lake area. Y.. „. i s sm a l l and Almandine has been set to 1.0 ( i d e a l s o l u t i o n ) because of the t e n t a t i v e nature of the s t a u r o l i t e s o l u t i o n model. FMQ oxygen b u f f e r has been assumed f o r a l l c a l c u l a t i o n s (Eugster and Wones 1962). D i f f e r e n t samples i n the Azure Lake area a l l c l u s t e r i n a narrow pressure-temperature i n t e r v a l i n f i g u r e 2-9. E r r o r l i m i t s due to thermodynamic u n c e r t a i n t y f o r each curve are approximately ± 15° C. The dashed l i n e i s the c a l c u l a t e d e q u i l i b r i u m curve f o r sample. 82 assuming that the a c t i v i t y of ^ 0 = 0.5. I t shows that the e q u i l i b r i u m curve f o r t h i s 159 500 600 700 800 TEMPERATURE, °C Figure 2-9. Displaced e q u i l i b r i u m curves E4, E5 f o r p e l i t e assemblages, Azure Lake, B r i t i s h Columbia. a^ . Q = 1.0. The e q u i l i b r i u m assemblage i s s t a u r o l i t e - q u a r t z - g a r n e t - A ^ S i O ^ . Numbers on curves denote the samples. Dashed l i n e corresponds to the d i s p l a c e d curve f o r sample 82 w i t h a H Q = 0.5. Al 2SiO,- t r a n s i t i o n s are from Holdaway (1971) . 160 assemblage i s not a p p r e c i a b l y d i s p l a c e d to lower temperatures f o r < P, T o t a l ' Muscovite-Quartz-Plagioclase-Al^SiO^ The mineral assemblage musc o v i t e - q u a r t z - p l a g i o c l a s e - A l ^ S i O ^ ( k y a n i t e , s i l l i m a n i t e ) provides another e q u i l i b r i u m which i s u s e f u l f o r e s t i m a t i n g metamorphic pressure and temperature c o n d i t i o n s . The compositions of muscovite and p l a g i o c l a s e can be used w i t h thermodynamic models of s o l i d s o l u t i o n to c a l c u l a t e displacement of curves (E8, E9). Experimental determination of the pressure-temperature l o c a t i o n of curve (E7) has been completed by Ivanov and Gusynin (1970) and Chatterjee (1972). Thermodynamic parameters f o r the A l ^ S i O ^ and the h i g h - a l b i t e to l o w - a l b i t e t r a n s i t i o n s were combined w i t h the experimental r e a c t i o n to o b t a i n the e q u i l i b r i u m curves: 1 Paragonite + 1 Quartz = 1 Kyanite, S i l l i m a n i t e + 1 Low A l b i t e These r e a c t i o n s correspond more c l o s e l y to mineral assemblages i n the Azure Lake area. Previous s t u d i e s using t h i s e q u i l i b r i u m have used e i t h e r high a l b i t e (Ghent 1975) or low a l b i t e (Pigage 1976) as the s t a h l e f e l d s p a r phase. Recently J.B. Thompson, Waldbaum, and Hovis (1974) suggested a thermo-dynamic model i n v o l v i n g a temperature-dependent gradual t r a n s i t i o n between low and high a l b i t e . These d i f f e r e n t models were designed f o r Na—rich' f e l d s p a r s . E x t r a p o l a t i o n to intermediate p l a g i o c l a s e compositions i s p r o b l e m a t i c a l u n t i l more inf o r m a t i o n i s a v a i l a b l e on thermodynamic p r o p e r t i e s of Ca-bearing p l a g i o c l a s e f e l d s p a r s . Consequently I have performed a l l c a l c u l a t i o n s using e i t h e r h i g h or low a l b i t e as the s t a b l e f e l d s p a r species. (E8, E9) 161 High a l b i t e r e q u i r e s H^ O a c t i v i t i e s greater than 1.0 f o r e q u i l i b r i u m assemblages to be co n s i s t e n t w i t h r e a c t i o n s ( E l , E4, and E5). Low . a l b i t e has t h e r e f o r e been used as the p r e f e r r e d s t a b l e phase i n a l l subsequent c a l c u l a t i o n s . Figure 2-10 i l l u s t r a t e s the d i s p l a c e d curves f o r e q u i l i b r i u m (E9). C o e x i s t i n g muscovite and p l a g i o c l a s e compositions from the twelve analyzed p e l i t e samples were used to c a l c u l a t e the d i s p l a c e d e q u i l i b r i u m curves. P T T _ was equal to P„ ., f o r a l l c a l c u l a t i o n s . Except f o r samples 492 H^ O - n T o t a l and 74, the d i f f e r e n t curves f a l l w i t h i n a narrow 30° temperature i n t e r v a l . Comparison of the c a l c u l a t e d curves w i t h sample l o c a t i o n s from f i g u r e 2-2 demonstrates t h a t the e q u i l i b r i u m curves do not have a systematic temperature gradient r e l a t e d to i n c r e a s i n g metamorphic grade. Apparently the metamorphic gradient n o t i c e d i n the f i e l d mapping i s masked by s c a t t e r from a n a l y t i c a l e r r o r and l o c a l d i s e q u i l i b r i u m . The o u t l y i n g curves (74, 492) probably a l s o represent l o c a l d i s e q u i l i b r i u m or imperfect a n a l y s i s of c o e x i s t i n g minerals. The s t i p p l e d area i n f i g u r e 2-10 i s the d i s p l a c e d e q u i l i b r i a (E4, E5) which were a l s o shown i n f i g u r e 2-9. With P„' n equal to P e q u i l i b r i a (E5) and (E9) i n t e r s e c t at pressures between 2.5 and 5.2 kbar and temperatures from 675 to 705° C. These c o n d i t i o n s represent much lower pressures than the i n t e r s e c t i o n of e q u i l i b r i a ( E l ) and (E5) or (El) and (E9) which a l s o occur i n the same samples. These widely d i f f e r i n g i n t e r s e c t i o n p o i n t s i n d i c a t e that P^ ^ was not equal to P f o t a i during metamorphism. Mutual coexistence of e q u i l i b r i u m ( E l ) w i t h d i s p l a c e d e q u i l i b r i a (E4, E5) and (E8, E9) there f o r e r e q u i r e s reduced H^ O a c t i v i t i e s . Figure 2-11 i l l u s t r a t e s s e v e r a l c a l c u l a t e d curves f o r e q u i l i b r i a (E4) and (E8) at d i f f e r e n t ^ 0 a c t i v i t i e s . M i n e r a l compositions from sample 82 have been 16 2 500 600 700 800 900 1000 TEMPERATURE, °C Figure 2-10. Displaced e q u i l i b r i u m curves (E9) f o r the assemblage m u s c o v i t e - q u a r t z - p l a g i o c l a s e - s i l l i m a n i t e w i t h a u =1.0. Numbers correspond to the analyzed samples. The s t i p p l e d area represents the di s p l a c e d e q u i l i b r i a (E4,E5) ( s t a u r o l i t e - q u a r t z - g a r n e t - A ^ S i O ^ . ) from i f i g u r e 2-9. The A l 9 S i 0 c . t r a n s i t i o n s are from Holdaway (1971). 163 Figure 2-11. I n t e r s e c t i o n of e q u i l i b r i a E4 and E8 f o r s e v e r a l d i f f e r e n t reduced R^O a c t i v i t i e s . S o l i d s o l u t i o n displacements correspond to compositions f o r the subassemblage g a r n e t - s t a u r o l i t e - m u s c o v i t e - q u a r t z -p l a g i o c l a s e - k y a n i t e from sample 82. The heavy l i n e marks the e q u i l i b r i u m coexistence of t h i s subassemblage f o r a^ l e s s than 1.0. 164 used to d i s p l a c e the e q u i l i b r i a f o r s o l i d s o l u t i o n e f f e c t s . Kyanite was used as the s t a b l e A l ^ S i O ^ polymorph In these p a r t i c u l a r c a l c u l a t i o n s . The heavy l i n e i n the diagram marks the coexistence of the sub-assemblages f o r e q u i l i b r i a (E4) and (E8) w i t h a f l u i d phase having an rl^O a c t i v i t y l e s s than or equal to 1.0. This e q u i l i b r i u m was generated from the i n t e r s e c t i o n of d i s p l a c e d curves f o r e q u i l i b r i a (E4) and (E8) at s p e c i f i e d H^ O a c t i v i t i e s . Since sample 82 contains both k y a n i t e and s i l l i m a n i t e , metamorphic c o n d i t i o n s f o r t h i s sample are defined by the po i n t i n pressure-temperature-a „ space where the heavy e q u i l i b r i u m l i n e p i e r c e s the k y a n i t e - s i l l i m a n i t e 2 t r a n s i t i o n plane. This occurs at P = 7.6 kbar, T = 705 C, and a = 0.5. 2° These estimated metamorphic c o n d i t i o n s are subject to e r r o r because of v a r i a t i o n s i n mineral compositions and e r r o r s i n c a l c u l a t e d thermodynamic parameters. I have examined both of the e f f e c t s of these u n c e r t a i n t i e s on the i n f e r r e d pressure, temperature, and a f o r sample 82. The l a r g e s t v a r i a t i o n i n mineral composition occurs i n a n o r t h i t e content of the p l a g i o c l a s e . With sample 82, a 10 mole % increase i n a n o r t h i t e content s h i f t s the i s o b a r i c i n t e r s e c t i o n of e q u i l i b r i a (E4) and (E8) by AT = +4.5° C and Aa = +0.05. The estimated metamorphic c o n d i t i o n s are not s e n s i t i v e to v a r i a t i o n s i n mineral composition. Conversely the range of p l a g i o c l a s e compositions both between or w i t h i n the d i f f e r e n t samples can be explained by small l o c a l v a r i a t i o n s i n f l u i d composition. Thermodynamic parameters f o r the t r a n s i t i o n between high and low a l b i t e have been taken from c a l o r i m e t r i c s t u d i e s by Hemingway and Robie (1977). E r r o r s are on the order of ± 1100 c a l o r i e s and r e s u l t i n a l a r g e temperature e r r o r bracket f o r e q u i l i b r i u m (E4) w i t h low a l b i t e . The e f f e c t of t h i s l a r g e e r r o r bracket on the: estimated metamorphic c o n d i t i o n s i s shown i n f i g u r e 2-12. Curve B i s the e q u i l i b r i u m l i n e r e p resenting the. i n t e r s e c t i o n of e q u i l i b r i a (E4) and (E8) using the tabulated thermodynamic 165 Figure 2-12. V a r i a t i o n s i n the P-T-a^ ^ p o s i t i o n of the i n t e r s e c t i o n of e q u i l i b r i a E4 and E8. I n t e r s e c t i o n of these e q u i l i b r i a corresponds to the subassemblage g a r n e t - s t a u r o l i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e - k y a n i t e . V a r i a t i o n r e s u l t s from thermochemical e r r o r s i n the thermodynamic parameters f o r the high a l b i t e to l o w i a l b i t e t r a n s i t i o n . Curve B i s the l i n e shown i n Figure 2-11. Curves A and C correspond to the upper and lower temperature u n c e r t a i n t y l i m i t s f o r e q u i l i b r i u m E8, r e s p e c t i v e l y . 166 parameters f o r the t r a n s i t i o n between high and low a l b i t e . I t i s the same as the c a l c u l a t e d l i n e shown i n f i g u r e 2-11. Curve A i s the same e q u i l i b r i u m using the upper temperature l i m i t f o r e q u i l i b r i u m (E8), and curve C i s the c a l c u l a t e d e q u i l i b r i u m f o r the lower temperature l i m i t . The major change i n the i n f e r r e d metamorphic c o n d i t i o n s i s i n the a c t i v i t y of R^O which v a r i e s from 1.0 to approximately 0.24. Temperature and pressure estimates f o r the i n f e r r e d metamorphic c o n d i t i o n s are w i t h i n ± 20° C and ± 325 bars, r e s p e c t i v e l y f o r the e n t i r e e r r o r range i n e q u i l i b r i u m (E8). A c t i v i t y of H^ O i s very s e n s i t i v e to e r r o r i n the thermodynamic parameters, w h i l e temperature and pressure do not change e x t e n s i v e l y w i t h s u b s t a n t i a l e r r o r brackets. Figure 2-13 i l l u s t r a t e s the c a l c u l a t e d d i s p l a c e d e q u i l i b r i u m curves f o r the assemblage s t a u r o l i t e - g a r n e t - p l a g i o c l a s e - m u s c o v i t e - q u a r t z - A l ^ S i O ^ ( k y a n i t e , s i l l i m a n i t e ) . The curves were generated by the method discussed w i t h f i g u r e 2-11. Therefore i n t h i s diagram P i s l e s s than H2° ]?Total w i t h a R ^ decreasing w i t h i n c r e a s i n g t o t a l pressure along each curve. The f i v e analyzed samples c o n t a i n i n g t h i s assemblage form two c l o s e c l u s t e r s of e q u i l i b r i u m curves. These p i e r c e the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n plane at the p o i n t s P = 7600 bars, T = 705° C and P = 7750 bars, T = 710 C. In both cases a n i s approximately 0.5. Mutual i n t e r s e c t i o n of e q u i l i b r i a ( E l ) w i t h (E4 and E8) r e s u l t s i n estimated metamorphic pressures and temperatures of 7600 bars and 705° C, r e s p e c t i v e l y . Combined e r r o r s f o r the d i f f e r e n t e q u i l i b r i a give estimated t o t a l e r r o r s of ± 400 bars and ± 40° C f o r these estimated c o n d i t i o n s . The range i n temperature e r r o r r e s u l t s l a r g e l y from thermochemical e r r o r i n the t r a n s i t i o n between low and high a l b i t e . C a l c u l a t i o n of a n f o r the f i v e samples c o n t a i n i n g s t a u r o l i t e r e s u l t s H 20 i n values around 0.5. Table 2-20 l i s t s ' t h e ' H O a c t i v i t y r e q u i r e d to b r i n g 167 600 700 800 TEMPERATURE, °C Figure 2-13. I n t e r s e c t i o n of e q u i l i b r i a ( E l ) , (E4,E5), and (E8,E9) f o r the f i v e samples c o n t a i n i n g the assemblage muscovite-quartz-p l a g i o c l a s e - s t a u r o l i t e - g a r n e t - A l 0 S i C v . P„ _ decreases w i t h i n c r e a s i n g P along each curve. !68 Table 2-20. C a l c u l a t e d a R Q required f o r e q u i l i b r i a (E8, E9) to pass through the estimated metamorphic c o n d i t i o n s : P = 7600 T o t a l b ars, T = 705° C. Sample a ^ 0 Paragonite 3 7 3 0.55 3.37 121 0.54 3.37 3 6 7 0.53 3.50 8 2 0.49 3.34 398 0.56 3.17 492 0.63 3.25 223 0.54 3.43 2-376 0.49 3.43 2-1 3 0.49 3.46 7 4 0.36 3.19 5 9 0.48 3.38 4 0 0.53 3.35 169 the c a l c u l a t e d curve f o r e q u i l i b r i a (E8, E9) f o r each sample through the i n f e r r e d metamorphic pressure (7600 bars) and temperature (705° C). i s a l s o l i s t e d i n the t a b l e to give an i n d i c a t i o n of the Paragonite c o r r e c t i o n a p p l i e d to the paragonite a c t i v i t i e s f o r the c a l c u l a t e d curves. For a l l twelve samples the IL^ O a c t i v i t e s range between 0.35 and 0.63 w i t h a mean value very c l o s e to 0.5. I t must be remembered that t h i s value i s subject to l a r g e e r r o r because of the s e n s i t i v i t y of a^ ^ to thermochemical e r r o r and the p a r t i c u l a r s o l i d s o l u t i o n models used. Plagioclase-Garnet-Quartz-A^SiO,. The sub-assemblage p l a g i o c l a s e - q u a r t z - g a r n e t - k y a n i t e , s i l l i m a n i t e has been suggested as a p o t e n t i a l geothermometer-geobarometer (Ghent 1976), These minerals are r e l a t e d through r e a c t i o n (E10, E l l ) . As a s o l i d - s o l i d r e a c t i o n i t has the advantage of being independent of a . U n c e r t a i n t i e s i n the experimental l o c a t i o n of t h i s curve and i n the choice of nonideal mixing models f o r p l a g i o c l a s e and garnet s o l i d s o l u t i o n c o n t r i b u t e to u n c e r t a i n t y i n the pressures and temperatures i n f e r r e d from t h i s e q u i l i b r i u m . Hays (1967) and Har i y a and Kennedy (1968) c a l i b r a t e d r e a c t i o n (ElO) experimentally using end-member compositions at pressures between 20 and 35 kbar w i t h p i s t o n c y l i n d e r apparatus. Although experimental brackets are moderately s m a l l at these h i g h pressures, e x t r a p o l a t i o n of maximum and minimum allowed slopes to lower pressures r e s u l t s i n a l a r g e i s o b a r i c temperature u n c e r t a i n t y (approximately ± 375° C at 10 kbar) i n the p o s i t i o n of the r e a c t i o n (see f i g u r e 2-25). To f u r t h e r r e s t r i c t t h i s temperature u n c e r t a i n t y , I have r e q u i r e d r e a c t i o n (ElO) to be c o n s i s t e n t w i t h experimental r e s u l t s from nine independently s t u d i e d r e a c t i o n s i n the system CaO-Al 20 3-Si0 2-H 20. Consistency was v e r i f i e d u s i n g i n e q u a l i t i e s 170 and l i n e a r programming f o l l o w i n g the approach o u t l i n e d by Gordon (1973). A l l r e a c t i o n s were stud i e d using outer l i m i t s of experimental u n c e r t a i n t y . D e t a i l s concerning e r r o r l i m i t s and experimental brackets used f o r each of the r e a c t i o n s are given i n Appendix 2-2. By i n c l u d i n g these other r e a c t i o n s the i s o b a r i c temperature u n c e r t a i n t y i n r e a c t i o n (E10) i s reduced to approximately ± 60° C (10 kbar) (see f i g u r e 2-25). This corresponds to a pressure u n c e r t a i n t y of ± 1.0 kbar i n the l o c a t i o n of the e q u i l i b r i u m r e a c t i o n . The curve suggested by Hariya and Kennedy (1968) i s approximately i n the center of t h i s r e s t r i c t e d pressure-temperature space and has been used i n a l l f u r t h e r c a l c u l a t i o n s . Figure 2-14 compares the d i s p l a c e d pressure-temperature p o s i t i o n s of e q u i l i b r i u m (E10) f o r sample 82 w i t h three d i f f e r e n t s o l i d s o l u t i o n models. The s t a b l e A l ^ S i O ^ polymorph f o r the c a l c u l a t i o n s was k y a n i t e . Curve A corresponds to i d e a l s o l u t i o n i n both garnet and p l a g i o c l a s e . Nonideal p l a g i o c l a s e - i d e a l garnet i s represented by curve B, and nonideal p l a g i o c l a s e — n o n i d e a l garnet corresponds to curve C. In a l l cases the c a l c u l a t e d curve occurs at higher pressures than the e r r o r p a r a l l e l o g r a m around the mutual i n t e r s e c t i o n of e q u i l i b r i a ( E l , E4, and E8) f o r the same sample. Ghent (1975, 1976) a l s o noted that estimates using t h i s e q u i l i b r i u m give c o n s i s t e n t l y higher pressures f o r a s p e c i f i e d temperature. The p r e l i m i n a r y nature of the garnet mixing model suggests that use of t h i s r e a c t i o n as a pressure-temperature i n d i c a t o r i s l i m i t e d without a d d i t i o n a l study of garnet thermochemistry. Figure 2-14 a l s o i n d i c a t e s the high s e n s i t i v i t y of t h i s e q u i l i b r i u m to u n c e r t a i n t i e s i n experimental e r r o r and mineral compositions. Isothermal u n c e r t a i n t y brackets f o r thermochemical e r r o r (±1.0 kbar) are. the experimental u n c e r t a i n t y i n the c a l c u l a t e d pressure-temperature p o s i t i o n I 7 I Figure 2-14. Displaced p o s i t i o n of e q u i l i b r i u m ElO f o r sample 82. Kyanite i s the s t a b l e A ^ S i O ^ polymorph. Curve A corresponds to i d e a l s o l i d s o l u t i o n f o r both garnet and p l a g i o c l a s e . Curve B represents i d e a l garnet-nonideal p l a g i o c l a s e s o l u t i o n , and curve C corresponds to nonideal garnet-nonideal p l a g i o c l a s e s o l i d s o l u t i o n . P a r a l l e l o g r a m encloses the estimated metamorphic co n d i t i o n s from the i n t e r s e c t i o n of e q u i l i b r i a E l , (E4, E5), and (E8, E9). A l 2 S i 0 5 t r a n s i t i o n s are from Holdaway (1971). 400 500 600 700 800 900 TEMPERATURE, °C Figure 2-15. Displaced e q u i l i b r i u m curves ElO f o r a l l 12 analyzed p e l i t e samples. A l l curves c a l c u l a t e d w i t h k y a n i t e s t a b l e . P a r a l l e l o g r a m i n d i c a t e s estimated metamorphic c o n d i t i o n s . A l t r a n s i t i o n s are from Holdaway (1971). 