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Plutonic rocks between Hope, B.C. and the 49th parallel Richards, Tom 1971

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PLUTONIC ROCKS BETWEEN HOPE, B.C. .AND'THE 49th PARALLEL by TOM RICHARDS B.Sc. U n i v e r s i t y of B r i t i s h Columbia, 1965 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF . DOCTOR OF PHILOSOPHY i n . the Department o f Geology \ accept t h i s t h e s i s as conforming to the r e q u i r e d standard _ THE UNIVERSITY OF BRITISH COLUMBIA June, 1971 'In present ing th i s thes i s in p a r t i a l f u l f i lmen t of the requirements fo r an advanced degree at the Un iver s i t y of B r i t i s h Columbia, I agree that the L ib ra ry sha l l make it f r e e l y ava i l ab le for reference and study. I fu r ther agree that permission for extens ive copying of th i s thes i s fo r s cho la r l y purposes may be granted by the Head of my Department or by his representat ives . It is understood that copying or pub l i ca t i on of th i s thes i s f o r f i nanc i a l gain sha l l not be allowed without my wr i t ten permiss ion. Department of The Un ivers i ty of B r i t i s h Columbia Vancouver 8, Canada Date ^W-yji Y\ , VA\ ABSTRACT An area of some 400 square miles between Hope, B.C. and the 49th p a r a l l e l , covering part of the northern Cascades and south-ern Coast Mountains, was investigated with the purpose of deter-mining the o r i g i n and history of the plutonic rocks* Five sepa-rate plutonic complexes, which range in age from Late Cretaceous to Miocene, underlie the area. The oldest complex investigated, the Late Cretaceous Spuzzum Intrusions (103-79 M.Y.) emplaced in the catazone-Mesozone, consists of two phases: d i o r i t e and t o n a l i t e . The older of the two, the d i o r i t e , i s a zoned intrusion which occupies the central part of the bat h o l i t h . Sheared s i l l s and stocks belonging to the early Tertiary Yale Intrusions (59-35 M.Y.) comprise the second oldest complex. These bodies crop out in a narrow belt that separates high grade metamorphic rocks of the Custer-Skagit Gneiss from the low grade metamorphic rocks of the Hozameen Group. The Early Oligocene S i l v e r Creek Stock (35 M.Y.) represents the oldest of three epizonal complexes. The epizonal Chilliwack Batholith (29-26 M.Y.) i s composed of seven intrusive phases which range in composition from hypersthene-augite d i o r i t e to a p l i t i c a l a s k i t e . Each of the phases of thi s batholith appears to have been emplaced in a pulse from an underlying, d i f f e r e n t i a t i n g magma that was r i s i n g through the crust. The youngest complex, the Mount Barr Batholith (21-16 M.Y.) i s composed of four i n t r u -sive phases, each of which appears also to nave been emplaced in a pulse from an underlying magma. One of the phases of this batho-l i t h i s in the form of a 3000-foot-thick s i l l - l i k e body. These 2 three epizonal plutons appear to be related to the north-trending Cascade volcanic-plutonic province, which overlaps the northwest-trending Coast C r y s t a l l i n e Complex, here represented by the Spuzzum and Yale Intrusions, PLUTONIC ROCKS BETWEEN HOPE, B.C. AND THE 49th PARALLEL by TOM RICHARDS TABLE OF CONTENTS INTRODUCTION GENERAL STATEMENT 1 LOCATION AND ACCESSIBILITY 1 PREVIOUS WORK 2 PRESENT INVESTIGATIONS 3 ACKNOWLEDGMENTS 3 GENERAL GEOLOGY INTRODUCTION A NON-PLUTONIC ROCKS 8 C h i l l i w a c k Group 8 Hozameen Group 8 C u s t e r - S k a g i t Gneiss 9 Skagit-Hannegan V o l c a n i c s 9 Eocene Conglomerates 10 INTRUSIVE ROCKS 10 Spuz*um I n t r u s i o n s 10 Yale I n t r u s i o n s 10 S i l v e r Creek Stock 11 C h i l l i w a c k B a t h o l i t h 11 Mount Barr B a t h o l i t h 11 STRUCTURE 12 K-Ar AGE DATES 12 SPUZZUM INTRUSIONS INTRODUCTION 15 MINERALOGY AND PETROLOGY 15 D i o r i t e 15 T o n a l i t s . 22 Zone Separating D i o r i t e from T o n a l i t e 24 U l t r a m a f i c Bodies 24 STRUCTURE 26 I n t e r n a l S t r u c t u r e 26 R e l a t i o n of T o n a l i t e t o Diorit© 26 X e n o l i t h s 26 F o l i a t i o n s 28 E x t e r n a l R e l a t i o n s 29 Contact R e l a t i o n s 29 Contact Metamorphism 30 CHEMISTRY 34 PETBQGENESE 38 Depth of Emplacement 38 O r i g i n of the Zoned D i o r i t e Complex 39 C r y s t a l l i z a t i o n of the T o n a l i t e 44 O r i g i n of the U l t r a m a f i c s 45 Emplacement of D i o r i t e and T o n a l i t e 47 (i) YALE INTRUSIONS INTRODUCTION 49 MINERALOGY AND PETROLOGY 49 O g i l v i e T o n a l i t e 49 Wi l l i a m s Peak T o n a l i t e 50 C o q u i h a l l a Quartz Mojizonite Stock 50 Gabbro-Diabase Complex 52 STRUCTURE 57 F o l i a t i o n s 57 I n t e r n a l R e l a t i o n s of the Yale I n t r u s i o n s 57 I n c l u s i o n s 53 Contact Metamorphism 58 AGE OF THE YALE INTRUSIONS 59 CHEMISTRY 60 EMPLACEMENT OF THE YALE INTRUSIONS 62 CORRELATION OF THE YALE INTRUSIONS 62 SILVER CREEK STOCK INTRODUCTION 66 MINERALOGY AKD PETROLOGY 66 CONTACT RELATIONS 70 AGE 70 DEPTH OF EMPLACEMENT 70 EMPLACEMENT AND CRYSTALLIZATION 70 CHILLIWACK BATHOLITH INTRODUCTION MINERALOGY MD PETROLOGY D i o r i t e Eastern Hypersthene-Augite D i o r i t e Western D i o r i t e T o n a l i t e E a s t e r n T o n a l i t e Western T o n a l i t e Paleface G r a n o d i o r i t e Radium Peak Phase A l a s k i t e Plugs Mount Rexford Phase Post Creek Phase STRUCTURE I n t e r n a l S t r u c t u r e Sequence of Emplacement F o l i a t i o n s Layering B r e c c i a s J o i n t s E x t e r n a l R e l a t i o n s R e l a t i o n t o Older Rocks Contact Metamorphism ( i i ) 72 75 75 79 79 82 84 85 85 85 86 87 87 87 87 90 90 91 91 91 93 AGE OF THE CHILLIWACK BATHOLITH 95 CHEMISTRY 96 PETROGENESIS 100 Introduction 100 Differentiation and Successive Intrusion 104 Crystallization and Differentiation at the Present Level of Exposure HO Introduction 110 Crystallization of the Tona|ite 110 Crystallization of the Radium Peak Phase 114 Depth of Emplacement of the Chilliwack Batholith 116 Mode of Emplacement of the Ghilliwack Batholith 116 MOUNT BARR BATHOLITH INTRODUCTION 120 MINERALOGY AND PETROLOGY 120 Conway Phase 120 Mount Barr Phase 125 Leucocratic Stocks 128 Wahleach Lake Phase ~ 128 STRUCTURE 129 Internal Relations 129 Relation Between Phases 129 Layering 129 External Relations 131 Intrusive Relations 131 Contact Metamorphism 133 AGE OF THE MOUNT BARR BATHOLITH 133 CHEMISTRY OF THE MOUNT BARR BATHOLITH 133 PETROGENESIS 137 Differentiatioh at the Present Level 140 Level of Emplacement 140 Mode of Emplacement 143 DEPTH-ZONE OF EMPLACEMENT OF THE PLUTONIC ROCKS IN THE HOPE AREA 145 CORRELATION CF THE INTRUSIVE ROCKS L48 ORIGIN OF THE MAGMAS 156 SUMMARY AND CONCLUSIONS 161 BIBLIOGRAPHY 164 Appendix 1 : Determinative Methods 171 Appendix : Table of .Chemical Analyses of Andesitic Rocks 177 Appendix : Topographic Map of the Hope Area 178 1 ( i i i ) LIST OF FIGURES F i g u r e 1 Geology of the P l u t o n i c Hocks Between Hope, B r i t i s h Columbia, and the 49th P a r a l l e l i n s e r t F i g u r e 2 L o c a t i o n of the Thesis area 1 F i g u r e 3 Non-plutonic U n i t 3 i n the Hope Araa 6 F i g u r e 4 P l u t o n i c Rocks i n the Hope Area 7 F i g u r e 5 Rock U n i t s of the Spuzzum I n t r u s i o n s 17 F i g u r e 6 Modal V a r i a t i o n s i n the D i o r i t e 19 F i g u r e 7 Sketch of the D i s t r i b u t i o n of the Three Types pf D i o r i t e s o u t h of the F r a s e r R i v e r 20 F i g u r e 8 Hypersthene-Amphibole R e l a t i o n s h i p s i n the D i o r i t e and Adjacent T o n a l i t e 21 F i g u r e 9 V a r i a t i o n i n Modal Percentage:of M i n e r a l s i n D i o r i t e and T o n a l i t e across the Contact Near Hunter Creek 23 F i g u r e 10 Sketches of U l t r a m a f i c Bodies i n the Spuzzum I n t r u s i o n s 25 F i g u r e 11 F o l i a t i o n s i n the Spuzsum I n t r u s i o n s and Adjacent Metamorphics of the C h i l l i w a c k Group 27 F i g u r e 12 P/T S t a b i l i t i e s f o r some of the Mi n e r a l s i n the Contact Aureole Adjacent t o the Spuzzum I n t r u s i o n s 31 F i g u r e 13 A-F-M Diagram f o r Regional and Contact Metamorphic Rocks Adjacent t o the S p U 3 2 u m T o n a l i t e 32 F i g u r e 14 V a r i a t i o n Diagram of Modes and Oxides f o r Analysed Specimens from the Three Types of D i o r i t e and the T o n a l i t e 36 F i g u r e 15 CaO-Na20-K20 P l o t f o r the Spuzzum I n t r u s i o n s 37 F i g u r e 16 T r i a n g u l a r P l o t of Modal Analyses from the Various Phases of the Spuzzum I n t r u s i o n s 37 F i g u r e 17 Schematic S t a b i l i t y Curves of Ainphibole-Pyroxene Under Conditions of =P t o t and P ^ P t o t 41 F i g u r e 18 Liquidus R e l a t i o n s i n the System An^Q-Di-En at 1 atmosphere and 15 K i l o b a r s 41 ( i v ) F i g u r e 19 Schematic Phase R e l a t i o n s i n the System Opx-Gpx-Hb-Liq-R^O, w i t h Reference t o the C r y s t a l l i z a t i o n H i s t o r y of the Mafic M i n e r a l s i n the D i o r i t e Phase of the Spuzzum I n t r u s i o n s A3 F i g u r e 20 I l l u s t r a t i o n of the Seouence of Emplacement of the Phases of the Spuzzum I n t r u s i o n s 48 F i g u r e 21 S t r u c t u r a l States of A l k a l i F e l d s p a r s from the Yale I n t r u s i o n s 53 F i g u r e 22 D i s t r i b u t i o n of Gabbro, Diabase and Agmatite i n the Gabbroic I n c l u s i o n i n the C o q u i h a l l a Stock, East of Hope, B.C. 55 F i g u r e 23 Contact R e l a t i o n s Between the C o q u i h a l l a Quartz Monzonite Sto ck and the Gabbro Complex 5 ° F i g u r e 24 I n t r u s i v e rocks P o s s i b l y C o r r e l a t i v e w i t h the Y a l e - I n t r u s i o n s . 6 3 F i g u r e 2 5 D i s t r i b u t i o n of U l t r a m a f i c and Mafic Rocks and A s s o c i a t e d F a u l t s i n the Hope Area 6 5 F i g u r e 2 6 General Geology Around the S i l v e r Creek Stock 6 7 F i g u r e 27 S t r u c t u r a l S t a t e s of A l k a l i Feldspars from the S i l v e r Creek Stock 6 9 F i g u r e 23 General Geology Adjacent t o t h e C h i l l i w a c k B a t h o l i t h 73 F i g u r e 29 I n t r u s i v e Phases of the C h i l l i w a c k B a t h o l i t h 74 F i g u r e 30 D i s t r i b u t i o n of Rock Types i n the E a s t e r n T o n a l i t e 80 F i g u r e 3 1 S t r u c t u r a l S t a t e s of A l k a l i Feldspars from the C h i l l i w a c k B a t h o l i t h 83 F i g u r e 32 Diagram ^howing Those I n t r u s i v e R e l a t i o n s Observed Between P l u t o n i c U n i t s Seen i n the F i e l d 88 F i g u r e 33 F o l i a t i o n s i n the T o n a l i t e and the Adjacent Metamprpbics 89 F i g u r e 34 Schematic P/T Diagram f o r Ca-Al s i l i c a t e s 92 F i g u r e 35 Sketch of a C r o s s - s e c t i o n of the Mount Rexford P l u t o n Between Middle Peak and the c h i l l i w a c k R i v e r 94 F i g u r e 36 L o c a t i o n of Specimens Used i n the Text 99 (v) Figure 37 Silica Variation Diagram 101 Figure 38 Silica Variation Diagram-Ghayes Transformation Plot 102 Figure 39 Ca0-Na20-K20 Plot for the Chilliwack Batholith 103 Figure 40 Mg0-Fe0tot-(Na20 • K20> Plot for the Chilliwack Batholith 103 Figure 41 Schematic Crystallization History of the Various Phases of the Chifcliwack Batholith 105 Figure 42 Variation of Plagioclase Compositions within some of the Fhases of the Chilliwack Batholith 106 Figure 43 Pyroxene Quadrilateral-Showing the Composition of clinopyroxene in equilibrium with orthopyroxene from the eastern tonalite and the Eastern ^iorite 107 Figure 44 Normalized Felsic Mineeals from some of the Phases of the Chilliwack Batholith 107 Figure 45 Ternary System Ab-An-Grj Schematic Crystallization History of Feldspar pairs from the phases of the Chilliwack Batholith 108 Figure 46 Liquidus Relations in the System An^-Di-En 109 Figure 47 Points of Minimum Melt Compositions s.nc Cotectic Lines in the System: Ab/An-0tz-0r for Various Ab/An Ratios at 2Kb Water Pressure 109 Figure 48 Illustration of the Change in Leyel of the Magma Chamber and Emplacement of the Phases of the Chilliwack Batholith 111 Figure 49 Estimate of the Amount of Fractional Crystalliz at ion Required at Each of the Successive Levels of the Magmas Chamber to Account for the Change in Composition of the Magma as it rose Through the Crust 112 Figure 50 Isobaric Phase Diagram for the Join Ab-Or-Qtz-An at 1000 bars 115 Figure 51 Illustration of the Sequence of Emplacement of the Phases of the Chilliwack Batholith 117 Figure 52 Relations of the Chilliwack Batholith to Major Faults and Lineaments 119 Figure 53 Phases of the Mount Barr Batholith 123 Figure 54 Location of Specimens Used in the Text 124 (vi) F i g u r e 55 20 060-204 S t r u c t u r a l S t a t e P l o t s f o r A l k a l i F e l d s p a r s from the Mount Barr B a t h o l i t h 127 F i g u r e 56 C r o s s - s e c t i o n of the Layered Zones North of Mount conway 130 F i g u r e 57 Schematic C r o s s - s e c t i o n s of the Mount Ba r r B a t h o l i t h 132 F i g u r e 58 S i l i c a V a r i a t i o n Diagram 135 F i g u r e 59 FeO t t-MgO-(Na20 + K20) p l o t 136 F i g u r e 60 CaO-Na20~K20 P l o t 136 F i g u r e 6l C r y s t a l l i z a t i o n H i s t o r y of the Mount Barr B a t h o l i t h 138 F i g u r e 62 Schematic H i s t o r y of P l a g i o c l a s e C r y s t a l l i z a t i o n from the Mount B a r r B a t h o l i t h 141 F i g u r e 63 Schematic Representation of Levels of Water S a t u r a t i o n f o r the Various Phases of the Mount Barr B a t h o l i t h a f t e r Being Tapped from the Underlying Magma Chamber 142 F i g u r e 64 I l l u s t r a t i o n of the Sequence of Emplacement of the Phases of the Mount Ba r r B a t h o l i t h 144 F i g u r e 65 Comparison of S t r u c t u r a l S t a t e s of A l k a l i F e l dspars from the various I n t r u s i v e U n i t s i n the Map Area 147 F i g u r e 66 P l u t o n i c Rocks of the Southern Coast C r y s t a l l i n e Complex and the Northern Cascades 149 F i g u r e 67 A l k a l i P l o t s f o r Various P l u t o n i c Rocks of the Western C o r d i l l e r a 153 F i g u r e 68 I n t e n s i t y of Flutonism w i t h ^ime i n the Southern Coast C r y s t a l l i n e Complex and the Northern Cascades 155 F i g u r e 69 Coast C r y s t a l l i n Complex and the Cascade Mountains 158 F i g u r e 70 Subducticn Zone: O r i g i n of Magmas 160 F i g u r e 71 Gligocene-Miocene Ridge-Trench System Off the West Coast of North America lbO F i g u r e 72 "Three Peak" S t r u c t u r a l State Diagram f o r A l k a l i F e l d s p a r s 172 F i g u r e 73 Rate of Horaogenization of A l k a l i f e l d s p a r s 173 F i g u r e 74 Topography of the Area Underlain.by ^ i g u r e 1 178 (vii) LIST OF TABLES Table 1 Table of Formations and Events i n the Hope-C h i l l i w a c k Lake Area 5 Table 2 K-Ar Samples and A n a l y t i c a l R e s u l t s f o r the P l u t o n i c Rocks Between Hope and the -49th F a r a l l e l 13 Table 3 Modes of the Spuzzum I n t r u s i o n s 16 Table 4 Mineralogy of the S p U z z u m I n t r u s i o n s 18 Table 5 M i n e r a l Assemblages from Various Layers i n the C a l c - s i l i : : a t e x e n o l i t h s i n the Spuzzum D i o r i t e 28 Table 6 Chemical Analyses of the Sp U Z Z Upi. I n t r u s i o n s 35 Table 7 Fre-Upper Cretaceous Sedimentary and V o l c a n i c Recks i n the Hope Map Area 39 Table 8 D i f f e r e n t i a t i o n of the D i o r i t e t o form the T o n a l i t e by F r a c t i o n a l C r y s t a l l i z a t i o n 46 Table 9 Modes of the Yale I n t r u s i o n s 51 Table 10 A l k a l i F e l d s p a r Data f o r the ^ a l e I n t r u s i o n s 53 Table 11 Modes of the G abbro Complex 54 Table 12 K-Ar Ages from the ^ a l e I n t r u s i o n s 59 Table 13 Chemical Analyses of the ^ a l e I n t r u s i o n s 6 l Table. 14 Modes of the s i l v e r Creek Stock 68 Table 15 Chemical analyses of the S i l v e r Creek Stock 68 Table 16 X-ray Data f o r A l k a l i F e l d s p a r s from the s i l v e r Creek Stock 69 Table 17 Modes of the C h i l l i w a c k B a t h o l i t h 76 Table 18 Compositions of P l a g i o c l a s e from the T 0 n a l i t e 81 Table 19 Mafic I n c l u s i o n s i n P l a g i o c l a s e from the -^onalite 81 Table 20 X-ray Data f o r Compositions and S t r u c t u r a l S t a t e s f o r A l k a l i F e l d s p a r s from the C h i l l i w a c k B a t h o l i t h 83 Tab}.e 21 K-Ar Ages from the C h i l l i w a c k B a t h o l i t h 95 ( v i i i ) Table 22 Chemical Analyses of the C h i l l i w a c k B a t h o l i t h 97 Table 23 Comparison of the Average Chemical Analyses of the Phases of the G h i l l i w a c k B a t h o l i t h w i t h the c a l u c u l a t e d Chemical Analyses of the L i q u i d - F r a c t i o n s produced by F r a c t i o n a l C r y s t a l l i z a t i o n of the D i o r i t i c Magma 113 Table 24 Modes of the Mount Barr B a t h o l i t h 121 T a b l e 25 X-ray Data f o r S t r u c t u r a l S t a t e s and Compositions f o r A l k a l i F e l d s p a r s from the Mount Barr B a t h o l i t h 126 Table 2 6 K-Ar Ages from the Mount Barr B a t h o l i t h 133 Table 27 Chemical Analyses of the Mount Ba r r B a t h o l i t h 134 Table 28 Change i n ^ n o r t h i t e Composition from Core- t o Rim P l a g i o c l a s e i n the Mount Ba r r B a t h o l i t h 140 Table 29 P l u t o n i c Rocks of the Southern Coast C r y s t a l l i n e Complex and the Northern Cascade Mountains 150 Table 30 Ages cf I n t r u s i v e Rocks from the ^outhern Coast C r y s t a l l i n e Complex and the Northern Cascades 151 Table 31 Accuracy of Rapid/Method 174 Table 32 M u l t i p l e c o u n t s from One T h i n s e c t i . o n ' 176 Table 33 R e p l i c a t e Modal Analyses from S i x Thin Sections from One Specimen of Pyroxene D i o r i t e 176 Table 34 Chemical Analyses From seme High Alumina B a s a l t i c -A n d e s i t e s and Andesites, and from the Spuzzum D i o r i t e and the Eastern D i o r i t e of the C h i l l i w a c k B a t h o l i t h (ix) 1. INTRODUCTION GENERAL STATEMENT This thesis i s a study of plutonic rocks of the northern part of the Northern Cascades and of the adjacent part of the Coast Range between Hope, British Columbia and the Canada-United States border (figure 2). The area provides an opportunity to study a group of plutonic rocks that were emplaced over a long period of time and at different levels in the crust. FIGURE 2 Location of the Thesis Area LOCATION AND ACCESSIBILITY The map area, covering about 350 square miles, l i e s 100 miles east of Vancouver, British Columbia. Plutonic rocks studied crop out between American Creek 5 miles north-west of Hopo and the 49th parallel (figures 1 and 3). The Trans-Canada Highway and numerous logging roads give good access into the northern part of the area. The southern part can be reached by a logging road along the Chilliwack R i v e r Valley, The terrain i s rugged, with r e l i e f l o c a l l y in excess of 6000 feet. Outcrops are plentiful except in valley bottoms. PREVIOUS WORK Daly (1912) mapping along the 49th parallel and Cairnes (1924) mapping the watershed of the Coquihalla River first provided a framework for the geology of the area. Plutonic rocks astride the 49th parallel were named the Chilliwack Batholith by Daly (1912) and were assigned a Miocene age on the basis of similarities with the Miocene Snoqualmie Batholith of north-western Washington. Tonalite and diorite along the western edge of this batholith were named the Slesse Diorites and assigned a post-Cretaceous to Pre-Miocene age (Daly 1912). The Miocene age of the Chilliwack Batholith was confirmed some 50 years later when Baadsgaard et a l (l96l) obtained two 18 million year old K-Ar dates on rocks 20 miles south-west of Hope. Cairnes (1924) subdivided plutonic rocks near Hope into three groups according to age: Upper Jurassic, Upper Cretaceous or possibly Tertiary, and Miocene. Cairnes (1944) revised much of his earlier work and included most of the plutonic rocks with the Chilliwack Batholith. The composite nature of the Chilliwack Batholith was f i r s t shown by Misch (1966). He included a l l plutonic rocks, extending from Hope southward for some 50 miles, as belonging to the Chilliwack Composite Batholith with a range in age from Eocene to Miocene. McTaggart and Thompson (1967) defined two new intrusive units older than the Chilliwack Batholith: the Upper Cretaceous Spuzzum Intrusions and the Upper Tertiary Yale Intrusions. Monger (1970) revised the Hope map sheet (Cairnes 1944) and incorporated some of the new work reported in this thesis. Various workers have investigated the sedimentary and volcanic rocks. To the east of the plutonic rocks, the Upper Paleozoic Hozameen Group (Daly 1912) was reportod on by Daly (1912), Cairnes (1924, 1944), Read (i960), Misch (1966), McTaggart and Thompson (1967), Roddick and Hutchinson (1969), Monger (1970) and McTaggart (1970). 3. Between the Hozameen Group and the plutonica are gneissic rocks which north of the 49th parallel are referred to as the Custer Granite-Gneiss (Daly 1912) and south of the 49th parallel are referred to as the Skagit Gneiss (Misch 1966). These gneissic rocks were reported on by Daly (1912), Cairnes (1924, 1944), Read (i960), Misch (1966), McTaggart and Thompson (1967) and McTaggart (1970). To the west of the plutonic rocks, the Upper Paleozoic Chilliwack Group (Daly 1912) have been investigated by Daly (1912), Cairnes (1944), Monger (1966), Misch (1966), Lowes (1968) and Monger (1970). PRESENT INVESTIGATIONS Data for this thesis were collected during seven months field mapping in the summers of 1966, 1967 and 1968 and from laboratory investigations in the intervening time. A l l mapping was done on 1:50,000 maps of the National Topographic Series. Only the plutonic rocks were investigated in detail. The non-plutonic rocks were napped only where relationships appeared to be important in working out the history of the plutonics. ACKNOWLEDGEMENTS This thesis was done under the supervision of Dr. K. C. McTaggart to whom the author is very indebted. Dr. W. H. white and J. Harakal aided greatly in the K-Ar age determinations. Dr. H. J. Greenwood offered many valueable suggestions. S. Schumann, K. More, A. Bentzen, R. Richards, M. Schau and my wife, S. Richards, assisted in the field. Chemical analyses were obtained through the courtesy of Dr. W. W. Hutchinson of the Geological Survey of Canada. I. Patterson, G. Payearle, and others 7 gave both moral support and assistance in thought. Thanks i s given to A r t S o r e g a r o l i and Noranda Mines f o r Xeroxing some needed copies of t h i s t h e s i s . 4. GENERAL GEOLOGY INTRODUCTION The Thesis area lies within the northern part of the Northern Cascades and the southeastern part of the Coast Crystalline Complex (figure 2). Here, the Coast Crystalline Complex (Roddick 1966) consists of granitic and high grade metamorphic rocks and the Northern Cascades are comprised mainly of low grade metamorphic and lesser amounts of granitic rocks. Structures in both systems trend northwesterly. Both belong to the same orogenic belt, but rocks of the Northern Cascades appear to be exposed at a higher crustal level than those of the Coast Crystalline Complex (McTaggart 1970 and Monger 1970). The central or axial part of this belt consists mostly of high grade metamorphic rocks and is flanked by rocks of lower metamorphic grade (Monger 1970). The plutonic roeks are found mainly within the axial region of this belt. Geologic units, their ages and the geologic events pertinent to this study are listed in table 1. Non-plutonic rocks, shown in figures 1 and 3 range in age from Upper Paleozoic to Oligocene. The plutonic rocks are flanked on both sides by low grade metamorphosed volcanic and sedimentary rocks. To the west of the plutonics, these rocks belong to the Chilliwack Group, and, to the east, to the Hozameen Group. The axial part of the area is underlain by high grade metamorphic and migmatitic rocks of the Custer-Skagit Gneiss which are possibly equivalent to the Hozameen Group (McTaggart and Thompson 1967)» A narrow belt of conglomerates of Eocene age runs southerly through the middle of the area. Small areas in the southern part of the map are underlain by Oligoceno volcanic rocks, called the Skagit volcanics (Daly 1912) or the Hannegan volcanics (Misch 1966). 5. TABLE 1. Table of Formations and Events in the Hope-Chilliwack Lake Area Era Period of Epoch Formation Pliestocene-Recent Glacial Deposits Miocene Oligocene Mount Barr Pluton (16-21 my) Chilliwack Batholith (26-29 my) S o (S3 o S3 W O Skagit Volcanics Chilliwack "Composite" Batholith Eocene Silver Creek Stock (35 my) Conglomerates (Chuckanut formation?) E oc ene-Pale oc ene Yale Intrusions (35-59 my) Upper Cretaceous o n o o CO o M O (SI o Jurassic or earlier? Triassic Late Paleozoic Spuzzum Intrusions (102-76 my) Custer Gneiss Cultus formation Hozameen Group Chilliwack Group Event unconformity upwarping north-east fracturing and faulting intru sion intrusion east to north-east faulting vulcanism unconformity intrusion intrusion block faulting block faulting unconformity intrusion shearing and motamorphism intrusion metamorphism north-west faulting metamorphism? 