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Metamorphism southwest of Yale, British Columbia Pigage, Lee Case 1973

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METAMORPHISM SOUTHWEST OF YALE, BRITISH COLUMBIA by LEE CASE PIGAGE B . S c , U n i v e r s i t y of Wyoming, 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of GEOLOGICAL SCIENCES We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February, 1973 In presenting t h i s thesis i n p a r t i a l fulfilment of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t freely available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of G e o l o g i c a l S c i e n c e s The University of B r i t i s h Columbia Vancouver 8, Canada ABSTRACT P e l i t i c metasediments immediately southwest of Yale, B r i t i s h Columbia contain mineral assemblages c h a r a c t e r i s t i c of s t a u r o l i t e through 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 . Isograds are steeply dipping. Two phases of deformation are recognized with metamorphism being syn- to p o s t - t e c t o n i c . Pseudomorphs a f t e r andalusite i n d i c a t e that contact metamorphism preceded r e g i o n a l upgrading of the p e l i t e s . Microprobe analyses of major s i l i c a t e phases i n the p e l i t e s are combined with l i n e a r regression techniques i n discussing p o s s i b l e kyanite- and 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 . A zone some 3 kilometers wide contains the assemblage s t a u r o l i t e - k y a n i t e - g a r n e t - b i o t i t e -muscovite-quartz which i s univariant i n AFM p r o j e c t i o n . Regression an a l y s i s of the s t a u r o l i t e - k y a n i t e assemblage reveals the s e n s i t i v i t y of regression methods to error l i m i t s associated with the d i f f e r e n t minerals"present. P r e c i s i o n of the analyses was not high enough f o r regression analysis to d i f f e r e n t i a t e between s t a b l e , d i v a r i a n t e q u i l i b r i u m and a bu f f e r e d , univariant r e a c t i o n r e l a t i o n f o r t h i s assemblage. P e l i t i c and c a l c - s i l i c a t e assemblages from the metasediments r e s t r i c t pressure-temperature conditions during r e g i o n a l metamorphism to 5i-8 k i l o b a r s and 550-700°C. I t i s suggested that deformation, emplacement of g r a n i t i c i n t r u s i o n s , and reg i o n a l metamorphism are a l l part of the Cretaceous orogeny which formed structures of the Cascades Mountains. ACKNO\VLELXJEMENTS The author would l i k e to thank the persons who have helped in the completion of this project. Dr. P.B. Read supplied c r i t i c a l supervision. Dr. H.J. Greenwood made available his linear regression computer program PROTEUS and reviewed the sections on metamorphism. Time on the University of Washington electron microprobe and basic microprobe techniques were provided by Dr. B. Evans and Lucia Leitz. Jon Pigage survived through a summer as f i e l d assistant. Field and laboratory expenses were funded through National Research Council Grant 67-7973. During the time of this study the author was supported by a National Science Foundation Graduate Fellowship. i v CONTENTS INTRODUCTION 1 REGIONAL GEOLOGY . 4 STRATIGRAPHY 7 Custer Gneiss 7 Settler Schist 9 Unit I 9 Unit II 11 Unit III 13 Unit IV 14 Calc-silicate Units 15 Streaky Amphibolites 17 Original Rock Types 17 Eocene Conglomerate 18 STRUCTURAL GEOLOGY . ' 19-MINERAL GROWTH and STRUCTURAL DEFORMATION 24 IGNEOUS ACTIVITY 28 Biotite'-streaked Meta-intrusion 28 Plagioclase Aplite 29 Garnet Cluster Dikes 30 Biotite Quartz Diorite 31 Biotite-spangled Quartz Diorite 31 Spuzzum Intrusions 33 Ultramafic Rocks 34 METAMORPHISM 36 Introduction 36 Mineralogy 38 Equilibrium Tests 40 CONTENTS (cont.) v Regression Analysis 40 Staurolite-kyanite Zone 42 Sillimanite Zone 47 Conditions of Metamorphism 48 SUMMARY 61 SELECTED REFERENCES. 67 APPENDIX I : E l e c t r o n microprobe analyses 72 APPENDIX I I : Displacement of hydrothermal equilibrium 82 by s o l i d solution APPENDIX III: V i s u a l l y estimated modal analyses 85 LIST OF TABLES Table 1 Regional table of formations 6 2 Regression equations 43 3 Staurolite analyses 76 4 Garnet analyses 77 5 Biotite analyses 78 6 Muscovite analyses 79 7 Chlorite analyses 80 8 Plagioclase analyses 81 9 Visually estimated modal analyses - Custer Gneiss 85 10 Visually estimated modal analyses Schist: Unit I - Settler 86 11 Visually estimated modal analyses Schist: Unit II - Settler 87 12 Visually estimated modal analyses Schist: Unit III - Settler 88 13 Visually estimated modal analyses Schist: Unit IV - Settler 89 14 Visually estimated modal analyses Schist: Calc-silicate Units - Settler 90 15 Visually estimated modal analyses Schist: Streaky Amphibolites - Settler 91 16 Visually estimated modal analyses streaked Meta-intrusion - Biotite-92 17 Visually estimated modal analyses Units - Igneous 93 18 Visually estimated modal analyses Intrusions - Spuzzum 94 19 Visually estimated modal analyses Rocks - Ultramafic 95 v i i 1 talc + 5 magnesite 58 v m LIST OF FIGURES (cont. ) Figure 17 Isobaric equilibrium curves for the reaction: 1 talc + 3C02 = 4- quartz + 3 magnesite + 1H20 58 18 Isobaric equilibrium curves at low CO2 content i n the T-X^Q f i e l d for the system MgO-Si02-H20-C02 60 Map 1 Geology southwest of Yale, B.C. pocket 2 Structure southwest of Yale, B.C. pocket 3 Specimen locations southwest of Yale, B.C. pocket LIST OF PLATES 63 General view of the map-area looking south. Low ridge east of power line consists of Custer Gneiss. Settler Schist underlies the central valley and western slope. Basaltic dike i n Custer Gneiss. Photograph was taken looking across at a steep c l i f f face. The dike i s estimated at being about 10 feet thick. Unit I I : Settler Schist i n the staurollte zone. Note the numerous pegmatitic quartz stringers. Hammer i s 28 cm. long. Metaconglomerate containing granitic pebbles forms lenses within Unit I I : Settler Schist. Streaky, discontinuous compositional layering i n Unit I I I : Settler Schist. Dark layers contain abundant kyanite and staurolite which are absent from light-coloured layers. Pencil i s 15 cm. long. Convoluted quartzite bands i n micaceous matrix; this "rolled" pattern i s the typical appearance of Unit IV: Settler Schist. 64 Isoclinal, asymmetric phase 1 fold outlined by calc-s i l i c a t e lens within Unit I: Settler Schist. Phase 1 folds outlined by quartz stringers and compositional layering i n Unit I I : Settler Schist. Load cast structures i n Unit I I I : Settler Schist. Pencil delineates surface trace of phase 1 foliation. Stratigraphic top i s upward. Numbers on f i e l d book indicate tenths of feet. Graded bedding i n Unit I I I : Settler Schist. Stratigraphic top i s upward; kyanite and staurolite are more abundant i n upper p e l i t i c portion of each graded bed. Pencil delineates surface trace of phase 1 foliation. , Plagioclase aplite dike i n Unit I I I : Settler Schist. i i White, metasomatic r i m s surrounding quartz-plagioclase veins i n biotite-streaked meta-intrusion. LIST OF PLATES (cont.) x Plate 3 65 13. Cross-cutting chlorite laths (center) i n Unit I: Settler Schists. Graded bedding i s noticeable i n the photograph. Scale - 0.5 mm. 14. Inclusion patterns i n garnets of Unit I I : Settler Schists. Scale - 0.5 mm. 15. Concentric inclusions i n staurolite for Unit I I : Settler Schists. Scale - 0.5 mm. 16. Staurolite enclosing idioblastic garnet i n Unit I I : Settler Schist. Note that enveloped garnets retain concentric inclusion patterns. Scale - 0.5 mm. 17. Ragged staurolite "fingers" extend into retrograde muscovite-chlorite aggregates. Unit I I : Settler Schist. Scale 0.5 mm. 18. Staurolite porphyroblast extending into pseudomorph after andalusite (clear area). Unit I I : Settler Schist. Scale - 0.5 mm. Plate 4 .• 66 19. Late muscovite cross-cuts biotite i n Unit I I I : Settler Schist. Scale - 0.5 mm. 20. Typical garnet (center) - staurolite (lower center) - kyanite (center) - biotite-muscovite-quartz-plagioclase 'assemblage i n Unit I I I : Settler Schist. Scale -0.5 mm. 21. Concentric zoning i n garnets i n Unit I I I : Settler Schist. Scale - 0.5 mm. 22. Kyanite p a r t i a l l y enclosing garnet i n Unit I I I : Settler Schist. Pale rim around kyanite i s sericite. Scale - 0.5 mm. 23. Fibrolite-biotite knots surrounding garnets i n s i l l i -manite zone. Unit I I I : Settler Schist. Scale -0.5 mm. 24. Fibrolite-biotite sheath enclosing garnet i n sillimanite zone. Unit I I I : Settler Schist. Scale - 0.1 mm. INTRODUCTION Previous reconnaissance geologic mapping near Yale, B r i t i s h Columbia has indicated that p e l i t i c metasediments i n the region contain a mineralogy ch a r a c t e r i s t i c of the Barrovian facies series (Lowes, 1972: McTaggart and Thompson, 1967: Monger, 1970: Read, I960). More detailed mapping of these schists was undertaken as a part of the continuing study of the metamorphic and s t r u c t u r a l h i story of the Fraser Canyon area. In t h i s report the metamorphic mineral assemblages are described and interpreted, and i n i t i a l information on the stratigraphic and s t r u c t u r a l relations of rocks within the mapped region i s provided. The region i s located just southwest of Yale ( F i g . l ) i n the L i l l o o e t Range of the Coast Mountains (Holland, 1964). The Trans-Canada Highway passes along the eastern margin of the f i e l d area. Numerous- logging roads provide access to portions west of the highway. The topography i s rugged with elevations ranging from 150 feet above sea l e v e l along the Fraser River to s l i g h t l y greater than 5000 feet on the higher ridges. Valleys and ridges generally trend i n a northerly d i r e c t i o n . Gordon and Emory Creeks, however, flow from west to east across t h i s trend. Valleys are V-shaped and stream gradients are high; Gordon Creek, for example, drops some 3500 feet i n elevation i n s l i g h t l y less than 4 miles. The major unnamed streams and ridges i n the mapped region have been assigned numbers and l e t t e r s respectively (see map 3) for convenient reference. Bedrock exposures form numerous north-trending c l i f f s i n the area. Outcrops are most extensive on the east-facing slopes. The north- and west-facing slopes tend to be covered with g l a c i a l d r i f t , and the v a l l e y f l o o r s mantled by Recent alluvium. Logging operations Figure I. Thesis area location. have exposed many outcrops. Field mapping covering about eight square miles was completed on a scale of 1:2.5,000 during the summer of 1971. Laboratory work was completed during the following winter. Early geologic work i n the region was restricted to the v i c i n i t y of the U.S.A.-Canada border (Bauermann, 1886: Daly, 1912) and the Fraser River (Selwyn, 1872: Dawson, 1879: Cams-ell, 1912: Bowen, 1914-). With the opening of mining operations near Hope, more extensive regional studies were completed (Crickmay, 1930: Horwood, 1936). Much of this early information was incorporated into the geologic map of the Hope area compiled by Cairnes, Crickmay, Horwood, and Snow (1944). Monger (1970) recently revised this comprehensive study. More detailed mapping projects have been completed i n different areas around Hope. McTaggart and Thompson (1967) studied the schists and gneisses from Yale southward to the International Boundary. Reconnaissance mapping northwest of this region has been completed by Roddick and Hutchison (1969). Read (i960) mapped the schists immediately south of Emory Creek i n the Fraser Valley. Richards (1971) completed an intensive study of the plutonic rocks between Hope and the 49 t h Parallel. Lowes (1968, 1969, 1972) recently finished a regional study of the geology between Harrison Lake and the Fraser River. Other work i n progress includes mapping projects east of Harrison Lake (Reamsbottom, 1971) and north of Yale (Bremner, i n progress). A. REGIONAL GEOLOGY Although the map-area l i e s i n the Coast Mountains, geologic structures of the region are continuous with those of the Northern Cascade Mountains. McTaggart (1970) has summarized the geology of the Northern Cascades i n Brit i s h Columbia, and much of the follow-ing regional summary i s based on his work. The geology of the Cascades i n northern Washington has been extensively reviewed by Misch (1966). The Cascades consist of a core zone of migmatitic gneisses flanked by faulted and folded sedimentary, volcanic,, and metamorphic rocks (Figure 2). In Bri t i s h Columbia the axial zone has been mapped as the Custer Gneiss (Daly, 1912); i t i s correlated with the Skagit Gneiss which forms part of the axial zone of the Cascades i n Washington. The layered rocks flanking this core zone range i n age from Devonian through Tertiary and record a complex history of eugeosynclinal deposition and volcanism. Intrusive rocks occur as scattered plutons ranging i n age from Jurassic through Tertiary. North and west of the Northern Cascades, composite plutons form the large Coast Crystalline Complex. Reconnaissance mapping and isotopic age dating delineate intrusive activity during Late Mesozoic and Early Tertiary. McTaggart (1970) has plausibly argued that the crystalline complex i s a deeper erosion level of the same Cretaceous-Tertiary orogen that formed the Cascade geologic structures. Differential u p l i f t of the Coast Mountains along the Fraser River Fault System has exposed the root zones of this orogen. Faulted Eocene conglomerates (McTaggart and Thompson, 1967) along the Fraser River Graben indicate that movement within the fault system has continued into the Tertiary. Figure 2. Regional Geology—Legend. Quaternary 8 Prift and Alluvium Tertiary 7 Eocene Conglomerate Cretaceous Jackass Mountain Group Jurassic Ladner Group Triassic ? Custer Gneiss Hozameen Group Late Paleozoic | | | Chilliwack Group Settler Schist (age uncertain) Tertiary Granitic Rocks Yale Intrusions (Early Tertiary) Cretaceous Granitic Rocks Ultramafic Rocks 5a I2I°30'W 4 9°30 ' N adapted from Monger (1970). Figure 2. Regional Geology. WESTERN BELT AXIAL BELT EASTERN BELT o o N O ZZL 1x1 o o o Nl o cn UJ o o N o LU 2 QUATERNARY TERTIARY CRETACEOUS JURASSIC TRIASSIC PERMIAN PENNSYLVANIAN MISSISSIPPIAN DEVONIAN PRE-DEVONIAN PLEISTOCENE PLIOCENE MIOCENE OLIGOCENE EOCENE PALEOCENE DRIFT and ALLUVIUM GRANITIC ROCKS GRANITIC ROCKS ULTRAMAFIC ROCKS CULTUS FORMATION CHILLIWACK GROUP DRIFT and ALLUVIUM CHILLIWACK BATHOLITH EOCENE CONGLOMERATE YALE INTRUSIONS SPUZZUM INTRUSIONS CUSTER GNEISS CRYSTALLINE BASEMENT DRIFT and ALLUVIUM NEEDLE PEAK PLUTON JACKASS PASAYTEN MOUNTAIN GROUP GROUP DEWDNEY CREEK GROUP LADNER GROUP ? t HOZAMEEN GROUP ULTRAMAFIC ROCKS ? SETTLER SCHIST ? - -I. WESTERN BELT TI. AXIAL BELT IIL EASTERN BELT Table I. Regional Table of Formations. adapted from Monotr (1970). 