173 of the end-member c a l i b r a t e d curve. The l a r g e r u n c e r t a i n t y of ± 1.3 kbar represents the s h i f t i n p o s i t i o n of the e q u i l i b r i u m curve w i t h a change i n p l a g i o c l a s e composition of ± 10 mole % a n o r t h i t e content. L o c a l e q u i l i b r i u m or patchy zoning i n p l a g i o c l a s e would have a s i g n i f i c a n t e f f e c t on the c a l c u l a t e d pressures and temperatures f o r t h i s e q u i l i b r i u m . C a l c u l a t e d curves f o r a l l twelve p e l i t e s samples are shown i n f i g u r e 2-15. Because of l i m i t e d information on s o l i d s o l u t i o n models, i d e a l s o l u t i o n was assumed f o r both p l a g i o c l a s e and garnet. A l l c a l c u l a t i o n s used k y a n i t e as the s t a b l e A l ^ S i O ^ polymorph. Using s i l l i m a n i t e i n the e q u i l i b r i u m c a l c u l a t i o n s would i s o b a r i c a l l y decrease the c a l c u l a t e d temperature of the e q u i l i b r i u m curve. The Azure Lake samples show a l a r g e s c a t t e r of approximately 100° C i n the estimated e q u i l i b r i u m p o s i t i o n f o r r e a c t i o n (ElO). As w i t h the other e q u i l i b r i a , there i s no systematic temperature gradient i n the c a l c u l a t e d p o s i t i o n of the e q u i l i b r i u m curves when compared to the r e g i o n a l metamorphic gra d i e n t . In summary, t h i s e q u i l i b r i u m c o n s i s t e n t l y r e s u l t s i n high pressure estimates f o r a given temperature when compared to other e q u i l i b r i a although i t i s c o n s i s t e n t when e r r o r brackets are taken i n t o c o n s i d e r a t i o n . I t s use as a r e l a t i v e estimator of metamorphic c o n d i t i o n s i s l i m i t e d by i t s s e n s i t i v i t y to sm a l l v a r i a t i o n s i n p l a g i o c l a s e compositions. Summary Metamorphic c o n d i t i o n s f o r the Shuswap Complex i n the Azure Lake area are estimated to be P = 7600 ± 400 bars, T = 705 ± 40° C, a = 0.5 H 2 ° &pprox.). These estimates r e s u l t from the mutual i n t e r s e c t i o n of s e v e r a l e q u i l i b r i a i n v o l v i n g garnet, s t a u r o l i t e , p l a g i o c l a s e , muscovite, quartz, and Al^ S i O ^ . The d i f f e r e n t e q u i l i b r i a have been thermodynamically d i s p l a c e d f o r s o l i d s o l u t i o n and reduced a _ e f f e c t s , a i n the twelve 174 analyzed p e l i t e samples ranges between 0.35 and 0.63 w i t h a mean of 0.5. These a n estimates are approximate because of the extreme s e n s i t i v i t y of H2° c a l c u l a t e d values to thermochemical e r r o r s ; e r r o r brackets f o r a s i n g l e sample r e s u l t i n a range of a „ between 0.25 and 1.0. H2° F l e t c h e r and Greenwood ( i n press) have presented estimated metamorphic c o n d i t i o n s of P = 7000 ± 1500 bars, T = 680 ± 30° C, a„• = 0.8 (approx.) H 2 ° f o r the Shuswap Complex j u s t northwest of the Azure Lake area. Their estimated c o n d i t i o n s overlap w i t h the c o n d i t i o n s presented here. Many of the same e q u i l i b r i a were used i n both sets of c a l c u l a t i o n s . D i f f e r e n c e s i n the r e s u l t i n g estimated metamorphic c o n d i t i o n s are r e l a t e d to d i f f e r e n t s o l i d s o l u t i o n , models f o r s e v e r a l minerals. The s o l u t i o n model f o r s t a u r o l i t e appears to be the major f a c t o r i n the d i f f e r e n t estimates. The s t a u r o l i t e s o l u t i o n model used i n t h i s paper increases estimated temperatures by 30° C when compared to the model used by F l e t c h e r and Greenwood. I t i s i n t e r e s t i n g to compare these estimates to those c a l c u l a t e d from the d i s t r i b u t i o n of Fe-Mg between garnet and b i o t i t e (A.B. Thompson 1976b). A.B. Thompson's g a r n e t - b i o t i t e geothermometer c o n s i s t e n t l y gives temperatures near 530° C f o r Azure Lake mineral compositions. S i m i l a r l y the experimentally c a l i b r a t e d geothermometer presented by Ferr y and Spear (1977) r e s u l t s i n temperatures near 550° C. In both cases the exceedingly low temperatures are probably r e l a t e d to a d d i t i o n a l components i n the p a r t i c i p a t i n g phases. CALCAREOUS ASSEMBLAGES Discontinuous marble u n i t s up to 30 in. t h i c k are s p a r s e l y d i s t r i b u t e d throughout the Kaza Group i n the Azure Lake area. T e x t u r a l l y these u n i t s range from massive, f i n e - g r a i n e d , f l i n t y , blue-gray outcrops tomedium-175 coarse, o f f - w h i t e , f r i a b l e aggregates of c a l c i t e . L o c a l brownish i r o n s t a i n i n g from o x i d i z e d s u l f i d e grains i s u b i q u i t o u s . S i l i c a t e minerals form streaky l a y e r s and nodules w i t h i n marble. Inequant minerals (muscovite, b i o t i t e , c a l c i c amphibole) are p o o r l y a l i g n e d p a r a l l e l to the dominant r e g i o n a l s c h i s t o s i t y . Marginal r e a c t i o n zones between marble and e n c l o s i n g p e l i t e or q u a r t z i t e u n i t s are minimal although some marbles c o n t a i n c a l c i c amphibole i n t h i n marginal selvages. P l a g i o c l a s e i n marginal zones i s p a r t l y to completely replaced by z o i s i t e . One marble u n i t c o n s i s t e n t l y contains pegmatitic v e s u v i a n i t e intergrown w i t h z o i s i t e i n the marginal zone. M i n e r a l assemblages were determined by combining t h i n s e c t i o n examination w i t h x-ray powder d i f f r a c t i o n study of i n s o l u b l e r e s i d u e s . K-feldspar was v e r i f i e d by s t a i n i n g i n s o l u b l e residues w i t h sodium c o b a l t i n i t r i t e . Calcareous metamorphic assemblages i n the three p e l i t e metamorphic zones are as f o l l o w s : Kyanite Zone c a l c i t e - m u s c o v i t e - q u a r t z - K - f e l d s p a r - p l a g i o c l a s e - ( z o i s i t e ) K y a n i t e - S i l l i m a n i t e Zone c a l c i t e - m u s c o v i t e - q u a r t z - p l a g i o c l a s e ± b i o t i t e ± K-feldspar - ( z o i s i t e ) c a l c i t e - q u a r t z - c a l c i c amphibole-plagioclase ± garnet ± b i o t i t e ± c a l c i c pyroxene - ( z o i s i t e ) S i l l i m a n i t e Zone c a l c i t e - q u a r t z - p l a g i o c l a s e ± K-feldspar ± muscovite - ( z o i s i t e ) c a l c i t e - q u a r t z - p l a g i o c l a s e ± c a l c i c amphibole ± c a l c i c pyroxene ± b i o t i t e ± K - f e l d s p a r ± s c a p o l i t e - ( z o i s i t e ) 176 Z o i s i t e i s included i n parentheses i n the above assemblages because i t t y p i c a l l y occurs as a l o c a l a l t e r a t i o n of p l a g i o c l a s e g r a i n s . Graphite, p y r r h o t i t e , sphene, and a p a t i t e are l o c a l l y accessory minerals i n each of these assemblages. The sequence of mineral assemblages w i t h i n the Azure Lake area may be described by the f o l l o w i n g r e a c t i o n s : 1 muscovite + 1 c a l c i t e + 2 quartz = 1 K-feldspar + 1 a n o r t h i t e + 1 H 20 + 1 C0 2 (E14) 5 phlogopite + 6 c a l c i t e + 24 quartz = 3 t r e m o l i t e + 2 H 20 + 6 C0 2 + 5 K-feldspar (E16) 1 t r e m o l i t e + 3 c a l c i t e + 2 quartz = 5 diopside + 1 R^O + 3 C0 2 (E17) 3 a n o r t h i t e + 1 c a l c i t e = 3 meionite ( s c a p o l i t e ) (E18) 3 a n o r t h i t e + 1 c a l c i t e + 1 H 20 = 2 z o i s i t e + 1 CC>2 (E19) These r e a c t i o n s are contained w i t h i n subsets of the seven component system K 20-Al 20 3-MgO-Si0 2-CaO-C0 2-H 20. A l l are i s o b a r i c a l l y u n i v a r i a n t (varying i n temperature or X ). A d d i t i o n a l components such as TiO„, FeO, and Na 20 cause the r e a c t i o n s to become m u l t i v a r i a n t . Isograd r e a c t i o n surfaces w i t h i n the carbonate u n i t s are p o o r l y defined because of scanty outcrop and compositional d i f f e r e n c e s between the u n i t s . Approximate l o c a t i o n s of the r e a c t i o n s surfaces f o r these r e a c t i o n s are i n d i c a t e d i n f i g u r e 2-16 (A-D) by p l o t t i n g product and reactant assemblages f o r each r e a c t i o n (Carmichael 1970). In each example the r e a c t i o n assemblage occurs over a geographic area. This i s r e a d i l y r e l a t e d to d i f f e r e n c e s i n compositions of the minerals and to the m u l t i v a r i a n t nature of most of the r e a c t i o n s . An assemblage map f o r r e a c t i o n (E19) was not included s i n c e t h i s r e a c t i o n assemblage i s l o c a l l y present throughout 177 Figure 2-16. Calcareous reactant and product assemblages f o r carbonate mineral e q u i l i b r i a . Carbonate l a y e r s w i t h i n the Kaza Group are i n d i c a t e d i n b l a c k . A) E q u i l i b r i a E13, E14 178 Figure 2-16. Calcareous reactant and product assemblages f o r carbonate mineral e q u i l i b r i a . Carbonate l a y e r s w i t h i n the Kaza Group are i n d i c a t e d i n b l a c k . B) E q u i l i b r i a E15, E16 179 Figure 2-16. Calcareous reactant and product assemblages f o r carbonate mineral e q u i l i b r i a . Carbonate l a y e r s w i t h i n the Kaza Group are i n d i c a t e d i n black. C) E q u i l i b r i u m E17 180 Figure 2-16. Calcareous reactant and product assemblages f o r carbonate mineral e q u i l i b r i a . Carbonate l a y e r s w i t h i n the Kaza Group are i n d i c a t e d i n b l a c k . D) E q u i l i b r i u m E18 181 the Azure Lake area. The r e l a t i v e i s o b a r i c T-X arrangement of r e a c t i o n s (E13, E14), (E15, E16) , E17, E18, and E19 f o r high grade metamorphic c o n d i t i o n s has been o u t l i n e d by Hewitt (1973b) and Fe r r y (1976) . Figure 2-17 i s a s i m i l a r T-X diagram constructed f o r a t o t a l pressure of 7600 bars. This pressure was chosen to be c o n s i s t e n t w i t h estimates from the p e l i t e assemblages. Several r e a c t i o n s around the d i f f e r e n t i s o b a r i c i n v a r i a n t p o i n t s have not been in c l u d e d . I t i s i m p r a c t i c a l to discu s s a complete Schreinemaker's a n a l y s i s because of u n c e r t a i n e q u i l i b r i u m r e l a t i o n s between t s c h e r m a k i t i c and t r e m o l i t i c amphiboles. The pr o g r e s s i v e sequence of r e a c t i o n s w i t h i n c r e a s i n g temperature i n f i g u r e 2-17 i s concordant w i t h the s e q u e n t i a l change of mineral assemblages w i t h i n c r e a s i n g metamorphic grade i n other r e g i o n a l l y metamorphosed t e r r a i n s (P. Thompson 1973; Ferry 1976). The pressure-temperature-X p o s i t i o n s of the curves i n f i g u r e 2-17 were c a l c u l a t e d using the methods o u t l i n e d e a r l i e r f o r the p e l i t e e q u i l i b r i a (see Appendix 2-2) . I n t e r n a l consistency of the thermodynamic parameters A G^ and A S^ f o r each experimental e q u i l i b r i u m was v e r i f i e d u sing l i n e a r i n e q u a l i t i e s (Gordon 1973). Table 2-21 l i s t s the r e l e v a n t experimental s t u d i e s and thermodynamic parameters f o r the d i f f e r e n t e q u i l i b r i a . Reactions (E13) and (E15) were experimentally s t u d i e d using s a n i d i n e as the p a r t i c i p a t i n g a l k a l i f e l d s p a r (Hewitt 1973b, 1975; Hoschek 1973). F i e l d observations f o r the same e q u i l i b r i a t y p i c a l l y report m i c r o c l i n e (A.B. Thompson 1975; Ferry 1976). The dotted l i n e s i n f i g u r e 2-17 i l l u s t r a t e the T-X^Q p o s i t i o n s of e q u i l i b r i a (E14) and (E16) w i t h maximum m i c r o c l i n e as the s t a b l e a l k a l i f e l d s p a r phase. Thermodynamic parameters f o r the 182 J I 1 I 1 1 1 1 L \ Me Figure 2-17. I s o b a r i c T - X Q Q diagram f o r the system CaO-MgO-A^O^-SiC^-H^O-CC^. P x o t a l = '^®® bars. Dotted l i n e s represent e q u i l i b r i u m r e a c t i o n s using m i c r o c l i n e (rather than sanidine) as the s t a b l e K - f e l d s p a r . Abbreviations are the same as l i s t e d i n Table 2- 2 2 . Dol - dolomite. Thermodynamic parameters f o r the d i f f e r e n t r e a c t i o n s are l i s t e d i n Table 2 - 2 1 . 183 s a n i d i n e - m a x i m u m m i c r o c l i n e t r a n s i t i o n were c a l c u l a t e d f r o m c a l o r i m e t r i c d a t a (Hemingway and R o b i e l 9 7 7 ) . B o t h r e a c t i o n s a r e d i s p l a c e d t o h i g h e r t e m p e r a t u r e s , and r e a c t i o n (E16) changes r e l a t i v e t e m p e r a t u r e p o s i t i o n w i t h r e a c t i o n ( E 1 7 ) . T h i s new sequence o f r e a c t i o n s w i t h i n c r e a s i n g t e m p e r a t u r e i s n o t c o m p a t i b l e w i t h f i e l d o b s e r v a t i o n s and s u g g e s t s t h a t t h e r e may be p r o b l e m s w i t h u s i n g maximum m i c r o c l i n e as t h e s t a b l e t r i c l i n i c K - f e l d s p a r p h a s e f o r t h e s e p r e s s u r e and t e m p e r a t u r e c o n d i t i o n s . Greenwood (1975a) h a s s u g g e s t e d t h a t c o n t i n u o u s r e a c t i o n s i n v o l v i n g c o e x i s t i n g m e t a m o r p h i c m i n e r a l s have a h i g h c a p a c i t y f o r b u f f e r i n g me tamorph i c f l u i d c o m p o s i t i o n s . O n l y s m a l l amounts o f r e a c t i o n a r e needed t o have a s i g n i f i c a n t e f f e c t on f l u i d c o m p o s i t i o n . I n t e r l a y e r e d c a r b o n a t e and p e l i t e u n i t s f r o m t h e A z u r e L a k e a r e a p r o v i d e an e x c e l l e n t examp le o f t h e b u f f e r i n g c a p a c i t y o f t h e c a l c a r e o u s a s s e m b l a g e s . The f o l l o w i n g s e c t i o n s w i l l show t h a t c a l c u l a t e d a A v a l u e s f o r t h e r m o d y n a m i c a l l y d i s p l a c H2° c a r b o n a t e e q u i l i b r i u m c u r v e s a r e c o n s i s t e n t l y l o w e r t h a n c a l c u l a t e d a u _ f rom t h e e n c l o s i n g p e l i t e u n i t s . T h i s i n d i c a t e s t h a t e a c h r o c k t y p e e f f e c t i v e l y b u f f e r e d i t s own f l u i d c o m p o s i t i o n d u r i n g me tamorph ism and t h a t no homogeneous, p e r v a s i v e f l u i d was p r e s e n t i n t h e r o c k s . S i n c e t h e d i f f e r e n t c a l c a r e o u s e q u i l i b r i a a r e a t l e a s t b i v a r i a n t i n P - T - X s p a c e , t h e i n d e p e n d e n t l y e s t i m a t e d p r e s s u r e and t e m p e r a t u r e c o n d i t i o n s f r o m t h e p e l i t e a s s e m b l a g e s were u s e d t o s o l v e f o r a u _ i n t h e c a r b o n a t e s . A n a l y z e d c a r b o n a t e samp les c o n t a i n r e a c t i o n a s s e m b l a g e s f o r e q u i l i b r i a ( E 1 4 ) , ( E 1 7 ) , and ( E 1 9 ) . These c a l c a r e o u s e q u i l i b r i a w e r e t h e r m o d y n a m i c a l l y d i s p l a c e d f o r s o l i d s o l u t i o n e f f e c t s u s i n g t he e q u i l i b r i u m c o n s t a n t a p p r o a c h . The a p p r o p r i a t e e q u i l i b r i u m c o n s t a n t s a r e d e f i n e d as f o l l o w s : f a ) * (a ) * / a J * fa 1 K E 1 4 = A n o r t h i t e ^ ^ K - f e l d s p a r 7 ^ H 2 0 J ^ C O ^ (a ) * (a ) M u s c o v i t e C a l c i t e 184 h u « ( a D i o P s i d e ) 5 * (V * ( a C 0 2 ) 3 3 ^Tremolite'* * ^ aCalcite^ (a )2 * (a ) K E 1 9 = ^ Z o i s i t e 7 CO ' fa ) 3 * fa ) * fa ) v Anorthite' ^ C a l c i t e ' Expressions relating mole fraction to activity are needed for the above components in order to evaluate the equilibrium constants. Solution models for the components are discussed in the following section. Calcic pyroxene, Calcite: Solid solution in both calcic pyroxene and calcite was considered ideal with activity being related to the mole fraction of the appropriate component. Nonideality in calcite is insignificant for the Ca-rich compositions listed in Table 2-10 (Gordon and Greenwood 1970). Substitution in calcic pyroxene was considered to be only on the Mg-site. The resulting activity expressions are: aCalcite = X C a l c i t e ( 1 0 ) Diopsxde Hg Calcic amphibole: The activity of tremolite in calcic amphibole is less obvious. The following expression has been adopted for tremolite activity (Kerrick and Darken 1975): aTremolite = <X • > * < X C / * * ( X 0 / ^ where X q represents the mole fraction of vacancies in the twelve-coordinated A site. The X term has not been included in this expression because substitution of Al for Si i s coupled to substitutions on the other 185 sites (Ferry 1976; Skippen and Carmichael 1977). This coupled substitution approach is s t r i c t l y valid only i f Mg/Fe ratios do not change with increased tetrahedral Al content. This model i s reasonable for actinolite because tetrahedral Al is insignificant, but the model may be inadequate for tschermakitic amphiboles. Saxena and Ekstrom (1969) have shown that in calcic amphiboles Fe-content increases with increasing tetrahedral Al content. The same trend is also present in the analyses in Table 2-14. Including a term for X would decrease tremolite activity and therefore increase the calculated temperature for equilibrium (E17) at constant total pressure and X . L U2 Muscovite: Activity-mole fraction relations for white micas were described previously, a,, . i s calculated in a manner analogous to paragonite: r J Muscovite Muscovite " Muscovite * (V * ( X A / * ( X0H ) 2 ( 1 3 ) Y „ . i s very close to 1.0. Muscovite Feldspar: Activity relations for anorthite were discussed i n connection with the pelites. K-feldspar ac t i v i t i e s were considered as equal to the mole fraction of KAlSi o0 o in the analyzed a l k a l i feldspar. Calculations involving equilibrium (E14) used maximum microcline as the preferred stable a l k a l i feldspar phase. Consequently the activity coefficient for K-feldspar was calculated from the Margules G-excess term (J.B. Thompson 1967, eqtn 80) with Margules W-parameters from the study of the microcline-low albite solvus by Bachinski and Muller (1971). The resulting expressions are: a = Y * X (14) K-feldspar Microcline K-feldspar 186 RTlnv„. -* . = (X ) 2 * (W„. „ + 2 * X. * ' M i c r o c l i n e a l b i t e ' M i c r o c l i n e ^ - f e l d s p a r ^ A l b i t e ^ M i c r o c l i n e ^ ( 1 5 ) A c t i v i t y c o e f f i c i e n t s f o r compositions l i s t e d i n Table 2-12 are n e a r l y 1.0. Z o i s i t e : Mossbauer s t u d i e s by D o l l a s e (1973) have demonstrated t h a t f e r r i c i r o n p r e f e r e n t i a l l y orders i n t o only one of the three A l - s i t e s i n the s t r u c t u r a l formula (13 oxygen b a s i s ) . Consequently z o i s i t e a c t i v i t y i s represented by the expression: Zoisite " ( 1 - ( F e + M S + M n ) ) <16> where Fe, Mg, and Mn are the number of atoms of each species i n the s t r u c t u r a l formula. These a c t i v i t y expressions have been s u b s t i t u t e d i n the e q u i l i b r i u m constants to d i s p l a c e e q u i l i b r i a (E14), (E17), and (E19) f o r s o l i d s o l u t i o n e f f e c t s . The e q u i l i b r i a were c a l c u l a t e d f o r d i f f e r i n g a T I contents at H20 the pressure estimated from the p e l i t e assemblages. The d i s p l a c e d curves correspond to the e q u i l i b r i a f o r c o e x i s t i n g m i n e r a l compositions i n the Azure Lake area. The f o l l o w i n g s e c t i o n s d i s c u s s the r e s u l t s f o r the d i f f e r e n t e q u i l i b r i a . C a l c i t e - Q u a r t z - C a l c i c amphibole-Calcic pyroxene The pressure-temperature-X p o s i t i o n of e q u i l i b r i u m (E17) has been experimentally determined by Slaughter, K e r r i c