6. F IGURE 3 Non-Plutonic Units i n t h e Hope' Area (compare with figure 4 showing plutonic units) Seal e in M i l e s 7. FIGURE 4 Plutonic Rocks in the Hope Area WILLIAMS PEAKS STOCK Mount 4 Slesse S c a l e in miles 8. Plutonic rocks were subdivided into five principle units (figure 4). These range in age from Upper Cretaceous to Miocene. The oldest unit is the Upper Cretaceous Spuzzum Intrusions whose origin appears to be related to a major orogeny. A Lower Tertiary plutonic complex, the Yale Intrusions, may be related to the waning stages of this Upper Cretaceous orogeny. The three youngest intrusive units, the Silver Creek Stock, the Chilliwack Batholith and the Mount Barr Batholith, are most likely related to the Upper Tertiary Cascade igneous activity (Waters 1955) of Washington and Oregon. NON-PLUTONIC ROCKS Chilliwack Group Monger (1966, 1970) subdivided the rocks of the Chilliwack Group into five stratigraphic units with an aggregate thickness of some 5,700 feet, while Misch (1966), mapping south of the 49th parallel, estimated their thickness to be more than 10,000 feet. Lower stratigraphic units are mostly pelites, sandstones and siltstones, overlain conformably and disconformably by limestone, pelites, sandstone and minor conglomerates. An upper unit is made up dominantly of greenstone volcanics, dacitic pyroclastics and subordinate chert. Adjacent to the plutonics, the rocks are dominantly pelites, siltstones with minor sandstones, and limestone. In the southern part of the area, the rocks belong to the greenschist facies, transitional to the lower glaucophane schist facies (Monger 1970). To the north, adjacent to the Spuzzum Intrusions (figures 1 and 4), the regional metamorphic grade reaches into the almandine-amphibolite facies. Hozameen Group The age of the Hozameen Group is based upon statigraphic similarities with the Upper Paleozoic Cache Creek Group (Daly 1912, Cairnes 1924, and 9. McTaggart and Thompson 1967). McTaggart and Thompson (1967) subdivided the Hozameen Group into four lithologic divisions with a maximum thickness of 26,000 feet (Monger 1970). The unit is composed of ribbon cherts, ^ green-stone volcanics, limestone and minor argillite. The rocks are metamorphosed in the lower greenschist to possibly the zeolite facies except near the Custer Gneiss where they reach into the almandine-amphibolite facies (McTaggart and Thompson 1967). Custer-Skagit Gneiss The Custer-Skagit Gneiss is a migmatitic complex consisting of finely bedded amphibolite, leucocratic gneiss, augen gneiss, minor marble and abundant trondhjemitic pegmatite. These latter bodies range in size from single layers of plagioclase augen to masses l/3 of a mile across (McTaggart and Thompson 1967). Dykes and s i l l s of leucocratic granodiorite, intrusive into the gneiss, are similar to some of the Lower Tertiary Yale Intrusions. Most of the gneisses are metamorphosed in the almandine-amphibolite facies. The trondhjemitic pegmatite appear to be metasomatic and in part anatectic in origin, although anatexis did not occur at the present level of exposure (Misch 1968). Shearing, common throughout the gneiss, post dates the metamorphism and migmatitization. Age of the gneisses is uncertain. An Upper Paleozoic age has been suggested by Misch (1966), an age younger than the Hozameen Group by McTaggart and Thompson (1967), a pre-Jurassic or possibly Cretaceous age by McTaggart (1970). An episode of metamorphism and migmatitization affected the gneisses apparently in the Upper Cretaceous (Mattinson 1970). Skagit-Hannegan Volcanics Five1 thousand feet of flows and pyroclastics, mainly andesitic in composition, comprise the bulk of the Skagit-Hannegan volcanics.'' Acidic tuffs, conglomerates and argillites occur in: minor amounts. The rocks 10. are, in general, unsheared and unmetaraorphosed. Apparently Oligocene in age, they rest unconformably on Eocene plutonics and have been intruded by Oligocene plutonics (Misch 1966). Before erosion, these volcanics probably formed part of a volcanic complex similar to some of the Pleistocene-Recent volcanic complexes of the High Cascades (Daly 1912). Eocene Conglomerate Non-marine conglomerate and sandstone, totalling about 2,000 feet in thickness, are thought to be Eocene in age (Rouse, in McTaggart and Thompson 1967). These rocks are in general weakly cemented. Monger (1970) correlated the conglomerate with the Lower Tertiary Chuckanut Formation of northwestern Washington. INTRUSIVE ROCKS Spuzzum Intrusions The Spuzzum Intrusions extends from five miles south of the Fraser River northward for some f i f t y miles. It forms one of the largest batholithic complexes in the Coast Crystalline Complex (Hutchinson 1970b). Hornblende-biotite tonalite is the dominant rock type, with pyroxene diorite common in the south and leucocratic tonalite (The Scuzzy Plutonj Roddick and Hutchinson 1969 and Hutchinson 1970b) common in the north. K-feldspar is absent from these rocks, except in the Scuzzy Pluton. K-Ar age determinations range from 103 to 79 million years in the south (Richards and White 1970) and from 76 to 70 million years in the north (McTaggart and Thompson 1967 and Hutchinson 1970b). Yale Intrusions McTaggart and Thompson (1967) assigned the name, Yale Intrusions, to a compositionally heterogeneous group of'sheared s i l l s and stocks that 11. crop out just north of Yale, and extend southward, in a narrow belt, to near the head of Silver Greek. K-Ar ages from these rocks east and south of Hope range from 59 to 35 million years (Richards and White 1970). Silver Greek Stock The Silver Creek Stock, covering some 10 square miles in area, is centered about Silver Lake five miles south of Hope. Dated by K-Ar methods at 35 million years (Richards and White 1970), the stock intrudes the Custer Gneiss, the Yale Intrusions and Eocene conglomerate. It is composed entirely of tonalite. Chilliwack Batholith Daly (1912) defined plutonie rocks adjacent to Chilliwack Lake as the Chilliwack Batholith. Misch (1966), however, included plutonic rocks that range in age from Eocene to Miocene as belonging to the Chilliwack Composite Batholith, which extends from the Fraser River southward for some 50 miles. In this thesis area the term Chilliwack Batholith will be restricted to rocks dated as Upper Oligocene (K-Ar ages range from 29 to 26 million years). Misch (1966) equates plutonic rocks of this age with the Perry Creek phase of the Chilliwack Composite Batholith. The Slesse Diorite, thought by Daly (1912) to be older than the Chilliwack Batholith, is included here as part of the Chilliwack Batholith. Rocks of the Chilliwack Batholith range in composition from pyroxene diorite to aplitlc granite. Mount Barr Batholith The Mount Barr Batholith, centered on Wahleach Lake 12 miles southwest of Hope, is the youngest plutonic complex found in the map area. K-Ar age determinations range between 16 and 21 million years (Baadsgaard et al 12. 1961 and Richards and white 1970). Rocks of this complex range in composition from tonalite to quartz monzonite. STRUCTURE Deformation in the mid-late Cretaceous time established the dominant north-west trending structural framework of the Northern Cascades and southeastern Coast Mountain systems (Monger 1970). Thrust faulting in the southern part of the area and steeply dipping north-west trending faults in the northern part of the area were developed at this time. Metamorphism and migmatitization of the Custer Gneiss appears also to have occurred in the Upper Cretaceous (Mattinson 1970). In the early Tertiary, shearing produced the pervasive cataclasis found in the Yale Intrusions. Normal faulting in the early Tertiary resulted in the development of the Fraser River graben. The present outcrop distribution-of Eocene conglomerates marks the trace of this graben. Upwarping of the Coast-Cascade mountains appears to have taken place during the Pliocene-Pleistocene (Monger 1970). K-Ar AGE DATES The twenty-two K-Ar age determinations (Richards and White 1970), reported in this thesis and the data pertinent to their calculations, are listed in table 2. The separation of the plutonic rocks into their various subdivisions was supported and in some cases modified by these age calculations. Two of these ages, numbers 8 and 15 in table 2, belong to plutonic rocks not studied in detail. Location of specimens dated are shown in figures 1 and 4. Discussion of the ages is reserved for future sections. 13. TABLE 2. K/Ar samples and analytical results for the plutonic rocks between Hope and the 49th p a r a l l e l Spec Min. No Rock % K A r 4 0* / A r40 Ar4°*:10-5 cm^stoVg Age m.v. Spuzzum Intrusions l a bio QD 5.73 t 0.07 0.82 2.404 103 t 5 lb bio QD n n 0.79 2.392 103 t 5 2a bio QD 6.10 + 0.06 0.89 1.930 79 t 4 2b hb QD 0.54 + 0.007 0.65 0.176 81 ± 4 3 bio QD 6.02 + 0.02 0.79 2.010 83 1 4 Yale Intrusions 4a bio QD 6.75 + 0.04 0.81 1.598 59 1 3 4b bio QD n n 0.53 1.588 59 • 3 5 bio QM 5.17 + 0.02 0.53 0.851 41 1 2 6 bio QD 7.65 • 0.08 0.41 1.054 35 t 2 7 rock QD 1.109 0.31 0.105 24 t 1 Custer Ridge Mica-Hornblende Peridotite 8 hb Hbite 0.280 + 0.005 0.26 0.049 44 t 3 Silver Creek Stock 9 hb QD 0.433 + 0.012 0.39 0.06 35 t 2 Chilliwack Batholith 10 bio Dio 6.24 • 0.06 0.30 0.723 29 i 1 11 bio QD 7.51 i . 0.05 0.67 0.824 28 1 1 12 bio QM 6.83 i 0.07 0.33 0.718 26 i 1 13 bio QM 6.97 • 0.04 0.77 0.732 26 i 1 14 bio QM 5.90 + 0.06 0.50 0.609 26 + 1 Hicks Stock 15a bio QD 6.87 • 0.05 0.50 0.643 24 1 1 15b bio QD n II 0.57 0.647 24 i 1 u. TABLE 2. Spec No Min. Rock % E Ax^/Ax^O Arf*:10-5 cm (stoVe Age m.v. Mount Barr Batholith 16 bio Gnd 4.85 + 0.03 0.61 0.411 21 i 1 17 bio QD 6.58 • 0.06 0.22 0.464 18+1 IS bio QM 6.91 + 0.03 0.25 0.438 16+1 Constanta used in age calculations: Xe= 0.58 x 10 y" \ = 4.27 x l O ^ V 1 , K40/K = 1.181 x 10~4 15. SPUZZUM INTRUSIONS INTRODUCTION The northern part of the area is underlain by the Spuzzum Intrusions (figures 1 and 4). Here, two intrusive units are present. The oldest one, a zoned complex of diorite, forms the central part. A younger unit of mafic tonalite completely surrounds the diorite complex. A few ultramafic bodies are found in the diorite. The tonalite, the youngest phase, intrudes high grade metamorphic schists that are possibly equivalent to the Chilliwack Group. MINERALOGY AND PETROLOGY  Diorite The composition of rocks from the central diorite complex varies continuously from two-pyroxene diorites in its core to hypersthene-hornblende diorite along its margins. For convenience of discussion, these have been subdivided into three petrographic types. Augite-hypersthene diorite (type I) of the core grades into and is partly surrounded by augite-hyper-sthene-hornblende diorite (type II) which is in turn rimmed by and grades * into hypersthene-hornblende-biotite diorite (type III). Boundaries between these three types, shown in figure 5 , are somewhat arbitrary. Modes for diorite are listed in table 3 . Type-I diorite, which in general forms the core of the diorite, is composed of plagioclase, hypersthene and augite with minor amounts of quartz and hydrous mafics. An increase in quartz and hornblende and a decrease in plagioclase and augite distinguishes type-II diorite from type-I diorite. Separation of type-Ill from type-II diorite is based upon a further increase in quartz and hornblende and a decrease in plagioclase and augite. Type-Ill diorite is usually found along the margins of the ii | \ diorite complex. Variation in modal mineralogy from type-I to type-Ill diorite is shown schematically in figure 6. Average modes and mineral 16 TABLE 3 . Modes of the Spuzzum Intrusions Pr-orits Tyoe I Type II QM. 1270 028 mi 262 126 631 plagioclase 78.0 70.5 66.7 71.3 72.4 67.6 65.9 62 quartz tr 2.1 1.2 4.3 4.9 6.7 4.8 4 hypersthene 7.7 7.7 12.4 12.6 11.8 7.6 10.8 9 augite 10.9 16.4 12.3 3.5 2.1 3.7 2.7 3 horneblende 0.8 2.3 4.7 7.7 6.5 11.5 12.9 17 biotite tr 0.3 0.5 tr 0.8 2.1 2.0 4 apatite t r tr t r t r t r t r t r tr opagues 2.6 0.9 1.4 0.6 1.5 0.5 0.7 1 Transition Type III Zone 26§ im 1378 69_rQ3. 2L£L 69-04 plagioclase 5S.8 58.9 62.3 59.8 54.0 61.6 quartz 11.3 10.3 5.3 7.0 8.4 11.4 hypersthene 7.2 7.0 10.9 8.2 8.3 3.2 augite 0.9 0.6 2.9 1.0 0.8 0.2 hornblende 18.8 18.3 16.7 20.1 19.6 18.2 biotite 1.5 4.4 2.8 • 2.6 6.7 4.8 apatite 0.7 0.2 t r 0.3 0.4 t r opagues 0.6 0.5 t r 1.0 0.6 0.2 Tonalite 216 211 251 25Z iQ6 516 69-58 plagioclase 54.0 52.8 49.0 59.4 54.9 52.2 54.3 50.0 quartz 16.7 16.1 17.3 16.0 18.3 18.2 21.7 17.5 hornblende 19.6 21.1 20.0 16.8 17.2 19.2 12.8 20.3 biotite 8.7 9.0 10.0 7.5 9.7 10.2 10.7 11.6 apatite 0.5 0.5 0.5 0.2 tr tr t r t r opagues 0.4 0.5 1.0 0.2 0.4 1.0 t r 0.6 17. FIGURE 5 Rock Units of the Spuzzum Intrusions + +•' Mount B a r r B a t h o I i t 0 I 2  + + + + Scale In Miles " ^ B l o t i t e - h o r n b l e n d e Tonalite HI* Biotite-hypersthene-hornblende Diorite || Augito - hyp'erst none - hornblende Diorite J Hypersthene - auglte Diorite O Hornblendite O Pyroxenlte X Calc-silicate Xenoliths Location of Specimens Used in the Text © Location of K-Ar Ages 18. compositions from each of the three types are listed in table 4. Type-I diorite is found in two areas (figure 5). South of Flood, i t grades laterally and vertically into type-II diorite (figure 7). TABLE 4. Mineralogy of the Spuzzum Intrusions Diorite Tonalite I II III plagioclase 72$ 68$ 59$ 54$ quartz 1$ 5$ 9$ 18$ hypersthene 9$ 9% 8$ augite 13$ 3$ 1$ hornblende 3$ 11$ 19$ 18$ biotite tr 2$ 4$ 10$ opagues 2$ 1$ 1$ t r accessories t r t r t r t r plagioclase unzoned An/0. An_, An zoning 48-43 51-40 42-28 plagioclase An An An An composition 1 0 « 45 36 hypersthene E n ^ En^ En^ composition augite Wo En Fs Wo En Fs Wo En Fs composition ^ 33 23 46 38 16 45 35 20 Textures vary in a systematic fashion across the diorite. Plagioclase from type-I are unzoned, An , while those from type-Ill show weak normal 45 and oscillatory zoning of An . Most plagioclase appears pale pinkish to 51-40 the unaided eye. This pink colour of most of the plagioclase is probably due to an abundance of very minute hematite (?) inclusions. Antiperthite, found mostly in type-I and -II diorite, occurs in crystals that are strorsgly deformed. Hornblende increases from 1$ to 20$ across the diorite (figure 6). Some of the increase in hornblende is the result of the replacement by magmatic reaction of augite. In type-II and -III diorite, however, F IGURE 6 M o d a l V a r i a t i o n s in the D i o r i t e r 80-Specimens arranged in schematic order from type I to type III diorite .Mount Ogilvie Wells Peak o Sketch of the Distribution of the Three Types of Diorite South of the Fraser River SCALE: Horizontal; Distance between Hope and Hunter Creek is about 6 miles Ver t i ca l , Elevation at Flood, 150 feet E levat ion at point 'A ' above F l o o d , 5 0 0 0 f e e t O K-Ar age (in million years) (Contacts between the various types of diorite are gradation and dips of contacts are highly speculative) FIGURE 8 21 Hypers thene -Amph ibo le Relat ionships in Dior i te and Adjacent Tonalite (a) type I (b) type II mm (c)type II (d)type (e) type (f) transition zone (g) tonalite L E G E N D iT-fi hypersthene "anthophyllite" | | pargasite green hornblende 2 2 . hornblende poikilitically encloses plagioclase and appears to have crystallized directly from the magma. The modal percentage of hypersthene is nearly constant from type-I to type-Ill. Hypersthene from type-I shows l i t t l e alteration. However, a very fine fibrous mineral with parallel extinction (possibly anthophyllite) first appears in hypersthene from type-II and replaces as much as 20-30$ of the hypersthene in type-Ill diorite. Green hornblende and minor amounts of colourless amphibole, possibly pargasite (2V2 75-80°), appears to have developed along with the "anthophyllite". Amphibole-hypersthene reactions are illustrated in figure 8. The reaction of augite to hornblende appears to take place with much greater ease than the reaction of hypersthene to hornblende, possibly, in part, as a consequence of the relatively close similarity in crystal structure of augite and hornblende. Tonalite Tonalite, rimming the diorite, is mesocratic, medium-grained and well foliated. On a regional it is homogeneous (as shown by modes listed in table 3) but in outcrops locally abundant mafic schlieren may give the rock a heterogeneous appearance. Plagioclase shows normal zoning, An^ Q to An2g. Crystals are subhedral with a tendency to be somewhat ovoid. The rocks contain no pyroxene, but worm-like quartz in some hornblende suggests its former presence. Close to the diorite, colourless pargasite cores are found in some green hornblende (figure 8). Quartz occurs mostly as irregularly rounded crystals, and, to a lesser extent, as fine granules along grain boundaries of plagioclase. The tonalite everywhere shows protoclastic textures. Deformation twin lamellae in plagioclase, bent biotites, undulose extinction in quartz, and fine mortar texture are found uniformly throughout the phase. These F I G U R E 7 0 - » 9 Variation in Modal Percentage of Minerals fn Diorite and Tonalite Across the Contact Near Hunter Creek D i o r i t e Transit ion Zone T o n a l i t e 6 0 -3 0 - 50' 2 0 -and - -o— BIOTITE 0 co CM Scale I" = 1 0 0 0 ' 24. textures are found in the tonalite up to the contact with the diorite but not in the diorite. Zone Separating Diorite from Tonalite A 100 foot wide zone between diorite and tonalite is exposed 500 feet west of Hunter Creek. A single mode from this zone is listed in table 3. Plagioclase is zoned from An^ to An^o* Hypersthene has been very strongly altered to colourless pargasite and "anthophylliteM (figure 8). In tonalite to the west of this zone hypersthene is absent; in diorite to the east of this zone hypersthene is a major mineral. The rapid transition from type-Ill diorite to tonalite (figure 9) across this zone is striking and abrupt. Ultraroafic Bodies Ultramafic bodies, found only in the diorite, are of two types: pyroxenite and hornblendite. Pyroxenite is largely confined to type-I diorite and hornblendite is largely confined to type-Ill diorite. Hornblendite is much more abundant and forms much larger bodies than pyroxenite. Figure 5 shows the distribution of these bodies and figure 10, sketches of their typical forms. One-half to two-inch thick pyroxenite lenses and dyke-like bodies which parallel and cross-cut the foliation of the diorite appear to be replacement features partly controlled by pre-existing fractures (figure 10). Augite (Wo^En^Fs-ic)) and hypersthene (En^o), the dominant minerals,, are similar in composition to pyroxenes from the diorite. Nearly a l l these bodies contain minor quartz. Plagioclase (An^j) appears to be relict from diorite. Brown to green pleochroic hornblende (0-15$) replaces pyroxenes. One thin section contained a single grain of alkali feldspar, the only alkali feldspar seen in the Spuzzum Intrusions. 25. FIGURE 10 Sketches of U l t r a m a f i c Bodies in the Spuzzum Intrusions Hornblendite in type III .Diorite near the head of America Creek. The spotted pattern represents amphibolite zones scale in feet Pyroxenite lens in type I Diorite, south of Flood. scale in inches scale in feet Pyroxenite replacement body in type I Diorite, north of the forks in Hunter Creek Dashed lines mark foliation in the Diorite 2 6 . Hornblendite "dykes" up to 5 feet across have sharp to gradational contacts with diorite. Hornblendite consists of brown to green pleochroic hornblende (2VX 75-80°, z Ac 15°). Feldspathic hornblendites with 75-85$ hornblende, 5-25$ plagioclase (^ 30-65)> minor biotite (0-5$), opaques and quartz are generally marginal to hornblendite. STRUCTURE Internal Structure Relation of Tonalite to Diorite Evidence of the relative ages of diorite and tonalite is inconclusive but the diorite seems to be the older of the two. In a few places, the foliation in the diorite has been truncated by the tonalite (figure 11). The more basic and mafic composition of the diorite is compatable with its being older than the tonalite. The ultramafites are confined to the diorite. If diorite were the younger phase then these crosscutting bodies should be found also in the tonalite. In addition, xenoliths of gneiss and calc-silicate rather than tonalite are found along the margins of the diorite. (figure 5). Xenoliths Two types of xenoliths occur in diorite. Small (2 inch to 1 foot) blocks of biotite-garnet gneiss and of pyroxene granulite are found mainly in type-I and type-II diorite. Calc-silicate and marble inclusions are found in type-Ill diorite along Hunter Creek and also l£ miles west of Haig Station. Most of these blocks range up to 5 feet across but a 40 foot block is found along the C.P.R. tracks west of Haig Station. These limey inclusions are found along the margins of the diorite (figure 5). The foliation of the diorite seems to sweep around the xenoliths. 27. FIGURE II F o l i a t i o n s in the Spuzzum Intrusions and the Adjacent Metamorphics of the Chilliwack G r o u p Sca le in milefe 28. Mineral assemblages developed in the calc-silicate xenoliths are confined to specific layers, originally beds. Plagioclase (AnD«5 to An^), scapolite, clinozoisite, augite, hypersthene, quartz, garnet (G^gAnd^Py^), sphene, hornblende, wollastonite and biotite are found in these xenoliths. The mineral assemblages from various layers in the calc-silicate xenoliths are listed in table 5. TABLE 5. Mineral assemblages from various layers in the Calc-silicate Xenoliths in the Spuzzum Diorite. Xenoliths along Hunter Creek a) plagioclase (An^^) - Scapolite-diopside-sphene-quartz. Xenolith !§- miles west of Haig Station a) Calcite b) Quartz-Calcite c) Wollastonite d) Grossular-Wollastonite e) Grossular-Clinozoisite-Diopside-Quartz f) Scapolite-Clinozoisite-Quartz-Diopside g) Scapolite-Plagioclase (An^g)-Quartz-Diopside h) Plagioclase (An^-Qua^z-Diopside-Hornblende i) Hypersthene (En7i)-Diopside-Biotite-Plagioclase j) Biotite-Homblende-Sphene k) Clinozoisite-Grossular-Sphene-Quartz Foliations Both diorite and tonalite are well foliated. The foliation in the diorite i s , in places, clearly not conformable to the foliation in the tonalite (figure 11). The distribution of foliations in diorite suggests the presence of two crude dome-like structures, one north of the Fraser River and the other south of Flood. The foliation is best developed in type-I diorite. Here, i t strikes easterly and dips gently to the north, but i t steepens 29. and tends to strike northerly in type-II and -III diorite. In type-I and -II diorite, bent plagioclase laths are surrounded by undeformed plagioclase, suggesting protoclasis. A foliation in tonalite is outlined by the alignment of plagioclase, mafics and schlieren. This foliation is partly cataclastic in origin. Bent plagioclase and biotite, strained quartz and fine mortar texture is distributed uniformly throughout the tonalite. Part of the foliation may be due to shearing associated with the Shuksan and Fraser River faults. Near these faults, prehnite, epidote, albite and tremolite have developed. This foliation, however, is not due entirely to shearing along these faults as protoclastically deformed tonalite is found immediately against unsheared type-Ill diorite. EfrtflrnaJ, Relations Contact Relations Only the tonalite is in contact with the schists. The foliations in the schists and the tonalite are concordant (figure l l ) , although on a small scale local discordance is found. Contacts between tonalite and metamorphics are gradational over 10 to 50 feet and in general may be ) called sharp. The pluton has not disrupted the regional foliation but has truncated the regional metamorphic isograds (Read I960, McTaggart and Thompson 1967 and Lowes 1968). No dykes of tonalite were seen in the metamorphics but a small stock of tonalite, probably a cupola, intrudes schists just north of America Creek. The eastern contact between tonalite and Eocene conglomerate is faulted. Both the Upper Tertiary Silver Creek Stock and the Mount Barr Batholith intrude the tonalite. 