7. STRATIGRAPHY The map-area straddles the transitional boundary between the Cascade and Coast Mountain terrains. The Hope Fault (Read, 1960a, 1960b) forms a part of the Fraser River Fault System and divides the region into two distinctive rock assemblages. East of the fault Custer Gneiss exposures form steep white bluffs. To the west the Spuzzum Quartz Diorite (McTaggart and Thompson, 1967) intrudes layered p e l i t i c schists and forms the western margin of the map-area. CUSTER GNEISS The Custer Gneiss (Daly, 1912) forms numerous steep, white c l i f f s on Ridge D (see maps 1, 3). Roadcut exposures are readily accessible along the Trans-Canada Highway and the Canadian Pacific Railway. In the southeastern part of the map-area the major rock type i s a mylonitic augen gneiss consisting of white plagioclase porphyroclasts i n a brown to gray microgranular matrix containing quartz and red-brown biotite. The gneiss i s banded with individual layers ranging from 2 to 20 cm. i n thickness. The layers differ i n the size and number of feldspar augen, the amount of biotite i n the matrix, and the degree of cataclasis. Commonly the gneiss has a mortar texture rather than being finely mylonitic. Numerous hinges and partial limbs of folds remain where the layering i s not obscured. Most outcrops are extensively shattered and fractured with laumontite and quartz f i l l i n g the fractures. Plagioclase augen range up to 1 cm. i n length. Narrow, indis-tinct twin lamellae are commonly kinked and distorted. Compositions range from Aix-,^ to An^Q, and some blebby antiperthites are developed. The matrix consists mainly of elongate, sutured quartz and bent and 8. shredded b i o t i t e . In the more c a t a c l a s t i c rocks the matrix displays marked flow structures around the augen. Accessory minerals include opaques and z i r c o n . Minor amounts of K-feldspar form i n t e r s t i t i a l , xenoblastic masses which apparently c r y s t a l l i z e d a f t e r the major c a t a c l a s t i c deformation. Towards the Hope Fault zones of strong shearing are r e a d i l y recognizable i n the gneiss. Layering i s t h i n and wispy, exposures are a chalky white, and recemented breccias with small angular c a v i t i e s are common. The gneiss has a mortar texture with a l b i t e c l a s t s occurring i n a fine-grained matrix containing quartz, K-feldspar, and a clay mineral(?). C h l o r i t e i s the only mafic mineral and i s most common along small f r a c t u r e s . The en t i r e rock has been p a r t i a l l y s e r i c i t i z e d . This whitening of color, s e r i c i t i z a t i o n , b r e c c i a t i o n , and intr o d u c t i o n of K-feldspar are f i r s t noticed i n shear zones about one-half" mile east of the Hope Fa u l t . Towards the f a u l t these shears become more pronounced and abundant and characterize a wide zone of movement associated with the f a u l t . P o r p h y r i t i c , u n f o l i a t e d b a s a l t i c dikes and lenses are scattered throughout the gneiss (photo 2). Small displacements of the dikes along minor f a u l t s i n d i c a t e that they were involved i n l a t e deformation of the gneiss. Thin s e c t i o n examination of the dikes reveals a r e l i c t i n t e r -granular texture. P l a g i o c l a s e l a t h s up to 0.7 mm. long are p a r t i a l l y to completely a l b i t i z e d and s e r i c i t i z e d . The aphanitic mesostasis contains r a d i a t i n g a c i c u l a r c r y s t a l s of blue-green hornblende, s k e l e t a l magnetite, and minor amounts of b i o t i t e and quartz.- In one s l i d e numerous a c i c u l a r tremolite c r y s t a l s are present. Fractures are f i l l e d by fine-grained prehnite and quartz. 9. Other minor rock types in the Custer Gneiss include medium-grained, foliated amphibolites and thin quartzites. Age relations of the Custer Gneiss have not been conclusively determined. McTaggart and Thompson (1967) suggested that the gneiss was formed by metamorphism and migmatization of part of the Hozameen Group. The Hozameen Group has not been definitively dated although i t is tentatively correlated with the Mid-Triassic Fergusson Group because of lithologic similarities (Cameron and Monger, 1971). In Washington shearing and mylonitization of the correlative Skagit Gneiss along Mid-Cretaceous faults provides a minimum Mid-Cretaceous age for the gneiss (Misch, 1966). Lack of coarse debris in Jurassic through Cretaceous sediments suggests that the metamorphism forming the gneiss was pre-Jurassic (Misch, 1966). SETTLER SCHIST Within the map-area the Settler Schist (Lowes, 1972) has been divided into four lithologically distinct, mappable units. Sparse information on structural and stratigraphic relations precludes placing a structural or stratigraphic top to the schist. For further reference the four units have been labelled I-IV from west to east and are discussed in that order. Unit I — Layered pelitic schist The westernmost unit consists of a fine-grained, brownish-gray, layered schist. The western margin of this unit is intruded by Spuzzum Quartz Diorite, and the eastern contact is sharp and subparallel with the regional foliation. . The schist has a distinct layering delineated by different shades of brown and gray with individual layers ranging up to 4 cm. 10. i n thickness. Graded bedding i s common and i n d i c a t e s a consistent s t r a t i g r a p h i c top to the west. Thin, l i g h t gray amphibolite lenses represent carbonate-rich l a y e r s i n the s c h i s t (photo 7). The centers of these lenses commonly contain l a r g e , unoriented hornblende c r y s t a l s . Quartz s t r i n g e r s , pegmatite pods, and g r a n i t i c lenses are ubiquitous on a small s c a l e . One t h i n q u a r t z i t e l a y e r was noted on the southwest side of Pddge A. Major constituents of the layered s c h i s t are pale green, magnesian c h l o r i t e , brown b i o t i t e , garnet, quartz, and p l a g i o c l a s e . Accessory minerals include r u t i l e , tourmaline, a p a t i t e , and z i r c o n . S t a u r o l i t e occurs s p o r a d i c a l l y as minute, ragged grains containing quartz and opaque i n c l u s i o n s . I d i o b l a s t i c garnet (0.5 mm. diameter) contains few quartz and opaque i n c l u s i o n s . Plagioclase ranges i n composition from A n ^ to &n.^y C h l o r i t e forms large (up to 2 mm. l o n g ) , twinned l a t h s which commonly cut across the r e g i o n a l f o l i a t i o n marked by oriented b i o t i t e flakes (photo 13). This c r o s s - c u t t i n g r e l a t i o n and the occurrence of c h l o r i t e p a r t i a l l y to completely enclosing b i o t i t e and garnet suggest that c h l o r i t e c r y s t a l l i z e d l a t e r than garnet and b i o t i t e . Nevertheless margins of c h l o r i t e c r y s t a l s against other minerals are sharp, and c h l o r i t e appears to be part of the equilibrium assemblage. Graded bedding i s obvious i n t h i n s e c t i o n . Towards the top of each graded l a y e r the rock i s more b i o t i t i c , g r a i n s i z e i s smaller, and opaque minerals are more abundant. The upper contact of each l a y e r i s sharp and s l i g h t l y undulatory. \ Amphibolite lenses consist mainly of quartz, p l a g i o c l a s e , \ i and hornblende. T r a n s i t i o n s to the surrounding s c h i s t s occur over 11. a few centimeters with "biotite r e p l a c i n g hornblende towards the enveloping p e l i t e . Unit II — Graphitic p e l i t i c s c h i s t The heterogeneous, fi n e - g r a i n e d , s c h i s t s of Unit II underlie most of Ridge A. T y p i c a l exposures are steel-gray or brown-gray with s t a u r o l i t e porphyroblasts weathering i n r e l i e f . Primary compo-s i t i o n a l l a y e r i n g up to 5 cm. t h i c k shows on many surfaces p a r a l l e l to the major r e g i o n a l l i n e a t i o n . In most outcrops t h i s l a y e r i n g i s o b l i t e r a t e d on surfaces normal to the r e g i o n a l l i n e a t i o n . Quartz s t r i n g e r s and pegmatite pods are l o c a l l y abundant (photo 3). Minor lenses of metaconglomerate, c a l c - s i l i c a t e l a y e r s , quartzo-f e l d s p a t h i c s c h i s t , and streaky amphibolite are scattered within t h i s unit (photo 4 ) . The metaconglomerates contain q u a r t z i t e , g r a n i t e , and s c h i s t pebbles i n a dark, schistose matrix. One mappable lens of quartzo-feldspathic, g a r n e t - b i o t i t e , _ l a y e r e d s c h i s t i s present i n the v a l l e y containing Stream 1 (Unit 7A on Map l ) . In the p e l i t i c s c h i s t s randomly oriented s t a u r o l i t e porphyroblasts range from 0.01 to 2.0 cm. long. Both s t a u r o l i t e and i d i o b l a s t i c garnet contain quartz and opaque dust inc l u s i o n s i n a c o n c e n t r i c a l l y zoned pattern (photo 14, 15). L o c a l l y f o l d e d quartz i n c l u s i o n t r a i l s pass undisturbed through s t a u r o l i t e porphyroblasts. Garnets enclosed by s t a u r o l i t e r e t a i n t h e i r sharp margins and zoned i n c l u s i o n patterns (photo 16). Large, p o i k i l o b l a s t i c kyanite blades belong to the e q u i l i b r i u m assemblage i n the northern part of the map-area. Marginal contacts with other minerals are sharp. L o c a l l y kyanite encloses i d i o b l a s t i c garnet. Large muscovite porphyroblasts are commonly associated with kyanite. 12. The mesostasis consists largely of fine, xenoblastic quartz, plagioclase (A^^-An.^)* muscovite, and brown biotite. Tourmaline, r u t i l e , zircon, ilmenite, and minor pyrite are accessory minerals. Plagioclase i s largely untwinned and d i f f i c u l t to distinguish from quartz. Biotite defines the foliation and i s mimetic around crenulation microfolds. Muscovite occurs i n two textural forms. The f i r s t consists of fine, narrow flakes intimately intergrown with biotite and defines the regional foliation. The second i s composed of large, equant flakes which commonly cut across the foliation. In this second form opaques outlining biotite crystal margins continue undisturbed through the muscovite indicating a later crystallization than biotit e . Typically idioblastic staurolite prisms are par t i a l l y surrounded by small aggregates of muscovite-biotite. Chlorite occurs as radiating laths replacing biotite and stauro-l i t e . The radiating, cross-cutting relations suggest replacement during retrograde reactions. Ragged fingers of staurolite extending into chlorite-muscovite clumps also suggest retrograde replacement of staurolite (photo 17). Contact effects of the Spuzzum Quartz Diorite are limited to the local development of andalusite porphyroblasts which have subse-quently been metamorphosed to the assemblage staurolite-muscovite-quartz with minor plagioclase, garnet, bi o t i t e , and kyanite. Chiastolite cross inclusion patterns are s t i l l v i s ible i n some of the porphyroblasts. These andalusite pseudomorphs may occur up to 300 feet away from the quartz diorite although commonly the distance i s measured i n tens of feet. Many of the prisms have been distorted and smeared along the plane of regional foliation. Micas i n the pseudomorphs do not consistently reflect the regional f o l i a t i o n i n the surrounding matrix. Staurolite prisms extending from the pseudomorphs into the matrix contain abundant opaque inclusions i n the matrix and are clear of inclusions within the outline of the former andalusite porphyroblasts (photo 18). Unit III — Quartzo-feldspathic schist The major rock type of Unit III i s a blue-gray, medium-grained, quartzo-feldspathic schist. Streaky compositional banding i s subparallel to the regional foliation; kyanite-rich layers weather to a very nubby surface, and the kyanite-poor layers have a smooth, light gray surface (photo 5). North of Gordon Creek the schists are massive, and primary layering i s uncommon. Quartz and pegmatite stringers are locally abundant. Thin calc-silicate layers and amphi-bolites within this unit are generally not mappable on the scale used. To the west, the contact with Unit II i s gradational over a few hundred feet. Intermediate rock types are interlayered with schists characteristic of the two units. Within this transition graded bedding and load cast structures indicate a stratigraphic top to the northeast. The eastern contact with Unit IV i s gradational over a few tens of feet and also consists of interlayered rock types. Porphyroblastic kyanite, garnet, and staurolite occur i n a fine (0.3 mm.), granoblastic mesostasis consisting mainly of quartz, plagioclase (Ar^-An^), brown bio t i t e , and muscovite (photo 20). Accessory minerals include tourmaline, zircon, apatite, r u t i l e , ilmenite, graphite(?), and minor pyrite. Mineral textures are similar to those described for Unit II schists. Garnets i n Unit III have more ragged outlines, staurolite i s markedly s k e l e t a l , and again two forms of muscovite can be tex-t u r a l l y distinguished. In the extreme northern part of the map-area, the appearance of f i b r o l i t e i n the equilibrium assemblage i s accompanied by the disappearance of s t a u r o l i t e and kyanite. F i b r o l i t e f i r s t develops i n small aggregates associated with b i o t i t e . With increased f i b r o l i t e content i n the sch i s t , garnets become rounded and are surrounded by extensive fibrolite-ilmenite-biotite-muscovite sheaths (photo 23, 24). Chlorite i s absent i n the s i l l i m a n i t e schists. Extensive regrograde a l t e r a t i o n of the schists i s related to the Hope Fault and small g r a n i t i c pods i n the area. A l t e r a t i o n i s indicated by s e r i c i t e rims surrounding kyanite and s t a u r o l i t e , p a r t i a l s e r i c i t i z a t i o n of plagioclase, and increased Ti content of b i o t i t e (noted by red-brown pleochroism). This a l t e r a t i o n i s f i r s t noticed only along fractures but becomes more pervasive closer to '• the f a u l t or g r a n i t i c pods. Unit IV — Micaceous quartzite Outcrops of Unit IV are l i m i t e d mainly to roadcuts and stream beds i n the large v a l l e y between Ridges A and D. Both to the north and south of the map-area, t h i s unit i s cut off by the Hope Fault. The major rock type i s a fine-grained quartzite containing micaceous layers ranging from paper t h i n streaks to 2.5 cm. thick bands composing roughly ha l f of the rock. In a l l outcrops the micaceous layers merge and bif u r c a t e , i s o l a t i n g q u a r t z i t i c lenses. Weathered sur-faces are a d i s t i n c t i v e l i g h t s i l v e r y tan. The q u a r t z i t i c lenses form strong, northwest-plunging mullion structures (photo 6). 