k , and Wall (1975). Their curve i s c o n s i s t e n t w i t h the c a l c u l a t e d p o s i t i o n of the r e a c t i o n according to Skippen (1971). Experimental s t u d i e s by Metz (1970) bracket the r e a c t i o n at higher temperatures f o r a given pressure and X . This c o 2 i n c o n s i s t e n c y i s apparently due to u n s p e c i f i e d F-content of the n a t u r a l 187 t r e m o l i t e used i n h i s experiments (P. Metz,' personal communication 1977). I n t e r n a l l y c o n s i s t e n t thermodynamic parameters were derived from the study by Slaughter et a l . (1975) and are l i s t e d i n Table 2-21. The e q u i l i b r i u m assemblage c a l c i t e - q u a r t z - c a l c i c amphibole-calcic pyroxene occurs i n s c a t t e r e d outcrops over p o r t i o n s of the s i l l i m a n i t e and k y a n i t e - s i l l i m a n i t e metamorphic zones. Grain boundaries are sharp; c o e x i s t i n g minerals appear to be i n t e x t u r a l e q u i l i b r i u m ( p l a t e 2-5A). Tables 2-10, 2-14 and 2-15 c o n t a i n microprobe analyses f o r the e q u i l i b r i u m assemblage from three samples (224, 20, 2-312). C a l c i c pyroxenes vary mainly i n Fe/Mg ratio:. . No zoning or chemical inhomogeneity was detected during a n a l y s i s . C a l c i c amphiboles range from a c t i n o l i t e s to f e r r o - t s c h e r m a k i t i c hornblendes (Leake 1968). A l l amphibole gra i n s c o n t a i n patchy to c o n c e n t r i c zoning. Table 2-14 contains two spot analyses f o r each sample; these analyses represent the f u l l range of analyzed compositions. The major v a r i a t i o n i s i n s u b s t i t u t i o n of t e t r a h e d r a l A l f o r S i . A l - r i c h amphiboles a l s o c o n t a i n increased amounts of Na, K, and Fe. In examples of c o n c e n t r i c zoning, g r a i n rims contained more aluminum. Figure 2-18 i l l u s t r a t e s the c a l c u l a t e d T-X e q u i l i b r i u m curves f o r L 2 the d i s p l a c e d e q u i l i b r i a corresponding to samples 224, 20, and 2-312. An assumed t o t a l pressure of 7600 bars i s c o n s i s t e n t w i t h the pressure estimated from the p e l i t e assemblages. S o l i d curves correspond to the e q u i l i b r i u m assemblage using the a c t i n o l i t i c compositions, and dotted curves represent the c a l c u l a t e d e q u i l i b r i u m using t s c h e r m a k i t i c amphibole compositions. C a l c u l a t e d r e a c t i o n assemblage curves with, a c t i n o l i t e s a l l r e q u i r e X values near 0.75 to be c o n s i s t e n t w i t h p r e v i o u s l y estimated 188 Figure 2-18. Displaced e q u i l i b r i u m curves E17 i n an i s o b a r i c T-X _ diagram f o r samples 20, 224, and 2-312. P x o t a l = bars. The e q u i l i b r i u m assemblage i s c a l c i c amphibole-calcic pyroxene-quartz-c a l c i t e . S o l i d l i n e s represent d i s p l a c e d e q u i l i b r i u m E17 using a c t i n o l i t i c amphibole compositions. Dotted l i n e s correspond to the same e q u i l i b r i u m using t s c h e r m a k i t i c amphibole compositions:. Dashed l i n e s represent e r r o r margins on estimated metamorphic temperature (from p e l i t i c assemblages) at 7600 bars. 189 metamorphic c o n d i t i o n s . The f l u i d composition appears to have been buff e r e d to low ^ (high' ) values near the T-X maximum by the e q u i l i b r i u m assemblage. In c o n t r a s t the e q u i l i b r i u m curves c a l c u l a t e d using t s c h e r m a k i t i c compositions i n d i c a t e that the c o e x i s t i n g f l u i d has a n values ranging from 0.5 to 0.2. Tschermakitic amphibole compositions r e q u i r e involvement of p l a g i o c l a s e i n the amphibole-forming r e a c t i o n . Patchy and c o n c e n t r i c zoning i n the Azure Lake amphiboles suggest that t s c h e r m a k i t i c amphibole growth occurred a f t e r i n i t i a l formation of c a l c i c pyroxene from a c t i n o l i t i c amphibole. C a l c u l a t e d temperature-X p o s i t i o n s of the C U 2 d i s p l a c e d e q u i l i b r i u m curves i n f i g u r e 2-18 i n d i c a t e that t s c h e r m a k i t i c amphiboles probably formed i n response to increased a i n the f l u i d phase. C a l c i t e - Q u a r t z - M u s c o v i t e - P l a g i o c l a s e - K - f e l d s p a r Reaction (E13) has been experimentally c a l i b r a t e d f o r end-member compositions by Hewitt (1973b). He suggested that the reactant assemblage ca l c i t e - m u s c o v i t e - q u a r t z should occur only r a r e l y i n s i l l i m a n i t e - b e a r i n g t e r r a i n s . The Azure Lake area i s of i n t e r e s t because the f u l l r e a c t i o n assemblage s t r a d d l e s the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n zone. A l l c a l c u l a t e d e q u i l i b r i u m curves have used maximum m i c r o c l i n e as the p r e f e r r e d s t a b l e a l k a l i f e l d s p a r . C a l o r i m e t r i c data from Hemingway and Robie (1977) were used to i n c o r p o r a t e m i c r o c l i n e i n r e a c t i o n (E14). Combined e r r o r s of ± 1600 c a l o r i e s i n the c a l o r i m e t r i c data r e s u l t i n a temperature bracket of ± 45° C i n the c a l c u l a t e d p o s i t i o n of the e q u i l i b r i u m curve. The p o s i t i o n of the most s t a b l e curve would be somewhere between the p o s i t i o n s c a l c u l a t e d f o r sanidine and maximum m i c r o c l i n e s i n c e the s t a b l e a l k a l i f e l d s p a r presumably has an intermediate degree of ordering (see f i g u r e 2-17). 190 Figure 2-19. Displaced e q u i l i b r i u m curves E14 f o r samples 387 and 69. = 0.5. The e q u i l i b r i u m assemblage i s c a l c i t e - m u s c o v i t e -q u a r t z - K - f e l d s p a r - p l a g i o c l a s e . The two dashed curves f o r sample 69 represent the range i n muscovite compositions i n 69 determined by microprobe a n a l y s i s . P a r a l l e l o g r a m o u t l i n e s estimated metamorphic con d i t i o n s from p e l i t e assemblages. A^SiO,- t r a n s i t i o n s are from Holdaway (1971). 191 Tables 2-10, 2-11, 2-12, and 2-13 cont a i n analyses of c o e x i s t i n g minerals f o r two samples (387, 69) which i n c l u d e the complete r e a c t i o n assemblage. Muscovite compositions c o n t a i n extensive c e l a d o n i t e component w i t h minimal paragonite content. C o e x i s t i n g minerals i n sample 387 are homogeneous. S l i d e 69, however, shows evidence of retrograde adjustment of mineral compositions. K-feldspar t y p i c a l l y contains extensive s e r i c i t e . Muscovite gr a i n s d i s p l a y a patchy zoning of c e l a d o n i t e and muscovite components. The s u l f i d e i s p y r i t e r a t h e r than p y r r h o t i t e . Table 2-13 contains two spot analyses f o r muscovites from sample 69; these represent the most muscovitic and c e l a d o n i t i c compositions i n the probe sample. Figure 2-19 i l l u s t r a t e s c a l c u l a t e d p o s i t i o n s of the d i s p l a c e d e q u i l i b r i u m (E14) f o r samples 387 and 69. Two curves are shown f o r 69; these correspond to the muscovitic and c e l a d o n i t i c compositions i n Table 2-13. F l u i d compositions were set to a = a = 0.5 which r e s u l t s i n H 2 ° C°2 the maximum temperature p o s s i b l e f o r t h i s r e a c t i o n . Both samples i n d i c a t e s l i g h t l y lower temperatures than those estimated from p e l i t e assemblages. Low temperatures could r e s u l t e i t h e r from retrograde adjustment of m i n e r a l compositions or from inadequate s o l i d s o l u t i o n models f o r the phases i n v o l v e d . The v i s i b l e r e t r o g r a d i n g i n sample 69 supports the former i n t e r p r e t a t i o n . C a l c i t e - Z o i s i t e - P l a g i o c l a s e Carbonate samples from a l l three p e l i t e metamorphic zones contain p l a g i o c l a s e grains which are p a r t l y to completely replaced by z o i s i t e ^ . This replacement t e x t u r e i s e s p e c i a l l y n o t i c e a b l e near the marginal contacts of carbonate u n i t s w i t h e n c l o s i n g p e l i t e s or q u a r t z i t e s . Figure 2-17 shows that the e q u i l i b r i u m r e a c t i o n assemblage c a l c i t e -192 p l a g i o c l a s e ( a n o r t h i t e ) - z o i s i t e denotes high Q i n the c o e x i s t i n g f l u i d phase. Sample 20 contains complete r e a c t i o n assemblages f o r both e q u i l i b r i u m curves (E17) and :(E19). Since the c a l c u l a t e d d i s p l a c e d curve (E17) f o r the t s c h e r m a k i t i c amphibole i n sample 20 i n d i c a t e s H^O-rich f l u i d s , i t seems reasonable to consider that patchy A l - r i c h amphibole zoning developed concomitantly w i t h a l t e r a t i o n of p l a g i o c l a s e to z o i s i t e . In the s i m p l i f i e d system represented by f i g u r e 2-17 the i n t e r s e c t i o n of these two curves generates an i s o b a r i c i n v a r i a n t p o i n t . Both curves become p o l y v a r i a n t through s o l i d s o l u t i o n w i t h a d d i t i o n of the components Na 20 and FeO. Their i n t e r s e c t i o n i s no longer i s o b a r i c a l l y i n v a r i a n t , but i t s t i l l marks the j o i n t coexistence of both r e a c t i o n assemblages f o r a given pressure. The i n t e r s e c t i o n may be regarded as a " d i s p l a c e d i n v a r i a n t p o i n t " although no longer i n v a r i a n t . Figure 2-20 i l l u s t r a t e s the temperature-X „ curve generated by the C U 2 mutual i n t e r s e c t i o n of e q u i l i b r i a (E17) and (E19). Both e q u i l i b r i a have been thermodynamically d i s p l a c e d f o r s o l i d s o l u t i o n e f f e c t s of p a r t i c i p a t i n g phases. This diagram i s p o l y b a r i c s i n c e i t shows the i n t e r s e c t i o n f o r s e v e r a l reasonable t o t a l pressures. The r e s u l t s show that the two d i s p l a c e d curves i n t e r s e c t at T = 710° C and X n = 0.25 f o r the pressure C U 2 estimated from the p e l i t e assemblages. Therefore reduced temperature ( i . e . r etrograding) i s not r e q u i r e d to produce replacement of p l a g i o c l a s e by z o i s i t e i n the amphibole-bearing assemblages. Rather z o i s i t e could have formed at the same estimated metamorphic c o n d i t i o n s w i t h an i n f l u x of H^O-rich f l u i d s . E n c l o s i n g p e l i t e and q u a r t z i t e u n i t s of the Kaza Group provide a ready source of H 20-rich. f l u i d s . The u b i q u i t o u s occurrence of z o i s i t e at margins of marble u n i t s I n d i c a t e s that t h i s i n f l u x of f l u i d s occurs to a l i m i t e d extent throughout the Azure Lake. area. L i m i t e d 8 0 0 S a m p l e 2 0 o o LU 7 0 0 -t Sill K y < a: UJ ^ 6 0 0 -I LU 7,6 kbar V 5 0 0 0 . 0 ^- 7,0 kbar 6 .0 kbar 5 .0 kbar 4 . 0 kbar (I kbar * IO5 kPa) 0.1 0 . 2 x c o 2 0 . 3 Figure 2-20. P o l y b a r i c Temperature-X diagram f o r the assemblage c a l c i t e - z o i s i t e - p l a g i o c l a s e - t s c h e r m a k i t i c amphibole-calcic pyroxene-quartz. The curve marks the p o l y b a r i c i n t e r s e c t i o n of e q u i l i b r i a E17 and E19 f o r sample 20. Dashed l i n e s represent e r r o r margins on the metamorphic temperature estimated from the p e l i t i c assemblages at 7600 bars. 194 8 0 0 7 0 0 -4 o o LU QC 3 < 6 0 0 tr UJ CL LU 5 0 0 4 0 0 Sample 3 8 7 S i l l Ky m y A 7.6 kbar 7.0 kbar . 6.0 kbar ^ 5 . 0 kbar * 4.0 kbar (I kbar = l 0 5 kPa) 0 . 0 0.1 0 .2 0.3 CO* Figure 2 - 2 1 . P o l y b a r i c Temperature -X- , - diagram f o r the assemblage c a l c i t e - m u s c o v i t e - q u a r t z - K - f e l d s p a r - p l a g i o c l a s e - z o i s i t e i n sample 3 8 7 . Curve marks the p o l y b a r i c i n t e r s e c t i o n of e q u i l i b r i a E14 and E 1 9 . Dashed l i n e s represent e r r o r margins on estimated metamorphic temperature ( p e l i t i c assemblages) at 7600 bars. A^SiO,- t r a n s i t i o n i s from Holdaway ( 1 9 7 1 ) . 195 experimental data (Holdaway 1972) concerning c l i n o z o i s i t e - z o i s i t e s t a b i l i t y r e l a t i o n s a l s o support formation of z o i s i t e at these estimated pressure-temperature c o n d i t i o n s . S i m i l a r l y the coexistence of r e a c t i o n assemblages f o r e q u i l i b r i a (E14) and (E19) i n sample 387 a l s o represents a " d i s p l a c e d i n v a r i a n t p o i n t " i n T-X space. As w i t h the previous example, s o l i d s o l u t i o n makes the 2 i n v a r i a n t p o i n t generated by t h e i r i n t e r s e c t i o n p o l y v a r i a n t . Figure 2-21 i l l u s t r a t e s the p o l y b a r i c t r a c e of t h i s " d i s p l a c e d i n v a r i a n t p o i n t " . For an estimated pressure of 7600 bars,.the i n t e r s e c t i o n of curves (E14) and (E19) occurs at T = 620° C, X = 0.12. Therefore the mutual coexistence of r e a c t i o n assemblages f o r both e q u i l i b r i a occurs at a temperature some 80° C lower than the temperature estimated from the p e l i t e assemblages. Formation of z o i s i t e i n the muscovite-bearing assemblages occurs as a retrograde r e a c t i o n as the metamorphic assemblages are c o o l i n g . This r e t r o g r a d i n g i s c o n s i s t e n t w i t h the e a r l i e r suggestion of lower temperature readjustment of mineral compositions f o r the same assemblage. As w i t h sample 20, the e n c l o s i n g p e l i t e and q u a r t z i t e u n i t s were a ready source of the r e q u i r e d H^O-rich f l u i d s . Summary Ca l c u l a t e d d i s p l a c e d e q u i l i b r i u m curves f o r the assemblage c a l c i t e -q u a r t z - a c t i n o l i t e - c a l c i c pyroxene show that carbonate u n i t s c o n t a i n i n g t h i s assemblage b u f f e r e d c o e x i s t i n g f l u i d compositions to a n =0.25. This a c t i v i t y i s much lower than a i n surrounding p e l i t e s and i n d i c a t e s that H 20 each rock type e f f e c t i v e l y b u f f e r e d i t s own f l u i d composition during the i n i t i a l stages of metamorphism. Patchy or c o n c e n t r i c zoning to t s c h e r m a k i t i c amphiboles and a l t e r a t i o n of p l a g i o c l a s e to z o i s i t e denote an i n f l u x of H o 0 - r i c h f l u i d s i n t o the 196 carbonate u n i t s . C a l c u l a t e d d i s p l a c e d e q u i l i b r i a f o r sample 20 show that a A = 0.75 i s r e q u i r e d f o r coexistence of z o i s i t e and p l a g i o c l a s e w i t h H2° the amphibole r e a c t i o n assemblage at temperature and pressure c o n d i t i o n s estimated from the p e l i t e assemblages. Ca l c u l a t e d d i s p l a c e d e q u i l i b r i a f o r the assemblage c a l c i t e - m u s c o v i t e -q u a r t z - p l a g i o c l a s e - K - f e l d s p a r c o n s i s t e n t l y give temperatures lower than estimated metamorphic c o n d i t i o n s . S i m i l a r l y the c a l c u l a t e d coexistence of z o i s i t e w i t h t h i s assemblage i n sample 387 re q u i r e s retrograde metamorphic c o n d i t i o n s . These r e s u l t s i n d i c a t e that mineral compositions f o r t h i s assemblage have homogeneously readjusted to lower temperature c o n d i t i o n s during i n i t i a l stages of c o o l i n g . In summary, at l e a s t some of the carbonate u n i t s i n i t i a l l y b u f f e r e d c o e x i s t i n g f l u i d compositions through continuous metamorphic r e a c t i o n s . I n f l u x of H^O-rich f l u i d s from surrounding p e l i t e s or q u a r t z i t e s l a t e i n metamorphism was re s p o n s i b l e f o r development of z o i s i t e - b e a r i n g assemblages. FLUID COMPOSITIONS Estimated metamorphic c o n d i t i o n s f o r p e l i t e assemblages i n d i c a t e that X = 0.5 (approx.) f o r the c o e x i s t i n g f l u i d phase. C a l c u l a t i o n s i n v o l v i n g carbonate assemblages i n the previous s e c t i o n assumed the existence of a b i n a r y C O 2 - H 2 O f l u i d . The occurrence of grap h i t e (?) i n p e l i t e s and g r a p h i t e - p y r r h o t i t e i n carbonates means th a t a d d i t i o n a l species i n the system C-O-H-S must be considered when d i s c u s s i n g metamorphic f l u i d compositions. Ohmoto and K e r r i c k (1977) have c a l c u l a t e d concentrations of d i f f e r e n t gas species i n the system C-O-H-S over a wide range of metamorphic temperatures and pressures. They assumed coexistence of the f l u i d phase 197 w i t h g r a p h i t e - p y r i t e - p y r r h o t i t e . None of the s u l f u r species considered i n t h e i r c a l c u l a t i o n s (S0„,C0S,S , S ,H,,S) occurred i n concentrations Z Z o Z greater than 1 mole %. Since p y r i t e i s only r a r e l y encountered i n the Shuswap Complex i n the Azure Lake area, g e n e r a l i t y i s not l o s t by considering only the species i n the system C-O-H when d i s c u s s i n g the Azure Lake assemblages. Figure 2-22 i l l u s t r a t e s mole f r a c t i o n s of major species c o e x i s t i n g w i t h graphite i n the system C-O-H. Temperature and pressure were set to 727° C and 7600 ba r s , r e s p e c t i v e l y to be c o n s i s t e n t w i t h estimated metamorphic c o n d i t i o n s . The species C0^, CO, H^O, H 2, and CH^ were considered to compose the t o t a l pressure of the f l u i d . C a l c u l a t i o n s f o l l o w e d the e q u i l i b r i u m constant approach o u t l i n e d by French (1966). The diagram shows that f l u i d compositions were c a l c u l a t e d f o r s p e c i f i e d oxygen f u g a c i t i e s . A c t i v i t y c o e f f i c i e n t s f o r the d i f f e r e n t species were computed using Redlich-Kwong equations of s t a t e ( R e d l i c h and Kwong 1949) (see appendix 2-2) . H 2 f u g a c i t y c o e f f i c i e n t s were e x t r a p o l a t e d from equations by Shaw and Wones (1964). Log K - e q u i l i b r i u m constants r e l a t i n g the d i f f e r e n t species are from JANAF t a b l e s ( S t u l l and Prophet 1971). The diagram shows that only the three species Co 2, ^ 0 , and CH^ occur i n s u b s t a n t i a l amounts. C0 2~ and H 2 0 - r i c h f l u i d compositions e x i s t only over a narrow range of oxygen f u g a c i t i e s . Furthermore H 2 0 - r i c h f l u i d s c ontain e i t h e r CH^ or C0 2 as the secondary species. I t has already been demonstrated that some of the carbonate assemblages buffered f l u i d compositions to high X values during metamorphism. uu2 Figure 2-22 i l l u s t r a t e s that the assumption of a f l u i d c o n s i s t i n g dominantly of H 20 and C0 2 i s reasonable f o r the estimated metamorphic temperature and pressure. The diagram a l s o shows that coexistence of a 198 Figure 2-22. Compositions of metamorphic f l u i d phase c o e x i s t i n g w i t h graphite i n the system C-O-H at P'j; o t- a^ =^600 bars, T=727 °C. Compositions were c a l c u l a t e d f o r a range of oxygen f u g a c i t i e s . 