30. Contact Metamorphism The tonalite intrudes kyanite-staurolite-garnet-biotite-sericite schists (Read I960), probably correlative with the Chilliwack Group. This regional metamorphism appears to be related to the emplacement of the Spuzzum Intrusions. McTaggart and Thompson (1967) state that near the type locality of the Spuzzum Intrusions northwest of Stout, British Columbia, "... regionally metamorphosed rocks and the Spuzzum Intrusions belong to the same episode of orogeny.M Read (i960), working on the metamorphic rocks west of Hope, related metamorphism to the Coast Range Intrusions. These views are supported by the occurrence of high grade metamorphics only in the vicinity of the Spuzzum Intrusions. Staurolite-garnet grade schists of the Chilliwack Group occurs adjacent to the Spuzzum Intrusions just south of Laidlaw, British Columbia, but five miles to the southwest these same rocks are metamorphosed only in the greenschist facies. The shaded area in figure 12 shows the P/T conditions of regional metamorphism developed adjacent to the Spuzzum Intrusions. The lower temperature limit is defined by the stability of staurolite; the upper temperature limit and lower pressure limit is defined by the stability of kyanite (Richardson et. al 1969). A later contact metamorphic aureole some 1000 yards wide was super-imposed on the regionally metamorphosed schists. In the schists close to the contact with the tonalite, fibrolite and sillimanite occur with muscovite and biotite, while further away coarse porphyroblasts of muscovite and chlorite pseudomorph staurolite. Thus, i t appears that the tonalite has truncated the earlier-formed regional metamorphic isograds and superimposed a younger thermal metamorphism upon the older regional metamorphism. Figure 13 illustrates the change in the mineral 31. F IGURE 12 P/T Stab i l i t ies for some .of the Minerals in the Contact Aureole Adjacent to the Spuzzum T o n a l i t e 81 to cr < co o UJ cc CO CO UJ cc a. I • A and C , a f ter Hoschek (I969) A1 and B1, univariant curves for A and B under conditions of P H o n ptnt » X H « O = 0 - 5 Hoschek (I969) H 2 ° , O T ' H 2 ° A l - s i l i c a t e triple poiint (Richardson et al I969) 4 0 0 5 0 0 6 0 0 T E M P E R A T U R E i 7 0 0 ° C 8 0 0 32 . FIGURE 13 Contact A - F - M Diagram for Regional and Metamorphic Rocks Adjacent to the Spuzzum Tona l i te Staurolite Almandini Kyanite, SilJimanite • Muscovite + Quartz Biotite Kyanit e - Staurolite - Almandine-Biotite-Muscovite-Quartz schists from the regional metamorphic rocks adjacent to the Spuzzum Tonalite (areas in the triangles represent assemblages) Sil l imanite-Biotite-Muscovite-Quartz schists developed by contact metamorphism from the regional metamorphic rocks adjacent to the Spuzzum Tonalite Only the composition of the biotite is known (Read I960) (after Thompson 1957) 3 3 . assemblage developed during regional metamorphism to the mineral assemblage developed during contact metamorphism close to contact with the tonalite. In the outer part of the contact aureole, muscovite and chlorite formed at the expense of staurolite. This reaction, muscovite + chlorite — s t a u r o l i t e • biotite (figure 12, curve A) has been determined by Hoscheck (1969). Near the tonalite, sillimanite, muscovite and biotite are stable. The formation of sillimanite was not controlled by the reaction: muscovite + quartz — s i l l i m a n i t e + K-feldspar + Water as muscovite and quartz are stable with sillimanite, and orthoclase is absent (figure 12, curve B). Hoscheck (1969) studied the reaction (figure 12, curve C) staurolite + muscovite +> quartz — A l - s i l i c a t e • biotite Alternative reactions for the formation of Al-silicate from staurolite have been suggested by Ganguly (1968); 6 staurolite + 3 quarts + 20? — - 27 Al-silicate + 4 magnetite + 3 H20 and Winkler (1967) staurolite • muscovite + biotite-^ + quartz - — ^ A l - s i l i c a t e + biotite 2 In the latter reaction (Winkler 1967) biotite 2 is richer in iron than biotite^. Read (i960) found biotite from the contact metamorphic sillimanite zone north of American Creek to be richer in iron than biotite from the regional metamorphic staurolite zone. Figure 13 illustrates the formation of sillimanite + fe-biotite from staurolite + kyanite + Mg-biotite in the contact aureole. The curves (A, B and C) shown in figure 12 probably represent maximum temperatures. However, i f these reactions occurred under conditions of PH 2O < ptot o r k^ S*1 ^02» the stability fields of staurolite would tend to shift to lower temperatures (Ganguly 1968, Hoscheck 1969). Moreover, i t is possible that the reaction of 34. staurolite — A l u m i n o - s i l i c a t e does not represent an increase in temperature close to the contact with the tonalite, but rather, may represent a region of higher PQ^ where staurolite is unstable (Ganguly 1968). The contact metamorphic mineral assemblage adjacent to the tonalite appears to have developed at a higher temperature and/or more oxidized environment than the regional metamorphic mineral assemblage. Assuming that the contact metamorphism occurred under Pg^ c- = ^tot» contact metamorphic mineral assemblage developed at a pressure of about 4^ kilobars (figure 1 2 ) . CHEMISTRY Of eight chemical analyses (table 6) from the Spuzzum Intrusions, five are from the diorite and three are from the tonalite. Chemically the diorites are nearly homogeneous. Silica and alumina show l i t t l e or no variation. The relatively high silica value for specimen 265 may be misleading as its modal quartz is higher than typical specimens of type-Ill diorite (table 3 ) . Lime, magnesia and iron decrease slightly from type-I to type-III diorite. Figure 14 B illustrates the degree of chemical variation across the diorites. The variation in modal mineralogy for the specimens analysed is plotted for comparison in figure 14 A. These two figures show that, although there is a very marked change in modes from type-I to type-III diorite, there is l i t t l e accompany-ing chemical change. The apparent petrographic uniformity of the tonalite is supported by the small variation of the few chemical analyses available. Specimen 004 (figure 1 4 ) , which differs slightly from the other two, was collected 400 feet from the diorite. Its lower silica and higher alumina, lime and magnesia may be due to contamination by the diorite. 35. TABLE 6. Chemical Analyses of the Spuzzum Intrusions D3.pr3.t3 Tonalite I II III 034 1220 262 126 265. 004 211 506 Si0 2 53.7 55.2 55.6 55.4 57.1 56.7 60.6 62.0 A1 20 3 19.4 19.1 20.4 18.4 19.0 17.9 17.1 17.2 MgO 5.4 5.8 4.8 5.2 4.1 4.9 3.2 4.3 FeO 6.9 5.8 4.9 5.4 4.1 4.8 4.0 4.3 Fe 20 3 0.9 1.0 1.2 0.7 1.4 0.9 1.0 1.4 MnO 0.13 0.12 0.08 0.11 0.09 0.09 0.09 0.09 CaO 8.4 8.0 7.1 7.4 7.1 6.7 5.9 5.6 Na20 3.6 3.6 4.2 3.8 4.1 4.0 3.9 3.6 K20 0.3 0.4 0.5 0.7 0.6 0.3 0.9 1.2 Ti0 2 1.28 0.76 0.31 0.72 0.67 0.77 0.67 0.71 P2°5 0.23 0.18 0.21 0.06 0.18 0.19 0.19 0.17 co2 0.1 *0.1 »0.1 *0.1 0.1 »0.1 0.1 0.1 H20 0.4 0.6 0.3 0.6 1.0 1.0 1.0 1.3 S 0.03 *0.01 0.01 0.03 0.01 0.01 0.02 0.01 * refers to a value less than the number indicated in the analysis 36. FIGURE 14 Variation Diagram of Modes and Oxides for Analysed Specimens from the Three Types of Diorite and the Tonalite a a> 8 0 1 75 70 65 60 55 5 0 204 ? 5 10 5 • 65 -60 . 0) •a 55 O 50 I 5-j hO 5 M O D E S p l a g i o c l a s e D I 0 R I T E T O N A L I T E type I type II type P hornblende quartz _i hypersthene -o-biotite augite O X I D E S S i 0 2 D I O R I T E T O N A L I T E - ° A l 2 0 3 type I type I I type + CaO FeO :--•»-<> MgO Na 2 0 K 2 0 i II 0 3 4 1 2 7 0 2 6 2 1 2 6 2 6 5 S p e c i m e n A n a l y s e d 0 0 4 211 50G 37. FIGURE 15 C a O - N a 2 0 - K 2 0 Plot for Spuzzum Intrusions • Spuzzum Intrusions + §cuzzy Pluton (from calculated chemical analyses from modes supplied by Dr. Hutchinson of thB Geological Survey of Canada) Gibson Peak Pluton (Lipman 1963) Trondhjemite Cornucopia Stock (Taubeneck 1967) Trondhjemite '» Southern California Batholith (Larsen 1948) - - - Calc-alkaline FIGURE 16 Triangular Plot of Modal Analyses from the Various Phases of the Spuzzum intrusions plagioclase mafic s • Spuzzum Qiorit-e o Spuzzum Tonalite in the map area, figure I + Spuzzum Tonalite from the type locality northwest of Yale x Scuzzy Pluton (modes of the Spuzzum Tonalite northwest of Yale and the Scuzzy Pluton supplied by Dr. Hutchinson) 38. Normalized Na20-K20-Ca0 values are plotted in figure 15. The trend shown in this figure suggests an a f f i n i t y with trondhjemitic rocks. The Scuzzy Pluton (Roddick and Hutchinson 1969) some twenty miles north of the map area i s thought to be a leucocratic phase of the Spuzzum Intrusions (Hutchinson 1970b). Modes from the Spuzzum Intrusions in the map area, modes from the type l o c a l i t y of the Spuzzum Intrusions north of Hope and modes from the Scuzzy Pluton are plotted i n figure 16. Tonalite from the present area i s similar to those from the type l o c a l i t y , hence correlation between the two areas of Spuzzum is possible. Three "chemical analyses" were calculated from the modes of the Scuzzy Pluton. Addition of these analyses to figure 15 reinforces the suggestion that the variation in the Spuzzum Intrusions follows a trondhjemite trend. PETROGENESIS . Depth of Emplacement Minimum depth of emplacement, deduced from contact metamorphic reactions, i s estimated to be about 15 kilometers. Determination of the thickness of cover over the intrusions can be estimated. On the eastern and western flanks of the axial belt, pre-Upper Cretaceous low grade metamorphic rocks are preserved. Thickness of these rocks (after Monger 1970) are lis t e d in table 7. Only the lowest stratigraphic unit, the Chilliwack Group, has been intruded by the Spuzzum Intrusions. Hence the thickness of cover i s a rough estimate of the depth of intrusion. The depth of emplacement estimated from stratigraphic thickness ranges between 12 and 17 kilometers, which i s comparable to the 15 kilometer estimate from the contact metamorphic assemblages. 39. TABLE 7 . Pre-Upper Cretaceous Sediments and Volcanics in the Hope Map Area. Western Belt Eastern Belt Formation or Group Thickness Formation or Grouo Thickness Lower Cretaceous Broken Back H i l l Fm Peninsula Fm Agassiz Prairie Fm 3700» 13001 5000' Jackass-Pasayten Gp 14,000' Kent Fm B i l l Hook Fm 3000' 18001 Dewdney Creek Gp 11,000' Jurassic Mysterious Fm Echo Island Fm 2900' 2800' Triassic Harrison Lake Fm Cultus Fm 9200' 4000' Ladner Gp 6,000' Upper Chilliwack Gp 5700' Hozameen Gp 26,000' Paleozoic Total Thickness 39,400' Total Thickness 57,000* Origin of the Zoned Diorite Complex^  Augite-hypersthene diorite (type-I) of the core grades into and is surrounded by augite-hypersthene-hornblende diorite (type-II) which is in turn rimmed by biotite-hypersthene-hornblende diorite (type-III). Little or no chemical variation accompanies the variation in mineralogy. The origin of the mineralogical zonation might be due to different conditions of P H 0 across the diorite melt during crystallization, type-I diorite 2 having crystallized under drier conditions than type-III diorite as suggested by the near absence of hydrous mafics in type-I diorite and the abundance of hydrous mafics in type-III diorite. 40. The replacement of augite crystals by hornblende implies an increase in PJJ^Q with time. Clinopyroxene-hornblende stability relations under varying conditions of water pressure are shown in figure 17 (after loder and Tilley 1962). In this figure, pyroxene is stable to the right of the dashed curves while hornblende is stable to the left of the dashed curves for a particular P^O* point "1", for example, in figure 17 under a Pg^ o o r > 1 kilobar (dashed curve Pg^ o = 1 Kb applies), pyroxene is the stable mafic, but i f Pg^g increases to 3 kilobars (dashed curve Pg^ Q = 3 Kb applies) then hornblende is the stable mafic. The ortho-pyroxene-hornblende reaction in the Hope area appears to be similar to the clinopyroxene-hornblende reactions. Hypersthene and augite were the first mafic minerals to crystallize from the diorite melt. As ^fi^O ^ the melt increased, whether by the precipitation of anhydrous minerals or by contamination from the adjacent country rock, both pyroxenes were replaced by hornblende. The conversion of augite to hornblende preceded the conversion of hypersthene to hornblende ( figures 6 and 8). Possible paths of crystallization in the system clinopyroxene-hypersthene-hornblende-liquid-vapour are shown schematically in figure 19. Of the four possible configurations in figure 19, B is considered to be the most probable crystallization path the mafics followed as i t conforms best to the sequence of mafic reactions outlined above. Crystallization followed one of the two univariant curves, Liq —»• opx • cpx + v , or , cpx • opx • L —*• Hb, to the invariant point. It remained at this point until one of the phases, (clinopyroxene) was used up. 41. FIGURE 17 Schematic Stability Curves of Amphibole-temperature >• temperature >• (diagram -modified after Yoder a'nd Tilley 1962) FIGURE 18 Liquidus Relations in the System A n R n - D i - E n at I Atmosphere and 15 Kilobars An so Diopside (after Emslie 1971) 42. Crystallization then proceeded along the univariant curve Liq • opx » Hb * V, until either the orthopyroxene was converted to hornblende or the liquid was consumed. The latter appears to be the case for the crystallization of the Spuzzum diorites. The bulk composition of the Spuzzum diorite appears to l i e within the shaded triangle bounded by Liq-Hb-opx in the ternary diagram B in figure 19. The estimate of 38$ plagioclase, 12$ hypersthene and 2$ augite that separated from the diorite to form the tonalite (table 8) supports the hypothesis that the mafic bulk composition of the diorite lies within this shaded triangle. The decrease in the percentage of plagioclase from type-I to type-III can also be explained by crystallization under different conditions of PJJ^Q. From a melt of constant bulk composition, plagioclase would tend to crystallize earlier from a "dry" magma than it would from a "wet" magma (figure 18). In this system (figure 18), the eutectic moves towards the plagioclase apex with an increase in Ptotal» a n increase in ^ H^ O and/or an increase in the amount of soda (Eraalie 1971). Under the "dry" conditions hypothesized for the crystallization of the core of the diorite, the eutectic might be at "A" in figure 18 and plagioclase would be the fir s t mineral to crystallize. With an increase in P H Q, the eutectic might shift to point "B" (figure 18), and a mafic mineral rather than plagioclase would be the first mineral to crystallize. However, as Pg Q increases, hornblende rather than pyroxene is the stable mafic. The crystallization of hornblende removes alumina from the melt. As alumina is a principal component in plagioclase, the removal of alumina limits the amount of plagioclase that can crystallize from the melt. Hence, i f the bulk composition of the system remains constant, then an increase in the amount of hornblende must be accompanied by a decrease in the amount of plagioclase. - 43. FIGURE 19 Schematic Phase Relations in the System Opx-Cpx-Hb-Liq-H20; with Reference to the Crystallization History of the Mafic Minerals in the Diorite Phase of the Spuzzum Intrusions A B C D 44. The crystallization of hornblende (and biotite) also increases the amount of silica in the melt. This enrichment of the melt in silica might explain the increase in quartz from type-I to type-Ill diorite. An increase in water pressure in the melt would tend to lower the liquidus-solidus curves in the system albite-anorthite. This might account for the change from unzoned An^ «j in type-I diorite to zoned ^51-40 type-Ill diorite (See figure 62). The development of hydrous minerals in type-Ill and the greater abundance of plagioclase in type-I is thus attributed to a greater water content in the marginal parts of the diorite magma than in the central parts. The relatively high water content of the margins of the diorite magma might simply have been a result of i n i t i a l distribution in the melt, or, i t might have been caused by contamination from the adjacent country rock. If the partial pressure of water in the country rock was higher than the partial pressure of water in the melt, water would have tended to diffuse into the magma. Also, i f the central part of the magma chamber was hotter than its marginal parts, one would expect a higher water content in its margin (Burnham 1967), or migration of water from its hotter parts (Kennedy 1955). Whether water diffused in from the country rock or migrated outward from the central part of the magma, i t could carry with i t silica and potash as contaminants, thus accounting for the higher amounts of these oxides in type-Ill diorite. Cr7gtaTaiz,ation off the Tonalite The tonalite is believed to represent a further differentiated part of the magmas from which the diorites crystallized. The abrupt transition between diorite and tonalite suggests that differentiation did not occur 45. at the present level of exposure. Plagioclase, with relict patchy zoned cores of An^ ,. and hornblende with wormy quartz and colourless pargasite cores marking the former presence of pyroxene, may indicate the former presence of minerals found in the diorites. The chemistry and mineralogy of tonalite (figure 14) could be developed by fractional crystallization of the dioritic magma. Tonalite apparently formed from diorite at depth (table 8) and subsequently intruded the diorite and the metamorphics. Judged by the abundance of cataclastic and protoclastic textures, the tonalite was probably largely crystalline at the time of its emplacement around the diorite. Origin of the Ultramaflcs The irregular bodies of hornblendite and pyroxenite appear to have formed, in part, by metasomatic replacement of the diorites along pre-existing fractures (figure 10). Compared to the diorite, the ultramafites are lower in silica and alumina. Formation of these rocks may develop by the addition of basic components to the diorite and/or by subtraction of acidic components from the diorite. Burnham (1967) has shown that a hydrous fluid may dissolve considerable amounts of silica, alumina, potash and soda (up to 9.2 weight percent at 10 kilobars) but negligible amounts of lime, magnesia and iron. Calcic-plagioclase (as seen in the feldspathic hornblendites) can be produced from sodic plagioclase in a hot hydro-thermal fluid by the selective solution of soda (Adams 1968). It is possible that these ultramafites were formed in part by the sub-traction of acidic components from the diorite by a "hot hydrothermal fluid". The occurrence of hornblendite along the margins of the diorite and pyroxenite in the core may be a function of a higher temperature in the latter region. At constant ^ H^ O* a -'•ower temperature favours the stability of hornblende in the presence of a vapour phase rather than pyroxenes (figure 19 B). 4 6 . TABLE 8. Differentiation of the Diorite to form the Tonalite by fractional Crystallization. Average Composition of the Diorite Composition of the Diorite meltj after removing 52$ Crystals Average Composition of the Tonalite Composition of the Crystal Residue S i 0 2 5 6 . 5 6 0 . 4 6 1 . 4 52.8 A1 2 0 3 19.6 17.0 17.7 2 2 . 0 MgO 5 .2 3 . 6 4 . 3 6 .5 FeO 6 . 6 7 .0 5.6 6 . 3 CaO 7.7 6 . 8 6 . 3 8 . 4 Na20 4 . 0 4 . 0 3.9 4 . 2 K20 0 . 5 1.1 1.1 0 . 0 Removing 38$ plagioclase (An^)» 2$ augite (Di^Hd-j^) and 12$ hypersthene (En^Fs^) from a melt of the composition of the diorite, a melt of the composition of the tonalite could be formed. * Analysis above were normalized to 100$, after the removal of T i 0 2 , MnO, P20^, C02, and H20. ** Minerals listed above are normative minerals. 47. Emplacement of Diorite and Tonalite The dome-like structures in the diorite, probably caused by the alignment of crystals in a mush during emplacement, suggests that i t was emplaced as a diapir. This unit was most likely completely crystalline before the emplacement of the tonalite. The tonalite magma, upon rising through the crust, apparently engulfed and, truncated structures in, the diorite. Emplacement of tonalite may have been facilitated by detachment and sinking of the diorite pluton. Figure 20 illustrates the sequence of emplacement of the phases of the Spuzzum Intrusions. The tonalite seems to represent a syn-orogenic intrusion while the diorite may represent an earlier, possibly even pre-orogenic intrusion, emplaced before the period of regional deformation. The concordance of the northwest-trending foliations in the tonalite and adjacent schists and the protoclastic texture in the tonalite suggests that the tonalite was emplaced during a period of regional deformation. If as suggested, the diorite is older than the tonalite, then the discordance of the foliation of the diorite to the regional foliation (figure l l ) suggests possibly that i t was emplaced prior to the time of the development of the northwest-trending foliation. The anomalous 103 million year age of tonalite, taken 400 feet from the diorite (figures 1 and 5), is possibly due to contamina-tion by the older diorite. 48 FIGURE 20 I l lustration Emplacement < a) Emplacement of the Diorite into the metamorphic rocks of the Chilliwack Group of the Sequence of the Phases of the Spuzzum Intrusions b) Development of the Ultramafic bodies, pyroxenite in the core and hornblendite in trre margins c) Emplacement of the Tonalite d) Schematic present day cross-section 49. TALE INTRUSIONS INTRODUCTION The Yale Intrusions (McTaggart and Thompson 1967) are a group of stocks and s i l l s that l i e along a belt extending from three miles north of Yale, British Columbia, southward to near the head of Silver Creek. Rocks included in this unit range in composition from granite to gabbro, with granodiorite the most abundant. A cataclastic texture, which varies from incipient mortar texture to mylonite, is everywhere present. Only the Yale rocks immediately east and south of Hope were studied in detail (figures 1 and 4). An older intrusion, the Ogilvie tonalite, crops out along the extreme eastern margins of the map area. South of Berkey Creek, this unit appears to grade into granodiorite. A 24 square mile area stock composed of leucocratic quartz monzonite (the Coquihalla Stock) underlies the area between Kakawa Lake and Wells Peak. Gneissic quartz monzonite bodies south of Wells Peak appear similar to the Coquihalla Stock. A gabbro-diabase complex, some 2 to 3 square miles in area, appears to be a large inclusion contained entirely within the Coquihalla Stock. A fourth unit, the Williams Peak tonalite, lies one mile northwest of Chilliwack Lake. Although at some distance from the known belt of Yale Intrusions, i t has been included in this section because of its petrographic and chemical similarities to the Ogilvie tonalite. MINERALOGY AND PETROLOGY  Ogilvie Tonalite A typical specimen of Ogilvie tonalite contains ovoid plagioclase (0.5 to 2 cm) surrounded by fine-grained quartz, hornblende and biotite. Alkali feldspar is absent. A cataclastic foliation is developed in the western exposures and at contacts with older rocks. Modes are listed in table 9. 50. Plagioclase (An^ to Ar^g), with up to 70 zones, is the dominant mineral in thin section. The coarse ovoid plagioclase crystals are composed of intergrowths of as many as six individual crystals in a synneusis relationship. Hornblende, as fine greenish to blue-greenish laths, is subordinate to brown biotite. Sphene, ilmenite, apatite and red brown tourmaline are accessories in most specimens. Williams Peak Tonalite The Williams Peak tonalite is very similar to the Ogilvie tonalite but tends to be more heterogeneous. Specimens show rounded to ovoid plagioclase in a matrix of quartz, hornblende and biotite. Alkali feldspar is lacking. A cataclastic foliation, related to faulting, is well developed along the margins of the stock. Modes are listed in table 9. Oscillatory-zoned (up to AO zones) plagioclase ranges in composition from An^^ to A J ^ . Synneusis aggregates are common. Acicular to stubby hornblende is green to blue green. Accessories are tourmaline, ilmenite, apatite and sphene. Alteration is intense. A l l plagioclase show partial to complete replacement by albite, clinozoisite, sericite and calcite. Biotite has been altered completely to chlorite and small amounts of prehnite, epidote and sphene (leucoxene). Tremolite after hornblende is not uncommon. Veins of coarse-grained epidote and quartz are pervasivej albite-epidote-chlorite veins are common. Secondary biotite has been developed at contacts with the Chilliwack Batholith. Coquihalla Quartz Monzonite Stock The Coquihalla phase is a homogeneous, leucocratic, medium-grained quartz monzonite. A complete gradation between unsheared and intensely sheared rocks marks the only obvious variation found in the pluton. 51. TABLE 9. Modes of the 126 plagioclase 31.9 quartz 38.1 orthoclase 26.1 hornblende t r biotite 3.3 opaques 0.4 132 plagioclase 58.4 quartz 25.1 orthoclase 4.3 hornblende 2.0 biotite 7.5 chlorite 0.8 epidote tremolite -sphene prehnite tourmaline apatite opaques 0.9 Tale Intrusions Coquihalla Stock 222 302 221 33.5 31.6 41.4 29.3 31.7 25.8 34.8 33.8 26.1 1.4 2.4 7.0 tr 0.4 tr Ogilvie Stock m 082 096 60.7 52.8 67.8 23.5 31.2 18.1 1.3 3.2 3.9 10.7 9.5 8.9 0.4 2.6 -3.2 tr -tr 0.4 0.4 — — tr t r t r t r t r 0.3 0.6 5M 586 36.9 48.2 26.8 25.8 32.3 19.6 tr 3.2 4.7 tr tr Williams Peak Stock 737 7J0 60.8 64.0 60.1 24.0 16.2 22.2 5.7 21.1 — - 0.5 • 1.8 6.6 7.6 5.3 2.4 0.6 1.1 - - 6.3 0.3 tr 1.7 — 0.6 0.4 - - 0.4 t r t r t r t r 0.5 t r 52. Eastern exposures are homophanous vhile west of Kakawa Lake and south of Hope Mountain the rocks are intensely sheared, showning augen of K-feldspar. Modes are listed in table 9. Fine- to medium-grained subhedral plagioclase (An-^ *° ^ n25^ B^0VB moderate oscillatory-zoning (10 to 30 zones) in its core and normally-zoned rims (An2<5 to An^). Alkali feldspar (0r^ to 0rg2) is interstitial to plagioclase, and commonly forms poikilitic crystals. As the degree of shearing increases, the poikilitic crystals take the shape of augen. A l l K-feldspars show patchy to incipient development of microcline twinning. Structural states (figure 21 and table 10) are transitional between microcline and orthoclase. (The method of study of alkali feldspar structural states and compositions is presented in the appendix.) Mafics are minor biotite and rare hornblende. Tourmaline, magnetite and sphene are common accessories. Gabbro-Diabase Complex A gabbro complex, 2 square miles in area, is contained entirely within the Coquihalla Stock (figure 22). Contact relations between mafic rock and quartz monzonite are varied. An agmatite zone, occasionally up to 100 yards across, most commonly separates massive gabbro and diabase from quartz monzonite (figure 22) but contacts may be sharp (figure 23) or indefinite (figure 23). Modes from the complex are listed in table 11. Table 10. A l k a l i Feldspar Data for the Yale Intrusions 29 26 26 specimen (060) CSOif) Or 220 41*79 5 0 . 