15. Thin c a l c - s i l i c a t e l a yers containing hornblende and garnet, coarse b i o t i t e - q u a r t z - p l a g i o c l a s e s c h i s t s , and f i n e g a r n e t - b i o t i t e s c h i s t s occur i n minor amounts with i n the q u a r t z i t e . Streaky to massive amphibolite lenses have been i n d i c a t e d on the geologic map (Map 1 ) . Major constituents i n the micaceous layers of the q u a r t z i t e are b i o t i t e , muscovite, quartz, p l a g i o c l a s e (An„,-An, n), c h l o r i t e , and garnet. P y r i t e , i l m e n i t e , r u t i l e , tourmaline, and ap a t i t e are accessory minerals. Narrow, elongate, red-brown b i o t i t e i n t i m a t e l y intergrown with muscovite delineates the r e g i o n a l f o l i a t i o n . L o c a l l y the micas are s l i g h t l y kinked and warped. Garnets are subround and contain randomly scattered quartz i n c l u s i o n s . The average g r a i n s i z e ranges up to 0.4 mm. Q u a r t z i t i c layers c o n s i s t of s l i g h t l y l a r g e r , i n t e r l o c k i n g quartz grains with minor amounts of the other minerals. Patchy retrograde a l t e r a t i o n i s r e l a t e d to the Hope F a u l t . Up to about one-half mile west of the f a u l t b i o t i t e has been p a r t i a l l y a l t e r e d to s e r i c i t e and/or c h l o r i t e , and ilmenite i s a l t e r e d to li m o n i t e . Close to the f a u l t , b i o t i t e and garnet are completely c h l o r i t i z e d , and pl a g i o c l a s e i s h e a v i l y s e r i c i t i z e d . C a l c - S i l i c a t e Units C a l c - s i l i c a t e l a y e r s are common i n the S e t t l e r S c h i s t . In many l o c a l i t i e s they are only a few inches t h i c k and consist of the assemblage hornblende-garnet-plagioclase-quartz. Two d i s t i n c t i v e c a l c - s i l i c a t e u n i t s , however, were c o n s i s t e n t l y noted i n the s c h i s t s . The f i r s t of these forms l a r g e , mappable lenses within Unit I I I . Outcrops are a d i r t y white and have hollow f o l d structures 16. concordant with the major regional l i n e a t i o n . The assemblage t y p i c a l l y contains plagioclase ( A ^ ^ - A n ^ ) , diopside, garnet (gross-u l a r ? ) , quartz, e p i d o t e - c l i n o z o i s i t e , c a l c i t e , and t r e m o l i t e - a c t i n o l i t e . Garnets are p o i k i l o b l a s t i c with extremely ragged o u t l i n e s . Both diopside and epidote-clinozoisite form abundant, xenomorphic grains scattered through the matrix. The average grain size ranges between 0.5 and 1.5 mm. i n diameter. The other c a l c - s i l i c a t e assemblage consists of coarsely c r y s t a l l -i n e , dark green amphibolite layers containing green, p o i k i l o b l a s t i c hornblende, quartz, and plagioclase ( A n ^ - A n ^ ) . Minor amounts of garnet, c h l o r i t e , r u t i l e , a p a t i t e , and opaques are also present. In places l i g h t green a c t i n o l i t e and z o i s i t e are associated with t h i s assemblage. This amphibolite assemblage i s separated from the surrounding schists by a coarse rim containing abundant b i o t i t e and c h l o r i t e with lesser amounts of hornblende, plagioclase, and quartz. The mica aggregates contain dustings of opaque inclusions o u t l i n i n g former i d i o b l a s t i c hornblende c r y s t a l s . Relations between b i o t i t e and c h l o r i t e suggest that some of the b i o t i t e has been replaced by c h l o r i t e . Thicknesses of the zones vary; the dark green amphibolite core ranges up to 3 m. t h i c k with the micaceous rim being up to 0.2 m. t h i c k . Vidale (1969) has experimentally formed s i m i l a r zoning patterns s t a r t i n g with adjacent c a l c i t e and muscovite-phlogopite-quartz assemblages held at 600°C and 200 bars for at least two weeks. O r v i l l e (1969) has suggested a model using a l k a l i exchange e q u i l i b r i a to account for s i m i l a r associations i n metasediments i n the Alps. 17. Streaky Amphibolites Fine-grained, foliated amphibolite lenses are scattered through the Settler Schist. Exposures have a streaky appearance due to discontinuous compositional layering marked by hornblende-rich and hornblende-poor bands. Quartz, green hornblende, garnet, and plagio-clase (Arig^-Ar^g) occur i n substantial amounts. Accessory minerals are sphene, epidote, bi o t i t e , and opaques. Idioblastic garnets range up to 8 mm. i n diameter, while the other minerals have a maximum grain size of about 0.5 mm. Inclusion t r a i l s i n garnet porphyroblasts indicate that deformation preceded garnet crystallization. Original Rock Types Staurolite-bearing rocks typically have restricted chemical compositions; they have low Mg:Fe ratios, high A l content, and low ^ amounts of alkalis and Ca (Hoschek, 1967). The mineral assemblages in the Settler Schist suggest a stratigraphic sequence consisting mainly of Fe- and Al-rich shales with lesser amounts of interbedded carbonate-rich layers, conglomerates, tuffs, and sandstones or cherts. The grain size, graded bedding, and presence of amphibolites suggest a eugeosynclinal environment. Correlation of the Settler Schist within the regional stratigraphy has not been possible. The schists form an isolated series of units bounded by major faults and large plutons (see Fig. 2). Earlier workers made preliminary correlations based mainly on lithologic and chemical similarities. Lowes (1972) correlated the fault bounding the schists on the west with the Shuksan Thrust Zone. In northern Washington the Shuksan Fault thrusts the Paleozoic(?) Shuksan Suite westward over the Chilliwack Group (Misch, 1966). Similar movement along the 18. fault i n Brit i s h Columbia implies a minimum age of Early- to Mid-Paleozoic for the Settler Schist. For schists east of Harrison Lake which are similar to the Settler Suite, Reamsbottom (1971) suggested a Mesozoic age. Metaconglomerates i n these schists (and i n the map-area) contain granitic pebbles, and exposed granitic rocks indicate that igneous activity does not locally predate Jurassic. In northern Washington, however, Misch (1966) describes metaconglomerates containing granitic clasts i n the Paleozoic(?) Cascade River Schist indicating that a pre-Mesozoic age for the Settler Schist i s possible. Eocene Conglomerate Small scattered patches of conglomerate unconformably overlie the Custer Gneiss immediately east of the Hope Fault. The conglomerate consists of rounded boulders up to 0.3 m. i n diameter of Spuzzum Quartz Diorite, greenstone, schist, quartzite, and amphibolite i n a light rusty-brown, arkosic matrix. The matrix and boulders are heavily fractured. Both the contact with the underlying Custer Gneiss and bedding i n the conglomerate are nearly vertical. The conglomerate has been dated as Eocene based on pollen studies near Hope (G.E. Rouse i n McTaggart and Thompson, 1967). j r 19. STRUCTURAL GEOLOGY East of the Hope Fault, alteration and fracturing associated with shearing along the fault have destroyed much of the earlier structure within the Custer Gneiss. Stereographic projection of poles to fol i a t i o n indicate a northwest-plunging structure (Fig. 3). Fold axes and poles to axial planes of minor folds i n the f o l i a t i o n substantiate the northwest trend (Fig. 3). The foliations are not consistent with a simple structure i n that they appear to define a synform i n the southern part of the map-area and an antiform farther north. The northwest-plunging trend i s consistent with antiformal structures in the gneiss near Hope (McTaggart and Thompson, 1967). West of the fault, the Settler Schist i s also deformed into northwest-plunging structures. Two phases of mesoscopic folds have been recognized. The regional fo l i a t i o n i s the axial-plane schistosity of phase 1 structures and has been folded by a coaxial phase 2 deformation. Phase 2 structures have overprinted and erased most of the phase 1 folds. Folds related to the f i r s t deformation were noted i n scattered locations. Unit I contains sharply asymmetric, i s o c l i n a l , similar style folds (see photo 7). Limbs are strongly sheared and attenuated. Displaced quartz veins i n the folds indicate movement along the axial-plane schistosity. Within Units II-IV phase 1 structures consist of tight, parallel style folds (photo 8). Hinges are thickened, the angle between limbs i s approximately 40°, and minor fold axes plunge northwest. In most outcrops bedding was subparallel to the axial-plane schistosity of these folds. 20. N I I Figure 3. Structures in Custer Gneiss—Equal area projection. • Poles to layering—29 points. +• Poles to axial planes of minor folds—10 points. ° Minor fold axes—12 points. I Poles to bedding. 59 point*. Polet to phose I axial plane schistosity. 500 points. Contour Interval • 8 - 6 - 4 - 2 — 0 . 2 % per 1% area. Calculated fold axis Is indicated. Figure 4. Equal area projections of mesoscopic structures in the Settler Schist —I. Undifferentiated phase I and phase 2 lineations. 340 points. Phase I and phase 2 minor folds. Contour interval=15-10-5—0.3% per 1% area. • Phase I fold axes. 10 points. + Phase I axial planes of minor folds. O Phase 2 fold axes. 11 points. A Phase 2 axial planes of minor folds. Figure 5 , Equal area projections of mesoscopic structures in the Settler Schist—2. to to 23. Phase 2 f o l d s dominate s t r u c t u r a l patterns i n the s c h i s t s . The phase 1 axial-plane s c h i s t o s i t y i s deformed i n t o a la r g e , open, northwest-plunging synform-antiform structure. A x i a l planes of these open phase 2 f o l d s dip steeply west. Lineations associated with t h i s deformation include mica o r i e n t a t i o n , quartz rodding, crenulations, and minor f o l d axes. The trace of the a x i a l plane of the synform crosses Ridge A, and that of the antiform i s cut o f f by the Spuzzum Intrusions near the Hope Fa u l t . C l u s t e r i n g of phase 1 minor f o l d axes i n the same northwest d i r e c t i o n as phase 2 l i n e a t i o n s suggests that the two deformations were c o a x i a l . Where two l i n e a t i o n s were observed i n the same specimen, the e a r l i e r i s at a very s l i g h t angle to the second. The co a x i a l nature of the f o l d i n g suggests that phase 1 and phase 2 are p o s s i b l y part of the same deformation with the l a t e r structures being formed by continued f o l d i n g of e a r l i e r ' s t r u c t u r e s . There i s . no evidence f o r a time i n t e r v a l between deformations. Quartz s t r i n g e r s are deformed i n t o complex f o l d patterns. The wide v a r i e t y of f o l d s t y l e s and f o l d orientations makes i t d i f f i c u l t to d i f f e r e n t i a t e the st r i n g e r s according to perio d of deformation. . Graded bedding w i t h i n Unit I and the quartzo-feldspathic lens i n Unit II i n d i c a t e s s t r a t i g r a p h i c top to the southwest and northeast r e s p e c t i v e l y on opposite sides of Ridge A (see map 2). Yet s t r a t i -graphic u n i t s are not repeated i n the map-area. This i n d i c a t e s a complex structure which precludes a simple cross s e c t i o n i n the map-area. 24. The Hope Fault juxtaposes Late Cretaceous Spuzzum Intrusions (Richards, 1971) against Eocene conglomerates. South of Hope the Miocene Chilliwack B a t h o l i t h intrudes the f a u l t zone and i s not f a u l t e d (Richards, 1971). Movement along the f a u l t , then, was post-Eocene and pre-Miocene. Since structures i n the Custer Gneiss and S e t t l e r Schist are o b l i t e r a t e d or cut o f f by the f a u l t , movement along the f a u l t was l a t e r than the other deformations. S t r u c t u r a l a t t i t u d e s near the f a u l t do not appear to be r a d i c a l l y a l t e r e d by t h i s l a t e r movement. MINERAL GROWTH and STRUCTURAL DEFORMATION Relations between metamorphic c r y s t a l l i z a t i o n and phase 1 f o l d i n g are uncertain due to the absence of i n c l u s i o n t r a i l s w ithin the d i f f e r e n t porphyroblasts. Textural r e l a t i o n s , however, permit some inferences concerning r e l a t i v e times of c r y s t a l l i z a t i o n of the d i f f e r e n t minerals. Fine b i o t i t e and muscovite define the phase 1 f o l i a t i o n and must have formed at that time. The lack of d i s t o r t e d and warped micas in d i c a t e s continued post-phase 2 r e c r y s t a l l i z a t i o n . Large, equant muscovite porphyroblasts formed a f t e r the f i n e biotite-muscovite intergrowth d e f i n i n g the reg i o n a l phase 1 f o l i a t i o n . Garnets contain concentric zones of i n c l u s i o n s i n d i c a t i n g at l e a s t two periods of growth. The absence of i n c l u s i o n t r a i l s , however, makes i t d i f f i c u l t to r e l a t e periods of c r y s t a l l i z a t i o n to deformation. B i o t i t e flakes commonly abut against garnets rather than wrapping a-round them; t h i s texture can be int e r p r e t e d as suggesting s t a t i c , p o s t -tectonic growth of the garnets. Phase 1 Phase 2 Post-tectonic Chlorite Biotite Muscovite Garnet Staurolite Kyanite Sillimanite Andalusite - • • Figure 6. Timing of mineral growth. Both s t a u r o l i t e and kyanite formed l a t e r than garnet. The random o r i e n t a t i o n of s t a u r o l i t e and kyanite porphyroblasts i n d i c a t e s post-phase 2 c r y s t a l l i z a t i o n . The occurrence of folded quartz i n c l u s i o n t r a i l s passing undisturbed through s t a u r o l i t e prisms a l s o i n d i c a t e s s t a t i c c r y s t a l l i z a t i o n . Garnets i n the 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 are surrounded by f i b r o l i t e sheaths. The appearance of f i b r o l i t e i s accompanied by the disappearance of s t a u r o l i t e and kyanite. These r e l a t i o n s suggest that f i b r o l i t e i s the l a t e s t prograde metamorphic mineral to have c r y s t a l l i z e d i n the p e l i t e s . Radiating chlorite- textures suggest l a t e retrograde formation of c h l o r i t e s . Andalusite pseudomorphs are smeared along the phase 1 f o l i a t i o n i n d i c a t i n g a pre- to syn-phase 1 formation. Andalusite c r y s t a l l i z e d before garnet and s t a u r o l i t e since both garnet and s t a u r o l i t e are c l e a r within former andalusite c r y s t a l margins and contain numerous opaque i n c l u s i o n s when extending i n t o the matrix (see photo 18). Micas wi t h i n the pseudomorphs are randomly oriented suggesting that a l t e r a t i o n of the andalusite occurred during s t a t i c , post-phase 2 con d i t i o n s . C a t a c l a s t i c textures i n the Custer Gneiss i n d i c a t e that a phase of deformation of the gneiss post-dates c r y s t a l l i z a t i o n of the g n e i s s i c mineral assemblage. R e c r y s t a l l i z a t i o n textures of b a s a l t i c dikes w i t h i n the Custer Gneiss are u n f o l i a t e d and apparently younger than the metamorphism of the gneiss. A l t e r a t i o n associated with the Hope Fault a f f e c t s mineral assemblages of both the Custer Gneiss and the S e t t l e r S c h i s t . P o s s i b l y r e c r y s t a l l i z a t i o n of the dikes i n the gneiss represents a l t e r a t i o n associated with movement along the f a u l t . 