199 CO^-rich fl u i d with graphite buffers oxygen fugacities to values equivalent to those of the FMQ oxygen buffer It was shown in the discussion on the pelites that the calculated a n in the pel i te assemblages is very sensitive to thermochemical error H 2 ° and solid solution models used for different phases. Therefore a i s F^ O only approximate and may range from 0.25 to 1.0 (in case of extreme errors). Ohmoto and Kerrick (1977) have shown that graphitic pelites in a closed system buffer ^ to the maximum possible value during metamorphism. This buffering is accomplished through continuous and discontinuous dehydration reactions. Figure 2-22 illustrates that the maximum 5L is approximately 2° 0.85 for estimated metamorphic conditions near Azure Lake with ...the remainder of the fl u i d phase consisting of equal amounts of CH^ and CO^. Since probable reactions for Azure Lake pelite assemblages are dehydration reactions, X^ ^  should reasonably be buffered to this maximum value. This value is within the error limits of the calculated X^ ^  for the pelites. Coexistence of a fl u i d phase consisting largely of U^O with graphite buffers oxygen fugacities to values between the MW and FMQ oxygen buffers. SUMMARY Pe l i t i c assemblages in the Shuswap Complex near Azure Lake, British Columbia contain the metamorphic transition from kyanite through f i r s t -sillimanite zones of the upper amphibolite facies. Textures indicate that garnet, staurolite, and kyanite were replaced by fibrolite-muscovite-biotite-ilmenite aggregates. Regression analysis of coexisting mineral rim compositions show that r u t i l e is probably a reactant phase in the reactions involving the breakdown of garnet and staurolite to sillimanite-bearing assemblages. Reaction textures are partly preserved because of 200 the exhaustion of a v a i l a b l e r u t i l e i n the matrix. Concentric zoning, growth p a t t e r n s , and replacement textures are r e l a t e d to continuous and discontinuous metamorphic r e a c t i o n s during a s i n g l e prograde metamorphic episode. The mutual i n t e r s e c t i o n of s e v e r a l experimentally s t u d i e d e q u i l i b r i a i n v o l v i n g garnet, s t a u r o l i t e , muscovite, p l a g i o c l a s e , quartz, and A l ^ S i O ^ r e s u l t e d i n a c o n s i s t e n t estimate of metamorphic c o n d i t i o n s : P = 7600 ± 400 bars, T = 705 ± 40° C, a u _ = 0.5 (approx.). Several i n t e r e s t i n g observations r e s u l t i n g from the d e t a i l e d c a l c u l a t i o n s are: 1. The estimated temperature and pressure were e s s e n t i a l l y determined by the i n t e r s e c t i o n of the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n ( E l ) w i t h the e q u i l i b r i a marking the upper s t a b i l i t y l i m i t of s t a u r o l i t e + quartz (E4, E5). E q u i l i b r i u m ( E l ) i s independent of a _ and r e a c t i o n s (E4, E5) do not s h i f t s i g n i f i c a n t l y f o r reduced a . H2° 2. Estimated a n values are determined by e q u i l i b r i a (E8, E9) which mark the upper s t a b i l i t y l i m i t of paragonite + quartz. a must be H 2 ° considered a "guesstimate" because i t i n c l u d e s a l l the d i f f e r e n t e r r o r s a s s o c i a t e d w i t h s o l i d s o l u t i o n models f o r muscovite and p l a g i o c l a s e as w e l l as thermochemical e r r o r s . 3. The assemblage p l a g i o c l a s e - g a r n e t - q u a r t z - A l ^ S i O ^ (E10, E l l ) c o n s i s t e n t l y r e s u l t s i n pressure estimates higher than estimates using the other e q u i l i b r i a . The use of t h i s assemblage as a r e l a t i v e geobarometer-geothermometer i s a l s o l i m i t e d by the high s e n s i t i v i t y of c a l c u l a t e d curve p o s i t i o n s to s l i g h t v a r i a t i o n s i n p l a g i o c l a s e composition. 4. Although a r e g i o n a l metamorphic gradient i s evident from the r e g u l a r d i s t r i b u t i o n of mineral assemblages i n the f i e l d , c a l c u l a t e d e q u i l i b r i u m curves do not confirm t h i s g radient. Apparently s c a t t e r from a n a l y t i c a l e r r o r and chemical zoning overwhelm the expected gradient 201 d i s t r i b u t i o n . 5. From s t r a t i g r a p h i c arguments metamorphic pressures cannot have exceeded 4 k i l o b a r s ( 12km). Yet estimated metamorphic pressures from the e q u i l i b r i a c a l c u l a t i o n s are greater than 7 k i l o b a r s ( 27km). Extensive t e c t o n i c t h i c k e n i n g i s r e q u i r e d to s a t i s f y both the s t r a t i g r a p h i c and thermodynamic data. A d e t a i l e d look at carbonate mineral e q u i l i b r i a i n d i c a t e that continuous r e a c t i o n s i n calcareous assemblages i n i t i a l l y b u f f e r e d c o e x i s t i n g f l u i d compositions to high a values near 0.75. Therefore the f l u i d phase, w h i l e i t may have been continuous, cannot have been homogeneous throughout a l l rock types during metamorphism. L o c a l occurrences of z o i s i t e r e p l a c i n g p l a g i o c l a s e i n carbonate assemblages r e s u l t e d from the l a t e i n f l u x of FL^O-rich f l u i d s i n t o the marbles. Surrounding p e l i t e and q u a r t z i t e u n i t s provided a ready source f o r the f l u i d s . C a l c u l a t i o n s a l s o show that part of the z o i s i t e formed during the retrograde readjustment of mineral compositions to lower temperatures. C a l c u l a t i o n s f o r the f l u i d phase c o e x i s t i n g w i t h graphite i n the system C-O-H show that CH^, C O 2 , and H^ O are the major species present at the estimated metamorphic c o n d i t i o n s . F l u i d s c o e x i s t i n g w i t h p e l i t e assemblages were probably b u f f e r e d to high ^ values near 0.85 w i t h equal amounts of CH^ and C0 2 making up the remainder. Carbonate assemblages coe x i s t e d w i t h a f l u i d c o n t a i n i n g mainly C0 2 and F^O. Oxygen f u g a c i t i e s f o r both s e t s of assemblages were b u f f e r e d to values near FMQ oxygen b u f f e r . 202 ACKNOWLEDGMENTS This paper represents part of a PhD t h e s i s completed at the U n i v e r s i t y of B r i t i s h Columbia. I am indebted to Dr. H.J. Greenwood f o r s u p e r v i s i n g the study w i t h continued i n t e r e s t and enthusiasm. Discussions w i t h Dr. T.H. Brown were u s e f u l i n debugging problems a s s o c i a t e d w i t h the e l e c t r o n microprobe and the thermodynamics of f l u i d s and s o l i d s . B. H a l l , P. M a r c e l l o , and N. Duncan a s s i s t e d w i t h the f i e l d work. J . Nelson kept my i n t e r e s t and enthusiasm f o r the p r o j e c t at a s u i t a b l e l e v e l . F i e l d and la b o r a t o r y expenses were defrayed through NRCC 67-4222 to Dr. H.J. Greenwood. During the course of t h i s study I was supported by graduate research f e l l o w s h i p s from the N a t i o n a l Science Foundation (NSF) and the I n t e r n a t i o n a l N i c k e l Company (INCO). i 203 SELECTED REFERENCES ALBAREDE, F. and PROVOST, A. 1 9 7 7 . 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Specimen 373 121 367 82 398 492 223 2-376 2-13 74 59 40 Metamorphic Zone Ky Ky K y - S i l l K y - S i l l K y - S i l l K y - S i l l K y - S i l l K y - S i l l S i l l S i l l S i l l S i l l Quartz (qtz) 20 30 2 25 30 20 50 25 30 10 30 25 Plagioclase (plag) 20 17 25 10 15 10 5 15 15 20 15 10 K-feldspar (K-sp) X X X 14 B i o t i t e (bio) 15 17 35 10 20 15 10 20 15 35 15 Muscovite (mus) 35 15 30 23 30 35 20 25 35 10 30 25 Garnet (gar) 5 10 5 12 3 5 5 5 2 10 6 15 Staurolite (stau) 2 X X 2 3 2 Kyanite (ky) 3 10 3 15 8 ? 7 Si l l i m a n i t e ( s i l l ) X 5 2 5 5 3 3 15 4 7 Ilmenite (ilm) X X X X X X X X X X X X Rutile (rut) i n i n i n i n Tourmaline (tour) X X X X X X X X X Zircon (zrcn) X X X X X X X X X X X X Apatite (ap) X X X X X X - present in - inclusion ro Table 2-2. Assemblages and modes for carbonate microprobe samples. Specimen 387 219 224 2-375 494 69 20 2-312 Metamorphic Zone Ky K y - S i l l K y - S i l l K y - S i l l K y - S i l l S i l l S i l l S i l l C alcite (cc) 80 85 85 50 50 89 75 90 Quartz (qtz) 7 2 7 30 25 1 10 3 Muscovite (mus) 5 3 5 Bi o t i t e (bio) 5 X Calcic amphibole (amph) 3 10 8 5 2 Calcic pyroxene (pyrx) 5 X 5 Garnet (gar) X 2 Plagioclase (plag) 2 5 10 X 4 4 K-feldspar (K-sp) 4 1 4 Z o i s i t e (zo) X X 15 2 X Scapolite (scap) X Graphite (gra) X X X X Sphene (sph) X X X X X X Pyrrhotite (po) 2 X X X X Pyrite (py) X Ilmenite (ilm) X X - present ro Table 2-3. Garnet analyses from p e l i t i c samples. Estimated standard e r r o r s are given i n parentheses. Specimen 373 121 367 edge core edge core edge core Analyses 39 1 11 1 14 1 s i o 2 37.91 (0.05) 37.85 37.05 (0.07) 37.88 36.51 (0.08) 36.42 T i 0 2 - - - - 0.02 (0.01) -A 1 2 ° 3 20.57 (0.03) 19.59 21.50 (0.04) 21.49 21.55 (0.04) 21.18 FeO* 34.55 (0.04) 32.92 34.97 (0.07) 33.48 34.18 (0.06) 30.15 MnO 1.19 (0.01) 3.36 1.67 (0.04) 1.99 1.38 (0.05) 4.35 MgO 2.75 (0.02) 2.16 2.87 (0.02) 3.11 2.90 (0.01) 1.24 CaO 2.44 (0.06) 3.30 2.41 (0.04) 3.00 3.49 (0.08) 6.42 Total 99.41 99.18 100.47 100.95 100.03 99.76 Si 3.057 (0.004) 3.080 2.971 (0 006) 2.972 Al 1.955 (0.003) 1.879 2.032 (0 004) 2.009 T i - - - -1.955 1.879 2.032 2.009 Fe 2.330 (0.003) 2.240 2.345 (0 005) 2.221 Mn 0.081 (0.0007) 0.232 0.113 (0 003) 0.134 Mg 0.331 (0.002) 0.262 0.343 (0 002) 0.368 Ca 0.211 (0.005) 0.288 0.207 (0 003) 0.255 2.953 3.022 3.008 2.978 formulae on the basis of 12 oxygens 2.941 (0.006) 3.004 2.046 (0.004) 2.025 0.001 (0.0006) 2.047 2.025 2.303 (0.004) 2.046 0.094 (0.003) 0.299 0.348 (0.001) 0.150 0.301 (0.007) 0.558 3.046 3.053 Almandine Spessartine Pyrope Grossular 78 3 11 8 74 8 9 10 molecular percent end-members f 78 75 77 4 4 3 11 12 12 7 9 9 67 10 5 18 * to t a l iron as FeO t - calculated using weighted linear regression analyst - L.C. Figage 82 edge core 23 1 37 74 (0.05) 37. 40 0 01 (0.004) 0. 02 21 49 (0.03) 21 37 36 22 (0.06) 34 84 1 04 (0.02) 2 70 2 81 (0.02) 2 97 2 18 (0.02) 2 22 101 49 101 52 2 996 (0.004) 2.975 2 010 (0.003) 2.004 0 001 (0.0002) 0.001 2 011 2.005 2 404 (0.004) 2.318 0 070 (0.001) 0.182 0 332 (0.005) 0.352 0 185 (0.002) 0.189 2 991 3.041 80 2 11 76 6 12 Table 2-3 (continued). Specimen 398 492 223 2-376 edge core edge core edge core edge core Analyses 14 1 18 1 16 1 15 1 S i 0 2 37.37 (0.03) 37.80 38 05 (0.06) 37 93 37. 54 (0 05) 37 76 37 91 (0.04) 37 95 T i 0 2 - 0.02 0. 01 (0.003) 0 55 0 01 0 02 (0.004) 0 01 A1 20 3 21.16 (0.06) 21.30 21. 37 (0.02) 21 07 21. 17 (0 04) 21 11 20 84 (0.03) 20 64 FeO* 35.81 (0.06) 34.98 36. 06 (0.06) 34 95 35 01 (0 05) 34 44 35 38 (0.04) 33 41 MnO 2.65 (0.03) 3.28 1. 49 (0.06) 2 57 1 46 (0 02) 2 57 0 75 (0.01) 3 72 MgO 2.76 (0.02) 3.11 3. 01 (0.03) 3 09 2 92 (0 01) 2 99 3 03 (0.02) 2 90 CaO 1.40 (0.04) 1.43 1 57 (0.07) 1 39 2 36 (0 03) 2 33 2 51 (0.04) 2 12 Total 101.15 101.92 101. 56 101 55 100 46 101 21 100 44 100 75 formulae on the basis of 12 oxygens Si 2.990 (0.002) 2.994 3 014 (0.005) 3 019 3 005 (0.004) 3 005 3 030 (0.003) 3.034 Al 1.996 (0.006) 1.988 1 995 (0.002) 1 995 1 997 (0.004) 1 980 1 963 (0.003) 1.945 Ti - 0.001 0 0006 (0.0002) 0 033 - 0 0005 0 001 (0.0002) 0.001 1.996 1.989 1 996 2 028 1 997 1 980 1 964 1.946 Fe 2.397 (0.004) 2.318 2 389 (0.004) 2 316 2 344 (0.003) 2 292 2 365 (0.003) 2.234 Mn .0.180 (0.002) 0.220 0 100 (0.004) 0 172 0 099 (0.001) 0 173 0 051 (0.0007) 0.252 Mg 0.329 (0.002) 0.368 0 355 (0.004) 0 365 0 348 (0.001) 0 354 0 361 (0.002) 0.346 Ca 0.120 (0.003) 0.122 0 133 (0.006) 0 118 0 202 (0.003) 0 198 0 215 (0.003) 0.182 3.026 3.028 2 977 2 971 2 993 3 017 2 992 3.014 molecular percent end-members t Almandine 79 77 80 78 78 76 79 74 Spessartine 6 7 3 6 3 6 2 8 Py rope 11 12 12 12 12 12 12 12 Grossular 4 4 5 4 7 7 7 6 * total iron as FeO t - calculated using weighted linear regression analyst - L.C. Pigage ro 03 Table 2-3 (continued). Specimen 2-13 74 59 edge core edge core edge core Analyses 18 1 14 1 52 1 S i 0 2 37.42 (0.03) 37. 70 38.03 (0.12) 38 43 37. 61 (0 02) 37 66 T i 0 2 - 0. 01 0.02 (0.004) 0 02 0 03 A1 20 3 20.58 (0.05) 20. 95 20.82 (0.07) 19 84 20. 56 (0 006) 21 03 FeO* 34.10 (0.05) 34. 30 33.40 (0.10) 30 13 34 59 (0 02) 33 33 MnO 1.69 (0.01) 2. 62 2.37 (0.04) 6 30 1. 27 (0 01) 4 34 MgO 2.42 (0.01) 2. 93 3.02 (0.01) 3 33 2 97 (0 006) 3 23 CaO 2.44 (0.02) 2. 28 2.71 (0.02) 1 98 2 10 (0 01) 1 59 Total 98.65 100. 79 100.37 100 02 99 10 101 21 formulae on the ba si s of 12 oxygens Si 3.047 (0.002) 3.013 3.037 (0.010) 3.083 3.044 (0.002) 3.001 Al 1.974 (0.005) 1.973 1.960 (0.007) 1.876 1.961 (0.0006) 1.975 T i - 0.001 0.001 (0.0002) 0.001 - 0.002 1.974 1.974 1.961 1.877 1.961 1.977 Fe 2.322 (0.003) 2.292 2.231 (0.007) 2.022 2.342 (0.001) 2.221 Mn 0.117 (0.0007) 0.177 0.160 (0.003) 0.428 0.087 (0.0007) 0.293 Mg 0.294 (0.001) 0.349 0.360 (0.001) 0.398 0.358 (0.0007) 0.384 Ca 0.213 (0.002) 0.195 0.232 (0.002) 0.170 0.182 (0.0009) 0.136 2.946 3.013 2.983 3.018 2.969 3.034 molecular percent end-members t Almandine 79 76 74 67 78 73 Spessartine 4 6 5 14 3 10 Pyrope 10 12 12 13 12 13 Grossular 8 6 8 6 6 4 * to t a l iron as FeO t - calculated using weighted linear regression analyst - L.C. Pigage 40 edge core 30 1 37.11 (0 04) 36 83 0.01 (0 002) 21.53 (0 02) 21 64 36.72 (0 05) 36 24 1.04 (0 05) 2 22 3.03 (0 01) 2 85 1.67 (0 03) 1 30 101.11 101 08 2.965 (0.003) 2.952 2.027 (0.002) 2.044 0.0006 (0.0001) 2.028 2.044 2.454 (0.003) 2.428 0.070 (0.003) 0.150 0.361 (0.001) 0.340 0.143 (0.003) 0.112 3.028 3.030 82 2 12 80 5 11 218 Table 2-4. Muscovite analyses from p e l i t i c samples. Estimated standard errors are given i n parentheses. Specimen ses 20 22 2 13 28 16 s i o 2 45. 17 (0.03) 46.03 (0.06) 46 17 (0.13) 46. 85 (0.08) 45 80 (0.05) 47.39 (0.09) T10 2 0.60 (0.01) 0.70 (0.01) 0 65 (0.01) 0. 69 (0.01) 0. 59 (0.01) 0.62 (0.01) A 1 2 ° 3 36.1 1 (0.07) 35.95 (0.03) 35 55 (0.06) 36 20 (0.06) 36 32 (0.02) 36.70 (0.07) FeO« 1.02 (0.005) 1. 18 (0.01) 1 13 (0.01) 1 21 (0.02) 1 06 (0.004) 0.99 (0.01) MnO - - -MgO 0.66 (0.006) 0.70 (0.01) 0 71 (0.02) 0 71 (0.01) 0 64 (0.01) 0.52 (0.01) CaO 0.01 (0.002) - 0.01 (0.004) BaO 0.26 (0.01) 0.35 (0.003) 0 27 (0.01) 0 41 (0.01) 0 34 (0.005) 0.50 (0.01) Na20 1.27 (0.006) 1.17 (0.01) 1 02 (0.01) 1 21 (0.02) 1 58 (0.02) 1.56 (0.03) K 20 9.18 (0.01) 9.40 (0.02) 9 77 (0.02) 9 42 (0.04) 9 11 (0.03) 8.59 (0.07) F 0.05 (0.003) 0.05 (0.001) 0 04 (0.002) 0 06 (0.003) 0 04 (0.002) 0.03 (0.002) H 20» 4.45 (0.004) 4.50 (0.004) 4 49 (0.008) 4 55 (0.005) 4 51 (0.003) 4.60 (0.006) Subtotal 98.78 100.03 99 80 101 31 99 99 101.51 less 0=F 0.02 0.02 0 02 0 03 0 02 0.01 Total 98.76 100.01 99 78 101 28 99 97 101.50 formulae on the basis of 24 (O.OH.F) Si 6 055 (0.004) 6. 102 (0.008) 6 1 38 (0.017) 6 130 (0 010) 6 069 (0 007) 6 155 (0 012) A1(IV)H 1 945 (0.004) 1 .898 (0.002) 1 862 (0.003) 1 870 (0 003) 1 931 (0 001) 1 845 (0 004) A1(VI)H 3 760 (0.007) 3.718 (0.003) 3 707 (0.006) 3 712 (0 006) 3 742 (0 002) 3 772 (0 007) T i 0 060 (0.001) 0.070 (0.001) 0 065 (0.001) 0 068 (0 001) 0 059 (0 001) 0 061 (0 001) Fe 0 114 (0.0006) 0. 131 (0.001) 0 126 (0.001) 0 132 (0 002) 0 117 (0 0004) 0 108 (0 001) Mg 0. 132 (0.001) 0. 138 (0.002) 0. 141 (0.004) 0. 138 (0 002) 0 126 (0.002) 0.101 (0 002) 4.066 4.057 4.039 4 050 4 044 4 .042 Ca 0.001 (0.0003) - - - - 0.001 (0 0006) Ba 0.014 (0.0005) 0.018 (0.0002) 0.014 (0.0005) 0. 02 1 (0 0005) 0 018 (0.0003) 0.025 (0 0005) Na 0.330 (0.002) 0. 301 (0.003) 0.263 (0.003) 0. 307 (0 005) 0 406 (0.005) 0. 393 (0 008) K 1.570 (0.002) 1 .590 (0.003) 1 .657 (0.003) 1 572 (0 007) 1 540 (0.005) 1 .423 (0 012) 1.915 1.909 1.9 34 1 900 1 964 1 .842 F 0.021 (0.001) 0.021 (0.0004) 0.017 (0.0008) 0. 025 (0 001) 0 017 (0.0008) 0.012 (0 0008) OH 3.979 (0.004) 3.979 (0.004) 3.983 (0.007) 3 975 (0 004) 3 983 (0.003) 3.988 (0 005) A K V D/Z 0.92 0.92 0.92 0 .92 0 .93 0.93 M g / ( M g + Fe) 0.54 0.51 0.53 .0 .51 0.52 0.48 N a / £ 0.17 0. 16 0.14 0.16 0 .21 0.21 OH/4 0.99 0.99 1.00 0 .99 1 .00 1.00 * - total Iron as FeO standard error for H 20 calculated from standard errors of other elements using Monte Carlo approach. - total standard error for Al Is divided proportionally between the two s i t e s , alyst - L.C. Pigage 219 Table 2-4 (continued). Specimen Analyses 223 14 2-376 31 2-13 26 74 23 59 19 40 29 sio 2 45.72 (0.09) 45.46 (0.04) 46.22 (0 08) 44.78 (0.07) 45.92 (0.05) 46.19 (0.03) Ti0 2 0.62 (0.02) 0.75 (0 01) 0.70 (0 02) 0.66 (0.005) 0.56 (0.01) 0.75 (0.02) A1203 35.74 (0.09) 35.60 (0 04) 35.53 (0 08) 35.25 (0.03) 35.39 (0.11) 36.29 (0.03) FeO* 1. 10 (0.01) 1.18 (0 01) 1.29 (0 02) 1.91 (0.01) 1.20 (0.01) 1.11 (0.01) MnO - - 0.01 (0 002) 0.01 (0.003) - -MgO 0.68 (0.02) 0.65 (0 01) 0.65 (0 01) 0.72 (0.004) 0.68 (0.01) 0.60 (0.003) CaO 0.02 (0.004) - 0.01 (0 002) 0.01 (0.004) 0.01 (0.005) -BaO 0.18 (0.01) 0.24 (0 005) 0.32 (0 01) 0.32 (0.009) 0.35 (0.01) 0.26 (0.004) Na20 1.17 (0.02) 1.11 (0 003) 1.02 (0 01) 0.89 (0.004) 1.14 (0.01) 1.32 (0.01) K20 9.64 (0.03) 9.36 (0 03) 9.46 (0 03) 9.92 (0.03) 9.37 (0.02) 9.13 (0.02) F 0.06 (0.003) 0.04 (0 001) 0.05 (0 002) 0.07 (0.002) 0.04 (0.002) 0.07 (0.003) H20// 4.47 (0.007) 4.45 (0 003) 4.49 (0 006) 4.41 (0.004) 4.46 (0.007) 4.51 (0.003) Subtotal 99.40 98.84 99.75 98.95 99.12 100.23 less 0=F 0.03 0.02 0.02 0.03 0.02 0.03 Total 99.37 98.82 99.73 98.92 99.10 100.20 formulae on the basis of 24 (O.OH.F) Si 6.101 (0.012) 6.095 (0.005) 6.143 (0.011) 6.049 (0.009) 6.142 (0.007) 6.096 (0 004) A1(IV)1 1.899 (0.005) 1.905 (0.002) 1.857 (0.004) 1.951 (0.002) 1.858 (0.006) 1.904 (0 002) A1(VI)1 3.722 (0.009) 3.721 (0.004) 3.709 (0.009) 3.660 (0.003) 3.720 (0.011) 3.741 (0 003) Ti 0.062 (0.002) 0.076 (0.001) 0.070 (0.002) 0.067 (0.0005) 0.056 (0.001) 0.074 (0 002) Fe 0.123 (0.001) 0.132 (0.001) 0.143 (0.002) 0.216 (0.001) 0.134 (0.001) 0.123 (0 001) Mn - - 0.001 (0.0002) 0.001 (0.0003) - -Me 0.135 (0.004) 0.130 (0.002) 0.129 (0.002) 0.145 (0.0008) 0.136 (0.002) 0.118 (0 0006) 4.042 4.059 4.052 4.089 4.046 4.056 Ca 0.003 (0.0006) - 0.001 (0.0003) 0.001 (0.0006) 0.001 (0.0007) -Ba 0.009 (0.0005) 0.013 (0.0003) 0.017 ( 0.0005) 0.017 (0.0005) 0.018 (0.0005) 0.013 (0 0002) Na 0.303 (0.005) 0.289 (0.0008) 0.263 (0.003) 0.233 (0.001) 0.296 (0.003) 0.338 (0 003) K 1.641 (0.005) 1.601 (0.005) 1.604 (0.005) 1.709 (0.005) 1.599 (0.003) 1.537 (0 003) 1.956 1.903 1.885 1.960 1.914 1.888 F 0.025 (0.001) 0.017 (0.0004) 0.021 (0.0008) 0.030 (0.0008) 0.017 (0.0008) 0.029 (0 001) OH 3.975 (0.006) 3.983 (0.003) 3.979 (0.005) 3.970 (0.004) 3.983 (0.006) 3.971 (0 003) AKVD/5T 0.92 0.92 0.92 0.90 0.92 0.92 Mg/(Mg + Fe) 0.52 0.50 0.47 0.40 0.50 0.49 Na/JT 0.15 0.15 0.14 0.12 0.15 0.18 OH/4 0.99 1.00 0.99 0.99 1.00 0.99 * - total Iron as FeO # - H20 calculated from structural formula assuming A (0,OH,F); standard error for HjO calculated from standard of other elements using Monte Carlo approach. 1 - total standard error for Al la divided proportionally between the two sltea. analyst - L.C. Pigage 220 Table 2-5. B i o t i t e analyses from p e l i t i c samples. Estimated standard e r r o r s are given i n parentheses. Specimen 373 121 36 7 82 398 492 A n a l y s e s 25 25 24 11 24 13 s i o 2 T 1 0 2 " 2 ° 3 35 .23 ( 0 . 0 7 ) 35.65 (0 , .03) 36. 73 (0 . 06) 36. 81 (0 .08 ) 3 5 . 71 (0 .04 ) 36.27 (0 . 15) 1.90 (0 .01 ) 2.02 (0 . .02) 1. 96 (0 . .02) 2 . 18 ( 0 .02 ) 1. 93 ( 0 .01 ) 2 .02 (0 . ,02) 19. 14 (0 .03 ) 19.48 I ( 0 .03 ) 19. 59 (0 . .05) 19. 50 ( 0 .06 ) 19. 24 (0 .03) 19.39 (0 . .03) FeO* 19.41 ( 0 . 0 4 ) 18.84 (0 . .02) 18. 72 (0 . .01) 19. 00 ( 0 .04 ) 19. 34 ( 0 .02 ) 18.80 (0 . ,03) MnO 0 .02 (0 .002 ) 0 . 0 3 (0. .001) 0 . 02 (0. ,001) 0 . 01 (0 .003) 0 . 06 (0 .002) 0 .02 (0. ,002) MgO 9 .69 ( 0 . 0 2 ) 10.00 (0 .03) 10. 36 (0, ,02) 9 . 