7 2 21.18 75 081 41.76 50-74 21.18 75 080 41.79 50.74 21-15 78 306 41 .72 50.71 21.19 73 303 41 .77 50.76 21.12 81 527 41 .85 50.79 21.11 82 FIGURE 21 Structural States of Alkali Feldspars from the Yale Intrusions Microcline High Albite 54. TABLE 11. Modes of the Gabbro Complex Oliyine-diabase Inclusion Gabbro Diabase Hybrid plagioclase 36.9 45.9 57.1 quartz - 1.0 10.9 orthoclase - • - 2.4 olivine 28.0 - -orthopyroxene 7.6 - -augite 12.2 11.7 0.6 hornblende 7.9 15.0 18.9 biotite 5.9 4.2 7.2 tremolite tr 17.8 -chlorite 0.4 1.5 0.5 sphene - - 0.7 apatite 0.4 0.7 tr opaques 2.1 2.3 1.7 In gabbro, phenocrysts are olivine (Fog*j) and weakly zoned plagioclase (AnyQ to An^) clouded with dust-sized inclusions. Augite (Wo^En^QFs-^) and hypersthene (Engg) are interstitial to olivine and plagioclase. Pyroxenes are replaced by brown pleochroic (2VZ 80-90°) and green pleochroic (2VX 80-90°) hornblende. Pale brown and greenish to colourless micas are associated with hornblende. Diabase shows plagioclase (An^Q^g) and augite in an ophitic relation-ship. Augite is partly to completely replaced, first by brownish hornblende and then by greenish hornblende. The replacement of augite by hornblende results in a striking poikilitic texture with plagioclase enclosed in hornblende. 55 F I G U R E 2 2 Distribution of Gabbro, Diabase and Agmat i te in the Gabbroic Inclusion in the Coquihal la S t o c k , East of H o p e , B . C . Mount Ogilvie I S c a l e in m i l e s Hope Mountain L E G E N D [v^vj Coquihal la Quar tz Monzonite S t o c k \\*\ Ogilvie T o n a l i t e Stock f-VVo| G a b b r o , D i a b a s e and minor Agmatite A g m a t i t e 6 4 Upper Pa leozo ic Rocks ( C u s t e r Gneiss Group) and Hozameen 56. FIGURE 23 Contact R e l a t i o n s Between C o q u i h a l l a Quar tz M o n z o n i t e and the Gabbro Complex the S t o c k a) C o n t a c t one-half mi le east of the north shore of Kakawa Lake t>r Contact one mile s o u t h - e a s t of Kakawa Lake 57. Many of the basic fragments in the agmatite are fine-grained, and do not resemble gabbro or diabase. Presumably they have been changed by contamination in the quartz monzonite. Plagioclase usually shows calcic cores of An^ Q to An^ Q replaced by Ang^^^* Hornblende, some with cores of augite, is the dominant mafic. Quartz, alkali feldspar and oligoclase were probably introduced from the quartz monzonite. STRUCTURE Foliations A l l the units of the Yale Intrusions display some degree of cataclastic foliation. McTaggart and Thompson (1967) relate the degree of shearing in the intrusions to proximity to the Fraser River fault zone. Their thesis is supported for the intrusive rocks east of Hope where the degree of cataclasis markedly increases towards the Fraser River. Distribution of shear zones in rocks of various ages suggests that several episodes of shearing took place. The Ogilvie tonalite east of outcrops of unsheared Coquihalla quartz monzonite shows abundant textures developed by cataclasis. Moderately cataclastically deformed Ogilvie tonalite is intrusive into highly sheared volcanics of the Hozameen Group. Adjacent to the southern extension of the Fraser River fault, the Williams Peak tonalite has been converted to an augen gneiss. Internal Relations of the Yale Intrusions The Ogilvie tonalite is the oldest of the Yale Intrusions studied. Dykes of the Coquihalla phase cut the Ogilvie tonalite. To the south, the Ogilvie seems to grade into K-feldspar-bearing tonalite and granodiorite. Here, the Coquihalla phase is also intrusive into the Ogilvie tonalite. Relative age relations between the gabbro complex and the Ogilvie phase are unknown. The Williams Peak tonalite is isolated from the other plutons of the Yale Intrusions. It resembles the Ogilvie phase. 58. Elusions, Inclusions, though not common, are large. Previously mentioned is the 2 square mile area of gabbro included within the Coquihalla phase. One meta-chert and meta-volcanic (fine-grained amphibolite) inclusion in the Ogilvie phase was traced for over 1000 feet. Three blocks of gneiss, each greater than 100 feet across, were found in the Williams Peak tonalite. These large blocks may be xenoliths or possibly pendants. In the Ogilvie phase, i t is likely that the inclusions are pendants as the roof of the stock is very near the present level of erosion, exposed along the south slopes of Mount Ogilvie. The large inclusions in the Williams Peak tonalite cannot be fragments of the roof of the pluton. There blocks are composed of kyanite, staurolite, garnet, quartz and plagioclase, which show metamorphic reactions to muscovite, biotite, cordierite, sillimanite and minor chlorite. These reactions are possibly controlled by the temperature and pressure conditions in the tonalite. The high grade gneissic inclusions cannot have been derived from the adjacent Chilliwack Group, as the highest grade of metamorphism reached for the Chilliwack Group in the vicinity of the stock is lower greenschist. They must, therefore, have originated at a deeper level in the crust where the Chilliwack Group is of higher grade metamorphism or possibly from some other gneissic unit such as the Custer Gneiss or a basement complex. Contact Metamorphism Near Hope, greenstones of the Hozameen Group are converted to fine-grained amphibolites. Near and in the Fraser River fault zone, contact effects are obscured by pervasive shearing, although Read (i960) notes smeared garnet and hornblende developed in phyllites adjacent to sheared 59. plutonics thought to be equivalent to the Coquihalla stock. Minor muscovite, fibrolite and quartz are found in argillaceous sediments of the Hozameen Group adjacent to the tonalites between Berkey and Wray Greeks. Staurolite, garnet, cordierite, biotite, minor muscovite and fibrolite are found in the Chilliwack Group east of the Williams Peak stock. The muscovite, biotite, cordierite and sillimanite found in the gneissic xenoliths, mentioned earlier, constitute a high temperature contact metamorphic assemblage. Cordierite found in the contact metamorphic rocks adjacent to the Yale Intrusions suggests a high temperature but only moderate pressure for contact metamorphism (Winkler 1967). Contact metamorphism of sediments adjacent to the Yale Intrusions appears to have taken place at a lower pressure than the contact metamorphism of sediments adjacent to the Spuzzum Intrusions, where cordierite is absent. AGE OF THE YALE INTRUSIONS . North of Yale, the Yale Intrusions intrude the Spuzzum Intrusions (McTaggart and Thompson 1967) and one-half mile north of Haig Station appear to be overlain unconformably by weakly indurated Eocene conglomerates. The Coquihalla phase has been intruded by the unsheared 35 million year old Silver Creek stock, which intrudes the Eocene conglomerates. K-Ar ages from the Yale Intrusions near Hope are listed in table 12. TABLE 12. K-Ar ages from the Yale Intrusions Pha.se, Berkey Creek (Ogilvie) Coquihalla Ogilvie Stock Williams Peak Stock Age (mtyt) 59 41 35 24 These K-Ar ages disagree with the relative ages of the Yale Intrusions 60. as determined from structural relations. The 59 million year old age from the Berkey Creek part of the Ogilvie tonalite is from the least sheared of the plutonic bodies related to the Yale Intrusions. The Ogilvie phase and the K-feldspar bearing tonalites about Berkey Creek appear to grade into one another, and are therefore probably of similar age. The Coquihalla stock intrudes the Ogilvie phase and is obviously younger. Lowering of the Ogilvie K^ar age may have been facilitated by intrusion and heating by the Coquihalla stock and by shearing related to the Fraser River fault zone. The Berkey Creek phase might represent the oldest, while the Coquihalla phase might represent the youngest of the Yale Intrusions. The 24 million year K-Ar age from the Williams Peak tonalite is anomalous. Its true age must almost certainly be pre-shearingj that is, older than the unsheared Eocene conglomerates. Its K-Ar age most likely reflects heating by the adjacent Chilliwack Batholith. CHEMISTRY Only general relationships can be inferred from the few chemical analyses of the Yale Intrusions, listed in table 13. The analyses of the three specimens from the Coquihalla stock (specimens 176, 220 and 581) are identical, except for a slightly higher value of Fe203 in specimen 176. A l l three display varying degrees of cataclasis; sepcimen 176 is undeformed, specimen 220 is weakly deformed and specimen 581 is strongly deformed. The similarity of the analyses from the Ogilvie tonalite (specimen 096) a'nd from the Williams Peak tonalite (specimen 1443) supports the petro-•graphic correlation of these two phases. Their low potash and high soda is noteworthy. 61. TABLE 13. Chemical A n a l y s i s of the Yale I n t r u s i o n s a. b. c. d. e. f . 126 220 5J1 026 1443 xm Si0 2 73.7 73.7 74.2 62.6 68.8 45.7 A 1 2 ° 3 14.3 14.6 14.3 16.6 15.2 18.3 MgO *0.5 *0.5 *0.5 1.7 1.5 7.3 FeO 0.7 0.9 0.8 3.3 1.7 6.5 Fe 2 0 3 2.9 0.2 0.3 1.9 1.1 1.9 CaO 1.1 1.2 1.3 4.3 3.2 10.6 Na20 4.0 3.9 3.5 4.5 4.7 2.7 K20 3.S 4.0 4.0 0.9 0.7 0.7 MnO 0.04 0.03 0.03 0.07 0.06 0.14 Ti0 2 0.19 0.17 0.17 0.67 0.36 1.49 P2°5 0.04 0.03 0.04 0.35 0.11 0.27 co 2 •0.1 *0.1 *0.1 0.1 0.2 *0.1 H20 0.4 0.3 0.3 1.0 1.3 2.0 s 0.02 0.02 0.03 0.05 0.01 0.03 a, b, c; C o q u i h a l l a Stock d; O g i l v i e Mountain Stock ej W i l l i a m s Peak Stock fj Gabbroic Complex The s i n g l e a n a l y s i s from the gabbroic complex, taken from the diabase (specimen 1339), i s s i m i l a r t o that of a high alumina b a s a l t . The norm of specimen 1339 shows 13$ normative o l i v i n e . Analyses of the C o q u i h a l l a p l u t o n f a l l near the t e r m i n a t i o n of a t y p i c a l c a l c - a l k a l i n e t r e n d ( f i g u r e 67). Both the O g i l v i e and W i l l i a m s Peak t o n a l i t e analyses show a f f i n i t i e s t o trondhjemites. I t i s p o s s i b l e t h a t these t o n a l i t e stocks represent the l a s t stages of Spuzzum i n t r u s i v e a c t i v i t y . 62. EMPLACEMENT OF THE YALE INTRUSIONS Most of the Yale Intrusions l i e along a belt of plutonic rocks that have been emplaced in abundance along or near an east dipping imbricate fault zone that separates the Hozameen Group from the Custer Gneiss (McTaggart and Thompson 1967). Evidence on the manner of emplacement of these intrusive bodies in the Hope area has been somewhat obscured by the pervasive cataclasis that affects both intrusive and metamorphic rocks. The large xenoliths included in the Ogilvie and Coquihalla phases suggest that stoping may have been important as a mechanism of emplacement. The alignment of foliations in the Hozameen Group parallel to the contact with the Ogilvie phase is suggestive of forceful emplacement or of convective flow during emplacement. The mode of emplacement for some of the larger stocks of the Yale Intrusions seems to have been by forceful emplacement and stoping along a fault zone. CORRELATION OF THE YALE INTRUSIONS Correlation between individual bodies of the Yale Intrusions (figure 24) is based primarily upon their sheared nature and relative age in reference to the Spuzzum Intrusions and the Eocene conglomerates. Except for the gabbro, nearly a l l units from the Yale Intrusions investigated show oscillatory-zoned plagioclase (An^^_20) and faint microcline twinning in alkali feldspar. However, the great variety of rock types does not allow a correlation based entirely upon mineralogy. Other units can be tentatively correlated with the Yale Intrusions. The Hells Gate Intrusion (Morris 1955), thirty miles north of Hope (figure 24), is mineralogically similar to the Coquihalla phase, shows a distinct cataclastic foliation, and has been cut by the Yale fault; its radiometric ages of 40 to 44 million years (Hutchinson 1970b) are 6 4 . similar to those of the Coquihalla Stock. Correlation of this stock with the Tale Intrusions has been suggested previously by McTaggart and Thompson (1967), Richards and White (1970) and Hutchinson (1970b). Monger (1970) has suggested that the Ruby Creek Heterogeneous Plutonic Belt (Misch 1966) is possibly correlative with the Tale Intrusions. South of Ross Lake, the north-northwest-trending Gabriel Peak quartz dioritic orthogneiss (Misch 1966) may be related to the Tale Intrusions (figure 24). A l l of these units belong to a post-Upper Cretaceous, post-metamorphic belt of sheared intrusive rocks that l i e in or near a fault zone separating the Custer-Skagit Gneiss from the Hozameen Group. The gabbroic complex at Kakawa Lake may not belong to the Tale Intrusions but may be related to a west-northwest-trending belt of ultramafic and mafic rocks found to the west of Hope (figure 25). This belt has been correlated by Monger (1970) with a north-trending belt, associated with the Shuksan fault, that extends from Mount Slesse, 20 miles south-west of Hope (figure 3). The abrupt change in strike of the fault zones and their associated ultramafites, however, from north-trending to west-northwest-trending suggests the possibility of two rather than a single belt of ultramafites. 65. F I G U R E 2 5 i Distribution of Ultramafic and Mafic Rocks and Associated Faults in the Hope Area 0 1 2 3 4 O 0 scale in miles LEGEND Upper Tertiary Intrusions Eocene Conglomerates \X| Yale Intrusions Spuzzum Intrusions and other Upper Cretaceous (?) bodies ylJ Chilliwack Group, Hozameen Group and Custer Gneiss Ultramafic and mafic rocks Faults Geology after McTaggart and Thompson (1967), Monger(l970) and this work 66 . SILVER CREEK STOCK INTRODUCTION The S i l v e r Creek Stock ( f i g u r e 26) represents the o l d e s t of the p o s t - t e c t o n i c p l u t o n i c bodies (found i n the map area. The s t o c k , composed e n t i r e l y of t o n a l i t e , i n t r u d e s the Eocene conglomerates and t r u n c a t e s t h e F r a s e r R i v e r graben. MINERALOGY AND PETROLOGY The t o n a l i t e i s composed of homogeneous, n o n - f o l i a t e d , mesocratic, hypidiomorphic, g r a n u l a r r o c k s . Modes ( t a b l e 14) and chemical analyses ( t a b l e 15) r e v e a l l i t t l e v a r i a t i o n . Subhedral p l a g i o c l a s e shows strong o s c i l l a t o r y - z o n i n g (up t o 30 zones). Compositions of cores of c r y s t a l s range from An^^ t o An^g and compositions of rims are normally-zoned from A ^ / j t o An 25« I n the cores of many of the c r y s t a l s t h e r e i s a c e n t r a l , h i g h l y corroded zone of composition An^g t o An^^. Areas of patchy zoning (Vance 1965) of composition An*;o_4.5 r e p l a c e s the bytownite zones and patchy-zoning of composition An^g r e p l a c e s both the bytownite and the l a b r a d o r i t e - a n d e s i n e cores. Hornblende and b i o t i t e are the dominant mafics. Hornblende may c o n t a i n cores of h i g h l y corroded pyroxene. Mafic i n c l u s i o n s i n p l a g i o c l a s e cores a r e , i n order of abundance, hornblende, a u g i t e , a u g i t e rimmed by hornblende, b i o t i t e and hypersthene. Quartz i s mainly i n t e r s t i t i a l t o p l a g i o c l a s e and mafics, but may show subhedral t o euhedral faces against a l k a l i f e l d s p a r . A l k a l i f e l d s p a r s (0rgy_gg, t a b l e 16) a l l show o r t h o c l a s e s t r u c t u r a l s t a t e s ( f i g u r e 27). F I G U R E 67. 2 6 General Geology Around the S i l v e r C reek Stock + ++ Mount Barr Batholith Silver Creek Stock % ° Eocene Conglomerate \ \ Yale Intrusions \ v v Spuzzum Intrusions % \ Custer Gneiss 68. TABLE 14. Modes of the Silver Creek Stock 525 25.2 5 9 6 plagioclase 55.2 54.1 58.5 6 1 . 8 quartz 2 1 . 0 21.6 17.8 1 6 . 0 orthoclase 3 .2 6 .2 1.4 t r clinopyroxene tr tr t r t r hornblende 9 . 0 5.9 9.1 10.1 biotite 8.1 7 .9 1 1 . 0 1 0 . 8 chlorite 0 . 8 1.6 0 . 9 t r epidote 0.3 t r t r — shpene tr 0 . 2 t r t r apatite tr 0.3 0 . 2 t r magnetite 2 . 0 0 . 8 0 . 8 1.4 TABLE 15. Chemical Analyses of the Silver Creek Stock 525 im S i 0 2 62.7 59.8 T i 0 2 0 . 6 1 0 . 6 5 A 1 2 0 3 16.1 17.1 FeO 3.7 3.9 F e 2 0 3 1 .8 2 . 8 MgO 2 . 3 2.9 MnO 0.11 0 . 1 3 CaO 5 .0 6.1 Na20 3.7 3.7 K 2 0 1.6 1.4 P 2 ° 5 0.13 0.14 co2 0.1 0 . 2 H 2 0 0.6 0.9 S 0 . 0 1 0.11 69 Table 16. X-ray Data f o r A l k a l i F e l d s p a r s from the S i l v e r Creek Stock specimen 26(060) 26(204) Or 049 41.70 50*79 21.07 86 669 41.72 50-77 21.05 8 7 002 41.71 50.77 21.13 8 0 524 41 . 6 7 50 - 7 6 21.07 86 F I G U R E 2 7 Structural States of Alkali Feldspars from the Silver Creek Stock Microcline High AI bite 70. CONTACT RELATIONS B i o t i t e and minor t r e m o l i t e are the only obvious contact metamorphic minerals developed i n the rocks adjacent t o the t o n a l i t e . The Eocene conglomerates adjacent t o the stock are s t r o n g l y hornfelsed and crop out as high mountain peaks and steep c l i f f s , but t o the n o r t h , two miles from the stock, they are weakly indurated and crop out as low rounded h i l l s . The contact between country rock and t o n a l i t e i s abrupt. I n c l u s i o n s of country rocks are uncpmmon, but l a r g e x e n o l i t h s of conglomerate are found north of S i l v e r Peak ( f i g u r e 26). Dykes of t o n a l i t e i n the country rock are common. AGE The stock i n t r u d e s the Eocene conglomerates and has been intruded by the Miocene Mount Ba r r B a t h o l i t h . A s i n g l e K-Ar determination gave an age of 35 m i l l i o n years ( t a b l e 2 ) , which i s most l i k e l y the time of emplacement of the stock. DEPTH OF EMPLACEMENT The stock i s e p i z o n a l . Thickness of o v e r l y i n g cover at the time of emplacement i s unknown. The high s t r u c t u r a l s t a t e s of the a l k a l i f e l d s p a r s , th6 presence of c h i l l e d margins, the hornfelsed t e x t u r e of the adjacent conglomerates, and s i m i l a r i t i e s with other e p i z o n a l plutons i n the area (the C h i l l i w a c k B a t h o l i t h and the Mount Barr B a t h o l i t h ) support the idea of a high l e v e l of emplacement f o r the stock. EMPLACEMENT AND CRYSTALLIZATION The stock i s d i s c o r d a n t t o the r e g i o n a l s t r u c t u r e and i s confined e n t i r e l y w i t h i n the F r a s e r R i v e r Graben ( f i g u r e 2 6 ) . A few l a r g e x e n o l i t h s of Eocene conglomerate are included i n the t o n a l i t e ( f i g u r e s 1 and 2 6 ) . These f e a t u r e s are compatable with stoping as a mechanism of emplacement. 71. Prior to emplacement at the present level, the melt most likely had plagioclase (An^_^) augite and minor hypersthene as early crystals. Subsequently, hornblende replaces augite. After emplacement into the present level, the precipitation of biotite, quartz, plagioclase (^25-25^ and orthoclase terminated the crystallization history of the stock. 72. CHILLIWACK BATHOLITH INTRODUCTION The Chilliwack Batholith north of the 49th parallel consists of seven intrusive phases, which range in composition from hypersthene diorite to granite. Figure 28 shows the general geology adjacent to the batholith and figure 29 shows the distribution of the intrusive phases. The oldest phase, of hypersthene diorite, crops out in two small areas, one south of Mount Thompson and the other adjacent to the north end of Chilliwack Lake. A small area of hornblende-biotite diorite crops out on the ridge north of the Illusion Peaks. Tonalite, which forms nearly a complete rim around the batholith, makes up 50 to 6C# of the batholith. Although the tonalite appears to constitute a single intrusive unit, tonalites west of Chilliwack Lake will be referred to as the western tonalite and tonalites east of Chilliwack Lake will be referred to as the eastern tonalite. Granodiorite with minor tonalite, termed the Paleface Granodiorite, intrudes the tonalite near Chilliwack Lake. Three quartz monzonite stocks, the Radium Peak Stock, the Mount Rexford Stock and the Post Creek Stock (figure 29), intrude the tonalite and, in part, the Paleface Granodiorite. A few aplite dykes and an aplitic alaskite body appear to be related to the Radium Peak stock. A small plug of albite granite is found just east of Mount Lockwood. F I G U R E 2 8 General Geology Adjacent to the Chilliwack Batholith \\ Scale /vl 0 10 A Middle Peak F I G U R E 2 9 Intrusive Phases of the Chilliwack Batholith Scale of miles •* Post Creek/ if* Stock + j LEGEND Diorite Tonalite Paleface Granodiorite Quartz Monzonite Aplitic Alaskite Western 4 P t o -D i o r i t e^n ^ \N e S ^ a W e -1 ^ 1 Paleface \\ * Mount V v \ \ Sfo n A Lockwood \ N £?\ Granite A Eastern \ N x i - \ - • i / / Tonalite \\ * Mount V x ' A r°Ci. >^Z0*.A * \ > \ * \ + \\ x \ SAIaskiteRucf. ; v \ i \ Rexford V v x x N \ "\ * V - • ' \ I \ ' t * \\ X N Western \ + M « Stock + V 4 / Tonalite \ L - - A - -V> - x - - - - L -I - C-AN^DA-* /!\V4|; •',]' UN,TED"s7! 'Eastern Diorite v 1 ^ Approximate strike of 1 the foliation in the Tonalite A A' x-section in figure 35-75. MINERALOGY AND PETROLOGY  Diorite Eastern Hypersthene-Augite Diorite The main body of diorite, covering an area of less than one square mile, is found near the eastern edge of the batholith. Smaller bodies occur at the north end of Chilliwack Lake. A l l of these are intruded by tonalite. Typically the diorite is an even-grained, non-foliated, weakly porphyritic rock. Adjacent to the contact with the gneiss i t is porphyritic, with phenocrysts of pyroxene and plagioclase in a fine-grained groundmass. South of Mount Thompson the diorites are locally layered. Modes for the diorites are listed in table 17. Plagioclase (average Anjj, with a range from AnjQ to An^g), augite (Wo^^E^^Fs]^) and hypersthene (En^) are the main minerals. Birefringent needles resembling rutile are common inclusions in some plagioclase. Quartz, orthoclase and biotite are interstitial but locally form large poiftilitic grains. Hornblende forms thin rims on pyroxene. In specimen 391, taken just west of Chilliwack Lake, hornblende has replaced most of the pyroxenes. Minor bent plagioclase and pyroxene associated with undeformed interstitial biotite and quartz suggest protoclasis. Western Diorite Hornblende-biotite diorite north of the Illusion Peaks (figure 29) forms an intrusion breccia containing abundant fragments of hornfelsed Chilliwack Group rocks. Tonalite has intruded and metamorphosed some of the diorite. Calcic plagioclase (AngQ_yQ)is common in some of the rocksj in others plagioclase is zoned from An^j to An^ Q. Augite and hypersthene 76. TABLE 17. Modes of the Chilliwack Batholith A. Dioyite m CR 877 plagioclase 75.4 65.2 65.3 quartz 2.4 3.9 4.5 orthoclase 0.4 2.4 tr hypersthene 0.6 13.9 5.3 augite tr 7.8 17.3 hornblende 13.6 1.3 1.4 biotite 1.9 2.9 3.3 apatite 0.3 0.4 1.0 opaques 1.9 2.3 1.4 B. Tonalite m Nes* m plagioclase 63.8 58.0 54.8 quartz 13.8 9.5 14.2 orthoclase t r tr 5.8 hypersthene 1.4 — 1.6 augite 7.1 4.3 5.0 hornblende 6.4 12.8 7.1 biotite 6.4 12.5 9.1 apatite tr tr t r opaques 1.0 0.8 0.7 1155* 1052 J21 plagioclase 55.5 60.6 57.5 quartz 14.2 15.7 16.2 orthoclase 1.0 0.4 t r hypersthene - - -augite 0.6 tr 1.9 hornblende 15.9 10.0 11.1 biotite 12.0 12.7 12.2 apatite 0.4 tr 0.3 opaques 0.3 0.4 0.6 m 1129* M184 plagioclase 51.3 60.5 60.3 quartz 25.2 25.7 17.2 orthoclase 3.7 tr 6.1 hypersthene - - -augite tr - tr hornblende 6.7 5.5 7.8 biotite 8.1 7.9 8.3 apatite tr tr tr opaques 0.6 0.7 0.2 1Q46 72.5 4.9 0.5 3.5 16.0 tr 1.2 t r 1.5 622 414 908 456 822 61.0 57.4 51.6 61.6 61.8 15.8 22.7 19.4 12.9 L4.0 1.2 1.3 5.1 tr 3.4 1.6 0.3 tr — tr 7.2 1.1 2.6 0.4 2.1 1.4 7.6 9.4 14.9 4.5 11.4 7.1 10.5 9.7 13.9 tr tr tr tr 0.3 0.5 1.1 0.8 1.3 0.4 mt 808* 924 Und* 912 64.4 60.5 56.0 55.7 58.0 17.2 17.3 17.6 19.1 22.7 1.6 1.0 3.6 2.0 3.9 tr 1.8 1.1 tr 0.3 11.2 9.1 11.8 11.1 10.6 4.1 9.3 12.1 10.3 9.4 tr tr 0.3 tr t r 0.8 0.9 0.9 1.3 0.4 A82 821 202 220 922 53.2 56.2 53.0 46.5 53.2 18.5 19.6 20.0 20.4 22.2 8.3 6.7 7.0 10.0 8.8 tr 1.4 1.0 0.5 tr 7.5 5.8 8.0 9.0 7.5 9.5 8.6 10.0 7.1 6.4 tr tr tr tr tr 0.7 1.0 0.4 0.5 1.3 * Western Tonalite 77. Tonalite Phase 80J* 8^6 M181 882 plagioclase 53.4 50.6 50.1 46.4 quartz 23.1 23.1 21.1 23.4 orthoclase 7.2 8.1 11.3 11.8 hypersthene - — tr t r augite tr 0.5 0.9 2.7 hornblende 5.6 10.7 8.3 5.0 biotite 9.4 8.8 9.4 10.0 apatite tr t r tr t r opaques 0.3 0.7 0 .3 0.3 * Western Tonalite C. Paleface Granodiorite 222 1148 S22 8JQ U22. 221 404 plagioclase 52.6 56.6 54.4 49.2 46.2 39.7 49.3 54.7 quartz 26.8 19.4 21.4 22.7 24.4 28.9 21.6 16.4 orthoclase 4.4 8.3 7.4 8.6 8.8 14.4 12.9 15.8 hornblende 6.0 7.2 9.1 7.2 8.4 10.1 7.4 6.0 biotite 9.3 8.3 6.7 11.6 12.1 5.2 8.1 7.0 apatite tr tr tr 0.3 tr tr tr tr opaques 0.9 0.3 0.9 0.3 0.7 0.8 0.2 tr D. Radium Peak Quartz Monzonite 429 282 412 42Q 789 427 418 plagioclase 60.0 48.5 41.7 44.3 43.4 50.2 42.0 38.4 quartz 21.3 25.0 36.1 29.4 28.5 20.6 23.3 29.0 orthoclase 12.0 14.3 16.4 19.7 17.4 20.6 25.1 21.6 hornblende t r 2.8 0.6 1.3 2.4 2.1 3.7 5.0 biotite 5.1 8.4 4.7 4.5 7.3 6.0 4.7 6.0 apatite tr tr t r tr tr tr tr tr opaques 0.9 0.4 0.7 0.6 0.7 0.4 1.0 0.4 143? plagioclase 37.3 38.8 quartz 33.2 36.4 orthoclase 23.2 20.0 hornblende 1.0 tr biotite 5.0 4.5 apatite t r t r opaques 0.6 0.3 78. E. Aplitic Alagkjte F. Rexford Quartz Monzonite 840 m IS36 1051 1023 plagioclase 28.7 . 