28. IGNEOUS ACTIVITY The Spuzzum Quartz D i o r i t e i s the major igneous mass i n the map-area. Small dikes, s i l l s , and lenses of g r a n i t i c m a t e r i a l , however, r e v e a l a complex h i s t o r y of i n t r u s i v e a c t i v i t y . Lack of c r i t i c a l outcrops has l i m i t e d exact determination of time r e l a t i o n s among the d i f f e r e n t igneous u n i t s i n the area. The following groupings are based mainly on mineralogy, texture, and mode of occurrence. BIOTITE-STREAKED META-INTRUSION Forming a se r i e s of p a r a l l e l , north-trending c l i f f s on the east side of Ridge A, t h i s massive, f o l i a t e d , quartzo-feldspathic s c h i s t i s the oldest i n t r u s i v e i n the map-area. Exposures weather to a smooth, f r i a b l e , gray to reddish-brown surface. P e n c i l streaks c o n s i s t i n g of b i o t i t e and l o c a l l y hornblende delineate a northwest-plunging l i n e a t i o n concordant with structures i n the surrounding s c h i s t s . Ubiquitous quartz veins are planar and l o c a l l y i r r e g u l a r l y f o l d e d . Where p l a g i o c l a s e occurs with quartz i n the v e i n s , white metasomatic rims containing abundant p l a g i o c l a s e , hornblende, and garnet surround the ve i n s . These rims weather i n r e l i e f , forming a d i s t i n c t i v e boxwork pattern (photo 1 2 ) . They probably represent healed fractures along which f l u i d s have been introduced, and exchange reactions have occurred. Several f i e l d observations require an i n t r u s i v e o r i g i n f o r t h i s quartzo-feldspathic u n i t . Narrow, elongate p e l i t e i n c l u s i o n s occur wi t h i n the b i o t i t e - s t r e a k e d s c h i s t near i t s margins, and the 29. enveloping p e l i t i c s c h i s t s are l o c a l l y b r e c c i a t e d . The uni t trends across both the r e g i o n a l f o l i a t i o n and primary l a y e r i n g i n the surround-in g p e l i t e s . F i n a l l y a small lens of layered s c h i s t w i t h i n Unit I I i s obscured and cut o f f by a pod of the b i o t i t e - s t r e a k e d s c h i s t (Unit 7A on Map l ) . F o l i a t i o n s are concordant with phase 1 axial-plane s c h i s t o s i t i e s i n the surrounding p e l i t e s i n d i c a t i n g pre- or syn-phase 1 emplacement. Lack of f i e l d data precludes more exact determination of time of i n t r u s i o n . Major constituents of the meta-intrusion are quartz, p l a g i o c l a s e (An2Q-An^), red-brown b i o t i t e , green hornblende, and garnet. Opaques, a p a t i t e , and z i r c o n are accessory minerals. Magnesian c h l o r i t e and hematite occur as a l t e r a t i o n products of b i o t i t e and opaques respec-t i v e l y . The average g r a i n s i z e ranges up to 0.5 mm. although ragged, p o i k i l o b l a s t i c hornblende and garnet are l a r g e r . P l a g i o c l a s e i s untwinned and d i f f i c u l t to d i s t i n g u i s h from quartz. A d d i t i o n a l b i o t i t e - s t r e a k e d s c h i s t s along Ridge C and j u s t south of Gordon Creek have been grouped with t h i s u n i t on the basis of t e x t u r a l and mineralogical s i m i l a r i t i e s . These s c h i s t s a l s o have discordant contacts with surrounding p e l i t i c s c h i s t s and contain p e l i t e i n c l u s i o n s along t h e i r margins. PLAGIOCLASE APLITE Small pods, dikes, and s i l l s of pale tan, f o l i a t e d p l a g i o c l a s e a p l i t e are scattered w i t h i n the b i o t i t e - s t r e a k e d meta-intrusion and p e l i t i c s c h i s t s (photo 11). Contacts with the surrounding s c h i s t s are sharp; s c h i s t i n c l u s i o n s i n the a p l i t e were noted i n only one l o c a t i o n . The p e l i t i c s c h i s t s generally are more micaceous near the contacts. 30. Major constituents of the a p l i t e are red-brown b i o t i t e , muscovite, quartz, p l a g i o c l a s e , and garnet. Minor amounts of m i c r o c l i n e , a p a t i t e , z i r c o n , hematite, and c h l o r i t e are also present. B i o t i t e commonly shows p a r t i a l to complete a l t e r a t i o n to muscovite and l i m o n i t e . The average g r a i n si z e i s 0.4 mm. although garnet porphyroblasts range up to 1.8 mm. i n diameter. Garnets form anastomosing, s k e l e t a l c r y s t a l s with numerous i n c l u s i o n s . B i o t i t e i n c l u s i o n s have a green pleochroism. Garnets are surrounded by white halos c o n s i s t i n g of quartz, p l a g i o c l a s e , and m i c r o c l i n e . The f o l i a t i o n i s concordant with phase 1 s c h i s t o s i t i e s and i n d i c a t e s emplacement during or p r i o r to phase 1 deformation. The a p l i t e s occur as dikes i n the b i o t i t e - s t r e a k e d meta-intrusions and were thus intruded at a l a t e r time. A p l i t i c dikes were not noted i n the other i n t r u s i v e u n i t s suggesting that emplacement of these other u n i t s i s l a t e r . GARNET-CLUSTER DIKES A f o l i a t e d hornblende quartz d i o r i t e forms numerous smaller dikes i n the map-area. The quartz d i o r i t e i s d i s t i n c t i v e because i t contains garnet c l u s t e r s surrounded by white quartz-plagioclase h a l o s . The major mafic mineral i s green hornblende with b i o t i t e occurring i n l e s s e r amounts. Minor constituents include r u t i l e , a p a t i t e , and opaques. Plagioclase i s commonly twinned with composi-ti o n s ranging from An_ 0 to An, 0. J<- 4V F i e l d r e l a t i o n s are scanty. The dikes are asymmetrically folded i n the same manner as the surrounding p e l i t e s . They are also cut by u n f o l i a t e d g r a n i t i c dikes and lenses. These r e l a t i o n s place the time of i n t r u s i o n as before or during phase 1 deformation. Relations with the b i o t i t e - s t r e a k e d meta-intrusion and p l a g i o c l a s e a p l i t e are unknown. BIOTITE QUARTZ DIORITE Scattered within the p e l i t i c s c h i s t s are pods of f o l i a t e d b i o t i t e quartz d i o r i t e . These lenses range from a few inches up to about 150 feet i n thickness. Most of the l a r g e r pods are located north of Gordon Creek. Weathered outcrops have a smooth, salt-and-pepper appearance. Borders with the surrounding s c h i s t s are sharp. , The f o l i a t i o n i s concordant with the re g i o n a l phase 1 f o l i a t i o n . Major constituents are red-brown b i o t i t e , muscovite, quartz, and p l a g i o c l a s e . Garnet, a p a t i t e , and opaques occur i n minor amounts. Grain s i z e i s generally about 1 mm. Plagioclase i s commonly twinned and d i s t i n c t l y normally zoned (An^^-An22). F i e l d r e l a t i o n s to other i n t r u s i o n s are not c l e a r . Time of emplacement•is sometime before or during the phase 1 deformation. BIOTITE-SPANGLED QUARTZ DIORITE Small pods of medium-grained, u n f o l i a t e d b i o t i t e quartz d i o r i t e are scattered through the S e t t l e r S c h i s t . V/eathered surfaces are a smooth, creamy white with large b i o t i t e flakes forming a splotchy spider web pat t e r n . Brown b i o t i t e , quartz, muscovite, and p l a g i o c l a s e (Ar^-An.^) a r e "the niajor minerals. Accessory minerals include garnet, a p a t i t e , and opaques. Small amounts of K-feldspar are l o c a l l y present. Plagioclase i s twinned and normally zoned. F i e l d r e l a t i o n s are unclear, but the u n f o l i a t e d nature of the quartz d i o r i t e i n d i c a t e s post-tectonic i n t r u s i o n . 32. Figure 7. Poles to foliation-Spuzzum Intrusions. 23 points. Equal area stereographic projection. 33. SPUZZUM INTRUSIONS The Spuzzum Intrusions (McTaggart and Thompson, 1967) form massive, cream-white c l i f f s of coarse quartz d i o r i t e along the western margin of the map-area (Ridges A and B). Dark green hornblende occurs as i r r e g u l a r splotches i n the white quartz-plagioclase matrix. F o l i a t i o n i s sporadic but c o n s i s t e n t l y s t r i k e s northwest (Figure 7 ) . The quartz d i o r i t e l o c a l l y contains fine-grained amphibolite i n c l u s i o n s up to 0.3 m. long. Small, coarsely c r y s t a l l i n e hornblendite masses are i r r e g u l a r l y scattered through the t o n a l i t e . Contacts with the surrounding t o n a l i t e are g r a d a t i o n a l . These bodies l o c a l l y contain garnet and p y r i t e . Major constituents of the t o n a l i t e are p l a g i o c l a s e ( A n ^ - A r ^ ) , green hornblende, and quartz. Accessory minerals include prehnite, b i o t i t e , c h l o r i t e , and opaques. Prehnite t y p i c a l l y forms lens-shaped aggregates along b i o t i t e cleavages. C h l o r i t e occurs as a t h i n a l t e r a t i o n rim around hornblende. Small c l u s t e r s of r a d i a t i n g , a c i c u l a r hornblende and opaque i n c l u s i o n s defining euhedral cores surrounded by i r r e g u l a r i n c l u s i o n - f r e e rims i n large hornblende c r y s t a l s suggest r e c r y s t a l l i z a t i o n and continued amphibole growth a f t e r i n t r u s i o n . This r e c r y s t a l l i z a t i o n i s probably r e l a t e d to the r e g i o n a l metamorphism. Irregular masses of hornblendite and quartz d i o r i t e are dispersed within the S e t t l e r Schist and are c o r r e l a t e d with the Spuzzum Intrusions on the bas i s of t e x t u r a l and mineralogical s i m i l a r i t i e s . i The l a r g e s t of these i s o l a t e d bodies l i e s immediately west of the Hope Fault on Gordon Creek. Thin, apple green mylonites, extensive 34. fracturing with prehnite f i l l i n g the fractures, and alteration to chlorite, prehnite, and epidote are associated with movement along the fault. Tonalite exposures near Gordon Creek contain a 13 m. wide dike presently consisting of serpentine and talc. The only sign of interaction between the dike and surrounding tonalite consists of fine chlorite aggregates replacing plagioclase in the quartz diorite. Marginal contacts are sharp, and the tonalite i s not excessively fractured or granulated near the contacts. These features suggest that the serpentinite formed by i n situ metamorphism of an original pyroxenite or hornblendite body within the tonalite. Recent work by Richards (1971) indicated that near Hope the Spuzzum Intrusions formed by part i a l melting of the lower crust or upper mantle. K-Ar dates from hornblende and biotite give ages ranging from 79 my to 103 my (Richards, 1971). These Late Cretaceous ages place the Spuzzum Intrusions i n the same orogenic episode as that forming the Cascade structures (McTaggart, 1970). Synorogenic emplacement'of the tonalite would account for the consistent northwest strike of foliations i n the tonalite. ULTRAMAFIC ROCKS •Ultramafic rocks i n the map-area are characterized by two different lithologies and occurrences. The f i r s t of these consists of minor ultramafic dikes scattered through the Settler Schist. The largest dike i s a pyroxenite located on the northeast side of Ridge A. Coarse hypersthene and olivine have been pa r t i a l l y altered to ta l c , magnesite, antigorite, and anthophyllite. Other small dikes i n the map-area consist mainly of anthophyllite and chlorite. Usually these 35. smaller dikes have metasomatic biotite-chlorite selvages. If the serpentinite described in the Spuzzum mass near Gordon Creek (page 34) was originally a pyroxenite dike, these ultramafites form a part of the Spuzzum Intrusions with emplacement being sometime later than the tonalite. Small, strongly sheared, serpentinite lenses dispersed in limited exposures along the Hope Fault are the second major ultra-mafite occurrence. They are typically associated with buff-colored quartz-carbonate rock. The serpentinite assemblage consists of antigorite, talc, chlorite, and magnetite, and the major constituents of the quartz-carbonate rock are quartz, magnesite, dolomite, and minor fuchsite. The quartz-carbonate assemblage is a common altera-tion product of serpentinites along major fault zones (Henderson, 1969). These ultramafites appear to be tectonically emplaced as slices within the fault zone. 36. METAMORPHISM INTRODUCTION In the map-area, pelitic mineral assemblages in the Settler Schist are typical of the Barrovian facies series. Boundaries on the geologic map mark first appearances of kyanite and fibrolite. Increasing grain size to the north is associated with increasing metamorphic grade. Mineral assemblages in the different units within the pelites are: Unit I biotite-chlorite-garnet-plagioclase-quartz-staurolite-opaques Unit II staurolite zone biotite-garnet-muscovite-plagioclase-quartz-staurolite-ilmenite-rutile . staurolite-kyanite zone biotite-garnet-kyanite-muscovite-plagioclase-quartz-staurolite-ilmenite-rutile Unit III staurolite-kyanite zone biotite-garnet-kyanite-muscovite-plagioclase-quartz staurolite-ilmenite-rutile sillimanite zone biotite-garnet-muscovite-plagioclase-quartz-sillimanite-ilmenite-rutile Unit IV biotite-muscovite-quartz-plagioclase-garnet-pyrite-ilmenite-rutile. AFM projections of each of the above assemblages (Figure 3) graphically display phase rule considerations in the simplified six component system Si02-Al20„-Mg0-Fe0-K20-H20 (Thompson, 1957). Staurol i te-Kyanite Zone S i l l iman i te Zone Figure 8 . Schematic AFM projections fo r pelit ic assemblages A - 3 Staurolite-Kyanite Zone in the Set t ler Schist. 38. Diagrams A-2, A-5, and A-6 are consistent with requirements for divariant equilibrium and constraints imposed by the AFM projection. Diagrams A - l , A-3, and A-4, however, have too many phases for divariant equilibrium. The AFM projection i s not appropriate for Unit I because muscovite i s not i n the assemblage. Without muscovite, the Unit I assemblage does not contain too many phases for divariant equilibrium. Since the assemblages i n Units I and IV are unchanging i n the map-area and denote divariant equilibrium conditions, more detailed study of the mineralogy of these two units was not undertaken. Diagrams A-3 and A-4- appear to be consistent with constraints imposed by the projection and merit further consideration. Crossing t i e lines i n any projection result from either disequilibrium, a univariant reaction relation, or omission of an essential component i n the system considered (Greenwood, 1967b). Linear regression techniques using electron microprobe analyses of major minerals i n the pelites of Units II and III are combined with f i e l d relations to resolve which of these three po s s i b i l i t i e s provides a reasonable explanation of metamorphic zones and t i e line relations i n the map-area. MINERALOGY Seven samples from different metamorphic zones i n Units II and III were selected for microprobe analysis of major constituent minerals (Fig. 9). Assemblages i n the samples are the same as those l i s t e d earlier (page 36) for the various zones; local retrograde chlorite i s present i n samples 1, 2, 3, and 4. Analyzed minerals are b i o t i t e , chlorite, garnet, muscovite, plagioclase, and staurolite Alumino-silicates are considered stoichiometric and free of impurities 39. Figure 9. Location of specimens used for microprobe analyses. See Map I for symbols. AO. (Albee and Chodos, 1969: Chinner, Smith, and Knowles, 1969: Kwak, 1971). With conrpositionally zoned minerals only the compositions of the outer edges are used i n the regression analysis. Total iron i s determined as FeO. Analyses together with operating conditions of the microprobe are l i s t e d i n Appendix I. EQUILIBRIUM TESTS Ascertaining i f a mineral assemblage attained equilibrium i s in most rocks d i f f i c u l t and uncertain (Zen, 1963). Various evidence presented below suggests that minerals i n Units II and III (excluding chlorite) possess near equilibrium compositions. Textural evidence for equilibrium i s inconclusive. Crystal margins are sharp and do not show extensive alteration except i n rocks adjacent to the Hope Fault. Microprobe analyses of several grains of a mineral in the same slide are homogeneous (see tables -Appendix I'). This compositional constancy i n the area of a thin section indicates near equilibrium conditions. The occurrence of muscovite, staurolite, and plagioclase forming pseudomorphs after andalusite i n contact metamorphosed schists denotes local mobility of Fe, Ca, Na, and K during regional metamorphism. Mobility over short distances i s also indicated by the presence of biotite-chlorite rims enclosing amphibolite layers i n the p e l i t i c schists. This mobility suggests the capability of attaining near equilibrium conditions by alleviating small chemical potential gradients over short distances. REGRESSION ANALYSIS l i i The linear regression technique (Greenwood, 1968) provides an extension of graphical methods for phase rule considerations to n 4 1 . dimensions by permitting consideration of a l l components i n a l l phases at the same time. Accounting f o r a l l components and a l l phases avoids the problems associated with simple p r o j e c t i o n s . The technique i s designed to t e s t f o r l i n e a r dependencies among sets of minerals i n one or more equ i l i b r i u m assemblages using a l e a s t squares approach. Consider two equ i l i b r i u m mineral assemblages containing minerals A^, k^, and B^, r e s p e c t i v e l y . One mineral from t h i s group i s modelled i n terms of the others to give the equation: V C 2 A 2 + C 3 B 1 + ° 4 B 2 where the c_ c o e f f i c i e n t s may be e i t h e r p o s i t i v e or negative. I f the equation has the form: A l + °2h = C 3 B 1 + ° 4 B 2 when rew r i t t e n to give p o s i t i v e c o e f f i c i e n t s , then assemblages A and B have a possible r e a c t i o n r e l a t i o n and formed at d i f f e r e n t pressure-temperature conditions. I f no equation of t h i s form e x i s t s , then di f f e r e n c e s i n bulk chemistry are necessary to explain the d i f f e r i n g mineral assemblages. Regression methods delineate p o s s i b l e reactions based on l i n e a r combinations of mineral compositions. Because of thermodynamic and k i n e t i c considerations, the d i f f e r e n t p o s s i b l e regression reactions do not n e c e s s a r i l y correspond to stable reactions that a c t u a l l y occurred i n the assemblages. Textural r e l a t i o n s , systematic changes i n mineral compositions, and modal amounts of minerals provide,the necessary constraints i n s e l e c t i n g probable reactions from among l the p o s s i b l e regression equations. i Testing for linear dependencies also allows an estimation of the number of independent components needed to describe a mineral assemblage. The number of independent components equals the rank of the mineral composition matrix containing composition vectors for a l l minerals i n an assemblage (Greenwood, 1968), A regression equation i s significant only i f residuals are less than claculated error limits for the modelled mineral. For this study error limits for each component i n each mineral are calculated using a linear scale directly proportional to the amount of that component present (Greenwood, pers. comm.). The maximum permissible error allowance for each component i n the equation i s the sum over a l l minerals of error limits for each mineral times the amount of the mineral present i n the equation. Maximum error limits for each component are scaled to correspond to ± 1 weight per cent i n 4-0 per cent SiOg, and minimum limits are a r b i t r a r i l y '• defined as 1/3 maximum limits. The best equation has the lowest residuals and also satisfies constraints imposed by f i e l d evidence. Increasing the error limits increases the number of linear dependencies found i n mineral assemblages; small error limits are important i n successful use of the regression approach. STAUROLITE-KYANITE ZONE Coexisting staurolite and kyanite i n Units II and I I I (Fig. 8) indicate possible univariant reaction relations. The f i r s t appearance of kyanite cuts across Unit II suggesting that a pro-grade reaction i s involved. Constraints on any such reaction include an increase i n Fe-content for biotites occurring with kyanite assemblages (see Tables) and the occurrence of ilmenite mantling r u t i l e . Garnet 43. Table 2 Regression Equation* Reaction Assemblages Regression Equation 1 1 and 2 1.00 STAUR(l-A) + 7.4o BI0T(1) + 3.61 QTZ - 7.70 KY + 8.10 BI0?(2) Element Residuals E r r o r 1 S i -0.13 0.07 A l -0.10 0.06 Fe l . » l 0.91 Kn 0.01 0.01 ** -0.03 0.02 Zn 0.06 0.04 Na -0.07 0.0} K - l . * 7 0.97 H -0.25 0.15 T i -0.0* 0.03 0 o.oe 0.02 Reaction Assemblages Regression Equation 2 1 and 3 1.00 STAUR(l-A) + 1.73 BI0T(3) + 3.01 RUTL + 1.75 QTZ «.8.80 KY + 0.98 H20 + 3.15 ILK + 1.89 B X O t ( l ) Element Residuals E r r o r R a t i o S l -0.21 0.26 A l -0.12? 0.16 Fe -0.07 0.11 Mn 0.01 0.02 Kg -0.10 0.15 Zn 0.06 0.10 tia -0.01 0.02 K -0.01) 0.07 H -0.1* 0.21 T i -0.02 0.03 0 -0.83 0.63 Reaction Assemblages Regression Equation 3 1 and 2 1.00 STAUR(l-B) + 30.48 KUSC(l) * 10.UO KY + 29.62 KUSC(2) + 5.72 QTZ + 3.27 HjO + 2.01 ILK Element Residuals E r r o r 1 S i - l . » l 0.23 A l -1.26 0.21 Fe 0.77 0.16 Kn 0.01 0.01 *e 1.07 0.23 Ca 0.13 0.03 Zn 0.06 0.01 Na -0.06 0.01 K -0.">2 0.09 H -0.90 0.16 T i -0.91 0.19 0 -5.18 0.51 assemblage - specimen in which the assemblage occurs equations have been computed using molecular proportions of the elements abbreviationsi BIOT - b i o t i t e i GNT - garnet, ILK - ilmenite, KY - kyanite, KUSC - muscovitei QTZ - q u a r t s , RUTL - r u t i l e i SILL - sillimanitei STAUR - staurolite. residuals • actual composition of modelled mineral - computed composition according to regression equation error ratio - (residuals] /permitted error 44. Table 2 (continued) Reaction Assemblages Regression Equation k 1.00 STAUR(^-B) + 1,7k QTZ + 2.48 RUTL - 8.37 KY + 2.01 H20 + 2.62 ILM + 0.20 BIOT(Jf) Blement Residuals Error I Si -0.05 0.08 Al -0.03 0.05 Fe -0.02 0.03 Mn. 0.02 0.03 *6 0.17 0.66 Zn 0.26 o.ko Ma -0.01 0.03 K -0.30 0.80 H -0.01 0.01 Ti -0.2? 0.17 0 0.02 0,08 Reaction Assemblages Regression Equation 5 6 1.00 STAUR(6-A) + 1.97 QTZ + 2.59 RUTL =- 8.50 KY + 2.65 H20 + 2.73 ILM + 0.16 BI0T(6) Blement Residuals Error I Si -0.03 0.05 Al -0.02 0.03 P . -0.02 0.02 Hn 0.02 0.03 «« 0.17 0.66 Zn 0.14 0.22 Na -0.01 0.03 It -0.26 0.6? K -0.01 0.01 -Ti -0.03 0.11 0 0.02 0.05 Reaction Assemblages .• . Regression Equation 6 6 and 7 1.00 STAUR(6-B) + 0.26 MUSC(6) + 2.50 RUTL + 1.1*3 QTZ » 9.19 SILL + 0.2? BI0T(7) • 1.85 HjO • 2.63 I I * Element Residuals Error I S i -0.04 0.08 Al -0.03 0.06 P . -0.01 0.0k Kn 0.02 0.04 «g -0.01 0.02 . C a 0.00 o.ot Zn 0.15 0.40 Na 0.06 0.16 K -0.02 0.05 H -0.01 0.02 T i -0.03 0.07 0 . -0.01 0.01 45. Table 2 (continued) Reaction Assemblages Regression Equation 7 7 1.00 CNT(7-B) + 0.19 MUSC(7) + 1.82 RUTL + 0.01 HgO » 1.26 SILL • 1.75 QTZ • 1.84 ILM + 0.21 BI0T(7) Element Residuals Error I Si -0.05 0.23 Al -0.04 0.1? fe -0.03 0.13 *n 0.14 0.7? *g -0.02 0.11 Ca 0.20 1.10 Na 0.05 0.25 K -0.03 0.14 H -0.01 0.0? T i -0.05 0.27 0 0.03 0.06 Reaction Assemblages Regression Equation 8 6 and 7 1.00 STAUR(6-B) • 0.02 MUSC(6)'+ 3.85 OTZ • 7.44 SILL + 1.38 GNT(?-A) • 0.03 BI0T(7) + 1.83 H20 Element Residuals Error I Si 0.00 0.00 Al -0.00 0.00 Fe 0.05 0.11 Mn -0.17 0.43 "g . -0.05 0.13 Ca -0.27 0.70 Zn 0.15 0.39 Na 0.01 0.01 K -0.01 0.02 H 0.00 0.00 Ti 0.14 0.35 0 -0.02 0.02 46. i s not d i r e c t l y involved i n a re a c t i o n since garnet c r y s t a l margins remain sharp and lack any compositional differences or p a r t i a l r e a c t i o n rims when mantled by s t a u r o l i t e . Regression equations 1 through 3 i l l u s t r a t e p o s s i b l e r e l a t i o n s between assemblages on both sides of the kyanite appearance boundary. The occurrence of b i o t i t e (3) with assemblage 1 i n r e a c t i o n 2 denotes a s i g n i f i c a n t bulk chemistry difference between assemblages 1 and 3. E i t h e r equation 3 or a combination of equations 1 and 3 account f or kyanite appearance and are concordant with t e x t u r a l r e s t r i c t i o n s . Equations 4 and 5-represent.typical regression equations f o r single assemblages i n the s t a u r o l i t e - k y a n i t e zone. These equations i n d i c a t e that assemblages 4 and 6 are u n i v a r i a n t . I f u n i v a r i a n t , the assemblages must be buffered i n some manner since pressure and temperature are c l e a r l y not constant i n the-area. I f P^.0^ .a^  i s ' a r b i t r a r i l y f i x e d and constant and temperature i s allowed to vary, then a l l compositions are in v a r i a n t which agrees with a n a l y t i c a l r e s u l t s (see Appendix I ) . Such r e l a t i o n s are possible i f P^ o ^ t o t a l f o r t h i s zone. P r e c i s i o n l i m i t s of regression methods are an important constraint i n i n t e r p r e t i n g univariant r e l a t i o n s . Components occuring i n small amounts (such as ZnO, 1^ ,0, Na 20) often occur i n only one phase i n the regression equations and f a l l w i t h i n error l i m i t s rather than be-ing balanced i n the r e a c t i o n s . With greater p r e c i s i o n these components may prove that the s t a u r o l i t e - k y a n i t e assemblage represents s t a b l e , d i v a r i a n t e q u i l i b r i u m rather than a univariant r e a c t i o n r e l a t i o n . Surface thickness of the s t a u r o l i t e - k y a n i t e zone i s roughly 3 km. i n the d i r e c t i o n of incr e a s i n g metamorphic grade. Boundaries 47. of t h i s zone are close to v e r t i c a l i n d i c a t i n g that the 3 km. distance i s not a r e s u l t of apparent d i p . This large thickness suggests a s t a b l e , d i v a r i a n t equilibrium assemblage although a b u f f e r e d , univariant r e l a t i o n i s p o s s i b l e . In summary, the a n a l y t i c a l p r e c i s i o n achieved i n t h i s study i s not good enough to use components occurring i n small amounts as a means of d i f f e r e n t i a t i n g between divar i a n t and univariant assemblages. F i e l d evidence i s a l s o i n c o n c l u s i v e . Regression methods have, however, delineated probable reactions f o r the f i r s t appearance of kyanite i n the map-area. These problems r e i n f o r c e the n e c e s s i t y f o r small e r r o r l i m i t s when using the regression method. SILLIMANITE ZONE F i b r o l i t e f i r s t appears with b i o t i t e and quartz i n small unoriented aggregates. Kyanite and s t a u r o l i t e are present but are not n e c e s s a r i l y associated with f i b r o l i t e - b i o t i t e masses. Farther north w i t h i n the s i l l i m a n i t e zone, f i b r o l i t e becomes much more abundant and occurs as knots enveloping garnets. These knots contain b i o t i t e and s i l l i m a n i t e with l e s s e r amounts of muscovite and i l m e n i t e . Garnets within the knots are rounded and appear to have been p a r t i a l l y replaced by the surrounding f i b r o u s aggregates. Muscovite porphy-r o b l a s t s also contain numerous s i l l i m a n i t e needles. R u t i l e i s mantled by i l m e n i t e . Three reactions are thought to have occurred i n the s i l l i m a n i t e zone: staurolite+muscovite+rutile = Regression 6 sillimanite+biotite+ilmenite+HJD 4 8 . garnet+muscovite+rutile = Regression 7 s i l l i m a n i t e + b i o t i t e + i l m e n i t e kyanite = s i l l i m a n i t e . Regression a n a l y s i s using muscovite, b i o t i t e , and s t a u r o l i t e compositions from specimens 6 and 7 delineated equations 6 and 8 as p o s s i b l y accounting f o r the disappearance of s t a u r o l i t e . The common a s s o c i a t i o n of b i o t i t e and f i b r o l i t e , the lack of any evidence of garnet nucleation or growth, and the mantling of r u t i l e by ilmenite suggest that r e a c t i o n 8 did not occur i n the map-area. Reactions s i m i l a r to equation 6 have been described i n d i f f e r e n t r e g i o n a l metamorphic t e r r a i n s (Chakraborty and Sen, 1967: Carmichael, 1969). Carmichael noted that reactants and products did not n e c e s s a r i l y have to be i n contact as long as l i m i t e d i o n i c m o b i l i t y was p o s s i b l e . With higher metamorphic grade, garnet and muscovite react to form s i l l i m a n i t e and b i o t i t e . Garnets i n specimen 7 are rounded and surrounded by 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 halos (photos 2 3 , 2 4 ) . This texture suggests that the assemblage i s univariant and represents an interrupted r e a c t i o n . Equation 7 represents a r e a c t i o n using only mineral compositions from specimen 7. Ca r e s i d u a l s are too large f o r the r e a c t i o n as w r i t t e n . A d d i t i o n of p l a g i o c l a s e to the regression equation does not reduce r e s i d u a l s below permissible error l i m i t s . Since textures support r e a c t i o n 7, p o s s i b l y components besides FLjO (such as Na or K) are mobile. CONDITIONS OF METAMORPHISM Broad l i m i t s on metamorphic conditions f o r the S e t t l e r Schist 4 9 . i n the map-area are provided by (Fig. 10): A. B. AXpSiO^ t r i p l e point (Richardson et a l . , 1969) chlorite+muscovite=staurolite+biotite+quartz+vapor (Hoschek, 1969) C. staurolite+muscovite+quartz=AlpSiO-+hiotite+vapor (Hoschek, 1969) D. Fe-staurolite+quartz=sillimanite+garnet+water (Richardson, 1968) E. muscovite+qiiartz=sillimanite+sanidine+water ... . (Evans, 1965). A l l of these reactions have been investigated experimentally with buffer system (Eugster & Wones, 1962). The ubiquitous occurrence of staurolite i n the least metamorphosed pelites defines a lower temperature limit for metamorphism i n the map-area. Reaction curve B (Fig. 10) has been chosen as representing a reasonable staurolite-forming reaction. Experimental work indicates that other reactions with staurolite as a product occur at roughly the same pressure-temperature conditions (Hoschek, 1969). The exact position of curve B w i l l vary slightly because of Mg-Fe partitioning between staurolite, b i o t i t e , and chlorite, but a minimum temperature of roughly 540°C i s indicated. Reaction C defines the upper s t a b i l i t y limit of staurolite+ quartz+muscovite, and reaction D delineates the upper lim i t of Fe-staurolite+quartz. Reaction C i s essentially the same as reaction 6 with Ti as an additional component. Since reaction D does not occur within the map-area, an upper pressure l i m i t i s marked by the intersection of reaction curves C and D. H20 PTotal* Where applicable, f n was buffered by the QFM solid 5 0 . T r PH 2 0 • k b 4 A A L j S i 0 5 System (Richardson, Gilbert, and Bell, 1969) B Chlorite + Muscovite = Staurolite • Biotite • Quartz «• Vapor (Hoschek, 1969) C Staurolite + Muscovite • Quartz = AKilicate • Biotite • Vapor (Hoschek, 1969) D Fe-staurolite • Quartz = Almandine • Sillimanite + Water (Richardson, 1968) E Muscovite + Quartz = Sanidine + Sillimanite • Water (Evans, 1965) _ i L. 100 200 300 400 500 600 700 800 Figure 10. T , * C Experimental reactions defining metamorphic conditions of pelitic assemblages. 51. The exact pressure-temperature positions of the natural analogues of C and D depend on solid solution effects within participating phases. Reaction C was determined using natural minerals with Mg-Fe fractions very similar to minerals i n the map-area (biotite: Fe/Mg+Fe=0.52, staurolite: Fe/Mg+Fe=0.83, Hoschek, 1969). The experimentally determined reaction was not reversed and represents the maximum temperature of the univariant boundary for the specific compositions involved. In the f i e l d kyanite disappears at roughly the same location as reaction 6. If one assumes that curve C i s similar to reaction 6 and i s thus i n roughly the same location i n pressure-temperature space, then the minimum temperature position for curve C i s near the A^SiO^ t r i p l e point (Fig. 11, curve C ). The actual position of the curve i s somewhere between C and C. Reaction D was determined experimentally using pure Fe end-member compositions for staurolite and garnet (Richardson, 1968). Pressure-temperature shifts i n position of the equilibrium curve result from solid solution i n staurolite and almandine. Thermodynamic calculations using mineral compositions from Unit III reveal a maximum pressure shift of -170 bars (at ^ - t o t a l ^ ^ ^ bars) with a correspondingly insignificant temperature shift for Unit III schists i n the map-area (Appendix I I ) . Solid solution effects, then, are insignificant i n shifting the pressure-temperature position of reaction curve D. The intersection of curves C and D represent maximum pressure conditions during metamorphism i n the map-area. From Fig. 11, this intersection i s between 54 and 8 kilobars depending upon the position of reaction curve C. 52. 