80 ( 0 .02 ) 9 . 45 (0 .01) 9 .95 (0, ,03) CaO 0 . 0 1 (0 .002) - 0. 01 (0. .002) 0 . 01 (0 .002) 0 .01 (0, .002) BaO 0 . 0 8 (0 .003 ) 0 . 18 (0. .003) 0. 12 (0 .003) 0 . 20 (0 .002) 0 . 14 (0 .004) 0 . 2 1 (0. .01) N a 2 0 0 .22 (0 .002) 0 .32 (0 .003) 0, ,29 (0 .01) 0 . 36 ( 0 .01 ) 0 . 21 (0 .003) 0 .35 (0. .01) K 2 ° 8 .91 ( 0 . 0 3 ) 8 . 8 3 (0 .02) 9. .03 (0 .03) 8 . 65 ( 0 .05 ) 9 . 06 ( 0 . 0 1 ) 8 .59 (0 .01) F 0 . 25 (0 .003 ) 0 .22 (0 .003) 0. .21 (0 .003) 0 . 24 (0 .002) 0 . 23 ( 0 .003 ) 0 .21 (0 .002) H 20# 3.80 (0 .005 ) 3 .86 (0 .003) 3. ,94 (0 .005) 3. 92 (0 .005) 3 . 84 (0 .003) 3.89 (0 .008) S u b t o t a l 98 .66 9 9 . 4 3 100. .98 100. 67 99 . 22 99 .71 l e s s 0=F 0 .11 0 .09 0. .09 0 . 10 0 . 10 0 .09 T o t a l 98 .55 99 .34 100 .89 100. 57 99 . .12 99 .62 formulae on the b a s i s SI 5 .390 (0 .011 ) 5 .391 (0 .005) 5 .450 A l ( I V ) l 2 .610 (0 .004) 2 .609 (0 .004 ) 2 .550 A 1 ( V 1 ) « 0 . 8 4 1 ( 0 . 0 0 1 ) 0 . 8 6 3 ( 0 . 0 0 1 ) 0 .876 T l 0 .219 (0 .001) 0 .230 (0 .002 ) 0 .219 Fe 2 .484 (0 .005 ) 2 .383 (0 .003) 2 .323 Mn 0 . 0 0 3 (0 .0003) 0 .004 (0 .0001) 0 .003 Mg 2 .210 (0 .005) 2 .254 (0 .007 ) 2 .292 5 .757 5 .734 5 .713 Ca 0 .002 (0 .0003) - 0 .002 Ba 0 .005 (0 .0002) 0 .011 (0 .0002) 0 .007 Na 0 .065 (0 .0006) 0 .094 (0 .0009) 0 . 0 8 3 K 1.739 (0 .006 ) 1.703 (0 .004 ) 1.709 1.811 1.808 1.801 F 0 .121 ( 0 . 0 0 1 ) 0 . 1 0 5 (0 .001 ) 0 .099 OH 3.879 (0 .005) 3 .895 (0 .003) 3.901 T l / £ 0 .04 0 .04 0 .04 Fe/Z! 0 .43 0 .42 0 .41 Mg/JI 0 . 3 8 0 . 3 9 0 . 4 0 M g / ( M g + Fe) 0 .47 0 .49 0 .50 Na/2 0 . 0 3 0 .05 0 .04 K/2 0 .87 0.85 0 .85 0H/4 0 .97 0 .97 0 .98 o f 24 ( O , 0 H , F ) (0 .009) 5 .478 (0 .012) 5.429 (0 .006) 5 .453 (0 . 023) (0 .007) 2 .522 (0 .008) 2 .571 (0 .004) 2.54 7 (0 . ,004) (0 .002 ) 0 .898 (0 .003 ) 0 .877 (0 .001) 0 .889 (0. .001) (0 .002) 0 .244 (0 .002 ) 0 .221 (0 .001) 0 .228 (0. .002) (0 .001) 2.365 (0 .005) 2 .459 (0 .003) 2 .364 (0. .004) (0 .0001) 0 .001 (0 .0004) 0 .008 (0 .0003) 0 . 0 0 3 (0. .0003) (0 .004) 2.174 (0 .004) 2 .142 (0 .002) 2 .230 (0. .007) 5.682 5 .707 5.714 (0 .0003) - 0.002 (0 .0003) 0 .002 (0 .0003) (0 .0002) 0 .012 (0 .0001) 0 .008 (0 .0002) 0 .012 (0 .0006) (0 .003) 0 . 104 (0 .003) 0 .062 (0 .0009) 0 .102 (0 .003) (0 .006 ) 1.642 (0 .009 ) 1.757 (0 .002) 1.647 (0. .002) 1.758 1.829 1.763 (0 .001) 0 . 113 (0 .0009) 0.111 (0 .001) 0. 100 (0 .001) (0 .005) 3.887 (0 .005) 3.889 (0 .003) 3 .900 (0 .008) 0 .04 0 .04 0 .04 0 .42 0 . 4 3 0 .41 0 . 3 8 0 . 3 8 0 .39 0 . 4 8 0 .47 0 .49 0 .05 0 . 0 3 0 . 05 0 .82 0 . 8 8 0 .82 0 .97 0 .97 0 . 9 8 * - t o t a l i r o n as FeO # - H 20 c a l c u l a t e d f rom s t r u c t u r a l f o r m u l a as suming A ( O . O H . F ) ; s t a n d a r d e r r o r f o r H^O c a l c u l a t e d from s t a n d a r d e r r o r s of o t h e r e lements u s i n g Monte C a r l o a p p r o a c h . 1 - t o t a l s t a n d a r d e r r o r f o r A l i s d i v i d e d p r o p o r t i o n a l l y between the two s i t e s , a n a l y s t - L . C . P l g a g e 22 Table 2-5 (continued). B i o t i t e analyses from p e l i t i c samples. Specimen 223 2-376 2-13 74 7 4 - l n c l 9 59 40 Ana lyses 22 27 13 18 4 11 18 sio 2 35.88 (0.06) 35.48 (0 .03) 35.65 (0.05) 34.81 (0.07) 35.49 (0 .15) 35.71 (C.06) 35.56 (0 .06) T10 2 1.76 (0.02) 2.23 (0 .02) 2.15 (0.003) 2.52 (0.005) 2.84 (0 .04) 2.30 (0.02) 2.06 (0 .02) A 1 2 0 3 19.43 (0.04) 19.11 (0 .03) 19.00 (0.01) 18.80 (0.02) 18.95 (0.19) 19.22 (0.03) 19.40 (0.03) FeO« 18.68 (0.04) 18.72 (0 .03) 19.45 (0.02) 18.99 (0.04) 18.10 (0 .15) 18.54 (0 .07) 18.88 (0.07) MnO 0.02 (0.002) 0.01 (0.002) 0.03 (0.003) 0.04 (0.002) 0.12 (0.01) 0.02 (0.004) 0.01 (0.002) MgO 10.22 (0.03) 9.75 (0.02) 9.26 (0.02) 9.76 (0.01) 10.20 (0 .09) 9.63 (0.02) 9.89 (0.05) CaO 0.01 (0.001) 0.01 (0.002) 0.02 (0.002) - 0.01 (0.005) 0.02 (0.002) -BaO 0.09 (0.004) 0.11 (0.002) 0.19 (0.003) 0.15 (0.005) 0.18 (0.02) 0.14 (0 .01) 0.14 (0.01) Na 2 0 0.32 (0.003) 0.28 (0.003) 0.31 (0.01) 0.26 (0.003) 0.27 (0.005) 0.36 (0.004) 0.35 (0.01) K 2 0 8.73 (0.01) 8.82 (0 .03) 8.76 (0.03) 9.13 (0 .01) 9.40 (0.05) 8.65 (0.03) 8.30 (0.03) F 0.32 (0.003) 0.27 (0.002) 0.27 (0.002) 0.24 (0.003) 0.28 (0 .02) 0.21 (0.003) 0.32 (0.009) H 2OI 3.82 (0.004) 3.80 (0.003) 3.80 (0.004) 3.79 (0.004) 3.83 (0 .02) 3.84 (0.005) 3.79 (0.006) Subto ta l 99.28 98.59 98.89 98.49 99.67 98.64 98.70 l e s s 0=F 0 .13 0.11 0.11 0.10 0.12 0.09 0.13 T o t a l 99.15 98.48 98.78 98.39 99.55 98.55 98.57 formulae on the b a s i s of 24 (0 ,0H,F) SI 5.423 (0.009) 5.411 (0.005) 5. ,439 (0.008) 5.346 (0.011) 5.365 (0.023) 5, .430 (0.009) 5.405 (0, ,009) A1(IV)I 2.577 (0.005) 2.589 (0.004) 2. .561 (0.0015) 2.654 (0.003) 2.635 (0.026) 2, .570 (0.004) 2.595 (0, ,004) A1(VI)1 0.884 (0.002) 0.846 (0.001) 0, .855 (0.0005) 0.749 (0.001) 0.741 (0.007) 0, .875 (0.001) 0.880 (0, .001) T l 0.200 (0.002) 0.256 (0.002) 0. .247 (0.003) 0.291 (0.0006) 0.323 (0.005) 0, .263 (0.002) 0.235 (0. .002) Fe 2.361 (0.005) 2.388 (0.004) 2, .482 (0.003) 2.439 (0.005) 2.288 (0.019) 2. .358 (0.009) 2.400 (0. .009) Mn 0.003 (0.0003) 0.001 (0.0003) 0. ,004 (0.0004) 0.005 (0.0003) 0.015 (0.001) 0. .003 (0.0005) 0.001 (0 .0003) Mg 2.303 (0.007) 2.217 (0.005) 2. ,106 (0.005) 2.235 (0.002) 2.299 (0.020) 2 .183 (0.005) 2.241 (0 .011) 5.751 5.708 5, ,694 5.719 5.666 5 .682 5.757 Ca 0.002 (0.0002) 0.002 (0.0003) 0, ,003 (0.0003) - 0.002 (0.001) 0. .003 (0.0003) -Ba 0.005 (0.0002) 0.007 (0.0001) 0. ,011 (0.0002) 0.009 (0.0003) 0.011 (0.001) 0 .008 (0.0006) 0.008 (0, .0006) tia 0.094 (0.0009) 0.083 ( 0 . 0 X 9 ) 0. .092 (0.003) 0.077 (0.0009) 0.079 (0.001) 0 . 106 (0.001) 0.103 (0, .003) K 1.683 (0.002) 1.716 (0.006) 1, .705 (0.006) 1.789 (0.002) 1.813 (0.010) 1 .678 (0.006) 1.609 (0, .006) 1.784 1.808 1, .811 1.875 1.905 1. .795 1.720 F 0.153 (0.001) 0.130 (0.001) 0 .130 (0.001) 0.117 (0.001) 0.134 (0.010) 0 .101 (0.001) 0.154 (0. .004) OH 3.847 (0.004) 3.870 (0.003) 3. .870 (0.004) 3.883 (0.004) 3.866 (0.020) 3, .899 (0.005) 3.846 (0. .006) z 0.03 0.04 0 .04 0.05 0.06 0. ,05 0.04 E 0.41 0.42 0. .44 0.43 0.40 0, .41 0.42 E 0.40 0.39 0 .37 0.39 0.41 0, ,38 0.39 Mg + Fe) 0.49 0 .48 0 .46 0.48 0.50 0, .48 0.48 0.05 0.04 0 .05 0.04 0.04 0, .05 0.05 0.84 0.86 0 .85 0.89 0.91 0. ,84 0.80 0.96 0.97 0 .97 0.97 0.97 0. ,97 0.96 * - total i r o n as FeO # - H20 calculated from structural fornula assuming 4 (O.OH.F); atandard arror for HjO calculated from standard errors of other elements using Monte Carlo approach. 1 - total standard error for Al Is divided proportionally between the two sites, analyst - L.C. Pigage Table 2-7. P l a g i o c l a s e analyses from p e l i t i c samples. Estimated standard e r r o r s are given i n parentheses. Specimen Zoning range (An) 373 367 398 Analyses 32 36 25 23 28 19 S i 0 2 61 22 (0.18) 60 60 (0.19) 58. 19 (0.13) 61. 60 (0.07) 63.54 (0.07) 63.96 (0.17) A1 20 3 24 25 (0.12) 26 30 (0.10) 26.35 (0.08) 23. 98 (0.04) 22.73 (0.04) 23.49 (0.04) CaO 5 74 (0.12) 6 41 (0.11) 8.09 (0.04) 5 94 (0.04) 4.39 (0.03) 4.74 (0.03) Na20 8 19 (0.08) 7 69 (0.04) 6.84 (0.03) 8 46 (0.03) 9.19 (0.03) 8.75 (0.03) K 20 0 07 (0.004) 0 07 (0.002) 0.06 (0.002) 0 07 (0.003) 0.08 (0.004) 0.05 (0.002) BaO 0 02 (0.004) 0 01 (0.003) 0.01 (0.002) 0.01 (0.003) 0.01 (0.003) Total 99 49 101 08 99.54 100 05 99.94 101.00 formulae on the basis of 8 oxygens Si 2 729 (0.008) 2 663 (0.008) 2.611 (0.006) 2 735 (0.003) 2.809 (0.003) 2.795 (0.007) Al 1 274 (0.006) 1 362 (0.005) 1.39 3 (0.004) 1 255 (0.002) 1.184 (0.002) 1.210 (0.002) 4 003 4 025 4.004 3 990 3.993 4.005 Ca 0 274 (0.006) 0 302 (0.005) 0.389 (0.002) 0 283 (0.002) 0.208 (0.001) 0.222 (0.001) Na 0 708 (0.007) 0 655 (0.003) 0.595 (0.003) 0 728 (0.003) 0.788 (0.003) 0.741 (0.003) K 0 004 (0.0002) 0 004 (0.0001) 0.003 (0.0001) 0 004 (0.0002) 0.005 (0.0002) 0.003 (0.0001) Ba tr t r t r - tr tr 0 986 0 961 0.987 1 015 1.001 0.966 molecular percent end-members t Anorthi te 27 7 33 8 39.2 26 8 20.0 22.5 Albite 71 9 66 .1 60.2 72 6 79.4 76.0 Orthoclase 0 4 0 4 0.3 0 4 0.5 0. 3 Range (An) 20 -33 23 -35 35-41 21 -30 20-25 17-25 reverse 15-33 reverse 19-32 reverse 17-22 reverse 16-20 tr - less than 0.0005 t - calculated using weighted linear regression analyst - L.C. Pigage ro ro OJ Table 2-7 (c o n t i n u e d ) . P l a g i o c l a s e analyses from p e l i t i c samples. Specimen 223 2-376 2-13 74 59 40 Analyses 12 19 31 10 33 22 S i 0 2 59.37 (0 11) 61 .24 (0 1 1 ) 60.24 (0. 10) 60.37 (0 18) 60.98 (0 10) 62.90 (0 07) A 1 2 0 3 25.03 (0 07) 24.31 (0 04) 24.76 (0.05) 25.13 (0 08) 24. 10 (0 02) 23.67 (0 03) CaO 7. 18 (0 11) 5.74 (0 06) 6. 50 (0.04) 7.31 (0 07) 5.33 (0 03) 5.08 (0 02) Na 20 7.71 (0 05) 8.16 (0 03) 7.91 (0.03) 7.20 (0 17) 8.46 (0 02) 8.88 (0 003) K 20 0.07 (0 003) 0.08 (0 003) 0.09 (0.006) 0.05 (0 005) 0.09 (0 003) 0.06 (0 003) BaO 0.02 (0 00A) - - - - 0.01 (0 002) T o t a l 99. 38 99.53 99.50 100.06 98.96 100.60 formulae on the b a s i s o f 8 oxygens S i 2.665 (0 005) 2 728 (0 005) 2 693 (0 004) 2 683 (0 008) 2 732 (0 004) 2 769 (0 00 3) A l 1.324 (0 004) 1 276 (0 002) 1 305 (0 003) 1 316 (0 004) 1 273 (0 001) 1 228 (0 002) 3.989 4 004 3 998 3 999 4 005 3 997 Ca 0. 345 (0 005) 0 274 (0 003) 0 311 (0 002) 0 348 (0 003) 0 256 (0 001) 0 240 (0 001) Na 0.671 (0 004) 0 705 (0 003) 0 686 (0 003) 0 620 (0 015) 0 735 (0 002) 0 758 (0 0003) K Ba 0.004 (0 0002) 0 005 (0 0002) 0 005 (0 0003) 0 003 (0 0003) 0 005 (0 0002) 0 003 (0 0002) 1.020 0 984 1 002 0 971 0 996 1 001 m o l e c u l a r p e r c e n t end-members A n o r t h i t e A l b i t e O r t h o c l a s e Range (An) Zoning range (An) 32.9 66.5 0.4 33-38 27.9 71.4 0.5 22-29 re v e r s e 21-25 30.9 68.6 0.5 26-34 r e v e r s e 20-32 33.5 66.0 0.3 33-38 26.4 73.6 0.5 24-30 23. 7 75.8 0. 3 23-26 t r - l e s s than 0.0005 ^ - c a l c u l a t e d u s i n g weighted l i n e a r r e g r e s s i o n a n a l y s t - L.C. Pigage ^ ro 225 Table 2-8. K-feldspar analyses from p e l i t i c samples. Estimated standard e r r o r s are given i n parentheses. Specimen 398 2-376 2-13 Analyses 2 7 5 Si0 2 64.46 (1.39) 64.81 (0.24) 64.50 (0.34) A1 20 3 19.24 (0.26) 18.22 (0.07) 17.75 (0.07) CaO 0.02 (0.00) 0.01 (0.004) 0.13 (0.09) Na20 0.22 (0.03) 0.20 (0.009) 0.18 (0.004) K20 15.04 (0.68) 15.74 (0.16) 15.51 (0.14) BaO 0.31 (0.02) 0.25 (0.005) 0.50 (0.01) Total 98.85 99.75 99.29 formulae on the basis of 8 oxygens SI 2.983 (0.064) 3.011 (0.011) 3.021 (0.016) Al 1.049 (0.015) 0.998 (0.004) 0.980 (0.004) 4.032 4.009 4.001 Ca 0.001 (0.000) tr 0.007 (0.005) Na 0.020 (0.003) 0.018 (0.0008) 0.016 (0.0004) K 0.888 (0.038) 0.933 (0.009) 0.927 (0.008) Ba 0.006 (0.0004) 0.005 (0.0001) 0.009 (0.0002) 0.915 0.956 0.959 molecular percent end-members t Anorthite 0.1 - 0.7 Albite 2.2 1.9 1.7 Orthoclase 97.0 97.6 96.7 Celsian 0.7 0.5 0.9 tr - less than 0.0005 analyst - L.C. Pigage t - calculated using weighted linear regression Table 2-9. Ilm e n i t e analyses from p e l i t i c samples. Estimated standard e r r o r s are given i n parentheses. Specimen 373 121 367 82 398 492 Analyses 5 9 11 6 8 11 T i 0 2 51.77 (0.08) 51.66 (0.17) 52.52 (0.21) 52.76 (0.11) 53.22 (0.25) 52.76 (0.11) A1 20 3 0.15 (0.11) 0.01 (0.007) 0.02 (0.006) 0.06 (0.008) 0.06 (0.05) 0.15 (0.11) FeO* 45.33 (0.12) 44.29 (0.12) 46.90 (0.08) 46.67 (0.09) 45.21 (0.22) 46.45 (0.17) ZnO na 0.03 (0.003) 0.03 (0.006) 0.04 (0.05) 0.04 (0.007) 0.06 (0.006) MnO 0.85 (0.01) 0.39 (0.01) 0.51 (0.02) 0.25 (0.01) 1.38 (0.03) 0.33 (0.02) MgO 0.06 (0.002) 0.04 (0.01) 0.05 (0.003) 0.07 (0.02) 0.03 (0.004) 0.10 (0.04) CaO - 0.09 (0.02) 0.02 (0.01) - 0.01 (0.004) _ Total 98.16 96.51 100.05 99.85 99.95 99.64 formulae on the basis of 6 oxygens Ti 1.999 (0.003) 2.022 (0.007) 1.995 (0.008) 2.003 (0.004) 2.014 (0.009) 2.005 (0.004) Al 0.009 (0.007) 0.001 (0.0004) 0.001 (0.0004) 0.004 (0.0005) 0.004 (0.003) 0.009 (0.007) 2.008 2.023 1.996 2.007 2.018 2.014 Fe 1.947 (0.005) 1.928 (0.005) 1.981 (0.003) 1.971 (0.004) 1.903 (0.009) 1.954 (0.004) Zn na 0.001 (0.0001) 0.001 (0.0002) 0.001 (0.002) 0.001 (0.0003) 0.002 (0.0002) Mn 0.037 (0.0004) 0.017 (0.0004) 0.022 (0.0009) 0.011 (0.0004) 0.059 (0.001) 0.014 (0.0009) Mg 0.005 (0.0002) 0.003 (0.0008) 0.004 (0.0002) 0.005 (0.002) 0.002 (0.0003) 0.008 (0.003) Ca - 0.005 (0.001) 0.001 (0.0005) - 0.001 (0.0002) -1.989 1.954 2.009 1.988 1.966 1.978 molecular percent end-members t Ilmenite Z n 2 T i 2 0 6 Pyrophanlte Geikiellte 1.9 0.2 97.7 0.1 0.9 0.2 0.1 0.1 98.9 0.1 1.1 0.2 tr 0.2 98.7 0.1 0.5 0.3 96.3 0.1 3.0 0.1 tr 98.2 0.1 0.7 0.7 na - not analyzed t - calculated using weighted linear regression * - total iron as FeO tr - leas than 0.05Z analyst - L.C. Pigaga ro Table 2-9 (continued). I l m e n i t e analyses from p e l i t i c samples. Specimen 223 2-376 2- 13 74 59 40 Analyses 11 9 9 1 5 8 TiO, 52.22 (0.11) 52.29 (0.21) 51. 23 (0.12) 49.62 52.73 (0.06) 52.84 (0.20) 2 A1,0, 0.02 (0.003) 0.17 (0.14) 0 02 (0.01) 0.02 0.04 (0.002) 0.02 (0.004) 2 3 FeO* 46.45 (0.17) 46.07 (0.27) 44 29 (0.16) 44.99 44.13 (0.09) 46.87 (0.10) ZnO 0.03 (0.006) 0.06 (0.007) 0 15 (0.06) 0.06 0.06 (0.009) 0.06 (0.005) MnO 0.31 (0.006) 0.27 (0.02) 0 76 (0.03) 1.78 1.18 (0.009) 0.18 (0.004) MgO 0.14 (0.02) 0.03 (0.003) 0 03 (0.01) 0.02 0.03 (0.004) 0.32 (0.02) CaO _ 0.01 (0.003) 0 05 (0.02) - 0.01 (0.004) -Total 99.17 98.90 96 53 96.70 98.18 100.29 T i Al Fe Zn Ma Mg Ca 1.998 (0.004) 0.001 (0.002) 1.999 1.977 (0.007) 0.001 (0.0002) 0.013 (0.0003) 0.011 (0.002) formulae on the basis of 6 oxygens 2.003 (0.008) 2.010 (0.005) 0.010 (0.008) 0.001 (0.0006) 2.013 2.011 1.962 (0.012) 0.002 (0.0003) 0.012 (0.0009) 0.002 (0.0002) 0.001 (0.0002) 1.979 1.933 (0.007) 0.006 (0.002) 0.034 (0.001) 0.002 (0.0008) 0.003 (0.001) 1.978 1.966 0.001 1.967 1.982 0.002 0.079 0.002 2.065 2.027 (0.002) 0.002 (0.0001) 2.029 1.886 (0.004) 0.002 (0.0003) 0.051 (0.0004) 0.002 (0.0003) 0.001 (0.0002) 1.942 1.997 (0.008) 0.001 (0.0002) 1.998 1.970 (0.004) 0.002 (0.0002) 0.008 (0.0002) 0.024 (0.002) Ilmenite Z n 2 T i 2 0 6 Pyrophanite Geikielite 0.1 98.7 0.1 0.7 0.5 molecular percent end-members t 98.9 97.7 96.4 0.1 0.4 0.6 1.7 3.9 0.1 0.1 0.1 0.1 97.3 0.1 2.6 0.1 tr 0.1 98.4 0.1 0.4 1.2 * - total iron as FeO t - calculated using weighted linear regression tr - lese than 0.05Z analyst - L.C. Flgage ro ro -4 Table 2-10. C a l c i t e analyses from carbonate samples. Estimated standard e r r o r s are given i n parentheses. Specimen Analyses FeC03 MgC03 MnCOj CaCO, 387 30 0.05 (0.002) 0.54 (0.008) 0.01 (0.002) 99.53 (0.08) Total 100.13 219 29 2.15 (0.006) 1.32 (0.005) 0.11 (0.002) 95.04 (0.16) 98.62 224 32 0.74 (0.01) 0 . 30 (0.006) 0.68 (0.003) 97.63 (0.22) 99.35 2-375 29 2.76 (0.01) 2.48 (0.01) 0.38 (0.002) 94.81 (0.33) 100.43 494 29 1.37 (0.006) 0.98 (0.007) 0.71 (0.005) 97.21 (0.22) 100.27 69 33 0.05 (0.002) 0.65 (0.01) 0.02 (0.002) 99.98 (0.11) 100.70 20 26 0.65 (0.01) 0.34 (0.009) 0.14 (0.002) 97.80 (0.32) 98.93 2-312 24 0.53 (0.006) 0.52 (0.01) 0.09 (0.002) 97.59 (0.09) 98.73 Siderite Magnesite Rhodochrosite Calcite 0.1 0.6 tr 99.3 1.9 1.6 0.1 96.4 0.6 0.4 0.6 98.4 molecular percent end-members 2.4 2.9 0.3 94.4 1.2 1.2 0.6 97.0 tr 0.8 tr 99.2 0.6 0.4 0.1 98.9 0.5 0.6 0.1 98.8 tr - less than 0.05 analyst - L.C. Figage ro ro 00 Table 2-11. P l a g i o c l a s e analyses from carbonate samples. Estimated standard e r r o r s are given i n parentheses. Specimen 387 219-rim 219-core 2-375 69-A Analyses 6 22 1 19 7 Si0 2 60.22 (0.18) 44.19 (0.06) 62.53 44.65 (0.09) 63.07 (0.13) A1203 25.90 (0.12) 36.41 (0.05) 24.05 36.64 (0.04) 23.27 (0.25) CaO 7.06 (0.06) 19.08 (0.06) 5.43 19.43 (0.04) 3.83 (0.12) Na20 7.35 (0.06) 0.36 (0.01) 8.28 0.49 (0.02) 8.50 (0.08) K20 0.20 (0.01) 0.01 (0.003) 0.05 0.01 (0.002) 0.23 (0.02) BaO 0.01 (0.005) - - 0.01 (0.002) 0.02 (0.01) Total 100.74 100.05 100.35 101.23 98.92 formulae on the basis of 8 oxygens Si 2.661 (0.008) 2.037 (0.003) 2.757 2.037 (0.004) 2.807 (0.006) Al 1.349 (0.006) 1.978 (0.003) 1.250 1.970 (0.002) 1.220 (0.013) 4.010 4.015 4.007 4.007 4.027 Ca 0.334 (0.003) 0.942 (0.003) 0.256 0.950 (0.002) 0.183 (0.006) Na 0.630 (0.005) 0.032 (0.0009) 0.708 0.043 (0.002) 0.733 (0.007) K 0.011 (0.0006) 0.001 (0.0002) 0.003 0.001 (0.0001) 0.013 (0.001) Ba tr - - tr tr 0.975 0.975 0.967 0.994 0.929 molecular percent end-members t A n ° r t h i t e 3 4 - ° 96-7 25 .7 95.9 2 0 7 M M t e 6 4 - 6 3 ' 3 72 .5 4.3 7 8 . ' o Orthoclase 1.1 2.0 - 1.4 tr - less than 0.0005 t - calculated using weighted linear regression analyst - L.C. Pigage 69-B 5 20 22 55.92 (0.61) 27.33 (0.25) 8.97 (0.27) 5.65 (0.20) 0.10 (0.02) 97.97 51.39 (0.28) 31.24 (0.23) 13.39 (0.25) 3.68 (0.12) 0.06 (0.004) 0.01 (0.004) 99.77 2.552 (0.028) 1.470 (0.013) 4.022 0.439 (0.013) 0.500 (0.018) 0.006 (0.001) 0.945 2.336 (0.013) 1.674 (0.012) 4.010 0.652 (0.012) 0.324 (0.011) 0.003 (0.0002) tr 0.979 46.2 53.2 0.6 66.7 33.1 0.3 PO ro 230 Table 2-12. K-feldspar analyses from carbonate samples. Estimated standard e r r o r s are given i n parentheses. Specimen 387 69 20 Analyses 23 16 16 Si0 o 65.22 (0.07) 64.85 (0.09) 64.73 (0.06) z Al 0 18.27 (0.03) 18.01 (0.07) 18.95 (0.01) CaO 0.01 (0.002) 0.04 (0.005) 0.05 (0.003) Na20 0.81 (0.02) 0.79 (0.02) 0.68 (0.003) K„0 14.64 (0.02) 14.74 (0.03) 15.00 (0.03) BaO 0.66 (0.06) 0.34 (0.02) 0.86 (0.02) Total 99.61 98.77 100.27 formulae on the basis of 8 oxygens SI 3.014 (0.003) 3.018 (0.004) 2.983 (0.003) Al 0.995 (0.002) 0.988 (0.004) 1.029 (0.0005) 4.009 4.006 4.012 Ca tr 0.002 (0.0002) 0.002 (0.0001) Na 0.073 (0.002) 0.071 (0.002) 0.061 (0.0003) K 0.863 (0.001) 0.875 (0.002) 0.882 (0.002) Ba 0.012 (0.001) 0.006 (0.0004) 0.016 (0.0004) 0.948 0.954 0.961 molecular percent end-members t Anorthite 0.1 0.2 0.3 Albite 10.3 9.1 6.2 Orthoclase 87.6 89.5 92.0 Celslan 1.3 0.7 1.9 tr - less than 0.0005 t - calculated using weighted linear regression analyst - L.C. Pigage 231 Table 2-13. Muscovite and b i o t i t e analyses from carbonate samples. Estimated standard e r r o r s are given i n parentheses. Specimen 387 219 69 -A 69 -B Specimen 219 Analyses 17 35 1 1 Analyses 22 s i o 2 T i 0 2 49. 82 (0.07) 46.88 (0.05) 46. 11 49. 36 S i 0 2 35.52 (0.07) 0. 12 (0.007) 0.83 (0.02) 0. 10 0. 31 T i 0 2 2.63 (0.02) A1 20 3 31. 60 (0.04) 33.28 (0.05) 36. 60 32. 55 A 1 2 0 3 18.13 (0.07) FeO * 0. 12 (0.003) 1.87 (0.008) 0. 15 0. 08 FeO * 19.38 (0.03) MnO - - MnO 0.02 (0.002) MgO 2. 95 (0.02) 1.34 (0.01) 0. 79 2. 41 MgO 9.44 (0.02) CaO 0. 04 (0.003) 0.04 (0.003) - 0. 01 CaO 0. 12 (0.009) BaO 0. 17 (0.O06) 0.19 (0.003) 0. 24 0. 09 BaO 0.09 (0.006) Na 20 0. 22 (0.003) 0.32 (0.003) 0. 32 0. 23 Na 20 0.12 (0.004) K 20 F 10. 80 (0.05) 10.66 (0.03) 10. 93 10. 92 K 20 9.10 (0.05) 0. 72 (0.006) 0. 15 (0.002) 0. 21 0. 21 F 0.54 (0.004) H 20 # 4. 22 (0.005) 4.42 (0.004) 4. 42 4. 47 H 20 t 3.65 (0.005) Subtotal 100. 78 99.98 99. 87 100. 64 Subtotal 98.74 less OEF 0. 30 0.06 0. 09 0. .09 less 05F 0.23 Total 100. 48 99.92 99. 78 100. 55 To t a l 98.51 formulae on the basis of 24 (O.OH.F) Si 6.548 (0.009) 6.265 (0.007) 6.120 Al(IV) H 1.452 (0.002) 1.735 (0.003) 1.880 Al(VI) 11 3.442 (0.004) 3.506 (0.005) 3.845 T l 0.012 (0.0007) 0.083 (0.002) 0.010 Fe 0.013 (0.0003) 0.209 (0.0009) 0.017 Mn - - -Mg 0.578 (0.004) 0.267 (0.002) 0.156 4.045 4.065 4.028 Ca 0.006 (0.0004) 0.006 (0.0004) -Ba 0.009 (0.0003) 0.010 (0.0002) 0.012 Na 0.056 (0.0008) 0.083 (0.0008) 0.082 K 1.811 (0.008) 1.817 (0.005) 1.851 1.882 1.916 1.945 F 0.299 (0.002) 0.063 (0.0008) 0.088 OH 3.701 (0.004) 3.937 (0.004) 3.912 formula on the basis of 24 (O.OH.F) 6.478 S i 5.448 (0.011) 1.522 Al(IV) 1 2.552 (0.010) 3.513 Al(VI) 1 0.726 (0.003) 0.031 Ti 0.303 (0.002) 0.009 Fe 2.486 (0.004) - Mn 0.003 (0.0003) 0.472 Mg 2.159 (0.005) 4.025 5.677 0.001 Ca 0.020 (0.001) 0.005 Ba 0.005 (0.0004) 0.059 Na 0.036 (0.001) 1.828 K 1.781 (0.010) 1.893 1.842 0.087 F 0.262 (0.002) 3.913 OH 3.738 (0.004) AKVI)/S! Mg/(Mg + Fe) Na/X OH/4 0.85 0.98 0.03 0.93 0.86 0.56 0.04 0.98 0.95 0.90 0.04 0.98 0.87 0.98 0.03 0.98 to t a l iron as FeO H 20 calculated from s t r u c t u r a l formula assuming 4 (OH.F); standard T i / ^ Fe/S Mg/SI Mg/(Mg + Fe) Na/2 K/2 OH/4 0.05 0.44 0.38 0.46 0.02 0.89 0.93 using Monte Carlo approach. 