28 27.8 37.4 49.1 quartz 35.4 37 24.9 40.3 26.9 orthoclase 34.5 33 42.9 21.3 22.0 biotite 1.1 2 4.4 tr 1.8 apatite tr t r t r tr t r opaques tr tr tr t r tr G. Post Creek Quartz Monzonite H. Lockwood Granite £1 462 59-23 M182 plagioclase 58.2 34 44 49 24.6 quartz 20.8 36 26 24 29.8 orthoclase 14.9 26 21 19 43.6 biotite 5.0 3 6 6 2.0 apatite tr tr t r tr t r opaques tr tr t r tr tr 79. are very rarej hornblende is the dominant mafic, with biotite subordinate to hornblende. Specimen 391, included with the eastern diorites, might well be included with the western diorite and suggests a possible transition between the two area of diorite. Tonalite Eastern Tonalite , Tonalite east of Chilliwack LaKe ranges in composition from a two-pyroxene bearing tonalite to mafic granodiorite (table 17). Relations between the various rock types appear to be gradational. Figure 30 outlines the distribution of rock types found in the eastern tonalite. Its most mafic part is a K-feldspar poor, hypersthene-augite tonalite found immediately east of the north end of Chilliwack Lake. These rocks grade southward into similar-looking biotite-hornblende tonalite. About Mount Paleface and adjacent to the gneisses on Custer Ridge the tonalite is less mafic and grades into granodiorite north of Mount Thompson. This granodiorite appears to represent the last stage of crystallization of the tonalite. Foliations are well developed in the more mafic parts, but towards the more felsic parts the foliation becomes less distinct and is absent in the granodiorite. Near Chilliwack Lake, subhedral medium-grained plagioclase in the pyroxene tonalite show l i t t l e oscillatory-zoning but in the granodiorite near Mount Thompson plagioclase has up to 25 zones. Plagioclase ranges in composition from Angrj to An20» average plagioclase compositions from the various types of tonalite are listed in table 18. Highly resorbed zones and rare patches of bytownite are found in the cores of plagioclase. 80. F I G U R E 3 0 Distribution of Rock Types in the Eastern Tonalite LEGEND (1) K - fe ldspar -poor hypersthene augite Tonalite (2) K - fe ldspar -poor biot i te hornblende Tonalite (3) pyroxene b i o t i t e hornblende Tona l i te (4) biotite hornblende Tonalite (5) Granodiorite 81. TABLE 18. Compositions of P l a g i o c l a s e from the T o n a l i t e Western Eastern T o n a l i t e * T o n a l i t e 1 2 1 L 1 Core 55-39 60-43 51-40 50-40 50-40 45-33 Rim 37-31 35-31 34-31 35-27 35-20 35-20 Patches 35 35 34 32 34 31 No. of Zones 2-10 2-4 2-4 2-15 2-25 2-25 TABLE 19. Mafic I n c l u s i o n s i n P l a g i o c l a s e from the T o n a l i t e (arranged i n order of r e l a t i v e abundance) Western T o n a l i t e I E a s t e r n T o n a l i t e * 2 1 A 1 1) hb cpx cpx hb hb hb 2) b i o opx hb cpx b i o b i o 3) cpx hb opx b i o cpx 4) opx b i o b i o ' opx hb: hornblende, cpx: clinopyroxene, opx: orthopyroxene, b i o : b i o t i t e * The numbers under the Eastern T o n a l i t e r e f e r s t o the s u b d i v i s i o n s shown i n f i g u r e 30. 82. Augite (W045E1135FS20 *° ^°42^n33^s25^ a n (* hypersthene (En^^) are found in abundance only along the margins of the eastern tonalite. Elsewhere, hornblende, frequently with cores of augite, is the dominant mafic. Hornblende and biotite, interstitial to plagioclase and pyroxene in the early tonalite, occur as subhedral crystals in the later tonalite and granodiorite. Common mafic inclusions in plagioclase consist of combinations of augite, hypersthene, hornblende and biotite. The assemblage of mafic inclusions in plagioclase varies in a systematic manner from the hyper-sthene-augite tonalite to the granodiorite (table 19) and roughly parallels the distribution of mafic minerals found throughout the tonalite. These inclusions most likely represent early-formed crystals. As the tonalite represents a single intrusive phase, and plagioclase, one of the earliest minerals to crystallize, the variation in mafic inclusions suggests that the tonalite was largely liquid at the time of its emplacement. Alkali feldspars (0rg2_g7) and quartz are interstitial to plagioclase and mafics, except in the granodiorite parts of the tonalite. Alkali feldspars from a l l of the phases of the Chilliwack Batholith are orthoclase (table 20 and figure 31). Western Tonalite The western tonalite resembles the eastern tonalite. Its marginal parts are composed of mafic tonalite and minor diorite which grade into granodiorite in its central parts. Feldspar compositions and types of zoning in plagioclase are similar to those of the eastern tonalite (table 18). Unlike the eastern tonalite, however, the western tonalite has a paucity of pyroxene, here found only as uncommon cores in hornblende and as inclusions in plagioclase. A foliation is well developed throughout these tonalites. The distribution of rock types is less obvious in this area than to the east due to an abundance of later intrusive units. 8 3 . Table 2 0 . X-ray Data for Compositions and Structural States for Alkali Feldspars from the Chilliwack Batholith specimen 29(060)* 29(20if) 2 e < 2 0 D h o m Or Tonalite 679 41.69 5 0 .76 21.11 82 772 41.69 50.77 21 .06 87 899 41.74 50.69 21-08 85 929 41.72 50.74 21.06 87 Paleface Granodiorite 404 41.74 50.73 21.09 84 792 41.70 50.77 21.09 84 828 41.69 50.75 21.07 86 830 41.71 50.76 21.10 83 1109 • 41.71 50.75 21.13 80 Radium Peak Phase 427 41.75 50 .70 21.14 79 429 41 .70 50-74 21.12 81 788 41.73 50.76 21.14 79 A p l i t i c Alaskite 840 41.74 50.75 21.12 81 F I G U R E 31 Structural States of Alkali Feldspars from the Chilliwack Batholith Low Albite 84. Paleface Granodiorite The Paleface Granodiorite (figure 29) consists of two rock types: an homophanous medium-grained biotite-hornblende granodiorite and a fine- to medium-grained porphyritic granodiorite (table 17). Rare phenocrysts of plagioclase are found in the former variety; phenocrysts of plagioclase, hornblende, biotite and quartz are found in the latter. As both types have similar mineralogy and chemistry, intrude the tonalite and are intruded by the Radium Peak phase, they have been considered as a single unit. Plagioclase occurs in a variety of crystal forms. Most common are blocky crystals with oscillatory-zoned cores (8-25 zones) of composition An50-38 a n (* n o r m a l l y - z o n e d rims of composition ^n^^O* ^ *"ew crystals in the non-porphyritic variety have a central core as calcic as AngQ. Some plagioclase show a synneusis relation. Other crystals, recognized by the presence of inclusions of "rutile" and pyroxene, appear to be xeno-crysts derived from both diorite and tonalite. Hornblendes from the non-porphyritic variety are subhedral to very irregular crystals interstitial to plagioclase, frequently with inclusions of plagioclase (An^)„ Hornblende from the porphyritic variety occurs as stubby laths to fine accicular prisms. Biotite, rarely subpoikilitic, is more common as fine- to medium-grained subhedral crystals. Mafic inclusions in plagioclase are hornblende and biotite. Orthoclase (OrgQ_g^)' and quartz are interstitial to other minerals. Subhedral quartz is common in the porphyritic variety. 85. Radium Peak Phase The Radium Peak phase (figure 29) is a leucocratic, medium-grained, homophanous, hornblende-biotite quartz monzonite (table 17) which forms prominent exfoliation domes along both sides of Chilliwack Lake. The unit is homogeneous, except for minor miarolitic quartz monzonite aplite dykes which are both intrusive and gradational into the quartz monzonite. Subhedral plagioclase shows oscillatory-zoned (12-30 zones) cores of An^^^g and normally-zoned rims of An^-IT Albite overgrowths or replace-ments are common at contacts with orthoclase. Core zones as calcic as An<j<j are rare. Biotite occurs as subhedral booklets. Orthoclase (0r»7^_g^), locally subpoikilitic, appears to corrode plagioclase. AJlaskjte Plugs Two small alaskite plugs crop out in the Chilliwack Batholith (figure 29). The smaller of the two, 2000 feet east of Mount Lockwood, is a fine-grained leucocratic, biotite-albite granite (table 17) showing chilled margins against gneiss and tonalite. The other body, on the west shore of Chilliwack Lake, intrudes only the Radium Peak phase. This unit is a pink, miarolitic, locally porphyritic aplitic biotite quartz monzonite (table 17) that resembles the aplite dykes in the Radium Peak phase. Composition of plagioclase is mainly An25„i8 rimmed by An^ _Q where adjacent to orthoclase (0rg]_). Some phenocrysts show oscillatory-zoned cores of An^2_32» Biotite is the only mafic. Mount Rexford Stock The Mount Rexford Stock is centered about Mount Rexford in the western part of the batholith (figure 29). The most common rock is a homophanous medium-grained biotite quartz monzonite (table 17). Some 8 6 . Some specimens are devoid of mafics. A small plug of plagioclase-quartz-orthoclase porphyry with a fine-grained granitic matrix crops out north of Mount Rexford. Minor granophyric quartz monzonite intrudes Eocene (?) conglomerates and Oligocene Skagit (?) volcanics southwest of Mount Lindeman. Two zones rich in mafic inclusions are found in the stock. The most extensive zone, one-half mile west of Middle Peak is exposed over a vertical distance of some 200 to 300 feet and possibly represents the region near the roof of the stock. The other zone, north of the Illusion Peaks, is some 50 to 100 feet across, and parallels the vertical contact with the Chilliwack Group and the western tonalite (figure 35). Composition of plagioclase, An^ yj, are uniform throughout the stock. Most crystals have oscillatory zoning (10 to 40 zones), the more intense zoning found in the porphyritic variety. Orthoclase is markedly perthitic. These perthites could not be homogenized and thus compositions could not be determined. Post Creek Phase The Post Creek phase (figure 29) is composed predominantly of leucocratic biotite quartz monzonite (table 17). Leucocratic plagioclase porphyries are frequently associated with hydrothermally altered breccias south of Greendrop Lake. A foliation, which is partly protoclastic, is present only at the southern contacts. The stock resembles the Mount Rexford stock. Plagioclase with normal to oscillatory-zoning (up to 50 zones) has a composition range of An2£ to An2Q. More calcic plagioclase An^_2Q is found in the porphyries. Orthoclase (0rg3) phenocrysts may show oscillatory zoning. 87. STRUCTURE Internal Relations Sequence of Emplacement The sequence of emplacement of the phases of the Chilliwack Batholith started with the diorite and ended with the Mount Rexford and the Post Creek phases. Observed intrusive relations are shown in figure 32. Intrusive relations between the various phases of the batholith are not everywhere obvious. Tonalite clearly intrudes the diorite. Near Mount MacDonald, the Paleface granodiorite contains abundant 5 to 50-feet-across inclusions of partly altered tonalite, but the contact between the two units on the west shore of Chilliwack Lake is abrupt and gives no indication of relative ages. On Mount MacDonald, the tonalite possibly forms the roof of the Paleface granodiorite. The relative ages of the three quartz monzonite bodies are not apparent. K-Ar ages and chemistry of the three are similar (see below). However, the greater abundance of hornblende and more calcic plagioclase in the Radium phase suggests that i t is possibly the oldest of the three. The aplitic alaskite body along the west shore of Chilliwack Lake is similar to aplite dykes in the Radium phase and is therefore probably of similar age. Foliations Only the tonalite is well foliated. The eastern diorite and the Post Creek phase show a foliation along their margins. Foliation is best developed in the marginal parts of the tonalite. Here, the foliation is steep and parallels the contacts with the country rock (figure 3 3 ) . Where the tonalite approaches granodiorite in composition, the foliation is indistinct. Protoclastic texture and randomly oriented 88. FIGURE 3 2 . Diagram showing those i n t r u s i v e r e l a t i o n s observed between p l u t o n i c u n i t s seen i n the f i e l d . C © U + 5 © >rl -P U m o c3 a © u -P -p to o . © - H © © Jn *rl JH * H © rH © rH M 2 w Cl © O aJ O E a s t e r n D i o r i t e . Western D i o r i t e . Western T o n a l i t e E a s t e r n T o n a l i t e P a l e f a c e ........ Radium C I I Rexford -Post Greek I Lockwood Gr a n i t e -C h i l l i w a c k Lake A p l i t e -I - C - I - I I I I I -- I I - - I © o 00 © rH cd Pi T3 •a o © © ^ (4 o -p M o © 2 +> o rt o u © © -P X ro o I • H r3 - P H • H rH X ! - U n i t s are arranged w i t h the ol d e s t at the top of the column; - Read the f i g u r e across from l e f t t o r i g h t ; I : u n i t i s i n t r u s i v e i n t o corresponding u n i t i n the h o r i z o n t a l column, C: probably contemporaneous -: r e l a t i o n not observed or unknown. Example: The E a s t e r n T o n a l i t e i s I n t r u s i v e (I) i n t o the Eastern D i o r i t e and probably Contemporaneous (C) with the Western T o n a l i t e . — ' — foliation in the Chilliwack Group > lineation or fold axis in the Custer Gneiss 90. poikilitic biotite flakes (up to l£" across) that contain aligned plagioclase suggest that this foliation is magmatic. The foliation in the Post Creek phase parallel to its southern contact with the tonalite and marked by aligned biotite and smeared quartz, cross-cuts thin aplite dykes at high angles to their strike. This texture, possibly protoclastic, was not seen in the adjacent older tonalite and may be due to the effect of drag along the margins of an acidic magma during its emplacement. Layering Layering is developed to a minor extent in the eastern diorite and the Paleface granodiorite. Layered zones in the diorite are found 150 feet from the contact with the gneiss on Custer Ridge, just south of Mount Thompson. There, 10 steeply dipping layers, one-half-foot to one-foot thick are parallel to the contacts with the gneiss. Within a layer, plagioclase and pyroxene are aligned perpendicular to the strike of the layering in a harrisite structure, similar to the Willow Lake layering described by Taubeneck and Poldervaart (1960). In the Paleface phase, one-half mile north of Paleface Creek, three layers (striking 135° and dipping 30°) are exposed over 10 vertical feet. Each layer consists of a thin (•§-.M to 1") base rich in hornblende and biotite overlain by normal granodiorite. The graded structure and shallow dip of these layers suggests a formation by gravity settling. Breccias Breccia zones are exposed south of Greendrop Lake and southeast of Mount Edgar. Both zones are confined to the intrusive rocks. 91. South of Greendrop Lake a 3000-foot-long east-trending zone i s marked by areas of extreme fracturing and breccia. The rocks in the zone are altered, grading from weak a r g i l l i c alteration in the peripheral parts to sericite-quartz alteration i n the central parts. In the brecciated areas, open spaces are common and angular fragments of altered rock are cemented by quartz veins and fine-grained rock that appears similar to the fragments. Similar intense fracturing and alteration is found southeast of Mount Edgar. Here, the fragments have been replaced by mosaics of clear albite, quartz, muscovite and minor tourmaline. Open spaces between the fragments and vuggy quartz veins are common. J oint s Studies of joints from various parts of the batholith revealed no systematic patterns. Relative ages of joint surfaces could be deduced only in road cuts north of Paleface Creek. Here, although not clearly defined, a suite of joints f i l l e d with various minerals show cross-cutting relations to one another. K-feldspar-coated joints appear to be the earliest.-. These are cut by abundant epidote-quartz and epidote-chlorite-quartz-coated fractures, which in turn are cut by much less abundant joints coated with prehnite and quartz. Laumontite-ccated fractures comprise the last set. Subsequent joint sets are barren of mineralization. The order cf development of minerals on the fractures i s consistent with formation in a cooling, water-rich environment (figure 34). External Relations Relations to Older Rocks The batholith i s generally discordant to the regional structure. Structures in the Custer Gneiss appear to have been l i t t l e affected by 92. F I G U R E 3 4 S c h e m a t i c P/T Diagram for Ca-AI S i l i c a t e s (Coombs i960) T e m p e r a t u r e Development of hydrothermal coatings on f rac tu res in the P a l e f a c e Granod io r i te , north of P r e f a c e C reek . 1) late magmatic stage, K-feldspar veins , plagioclase stable 2) epidote-quartz and epidote-chlorite-quartz veins 3) prehnite-quartz veins 4) laumontite - coated f r a c t u r e s approximate position of the reaction' prehnite—* zoisite-rgrossular + quartz +fluid (after Lou 93. emplacement o f t h e b a t h o l i t h (McTaggart and Thompson 1967) but t h e f o l i a t i o n s i n t h e C h i l l i w a c k Group have been d e f l e c t e d t o c o n f o r m t o t h e o u t l i n e s o f t h e b a t h o l i t h ( f i g u r e 33). The d i f f e r e n t s t y l e s o f c o n t a c t r e l a t i o n s r e f l e c t d i f f e r e n t t y p e s o f h o s t r o c k ; t h e C u s t e r G n e i s s b e i n g a m a s s i v e u n i t i n c o n t r a s t t o t h e f i s s i l e - p h y l l i t i c C h i l l i w a c k Group. The r o o f o f t h e b a t h o l i t h i s p r e s e r v e d l o c a l l y . N o r t h o f t h e I l l u s i o n P e a k s , a cap of h o r n f e l s , d i o r i t e and m i g m a t i t e up t o 1000 f e e t t h i c k o v e r l i e s t h e w e s t e r n t o n a l i t e . To t h e s o u t h , n e a r M i d d l e Peak, c o n g l o m e r a t e and p y r o c l a s t i c s f o r m a r o o f over q u a r t z m o n z o n i t e and g r a n o p h y r e . One-h a l f m i l e t o t h e w e s t , i n t h e i n c l u s i o n - r i c h zone i n t h e R e x f o r d S t o c k , t a b u l a r s l a b s and s l i v e r s of m e t a - v o l c a n i c s v e i n e d by t h e R e x f o r d q u a r t z m onzonite p r o b a b l y c o n s t i t u t e a r e l i c o f t h e r o o f . A c r o s s - s e c t i o n s k e t c h between M i d d l e Peak and t h e C h i l l i w a c k R i v e r shows t h e i n f e r r e d r e l a t i o n s between i n t r u s i v e and c o u n t r y r o c k ( f i g u r e 35). A t Mount Lockwood, 200-f o o t b l o c k s o f g n e i s s i c f r a g m e n t s a r e e n g u l f e d by h e t e r o g e n e o u s t o n a l i t e and a n a r r o w tongue of Hozameen r o c k s seems t o f o r m a r o o f o v e r t h e e a s t e r n t o n a l i t e . C o n t a c t Metamorphism A d j a c e n t t o t h e C h i l l i w a c k B a t h o l i t h , t h e C u s t e r G n e i s s shows l i t t l e o r no c o n t a c t metamorphism. The w e s t e r n d i o r i t e s , however, c o n s i s t i n g o f t h e same m i n e r a l s a s found i n t h e C u s t e r G n e i s s , have been a f f e c t e d by t h e t o n a l i t e . T h e r e , s e c o n d a r y b i o t i t e , p l a g i o c l a s e ( A n - ^ ^ ) and q u a r t z have developed, a t t h e expense o f c a l c i c p l a g i o c l a s e , h o r n b l e n d e and p y r o x e n e . The C h i l l i w a c k Group s e d i m e n t s have been h o r n f e l s e d and m i g m a t i z e d . The c o n t a c t a u r e o l e x t e n d s f o r some 1000 f e e t f r o m t h e b a t h o l i t h . Near t h e c o n t a c t , f i n e - g r a i n e d s e d i m e n t a r y r o c k s show t h e development of Sketch of a Cross -sec t ion of the Mount Rexford Pluton Between Middle Peak and the Chilliwack River Scale: about 8 miles from north to 60uth 9 5 . andalusite, biotite, plagioclase (AIX^Q), cordierite, minor garnet, hornblende, and K-feldspar. Calcareous rocks show wollastonite, dlopside and garnet. Near the tonalite, the metamorphic grade reaches into the K-feld spar-cordierite hornfels facies (Winkler 1 9 6 7 ) . A migmatite zone, some 5 0 to 2 0 0 feet across, between hornfels and tonalite, i s well exposed north of the Illusion Peaks (figure 3 5 ) . Closest to the contact with the tonalite, the migmatite i s composed of swirled, fine-grained, biotite-rich, heterogeneous tonalite with disoriented inclusions of limey and siliceous sediments. This zone grades, through a zone containing lesser amounts of biotite-rich heterogeneous tonalite and many p e l i t i c inclusions, into finely laminated hornfels containing no obvious granitic material. Conspicuous metamorphism and migmatitization of the Chilliwack Group and the western diorite adjacent to the western tonalite, lacking in the Custer Gneiss, possibly reflects a greater abundance of water i n the western area than in the eastern area. A possible source of the water i s the Chilliwack Group, with i t s abundance of p e l i t i c sediments. AGE OF THE CHILLIWACK BATHOLITH The batholith intrudes Eocene conglomerates and the Oligocene (?) Skagit-Hannegan volcanics. K-Ar age determinations from the various phases of the batholith f a l l between 29 and 2 6 million years (table 2 1 ) . TABLE 21. K-Ar Ages From the Chilliwack Batholith Specimen Intrusive Phase Age (million years) C R . 679 429 1041 59-22B Eastern Diorite Eastern Tonalite Radium Peak Phase Mount Rexford Stock Post Creek Stock Perry Creek Phase* 29 28 2 6 2 6 2 6 3 0 * * young phase of the Chilliwack Composite Batholith, located just south of the 49th parallel (Misch 1966) 96. As the pluton was emplaced at a shallow depth (see below), where cooling was likely to be rapid, the K-Ar ages probably represent the time of emplacement. CHEMISTRY Chemical analyses for the Chilliwack Batholith are listed in table 22j locations of specimens analysed are shown in figure 36. Specimen C.R., from the eastern diorite, taken within 100 feet of the chilled contact, probably represents closely the i n i t i a l composition of the diorite magma. This analysis, similar to that of high-alumina basic rocks (Kuno 1968), is comparable with analyses of Cenozoic andesites from western North America (Chayes 1969) (table 34). Of the nine tonalite analyses, three (Nes., 748, and Lind.) are from the western tonalite. Analyses of tonalite are alumina rich (l6.4 to 18.6$). In general, the chemistry of the western biotite-hornblende tonalites is similar to the chemistry of the eastern pyroxene-bearing tonalites. The high potash values for specimens Nes. and Lind. may be due to analytical error or to contamination by the Chilliwack Group sedimentary rocks. The overall greater abundance of hydrous mafic minerals in the western tonalite compared to the eastern tonalite is thought to reflect a higher water content in the west, a relationship suggested earlier by differences in the contact metamorphism between the two areas. The chemistry of the Paleface granodiorite is similar to the chemistry of the tonalites and granodiorites on Custer Ridge, except for a lower alumina content in the former unit. A lower alumina percentage is found in a l l phases younger than the tonalite. A higher silica and potash and lower lime, magnesia and iron content separates the quartz monzonite stocks from the Paleface granodiorite. Specimen 769, from the aplitic alaskite plug that is thought to represent the final stage of crystallization of the Radium Peak phase, shows extreme potash enrichment. 97. TABLE 22. Chemical Analysis of the Chilliwack Batholith Diorite and Tonalite (a.) CR, Nes* m Lind* 1053 672 478 2P0 m m Si0 2 55.3 56.9 60.2 60.4 60.5 60.3 61.2 63.6 63.9 64.2 T I O 2 1.3 0.3 0.4 0.7 0.5 0.6 0.5 0.5 0.5 0.6 A 12° 3 17.4 18.2 18.2 17.2 17.9 18.6 17.4 16.4 17.6 18.2 FeO 6.1 5.9 2.3 3.7 4.4 3.3 3.6 3.1 2.7 3.3 Fe 20 3 2.4 1.2 2.1 1.9 0.1 1.3 1.6 1.6 1.3 1.5 MgO 5.2 4.3 2.9 3.7 3.2 2.2 2.2 2.2 1.0 2.2 MnO 0.16 0.21 0.10 0.14 0.09 0.08 0.10 0.09 0.08 0.09 CaO 7.5 6.5 6.6 6.1 6.4 6.0 6.6 5.1 5.5 5.0 Na20 3.3 3.2 3.3 3.6 3.8 3.3 3.9 3.6 3.7 3.7 K20 0.7 1.6* 0.9 1.7* 1.1 1.3 1.1 1.8 1.6 2.1 P2°5 0.37 0.10 0.16 0.11 0.15 0.15 0.16 0.14 0.14 0.13 c o 2 0.10 0.08 0.10 0.08 - - - - - -H20 0 . 6 0 0.90 1.00 0.60 0.30 0.80 0.70 0.30 0.05 1.00 S 0.02 _ 0.01 0.02 0.01 0.03 0.02 0.03 0.03 * Daly (1912) (a.) analysis from the eastern diorite 98 Paleface Phase Radium Peak Phase 292 1402 U Q 2 789 1144 42Z 782 (b.) 762 ( c ) 1036 (d . ) PC Si0 2 64.0 67.4 68.6 68.4 71.0 72.9 74.0 77.1 73.4 71.4 TiC-2 0.6 0.5 0.4 0.4 0.3 0.3 0.2 0.2 0.2 0.3 A1 20 3 15.0 15.5 15.9 15.1 14.4 14.8 15.3 14.1 12.7 14.4 FeO 3.3 . 