4 •A AlgSiOj System (Richardson, Gilbert, and Bell, 1969) B Chlorite + Muscovite:Staurolite t Biotite * Quartz • Vapor (Hoschek, 1969) C Staurolite + Muscovite + Quartz* Al-silicate <• Biotite •*• Vapor (Hoschek, 1969) C Minimum temperature equilibrium position of curve C based on field evidence. D Fe-staurolite +• Quartz: Almandine «- Sillimanite (Richardson,1968) Water E Muscovite + Quartz: Sonidine + Sillimanite + Water £ (Evane, I96S) D '. Pressure-Temperature gradient assuming stable formation of andaluslte. I - f Pressure-Temperature gradient assuming metastable formation of andaluslte. 100 200 300 400 500 600 700 800 Figure l l . Possible pressure-temperature gradients for the pelitic assemblages. 53. The absence of K-feldspar and the presence of muscovite + quartz i n sillimanite schists i n the area indicate that conditions of reaction E (Fig. 10) were not reached. Andalusite pseudomorphs near the Spuzzum Intrusions indicate that an earlier contact metamorphism has been superseded by regional metamorphism. If stable reactions are assumed, a strongly increasing pressure gradient with time i s suggested by the pseudomorphs (Fig. 11). This particular path could be caused by continuing rapid sedimentation and burial of the schists during metamorphism. With similar pseudo-morphs to the north, Hollister (1969b) suggested that andalusite i n i t i a l l y formed metastably and was replaced by stable metamorphic assemblages. This explanation would result i n a large temperature change with time rather than a pressure gradient. Conclusive evidence i n distinguishing between these two gradients i s lacking; the absence of any andalusite remnants i n slides studied suggests equilibrium conditions which would favor the stable formation of andalusite. Calc-silicate assemblages provide a means of approximating compositions of the f l u i d phase. Calc-silicate layers occur mainly in the staurolite-kyanite zone and contain the assemblages: biotite-hornblende-garnet-quartz-plagioclase-chlorite, ziosite-quartz-actinolite-chlorite, diopside-actinolite-epidote-garnet(grossular?)-quartz-plagioclase-calcite, diopside-quartz-epidote-garnet(grossular?)-plagioclase. Most experimental work with isobaric temperature-X^Q diagrams has been done at P - t o t a l = ^ ^ bars. Recently Gordon and Greenwood (1971) included a theoretical discussion of calc-silicate equilibria at a t o t a l pressure of 6000 bars (Figs. 12, 13). With P , .=6 kb. the Figure 12 . Schematic T - X C 0 2 diagram for the system CaO-AlgOj-SiC^-HgO-CO^. Abbreviations: An-anorthite; Ca-calctte; Co—corundum; Ge-aehlinite; Gr-grossularlte; Pr-prehnite; Q-quartz; Wo—wollastonite; Zo—zoisltt. adapted from .Gordon and Greenwood (1971). 'C02 800 700 o o O a. ® 600 500 An + Wo Figure 13 . 6r + Q relations in the Gr + An / \/O* S i 0 2 - H 2 0 - C 0 2 Zo + Q /ySS. ft \ See above r \ Rf=6 kbars adapted from Gordon and Greenwood (1971). i i i 0.2 0.4 0.6 XO2 55. above assemblages (with pure anorthite, grossular, and clinozoisite) are stable up to a maximum of 30 mole per cent C02 i n the f l u i d phase. Temperatures are within the range outlined for p e l i t i c schist assemblages. Plagioclase solid solution and Fe substitution i n diopside, zoisite, and epidote would affect the positions of these equilibrium curves (Kerrick, 1970). Fluids i n the p e l i t i c schists probably contained less C02 than fluids i n the calc-silicate layers. The anthophyllite-talc-olivine-magnesite assemblages i n the pyroxenite dike on the northeast side of Ridge A i s isobarically invariant (Fig. 14) i n the system Mg0-Si02-H20-C02 (Greenwood, 1967a). Theoretical and experimental calculations (Johannes, 1967, 1969: Greenwood, 1967a) at p t o t a l = 2 0 0 0 D a ? s indicate that f l u i d at this isobaric invariant point contains approximately 0.85 mole fraction C0 2 (Fig. 15). Shifting of the invariant point with increasing pressure may-be approximately delineated by examining the two reactions: talc + magnesite = forsterite (9) talc + forsterite = anthophyllite (10) Experimental work (Johannes, 1969: Greenwood, 1967a) indicates that reaction (9) i s sensitive to variations i n P^.Q^a]_ (Fig. 16). Thermodynamic calculations by Trommsdorff and Evans (1972) demonstrate that solid solution i n coexisting t a l c , anthophyllite, and olivine i n common ultramafites shift reaction (10) a maximum of -10°C for any given pressure. Assuming minimal Fe-substitution i n magnesite, similar small temperature shifts can be expected for reaction (9). Since the two reactions intersect at a f a i r l y high angle," solid solution w i l l not significantly shift the isobaric invariant intersection. 56. adapted from Johannes (1969) Figure 14. Schematic T—X CQ 2 diagram for the system Mg0-Si02-H20-C02 at elevated pressures and temperatures. Abbreviations: A—anthophyllite; B—brucite; E—enstatlte; F—forsterite; M—magnesite; P—periclase; Q—quartz; S—serpentine; T—talc. 57. T + M Pf=2000 bars — experimentally determined position estimated adapted from Johannes (1969) J I I l _ 600 o 550 o a. E a> 500 .7 .8 .9 mole fraction Xco5 1.0 Figure 15, Phase relations al high CO2 content in the T-X__ field. See fig 14V for CO2 abbreviations. The system is Mg0-Si02— H20-C02-700 u e £ 600 a. E 5 0 0 -400 -H 20 forsterite 7000 ban 4000 bars 2000 bars 1000 bars 500 bars talc + magnesite adapted from Johannes(l969) J I I ' .4 .9 C 0 2 mole fraction C 0 2 Figure 16. Isobaric equilibrium curves for reaction 9 4 forsterite + | H20 + 5C0 2 = ltalc + 5 magnesite. 600 -o o o 500 k_ a ,. . a. E e> 400 3 0 0 - / 200 HgO .1 7000 bars 2000 bars 1000 bars 330 bars quartz + magnesite adapted from Johannes (1969) I I I l .3 .5 .6 .7 -8 .9 mole fraction C0£ C02 Figure 17. Isobaric equilibrium curves for the reaction: I talc *• 3C0 2 = 4quartz + 3 magnesite + I H 2 0 . Using these considerations, Fig. 16 indicates a temperature of roughly 650° C for the pyroxenite dike assemblage with P - t o t a l ^ ^ ^ bars. This temperature i s consistent with temperatures delineated by experimental work pertaining to the surrounding p e l i t i c assemblages in the map-area. Alteration mineral assemblages along the Hope Fault place broad limits on conditions of hydrothermal activity within the fault zone. Ultramafites along the fault contain the assemblage antigorite-talc-chlorite-magnetite. Alteration assemblages from the ultramafites include dolomite-magnesite-quartz-fuchsite and talc-chlorite. Coexisting serpentine and talc indicate a temperature below 500° C with less than 0.1 mole fraction C0 2 i n the f l u i d phase (Greenwood, 1967a: Johannes, 1969). Different P.{.otal values do not radically alter the temperature-fluid composition relations (Fig. 18)(Johannes, 1969). The alteration assemblages can be formed at similar temperatures with increase of C02 content i n the fluids. The absence of ta l c -magnesite assemblages i n the fault zone indicates that temperatures were within the quartz-magnesite s t a b i l i t y f i e l d rather than the talc-magnesite f i e l d (see Fig. 14-). The reaction: talc = quartz + magnesite ( l l ) i s highly sensitive to total pressure variations (Johannes, 1969), but i t provides an upper temperature l i m i t of approximately 450° C for the assemblage quartz-magnesite at pressures less than 4 kb. (Fig. 17). The serpentine-talc association provides a lower tempera-ture l i m i t of roughly 300°C (Fig. 18) for the alteration assemblages. The occurrence of both serpentine and carbonate assemblages in the 0.15 500 JMoo a. I 300 200 1000 bars 0.05 0.10 XC02~^ ais adapted from Jonanntt (1969). Figure 18. Isobaric equilibrium curves at low CO2 content the T—XCO2 f i e , d f o r t n e system Mg0-Si02—H2O-CO2 See fig. 14 for abbreviations. 61. fault zone requires local variations in fluid phase composition. Pressure conditions are not readily ascertained from the various fault alteration assemblages. The absence of blueschist facies mineral and the presence of prehnite suggest a pressure less than 4 kb. Basaltic dikes in the Custer Gneiss contain the metamorphic assemblage actinolite-plagioclase-quartz-biotite which corresponds to the biotite zone of the greenschist facies as defined by Winkler (1967). Temperature-pressure conditions are the same as those for the hydrothermal mineral assemblages within the fault zone. It is uncertain whether the dike assemblage is related to the fault zone or represents a separate, late, low grade regional metamorphism. SUMMARY Deformation, emplacement of the Spuzzum Quartz Diorite, and metamorphism of the pelites a l l appear to be part of the same Late Cretaceous orogeny. Two deformation phases in the schists probably represent continued folding within the same period of deformation. Metamorphic growth of the different minerals was syn- to post-tectonic. Andalusite pseudomorphs near the Spuzzum Intrusions suggest an i n i t i a l low pressure environment during emplacement of the quartz diorite. Experiments and calculations have delineated the subsequent regional metamorphism as occurring at pressures between 5§-8 kb. (18-26 km.) and temperatures between 550-700°C. The implied pressure increase possibly results from rapid burial during metamorphism. The Spuzzum Intrusions would provide a ready heat source for regional metamorphism. The sillimanite zone is not located near a visible pluton, but Spuzzum lenses scattered through the schists suggest that intrusions are not far from the surface. 62. According to Lowes (1972) re g i o n a l metamorphism of the S e t t l e r S c h i s t was pre- mid-Cretaceous with l o c a l s i l l i m a n i t e upgrading "being a contact e f f e c t of the l a t e Cretaceous Spuzzum Int r u s i o n s . This i n t e r p r e t a t i o n i s based on c o r r e l a t i o n of f a u l t zones east of Harrison Lake with the mid-Cretaceous Shuksan Thrust F a u l t i n Washington. Not enough information i s presently a v a i l a b l e to incorporate these d i f f e r e n t time schemes i n the r e g i o n a l geologic h i s t o r y . B a s a l t i c dikes i n the Custer Gneiss suggest a low grade green-s c h i s t f a c i e s metamorphism. Exposures are too l i m i t e d to a s c e r t a i n whether these assemblages are of r e g i o n a l extent or r e l a t e d to hydrothermal a c t i v i t y along the Hope Fault zone. 1. General view of the map-area looking south. Low ridge east of power l i n e consists of Custer Gneiss. S e t t l e r Schist underlies the central v a l l e y and western slope. 2. Ba s a l t i c dike i n Custer Gneiss. Photograph was taken looking across at a steep c l i f f face. The dike i s estimated at being about 10 feet t h i c k . 3. Unit I I : S e t t l e r Schist i n the s t a u r o l i t e zone. Note the numerous pegmatitic quartz s t r i n g e r s . Hammer i s 28 cm. long. 4. Metaconglomerate containing g r a n i t i c pebbles forms lexises within Unit I I : S e t t l e r Schist. 5. Streaky, discontinuous compositional layering i n Unit I I I : S e t t l e r S chist. Dark layers contain abundant kyanite and s t a u r o l i t e which are absent from lig h t - c o l o r e d l a y e r s . Pencil i s 15 cm. long. 6. Convoluted quartzite bands i n micaceous matrix; t h i s " r o l l e d " pattern i s the t y p i c a l appearance of Unit IV: S e t t l e r S c hist. 7. I s o c l i n a l , asymmetric phase 1 f o l d o u t l i n e d by c a l c - s i l i c a t e lens within Unit I: S e t t l e r S c h i s t . 8. Phase 1 f o l d s o u t l i n e d by quartz s t r i n g e r s and compositional l a y e r i n g i n Unit I I : S e t t l e r S c h i s t . 9. Load cast structures i n Unit I I I : S e t t l e r S c h i s t . P e n c i l delineates surface trace of phase 1 f o l i a t i o n . S t r a t i g r a p h i c top i s upward. Numbers on f i e l d book i n d i c a t e tenths of f e e t . 10. Graded bedding i n Unit I I I : S e t t l e r S c h i s t . S t r a t i g r a p h i c top i s upward; kyanite and s t a u r o l i t e are more abundant i n upper p e l i t i c p o r t i o n of each graded bed. P e n c i l delineates surface trace of phase 1 f o l i a t i o n . 11. P l a g i o c l a s e a p l i t e dike i n Unit I I I : S e t t l e r S c h i s t . 12. White, metasomatic rims surrounding quartz-plagioclase veins • i n b i o t i t e - s t r e a k e d meta-intrusion. 64a 13. Cross-cutting chlorite laths (center) in Unit I: Settler Schist. Graded bedding i s noticeable i n the photograph. Scale - 0.5 mm. 1-4. Inclusion patterns i n garnets of Unit I I : Settler Schist. Scale - 0.5 mm. 15. Concentric inclusions i n staurolite for Unit I I : Settler Schist. Scale - 0.5 mm. 16. Staurolite enclosing idioblastic garnet i n Unit I I : Settler Schist. Note that enveloped garnets retain concentric inclusion patterns. Scale - 0.5 mm. 17. Ragged staurolite "fingers" extend into retrograde muscovite-chlorite aggregates. Unit I I : Settler Schist. Scale 0.5 mm. 18. Staurolite porphyroblast extending into pseudomorph after andalusite (clear area). Unit I I : Settler Schist. . Scale -0.5 mm. 19. Late muscovite cross-cuts biotite in Unit III: Settler Schist. Scale -0.5 mm. 20. Typical garnet (center) - staurolite (lower center) - kyanite (center) - biotite-muscovite-quartz-plagioclase assemblage in Unit III: Settler Schist. Scale - 0.5 mm. 21. Concentric zoning in garnets in Unit III: Settler Schist. Scale - 0.5 mm. 22. Kyanite partially enclosing garnet in Unit III: Settler Schist. Pale rim around kyanite is sericite. Scale - 0.5 mm. 23. Fibrolite-biotite knots surrounding garnets in sillimanite zone. Unit III: Settler Schist. Scale - 0.5 mm. 24. Fibrolite-biotite sheath enclosing garnet in sillimanite zone. Unit III: Settler Schist. Scale - 0.1 mm. 6 6 a 67. SELECTED REFERENCES Albee, A.L., 1962. Relationships between the mineral association, chemical composition, and physical properties of the c h l o r i t e series. Amer. Mineral., 47, 851-870. Albee, A.L., and Chodos, A.A., 1969. Minor element content of coexistent AlgSiO^ polymorphs. Amer. J. S c i . , 267, 310-316. Bancroft, G.M., Maddock, A.G., and Burns, R.G., 1967. Applications of the MSssbauer effect to s i l i c a t e mineralogy-I. Iron s i l i c a t e s of known c r y s t a l structure. Geochim. Cosmoschim. Acta, 31, 2219-2246. Bauermann, H., 1886. Report on the geology of the country near the forty-ninth p a r a l l e l of north l a t i t u d e west of Rocky Mountains. Geol. Surv. Can., Rept. Prog. 1882-3-4, 1B-42B. Bowen, N.L., 1914. A geological reconnaissance of the Fraser River Valley from Lytton to Vancouver, B r i t i s h Columbia. Geol. Surv. Can., Sum. Rept. 1912, 108-114. Bremner, T., M.Sc. thesis i n progress. Geology of the Fraser Canyon between Yale and Spuzzum, B r i t i s h Columbia. Univ. B r i t . Columbia. Burnham, C.W., Holloway, J.R., and Davis, N.F., 1969. Thermodynamic properties of water to 1000°C and 10,000 bars. Geol. Soc. Amer. Spec. Paper 132, 96p. Cairnes; C.E., 1944. Hope area. Geol. Surv. Can. Map 737A. Cameron, B.E.B., and Monger, J.W.H., 1971. Middle T r i a s s i c conodonts from the Fergusson Group, northeastern Pemberton map-area (92J), B r i t i s h Columbia. Geol. Surv. Can. Paper 71-1B, 94-96. Camsell, C , 1912. Fraser Canyon and v i c i n i t y . Geol. Surv. Can., Sum. Rept. 1911, 108-111. Carmichael, D.M., 1969. On the mechanism of prograde metamorphic reactions i n quartz-bearing p e l i t i c rocks. Contr. Mineral, and P e t r o l . , 20, 244-267. Chakraborty, K.R., and Sen, S.K., 1967. Regional metamorphism around Kandra, Singhbhum, Bihar. Contr. Mineral, and P e t r o l . , 16, 210-232. Chinner, G.A., 1966. The significance of the aluminum s i l i c a t e s i n metamorphism. Earth S c i . Rev., 2, 111-126. 