5 - t o t a l standard error for Al Is divided proportionally between the two s i t e s analyst - L.C. Pigage 2 3 2 Table 2-14. C a l c i c amphibole analyses from carbonate samples. A - Tschermakitic amphibole , B - A c t i n o l i t i c amphibole Specii men 224 2- 375 494 20 2- 312 A B A B A B A B A B rseB 1 1 1 1 1 1 1 1 1 1 s i o 2 50.26 54.43 42.88 49.45 50.34 54.89 42.38 55.91 52.00 55.25 T i 0 2 0.13 - 0.58 0.31 0.15 0.05 0.21 0.04 0.05 -A 1 2 0 3 6.65 0.84 16.54 7.96 6.75 1.51 13.58 0.94 5.14 1.14 FeO* 18.74 18.01 16.90 14.31 13.52 13.71 18.14 16.91 10.52 9.90 MnO 0.48 0.58 0.09 0.11 0.30 0.28 0.08 0.12 0.05 0.01 MgO 10.52 12.81 7.55 12.41 12.85 (4.69 9.08 13.25 15.27 17.34 CaO 12.20 12.38 12.39 12.27 12.57 12.71 11.98 12.46 12.21 12.70 NajO 0.49 0.07 0.96 0.51 0.47 0.09 0.88 0.05 0.49 0.11 K 2 0 0.28 0.02 0.69 0.28 0.21 0.03 1.13 0.03 0.24 -F 0.16 0.16 0.15 0.15 0.10 0.10 0.13 0.13 0.43 0.43 H 2 0J 1.98 1.99 1.96 1.99 2.01 2.04 1.92 2.04 1.86 1.89 Subtotal 101.89 101.29 100.69 99.75 99.27 100.10 99.51 101.88 98.26 98.77 less 0=F 0.07 0.07 0.06 0.06 0.04 0.04 0.05 0.05 0.18 0.18 Total 101.82 101.22 100.63 99.69 99.23 100.06 99.46 101.83 98.08 98.59 formulae on the bas is of 24 (0.0H.F) Si 7.318 7.906 6.323 7.207 7.346 7.898 6.401 7.989 7.547 7.924 Al(IV) 0.682 0.094 1.677 0.793 0.654 0.102 1.599 0.011 0.453 0.076 Al(VI) 0.459 0.050 1.197 0.574 0.507 0.154 0.819 0.148 0.426 0.117 T l 0.014 - 0.064 0.034 0.016 0.005 0.024 0.004 0.005 -Fe 2.282 2.188 2.084 1.744 1.650 1.650 2.292 2.021 1.277 1. 187 Mn 0.059 0.071 0.011 0.014 0.037 0.034 0.010 0.015 0.006 0.001 Mg 2.284 2.774 1.660 2.696 2.795 3. 151 2.045 2.823 3. 304 3.707 5.098 5.083 5.016 5.062 5.005 4.994 5.190 5.011 5.018 5.012 Ca 1.903 1.927 1.957 1.916 1.965 1.959 1.939 1.908 1.899 1.952 Na 0. 138 0.020 0.274 0.144 0.133 0.025 0.258 0.014 0.138 0.031 K 0.052 0.004 0.130 0.052 0.039 0.006 0.218 0.005 0.044 -2.093 1.951 2.361 2.112 2.137 1.990 2.415 1.927 2.081 1.983 F 0.074 0.074 0.070 0.069 0.046 0.046 0.062 0.059 0. 197 0.195 OH 1.926 1.926 1.930 1.931 1.954 1.954 1.938 1.941 1.803 1.805 S i /8 0.91 0.99 0.79 0.90 0.92 0.99 0.80 1.00 0 94 0.99 Fe/Z 0.45 0.43 0.42 0.34 0.33 0.33 0.44 0.40 0 25 0.24 Mg/r 0.45 0.55 0.33 0.53 0.56 0.63 0.39 0.56 0 66 0.74 Mg/(Mg + Fe) 0.50 0.56 0.44 0.61 0.63 0.66 0.47 0.58 0 72 0.76 Ca/2 0.95 0.96 0.98 0.96 0.98 0.98 0.97 0.95 0 95 0.98 a/i 1 0.91 1.00 0.64 0.89 0.86 1.00 0.58 1.00 0 92 1.00 0H/2 0.96 0.96 0.96 0.97 0.98 0.98 0.97 0.97 0 90 0.90 * - t o t a l Iron as FeO # - HjO ca lcu la ted from s t r u c t u r a l formula assuming 2 (OH,F). 1 - Q Is the mole f r a c t i o n of vacancy i n the A - s l t e . analyst - L . C . Pigage 2 3 3 Table 2-15. C a l c i c pyroxene analyses from carbonate samples. Estimated standard e r r o r s are given i n parentheses. Specimen 224 20 2-312 Analyses 68 11 16 S i 0 2 52.59 (0.02) 52.97 (0.10) 54.16 (0.04) T i 0 2 - 0.03 (0.003) A 1 2 0 3 0.29 (0.004) 0.71 (0.02) 0.33 (0.01) FeO* 12.53 (0.03) 11.42 (0.05) 6.98 (0.01) MnO 0.62 (0.004) 0.13 (0.003) 0.04 (0.002) MgO 9.92 (0.02) 11.44 (0.05) 13.44 (0.03) CaO 23.94 (0.01) 24.37 (0.04) 24.64 (0.03) Na 20 0.07 (0.001) 0.18 (0.008) 0.09 (0.005) Tota l 99.96 101.25 99.68 formulae on the basis of 6 oxygens S i 2.007 (0.0008) 1.983 (0.004) 2. 015 (0.001) T i - 0.001 (0.0001) -Al 0.013 (0.002) 0.031 (0.0009) 0. 014 (0.0004) Fe 0.400 (0.001) 0. 358 (0.002) 0. 217 (0.0003) Mn 0.020 (0.0001) 0.004 (0.0001) 0. 001 (0.0001) Mg 0.564 (0.001) 0.6 39 (0.003) 0. 745 (0.002) 0.997 1.033 0. 977 Ca 0.979 (0.0004) 0.978 (0.002) 0. 982 (0.001) Na 0.005 (0.0001) 0.013 (0.0006) 0. 006 (0.0004) 0.984 0.991 0. 988 Fe/Z. Mg/5~ Mg/(Mg + Fe) 0.40 0.57 0.59 0.35 0.62 0.64 0.22 0. 76 0.77 * - t o t a l i r o n as FeO analyst - L . C . Pigage Table 2-16. Z o i s i t e analyses from carbonate samples. Estimated standard e r r o r s are given i n parentheses. men 387 224 494 20 2-312 ses 74 8 29 17 18 Si0 2 40.06 (0.03) 38 58 (0 06) 39.28 (0 02) 39.61 (0.04) 39.75 (0.05) Ti 0 2 - 0 16 (0 005) 0.06 (0 007) 0.01 (0.003) 0.02 (0.004) A1 20 3 32.79 (0.02) 28 82 (0 17) 29.89 (0 06) 28.89 (0.02) 31.70 (0.04) F e2°3* 0.07 (0.002) 7 59 (0 18) 6.09 (0 06) 7.20 (0.08) 1.30 (0.01) MnO - 0 14 (0 01) 0.14 (0 00 3) 0.03 (0.002) -MgO - 0 04 (0 005) 0.03 (0 002) 0.03 (0.002) -CaO 24.17 (0.02) 23 36 (0 06) 24.44 (0 02) 24.46 (0.02) 24.01 (0.02) F 0.01 (0.003) 0 02 (0 002) 0.01 (0 001) 0.01 (0.002) 0.01 (0.002) H20# 1.96 (0.002) 1.93 (0 005) 1.97 (0 002) 1.97 (0.002) 1.95 (0.002) Total 99.06 100 64 101.91 102.21 98.74 formulae on the basis of 13 (0,0H,F) Si 3.052 (0.002) 2.975 (0.005) 2 981 (0.002) 3.006 (0 003) 3.053 (0 004) Al 2.944 (0.002) 2.619 (0.015) 2 673 (0.005) 2.584 (0 002) 2.869 (0 004) Ti - 0.009 (0.0003) 0 003 (0.0004) 0.001 (0 0002) 0.001 (0 0002) Fe 0.004 (0.001) 0.440 (0.010) 0 348 (0.003) 0.411 (0 005) 0.075 (0 0006) Mn - 0.009 (0.0007) 0 009 (0.0002) 0.002 (0 0001) -Mg - 0.005 (0.0006) 0 003 (0.0002) 0.003 (0 0002) -2.948 3.082 3 036 3.001 2.945 Ca 1.973 (0.002) 1.930 (0.005) 1 987 (0.002) 1.989 (0 002) 1.976 (0 002) F 0.002 (0.0007) 0.005 (0.0005) 0 002 (0.0002) 0.002 (0 0005) 0.002 (0 0005) OH 0.998 (0.001) 0.995 (0.003) 0.998 (0.001) 0.998 (0 001) 0.998 (0 001) 1.00 0.85 0 88 0.86 0.97 * - total iron as Fe 20 3 # - H20 calculated from structural formula assuming 1 (0H,F); standard error for H20 calculated from standard errors of other elements using Monte Carlo approach analyst - L.C. Pigage ro OJ 235 Table 2-17. Sphene analyses from carbonate samples. Estimated standard e r r o r s are given i n parentheses. Specimen 387 2-375 494 20 2-312 Analyses 20 13 7 17 4 sio 2 32.58 (0.03) 30.33 (0.05) 30.45 (0.08) 30.52 (0.04) 31.28 (0.08) T i 0 2 25.00 (0.04) 38.18 (0.06) 37.69 (0.18) 35.84 (0.23) 30.20 (0.69) A1 20 3 10.03 (0.01) 1.79 (0.04) 1.96 (0.10) 3.34 (0.13) 6.03 (0.37) F e 2 ° 3 * 0.01 (0.002) 0.40 (0.02) 0.31 (0.03) 0.29 (0.002) 0.29 (0.04) MnO - 0.03 (0.003) 0.07 (0.004) 0.01 (0.002) -MgO 0.02 (0.002) - - 0.01 (0.002) 0.04 (0.01) CaO 29.14 (0.03) 29.17 (0.08) 27.92 (0.22) 28.95 (0.03) 29.48 (0.08) Na20 - 0.01 (0.003) - 0.01 (0.002) -F 2.08 (0.02) 0.25 (0.003) 0.32 (0.01) 0.48 (0.01) 0.89 (0.01) H20# 0.79 (0.009) 0.25 (0.008) 0.24 (0.02) 0.40 (0.02) 0.69 (0.07) Subtotal 99.65 100.41 98.96 99.85 98.90 less 0=F 0.88 0.11 0.13 0.20 0.37 Total 98.77 100.30 98.83 99.65 98.53 formulae on the basis of 5 (0,0H,F) Si 1.033 (0.001) 0.983 (0.002) 0.997 (0.003) 0.989 (0.001) 1.014 (0.003) T i 0.596 (0.001) 0.931 (0.001) 0.928 (0.004) 0.873 (0.006) 0.736 (0.017) Al 0.375 (0.0004) 0.068 (0.002) 0.076 (0.004) 0.128 (0.005) 0.230 (0.014) Fe t r 0.010 (0.0005) 0.008 (0.0007) 0.007 ( t r ) 0.007 (0.001) Mn - 0.001 (0.0001) 0.002 (0.0001) t r Mg 0.001 (0.0001) - - t r 0.002 (0.0005) 0.972 1.010 1.014 1.008 0.975 Ca 0.990 (0.001) 1.013 (0.003) 0.980 (0.008) 1.005 (0.001) 1.023 (0.003) Na - 0.001 (0.0002) - 0.001 (0.0001) 0.990 1.014 0.980 1.006 1.023 F 0.209 (0.002) 0.026 (0.003) 0.033 (0.001) 0.049 (0.001) 0.091 (0.001) OH 0.168 (0.002) 0.053 (0.002) 0.052 (0.004) 0.086 (0.004) 0.148 (0.015) 0.377 0.079 0.085 0.135 0.239 Ti/2! 0.61 0.92 0.92 0.87 0.75 to t a l i r o n as PejOj # - HjO calculated from s t r u c t u r a l formula assuming (OH + F) » (Al + Fe + Mn + Mg) (Higgins and Ribbe 1976); standard error for H20 calculated from standard errors of other elements using Monte Carlo technique, t r - less than 0.0005 analyst - L.C. Pigage Table 2-18. S c a p o l i t e a n a l y s i s from carbonate samples. Estimated standard e r r o r s are given i n parentheses. Specimen 20 formula on the b a s i s of 27 oxygens Analyses 12 S i 0 2 45.91 (0.09) S i 7.006 (0.014) A1 2 0 3 28.12 (0o04) A l 5.057 (0.007) CaO 18.19 (0.05) 12.063 Na 20 2.79 (0.01) Ca 2.974 (0.008) K 20 0.16 (0.006) Na 0.825 (0.003) c o 2 # 4.80 (0o005) K 0.031 (0.001) T o t a l 99.97 3.830 C 1.000 (0.001) Ca/(Ca + Na) 0.78 # - C0 2 c a l c u l a t e d from s t r u c t u r a l formula assuming 1 CO^ (Evans, Shaw, and Haughton 1969); standard e r r o r f o r C 0 2 c a l c u l a t e d from standard e r r o r s of other elements u s i n g Monte Ca r l o approach a n a l y s t - L.C. Pigage 237 APPENDIX 2-2 A l l c a l c u l a t i o n s of mineral e q u i l i b r i a have been done w i t h the thermodynamic parameters AG r, AS^ ., and AV r. These parameters are i n t e r n a l l y c o n s i s t e n t r e p r e s e n t a t i o n s of e q u i l i b r i a which have been experimentally determined. The thermodynamic data have been reduced to a common reference s t a t e of 298.15 K and 1 bar t o t a l pressure to f a c i l i t a t e comparison between the d i f f e r e n t r e a c t i o n s . The f o l l o w i n g s e c t i o n s o u t l i n e the general equations and assumptions used i n d e r i v i n g and manipulating the thermodynamic parameters. Consider the general e q u i l i b r i u m r e a c t i o n E n . A. + £ m . B . = 0 (A i J where the A^ r e f e r to s o l i d species and B.. to v o l a t i l e s p e c i e s . Each n^ and m_. i s p o s i t i v e f o r r e a c t i o n products and negative f o r r e a c t a n t s . For t h i s e q u i l i b r i u m , a general expression r e l a t i n g the AG of r e a c t i o n at the reference temperature T^ , and pressure P r to the AG of r e a c t i o n at any other temperature T and pressure P i s ( U l b r i c h and Merino 1974) : AG r(T,P) = E n i HA.(VV + E m j HB.< Tr' Pr> + E n i J Cp i i J 3 i U T FA. r I dT (A2) 238 By i n s p e c t i o n i t i s obvious that AH r(T r,P r) = E n. H A ( T ^ ) + Z m H (T ,P ) (A3) AS r(T r,P r) = £ n. S A_(T r,P r) + E m S ( T r , P r ) 1 1 j j Ac (T r,P r) = £ n. c (T r,P r) + E m c <T r,P r) . r l A^. j J FB. (A4) (A5) By d e f i n i t i o n AH r = AG r + T AS r a t a given pressure and temperature. S u b s t i t u t i n g these two s e t s of r e l a t i o n s i n t o equation (A2), the r e l a t i o n then becomes Ac dT T P r r J^T OP (Ac /T) dT + E n. I V. dP (A6) T P r i 1 Jp A i r r f p Adopting the e m p i r i c a l M a i e r - K e l l e y heat c a p a c i t y f u n c t i o n c = a + b T + c T ~ 2 P and i n t e g r a t i n g from T to T, equation (A6) becomes AG r(T,P) = AG r(T r,P r) - (T-T r) A S r ( T r , P r ) + Aa r (T-T r) + (Ab r/2)(T 2-T r 2) - Ac r (1/T - 1/Tr) - Aa r T l n ( T / T r ) - Ab r (T-T r) + (Ac r/2) (1/T2 - 1/T r 2) (A7) J^P pP V. dP + E m. I V_ dP P A i j J J P B j r r 239 The c o e f f i c i e n t s a, b, c f o r the c^ terms were obtained from a p r e p r i n t of the recent c o m p i l a t i o n by Helgeson et a l . (1978). These were modified f o r the alpha-beta quartz t r a n s i t i o n by T.H. Brown (personal communication, 1977). The volumes of s o l i d species are assumed to be independent of pressure, r e s u l t i n g i n the expression OP E n . V. i X J P A i dP = ( A V A ( T r , P r ) ) (P - P r) . (A8) The d e f i n i t i o n of f u g a c i t y conveniently allows the e x p l i c i t e v a l u a t i o n of the pressure i n t e g r a l f o r the v o l a t i l e species Z m j V B dP = Z m R T l n ( f ( T , P ) / f B (T,P r) . (A9) j " P r J j j j F u g a c i t i e s f o r E^O and CO^ were c a l c u l a t e d u s i n g the Redlich-Kwong equation of corresponding s t a t e s ( R e d l i c h and Kwong 1949). This equation contains two a d j u s t a b l e c o e f f i c i e n t s . These c o e f f i c i e n t s were e m p i r i c a l l y d erived by a nonl i n e a r l e a s t squares r e g r e s s i o n to tabu l a t e d f r e e energy values f o r the pure gas species a t d i f f e r e n t pressures and temperatures. The c o e f f i c i e n t s were assumed to be l i n e a r f u n c t i o n s of temperature f o r the r e g r e s s i o n (T.H. Brown, personal communication 1978). Free energy values f o r were taken from Burnham, Holloway, and Davis (1969); CC^ f r e e energy values were computed from f u g a c i t y c o e f f i c i e n t s reported by Shmulovich and Shmonov (1975). In both cases the l e a s t squares r e s i d u a l s were l e s s than 100 c a l o r i e s . F u g a c i t i e s f o r CO and CH^ were a l s o determined u s i n g the R e d l i c h -Kwong equation. The c r i t i c a l temperature and pressure of the appr o p r i a t e species was used to c a l c u l a t e the f u g a c i t y c o e f f i c i e n t . Equations by Shaw and Wones (1964) were ex t r a p o l a t e d to c a l c u l a t e f u g a c i t i e s f o r H 0. 240 For oxygen-buffered dehydration r e a c t i o n s , the I^O f u g a c i t y was c a l c u l a t e d using the method o u t l i n e d by Zen (1973). I d e a l mixing of the d i f f e r e n t gas species i s assumed. Oxygen f u g a c i t i e s f o r s o l i d b u f f e r s were c a l c u l a t e d from the equations given i n Huebner (1971). V o l a t i l e s were assumed to be i d e a l mixtures of r e a l gases. With t h i s assumption the f u g a c i t y f o r each species B.. i s p r o p o r t i o n a l to the mole f r a c t i o n of B. i n the v o l a t i l e phase fB (P,T) = f° (P,T) . (AlO) j J where f° (P,T) i s the f u g a c i t y of pure B. at the pressure P and temperature j 3 T of i n t e r e s t . Displacement of the r e a c t i o n curve due to s o l i d s o l u t i o n i s c a l c u l a t e d by i n c l u d i n g an a d d i t i o n a l term d e s c r i b i n g the change i n f r e e energy of each s o l i d species r e s u l t i n g from s o l u t i o n . The form of t h i s term i s r e a d i l y d erived by r e c a l l i n g the r e l a t i o n f o r the molar f r e e energy of a species i n s o l i d s o l u t i o n y A = V°A + R T In a A . ( A l l ) i i i For a l l i s o l i d species i n the r e a c t i o n , t h i s a d d i t i o n a l term assumes the form R T ln(JI a " i ) . (A12) i A i The s o l u t i o n models r e l a t i n g composition to a c t i v i t y f o r each species A^ are discussed i n the main part of t h i s paper. The a c t i v i t y f o r each pure species A^ i s 1.0. I f a l l s o l i d species are pure, term (A12) i s zero. S u b s t i t u t i n g expressions (A8), (A9), (AlO), and (A12) i n t o equation (A7) , t h i s equation assumes the form 241 AG r(T,P) = AG r(T r,P r) - (T-T r) AS r(T r,P r) + A a r (T-T r) + (Ab r/2) ( T 2 - T r 2 ) - Ac r (1/T - 1/T.) - A a r T l n ( T / T r ) - Ab r (T-T r) + (Ac r/2) (1/T 2 - 1/T r 2) (A13) + AV A(T r,P r) ( P - l ) + E m R T l n ( X R f°(T,P)) i j j j + R T l n ( n a A n i ) i i Note that f o r the chosen reference pressure P = 1 bar, f^ = P_ = 1 . r r B. B. 3 3 At e q u i l i b r i u m AG r(T,P) = 0 , (A14) and equation (A13) may be solved i t e r a t i v e l y f o r temperature T at a s p e c i f i e d pressure P. t e r s f o r s e l e c t e d mineral e q u i l i b r i a . Table 2-21. Thermodynamic parame Units a s s o c i a t e d w i t h the d i f f e r e n t parameters are: A V cm 3 (cal/bar) r,s Ac P r Aa j K- 1 ( c a l K l) r _ 9 o 3 J K~ 2 * 10 3 ( c a l K * 1(T) Ab *10 Ac *10" 5 J K * 10" 5 ( c a l K * 10 ) r AG r AS r J ( c a l ) j K " 1 ( c a l K " 1 ) Ml if iii i Mi | iiiii M . i ! 35 = § = 1 J i PP!1111 + + - I lie I . i LI M I'lilS S i i i i ! ISiij !. j s a i s \\ H I ifiii« I i I 1 i ! i 1 1 I i I I1 P I 1 =• i! il i i I«ii ii ii if Ii il tl i i i i i i\ } !! !l il 11! 51! IIII il !I, iiiii, J I l M f l ;- si;!!! If!!, If ?! 111!, 1! I! IS 111!, i!!! mi ih!!! , Mmdiiiiiimitiniiiii j i i i I i i i i i i I i i i 11 i ! A i A i i if i i e a < 3 CD- O-o °~ »~ + "* + + -< 1 a- a 8 8 + o o =~ ° ~ =~ a " o" 1 5 5 3 5 S + + ^ 2 - - - 3 3 7 -& 2 1 b k 1 : o O-l EC M M . + N + + -a O- * — + + + 1  + + * * + + + + + + « * * * s a + + 2 s 244 Table 2-22. Volume and heat capacity data f o r s e l e c t e d minerals. Mineral Volume @ Ref(vol) a II C p - a + b*T + c*T" b * 10 3 $ c * 10 Carbon Dioxide CO2 Steam H 20 Corundum (Co) A 1 2 ° 3 o-Quartz (Qtz) S i 0 2 Calcite (Cc) CaC0 3 Fe-Staurolite (Fe-stau) F e 2 A l 9 S i 4 0 2 3 ( 0 H ) Gehlenite (Ge) C a 2 A l 2 S i 0 ? Zoisite (Zo) C a 2 A l 3 S i 3 0 1 2 ( O H ) Andalusite (And) Al„Si0„ Kyanite (Ky) A l 2 S i 0 5 S i l l i m a n i t e ( S i l l ) A l 2 S i 0 5 Almandine (Aim) F e 3 A l 2 S i 3 0 1 2 Grossular (Gr) C a 3 A l 2 S i 3 0 1 2 24464.98 (584.727) 24464.98 (584.727) 25.575 (0.61126) 22.688 (0.54226) 36.934 (0.88274) 223.38 (5.3389) 90.236 (2.1567) 136.52 (3.263) 51.53 (1.2316) 44.09 (1.05378) 49.90 (1.19264) 115.27 (2.7551) 125.3 (2.9947) 44.22 (10.57) 30.54 (7.3) 115.02 (27.49) 69.94 (16.716) 104.52 (24.98) 866.59 (207.12) 266.69 (63.74) 494.875 (118.278) 172.845 (41.311) 173.18835 (41.39301) 167.46 (40.024) 476.926 (113.988) 471.32 (112.648) 8.79 (2.1) 10.29 (2.46) 11.80 (2.82) 2.5292 (0.6045) 21.92 (5.24) 154.56 (36.94) 33.47 (8.0) 51.5615 (12.3235) 26.3282 (6.2926) 28.5202 (6.8165) 30.922 (7.3905) 45.411 (10.8535) 32.9427 (7.8735) -8.62 (-2.06) 0 -35.06 (-8.38) -19.27385 (-4.60656) -25.94 (-6.2) -239.41 (-57.22) -63.26 (-15.12) -141.9035 (-33.91575) -51.84838 (-12 . 39 2 06) -53.8987 (-12.8821) -48.84423 (-11.67405) -120.73246 (-28.85575) -130.89958 (-31.28575) Volume references 1 - Robie, Bethke, and Beardsley (1967) 2 - Robie and Waldbaum (1968) 3 - Ganguly (1972) 4 - Chatterjee and Johannes (1974) 5 - Chatterjee (1972) 6 - Newton and Goldsmith (1976) @ - cm (cal/bar) # - J mol" 1 K"1 (cal mol" 1 K~') $ - J mol" 1 K"2 * 1 0 3 (cal mol" 1 K~2 * 1 0 3 ) & - J mol" 1 K * 1 0 " 5 (cal mol" 1 K * 1 0 " 5 ) Table 2-22 (continued). Mineral Volume @ Ref(vol) C = a + b*T + c*T P b * 10 3 S -2 c * 10 -5 Wollastonlte (Wo) CaSiO. 