2.7 2.2 1.3 1.2 1.5 0.9 0.2 0.9 1.2 Fe 20 3 1.3 1.4 1.2 1.4 1.2 1.0 0.8 0.1 2.5 1.3 MgO 3.2 2.0 1.6 1.8 1.0 1.0 0.9 0.8 0.9 1.1 MnO 0.10 0.08 0.06 0.06 0.03 0.05 0.04 0.01 0.02 0.04 CaO 4.6 3.8 3.8 3.0 2.2 2.6 2.2 0.9 1.3 2.5 Na20 3.2 3.2 3.4 3.3 3.2 3.3 3.7 2.9 3.7 4.1 K20 2.4 2.7 2.4 3.2 3.6 2.9 3.0 4.8 2.7 3.0 P2°5 0.13 0.10 0.09 0.07 0.06 0.06 0.04 0.02 0.03 0.13 G02 - - - - - - - - - 0.12 H2° 0.9 0.6 0.8 0.7 0.7 0.6 0.4 0.4 0.3 0.4 0.12 0.03 0.01 0.03 0.01 0.02 0.02 0.02 0.02 (b.) Aplitic Alaskite (c.) Rexford Phase (d.) Post Creek Phase F I G U R E 3 6 L o c a t i o n of Specimens Used in the Tetft 100. F i g u r e s 37.and 33 are s i l i c a v a r i a t i o n diagrams f o r a l l the phases of the C h i l l i w a c k B a t h o l i t h . F i g u r e 37 i s the usual s i l i c a v a r i a t i o n diagram. A d i f f e r e n t type of v a r i a t i o n diagram ( f i g u r e 38)is favoured by Chayes (1967) as i t c o r r e l a t e s "... the amount of s i l i c a , not w i t h the amount of some other oxide, but with the p o r p o r t i o n of the a v a i l a b l e space occupied by that oxide." From f i g u r e 37, there appear t o be two and probably t h r e e d i s t i n c t trends of e v o l u t i o n f o r the phases of the C h i l l i w a c k B a t h o l i t h . These trends are even more apparent when p l o t t e d i n f i g u r e 38 using the Chayes 1 p l o t . No obvious break between the d i o r i t e and the t o n a l i t e i s i n d i c a t e d from these p l o t s , although the t o n a l i t e c l e a r l y i n t r u d e s the d i o r i t e . A break i n smooth curve r e l a t i o n s between t o n a l i t e and P a l e f a c e g r a n o d i o r i t e i s suggested f o r alumina, magnesia, l i m e , soda, and potash. Less marked, but s t i l l apparent, are breaks i n the s i l i c a v a r i a t i o n curves between the P a l e f a c e and the Radium phases. Analyses from the Rexford and the Post Creek phases g e n e r a l l y f i t w e l l with the Radium phase. The chemistry, p l o t t e d i n f i g u r e s 37 and 38, suggests that the marginal p a r t s of each phase are a l i t t l e more b a s i c than i t s c e n t r a l p a r t . Ca0-Na20-K20 p l o t s ( f i g u r e 39) and a l k a l i - F e O t o t - M g O p l o t s ( f i g u r e 40) both i n d i c a t e c a l c - a l k a l i n e d i f f e r e n t i a t i o n t rends f o r the b a t h o l i t h . The. trends of d i f f e r e n t i a t i o n shown i n these f i g u r e s are i n d i s t i n g u i s h a b l e from those of other T e r t i a r y Cascade pl u t o n s ( f i g u r e 67). PETROGENESIS I n t r o d u c t i o n D i f f e r e n c e s i n the chemistry ( f i g u r e 37) and the mineralogy ( f i g u r e s 41, 42, 43, 44 and 45) of the v a r i o u s phases of the C h i l l i w a c k B a t h o l i t h can be accounted f o r p a r t l y by d i f f e r e n t i a t i o n of a magma, probably a n d e s i t i c ( d i o r i t i c ) i n composition. The d i o r i t e , which i s the most b a s i c phase of 18 17 16 15 14 13 12 6 5 4 3 2 I 9 8 7' 6 5 4 3 2 I 9 8 7 6 5 4 3 2 I 4 3 2 I 4 3 2 I 6 U R E 3 7 101. Sil ica Variation Diagram _ - O — AX A l 2 0 3 MgO FeO tot CaO • -o—o_ - A _ -o° o ° _o o —-sQ- - A A-Na 2 0 SiO* 102. F I G U R E 3 8 S i l i c a Variation Diagram - Chaves' Transformation Plot (The oxide value along the vertical axis represents the porportion of an oxide in an analysis exclusive of silica. This oxide value is obtained from the Creldllonship. value of o»ide* l 0 ^ i l i c F ) " ~ — 6 0 5 8 -5 6 -5 4 -5 2 -5 0 -4 8 -4 6 -4 4 -4 2 4 0 - | 10 8 -6 -4 -18-16-[4 -12-10 8 6 4 1 2 14-1 12 10-8 -6 -18-14-I07-8 t -5 5 A l 2 0 3 if* / X A * • MgO •A« ' X ^ ' _P CaO NagO o_~ — O B — —BtO— A-K 2 0 "A "A-JTA-— 6 0 6 5 7 0 7 5 8 0 SiO, Symbols used are the same as in figure 103 F I G U R E 3 9 Ca0-Na 2 0-K 2 0 Plot for the Chilliwack Batholith 104. the Chilliwack Batholith, is chemically similar to Cenozoic andesites of the Cascades of Washington and Oregon. A common origin for Upper Tertiary plutonic and volcanic rocks from northern Washington is indicated by Sr 8 7/Sr 8o ratios determined by Hedge et al (1969). As the diorite magma rose through the crust, i t differentiated, and at successively higher levels in the crust, fractions were tapped off, intruded upwards and emplaced. Once a magma was emplaced into the present level of exposure, it underwent further differentiation. Differentiation and Successive Intrusion The magmas for a l l the phases of the Chilliwack Batholith were probably derived from a single magma chamber. However, the magma chamber from which the diorite and tonalite magmas were tapped was probably at a deeper level in the crust than the ones from which the younger phases were tapped. Fractional crystallization of an andesitic (dioritic) magma deep in the crust possibly accounts for the high alumina content of the diorite and tonalite (figure 46). The diorite and tonalite magmas, tapped from a chamber deep in the crust, would have to rise at a rapid rate to their final level of emplacement, otherwise they would be depleted in alumina by the precipitation of plagioclase (Emslie 1971) as the magma adjusted to its new pressure conditions (figure 46). A l l the phases of the batholith younger than the tonalite have normal alumina contents (table 22). The magmas of the younger phases were tapped, either from a chamber at a similar level as the chamber from which the tonalite magma was tapped and then rose slowly through the crust, or, from a chamber at some shallower level in the crust. The Rexford phase, one of the youngest of the batholith, seems to l i e on a cotectic curve appropriate to about four miles of depth (figure 47). The chamber from which the magmas of the Rexford phase developed is about two to three miles below the level of emplacement of the Chilliwack Batholith (see below). This shallow level from which the Rexford F I G U R E 4 1 Schemat ic Crysta l l i zat ion History of the Various Phases of the Chilliwack Batholith Diorite F I G U R E 4 2 Var iat ion of Plagioclase Compositions Within Some of the P h a s e s of the Chi l l iwack Batholith O 70 6 0 -50 o < 4 0 c a> u 130 2 0 -Eastern Tonalite \ V V •T" r-i i i i II i • i » i < i * ( O l O W * * < D * S O - < l ) O G*> l O s i n s o o o O N c o o m o i roeo ^ o &) o> o> cn *t oi CD oo a> co Paleface 01 ^ O (vi O O N - * CO <t — Radium •70 o Normative plagioclas - 6 0 - 5 0 - 4 0 - 3 0 - 2 0 o a o Is- t*- w c> CVJ oo ro CM ro oo co * N T t <t N N 107 F I G U R E 4 3 Pyroxene Quadr i la te ra l -Showing the composition of clinopyroxene in equilibrium with orthopyroxene from the eastern tonalite and the eastern diorite Wp 0— —0 -augite-hypersthene from the Diorite 1 9 augite^-hypersthene from the Tonalite clinopyroxene from the Skaergaard Intrusion F I G U R E 4 4 Normalized Felsic Minerals from some of the Phases of the Cfiilliwack Batholith 108. F I G U R E 4 5 T e r n a r y S y s t e m Ab-An-Or i Schematic C r y s t a l l i z a t i o n History of Feldspar Pairs from the Phases of the Chi l l iwack B a t h o l i t h 4 An Orthoclase compositions1 determined by x - ray diffraction Plagioclase compositions -- determined optically (after Tuttle and Bowen 1958) 109. F I G U R E 4 6 Liquidus Relations in the System' (modified after Emslie 1971) F I G U R E 4 7 Po in ts of Min imum Melt Compos i t ions and C o t e c t l c Lines in the System « A b / A n - O t z - O r , for Various Ab/An Rat ios at 2Kb Water Pressure Ab/An = 1.8 - - -• Ab/An =3.8 Ab/An =5.2 Ab/An =7.8 ~ Ab/An =>o Ab/An © Normative Qtr-Ab/An-Or for the Rexford Quartz Monzonite with an Ab/An ratio of 6 (after Winkler 1967) 110. magma was tapped, coupled with the deep level from which the tonalite magma was tapped, favours the hypothesis that the magma chamber from which the phases of the Chilliwack Batholith developed was progressively rising through the crust (figure 48) rather than remaining at some constant level. , Fractional crystallization of a magma initially andesitic in composition, involving the separation of pyroxene and plagioclase with a superimposed effect of decreasing pressure, seems adequate to explain the observed differences between the various phases of the batholith. With continued fractional crystallization, the water content of the magma might be expected to increase, thus accounting for further differences between the phases. Figure 49 and table 23 illustrate the stages of fractional crystallization of a magma initially of the composition of the diorite, and ending with a magma of the composition of the Mount Rexford quartz monzonite. Crystallization and Differentiation at the Present Level  of Exposure. Introduction Once each magma was emplaced, i t was modified by combinations of fractional crystallization, crystal settling, diffusion and minor contamination. The order of crystallization of the various minerals within each phase is shown in figures 41 and 42. Differentiation at the present level of exposure is best developed in the tonalite and Radium Peak phases. Crystallization of the Tonalite. It was shown earlier that from evidence of mineral inclusions in plagioclase, there is reason to believe that most of the crystallization of the tonalite took place at the present level of exposure. The tonalite is weakly differentiated (figures 37, 42 and 44). Boundaries between rock types (figure 30) parallel the magmatic foliation (figure 33). Convection 111. F I G U R E 4 8 I l lustration of the Change in Level of the Magma Chamber and Emplacement of the Phases of the Chilliwack B a t h o l i t h p Diorite Tonalite Paleface Granodiorite < Radium Peak Phase V Rexford and Post Creek Phases 112. F I G U R E 4 9 Estimate of the Amount of Fractional Crystall ization Required at Each of the Successive Levels of the Magma Chamber to Account for the Change in Composition of the Magma as it Rose Through the Crust % Volume of original magma (100%) Diorite Magma- leve l A (figure ( 2 7 % ) ( 2 0 % ) )- Emplacement into present level Separate 4 5 % crystals - 2 6 % An 6 |,4% D i 7 0 Hd3 0 , l 2%En 75Fs 25,3%Mt (formation of the Tonalite Magma) ( 5 5%) Tonalite Magma-level B •* Emplacement into present level Separate 2 0 % crystals- !7%An5o ,2%En67Fs33 , l%Di33Hdg7, + M t (formation of the Paleface Magma) ( 35%) Paleface Magma-level C -*> Emplacement into present level Separate 8%crystals- 5 % A n 6 o,2% E n 6 2 i rS3 8 , l % D i ) 0 0 , + Mt (f6rmation of the Radium Peak Magma) Radium Magma-level D' Emplacement into present level Separate 7 % c r y s t a l s - 4 % A n g 0 | l % E n 5 0 F S 5 0 » , O / o 0 > | O / o 0 r > + M t (formation of the Rexford Magma) Rexford Magma-level E- -^Emplacement into present level The minerals listed are normative minerals. For the period of fractional crystallization after the Tonalite Magma differentiated to the Paleface Magma , the mafic phase which separated out was probably hornblende. An—anorthite E n — enstatite Fs —ferrosi l i te Di —diopside Hd —hedenbergite Q —quartz Or —orthoclase Mt—magnetite 113. TABLE 23. Comparison of the average chemical analysis of some of the various phases of the Chilliwack Batholith with the calculated chemical analysis of the liquid fractions produced by fractional crystallization of the Dioritic Magma (See figure 49). Calculated analysis of liquid fraction from: Average Composition of a) Diorite Magma (Figure 49) a) Tonalite (table 22) Si0 2 63.5 63.3 A1 20 3 18.0 18.1 MgO ' 3.1 2.3 FeO 3.6 5.0 CaO 6.3 6.0 Na20 4.2 3.9 K20 1.2 1.4 Si0 2 A1 20 3 MgO FeO CaO Na20 K20 Si0 2 A1 20 3 MgO FeO CaO Na20 K20 b) Tonalite Magma 68.3 16.0 2.6 2.6 3.9 4.1 2.4 c) Paleface Magma 72.8 14.6 1.2 1.6 2.6 3.8 3.4 b) Paleface Granodiorite 67.5 15.7 2.9 4.1 4.2 3.3 2.5 c) Radium Peak Phase 72.3 15.0 1.2 2.4 2.5 3.4 3.2 114. i n the magma ( B a r t l e t t 1969) combined with c r y s t a l l i z a t i o n from the w a l l inward (Compton 1955 and Best 1963) probably accounts f o r the f o l i a t i o n . F r a c t i o n a l c r y s t a l l i z a t i o n , f a c i l i t a t e d by convection combined with d i f f u s i o n over short d i s t a n c e s (Hess I960) between the magma and i t s c r y s t a l l i z i n g w a l l s p o s s i b l y e x p l a i n s the chemical and m i n e r a l o g i c a l v a r i a t i o n seen i n the t o n a l i t e . The absence of a f o l i a t i o n i n the grano-d i o r i t e of Custer Ridge may be due t o the i n h i b i t i o n of convection as the magma chamber became c o n s t r i c t e d and more v i s c o u s during the l a t t e r stages of c r y s t a l l i z a t i o n , of the t o n a l i t e . The pyroxene t o n a l i t e t h a t lie3 along the northern contact (figure 30) i s a r e l a t i v e l y anhydrous phase. Two thousand f e e t inwards, however, pyroxene i s succeded by hornblende with no change i n the b u l k chemistry of the rock (compare analyses and modes of specimens 679 and 1053). This change was probably caused by an increase i n P^O ^ ^ e melt. A f t e r about 6000 f e e t of growth inward from the w a l l s , the magma chamber appears t o have enlarged towards the east and l e s s mafic t o n a l i t e formed the marginal p a r t s ( f i g u r e 30). C r y s t a l l i z a t i o n of t h i s l e s s mafic t o n a l i t e on Custer Ridge proceeded inwards and ceased w i t h the c r y s t a l l i z a t i o n of the g r a n o d i o r i t e s near Mount Thompson ( f i g u r e 30). C r y s t a l l i z a t i o n of the Radium Peak Phase A decrease i n p l a g i o c l a s e from the r i m inwards i s the most obvious v a r i a t i o n i n the Radium phase. The l a s t stage of c r y s t a l l i z a t i o n r e s u l t e d i n the formation of a p l i t i c dykes and the l a r g e a p l i t i c a l a s k i t e p l u g . F i g u r e 50 o u t l i n e s the path of c r y s t a l l i z a t i o n of the Radium phase. The composition of the a p l i t e i s c l o s e t o the composition of the e u t e c t i c p o i n t s i n the a r t i f i c i a l system stu d i e d by James and Hamilton (1969) and judged by the abundance of m i a r o l i t i c c a v i t i e s i t was saturated w i t h water. I n g e n e r a l , the c r y s t a l l i z a t i o n path from the o l d e s t t o the youngest r o c k s of the Radium phase t r e n d s towards the e u t e c t i c . 115. F I G U R E 5 0 Isobar ic Phase Diagram for the Jo in A b - O r - Q t z - A n at IOOO Bars Eutectic A for A n 3 — 730°C 'Eutectic" B for A n 5 — 7 4 5 ° C 'Eutectic" C for A n y — 7 8 0 ° C (after James and Hamilton 1969) Radium Peak Phase specimens plotted, arranged in order from oldest to youngest 1. 7 8 9 2. 4 2 7 3. 7 8 2 4. 114 4 5. 7 6 9 ; Aplitic Alaskite with normative composition Ab380r29Qtz28Ari4 116. Depth of Emplacement of the Chilliwack Batholith The pluton is epizonal in character. The youngest unit intruded by the batholith is the Oligocene Skagit-Hannegan volcanics. A minimum thickness of 5000 feet for these volcanics gives an estimate of the thickness of cover over the tonalite. The aplitic alaskite crystallized about 5000 feet below the roof of the batholith. This plug, which represents the final level of emplacement of the Chilliwack Batholith, crystallized at . about two miles below the surface (figure 50). A maximum depth of emplacement of 2 miles is' indicated from the thickness of cover and from the depth of crystallization of the aplitic alaskite. Mode of Emplacement of the Chilliwack Batholith The plutonic rocks of the Chilliwack Batholith made room for themselves by a combination of shouldering aside, updoming and stoping. Assimilation is of minor importance. The sequence of intrusion of the phases is shown in figure 51. The early tonalite magmas appear to haV9 been emplaced by shouldering aside of the highly fis s i l e and incompetent sediments of the Chilliwack Group and to have been emplaced, possibly by stoping or updoming, into the southward extension of the Fraser River graben (figure 52). The eastward extension of the tonalite towards Custer Ridge (figure 52) may have been facilitated by pre-existing structures. The tonalite south of Mount Edgar extends along a known easterly-trending fault that separates the Skagit volcanics from the Hozameen Group (figure 52). East to northeast trending fracture zones, termed transverse structural belts by Grant (1969), are common in the Northern Cascades. A east-northeast trending lineament marked by the Skagit River and Snass Creek (figure 52) may indicate a structure that controlled the eastward extension of the Chilliwack Batholith. 117 F I G U R E 51 I l l us t ra t ion of the Sequence of Emplacement of the Phases of the Chi l l iwack Batholith df Geology prior to intrusion b)\Emplacement of the Diorite >> N N 1-3 i / ' / G) Emplacement of the western and the earjy part of the eastern Tonalite > d) Edstward extension of the Tonalite e) Emplacement of the Paleface Granodiorite f) Emplacement of the Radium Phase -a) Emplacement of the Rexford Phase h) Schematic present day cross-section 118. A l l t h e p h a s e s y o u n g e r t h a n t o n a l i t e e x c e p t t h e P o s t C r e e k phase i were emplaced i n t h e t o n a l i t e . S i m i l a r i t y o f K-Ar ages o f t h e v a r i o u s p h a s e s and some c o n t a c t s between t o n a l i t e and o t h e r p h a s e s t h a t show no i n d i c a t i o n o f age r e l a t i o n s s u g g e s t s t h a t t h e t o n a l i t e might have s t i l l been p l a s t i c when i t was i n t r u d e d , t h u s a l l o w i n g f o r emplacement o f t h e y o u n g e r p h a s e s i n t o t h e t o n a l i t e . The volume o f t h e P a l e f a c e g r a n o d i o r i t e was p r o b a b l y not l a r g e , a s i t a p p e a r s t o have a r o o f composed o f t o n a l i t e on Mount MacDonald, and t h e s h a l l o w d i p p i n g l a y e r s n o r t h of P a l e f a c e C r e e k might i n d i c a t e a n e a r b y b a s e . The abundance o f i n c l u s i o n i n t h e R e x f o r d s t o c k s u g g e s t s emplacement b y s t o p i n g . The P o s t C r e e k phase was emplaced e n t i r e l y w i t h i n t h e F r a s e r R i v e r g r a b e n . 119. F I G U R E 5 2 Re lat ions of the Chill iwack Batholith to Major Faults and Lineaments "wvfc^ Known faults Extensions of known faults or lineaments 120. THE MOUNT BARR BATHOLITH INTRODUCTION The Mount Barr Batholith is composed of four intrusive phases, (figure 53). The oldest, the Conway phase, which lies along the margins of the pluton, is composed mostly of tonalite. Central and eastern parts of the batholith are underlain by tonalite, granodiorite and quartz monzonite of the Mount Barr phase. Three small stocks, one near the eastern edge of the batholith and the others near Wahleach Lake, are leucocratic quartz raonzonites. The youngest, the Wahleach phase, a six-square-mile area stock centered on Wahleach Lake, is composed mostly of tonalite. The Hicks Lake stock, located to the north across the Fraser River (figure 4) is composed of mafic tonalite. This stock may be related to the earliest intrusive phase of the Mount Barr Batholith. Modes of these phases are listed in table 24. MINERALOGY AND PETROLOGY  Conway Phase The Conway phase is composed of medium-grained massive tonalite and minor granodiorite that is locally porphyritic with phenocrysts of plagioclase. A sequence of layered rocks is exposed just north of Mount Conway (figure 56). The colour index decreases from the margins inward and from exposures at lower elevations to exposures at higher elevations. Plagioclase, common as phenocrysts and synneusis aggregates, shows cores of An^g to An^Q with well developed oscillatory-zoning (20 to 70 zones). Cores are mantled by rims normally-zoned from An.^ to An^^. The break between An^ Q and An^ is usually sharp. 121. TABLE 24. Modes of the Mount Barr Batholith CONWAY PHASE 116 m 245. 292 274 HI m m plagioclase 50.0 55.7 50.4 54.6 54.4 55.7 54.0 51.2 56.2 quartz 22.1 23.1 22.0 15.9 13.0 20.9 24.4 18.8 20.4 orthoclase 6.1 6.5 12.9 7.1 11.2 12.1 7.5 10.2 12.9 clinopyroxene 0.5' - tr 1.3 0.6 tr - 0.6 tr hornblende 7.8 5.1 7.1 8.7 7.9 3.5 8.4 7.2 5.1 biotite 12.9 7.3 6.6 11.7 6.1 6.9 5.1 11.1 4.7 sphene tr tr tr tr tr tr tr tr 0.4 apatite tr tr tr tr tr tr tr tr tr magnetite 0.6 1.0 0.7 0.6 0.8 0.6 0.6 0.8 0.4 267 1457* 386 M61 1412* plagioclase 47.2 31.6 55.3 54.4 47.9 quartz 21.8 14.7 19.7 17.6 16.1 orthoclase 12.3 8.3 8.6 12.4 7.4 clinopyroxene 0.3 tr tr 0.3 0.3 hornblende 11.8 25.3 6.4 7.8 8.4 biotite 5.3 16.6 9.8 6.8 17.4 sphene tr 0.3 tr tr 0.4 apatite tr tr tr tr tr magnetite 1.2 2.8 tr 0.7 1.9 * From layered zones north of Mount Conway MOUNT BARR PHASE m 187 M76 m. 022 272 282 1251* 235 plagioclase 49.2 51.4 52 44.8 53.1 47.9 51.4 31.5 48.2 quartz 24.3 20.9 22 25.9 24.4 21.0 19.9 13.3 23.4 orthoclase 11.4 11.1 10 12.7 11.8 21.8 18.1 13.3 15.8 hornblende 6.2 6.9 8 8.4 3.6 4.9 3.5 31.3 6.3 biotite 8.1 7.9 6 8.0 5.4 4.0 6.0 8.7 5.3 sphene tr tr tr tr tr tr tr tr tr zeolite - - — — — — _ _ _ apatite tr tr tr tr tr tr tr tr tr magnetite 0.7 1.6 1 tr 1.3 0.4 0.7 1.3 1.0 134 m m m. plagioclase 43.6 41.2 43.7 43.0 * 1251: layered zone, quartz 19.7 20.8 22.0 23.1 south of Mount Bar orthoclase 22.5 22.2 21.0 17.5 hornblende 8.1 7.9 5.2 5.0 biotite 4.1 6 .3 6.9 5.6 sphene tr 0.3 0.2 tr zeolite — - — 0.2 apatite tr 0.2 tr tr magnetite 1.2 0.9 0.7 0.7 122 LEUCOCRATIC PHASE WAHLEACH LAKE PHASE 1321 227 021 1S2 ILL WAH p l a g i o c l a s e 33.3 33.5 46.5 38.0 34.9 45.6 49.6 q u a r t z 35.4 35.2 37.2 36.9 28.7 24.5 28.8 o r t h o c l a s e 23.8 27.1 15.6 21.5 34.4 5.8 11.2 h o r n b l e n d e t r t r 0.3 — - 14.3 3.4 b i o t i t e 5.4 3.7 2.8 2.5 l . S 9.7 6.1 sphene t r t r t r t r t r 0.5 t r z e o l i t e t r - t r ' — — — — a p a t i t e t r t r t r t r t r t r t r m a g n e t i t e 0.6 0.6 t r t r 0.2 t r 0.9 L o c a t i o n s o f Specimens i n F i g u r e 54. 123. FIGURE 53 Phases of the Mount Barr Batholith LEGEND Silver Creek Stock Eocene Conglomerate Williams Peak Stock Spuzzum Intrusions Custer Gneiss Chilliwack Group Mount Barr Batholith Wahleach Lake Phase Leucocratic Stocks Mount Barr Phase Conway Phase + + 0 I S c a l e 2 i of "Miles 4 A — B and C — D ; cross sections shown in figure 57 FIGURE 54 Location of Specimens Used in the Text 125. Hornblende and biotite occur in about equal porportions. Minor augite, as cores in hornblende, is most abundant in rocks from lower elevations east of the Trans-Canada Highway and adjacent to the Spuzzum Intrusions. Augite, minor hornblende and biotite inclusions in plagioclase cores are abundant. K-feldspar (Org^gy) show orthoclase structural states (figure 55 and table 25). Mount Barr Phase The Mount Barr phase is composed mainly of granodiorite with common phenocrysts of plagioclase and hornblende. The unit is massive, except for local patches and thin layers of hornblende-rich rock. The rocks are chilled against the Spuzzum Intrusion. The phase differs from the Conway phase in its conspicuous hornblende phenocrysts. A dyke, some 200 to 300 feet wide, with phenocrysts of quartz, hornblende and plagioclase in a granophyric groundmass, lies between the Eocene conglomerates and the Silver Creek stock. This body appears to be an offshoot of the Mount Barr phase. Plagioclase is similar to that found in the Conway phase, but is more strongly-zoned (30 to 100 zones). Cores, zoned from An^g to An^ Q, are mantled by rims, zoned from An^ to A^Q. Phenocrysts of hornblende, one-half to two inches long, are character-istic of this phase. These are most abundant in exposures at the low elevations. Most of the hornblende phenocrysts have been partly replaced by fine-grained biotite. Pyroxene is absent except as inclusions in plagioclase. Orthoclase (figure 55) ranges in composition from Orgy to Ory^ (table 25). The mineral is everywhere interstitial to mafics and plagioclase. Sphene 126. Table 25. X - r a y Data f o r S t r u c t u r a l S t a t e s and C o m p o s i t i o n s f o r A l k a l i F e l d s p a r s from t he Maunt B a r r B a t h o l i t h Specimen 060 Conway Phase 384 41.72 1364 41.71 1236 41.69 1233 41.65 11/+ 41. 71 1373 ' 41.70 379 41.69 354 41.71 Mount B a r r Phase 134 41.73 348 41.71 223 41 .72 1259 41.72 364 41.67 321 41.66 1254 41.73 M73 41 .72 1242 41.69 1248 41.67 SCP 41 .67 L e u c o c r a t i c S t o c k s 138 41.77 22.7 41.70 Wahleack Phase 390 41.75 Wah 41.75 142 41.70 148 41.70 20jt 50.75 50.75 50.79 50.79 50.77 50.82 50.75 50.73 50.75 50.73 50.74 50.76 50.76 50.79 50.79 50.75 5 0.30 50.75 50.77 50.74 50.76 50.88 50.76 50.77 50.75 >01 horn 21.06 21.06 21 .05 21.06 21 .05 21.06 21.06 21.00 21.12 21.07 2 1 . 1 0 2 1 . 1 1 21.14 2 1 . 0 9 2 1 . 1 4 2 1 . 1 0 2 1 . 0 9 2 1 . 0 ? 2 1 . 1 6 21.18 21.15 21.10 21.12 21.11 Or 87 87 SI 87 83 87 87 84 81 86 83 82 79 84 79 83 84 86 77 68 75 1 81 82 127. FIGURE 55 2 6 0 6 0 - 2 0 4 Structura l State Plots for A lkal i Feldspars from the Mount Barr B a t h o l i t h .low a I bite microcline low albite high sanidine Conway Phase high sanidine Mount Barr Phase ow albite microclim low albite high sanidine Leucocratic Stocks high albite microcline high sanidine Wahleach Phase high albite 128. is a common accessory, expecially i n areas rich in hornblende. Minor s t i l b i t e , i n t e r s t i t i a l to orthoclase, appears to be a deuteric mineral. Leucocratic Stocks, The three leucocratic stocks are generally massive, even-grained quartz monzonites. Locally, however, they are chilled, with phenocrysts of quartz, orthoclase, plagioclase and minor altered hornblende i n an a p l i t i c groundmass. Miarolitic cavities and granophyre are not uncommon. Few breccia zones, comprised of angular fragments of quartz monzonite in a matrix of comminuted rock, are present. These are associated with an area of intense fracturing that l i e s between Wahleach Lake and the Trans-Canada Highway. Zoned plagioclase (oscillatory, 10 to 30 zones) cores of composition An^ to An^g are rimmed by plagioclase zoned from An 2g to An2Q. These crystals d i f f e r from those of the Conway and the Mount Barr phases in as much as they show less well developed zoning, smaller cores and wider rims and contain only hornblende and biotite as inclusions. In the eastern part of the stock centered on Wahleach Lake, plagioclase i s unzoned An,,^ . 2^. Mafics are not abundant} biotite predominates and many specimens are devoid of hornblende. In the stock located south of Mount Ludwig, hornblende phenocrysts have been pseudomorphed by mosaics of fine-grained biotite. Orthoclase (Or^g) and quartz may loca l l y be found as phenocrysts. Wahleach Lake Phase Rocks from the Wahleach Lake phase are u r ; f o l i a t e d , non-porphyritic and characteristically f i n e - g r a i n e d . Small (one-inch diameter) mafic i n c l u s i o n s are common throughout the stock. 