68. Chinner, G.A., Smith, J.V., and Knowles, C.R., 1969. Transition metal contents of AlpSiCv polymorphs. Amer. J. Sci., 267-A, 96-113. Crickmay, C.H., 1930. The structural connection between the Coast Range of Brit i s h Columbia and the Cascade Range of Washington. Geol. Mag., 67, 4-82-491. Daly, R.A., 1912. Geology of the North American Cordillera at the 49th parallel. Geol. Surv. Can. Mem. 38, 840p. Dawson, G.M., 1879. Preliminary report on the physical and geolo-gical features of'the southern portion of the interior of Br i t i s h Columbia. Geol. Surv. Can., rept. Prog. 1877-8, 1B-186B. Eugster, H., and Wones, D., 1962. Stability Relations of the Ferruginous Biotite, Annite. J. Petrology, 3, 82-125. Evans, B.W., 1965. Application of a reaction-rate method to the breakdown equilibria of muscovite and muscovite plus quartz. Amer. J. Sci., 263, 647-667. Gordon, T.M., and Greenwood, H.J., 1971. The s t a b i l i t y of grossu-l a r i t e i n R2O-CO2 mixtures. Amer. Mineral., 56, 1674-1688. Greenwood, H.J., 1961. The system NaAlSipOk-H^O-argon: total pressure and water pressure i n metamorunism. J. Geophys. Res., 66, 3923-3946. , 1963. The synthesis and s t a b i l i t y of anthophyllite. . J. Petrol., 4, 317-351. , 1967a. Mineral equilibria in the system Mg0-Si0p-H20-C02. IN P.H. Abelson (ed.), Researches i n Geochemistry, 2. John Wiley & Sons, New York. 542-567. , 1967b. The n-dimensional t i e - l i n e problem. Geochim. Cosmochim. Acta, 31, 465-490. , 1968. Matrix methods and the phase rule i n petrology. XXIII Inter. Geol. Congr. (Prague), 6, 267-279. , 1971. Anthophyllite, corrections and comments on i t s s t a b i l i t y . Amer. J. Sci., 270, 151-154. Henderson, F.B., I I I , 1969. Hydrothermal alteration and ore deposition i n serpentinite-type mercury deposits. Econ. Geol., 64, 489-499. Holland, S.S., 1964. Landforms of B r i t i s h Columbia a physiographic outline. B.C. Dept. Mines Petrol. Resources Bull. 48, 138p. Hollister, L.S., 1969a. Contact metamorphism i n the Kwoiek area of B r i t i s h Columbia: an end member of the metamorphic process. Geol. Soc. Amer. Bull., 80, 2465-2494. 69. , 1969b. Metastable paragenetic sequence of andalusite, kyanite, and sillimanite, Kwoiek area, British Columbia. Amer. J. Sci., 267, 352-370. , 1970. Origin, mechanism, and consequences of compositional sector-zoning in staurolite. Amer. Mineral, 55, 742-766. Horwood, H.C., 1936. South part Fraser River-Harrison Lake region, British Columbia. Geol. Surv. Can. Paper 36-4, 1-8. Hoschek, G., 1967. Untersuchungen zum stabilitatsbereich von chloritoid und staurolith. Contr. Mineral, and Petrol., 14, 123-162. , 1969. The stability of staurolite and chloritoid and their significance in metamorphism of pelitic rocks. Contr. Mineral, and Petrol., 22, 208-232. Johannes, W., 1967. Zur bildung und stabilitat von forsterit, talk, serpentin, quartz, und magnesit im system Mg0-Si02~H20-CO2: Beitr. Mineralogie und Petrologie, 15, 233-250. Johannes, W., 1969. An experimental investigation of the system MgO-SiO^IL^O-CO^ Amer. J. Sci., 267, 1083-1104. Kerrick, D.M., 1970. Contact metamorphism in some areas of the Sierra Nevada, California. Geol. Soc. Amer. Bull., 81, 2913-2938. Kwak. T.A.P., 1971. Compositions of natural sillimanites from volcanic inclusions and metamorphic rocks. Amer. Mineral., 56, 1750-1759. Lowes, B.E., 1967. Chilliwack Group, Harrison Lake area. Geol. Surv. Can. Paper 67-1, 74A-75A. , 1968. Chilliwack Group-Harrison Lake area, British Columbia. Geol. Surv. Can. Paper 68-1, 33A. Lowes, B.E., 1972. Metamorphic Petrology and Structural Geology of the area east of Harrison Lake, British Columbia. Ph.D. thesis. U. Washington, Seattle, I6lp. McTaggart, K.C., 1970. Tectonic history of the Northern Cascade Mountains. IN J.0. Wheeler (ed.), Structure of the southern Canadian Cordillera. Geol. Assoc. Can. Spec. Paper, 6, 137-148. McTaggart, D.C, and Thompson, R.M., 1967. Geology of part of the Northern Cascades in southern British Columbia. Can. J. Earth Sci., 4, 1199-1228. Misch, P., 1966. Tectonic evolution of the Northern Cascades of Washington state. IN Tectonic history and mineral deposits of the western Cordillera. Can. Inst. Mining Metall. Spec. Vol., 8, 101-148. 70. Monger, J.W.H., 1970. Hope map-area, west-half Brit i s h Columbia. Geol. Surv. Can. Paper 69-47, 75p. ' Orville, P.M., 1969. A model for metamorphic differentiation origin of thin-layered amphibolites. Amer. J. Sci., 267, 64-86. Read, P.B., 1960a. Geology of the Fraser Valley between Hope and Emory Creek, British Columbia. Unpublished M.Sc. thesis, Univ. of Br i t . Columbia, 14 5p. , 1960b. Geology of the Fraser Valley from Hope to Emory Creek, Brit i s h Columbia (abstr.). Geol. Soc. Amer. Bu l l . , 71, 2072. Reamsbottom, S., 1971. The geology of the Mount Breakenridge area, Harrison Lake, B.C. Unpublished M.Sc. thesis, Univ. of Br i t . Columbia, l6lp. Richards, T., 1971. Plutonic rocks between Hope, B.C. and the 49th parallel. Unpublished Ph.D. thesis, Univ. of Brit . Columbia, 178p. Richardson, S.W., 1968. Staurolite s t a b i l i t y i n .a part of the system Fe-Al-Si-0-H. J. Petrol., 9, 467-488. Richardson, S.W., Gilbert, M.C, and B e l l , P.M., 1969. Experimental determination of kyanite-andalusite and andalusite-sillimanite equilibria; the aluminum s i l i c a t e t r i p l e point. Amer. J. Sci., 267, 259-272. Roddick, J.A., and Hutchison, W.W., 1969. Northwestern part of Hope map area, Brit i s h Columbia. Geol. Surv. Can. Paper 69-1, 29A-38A. Rucklidge, J., and Gasparrini, ., 1969. Specification of computer program for processing electron microprobe analytical data. EMPADR VII.'' Dept. Geol., Univ. of Toronto, Toronto, Ontario. Selwyn, A., 1872. Journal and report of preliminary explorations in B r i t i s h Columbia. Geol. Surv. Can., Rept. Prog. 1871-72, 16-72. Smith, J.V., 1968. The crystal structure of staurolite. Amer. Mineral., 53, 1139-1155. Smith, J.V., 1965. X-ray-emission microanalysis of rock-forming minerals I. experimental techniques. J. Geol., 73, 830-864. Thompson, J.B., Jr., 1957. The graphical analysis of mineral assemblages i n p e l i t i c schists. Amer. Mineral., 42, 842-858. Trommsdorff, V., and Evans, B.W., 1972. Progressive metamorphism of antigorite schists i n the Gergell Tonalite Aurole (Italy). Amer. J. Sci., 272, 423-437. Vidale, R.M., 1969. Calc-silicate "bands and metasomatism i n a chemical gradient. Amer. J. Sci., 267, 857-874-. Winkler, H.G.F., 1967. Petrogenesis of metamorphic rocks, 2. Springer-Verlag New York, Inc., New York, 237p. Zen, E-An, 1963. Components, phases, and c r i t e r i a of chemical equilibrium i n rocks. Amer. J. Sci., 261, 929-942. , 1971. Comments on the thermodynamic constants and hydrothermal s t a b i l i t y relations of anthophyllite. Amer. J. Sci., 270, 136-150. 72. APPENDIX I Mineral analyses were completed using a f i v e channel ARL e l e c t r o n microprobe at the U n i v e r s i t y of Washington, S e a t t l e . A l l elements were analyzed using constant beam current with a 15 Kv. ac c e l e r a t i o n p o t e n t i a l and a specimen current set between 0.05 and 0.15 microamps. The beam diameter was approximately f i v e microns except when a l a r g e r beam was necessary to avoid damaging the sample. Analyzed synthetic and n a t u r a l minerals from the U n i v e r s i t y of Washington c o l l e c t i o n were used as standards. Whenever pos s i b l e the mean atomic numbers of the standards were roughly equivalent to those of the unknowns. A l l readings were corrected f o r d r i f t , dead time, and background. Garnet, c h l o r i t e , b i o t i t e , and p l a g i o c l a s e analyses were computed using a l e a s t squares l i n e a r regression working curve f i t to the standards. For s t a u r o l i t e and muscovite, corrections were considered to be l a r g e , and procedures developed by Rucklidge i n the computer program EMPADR VII (Rucklidge and G a s p a r r i n i , 1969) were used. For each mineral i n a s l i d e , several grains were analyzed with repeated counts on each g r a i n . The d i f f e r e n t minerals were i n v e s t i -gated i n close c l u s t e r s to take i n t o account po s s i b l e l o c a l e q u i l i b r i u m e f f e c t s . D i f f e r e n t c l u s t e r s i n the same s l i d e were compared as a check on a r i l y t i c a l techniques and degree of l o c a l e q u i l i b r i u m . 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 with the microprobe. In a l l minerals i r o n was computed as FeO. •Except f o r s t a u r o l i t e , t h e o r e t i c a l values were used f o r water content. With s t a u r o l i t e water content was cal c u l a t e d by subtraction of the oxide t o t a l from 100 per cent. The following section b r i e f l y discusses analyses f o r each mineral. 73. Staurolite: Staurolite porphyroblasts were traversed i n different directions to check for possible radial or sectoral zoning. Like many staurolites i n regionally metamorphosed rocks, the crystals were homogeneous (Hollister, 1970). Staurolites from Units II and III have different Zn contents, but the Fe/(Fe+Mg) fraction i s the same within error lim i t s . Reporting total iron as FeO i s consistent with Mossbauer studies (Bancroft, Maddock, and Burns, 1967). Structural formulae based on 48(0,OH) are i n agreement with the latest available structural information (Smith, 1968). Garnet: Traverses across garnet porphyroblasts i n different directions reveal strong concentric zoning i n Mn, Fe, Ca, and Mg. Mn and Ca increase toward the center of a porphyroblast, and Fe and Mg concen-trations increase toward crystal margins. The major variation i s i n Mn and Fe concentrations. Ti i s sporadically distributed but tends to become more concentrated inward from crystal margins. Percentages of end members were determined using a least squares linear regression f i t . In most specimens andradite occurs i n negligible amounts. Ferric iron content i s computed by assuming a total octahedral occupancy of 4.0 cations. Biotite: Biotite compositions are uniform within a single slide. A theoretical four per cent water brings the oxide totals close to 100$. The high oxide totals and light brown pleochroism suggest a minimal amount of f e r r i c i r o n i n the b i o t i t e s t r u c t u r e . S t r u c t u r a l formulae are c a l c u l a t e d on the bas i s of 22 oxygen atoms with te t r a h e d r a l s i t e s being completely f i l l e d by S i and A l . T i content v a r i e s considerably due to numerous small opaque dust i n c l u s i o n s . Octahedral and i n t e r l a y e r cation s i t e s are incom-p l e t e l y f i l l e d . Muscovite: Muscovite compositions are uniform within each t h i n s e c t i o n . A d d i t i o n of a t h e o r e t i c a l 4.5 weight per cent water brings the oxide t o t a l s close to 100$. F e r r i c i r o n content i s low because of the low amount of t o t a l i r o n present. S i and A l are assumed to completely f i l l the t e t r a h e d r a l s i t e s i n the s t r u c t u r a l formula based on 22 oxygen atoms. Muscovite can be described i n terms of the two s e r i e s muscovite-paragonite and muscovite-phengite. Percentages of end members fo r ' these serie s have been determined i n the following manner: paragonite = (Na/(Na + K))l00 phengite = ((Fe + Mg)/1.0)100 muscovite = (K/(Na + K))l00 - phengite $. The amount of Ca present i n the i n t e r l a y e r s i t e i s n e g l i g i b l e . The most obvious change i n composition i s the lower paragonite content f o r muscovites i n Unit I I I as compared to Unit I I . C h l o r i t e : Analyses c o n s i s t e n t l y t o t a l l e s s than 100$ ( 99$) even a f t e r adding the t h e o r e t i c a l l y necessary 11.5 weight per cent water. The low t o t a l s may be r e l a t e d p a r t l y to problems with sample preparation and p a r t l y to assuming a l l i r o n i s i n the ferrous s t a t e . Formulae 75. are calculated on the basis of 28 oxygens (anhydrous) with Si and A l completely f i l l i n g the tetrahedral sites. Chlorites i n fractures i n staurolite porphyroblasts have higher Fe content and lower Mg content than chlorites in the matrix. This unequal distribution suggests local equilibrium with the surrounding cluster of grains and contrasts with the more uniform compositions of garnet and staurolite. Plagioclase: Plagioclase i s fine-grained and untwinned, making probe investi-gation of the feldspars essential. Analyses represent the average of a l l analyzed grains i n each thin section. Formulae are calculated on the basis of 32 oxygens with an ideal occupancy of 16 and 4 for Z and X respectively. Compositions range between andesine and oligoclase. 76. Tabla 3 Staurolite Analyses Specimen Stratigraphic Unit 3-A FeO* KgO KnO ZnO Si Al Ti II 28.1 0.66 54.3 13.8 1.6 0.06 0.29 2.0 7.8 17.9 0.1 Hxi+Ti 18.0 P« 3.2 Kg 0.6 Kn t r Zn 0.1 ^JefMg+Mn+Zn j - 0 OH 2.4 I I 27.9 0.68 53.8 13.9 1.6 0.06 0.28 1.8 7.8 17.7 0.1 17.8 3.2 0.7 t r 0.1 4.0 3.2 II II 27.8 28.0 0.71 0.70 53.9 53.5 13.8 13.9 1.5 1.5 0.07 0.07 0.33 0.32 1.9 2.0 formulae on 7.7 ' 7.8 17.7 17.5 0.2 0.2 17.9 17.7 3.2 3.2 0.6 0.6 t r t r 0.1 0.1 3.9 3.9 3.6 3.9 II 3-B II 27.7 27.6 0.70 0.66 54.8 54.1 13.8 1.2 0.09 0.09 0.23 0.24 1.5 4-A III 27.9 0.70 53.3 13.6 13.3 1.3 1.4 0.10 1.29 2.0 2.4 the basis of 48(0, OH) 7.7 7.6 18.0 17.6 0.2 0.1 18.2 17.7 3.2 3.1 0.5 t r t r 3-7 2.9 0.5 t r t r 3.6 4.7 7.8 17.5 0.2 17.7 3.1 0.6 t r 0.3 4.0 3.6 4-B 5-A III III 27.8 27.6 0.64 0.75 53.2 54.5 12.9 13.4 1.5 1.4 0.08 0.12 1.25 0.43 2.6 7.7 17.4 0.1 17.5 3-0 0.6 t r 0.3 3.9 4.6 1.8 7.7 17.9 0.2 16.1 3.1 0.6 t r 0.1 3.8 3.5 5-B 6-A 6-B III III III 26.8 26.9 27.6 0.76 0.72 0.68 55.2 53.9 5*.0 13.5 13.2 13.6 1.4 1.3 1.4 0.13 0.06 0.08 0.46 0.70 0.73 1.7 3.2 1.9 7.5 7.4 7.7 18.1 17.5 17.7 0.2 0.2 0.1 18.3 17.7 17.8 3.2 3.0 3.2 0.6 0.5 0.6 t r t r t r 0.1 0.1 0.2 3.9 3.6 4.0 3.3 J-9 3.7 Fe/(Pe • Mg) 0.83 O.83 0.84 0.84 0.87 0.85 0.84 0.83 0.85 0.85 0.86 0.85 PeO» - total iron as PeO H20 calculated to make oxide total equal 100£ analyst - L.C. Pigage tr - tracei less than 0.05 77. Specimen S t r a t i g r a p h i c U n i t FeO» KgO KnO CaO Z Table * Garnet Analyses I I 1-B I I 2-A I I I I I I 3-A I I 3-B I I 4-B I I I 4-C I I I 5-A I I I 5-B 6-A I I I I I I 37.6 37.* 37.7 37.2 36.3 36.0 36.5 37.7 37.6 37.2 37.4 37.3 0.03 0.03 0.01 0.02 0.02 0.02 0.02 0.01 0.02 0,01 0.01 21.8 21.7 21.6 21.6 20.8 20.4 20.5 21.5 21.5 21.0 33.7 33.7 32.6 32.3 3.* 3.* 3.1 3.2 1.5 1.3 1.2 1.6 3.1 3.1 4.8 4.8 31.9 3.2 0.9 4.6 32.0 33.3 3-2 3.0 1.0 4.8 1.1 3.7 33-4 3.2 1.2 3.* 1CO.0 100.1 100.4 100.0 33.9 3.* 1.4 3.0 98.8 21.4 21.6 34.0 33.7 33.1 3.3 2.1 2.4 3.2 2.0 2.2 3.3 1.2 2.5 6-B I I I 37.6 21.9 34.0 3.2 1.3 2.5 98.1 98.5 100.9 101.0 99.6 100.3 99.0 100.5 formulae on the b a s i s o f 24 oxygens 6.0 6.0 t r 6.0 6.0 4.0 4.1 t r 4.0 4.1 S i 6.0 6.0 6.0 6.0 5.9 5.9 6.0 6.0 6.0 6.0 A 1I V t r t r t r t r 0.1 0.1 t r t r t r -z 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 A 1V I 4.1 4.0 4.0 4.0 3.9 3.9 3.9 4.0 4.0 4.0 - - - - q . l 0.1 0.1 t r t r t r T i t r t r t r t r t r t r t r t r t r t r z 4.1 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.1 7-A 7-B I I I I I I 37.5 37.3 0.01 22.7 21.8 33.6 33.5 3.5 3.5 2.0 2.0 2.3 2.3 101.6 100.4 6.0 5.9 5.9 t r 0.1 0.1 6.0 6.0 6.0 4.1 t r 4.1 molecular per cent end members 4.0 4.0 r e2* 4.2 4.3 4.4 4.5 4.5 4.6 4.5 4.3 4.2 4.6 4.5 4.5 4.5 4.4 4.5 Kg 0.8 0.8 0.7 o.e 0.8 0.8 0.8 0.7 0.8 0.8 0.8 0.8 0.7 0.8 o.e Kn 0.1 0.1 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.2 0.2 0.3 0.3 Ca 0.8 0.8 0.6 0.6 0.5 0.6 0.5 0.8 0.8 0.4 0.4 0.4 0.4 0.4 0.4 z 5.9 6.0 5.9 6.1 6.0 6.2 6.0 6.0 6.0 6.1 6.0 5.9 5.8 5.9 6.0 Almandine 71.1 71.1 74.1 74.6 76.2 76.4 76.1 71.9 71.0 76.5 75.2 74.9 75.8 74.1 74.5 Andradite - - - - - 0.6 0.7 - - - - - - - -G r o s s u l a r 13.5 13.7 10.9 9.8 8.1 7.6 7.8 13.3 13." 