39.93 (0.95435) 111.46 (26.64) 15.06 (3.6) -27.28 (-6.52) Diopside (Di) CaMgSi.O, 2 0 66.09 (1.5795) 221.21 (52.87) 32.80 (7.84) -65.86 (-15.74) Tremolite (Tr) Ca 2Mg 5Si g0 2 2(OH) 2 272.92 (6.5229) 787.52 (188.222) 239.72 (57.294) -187.535 (-44.822) Muscovite (Mus) K A l 2 A l S i 3 O 1 0 ( O H ) 2 140.81 (3.3654) 408.19 (97.56) 110.37 (26.38) -106.44 (-25.44) Paragonite (Pa) N a A l 2 A l S i 3 0 1 Q ( O H ) 2 131.98 (3.1545) 407.65 (97.43) 102.51 (24.5) -110.62 (-26.44) Phlogopite (Phi) KMg 3AlSi 30 1 ( )(OH) 2 149.91 (3.583) 420.95 (100.61) 120.42 (28.78) -89.96 (-21.5) Anorthite (An) C a A l 2 S i 2 O g 100.79 (2.4089) 269.53 (64.42) 57.32 (13.7) -70.67 (-16.89) High-Albite (H-ab) NaAlSi,0_ 3 o 100.43 (2.4003) 258.15 (61.7) 58.16 (13.9) -62.80 (-15.01) Low-Albite (L-ab) N a A l S i 3 0 g 100.07 (2.3917) 258.15 (61.7) 58.16 (13.9) -62.80 (-15.01) Sanidine (Sa) KAlSi.0 o J a 109.05 (2.6063) 267.06 (63.83) 53.97 (12.9) -71.34 (-17.05) Microcline (Mi) K A l S i 3 0 g 108.72 (2.5984) 267.06 (63.83) 53.97 (12.9) -71.34 (-17.05) Meionite (Me) Ca.Al,Si,0„,C0, 4 6 6 24 3 340.524 (8.1387) Volume references 1 - Robie, Bethke, and Beardsley (1967) 2 - Robie and Waldbaum (1968) 3 - Ganguly (1972) 4 - Chatterjee and Johannes (1974) 5 - Chatterjee (1972) 6 - Newton and Goldsmith (1976) @ - cm ( c a l / b a r ) // - J m o l " 1 K _ 1 ( c a l m o l " 1 K _ 1 ) $ - J m o l " 1 K - 2 * 1 0 3 ( c a l m o l - 1 K - 2 * 10 3) & - J m o l " 1 K * 10" 5 ( c a l m o l " 1 K * 1 0 - 5 ) 246 Fe-s t a u r o l i te-Quar t z-Almand i n e - A l 2 S iO The upper s t a b i l i t y l i m i t of F e - s t a u r o l i t e + quartz i s denoted by the general r e a c t i o n : F e - s t a u r o l i t e + Quartz = Almandine + Al 2SiC> 5 + H 20 (unbalanced) . This r e a c t i o n has been experimentally studied f o r s i l l i m a n i t e (Richardson 1968) and k y a n i t e (Ganguly 1972). C o e f f i c i e n t s i n the balanced r e a c t i o n depend upon the composition assumed f o r F e - s t a u r o l i t e . Ganguly (1972) synthesized s t a u r o l i t e from the bulk composition Fe 2AlgSi^0 2-j(OH) . Richardson (1967) reported that h i s attempts to s y n t h e s i z e s t a u r o l i t e from the same bulk composition c o n s i s t e n t l y r e s u l t e d i n a mixture of s t a u r o l i t e + quartz. E l e c t r o n microprobe analyses of h i s s t a u r o l i t e s approximated the composition F e ^ l ^ S i ^ ^ ( ^ ( O H ) , , . The l a t t e r composition i s more compatible w i t h the hydroxyl content of n a t u r a l s t a u r o l i t e ( G r i f f e n and Ribbe 1976). In d e r i v i n g thermodynamic parameters f o r e q u i l i b r i a E4 and E5, I have used the same balanced r e a c t i o n c o e f f i c i e n t s ( i . e . s t a u r o l i t e formulae) f o r both experimental s t u d i e s . Since the two r e a c t i o n s are r e l a t e d by the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n , i t should be p o s s i b l e to de r i v e parameters f o r each r e a c t i o n which d i f f e r by the AG r and AS r of the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n m u l t i p l i e d by the A l 2 S i O ^ r e a c t i o n c o e f f i c i e n t . This c o n s t r a i n t should e l i m i n a t e a number of p o s s i b l e s t a u r o l i t e formulae and balanced r e a c t i o n s . Thermodynamic parameters were derived f o r balanced r e a c t i o n s corresponding to the s t a u r o l i t e formulae F e 2 A l g S i ^ 0 2 ^ ( O H ) , F e ^ l ^ S i ^ y^0 2 2(OH) F e 1 < 5 A l 9 S i 4 0 2 2 ( O H ) 2 , F e ^ g ^ S ^ O ^ O H ) 2, and F e i ^ A l g ^ S i ^ O H ) r Heat capacity c o e f f i c i e n t s f o r each of these s t a u r o l i t e formulae were estimated using the approach o u t l i n e d by Helgeson et_ a l . (1978) . The only 2 4 7 Figure 2-23. Experimental r e v e r s a l s and c a l c u l a t e d e q u i l i b r i a curves f o r E4 and E5. Experimental r e v e r s a l s are from Ganguly (1972) and Richardson . (1968). Thermodynamic parameters f o r E4 and E5 are l i s t e d i n Table 2-21. 248 s t a u r o l i t e formula and balanced r e a c t i o n c o n s i s t e n t w i t h the c o n s t r a i n t s imposed by the k y a n i t e - s i l l i m a n i t e t r a n s i t i o n and the experimental brackets corresponded to the formula presented by Ganguly (1972) -Fe2AlgSi^022(OH). Figure 2-23 i l l u s t r a t e s the c a l c u l a t e d e q u i l i b r i u m curves E4 and E5 and the experimental brackets when using the Ganguly s t a u r o l i t e formula and balanced r e a c t i o n . Muscovite A c t i v i t y Model A c t i v i t y - m o l e . f r a c t i o n r e l a t i o n s f o r muscovite and paragonite components i n metamorphic white micas are complicated by the ubiquitous presence of c e l a d o n i t e component and n o n i d e a l i t y of the Na-K i n t e r a c t i o n at l e a s t along the muscovite-paragonite j o i n (Eugster e t a l . 1972). Any a c t i v i t y model f o r white micas should at l e a s t consider these two e f f e c t s . In t h i s paper these problems have been handled by f i r s t computing an i d e a l a c t i v i t y based upon an i d e a l s i t e mixing model ( K e r r i c k and Darken 1975) and then m u l t i p l y i n g the i d e a l a c t i v i t y by an a c t i v i t y c o e f f i c i e n t d e r i v e d from the st u d i e s by Eugster e_t al_. (1972) and Blencoe (1977). The r e s u l t i n g expressions are where the X's r e f e r to mole f r a c t i o n s of the i n d i c a t e d s p e c i e s . These equations correspond to the s t o i c h i o m e t r i c formulae NaA^AlSi^O^QtOH) ^  and KA^AISI-JO^QCOH) ^  f o r paragonite and muscovite, r e s p e c t i v e l y . The term Xg^ i s not included i n the a c t i v i t y expressions because s u b s t i t u t i o n of t e t r a h e d r a l A l f o r S i i s coupled to s u b s t i t u t i o n of b i v a l e n t c a t i o n s (Mg, Fe) f o r octahedral A l . Appropriate y c o e f f i c i e n t s were c a l c u l a t e d f o r the analyzed muscovite compositions by d e s c r i b i n g the excess f u n c t i o n s i n Paragonite Paragonite * ( X N a > * ( X A l ) 2 * ( W 2 (A 15) (A16) 249 terms of asymmetric Margules parameters (J.B. Thompson 1967) taken from . stu d i e s by Eugster et a l . (1972) and Blencoe (1977). As a f i r s t approximation Azure Lake muscovites can be described by the four component system KAlgSi^Uj^OH) 2 - muscovite, NaAlgSigOj^OH) ^  _ paragonite, K A l ( M g , F e ) S i 4 0 1 0 ( O H ) 2 - K c e l a d o n i t e , and NaA l ( M g , F e ) S i 4 0 1 0 ( O H ) 2 Na c e l a d o n i t e . This assumes th a t Mg and Fe are e q u i v a l e n t when s u b s t i t u t i n g f o r o c t a hedral A l . Ti-content of the muscovites was not considered. These components are i l l u s t r a t e d i n f i g u r e 2-24 w i t h X re p r e s e n t i n g an analyzed white mica. From the diagram i t can be seen that the mole f r a c t i o n of each component i s p r o p o r t i o n a l to the area of the r e c t a n g l e opposite the s p e c i f i e d component. Therefore the mole f r a c t i o n of each component i s given by: *Pa = ( X Na>*< 1- X Mg,Fe ) ( A 1 7 ) ^ u s = < 1" X»a>^ 1- X Mg,Fe> ( A 1 8 ) ' ^ a c e l = <XKa>^XMg,Fe) ( A 1 9 ) ^ c e l = ( 1- XNa )* ( XMg,Fe> " ( A 2 0 ) Excess f u n c t i o n s between these components have been experimentally determined only f o r the Na-K i n t e r a c t i o n along the muscovite-paragonte b i n a r y j o i n . I t seems reasonable to assume that the Na-K i n t e r a c t i o n between the two c e l a d o n i t e end-members i s s i m i l a r . Since no f u r t h e r i n f o r m a t i o n i s a v a i l a b l e , a l l other i n t e r a c t i o n Margules parameters between the d i f f e r e n t components are assumed to be zero ( i d e a l s o l u t i o n ) . This r e s u l t s i n the excess f r e e energy f u n c t i o n given i n equation (A21). G = X. 2L, (WD 2L. + WM X_ ) ex MUS T a Pa Mus Mus T a (A21) + ^Kcel^Nacel^Pa^ S c c e l + ^ M u s ^ a c e l ^ where the W's are defined as (Blencoe 1977; Eugster et a l . 1972) 250 K-Celadonite KAI(Mg,Fe)Si40i0(0H)2 Na-Celadonite NaAI(Mg,Fe)Si40|(/0H)2 Muscovite KAI3Si30,0(OH)2 Paragonite NaAI3Si30 | 0(0H)2 Figure 2-24. White mica composition i n terms of four end-member components. Mole f r a c t i o n of each component i s p r o p o r t i o n a l to area of ::.rectangle d i a g o n a l l y opposite from the component. 251 W„ = 3096.8 + 0.075 P (bars) + 0.1698 T (K) Pa W„ = 4305.9 + 0.0571 P (bars) + 0.3954 T (K) Mus To d e r i v e appropriate expressions f o r y„ • and YT> -4. i t * v * * 'Muscovite 'Paragonite i s e a s i e s t to consider the general case w i t h the four components X^, i = l , 4 . With the same assumptions concerning the W parameters as o u t l i n e d f o r the mica system, equation (A21) becomes G £ x = X 1 X 2 ( W 1 2 X 1 + W 2 1X 2) + X 3 X 4 ( W 1 2 X 3 + W 2 1X 4) . (A22) But G i s a l s o defined by the r e l a t i o n ex G = E X. R T I n y. • ( A 2 3 ) ex , l I 4 In order to d e r i v e an expression f o r i t i s necessary to e l i m i n a t e the other Yj_ from equation (A23). The procedure followed i n doing t h i s i s o u t l i n e d f o r . The p a r t i a l d e r i v a t i v e of equation (A23) w i t h respect to X^ (X^ and X^ constant) i s given by 9G 3 X = R T In y x - R T l n Y ex „ „ , „ „ , ^ ( A 2 4 ) 1 T ' P ' X 3 , 3*1,2 sin c e dX^ = -dX 2. By rearranging terms t h i s becomes 9G R T l n y 9 = R.T I n y, - — — . (A25) 1 T P Y S u b s t i t u t i n g (A25) i n t o (A23) e l i m i n a t e s Y 2 from expression (A23). With s i m i l a r s u b s t i t u t i o n s f o r X^ and X^, equation (A23) becomes, upon rearrangement _ 4 9G R T I n Y I = G + E X. 1 ex l aX e X . (A26) 2 1 T,P,X. ..... Su i t a b l e expressions f o r the p a r t i a l d e r i v a t i v e s of G are obtained from 252 equation (A22).. : A f t e r s u b s t i t u t i n g these d e r i v a t i v e s i n t o (A26) , c o l l e c t i n g terms, and using the f a c t that the four components sum to 1, the expression f o r i s R T I n y = X 2 2W 2 1(1-2X 1) + 2V^^(l-XY) - 2X 3X 4(W 1 2X 3 + W 2 1X 4> . (A27) In the four component mica system t h i s equation becomes R T l n ^Pa - ^usM 1- 2^ + ^ M ^ a W 1 ^ (A28) 2^Nacel^Kcel^Mus^Nacel + ^Pa^Kcel^ R T l n % u s = X P ^ M U 8 ( 1 - 2 X M U 8 ) + 2 W P a X P a i M u 8 ( 1 - X M u B ) (A29) 2^Nacel^Kcel^Mus^Nacel + ^Pa^Kcel^ where W„ andW., are as defined p r e v i o u s l y . Pa Mus J Gro s s u l a r - K y a n i t e-Quar t z-Anor t h i te E x t r a p o l a t i o n of experimental data f o r e q u i l i b r i u m ElO to lower pressures r e s u l t s i n l a r g e u n c e r t a i n t i e s i n the pressure-temperature p o s i t i o n of t h i s curve (see f i g u r e 2-25). Choosing a best f i t curve i s d i f f i c u l t to j u s t i f y from the reversed experiments. Yet use of t h i s r e a c t i o n as a geobarometer-geothermometer r e q u i r e s s e l e c t i o n of thermodynamic parameters c o n s i s t e n t w i t h one of the many p o s s i b l e curves. The choice i s e s p e c i a l l y c r i t i c a l s ince t h i s e q u i l i b r i u m i s s e n s i t i v e to a n a l y t i c a l e r r o r (see f i g u r e 2-14). To f u r t h e r r e s t r i c t the u n c e r t a i n t y i n d i c a t e d i n f i g u r e 2-25, experimental s t u d i e s of e q u i l i b r i u m ElO were combined w i t h experimental r e s u l t s from nine independently stu d i e d r e a c t i o n s i n the system CaO-Al 20.j-S i 0 2 - H 2 0 . Reactions i n c l u d e d i n t h i s study are i n d i c a t e d w i t h a s t e r i s k s J I I I L 200 400 600 800 1000 1200 1400 TEMPERATURE, °C Figure 2-25. Experimental r e v e r s a l s f o r e q u i l i b r i u m E10 (Hariya and Kennedy 1968). S o l i d l i n e s a re maximum and minimum slopes permitted by experimental b r a c k e t s . Dashed l i n e s are maximum and minimum allowed slopes from the l i n e a r programming study i n t h i s paper. Dot-dash l i n e i s the p r e f e r r e d p o s i t i o n of the curve. ro 01 O J Table 2-23. Experimental u n c e r t a i n t i e s f o r s e l e c t e d exp REACTION El E2 E3 E10 E20 E21 E22 E23 E24 E25 REFERENCE APPARATUS Newton (1966b) pstn cyl Richardson et a l . (1968) gas app Newton (1966a) pstn cyl Richardson et a l . (1969) gas app Holdaway (197lT^ cold seal Holdaway (1971) cold seal Weill In Holdaway (1971) calorlmetry Harlya and Kennedy (1968) pstn cyl Hensen et a l . (1975) pstn cyl Newton and Kennedy (1963) pstn cyl Newton (1966c) pstn cyl Newton (1966c) cold seal Newton (1966c) pstn cyl Boettcher (1970) cold seal Newton (1966c) cold seal Newton (1966c) pstn cyl Boettcher (1970) cold seal Huckenholz et a l . (1975) gas app Newton (1965) cold seal Newton (1965) pstn cyl Boettcher (1970) cold seal Huckenholz e_t a l . (1975) gas app Huckenholz et a l . (1975) cold seal Huckenholz et a l . (1975) gas app Newton (1965) cold seal Newton (1965) pstn cyl Boettcher (1970) cold seal t a l r e a c t i o n s t u d i e s . ERROR BRACKET ± T <°C) + P (bars) 10 400 5 100 15 5 Z 5 100 5 1.5 Z 5 1.5 Z 20 5, 15 1000 5 1000 10 500 10 400 5 50 10, 20 200 5 50 5 50 10 400 5 50 5 50 5 50 10 400 5 50 5 2 Z 5 50 5 2 X 5 50 15 400 5 50 r o c n - A 255 i n Table 2-21. Since only seven of the ten e q u i l i b r i a are l i n e a r l y independent, the a l g e b r a i c r e l a t i o n s between the r e a c t i o n s can be used to r e s t r i c t the u n c e r t a i n t y i n the pressure-temperature p o s i t i o n of ElO. This r e s t r i c t i o n was completed usi n g the l i n e a r programming approach o u t l i n e d by Gordon (1973). Experimental brackets f o r each r e a c t i o n formed a set of i n e q u a l i t y c o n s t r a i n t s . I n a d d i t i o n s i x e q u a l i t y c o n s t r a i n t s r e l a t e d the thermodynamic parameters AH r and AS r of the d i f f e r e n t r e a c t i o n s . Outer l i m i t s of experimental e r r o r were used i n c o n s t r u c t i n g the i n e q u a l i t i e s . I n most cases the e r r o r l i m i t s suggested by the authors were used. Table 2-23 contains the e r r o r l i m i t s used i n the l i n e a r programming. The o b j e c t i v e f u n c t i o n c o n s i s t e d of the AH or AS f o r r e a c t i o n ElO. r r This f u n c t i o n was both maximized and minimized to f i n d the f u l l range i n permitted v a l u e s . Maximum and minimum values are: AH r(max) = 76366 Joules AH r(min) = 32995 Joules AS r(max) = 186.86 J mol" 1 K " 1 AS r(min) = 147.74 J mol" 1 K _ 1 . (These values are reduced to the standard reference temperature 298.15 K and pressure 1 bar.) These values correspond to the dashed curves i l l u s t r a t e d i n f i g u r e 2-25. I n c l u d i n g the nine other r e a c t i o n s causes a s i g n i f i c a n t decrease i n the t o t a l u n c e r t a i n t y a s s o c i a t e d w i t h r e a c t i o n ElO. Since the curve suggested by Hariya and Kennedy (1968) (dot-dash l i n e i n f i g u r e 2-25) i s approximately i n the center of the r e s t r i c t e d u n c e r t a i n t y b r a c k e t s , t h i s curve was used i n a l l f u r t h e r c a l c u l a t i o n s . 256 APPENDIX 2-3 257 Table 2-24. Standards used f o r e l e c t r o n microprobe a n a l y s i s . Number i n parenthesesi corresponds to reference number i n microprobe standards c o l l e c t i o n , G e o l o g i c a l Sciences, U n i v e r s i t y of B r i t i s h Columbia. ab(20) a l b i t e (Oregon) an(102) a n o r t h i t e ( s y n t h e t i c ) and(26) a n d a l u s i t e ( B r a z i l ) angl(32) a n o r t h i t e glass ben(35) b e n i t o i t e ( C a l i f o r n i a ) cc(76) c a l c i t e (Cumberland) dol(10) dolomite ( A u s t r i a ) en(81) e n s t a t i t e ( s y n t h e t i c ) fa(104) f a y a l i t e ( s y n t h e t i c ) fo(22) f o r s t e r i t e ( s y n t h e t i c ) gr(83) g r o s s u l a r (New York) jd(41) j a d e i t e (Burma) ky(4) k y a n i t e ( B r i t i s h Columbia) lab (97) l a b r a d o r i t e (Oregon) mus(49) muscovite M or(28) or t h o c l a s e OR-1 phl(24) 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 ) py(84) pyrope ( s y n t h e t i c ) qtz(36) quartz ( s y n t h e t i c ) rho(88) rhodochrosite (New Mexico) rut(13) r u t i l e ( s y n t h e t i c ) s i ( l l ) s i d e r i t e (Greenland) sp(15) s p e s s a r t i n e ( B r a z i l ) w i ( l ) w i l l e m i t e (New Jersey) wo(21) w o l l a s t o n i t e (New York) Table 2-25. Standards used f o r garnet analyses. Specimen S i T i A l Fe Mn Mg Ca 373 wo(21) rut(13) and(26) fa(104) sp(15) fo(22) wo(21) 121 gr(83) py(84) . i py(84) gr(83) 367 gr(83) py(84) py(84) gr(83) 82 gr(83) py(84) I I .1 py(84) gr(83) 398 gr(83) py(84) n py(84) gr(83) 492 wo(21) and(26) I I en(81) wo(21) 2-376 gr(83) py(84) I I py(84) gr(83) 2-13 wo(21) and(26) n I I fo(22) wo(21) 74 qtz(36) and(26) i , I I fo(22) angl(32) 59 wo(21) and(26) I I fo(22) wo(21) 40 gr(83) py(84) .. py(84) gr(83) Table 2-26. Standards used f o r muscovite and b i o t i t e analyses. Specimen S i T i A l Fe Mn A l l phl(24) rut(13) mus(49) fa(104) sp(15) Specimen K F A l l phi(24) phi(24) Table 2-27. Standards used f o r s t a u r o l i t e analyses. Specimen S i T i A l Fe • Zn 373 wo(21) rut(13) and(26) fa(104) w i ( l ) 82 and(26) 492 and(26) 11 223 and(26) 40 and(26) Mg Ca Ba Na phi(24) wo(21) ben(35) ab(20) Mn Mg Ca F sp(15). fo(22) wo(21) phl(24) en(81) en(81) en(81) en(81) Table 2-28. Standard used f o r p l a g i o c l a s e analyses. Specimen S i A l Ca Na K Ba 373 ab(20) angl(32) angl(32) ab(20) or(28) ben(35) 121 or(28) ky(4) wo(21) " 367 or(28) lab (97) lab(97) " 82 or(28) and(26) wo(21) 398 or(28) and(26) wo(21) " 492 or(28) and(26) wo(21) " 223 or(28) and(26) wo(21) 2-376 or(28) ky(4) wo(21) " 2-13 ab(20) angl(32) angl(32) " 74 qtz(36) and(26) angl(32) n.a. 59 ab(20) angl(32) angl(32) ben(35) 40 or(28) and(26) wo(21) " " i i 387 ab(20) and(26) wo(21) » I I 219 or(28) ky(4) wo(21) " ir 2-375 or(28) and(26) wo (21) I I 69 or(28) an(102) an(102) I I 20 or(28) an(102) an(102) I I i b l e 2-29. Standards used f o r K-fe l d s p a r analyses. Specimen S i A l Ca Na K Ba 398 or(28) an(102) an(102) ab(20) or(28) ben(35) 2-376 6r(28) ky(4) wo (21) I I I I I I 2-13 ab(20) an(102) an(102) I I I I I I 387 ab(2Q) and(26) wo(21) I I I I I I 69 or(28) an(102) an(102) I I i i I I 20 or(28) an(102) an(102) I I i i I I Table 2-30. Standards used f o r i l m e n i t e analyses. Specimen T i A l Fe Zn Mn Mg Ca 373 rut(13) and(26) fa(104) w i ( l ) sp(15) fo(22) wo(21) 2-375 " ky(4) " n.a. " fo(22) a l l " and(26) " w i ( l ) " en(81) others Table 2-31. Standards used f o r c a l c i t e analyses. Specimen Ca Fe Mn Mg A l l cc(76) s i ( l l ) rho(88) dol(10) to Table 2-32. Standards used f o r c a l c i c amphibole analyses. Specimen S i T i A l Fe Mn Mg Ca Na K 224 w o(21) rut(13) and(26) fa(104) sp(15) en(81) wo(21) jd(41) or(28) 2-375 " " ky(4) 11 " en(81) 494 " " ky(4) " " en(81) 20 " " and(26) " " en(81) 2-312 " " and(26) " " fo(22) F 224 phl(24) 2-375 494 20 2-312 Table 2-33. Standards used f o r c a l c i c pyroxene analyses. Specimen S i T i A l Fe Mn Mg Ca Na 224 w o(21) rut(13) and(26) fa(104) sp(15) fo(22) wo(21) jd(41) 20 " " " " " en(81) 2-312 " " 11 11 " " fo(22) Table 2-34. Standards used f o r z o i s i t e analyses. Specimen S i T i A l Fe Mn Mg Ca F 387 wo(21) rut(13) and(26) fa(104) sp(15) fo(22) wo(21) phl(24) 224 I I . I I W ; and(26) I I I I . • • en(81) 11 494 I I I I ky(4) I I I I en(81) I I I I 20 I I I I and(26) I I I I en(81) I I I I 2-312 I I I I and(26) I I I I fo(22) I I I I Table 2-35. Standards used for sphene analyses. Specimen S i T i A l Fe Mn Mg Ca Na F 387 wo(21) rut(13) and(26) fa(104) sp(15) fo(22) wo(21) jd(41) phi(24) 2-375 wo(21) t i ky(4) I I I I en(81) wo(21) jd(41) I I 494 wo(21) I I ky(4) I I I I en(81) wo(21) jd(41) I I 20 wo(21) I I and(26) i i I I en(81) wo(21) jd(41) I I 2-312 qtz(36) i i and(26) I I I I fo(22) angl(32) ab(20) I I Table 2-36. Standards used f o r s c a p o l i t e analys es. Specimen S i A l Ca Na K Ba 20 or(28) an(102) an(102) ab(20) or(28) ben(35) PLATE 2-1 A) S c h i s t f r o m the s i l l i m a n i t e z o n e , Shuswap Comp lex . S t a u r o l i t e ( s ) and g a r n e t ( G ) a r e s u r r o u n d e d by e q u a n t , p o r p h y r o b l a s t i c m u s c o v i t e w i t h f i b r o l i t e ( m + f ) . I n c l u s i o n t r a i l s i n g a r n e t a r e s t r a i g h t , ( x - n i c o l s ) B) S c h i s t f r o m t h e k y a n i t e - s i l l i m a n i t e z o n e , Shuswap Comp lex . F i r s t s t a g e g a r n e t c o n t a i n s S - s h a p e d i n c l u s i o n t r a i l s . S e c o n d s t a g e g a r n e t r i m ( o u t e r m a r g i n ) c o n t a i n s o n l y a few s c a t t e r e d i n c l u s i o n s . G a r n e t i s p a r t l y s u r r o u n d e d by p o r p h y r o b l a s t i c m u s c o v i t e - f i b r o l i t e a g g r e g a t e ( M + F ) . K y a n i t e ( K ) i s common i n the s c h i s t m a t r i x , ( x - n i c o l s ) 265 B PLATE 2-2 A) Schist from the kyanite-sillimanite zone, Shuswap Complex. Quartz inclusions outline a r e l i c crenulation cleavage in this large stage one garnet. Opaque inclusions are continuous with the external PI schistosity although rotated relative to i t . Fibrolite aggregates occur in the lower portion of the photomicrograph, (plane light) B) Schist from the sillimanite zone, Shuswap Complex. Idioblastic second stage garnets(g) are enclosed by porphyroblastic muscovite with minor fibrolite(m + f ) . The large muscovite grains have a random orientation and interlocking grain margins, (x-nicols) I mm B i i I mm PLATE 2-3 S c h i s t from the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex. Garnet and s t a u r o l i t e ( s ) are p a r t l y enclosed by f i b r o l i t e - m u s c o v i t e - i l m e n i t e aggregates. Kyanite(k) i s abundant i n the s c h i s t matrix. Arrow p o i n t s to area where f i b r o l i t e i s p a r t l y enclosed by second stage garnet. Second stage garnet rims are euhedral against the f i b r o l i t e aggregates. A) (plane l i g h t ) B) ( x - n i c o l s ) 269 B Imm PLATE 2-4 S c h i s t from the s i l l i m a n i t e zone, Shuswap Complex. P o r p h y r o b l a s t i c muscovite(M) i s randomly o r i e n t e d i n the s c h i s t matrix. F i b r o l i t e - b i o t i t e aggregates form attenuated wispy t r a i l s through the muscovite (arrows). R e l i c s t a u r o l i t e ( s ) i s enclosed by f i b r o l i t e or muscovite. Arrow i n second generation garnet shows where f i b r o l i t e has been enclosed by garnet. A) (plane l i g h t ) B) ( x - n i c o l s ) 271 B i i I m m PLATE 2-5 A) C o e x i s t i n g c a l c i c amphibole ( a ) , c a l c i c pyroxene ( p ) , quartz ( q ) , and c a l c i t e (c) from a discontinuous marble u n i t i n the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex, (plane l i g h t ) B) C o e x i s t i n g muscovite (m), quartz ( q ) , and c a l c i t e (c) from a small marble u n i t i n the k y a n i t e - s i l l i m a n i t e zone, Shuswap Complex, ( x - n i c o l s ) 273 B i J I mm 274 Rb-Sr Dates f o r G r a n o d i o r i t e I n t r u s i o n s on the Northeast Margin of the Shuswap Metamorphic Complex, Cariboo Mountains, B r i t i s h Columbia* Lee C. Pigage Department of G e o l o g i c a l Sciences U n i v e r s i t y of B r i t i s h Columbia Vancouver, B.C. V6T 1W5 Canada *published as a Note i n Canadian J o u r n a l of Ea r t h S c i 14, 1690-1695. 