129. Oscillatory zoned (20 to 40 zones) plagioclase cores (An^ to An^g) are rimmed by An 2 r , _ ? Q . Orthoclase (Oryo^g-j) show orthoclase struct'oral states (figure 5 5 ) . Unaltered hornblende and fine-grained biotite occur in nearly equal porportions. Pyroxene i s absent. Inclusions of hornblende and bioti t e in plagioclase are not abundant. STRUCTURE Internal Relations Relations between Phases Age relations between phases are not obvious; dykes of one phase cutting another, chilled margins (except in the leucocratic phases) and other structural evidence for relative ages i s not abundant. The lack of these features i s believed to be due to the rapid succession of intrusions, so that many of the phases were s t i l l hot and possibly plastic at the same time. The Conway phase appears to be the oldest intrusive unit, followed by the Mount Barr phase. The leucocratic stocks clearly intrude the Mount Barr phase. The relative age of the Wahleach Lake phase i s in doubt, but i t s markedly finer grain-size suggests that i t i s the youngest. However, a sequence of events deduced from changes i n textures, mineral porportions and chemistry between the Conway, Mount Barr and the leucocratic phases f i t s a reasonable hypothesis of fractional crystallization from a single underlying magma chamber. The Wahleach Lake phase does not f i t into this sequence. Layering Layered sequences, probably cumulates, are found i n the Conway and Mount Barr phases. Ten layered zones, s i x inches to three f e e t t h i c k , are exposed over 150 vertical feet just north of Mount Conway (figure 56)« 130. FIGURE 56 C r o s s - s e c t i o n of the Layered Zones Norfh of Mount Conway Conway Tonalite on Conway Ridge Foley Peak 0 1/4 1/2 I Scale of Feet 0 500 IOOO 2 0 0 0 • 1 1 — ' Single Layered Zone 131. Layers strike 065° and dip 25° to the south. Some of the units are graded (figure 56). Minerals in the layered rook are identical to those in the adjacent unlayered rock. Layering in the Mount Barr phase i s less well developed than in the Conway phase, but i s more extensive. Two and one-half miles east of the north end of Wahleach Lake, five f l a t - l y i n g layers, two inches to one foot thick, are exposed in the valley bottom. These layers contain up to 30$ hornblende phenocrysts. At elevations of 2500 feet in the west and 3000 feet in the east, hornblende forms in many places up to 50% of the Mount Barr phase. The porportion of hornblende decreases upwards (figure 57). On the slopes east of the Fraser River, hornblende-rich granodiorite overlies the Conway tonalite at the 2500 foot level. The abundance of hornblende again decreases upwards. The general concentration of hornblende at a low level may mark the base of the Mount Barr phase. In the fork of Sowerby Creek, the Conway phase seems to overlie the Mount Barr phase (figures 1 and 57). This "outlier" of the Conway phase i s some 3000 feet above the base of the Mount Barr phase (suggested above) and suggests that the Mount Barr phase may be a 3000 foot thick s i l l - l i k e body. Cross-sections of the batholith are shown in figure 57. External Relations Intrusive Relations The Mount Barr Batholith i s intrusive into the Eocene conglomerates and the Silver Creek stock. Foliations in the Chilliwack Group sediments are parallel to the contact. Inclusions of country rock are present only within 100 to 200 feet of contacts. 132. FIGURE 57 Schemat ic C ross - sec t ion of the Mount Barr Batho l i th west LEGEND Wahleach Phase Leucocratic Stocks Mount Barr Phase Conway Phase Spuzzum Intrusions Chilliwack Group east o m o o - - i -rv - Sea Level C-north south-D Horizontal scale 1 l"= 2 miles Vertical scale- I = I mile The concentration of hornblende phenocrysts is represented schematically by the density of the symbol " • " 133. , The batholith truncates two major fault zones, the Shuksan fault and the Hope fault (figure l ) . The bulk of the intrusive rocks appear to have been emplaced mainly in an area formerly underlain by the Chilliwack Group and transected by the Shuksan fault. Contact Metamorphism P e l i t i c rocks of the Chilliwack Group have been converted to cordierite-andalusite hornfels, basic rocks to biotite amphibolites and limey rocks to garnet-wollastonite-diopside skarns. Tremolite, albite, tourmaline and secondary biotite were formed loca l l y in the Spuzzum Intrusions near the Mount Barr phase. AGE OF THE MOUNT BARR BATHOLITH K-Ar ages from the various phases range from 16 to 21 million years (table 26). TABLE 26. K-Ar Ages from the Mount Barr Batholith Phase Age (million years) Conway 18, 18 (Baadsgaard et a l 196l) Mount Barr 21, 16 Wahleach Lake 18 The 21 million year age from the Mount Barr phase was obtained from the granophyre dyke just east of Silver Peak (figure l ) . This age probably reflects most closely the age of emplacement of the batholith while other ages, taken from the interior of the batholith, probably reflect the time of cooling of the batholith. CHEMISTRY OF THE MOUKT BARR BATHOLITH Chemical analyses are listed i n table 27 and shown graphically in figures 58, 59 and 56. The sequence of emplacement of the phases, inferred from structural relations, conforms to the variation in chemistry from the most basic Conway phase to the most acidic leucocratic stocks. 134. TABLE 27. Chemical Analysis of the Mount Barr Batholith Conway Phase Mount Barr Phase (b.) m 379 222 274 1243 m M76 sc 185. 144 Si02 65.8 64.3 64.0 63.3 65.3 69.1 67.4 67.2 77.3 69.9 A 12°3 16.7 17.4 17.4 16.9 16.3 14.3 16.5 15.6 14.2 16.0 MgO 2.0 2.4 1.8 1.9 2.1 1.7 1.7 1.5 SO. 5 1.3 FeO 2.3 2.6 2.2 2.5 2.8 1.8 2.3 2.1 0.7 2.0 F e2°3 1.6 1.8 2.1 1.4 1.7 1.6 1.6 1.2 0.3 1.3 MnO 0.08 0.08 0.08 0.08 0.08 0.07 0.08 0.06 0.03 0.08 CaO 3.2 4.9 4.9 4.6 4.5 3.4 4.1 3.2 1.6 3.1 Na20 3.6 3.6 3.6 3.5 3.6 3.1 3.5 4.0 3.2 3.5 K20 1.3 2.1 2.3 2.6 2.6 3.9 2.2 2.0 3.0 2.3 Ti02 0.41 0.48 0.45 0.49 0.47 0.38 0.42 0.35 0.17 0.38 p 2 o 5 0.17 0.13 0.14 0.12 0.12 0.11 0.15 0.06 0.05 0.10 C02 *0.1 *0.1 0.1 0.1 0.3 *0.1 *0.1 0.2 *0.1 0.1 H20 1.3 0.8 0.6 0.4 0.7 0.5 0.8 0.7 0.4 1.0 S 0.02 0.01 0.02 0.03 0.02 0.01 0.02 0.01 0.01 0.02 $ value is less than 0.5$ * value is l e s s than 0.1% (a.) Leucocratic Stock (b.) Wahleach Phase Location of specimens i n figure 54. 135. F I G U R E 5 8 Silica Variation Diagram •0.4 0.3 0.2 o.i Ti02 • 5 •4 • 3 2 I CaO ' 4 * + •4 • 3 •2 I K 2 0 V h •17 •16 15 •14 A l 2 0 3 2 I MgO 4 3 2 I 1% F e O t o t 4 • 3 2 N a 2 0 •H 1— 1 h-o Wahleach Phase A Leucocratic Stocks . Mount Barr Phase + Conway Phase i i I i 50 60 70 80 % Si 0 2 136. FIGURE 59 F e O ^ i - M g O - ( N a 2 0 + K 2 0 ) Plot FIGURE 60 C a O - N a 2 0 - K 2 0 Plot 137. L i t t l e v a r i a t i o n i n chemistry was noted i n the Conway phase. K20 shows the l a r g e s t v a r i a t i o n . The lowest value of K20, 1.3% from specimen 114, was obtained from the lowest e l e v a t i o n and the highest value of K20, 2.6% from specimen 274, was obtained at the highest e l e v a t i o n . Chemical v a r i a t i o n s w i t h i n the Mount Barr phase appear r e l a t e d t o the d i s t r i b u t i o n of hornblende phenocrysts. The most b a s i c specimen (number 1248) was taken from the zone enriched i n hornblende t h a t o v e r l i e s the Conway phase. Specimen 134, enriched i n potash and s i l i c a r e l a t i v e t o the mafic l a y e r s , was taken from j u s t above the la y e r e d r o c k s east of Wahleach Lake. The trend shown i n f i g u r e 60 conforms t o a c a l c - a l k a l i n e t r e n d of d i f f e r e n t i a t i o n . The sm a l l d i f f e r e n c e s i n chemistry between the Conway and Mount Ba r r phases f i t s the hypothesis t h a t minor d i f f e r e n t i a t i o n occurred between the time of emplacement of these two phases, while a l a r g e d i f f e r e n c e i n chemistry between the Mount Barr phase and the l e u c o c r a t i c phases suggest a l a r g e degree of d i f f e r e n t i a t i o n . PETROGENESIS The emplacement of the phases of the Mount Barr B a t h o l i t h occurred i n p u l s e s , each more a c i d i c than i t s predecessor. F r a c t i o n a l c r y s t a l l i z a t i o n i n an underlying magma, from which p o r t i o n s were tapped and emplaced above, best accounts f o r the sequence: Conway phase-Mount Barr p h a s e - l e u c o c r a t i c stocks. T h i s sequence i s o u t l i n e d i n f i g u r e 6l. Once emplaced, some of the magmas underwent f u r t h e r f r a c t i o n a l c r y s t a l l i z a t i o n , mainly by c r y s t a l s e t t l i n g . Plutonism ended with the emplacement of the Wahleach Lake phase. The presence of p l a g i o c l a s e , pyroxene and hornblende on the l i q u i d u s of the underlying magma p r i o r t o emplacement of the Conway phase ( f i g u r e 6l) i s suggested by: p l a g i o c l a s e phenocrysts; pyroxene cores i n hornblende; and pyroxene, hornblende and minor b i o t i t e i n c l u s i o n s i n p l a g i o c l a s e . 138. crystallization and lower differentiation in chamber the r a Q' o a cn CD TD >< - l O X CD 3 CD Z m CD 3 a. a > CD > 3 Q c r o CD crystallization and differentiation at the present level —I 1 > 3 OJ Ul cr ar CL co CO 3 o o -1 *< Intrusion of the Conway Phase 3" O 3 c r CD 3 CL c r O CD .Q c a 3 ro CD M o —* -j 1 00 l 1 1 o —• 3 CD cr a> a o CD </> > 3 31 CD c m CD o in N Q o X c/> —4-o Intrusion of the 4^  00 > OQ Mount Barr Pha^e > 3 ro I- i — c I O CO ro N CD O CZ Q O o_ a a> Intrusion of the 3 ro Leucocratic Stocks c r O .o c Q a> o c 3 CD Q -=? ro e •=> o > _3 CO CD 00 CD O CD I 139 . A f t e r emplacement of the Conway magma, c r y s t a l l i z a t i o n f o l l o w e d a s l i g h t l y d i f f e r e n t path from the path of c r y s t a l l i z a t i o n of the underlying magma. At t h i s l e v e l , An^g_^Q was rimmed by A n ^ , hornblende and b i o t i t e continued t o c r y s t a l l i z e , and towards the end of c r y s t a l l i z a t i o n o r t h o c l a s e and quartz appeared. A short i n t e r v a l of time elapsed between the emplacement of the Conway phase and the Mount Barr phase. During t h i s i n t e r v a l the underlying melt, r e l a t i v e t o i t s e a r l i e r composition, was s l i g h t l y enriched i n s i l i c a and potash and depleted i n alumina, magnesia and l i m e . Large phenocrysts of hornblende and f u r t h e r a d d i t i o n s of o s c i l l a t o r y zones on p l a g i o c l a s e were developed during t h i s p e r i o d . The absence of pyroxene and abundance of hornblende and b i o t i t e probably r e f l e c t s an increase i n ^ H^O ^ ^ E M E ^ * The l a r g e d i f f e r e n c e s i n chemistry and i n p o r p o r t i o n s of minerals between the l e u c o c r a t i c phases and the Mount Barr phase suggest that a s u b s t a n t i a l p e r i o d of time separated the emplacement of these phases. T h i s hypothesis i s supported somewhat by the c h i l l e d margins i n the l e u c o c r a t i c stocks adjacent t o the Mount Ba r r phase. The melt i n the underlying magma chamber was f u r t h e r enriched i n s i l i c a and potash and depleted i n alumina, i r o n , magnesia and lime ( f i g u r e 5 8 ) . C r y s t a l l i z a t i o n of minerals from these magmas once emplaced i n t o the present l e v e l i s shown i n f i g u r e 61. The sodic p l a g i o c l a s e rims that mantle the o s c i l l a t o r y zoned phenocrysts mark a prominant unconformity i n p l a g i o c l a s e c r y s t a l l i z a t i o n . The abrupt decrease i n a n o r t h i t e composition from core t o r i m seen i n each i n t r u s i v e phase ( t a b l e 28) may be a t t r i b u t e d t o a decrease i n Q (Yoder 1 9 6 8 ) . The magnitude of the decrease i n ^ u^O ^ s smaller f o r the Conway phase than f o r the Mount Barr phase, as evidenced by the 5% a n o r t h i t e d i f f e r e n c e between core and r i m i n the Conway phase compared t o the 9% a n o r t h i t e d i f f e r e n c e f o r the Mount Barr phase ( f i g u r e 62). L 4 0 . TABLE 28. Change i n A n o r t h i t e Compositions from Core t o Rim P l a g i o c l a s e i n the Mount Barr B a t h o l i t h I n t r u s i v e Phase An-Core Margin An-Inner Rim Conway Phase An42-40 An35 Mount Ba r r Phase A n ^ 0 An-^ Le u c o c r a t i c Stocks An40-38 An29 T h i s r e l a t i o n s h i p suggests t h a t the magma of the Conway phase reached water s a t u r a t i o n at a higher c r u s t a l l e v e l than the magma of the Mount Barr phase, thus undergoing a smaller decrease i n P R ^ 0 ( f i g u r e 63). Once a magma reached water s a t u r a t i o n , and rose t o subsequently higher l e v e l s i n the c r u s t , b o i l i n g would occur and thus account f o r the normally-zoned rims on p l a g i o c l a s e (Vance 1962). The r e l a t i o n between the Mount Barr phase and the l e u c o c r a t i c stocks i s s i m i l a r t o the one described above (see f i g u r e s 62 and 63). D i f f e r e n t i a t i o n a t the Present L e v e l Once emplaced i n t o the present l e v e l of exposure both the Conway and Mount Barr magmas underwent d i f f e r e n t i a t i o n p r i m a r i l y by c r y s t a l s e t t l i n g . In the Conway phase, the lower exposures are s l i g h t l y more b a s i c and mafic than the higher exposures. The layered zones north of Mount Conway, although not ex t e n s i v e , tend t o support the idea t h a t t h i s d i f f e r e n c e could be the r e s u l t of c r y s t a l s e t t l i n g . The d i s t r i b u t i o n of hornblende phenocryst i n the Mount Barr phase i s compatible with c r y s t a l s e t t l i n g . F i g u r e 6l represents i n schematic f a s h i o n the d i f f e r e n t i a t i o n of the Mount Barr phase at i t s present l e v e l of exposure. L e v e l of Emplacement An e p i z o n a l environment of emplacement i s i n d i c a t e d f o r the Mount Barr B a t h o l i t h by the presence of m i a r o l i t i c c a v i t i e s , granophyric t e x t u r e s , 141. FIGURE 62 Schemat ic History of P lag ioc lase Crysta l l i zat ion of P l a g i o c l a s e f rom the Mount B a r r Bathol i th % Anorthite Anorthi te - albite-water system (modified after Yoder 1969) showing the change in composition of plagioclase with a decrease in water pressure j ' a ' representing a higher water pressure than V , 'a' represents the composition of the outer part of the core of a plagioclase crystal (table 2 8 ) ; V represents the composition of the inner part of the r im ad jacent the core for the Conway Phase (table 2 8 ) , V for the Mount Barr Phase and ' d ' for the Leucocrat ic S t o c k s . 142. FIGURE 63 Schematic Representation of Levels of Water Saturation for the Various Phases of the Mount Barr Batholith After Being Tapped f rom the Underlying Magma Chamber A, A 'and A" represents the levels where the magmas became saturated with HgO A _ B ) ^ _ B ' and A — B " represents the distance magmas travel between their level of water saturation and their final level of emplacement 143. b r e c c i a bodies and c h i l l e d margins i n the v a r i o u s phases. Although no q u a n t i t a t i v e estimate of the amount of cover can be obtained, the one-to two-mile depth of emplacement of the Oligocene C h i l l i w a c k B a t h o l i t h seems t o g i v e a maximum depth of emplacement f o r the Mount Barr B a t h o l i t h . Mode of Emplacement The phases of the Mount Barr B a t h o l i t h were emplaced i n a s e r i e s of pul s e s ( f i g u r e 64). Deformation i n the C h i l l i w a c k Group suggests t h a t shouldering a s i d e of sediments was an important mechanism f o r emplacement. Although the evidence i s not c o n c l u s i v e , i f the Mount Barr phase i s s i l l - l i k e then some room might have been made by u p l i f t i n g of the roof r o c k s . Old f a u l t s , such as the Shuksan and F r a s e r R i v e r f a u l t s , reaching deep i n t o the c r u s t , might have o f f e r e d easy routes f o r the emplacement of the Mount Barr magmas. L44. FIGURE 6 4 I l lustrat ion of the Sequence of Emplacement of the Phases of the Mount Bar r Batho l i th Emplacement of the Mount Barr Phase d) Emplacement of the Leucocratic St-ocks e) Emplacement of the Wahleach Phdse f) Schematic present day cross-section 145. DEPTH-ZONE OF EMPLACEMENT OF THE PLUTONIC ROCKS IN THE HOPE AREA In the Hope area, the five plutonic complexes, ranging in age from Upper Cretaceous to Upper Tertiary, were emplaced at successively shallower depths in the crust. The depth-zone of emplacement for each of the complexes according to Buddington's (1959) classification i s : catazone-mesozone for the Spuzzum Intrusions, mesozone (epizone?) for the Yale Intrusions and epizone for the Silver Creek Stock, the Chilliwack Batholith and the Mount Barr Batholith. The 12-17 kilometer (8-10 mile) depth of emplacement estimated for the Spuzzum Intrusions i s compatible with the depth of the mesozone-catazone. Features from the Spuzzum Intrusions in accordance with the catazone using Buddington's criterea are: the association with high grade regional metamorphics, a through-going fo l i a t i o n , and the concordance of the foliations in the tonalite and the metamorphics. Placing of the Yale Intrusions into the mesozone is based upon the general concordance of the Yale Intrusions to the northwest-trending regional structures and the lack of any obvious features characteristic of the epizone. If relating the Yale Intrusions to the waning stages of Spuzzum plutonism i s valid, then a depth-zone of emplacement in the mesozone i s reasonable. Buddington (1959), however, states that a l l Tertiary plutons belong to the epizone. Very rapid erosion in the early Tertiary might explain the presence of Tertiary plutons in the mesozone, a hypothesis supported somewhat by the unconformity between Eocene plutonics (the Coquihalla Stock) and the Eocene conglomerates. The pervasive shearing that affects the Yale Intrusions may have obliterated features such as granophyre and miarolitic cavities, hence the Yale Intrusions may indeed belong to the epizone. 146 . The S i l v e r Creek Stock, the C h i l l i w a c k B a t h o l i t h and the Mount Barr B a t h o l i t h were c l e a r l y emplaced i n the epizone. A l l are Upper T e r t i a r y i n age and in t r u d e unmetamorphosed sediments. M i a r o l i t i c c a v i t i e s , granophyric t e x t u r e s and c h i l l e d margins are common i n these p l u t o n i c bodies. S t r u c t u r a l s t a t e s of a l k a l i f e l d s p a r s may g i v e an i n d i c a t i o n of the r e l a t i v e depths of emplacement f o r adjacent p l u t o n s . F i g u r e 65 compares the s t r u c t u r a l s t a t e s of K - f e l d s p a r s from the v a r i o u s p l u t o n i c complexes i n the Hope area. K - f e l d s p a r s from the Yale I n t r u s i o n s are more ordered than those from the C h i l l i w a c k B a t h o l i t h , which are i n t u r n more ordered than those from the Mount Barr B a t h o l i t h . The high degree of d i s o r d e r of a l k a l i f e l d s p a r s from the S i l v e r Creek Stock ( f i g u r e 65) might be due t o a f a s t c o o l i n g r a t e r e s u l t i n g from the small s i z e of the stock. L47. FIGURE 65 Comparison of Structural States of Alkali Feldspars from the Various Intrusive Units in the Map Area Microcline High Albite High Sanidine © Yale Intrusions Silver Creek Stock O Chilliwack Batholith O Mount Barr Batholith 148. CORRELATION OF THE INTRUSIVE ROCKS The Spuzzum Intrusions, related to an Upper Cretaceous orogeny, represents the oldest of three stages of plutonism. The Yale Intrusions may mark the second stage but alternatively may be interpreted as representing the waning stages of the Spuzzum Intrusions. Imprinted upon these earlier episodes i s an Upper Tertiary episode of plutonism consisting of the Silver Creek Stock, the Chilliwack Batholith and the Mount Barr Batholith. Upper Cretaceous to Upper Tertiary plutonic bodies in southwestern British Columbia and Washington State, probably correlative with the plutonic rocks in the map area, are shown in figure 66 and their ages, when available, listed in table 30. The Coast Crystalline Complex (Roddick 1965) to the west of the map area and the Mount Stuart Batholith (Yeats 1968) and the Black Peak Batholith (Adams 1964) to the south are probably correlative with the Spuzzum Intrusions. U-Pb dating (Mattinson 1970) on the Eldorado Gneiss (Misch 1966) indicates that some intrusive units within the Skagit metamorphic suite (Misch 1966) crystallized at about the same time as the Spuzzum Intrusions. Deeper erosion of the Coast Crystalline Complex north of Hope relative to the level of erosion of the Northern Cascades (McTaggart 1970) might explain, in part, the general paucity of exposure-of Upper Cretaceous plutons south of the 49th parallel (figure 66). The lack of Upper Cretaceous volcanics in the area suggests that these Upper Cretaceous plutonics did not rise to a high level in the crust. The Yale Intrusions consist of a belt of Early Tertiary variably sheared intrusions that l i e near or along a northwest trending fault zone that separates the Custer-Skagit Gneiss from the Hozameen Group. The ubiquitous cataclastic texture distinguishes these plutonics from the 149. FIGURE 6 6 Plutonic Rocks of the Southern Coast Crysta l l ine Complex and the Northern C a s c a d e s 150 TABLE 29. Plutonic Rocks of the Southern Coast Crystalline Complex and Northern Cascade Mountains (to accompany figure 66). Upper Cretaceous Plutonics 1. Eagle Granodiorite 2. Spuzzum Intrusions 3. Scuzzy Pluton 4. The Nipple Pluton 5. Coast Crystalline Complex 6. Black Peak Batholith 7. Eldorado Orthogneiss 8. Hidden Lake Stock 9. Snowking Batholith 10. Mount Stuart Batholith Lower Tertiary Plutonics 11. Hells Gate Stock 12. The Needle Pluton 13. Yale Intrusions 14. Williams Peak Stock 15. Ruby Creek Intrusions 16. Golden Horn Batholith Upper Tertiary Intrusions 17. Silver Creek Stock 18. Hicks Lake Stock 19. Mount Barr Batholith 20. Chilliwack Batholith 21. Perry Creek Phase 22. Chilliwack Composite Batholith 23. Cascade Pass Pluton 24. Cloudy Pass Batholith 25. Squire Creek Stock. 26. Grotto Batholith 27. Index Batholith 28. Snoqualmie Batholith 29. Carbon River Stock 30. Tatoosh Pluton 31. Bumping Lake Stock 32. Spirit lake Stock 33. Silver Star Stock 34. S t i l l Creek Stock 151 TABLE 3 0 . Ages of I n t r u s i v e Rocks from the Southern Coast C r y s t a l l i n e Complex and the Northern Cascades. Plutonic Unit Upper Cretaceous Plutons Spuzzum Intrusions The Nipple P l u t o n Scuzzy Pluton Black Peak Quartz D i o r i t e Hidden Lake Stock Mount St u a r t B a t h o l i t h Beckler Peak Stock "Skagit Stock" Eldorado Orthogneiss Snowking B a t h o l i t h Eagle G r a n o d i o r i t e Coast Range Complex Lower T e r t i a r y Plutons Age 102, 103, 83, 81, 79 76, 76 72 70 70 UK U.K.-Lower T e r t . 86, 77, 80 94 84 92-59 UK 143, 100 97, 95 Reference T h i s Work McTaggart and Thompson (1967) Hutchinson (1970b) Hutchinson (1970b) Hutchinson (1970b) Adams (1964) Misch (1966) Yeats et a l (1968) Yeats et a l (1968) Coates (1970) Mattinson (1970) E r i c s o n (1970) McTaggart (1970) McTaggart (1970) H e l l s Gate Stock 35 Baadsgaard (l96l) 40, 45 Hutchinson (1970) C o q u i h a l l a Stock 41 T h i s Work O g i l v i e Stock 35 T h i s Work Berkey Creek Phase 59 T h i s Work Yale I n t r u s i o n s Lower T e r t i a r y McTaggart et a l ( Ruby Creek I n t r u s i o n s Lower T e r t i a r y Monger (1970) Skagit Mica P e r i d o t i t e 44 This Work Wi l l i a m s Peak T o n a l i t e 24 This Work Upper T e r t i a r y Plutons > Hicks Stock 24, 24 This Work. Mount Barr B a t h o l i t h 21, 18, 16 T h i s Work 18, 18 Baadsgaard (1961) S i l v e r Creek Stock 35 This Work C h i l l i w a c k B a t h o l i t h 29, 28, 26, 26, 26 T h i s Work Perry Creek I n t r u s i o n 30 Misch (1966) C h i l l i w a c k Composite Bath. Eocene Misch (1966) Squire Creek Stock 34, 34 Yeats (1970) 34 Grant (1969) Index B a t h o l i t h 40, 35, 33 Yeats (1968) 32, 32 Yeats (1970) Grotto B a t h o l i t h 26, 25 Yeats (1970) Cloudy Pass P l u t o n 22 Cater (1966) Cascade Pass Pluton 20 Misch (1966) Snoqualmie B a t h o l i t h 18 Baadsgaard (l96l) 15 E r i c k s o n (1969) 17 C u r t i s (1961) Tatoosh P l u t o n 15, 13 F i s k e (1963) S t i l l Creek Stock 12 Wise (1969) 152. unsheared Upper Tertiary plutonics. Three K-Ar ages of 40, 44 and 48 million years on sheared Custer-Skagit Gneiss from south of the 49th parallel (Kulp 196l) and a single 44 million year age from a sheared hornblendite ultramafic intrusion on Custer Ridge (figure 1 and table 2) may be interpreted as marking shearing that accompanied and controlled the emplacement of the lale Intrusions. The Upper Tertiary plutons near Hope are correlative with an array of dykes, stocks and batholiths that extend from Hope to northern Oregon (figure 66 and table 30). A l l these bodies show features typical of the epizone. Many have been emplaced into graben-like structures. A l l the Upper Tertiary plutons studied in this work li e within the Fraser River graben. The Cloudy Pass Batholith truncates the north-northwest trending Chiwaukum graben (Cater 1969). The Snoqualmie, Index and Tatoosh plutons (Ericson 1969) lie along the southward extension of the Fraser River-Straight Creek fault system. These plutons have been linked to the Cascade volcanics (Water 1955, Fiske et al 1963). Upper Tertiary volcanics overlie the Chilliwack Composite Batholith (Misch 1966), the Cloudy Pass Batholith (Cater 1969, Tabor and Crowder 1969), the Snoqualmie Batholith (Ericson 1969) and the Tatoosh Pluton (Fiske et al 1963). Fiske et al (1963) states that plutonic rocks of the Tatoosh Pluton can be traced directly into the overlying volcanics. Similarities of lead isotopic compositions from associated volcanics and plutonics from Mount Kood, Mount St. Helens, Mount Baker and Mount Rainier indicate a genetic relation between extrusive and intrusive rock (Tilton et al 1970). Similarity in chemical evolution between volcanics and plutonics is shown in figure 67. 