6.3 6.8 7.8 7.7 7.0 6.7 Pyrope 12.9 12.8 12.3 12.9 13.1 12.9 13.0 12.2 12.2 12.8 13.2 13.9 13.1 14.0 14.1 Spessartine 2.5 2.4 2.7 2.7 2.6 2.5 2.4 2.6 3.4 4.4 4.8 3.4 3.4 4.9 4.7 1 + Kg) o .es 0.85 0.86 0.85 0.85 0.85 0.85 O.85 0.85 0.86 0.85 0.85 0.86 0.84 0.84 ag a m e t €nclo=«d In F t a u r o l i t e FeO* - t o t a l i r o n as PeO a n a l y s t - L.C. Pigage t r - t r a c e 1 l e s s than 0.05 78. TabU 5 BiotitB analyses Speciiren 1 2 3 4 5 6 7 Stratigraphic Unit II II II III III III III S i 0 2 39.5 39.4 39.1 39.4 38.2 38.8 39.4 T i 0 2 1.7 1.8 1.8 1.8 2.0 2.1 2.2 18.7 19.0 19.0 19.0 18.9 18.9 18.9 FeO» 16.4 16.8 17.2 16.7 17.5 17.0 17.5 KgO 11.2 10.7 10.3 10.9 9.9 10.0 10.0 KnO 0.03 0.03 0.03 0.04 0.05 0.03 0.06 Na20 0.23 0.24 0.23 0.21 0.26 0.22 0.26 K 20 8.1 8.4 8.7 8.4 8.8 . 8.8 8.7 z 95.9 96.4 96.4 96.4 95.6 95.8 97.0 • 4jt H20 99.9 100.4 100.4 100.4 99.6 99.8 101.0 formulae on the bas ie of 22 oxygens Si 5.8 5.8 5.7 5.8 5.7 5.7 5.8 A1 I ¥ 2.2 2.2 2.3 2.2 2.3 2.3 2.2 A1 V 1 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Ti 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Fe 2.0 2.0 2.1 2.0 2.2 2.1 2.1 Kg 2.4 2.3 2.2 2.4 2.2 2.2 2.2 Kn t r t r t r t r t r t r t r z 5.6 5.5 5.5 5.6 5.6 5.5 5.5 Na 0.1 0.1 0.1 0.1 0.1 0.1 0.1 K 1.5 1.6 1.6 1.6 1.7 1.7 1.6 z 1.6 1.7 1.7 1.7 1.8 1.8 1.7 Fe/(Fe + Kg) 0.45 0.47 0.48 0.46 0.50 0.49 0.50 Pe0 # - total iron as FaO analyst - L.C. Pigage tr - trace 1 lest* than 0.05 Table 6 Muscovite Analyses 79. Specimen 1 2 3 4 5 6 7 Stratigraphic Unit II II II III III III III sio 2 06.2 45.8 45.4 45.8 46.0 45.3 45.8 i i o 2 0.62 0.48 0.31 0.69 0.64 0.76 0.66 A1 20 3 35.8 36.0 36.2 35.5 36.3 35-8 36.5 FeO* 1.0 1.2 1.2 1.2 1.2 1.2 1.0 HgO 0.23 0.20 0.17 0.25 0.20 0.22 0.19 KnO 0.01 - 0.01 0.01 - - 0.01 CaO 0.05 0.04 0.02 0.04 0.02 0.04 0.02 Na20 1.6 1.6 1.6 1.3 1.3 1.2 1.2 K20 8.7 8.7 8.9 9.2 8.8 9.3 9.4 Z 94.2 94.0 93.8 94.0 94.5 93.8 . 94.8 * 4.5* H20 98.7 98.5 98.3 98.5 99.0 98.3 99.3 formulae on the basie of 22 oxygens Si 6.2 6.1 6.1 6.2 6.1 6.1 6.1 A1 I V 1.8 1.9 1.9 1.8 1 1.9 1.9 1.9 A l " 3.8 3.8 3.8 3.8 3.8 3.8 3.8 T i 0.1 t r t r 0.1 0.1 0.1 0.1 Fe 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Kg t r t r t r t r t r t r t r Kn t r - t r t r - - t r z 4.0 3.9 3.9 4.0 4.0 4.0 4.0 Ca t r t r t r t r t r t r t r Na 0.4 0.4 0.4 0.3 0.3 0.3 0.3 K 1.5 1.5 1.5 1.6 1.5 1.6 1.6 z 1.9 1.9 1.9 1.9 1.8 1.9 1.9 molecular per cent end members Muscovite 63 61 62 64 65 67 68 Faragonite 22 22 21 17 18 16 16 Phengite 15 17 17 19 17 17 16 tr - tracet less than 0.05 FeO* - total iron as FeO analyst - L.C. Pigage 8 0 . Table 7 C h l o r i t e Analyses Specimen 1-A 1-8 2-C 3-C- 3-C 0-C S t r a t i g r a p h i c Unit I I 11 I I I I I I I I I s i o 2 26.1 26.3 26.0 25.1 25.9 26.1 T i 0 2 0.06 0.08 0.06 0.07 0.07 0.10 A1 20 3 20.1 20.2 20.8 20.5 20.5 20.3 PeO* 21.0 20.6 21.2 25.6 23.9 21.6 MgO 19.1 19.1 18.6 10.0 16.7 18.7 KnO ' 0.02 0,02 0.03 0.06 0.06 0.05 CaO 0.00 0.02 0.03 0.01 0.01 0.00 Na20 • 0.05 0.00 0.01 0.01 -K20 0.02 0.00 0.15 0.03 0.03 0.02 z 86.lt 86.0 87 .3 85.8 87.1 66.9 • 11.5* H20 97.9 97.9 98.8 97:3 98.6 98.0 formulae on the b a s i s of 26 Oxygens S i 5-5 5.5 5.5 5.0 5.0 5.0 A l " 2.5 2.5 2.5 2.6 2.6 2.6 A 1V I 2.0 2.5 2.5 2.6 2.5 2.0 T i t r t r t r t r t r t r Fe 3.7 3.6 3.7 0.6 0.2 3.8 Kg 5.9 5.9 5.7 0.6 5.2 5.8 Hn t r t r t r t r t r t r Ca t r t r t r t r t r t r 14a - t r t r t r t r -K t r t r t r t r t r t r z 12.0 12.0 11.9 11.8 11.9 12.0 i n s t a u r o l i t e f r a c t u r e FeO* - t o t a l i r o n as FeO an a l y s t - L.C. Pigage t r - t r a c e i l e s s than 0.05 81. Table 8 P l a g i o c l a s e Analyses Specimen 1 2 3 4 5 6 7 S t r a t i g r a p h i c U n i t I I I I I I I I I I I I I I I I I I s i o 2 60.2 61.0 61.6 59.2 61.2 .59.0 60.0 A 1 2 0 3 25.5 25.2 24.8 25.7 24.8 25.9 26.0 CaO 6.6 6.2 5.8 6.9 6.0 6.9 7.1 Ha 20 7.8 8.0 8.3 7.5 8.0 7.5 7.6 z 100.1 100.4 100.5 99.3 100.0 99.3 100.7 formulae on the b a s i s of 32 oxygens S i 10.7 10.8 10.9 10.6 10.8 10.6 10.6 A l 5.3 5.2 5.2 5.4 5-2 5.5 5.5 Ca 1.3 1.2 1.1 1.3 1.1 1.3 1.4 Na 2.7 2.8 2.8 2.6 2.8 2.6 2.6 Z 16.0 16.0 16.1 16.0 16.0 16.1 16.1 X 4.0 4.0 3.9 3.9 3-9 3.9 4.0 molecular per cent end members A l b i t e 68 70 72 66 71 66 66 A n o r t h i t e 32 30 28 34 29 34 34 a n a l y s t - L.C. Plgage 82. APPENDIX II Displacement of Hydrothermal Equilibrium by Solid Solution Consider the general reaction: Solid reactants —^ Solid products + m HgO (12) AG_ = AG + AG „ n R s HgO = AGg + m GjHgO (13) at T, P of interest. Considering only isothermal changes i n pressure and ac t i v i t i e s of solids, d(AGR) = f 3AGR^ d p + f 3AGR ^ ^ + / 3AGR \ d ^ + _ 3P / \ '31n \ 31n ^ 3 A GR\ dP + E / 3 A GR \ d l n a. (14) V 3P / i \ 31n a / . l with the summation occurring over a l l i solid phases. Substituting the relation / 3AG \ = AV into expression (13), \ 3P/ (^1) - W , * *\o (15). 3P 3 AG Now consider R for any given phase i . 31n a. i G. = G. + RT In a. (16) i i i Small changes i n the activity a^ of a phase i affect only the G for that particular phase. Consequently: 3AGn / 3G. R = n. /. l l 31n a. V 3In a./ I \ I 83. Differentiating expression (16) with respect to In a. (17) Integrating (14) using the different substitutions: P2 AGR = AV^P^) + m f + R T E (m a. , - in a. , ) j rLjO ^ I 1,2 1,1 Since the reaction continues to be at equilibrium, AGD = 0 it 0 = AV s(P 2- P l) + m(G H 2^ p 2 - G^Q^) + RT E n.(ln a.^ 2 - In a.^) If i n i t i a l l y a^ = 1, then: 0 = AV s(P 2- P l) + m(G - G ) + RT E n. In a 2 2 2 ' 1 i ' Or, using fugacities: 0 = AV (P~-P, ) + mRT(ln f p - ln f p ) + RT I n. In a. 0 (l8) s *w A. 2 1 i "^ y The reaction studied experimentally by Richardson (1968) 6 Fe^Al l 8Si 7 50^(0H) 4 + 25Si02 = SFey^Si^O.^ + 46Al 2Si0 5 + 12H20 Fe-staurolite Quartz Almandine Sillimanite 84. can be rewritten to correspond to a single-site replacement model assuming ideal mixing according to Raoult's Law in staurolite and garnet. 24 Fe A l l 8 S i ? 5 0 U (OH) + 25 Si0 2 4 4 - ( 1 9) 24Fe A l 2 SiO^ + 46 Al 2Si0 5 + 12 H20 3 Pertinent data for this equation are: AV g = +31.37 cal bar" 1 aFe-ST ( U n i t 1 1 1 ^ = 0 , 8 4 aALM ( U n i t 1 1 1 ) = ° ' 7 5 R =1.987 cal deg"1 mol"1 The experimental curve passes through the points 1. 5000 BARS 687°C 2. 8000 BARS 695°C Approximate fugacity coefficients for H20 at these two points are 1. T ^ 0.73 2. T ^ 1.1 Burnham, Holloway & Davis (1969) Solving equation (18) for P2, 1. P 2 = 4840 bars AP = -160 bars 2. P 2 = 7830 bars AP = -170 bars OJ u OJ to +* OJ a +> OJ rt G •H +> OJ (X •H +» rH 0J 0) rH •H OJ OJ +> 10 -r 1 •H CO o -4-> B O rH +> +> •H T3 > OJ o •H o> c •H O •H •H u iH O O •H c +» c o O •H E -H o OJ E o W) xi u 0J o OJ +> Q> rt o rH «M P» rt rt 0J rt XI u p. O U P. •H 1 rH (X •H EH <«: PQ o o or CO tSJ ^ 7 - - - 1 - t r - - t r 6 5 - 3 4 - t r 5 9 * 3 6 - t r 4 - - - - • 5 5 5 + t r t r t r -6 4 - - • - - t r t r - t r - 3 0 + - 7 0 - -E* 3 5 1 - 2 - - - - 7 5 0 - 5 t r -F - - t r t r t r 1 - - 6 4 - 3 5 - t r • b a s a l t i c dike a l b i t e Table 9 . V i s u a l l y estimated modal analyses-Ouster Gneiss. •fr -fr *oJ t-» l-» M ro t-* CO vO vO ~o O t\> NO -\J f\) ON cf cf cf I cf H K N H U N CO O o o c f c+ *"t \j) \J\ H* I I I I I o i i i i i i i cf cf cf cf cf cf cf H r j •* r-j r\J r-» K* t-» r- 1 H» O O \JA O O NO ON ON VJ\ -P" v^ n -P^ o o\ ro <o\ ON o cf cf cf cf cf *1 . *1 1 1 1 « I I I I I I 1 1 1 1 cf cf 1 cf •1 I I I I Specimen Apatite Biotlte Chlorite Garnet Hornblende Kyanite Muscovite Opaques Plagioclase Quartz Rutile Sillimanite Staurolite Tourmaline Zircon '98 Specimen Apatite Biotite Chlorite Garnet Hornblende Kyanite Muscovite Opaques Plagioclase Quartz Rutlie Sillimanite Staurolite Tourmaline Zircon 173 - 20 2 5 - - 3 2 60 t r 8 t r — 1* t r 30 t r 5 - - 10 t r 50 t r - 5 t r • - • 211 - 20 t r 10 - 5 5 55 t r - 5 t r 2* - 25 - 5 - t r 5 3 60 - - 2 t r -3* - 20 t r 15 - t r 5 2 *3 - - 15 t r -360 t r 20 - 10 - t r 5 t r 55 t r - 10 -364 - 20 t r 5 - - 5 2 55 t r - 15 t r -367 + - 20 - t r - - - t r 30 50 t r - - - t r 382' t r 30 t r t r - t r 5 t r 60 - - 5 - -386 t r 30 t r 5 - - t r 1 55 - - 10 t r -403' - 15 t r 5 - t r 10 t r 60 t r 10 t r • -418 17 - 3 - - t r t r 80 t r - - -* microprobe specimens q u a r t z o - f e l d s p a t h i c s c h i s t • c o n t a i n s a n d a l u s i t e pseudomorphs Table 11. V i s u a l l y estimated modal a n a l y s e s - S e t t l e r S c h i s t t U n i t I I . Specimen Apatite Biotite Chlorite Garnet Hornblende Kyanite Muscovite Opaques Plagioclase Quart z Rutile Sillimanite Staurolite Tourmaline Zircon 30 t r 20 - 12 - 10 5 2 56 - - t r t r 37 t r 20 t r 3 - 3 - 1 68 - - 5 t r -^5 t r 30 - 8 - 12 t r 1 50 - - 1 t r -50 t r 20 - 3 - 3 5 3 65 - . - 1 t r t r 106 t r 22 t r 10 - 6 t r 1 60 t r - 1 t r -137 - 20 - 5 - t r 5 t r 55 - - 15 t r -151 - 25 - k - 5 1 t r 65 t r - 10 t r -t r 25 - 10 - 5 - 1 59 t r t r t r -4* t r 25 t r 2 - 10 10 „ t r 52 t r - t r t r -5* t r 20 t r 1 - 5 5 t r 65 - - 9 t r -291 t r 20 - 1 - 3 1 65 t r - 6 t r t r 337 t r 20 t r 10 - - - t r 60 t r - 10 t r -6* - 20 - 10 . - 8 1 t r 59 - - 2 t r -7* t r 25 - 5 - - t r 1 59 t r 10 - t r -397 t r 25 - 3 - t r t r 1 70 - 1 t r t r t r •microprobe specimens Table 12. V i s u a l l y estimated modal a n a l y s e s - S e t t l e r S c h i s t l U n i t I I I . ro vo co »-» VJ H W >3 4 1 I ro l ro o Vn i i i r-» cf VJ o 4 o cf cf 4 -p- I 4 I I I I I I I I I H» ro VjJ OO I v_n Vn H» VO rO VJ H* H» VJ cf M I VJ I 4 ON oo vn co -P" O vn vn o O cf 4 l i I I I i i l I l I l cf cf 1 4 4 4 I I I I I Specimen A p a t i t e B i o t i t e C h l o r i t e Garnet Hornblende K y a n i t e Muscovite Opaques P l a g i o c l a s e Quart z R u t i l e S i l l i m a n i t e S t a u r o l l t e Tourmaline Z i r c o n Specimen Actinolite-tremolite Apatite Biotite Calcite Chlorite Diopside Epidote-clinozoisite Garnet Hornblende Muscovite Opaques Plagioclase Quartz 1 Rutile Sphene Zoisite 112 - t r 15 - t r - - t r 40 - t r 15 30 t r - -113* t r 15 - 60 - - - 15 - t r - 10 t r - -167 25 - - 5 - 7 7 • 5 - 7 4 5 35 - t r -246 - t r - - t r - t r -• 65 - t r 15 20 t r - -247 90 - - - 2 - - • - - - - 3 - - 5 256 t r - t r 5 t r 20 10 10 - - t r 25 30 - - -289 t r - - t r t r 23 7 10 - t r t r 20 40 - - -• b i o t i t e - c h l o r i t e r i m enveloping assemblage 112 Table 14, V i s u a l l y estimated modal a n a l y s e s ^ S e t t l e r S c h i s t i C a l c - s i l i c a t e U n i t s . 0) 0) a> to p 0) rt c •H -p c rH rH crj o> 10 O O +» C -p p rH <D O 0) •H C •H O o 0) AO •H •p c o •H -P .O T3 d C cr1 W) 0) +> O U •H U rt rt rt ft O rt ft crj O ft •H ft I/O •< « o W O « O (X. Of in 93 97 3 - - - t r - - -109 - - - t r t r 50 t r 44 5 1 344 - t r - t r 30 25 5 40 -Table 15. V i s u a l l y estimated modal analyses-Settler S c h i s t i S t r e a k y Amphibolites. vO •3 P C <D ON < CQ P fD CQ cf H* 3 P> cf CD a 3 o CL p p CQ CD CQ I W H-O cf H« cf (T> I CQ cf 1 fD P *• CD 3 CD cf P I H* 3 cf C CO H« O 3 o -0 V*) NO vn vo vo ro ro vo Vn co vo ON Specimen cf •1 cf *1 cf cf I cf 1 A p a t i t e o vn O vn O o B i o t i t e cf »1 l 1 ro i ro 1 C h l o r i t e Vn Vn cf vn VO ro Garnet ro 1 t-» Vn i o cf • • i i Hornblende cf cf 1 cf cf n cf cf Opaques CO VO Vn ro vn ro CO vo o H* O VO O P l a g i o c l a s e Vn •e-Vn Vn O vn o •p-vn Vn Vn CO Quartz cf 4 cf n I cf 4 cf 4 • Z i r c o n *26 Specimen Apatite Biotite Chlorite Epidote Garnet Hornblende K-feldspar Muscovite Opaques Plagioclase i Quartz i Rutile Zircon 32° t r 1 - - t r - 1 0 5 t r 39 4 5 - t r 1 1 1 ° t r 1 t r - 1 - - 5 t r 93 - -5 3A t r t r - - - 4 5 - - t r 4 5 1 0 t r -I O IA t r 1 0 - - 15 15 - - t r 4 0 2 0 - -4 2 ° t r 15 2 2 - - t r 1 7 0 1 0 - -4 4 ° t r 5 - t r - - 3 t r 72 2 0 - -4 O " - 5 - t r - - 1 1 t r 5 7 36 -3 4 1B t r 2 5 t r t r t r - - t r t r 60 15 - -o p l a g i o c l a s e a p l i t e , A garnet c l u s t e r d i k e s , a b i o t i t e q u a r t z d i o r i t e , • b i o t i t e - s p a n g l e d q u a r t z d i o r i t e . Table 17. V i s u a l l y estimated modal analyses-Igneous U n i t s . Specimen Apatite Biotite Chlorite Epidote Garnet Hornblende Opaques Plagioclase Prehnite Quartz Rutile Sphene Zircon 73 t r _ 1 t r — 29 t r 60 t r 10 - t r t r 330 t r 1 - - - 25 t r 64 - 10 - - -357 - - t r t r - 60 - 40 - - - - -408* - t r t r 7 66 mm 25 - 2 t r t r t r 422 t r 2 t r t r - *5 t r 38 t r 15 - t r -HBL - t r t r - - 60 - 27 - 3 t r t r -PYR* - t r t r - 100 - t r - t r t r t r -* h o r n b l e n d i t e Table 18. V i s u a l l y estimated modal analyses-Spuzzum I n t r u s i o n s . •p-r-» VO vo VO O ON Specimen VO 1 1 1 A n t h o p h y l l i t e o Vn Vn Vn Vn 1 Carbonate 1 l l cf C h l o r i t e 1 cf 1 F u c h s i t e VO o 1 1 1 O l i v i n e VO o 1 I 1 Orthopyroxene ro cf n cf Opaques I -p-•P--p-Vn 1 Quartz Vn i 1 ^3 NO Serpentine O i ro O T a l c S Y M B O L S Geologic contact Geologic contact-approximate Geologic contact-inferred *»<mm* Geologic contact-gradational vv^vow w^w^ Fault-approximate—inferred / Isograd Staurollte/ staurolite-Kyanite Z o n e/ Zone Staurolite-^ Kyanite^ Isograd ' .Sillimanite Z 0 n 6^ Zone 130° 200 Miles Topographic Base-Notional Topographic Series Maps: 92 H/ll West Half 92 H/12 Fast Half 49° 30' METAMORPHIC and SEDIMENTARY UNITS Drift and Alluvium-Quaternary Eocene Conglomerate Settler Schist-Paleozoic ? Unit IV—Micaceous Quartzite Unit III -Quartzo-feldspathic Schist .—Graphitic Pelitic Schist Unit " _ 7 A _ L a y e r e d Quartzo-feldspathic Schist Unit | —Layered Pelitic Schist Calc-silicate Layer Streaky Amphibolite Custer Gneiss-Triassic p IGNEOUS UNITS Ter t ia ry P P*l Biotite-Spangled Quartz Diorite Late Cretaceous Spuzzum Intrusions Cretaceous or Older Biotite Quartz Diorite • Biotite-Streaked Meta-lntrusion Ultramafic Rocks Age uncertain 49°30 N | S | Pyroxenite Serpentinite I2l°30'w TRUE NORTH 1/2 S C A L E 1 - 2 5 , 0 0 0 0 M I L E MAGNETIC NORTH I .5 I—I I—I F T ~ K I L O M E T E R C O N T O U R I N T E R V A L 2 0 0 F E E T Datum is mean sea level, 1927 G E O L O G Y S O U T H W E S T o f Y A L E , B . C L E E C . PIGAGE 1971 MAP I 200 Miles Base—National Topographic Series Maps' 92 H/ll West Half 92 H/12 East Half 49°30' N I2I°30'W TRUE NORTH 1/2 SCALE 1 = 25,000 0 I MILE MAGNETIC NORTH 1 . 5 0 I KILOMETER SYMBOLS Geologic Contact—defined, approximate, inferred „i.lUW> Geologic Contact—gradational ^ H  Fault—approximate, inferred Custer Gneiss Layering—inclined, vertical Minor Fold Axis Minor Fold Axial Plane Layered Pelitic Schists V f \ 49°30'N Bedding—inclined, vertical, overturned Lineation—phase I Axial Plane Schistosity—phase I X • Lineation—phase 2 Minor Fold Axial Plane—phase 2 Antiform Trace—phase 2—defined, approximate Synform Trace—phase 2—defined, approximate, inferred Spuzzum Intrusions Foliation—inclined, vertical S T U S O U T H W E S T o f Y A L E h t 0 . r l b A b t 1971 MAP 2 130° SYMBOLS • ) 0 Specimen Number and Location •4* Microprobe Specimen Number and Location A Unnamed Ridge Unnamed Stream Topographic Bait —National Topographic S i r l n Maps' 92 H/ll Witt Half 92 H/12 Ea«t Half I2I°30'W TRUE h NORTH 22 1/2° MAGNETIC NORTH 1/2 I MILE CONTOUR INTERVAL 200 FEET Datum Ii mean sea l i v i l , 1927 j KILOMETER 49°30'N S P E C I M E N L O C A T I O N S SOUTHWEST of Y A L E , B.C. L E E C. P S G A G E 1971 MAP 3 T 

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