275 ABSTRACT Whole rock Rb-Sr dates of 138 ± 12 Ma ( a l l f i v e whole rocks) and 163 ± 7 Ma were obtained f o r g r a n o d i o r i t e stocks i n Wells Gray P r o v i n c i a l Park, Cariboo Mountains, B r i t i s h Columbia. These dates bracket the b i o t i t e K-Ar date of 143 ± 14 Ma determined p r e v i o u s l y by the G e o l o g i c a l Survey of Canada. Two b i o t i t e - whole rock ± hornblende dates of 119 ± 11 Ma and 77 ± 20 Ma i n d i c a t e i s o t o p i c r e s e t t i n g . I n i t i a l 8 7 S r - 8 6 S r r a t i o s vary from 0.7061 ± 0.0001 to 0.7103 ± 0.0002 f o r rock and mineral dates. When combined w i t h f i e l d r e l a t i o n s , these dates r e s t r i c t r e g i o n a l deformation and metamorphism i n t h i s area to the time i n t e r v a l between Upper T r i a s s i c and Upper J u r a s s i c . The r e s e t t i n g event was probably Eocene, as shown i n other areas along r e g i o n a l s t r i k e to the n o r t h and south. 276 INTRODUCTION Metamorphic rocks belonging to the Hadrynian to lower P a l e o z o i c Kaza and Cariboo Groups border the northeast margin of the Shuswap Metamorphic Complex i n the Cariboo Mountains, B r i t i s h Columbia (Campbell 1963, 1968). D e t a i l e d mapping i n Wells Gray P r o v i n c i a l Park ( F i g . 3-1, 3-2) has o u t l i n e d a complex, polyphase h i s t o r y w i t h four deformational and two metamorphic episodes (Pigage 1978). North-plunging i s o c l i n a l F^ s t r u c t u r e s are accompanied by a pervasive a x i a l plane s c h i s t o s i t y . F^ minor f o l d s and a s s o c i a t e d c r e n u l a t i o n cleavage are c o r r e l a t e d w i t h l a r g e s c a l e a n t i c l i n o r i a and s y n c l i n o r i a described by Sutherland Brown (1963) and Campbell et a l . (1973). These s t r u c t u r e s plunge northwest and verge towards the west. F 3 and F^ s t r u c t u r e s are l o c a l l y developed as f r a c t u r e s , f a u l t s , and angular f o l d s w i t h ruptured hinge zones. These s t r u c t u r e s trend north and no r t h e a s t , r e s p e c t i v e l y . Regional metamorphic assemblages r a p i d l y i n c r e a s e from lower greenschist f a c i e s i n the northern part of F i g . 3-2 to upper amphibolite f a c i e s at the margin of the Shuswap Complex. Rotated planar i n c l u s i o n t r a i l s i n garnet and c h l o r i t o i d i d e n t i f y the pervasive r e g i o n a l metamorphism as syn- to post-F^, c o n t i n u i n g i n t o F^. Fine grained s e r i c i t e - c h l o r i t e a l t e r a t i o n of garnet represents l a t e regrograde metamorphism. SCOPE OF STUDY F i e l d evidence confirms that g r a n o d i o r i t e stocks i n the area were emplaced between deformation events F 2 and F . This dates i n t r u s i o n a f t e r the pervasive r e g i o n a l deformation and metamorphism. Dating of these Figure 3-1. Index map of s o u t h - c e n t r a l B r i t i s h Columbia. D e t a i l e d study area (Figure 3-2) i s o u t l i n e d . Ruled area represents the Shuswap Metamorphic Complex. Modified from Campbell (1973). Figure 3-2. Geologic sketch map of study area, Wells Gray Provincial Park, British Columbia. Samples collected for Rb-Sr dating are indicated by circles. Triangle marks location of sample collected by the Geological Survey of Canada for K-Ar dating (Wanless e_t a l . 1965) . Geology modified from Pigage (1978) and Campbell (1963, 1968). Dotted lines outline permanent snow and ice fields. 279 intrusions should therefore place a minimum age on the regional ^-y^2 events. A maximum age for F-^-!^ deformation is provided by the involvement of Upper Triassic phyllites in a l l of the deformational history (Brown 1968; Campbell 1971). Previous dating of these intrusions consists of a biotite K-Ar date of 143 ± 14 Ma for the largest granodiorite pluton (Wanless et a l . 1965). (Using K-Ar decay constants of Beckinsale and Gale (1969) this date becomes 148 Ma.) During 1975 I collected several samples (grapefruit-sized or larger) from offshoots or satellites of the large stock for Rb-Sr dating. Sample locations are indicated in Fig. 3-2 and lis t e d in Table 3-1. Brief notes on samples and analytical methods are presented in Appendix 3-1. RESULTS AND INTERPRETATION Table 3-1 l i s t s analytical results for five whole rock and three mineral separate samples. Calculated ages and i n i t i a l ratios are presented in Table 3-2 and illustrated in Figs. 3-3 and 3-4. Whole rock samples do not l i e on a single isochron. Sample AP2 controls the calculated whole rock dates because a l l other samples are 87 86 clustered near the Sr/ Sr coordinate. If AP2 is not considered in the calculations, the resulting Paleozoic dates are not consistent with involvement of Triassic strata in the F^-F^ events. When a l l whole rock samples are included, the calculated errorchron has an i n i t i a l ratio of 0.7084 ± 0.0003 with a slope corresponding to a date of 138 ± 12 Ma. This errorchron is probably not valid because the samples come from two different granodiorite stocks which appear to have significantly different TABLE 3-1. Rb-Sr data f o r a l l analyzed samples. Sample L a t i t u d e Longitude M a t e r i a l Sr (ppm) Rb (ppm) 8 7 R b / 8 6 S r ^ S r / 8 6 ! HBL1 52°32.5' 120°05.2' rock 259 83 0.930 0.7105 hornblende 234 38 0.469 0.7092 b i o t i t e 10 528 159 0.8814 GDI 52°33.1' 120°06.3' rock 707 94 0.386 0.7110 b i o t i t e 28 517 53.9 0.8019 API 52°33.1' 120°06.3' rock 449 110 0.708 0.7102 GD2 52°33.5' 120°09.7' rock 1003 91 0.262 0.7067 AP2 52°33.5' 120°09.7' rock 135 260 5.60 0.7191 NOTE: A n a l y t i c a l e r r o r s : Rb-Sr r a t i o , 2% ( l a ); 8 7 S r / 8 6 S r , 0 .00013 ( l a ). See Appendix f o r sample d e s c r i p t i o n s and a n a l y t i c a l methods. TABLE 3-2. I n t e r c e p t s and apparent ages f o r whole rock and m i n e r a l separate data l i s t e d i n Table 3-1. Samples used i n c a l c u l a t i o n I n t e r c e p t ± 2 0 ( 8 7 S r / 8 6 S r ) Apparent age 1 2 a (Ma BP) Whole rock WR1: a l l whole rock samples WR2: GD2 and AP2 0.708410.0003 0.706110.0001 138112 16317 B i o t i t e - whole rock Ml: GDl-bt and GDI-rock M2: HBLl-bt, H B L l - h b l , and HBLl-rock 0.710310.0002 0.709110.0013 119111 77120 NOTE: x_. = 1.42 X 10 1 1 /year. Rb oo 282 Figure 3-3. Isochron diagram f o r b i o t i t e - w h o l e rock + hornblende isochrons l i s t e d i n Table 3-2. R. i s the i n i t i a l 8 7 S r - 8 ^ S r r a t i o . l 283 0 . 7 2 0 i 0 . 7 1 5 H 0 . 7 1 0 0 . 7 0 5 0 . 7 0 0 WR WR2 T 119 ±11 Ma 0 . 7 1 0 3 ± 0 . 0 0 0 2 7 7 ± 2 0 Ma 0 . 7 0 9 1 ± 0 . 0 0 1 3 163 ± 7 Ma 0 . 7 0 6 1 ± 0 . 0 0 0 1 l 3 8 ± l 2 M a 0 . 7 0 8 4 ± 0 . 0 0 0 3 8 7 R b / 8 6 S r 0 . 0 —I 2 . 0 4 . 0 - 1 — 6 . 0 8 . 0 Figure 3-4. D e t a i l of area shown i n Figure 3-3. M i n e r a l separate p o i n t s are i n d i c a t e d w i t h t r i a n g l e s . C i r c l e s i n d i c a t e whole rock p o i n t s . S o l i d l i n e s are b i o t i t e - w h o l e rock + hornblende dates. Dashed l i n e s are whole rock c a l c u l a t e d dates. 284 87 86 i n i t i a l Sr- Sr r a t i o s . The two point isochron f o r samples GD2 and AP2 has an i n t e r c e p t of 0.7061 ± 0.0001 and a slope corresponding to an age of 163 ± 7 Ma. This date i s probably more r e p r e s e n t a t i v e because the samples were c o l l e c t e d from the same l o c a t i o n . These two whole rock dates bracket the K-Ar date determined by the G e o l o g i c a l Survey of Canada. V a r i a b i l i t y of i n i t i a l r a t i o s i s l i k e l y the r e s u l t of unequal a s s i m i l a t i o n of s m all amounts of r a d i o g e n i c S r - r i c h country rock. B i o t i t e - whole rock ± hornblende isochrons are i n d i c a t e d by s o l i d l i n e s i n F i g s . 3-3 and 3-4. The younger dates (119 ± 11 Ma and 77 ± 20 Ma) i n d i c a t e p o s t - i n t r u s i o n disturbance of Rb-Sr. The 77 ± 20 Ma date i s a maximum age f o r e i t h e r the event causing i s o t o p i c r e s e t t i n g or the time of f i n a l c o o l i n g below the threshold temperature f o r Rb or Sr m i g r a t i o n . Several workers f u r t h e r south i n the Shuswap Complex have recognized the presence of an Eocene thermal event that caused r e s e t t i n g of K-Ar and Rb-Sr dates (Ryan 1973; Medford 1975). Recent s t u d i e s f u r t h e r n o r t h have a l s o produced T e r t i a r y dates ( P a r r i s h 1976). The younger mineral dates from Wells Gray Park suggest that t h i s same event may have p a r t i a l l y reset i s o t o p i c ages. A maximum age of 77 ± 20 Ma f o r r e s e t t i n g i s compatible w i t h the 40-50 Ma dates encountered to the n o r t h and south. CONCLUSIONS A whole rock Rb-Sr date of 163 ± 7 Ma f o r a g r a n o d i o r i t e - a p l i t e p a i r from Wells Gray P r o v i n c i a l Park i s only s l i g h t l y o l d e r than a previous K-Ar date (143 ± 14 Ma) obtained from the same s u i t e of i n t r u s i o n s . When combined w i t h f i e l d r e l a t i o n s , these dates c o n s t r a i n the r e g i o n a l F'1-F9 deformation and metamorphism to the time i n t e r v a l between 285 Upper T r i a s s i c and Upper J u r a s s i c . B i o t i t e Rb-Sr dates are younger than the whole rock dates. In other areas to the north and south s i m i l a r d i s t u r b e d dates have been a t t r i b u t e d to an Eocene thermal event. The HBL1 b i o t i t e age (77 ± 20 Ma) i s consistent w i t h t h i s i n t e r p r e t a t i o n . ACKNOWLEDGEMENTS During t h i s study I was supported by an INCO ( I n t e r n a t i o n a l N i c k e l Company) graduate research f e l l o w s h i p . F i e l d expenses were defrayed by NRCC (N a t i o n a l Research C o u n c i l of Canada) grant 67-4222 to H.J. Greenwood. A n a l y t i c a l work was supported i n part by NRCC grant 67-8841 to R.L. Armstrong. Ms. K. Scott helped g r e a t l y w i t h lab techniques and q u i r k s of the mass spectrometer. Discussions w i t h B. Ryan and R.L. Armstrong sharpened my ideas concerning r a d i o m e t r i c age d a t i n g . 286 SELECTED REFERENCES BECKINSALE, R.D. and GALE, N.H. 1969. A reappraisal of the decay constants and branching ratio of ^ K. Earth and Planetary Science Letters, 6, pp. 289-294. BROWN, A. 1968. McBride area (93H), British Columbia, structural study. Geological Survey of Canada, Paper 68-1, part A, pp. 20-21. CAMPBELL, K.V. 1971. Metamorphic petrology and structural geology of the Crooked Lake area, Cariboo Mountains, British Columbia. PhD thesis, University of Washington, Seattle, WA, 192p. CAMPBELL, R.B. 1963. Quesnel Lake (east half) British Columbia. Geological Survey of Canada, Map 1-1963. . 1968. Canoe River, British Columbia. Geological Survey of Canada, Map 15-1967. . 1973. Structural cross-section and tectonic model of the southeastern Canadian Cordillera. Canadian Journal of Earth Sciences, 10, pp. 1607-1620. CAMPBELL, R.B., MOUNTJOY, E.W., and YOUNG, F.G. 1973. Geology of McBride map-area, British Columbia. Geological Survey of Canada, Paper 72-35. 104p. HUSTER, E. 1974. The h a l f - l i f e of natural 8 7Rb measured as difference between the isotopes of and 85jfo (abstract). International Meeting for Geochronology, Cosmochronology, and Isotope Geology. Paris, France, August 1974. McINTYRE, G.A. , BROOKS, C , COMPSTON, W., and TUREK, A. 1966. The st a t i s t i c a l assessment of Rb-Sr isochrons. Journal of Geophysical Research, 71, pp. 5459-5468. MEDFORD, G.A. 1975. K-Ar and fission track geochronometry of an Eocene thermal event in the Kettle River (west half) map area, southern British Columbia. Canadian Journal of Earth Sciences, 12, pp. 836-843. PARRISH, R.A. 1976. Geology and geochronology of the Wolverine Metamorphic Complex near Chase Mountain, Aiken Lake map area, British Columbia. MSc thesis, University of British Columbia, Vancouver, B.C. PIGAGE, L.C. 1978. Metamorphism and deformation on the northeast margin of the Shuswap Metamorphic Complex, Azure Lake, British Columbia. PhD thesis, University of British Columbia, Vancouver, B.C. 287 RYAN, B.D. 1973. Geology and Rb-Sr geochronology of the A n a r c h i s t Mountain area s o u t h c e n t r a l B r i t i s h Columbia. PhD t h e s i s , U n i v e r s i t y of B r i t i s h Columbia, Vancouver, B.C. 256p. SUTHERLAND BROWN, A. 1963. Geology of the Cariboo R i v e r area, B r i t i s h Columbia. B r i t i s h Columbia Department of Mines and Petroleum Resources, B u l l e t i n 47, 60 p. WANLESS, R.K., STEVENS, R.D., LACHANCE, G.R., and RIMSAITE, R.Y.H. 1965. Age determinations and g e o l o g i c a l s t u d i e s . G e o l o g i c a l Survey of Canada, Paper 64-17, part 1. pp. 15-16. YORK, D. 1969. Least squares f i t t i n g of a s t r a i g h t l i n e w i t h c o r r e l a t e d e r r o r s . Earth and Pl a n e t a r y Science L e t t e r s , 5, pp. 320-324. 288 APPENDIX 3-1 A n a l y t i c a l Methods Rb and Sr concentrations were determined by X-ray fluo r e s c e n c e using United States G e o l o g i c a l Survey (USGS) standards f o r c a l i b r a t i o n . R e p l i c a t e analyses i n d i c a t e that Rb-Sr r a t i o s have a p r e c i s i o n of 2% ( l a ) . Sr isotope data were measured on a s o l i d - s o u r c e mass spectrometer of U.S. N a t i o n a l Bureau of Standards (NBS) design w i t h o n - l i n e d i g i t a l data c o l l e c t i o n and r e d u c t i o n . Experimental measurements were normalized and 87 86 adjusted to correspond to a Sr- Sr r a t i o of 0.71022 f o r NBS standard SrC0 3, SRM 987 ( t h i s i s equivalent to a value of 0.7080 f o r the Eimer and 87 86 Amend Sr isotope standard). The p r e c i s i o n of a s i n g l e Sr- Sr measurement i s 0.00013 ( l a ) . Slopes and e r r o r s of isochrons were computed usi n g the procedure of Mclntyre et a l . (1966) f o r f i t s w i t h more than two p o i n t s . Two p o i n t isochrons were computed using the method of York (1969). Isochron e r r o r s have 95% confidence l i m i t s . Dates reported are based on a Rb decay constant of 1.42 X 1 0 - 1 1 / y e a r (Huster 1974). Petrographic D e s c r i p t i o n s HBL1 - Medium-grained Hornblendite P o i k i l i t i c hornblende (70%) encloses a l l other m i n e r a l s . Hornblende i s zoned w i t h brown cores and blue-green rims. B i o t i t e (20%) i s commonly i n t e r s t i t i a l . Accessory minerals i n c l u d e sphene ( 3 % ) , a p a t i t e ( 2 % ) , and opaques ( 5 % ) . Sphene i s t y p i c a l l y a s s o c i a t e d w i t h the opaques. GDI - Medium-grained Hornblende-Biotite Quartz D i o r i t e Subhedral p l a g i o c l a s e (67%) occurs w i t h l e s s e r amounts of quartz (15%), hornblende ( 8 % ) , and b i o t i t e ( 7 % ) . P l a g i o c l a s e t y p i c a l l y has complex 289 twinning and c o n c e n t r i c normal zoning ( A n ^ - A ^ ^ ) . M a f i c minerals form i n t e r s t i t i a l c l o t s . Epidote (3%) w i t h brown p l e o c h r o i c cores and c l e a r rims i s intergrown w i t h b i o t i t e and hornblende. Quartz forms anhedral, i n t e r s t i t i a l g r a i n s . S e r i c i t e a l t e r a t i o n of p l a g i o c l a s e i s minor; c h l o r i t e a l t e r a t i o n i s not present. Accessory minerals i n c l u d e sphene, a p a t i t e , z i r c o n , and opaques. API - Fine-grained A p l i t e Equant, anhedral quartz (30%) and p l a g i o c l a s e (55%) are the major minerals. Myrmekite i s a s s o c i a t e d w i t h minor m i c r o c l i n e (10%). Other minerals present are garnet, epidote, and opaques. Epidote i s commonly intergrown w i t h v e r m i c u l a r quartz. P l a g i o c l a s e i s l o c a l l y a l t e r e d to s e r i c i t e . GD2 - Medium-grained B i o t i t e G r a n o d i o r i t e Subhedral p l a g i o c l a s e l a t h s (45%) are l o c a l l y r eplaced by s e r i c i t e and epidote. A vague c o n c e n t r i c zoning i s evident i n p l a g i o c l a s e . Smaller amounts of quartz (30%), m i c r o c l i n e (10%), b i o t i t e ( 5 % ) , and epidote (5%) form anhedral, i n t e r s t i t i a l g r a i n s . Accessory minerals i n c l u d e garnet, sphene, tourmaline, and z i r c o n . AP2 - Fine-grained A p l i t e Equant, anhedral quartz (30%), p l a g i o c l a s e (35%), and m i c r o c l i n e (30%) are the major m i n e r a l s . P l a g i o c l a s e and m i c r o c l i n e show a n t i p e r t h i t i c and p e r t h i t i c t e x t u r e s , r e s p e c t i v e l y . A s l i g h t s e r i c i t e d u s t i n g i s c o n s i s t e n t l y present i n p l a g i o c l a s e . Minor minerals i n c l u d e muscovite ( 2 % ) , epidote ( 3 % ) , and garnet. Epidote t y p i c a l l y contains v e r m i c u l a r quartz. 

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