153. FIGURE 67 A lka l i Plots for Various Plutonic Rocks of the Western CordiUera Snoqualmie Batholith (Ericson 1969) Chilliwack Batholith Mount Barr Batholith Cloudy Pass Batholith (Cater 1969) Cascade Volcanics (Carmichael 1964) • Bald Mountain Batholith (Taubeneck 1957) -••••••••«•-•» Southern California Batholith (Larsen 1948) - o - o - o Bald Rock Bathol ith (Larsen and Taubeneck I960 1 Cornucopia Stock ( Taubeneck 1968) Caribou Mountains Pluton (Davis 1963) . < . - « . « Spuzzm-Scuzzy Pluton © Coquihalla Stock + Mount Ogilvie and Will iams Peak Stocks 154 . Plutonium in this part of the Cordillera was not continuous through time but tended rather to occur in irregular pulses (figure 6 8 ) . Although plutonism occurred in the pre-Middle Jurassic (White 1966) and in the Middle to Upper Jurassic (Roddick 1 965 , Mathews 1968) i t reached i t s climax in the Upper Cretaceous. Cascade plutonism and vulcanism began in the Eocene. In the Hope area, the Cascade igneous activity was much less prominent than the Upper Cretaceous igneous activity. However, the 100 ,000 cubic miles of Upper Tertiary volcanic rocks i n Oregon (Waters 1955) i s comparable to the volume of Upper Cretaceous igneous rocks i n south-western British Columbia. Upper Tertiary intrusive activity in the Northern Cascades was continuous from Eocene to Pliocene (see table 3 0 ) . The number of plutonic bodies buried beneath the volcanic cover in southern Washington and Oregon i s unknown. Intensity of plutonism through time can be estimated semiquantitatively by plotting surface area of the plutonic rocks against time (figure 6 8 ) . Although Upper Tertiary plutonic activity i s continuous, the plot in figure 68 suggests the possibility of three periods of maximum intensity. There i s , in figure 6 8 , a marked gap between the Upper Cretaceous and Upper Tertiary plutonic activity; a gap only partly f i l l e d by the Yale Intrusions. Figure 68 refers only to southwestern British Columbia and Washington. If such a plot was made for the entire Cordillera of North America, then i t i s l i k e l y that i t would show plutonism to be continuous with time. 1 5 5 . FIGURE 68 Intensity of Plutonism with Time in the Southern Coast C rys ta l l i ne Complex and the Northern Cascades o Pliocene Oligocene Miocene Eocene 30 40 50 60 Time (in millions of years) Pateocene Upper Cretaceous 156 ORIGIN OF THE MAGMAS The plutonic rocks studied probably crystallized from magmas formed by partial melting of lower crust or upper mantle material. Temperatures attained during conventional regional metamorphism would not be high enough to develop, by anatexis, magmas as basic as those of the Spuzzum diorite or the diorite phase of the Chilliwack Batholith. At 900°C, par t i a l l y melted tonalite under a pressure of two kilobars H2O has hornblende and plagioclase on the liquidus (Piwinskii 1968). The earliest intruded magmas from the plutonic rocks studied were not saturated with water, and thus 900°C would be a minimum temperature for these melts. Andesite lavas, similar in composition to Cascade andesites and the diorite phase of the Chilliwack Batholith, attain temperatures of up to 1200° C at the time of their extrusion.(Osborn 1969). It seems l i k e l y , therefore, that these magmas originated in the mantle or deep in the crust. Partial melting of gabbroic or peridotitic material in the mantle could develop magmas cf calc-alkaline andesite a f f i n i t i e s (Green and Ringwood 1968). Experiments by Green and Ringwood (1968) have shown that partial melting of a hydrous basalt (amphibolite) at 15 to 45 kilometers, or eclogite at 45 to 150 kilometers, results in the formation of andesitic melts. Pligh alumina melts can be obtained from par t i a l melting of basaltic rocks at high pressures (15 kilobars) under either wet or dry conditions (Emslie 1971). Melts low in potash can develop either by the removal of hornblende from pa r t i a l l y melted hydrous basalt or amphibolite (Dickinson et at 1968, Yoder 1969, and Green and Ringwood 1969), or by melting of host rocks low in potash. In the latte r case, partial melting must nearly be complete, otherwise melts of the granite family would be produced (Brown and Fyfe 1970). However, i f the melts formed by partial melting during deep-seated metamorphism were removed, 157. then the residue remaining might be of andesitic composition.' This process i s unlikely for the Upper Tertiary plutons but i s possible for the Upper Cretaceous Spuzzum Intrusions. The composition of the Spuzzum dicrite and the diorite phase of the Chilliwack Batholith i s nearly identical to the experimentally derived early liquid fraction formed from melting of a hydrous high alumina basalt, at 27 kilometers (table 34), (Green and Ringwood 1969). A l l the early crystallized phases cf the plutonic complexes, except the Yale Intrusions, are high in alumina. The Spuzzum Intrusions, the diorites of the Chilliwack Batholith, the Ogilvie tonalite and the Williams Peak tonalite are a l l low i n potash. It appears that some of the chemical characteristics of the early phases of the intrusive complexes can be accounted for by anatexis of basic and ultrabasic rocks at great depths. Both the Upper Cretaceous and the Upper Tertiary intrusions are part of elongate, narrow belts (the Coast Crystalline Complex and the Cascade volcanic-plutonic province) that are some 1000 miles long and 100 miles wide (figure 69). Development of such belts i s probably in some way related to events that took place in the mantle. Ultramafic bodies, found along a l l major faults in the area, may be taken as evidence in support of the hypothesis that orogenic events reached into the mantle, Underthrusting cf oceanic crust under continental crust might, best explain the development of the extensive areas of plutonic rocks that occupy the coastal areas of western North America. If subduction of oceanic crust under continental crust was the principal mechanism for magma generation (figure 70), then a trench system to the west of the map area must have been present during the late Cretaceous and again during the late Tertiary. 158. FIGURE 69 Coast Crysta l l ine Complex and the C a s c a d e Mountains 159 . There i s l i t t l e evidence for the presence of a late Cretaceous trench system, as post-Cretaceous crustal plate movement has probably obliterated a l l evidence of i t s former existence (Atwater 1970). Plutonic rocks of the Coast Range Complex south of Prince Rupert, British Columbia, are thought not to have been formed by additions of material from the mantle (Hutchinson 1970a). However, Hutchinson (1970b) suggests that the garnet-bearing Needle Peak pluton, 30 miles north of Hope (figure 6 6 ) , crystallized from a mantle-derived magma. K-Ar age of the Needle Peak pluton i s similar to the K-Ar ages of the Spuzzum Intrusions (Hutchinson 1970b). The origin of magmas of the Mesozoic Sierra Nevada Batholith of California, a plutonic complex comparable tc the Coast Crystalline Complex, i s thought by Hamilton (1969) to be possibly related to a Benioff or subduction zone. During the Upper Tertiary, a ridge-trence system existed off the west coast (figure 71) that reasonably accounts for the development of the Cascade volcanic-plutonic province (Atwater 1970). Smith and Carmicheal (1968), studying the chemistry and mineralogy of the southern High Cascade volcanics, suggested that the most l i k e l y origin for these lavas i s by part i a l melting of the upper mantle. Sr 8 7/Sr 86 ratios of 0.7039 to 0.7030 from Eocene to Quaternary volcanics of the Cascades (Hedge et a l 1969) are similar to the mean S r 8 7 / S r 8 6 ratio (0.7037) for oceanic basalts. The chemical and isotopic characteristics of the Cascade igneous rocks, together with the presence of an appropriately positioned late Tertiary ridge-trench system seems to support the hypothesis that magmas for these rocks formed by par t i a l melting in the upper mantle. 160. FIGURE 70 Subduct ion Zone 1 Origin of Magmas oceanic crust continental crust B basalt amphibolite"^ * ^ "Ufiff granulite ~~ mantle mantle A) Melt of hydrous basalt, hornblende on the liquidus of the first formed melt (low potash melts) B) Pyrox&ne-garnet-hornblende on the liquidus of the first formed melts C) Pyroxene-garnet on the liquidus of the first formed melts FIGURE 71 O l igocene-Miocene R idge -T rench System Off the West Coast of North America (after Atwater 1970) 161. SUMMARY AND CONCLUSIONS P l u t o n i c rocks between Hope and the 49th p a r a l l e l range i n age from Upper Cretaceous t o Mid-Miocene. The dominant rock type i s t o n a l i t e , with subordinate g r a n o d i o r i t e and d i o r i t e . G r a n i t i c i n t r u s i o n occurred i n three stages, each p l u t o n i c complex emplaced at s u c c e s s i v e l y higher and higher l e v e l s i n the c r u s t . The o l d e s t and deepest seated of the complexes, the Spuzzum I n t r u s i o n s , was emplaced i n the mesozone-catazone. The development of r e g i o n a l B a r r o v i a n metamorphism i s p o s s i b l y r e l a t e d t o the emplacement of t h i s complex. A minor episode of plutonism i n the Lower T e r t i a r y i s represented by the Yale I n t r u s i o n s whose stocks and s i l l s were probably emplaced i n the mesozone. F i n a l l y , three i n t r u s i v e bodies: The Eocene S i l v e r Creek Stock, the Oligocene C h i l i w a c k B a t h o l i t h and the Miocene Mount Barr B a t h o l i t h were emplaced i n the epizone. The Spuzzum I n t r u s i o n s form the southeastern part of the northwest-trending Coast C r y s t a l l i n e Complex and the i n t r u s i o n s of the epizone form the most northern part of the north-trending Cascade v o l c a n i c - p l u t o n i c p r o v i n c e . The Yale I n t r u s i o n s may be r e l a t e d t o e i t h e r b e l t . SPUZZUM INTRUSIONS The Spuzzum I n t r u s i o n s west of Hope are composed of two i n t r u s i v e phases. A c e n t r a l d i o r i t e phase i s completely surrounded by a younger t o n a l i t e phase. The d i o r i t e shows a w e l l developed m i n e r a l o g i c a l zonation, with hypersthene-augite d i o r i t e i n i t s core and h y p e r s t h e n e - b i o t i t e -hornblende d i o r i t e along i t s margins. The rocks of the core of the d i o r i t e have apparently c r y s t a l l i z e d under d r i e r c o n d i t i o n s than the rocks of the margins of the d i o r i t e . C r y s t a l l i z a t i o n of the Spuzzum I n t r u s i o n s f o llowed a trondhjemite t r e n d . The f o l i a t i o n i n the t o n a l i t e i s concordant t o the f o l i a t i o n i n 162. the adjacent metamorphics but the tonalite has truncated isograds of regional Barrovian metamorphism and superimposed on i t a sillimanite-muscovite-quartz aureole. Contact metamorphic mineral assemblages and estimates of the amount of cover eroded suggest that the tonalite was emplaced at a depth of 12 to 17 kilometers. YALE INTRUSIONS The Yale Intrusions are a heterogeneous series of stocks and s i l l s that were emplaced mainly along or near the fault zone that separates the high grade metamorphic rocks of the Custer-Skagit Gneiss from the low grade metamorphic rocks of the Hozameen Group. Their age appears to be early Tertiary, as they intrude the Spuzzum Intrusions and are overlain unconfcrmably by the Eocene conglomerates. K-Ar ages range from 59 to 35 million years. The extent of the Yale Intrusions is unknown, but they might extend from Hell's Gate southward for some 80 miles to near the south end of Ross Lake. SILVER CREEK STOCK The Silver Creek tonalite represents the earliest of the epizonal intrusions. It was emplaced along the north trending Fraser River fault system. CHILLIWACK BATHOLITH The Chilliwack Batholith is composed of seven intrusive phases which range in composition from hypersthene-augite diorite to a p l i t i c alaskite. Tonalite i s the dominant rock type. Emplacement of the phases occurred in pulses; successive magmatic phases were tapped from an underlying, differentiating magma that was gradually rising up through the crust. 163. A f t e r emplacement of each magma i n t o the present l e v e l of exposure, i t underwent d i f f e r e n t i a t i o n t h a t produced m i n e r a l o g i c a l , t e x t u r a l and chemical v a r i a t i o n s now observed w i t h i n each i n t r u s i v e u n i t . Ab/An-Qtz-Or p l o t f o r the a p l i t i c a l a s k i t e plug and estimates of th e ' t h i c k n e s s of the o v e r l y i n g v o l c a n i c s suggests t h a t the b a t h o l i t h c r y s t a l l i z e d about one t o two miles below the Oligocene-Miocene surface. Emplacement of the magmas appears t o have been c o n t r o l l e d by the n o r t h -t r e n d i n g F r a s e r R i v e r f a u l t zone and p o s s i b l y by nor t h e a s t - t r e n d i n g s t r u c t u r e s . Magmas of the C h i l l i w a c k B a t h o l i t h made room f o r themselves i n the western area mainly by shouldering a s i d e the f i s s i l e sediments of the C h i l l i w a c k Group, and i n the eastern area mainly by updoming of the Custer-Skagit Gneiss. MOUNT BARR BATHOLITH The e p i z o n a l Mount Barr B a t h o l i t h i s made up of f o u r i n t r u s i v e phases, ranging i n composition from t o n a l i t e t o quartz monzonite. The e a r l i e s t u n i t s are pyroxene-bearing t o n a l i t e s and g r a n o d i o r i t e s , found mainly along the margins of the b a t h o l i t h . A 3000 f o o t t h i c k s i l l - l i k e body composed of p o r p h y r i t i c hornblende g r a n o d i o r i t e and quartz monzonite int r u d e s the e a r l y t o n a l i t e s . The l a s t i n t r u s i v e phase of t h i s episode of magmatism i s represented by three small l e u c o c r a t i c quartz monzonite stocks. A small s i x square mile plug of f i n e - g r a i n e d mafic t o n a l i t e i n t r u d e s the c e n t r a l part of the b a t h o l i t h . \ 164. BIBLIOGRAPHY Adams, J.E. (1964) Origin of the Black Peak quartz diorite, Northern Cascades, Washington, Am Journ of Sci . , vol 262, pp 290-306. Adams, J.B. (1968) Differential solution of plagioclase in super c r i t i c a l water. The American Mineralogist, vol 53 pp l603-l6l3» Atwater, T. 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(1968) Chilliwack Group-Harrison Lake area, Br i t i s h Columbia, Geol. Surv. of Canada, paper 68-1, part A, pp 33. MacKenzie, W.S. and Smith, J.V. (1961) Experimental and geological evidence for the st a b i l i t y of a l k a l i feldspars, Institute "Lucas Mallada" C.S.I.C. (Espana), Cursillos Y Conferencia Fas VIII pp 53-69. Mathews, W. (1968) Editor: Guide book of geological f i e l d t r i p s i n southwestern British Columbia, Dept. of Geol., the Univ. of British Columbia, Vancouver, B. C , Report No. 6. Mattinson, J. M. (1970) Uranium-Lead Geochronology of the Northern Cascades, Washington (abs) Geol. Soc. of America, Cordilleran Section 66th. Annual Meeting pp 116. McTaggart, K.C. and Thompson, R.M. (1967) Geology of part of the northern Cascades in southern British Columbia, Canadian Journal of Earth Sci., Vol. 4 pp 1199-1228. McTaggart, K.C. (1970) Tectonic history of the Northern Cascade Mountains, The Geol. Assoc. of Canada, special paper No. 6 pp 137-148. Misch, P. 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(1968) Geology and geochronology of the Guichon Creek Batholith, B.C., Unpublished PhD thesis, Univ. of British Columbia, Vancouver B. C. Osborn, E.F. (1969b) The compementariness of orogenic andesites and alpine peridotite, Geochem. et cosmo. acta, Vol. 33, pp 307-324. Piwinskii, A.J. and Wyllie, P.S. (1968), Experimental studies of igneous rock serie: : A zoned pluton in the Wallowa Batholith, Oregon, Journ. of Geol. Vol. 76, pp 205-234. 168 Read, P.B. (i960) Geology of the Fraser River Valley between Hope, Emory Creek, Bri t i s h Columbia. Unpublished M.A.Sc. thesis Univ. of British Columbia, Vancouver, B.C. Richards, T. and White, W.H. (1970) K-Ar ages of plutonic rocks between Hope, British Columbia and the 49th parallel, Can. Journ. of Earth Sc., Vol. 7, No. 5, pp 1203-1207. Richardson, S.W., Gilbert, M.C. and Bell, 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. 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(1958) Origin of granite in the light of experimental studies in the system NaAlSi^0g-KAlSi20g-Si02-H20; Geol. Soc. of America, Memoir 74. Vance, J.A. (1962) Zoning in igneous plagioclase: normal and oscillatory zoning; Am. Jour, of Sc. Vol. 260 pp 746-760, Vance, J.A. (1965) Zoning in igneous plagioclase: patchy zoning: Journ. of Geol. Vol. 73, p. 636-651. Van der Plas, L. and Tobi, A.C. (1965) A chart for judging the r e l i a b i l i t y of Point Counting results. Am. Journ. of Sc. Vol. 263, p. 87-90. Wager, L.R. (1968) Rhythmic and cryptic layering in mafic and ultramafic plutons, In Basalts: The Poldervaart Treatise on Rocks of Basaltic Composition, Vol. 2, Editor Hess, H.H. and Poldervaart, A. , Interscience, pp 573-622. Waters, A.C. (1955) Volcanic rocks and the tectonic cycle; Geol. Soc. of America, special paper 62, pp 703-722. Westermann, C.J. (1970) A petrogenetic study of the Guichon Creek Batholith, B. C.; Unpublished MSc. thesis, Univ. of Brit. Columbia, Vancouver, B. C. ' White, W.H. (1966) Summary of Tectonic Events; In Tectonic History and Mineral Deposits of the Western Cordillera; The Can. Inst, of Mining and Met., special Vol. 8, pp 185-189. White, W.H., Ericson, G.P., Northcote, K.E., Dirora, G.E. and Harakal, J.E. (1967) Isotopic dating of the Guichon Batholith, B.C., Canadian Journal of Earth Science, Vol. 4, pp 677-690. Winkler, H.G.F. (1967) Petrogenesis of Metamorphic Rocks, revised second edition; Springer-Verlag, New York, Inc. Wise, S.W. (1969) Geology and petrology of the Mount Hood area, a study of High Cascade vulcanism; Geol. Soc. of America, Bull., Vol. 80, pp 969-1006. Wright, T.L. (1963) X-ray and optical study of a l k a l i feldspars II; An x-ray method for determining the composition and structural state from measurement of 26 values for three reflections; Am. Mineral. Vol. 53, pp 88-104. Yeats, R.S. and MacLaughlin, W.A. (1968) Radiometric age of three Cascade Plutons, Skykomish Area, Washington, (abs) Geol. Soc. of America, 1968 Annual Meetings pp 332. Yeat3, R.S. and Engels, J.C. (1970) Potassium-argon Ages of Tertiary Plutons in the Northern Cascades of Washington (abs) Geol. Soc. of America, 1970 Annual Meetings, pp 730. 170. Yoder, H.S. and T i l l e y , C.E. (1962) Origin of Basalt Magmas: An experimental study of natural and synthetic rock systems. Journ. of Petrology. Vol. 3, No. 3, PP 342-532. Yoder, H.S. (1969) Calc-alkaline andesites: experimental data bearing on the o r i g i n of t h e i r assumed c h a r a c t e r i s t i c s , In Proceedings of the Andesite Conference: International Upper Mantle Project, s c i e n t i f i c report No. 1 6 , pp 77-90. 171. APPENDIX 1 Determinative Methods Mineral Determinations a) Plagioclase Plagioclase compositions were determined on both the U-stage and f l a t stage using the ± to "a" and carlsbad-albite methods. Compositions i n the AnQ to A n ^ range are estimated to be reliable to An 2 while those in the A n ^ to An^ QQ range are probably reliable to An^. b) A l k a l i Feldspars Structural states and compositions of a l k a l i feldspars were determined by x-ray diffraction according to the "three peak" method outlined by Wright (i960). Structural states can be estimated from a knox^ledge of the position of the 20(060) and the 20(204) x-ray diffraction peaks plotted on a figure similar to figure 72. When 29(o6o) and 26(204) are plotted in figure 72, 20(201) may be estimated. When 29(20]) measured from the x-ray diffraction trace d i f f e r s from the 26(201) estimated from figure 72 by a 29 value greater than 0.01°, the feldspars are said to be "anomalous"(Wright 1968). He suggested that the "anomalous" character of a feldspar i s related to strains imposed on the structure of a feldspar during perthitic unmixing. A l l the feldspars studied from the plutonic rocks in the Hope area are anomalous. Standard deviations for 29 values recorded are between 0.01° and 0.02°. Compositions were obtained by measuring 26(201) for specimens heated for 72 hours at 960°C in s i l i c a glass tubes. This heating time proved adequate for homogenization of most specimens (figure 73). 29 values measured were compared to the Or vs 29(201) graph given by Wright (1968, page 93). 172 FIGURE 72 " T h r e e P-eak " structural state diagram for a l k a l i f e l d s p a r s plotting 2 0 ( 2 0 4 ) against 2 9 ( 0 6 0 ) . 2 6 ( 2 0 1 ) values are est imated from plot t ing 2 9 ( 2 0 4 ) and 2 9 ( 0 6 0 ) . ( D i a g r a m modi f ied after Wr igh t , 1 9 6 8 ) FIGURE 73 e of o spcir 21.10 ° 21.05 ,S 2I.OO<5 CD CM 20.95 2I.I0-I => 21.05 g 20.00 © 20.95-1 CVJ 20.90 Specimen 83 0 20 30 H e a t i n g Specimen 225 10 20 30 40 50 60 T i m e in H o u r s 40 50 60 ©- -70 70 80 174. c) Olivine and Pyroxene Compositions were obtained by determining n^ and 2V, and plotting the values on the appropriate determination chart given in Trogger (1959) d) Amphiboles 2V 1s and z Ac values determined on the U-stage were useful only in distinguishing pargasitic hornblende from common hornblende (Deer et a l 1969). e) Other Minerals The reported occurrence of s t i l b i t e , laumontite, prehnite, scapolite and wollastonite have been verified by x-ray diffraction. Chemical Analyses A l l chemical analyses but three (specimens Nes., Lind. and P.C. from the Chilliwack Batholith, after Daly 1912) were done by rapid analysis by the Geological Survey of Canada. Errors for analyses listed by the Geological Survey are given in table 31. TABLE 31. Accuracy of Rapid Method Chemical Analysis a) elements determined simultaneously by x-ray fluorescence spectroscopy oxide range in value one <r S i 0 2 30-75% t 1.2 A1 20 3 0-20% t 0.7 ^ t o t ^ V 0-15% ±0.5 CaO 0-40% t 0.3 MgO 0-40% t i . o K 20 0-5% i o . i T i 0 2 0-2% t 0.05 MnO 0-1% t 0.02 175. b) elements determined separate ly by chemical methods oxide. range i n value error i n the reported value FeO 0-15% + 0.2 Na 0 2 0-10% t 0.15 0-1% t 0.04 c o 2 + 0.1 + 0.1 Modal Analyses 800 to 1000 po in t s were counted f o r each specimen. Standard dev ia t ions i n . t h e modal porport ions of minerals from m u l t i p l e counts of a s ing le t h i n sect ion and from counts of s ix t h i n s e c t i o n s . o f a s ing le specimen, showed that counts were reproducable wi th in respectable l i m i t s ( table 32). The e r r o r s shown i n tab les 32 and 33 are s i m i l a r to those estimated from the curves ca l cu la ted by Van der P las and Tob\ (1965). K - A r Age Dating A n a l y t i c a l methods used to obtain K - A r ages reported i n t h i s study are s i m i l a r to those reported i n Dirom (1965), White et a l (1967) and Northcote (1968). 176. TABLE 32. Multiple Counts from one This Section JL(b) JL(c) 482(*) 48?(b) 482(c) cr plag. 25.0 29.0 29.7 2.6 54.1 52.4 53.9 0.9 Qt 3 36.7 33.3 35.4 1.7 19.4 17.7 18.5 0.8 Or 36.4 35.2 33.2 1.6 8.6 8.1 9.2 1.0 Hb - - 9.0 6.1 8.0 1.4 Bio. 2.0 2.1 1.7 0.2 9.0 10.0 9.8 0.6 Acc. - - 0.4 0.7 0.6 0.1 TABLE 33. Replicate Modal Analysis from S ix Thin Sections from One Specimen of Pyroxene Diorite (Spi BC. 1379) 1 2 1 1 6 plagioclase 57.7 56.4 55.6 64.8 61.1 56.5 quartz 10.4 8.1 12.1 8.0 10.9 11.5 hypersthene 7.6 5.9 7.4 7.0 7.3 6.8 augite 0.2 1.3 t r t r 0.5 1.2 hornblende 19.7 22.6 20.4 13.6 15.8 17.6 biotite 3.9 4.2 4.3 6.2 3.8 5.8 apatite 0.4 0.4 t r 0.3 0.2 tr magnetite 0.4 0.9 0.5 t r 0.5 0.6 mean o- Van der Plas (1000 counts) plagioclase 58.9 3.7 + 3% . quartz 10.3 1.8 + 2% hypersthene 7.0 0.6 + 2% augite 0.6 0.6 hornblende 18.3 3.1 + 3% biotite 4.4 1.1 + 1% 177. TABLE 34. Chemical Analysis from some High-Alumina Basaltic-Ahdesites and Andesites from the Diorites of the Spuzzum Intrusions and the Chilliwack Batholith. cr 2* Si0 2 58.17 4.06 55.9 55.3 55.4 53.81 A 12°3 17.26 1.55 19.4 17.4 19.5 17.79 Fe 20 3 3.07 1.38 0.4 2.4 1.2 2.44 FeO 4.18 1.62 7.2 6.1 5.4 6.60 MgO 3.24 1.24 4.4 5.2 5.1 5.87 CaO 6.93 1.63 7.8 7.5 7.6 8.79 Na20 3.21 0.72 3.3 :•: 3.3 3.9 2.76 K20 1.61 ; 0.75 0.8 0.7 0.5 0.62 Ti0 2 0.8 0.35 0.8 x«3 0.85 0.95 P2O5 0.21 0.15 - 0.37 0.17 0.19 1. Cenozoic andesites; mean values and standard deviations (Chayes 1969) 2. Calculated composition of liquid fractionates derived from partial melting of a high-alumina quartz tholeiite at 9 Kb under wet conditions (Green and Ringwood 1969). 3. Chemical analysis of the eastern Diorite, Chilliwack Batholith. 4. Average composition of the Spuzzum Diorite. 5. Basalt-andesite, Izu-Hakone region, Japan, Kuno (1968). 178. FIGURE 74 Topography of the Area Underlain by Figure I F I G U R E Geology of the Plutonic Rocks between Hope, British Columbia, and the 49th Parallel — 49° 15' - - I L E G E N D ' N O N - P L U T O N I C R O C K S I Oligocene Skagi t -Hannegan Volcanics Eocene Conglomerates Hozameen Group (Upper Poieozoic) Chi l l iwack Group (Upper Paleozoic) Cus te r -Skag i t Gneiss (Juross-c or eon.er) Ultramaf ites I2lo |30' I2H5' Faults —•-• Foliation in the plutonic rocks —•- Foliation In the non-plutonic rocks (2)(6)35 K-Ar age determination (table 2) £ ) l 8 K-Ar age determination (Boodsgaard et al I960 Roods ———~ Railways Contact Known Contact Suggested Contact Inferred 49*15' — N ^ . i -Geology between Crescent Lake and Mount Wetikwo, ond eott of Yolo Creeki oftor McTaggart ond Thompson (1967) 4 Middle - CANADA _ UNITED" STATES Peak-Scale of 121*115' Miles I2l*il5' 

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