Geology and Tectonics of the Nootka Island Region, British Columbia

GEOLOGY AND TECTONICS OF THE NOOTKA ISLAND REGION, BRITISH COLUMBIA

Scott Close BSc., Montana State University, 2004

THESIS SUBMI-TTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

In the Department of Earth Sciences

@ Scott Close 2006

SIMON FRASER UNIVERSITY

Fall 2006

All rights reserved. This work may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. APPROVAL

Name: Scott Close

Degree: Master of Science

Title of Thesis: Geology and Tectonics of the Nootka Island Region, British Columbia

Examining Committee: Chair: Dr. Andrew Calvert Professor, Department of Earth Sciences

Dr. D. D. Marshall Senior Supervisor Associate Professor, Department of Earth Sciences

Dr. D. J. Thorkelson Supervisor Professor, Department of Earth Sciences

Dr. John M. Moore External Examiner Adjunct Professor, SFU

Date DefendedIApproved: July 28.2006 SIMON FRASER &&tP UN~VERS~TY~ibrary

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Simon Fraser University Library Burnaby, BC, Canada ABSTRACT

Nootka Island represents a portion of an accreted volcanoplutonic arc, on the western coast of Vancouver Island, British Columbia, of the Canadian Cordillera lnsular Belt . This work provides a 1: 110,000 scale geologic map and synthesises the regional tectonics.

Two main protolith groups are evident on Nootka Island. Group Icontains tholeiitic basalts that have within-plate 1 E-MORB element signatures. Limestones and siltstones comprise the intervening sedimentary strata. Group 2 comprises the youngest and consists of calc-alkaline, arc-like basalts, a plutonic suite, and minor hypabyssal bodies. Groups 1 and 2 resemble the Triassic Karmutsen and Jurassic Bonanza Formations.

Plagioclase-hornblende thermometry and aluminium-in-hornblende barometry indicate metamorphism at up to 710' Celsius and 3.2 kbar of early Jurassic and older rocks. Whole rock argon dating of a basalt dyke post-deformation reveals crystallization ages of 168 Ma, and metamorphism at 158 Ma from an older Group 1 hyaloclastite.

Key Words: Nootka Island, Westcoast Crystalline Complex, Wrangellia, Accretion, lnsular Belt ACKNOWLEDGEMENTS

I thank my senior advisor, Dan Marshall, and committee member Derek Thorkelson for providing the opportunity to work in this area. They graciously permitted my endless questions and pursuance of answers. Working alongside them is akin to a living microscope of geochemical advice and insight. John Moore offered sound advice on how to communicate this research. Nick Massey and JoAnne Nelson, who journeyed with me into the field and mind for a foray of exploration, also provided generous support. Randy Enkin, of the Pacific Geoscience Center, taunted me with external academic interests, and Peter Mustard provided support, friendship, and educational advice.

Magdelena Lesiczka persisted with me onto the high passes, through alder thickets, and on an epic adventure on a mountainside in darkness. Tanner Liskop gave assistance during the second field season while circumnavigating Nootka Island by sea kayak. Ken Knadle, Adolf Aichmeier, Glenn McCall and Mike Taylor provided transport tolfrom and during our stay on Nootka Island. Friends at the Yuquot Native Reserve presented us with history, fictional stories, bread, and warmth while camping adjacent to the high tide and thunderstorm on their beach.

My parents never suggested that life was anything but whatever I wanted it to be, therefore instilling the self-motivation to manifest my dreams. My partner, Katherine Whitney, stood alongside me through the easy times and stood up for me when they were not. I lastly thank Danner, my dog, for his never-ending faith.

Funding for this research was provided by NSERC and Geoscience BC. DEDICATION

" Chi va fiano, va Sano; Chi va Sano, va Lontam. . . "

. . .go sGowGy andyou go welt

go we[( andyou gofar" TABLE OF CONTENTS

Approval ...... ii ... Abstract ...... 111 Acknowledgements ...... iv Dedication ...... v Table of Contents ...... vi ... List of Figures ...... VIII List of Tables ...... ix List of Abbreviations ...... x Chapter 1: Introduction ...... 1 Chapter 2: Geologic Setting ...... 3 2.1 Wrangellia ...... -5 2.1.1 Sicker Group; Devonian ...... 6 2.1.2 Buttle Lake Group; Carboniferous-Permian...... -7 2.1.3 Vancouver Group; Triassic ...... 8 2.1.4 Bonanza GroupJTalkeetna Volcanics; Jurassic ...... 9 2.1.5 Westcoast Crystalline Complex; Jurassic...... 10 2.1.6 Carmanah Group; Eocene-Oligocene...... 11 Chapter 3: Nootka Island ...... 12 3.1 Geology ...... 12 3.2 Unit Definitions and Nomenclature ...... 12 3.3 Volcanic Rocks ...... 13 3.3.1 Group 1 (new). Tglv ...... 13 3.3.2 Amygdaloidal Flows...... 16 3.3.3 Group 2 (new), Jg2v ...... 16 3.3.4 Group 2b (new), Jg2bv ...... 18 3.4 Sedimentary Rocks ...... 19 3.4.1 Crawfish group (new). TCI ...... 20 3.4.2 Ewart group (new), TEssj-TEbp ...... 22 3.4.3 Carmanah Group- Eocene to Oligocene. ECe/OCh/OCs ...... 25 3.5 Plutonic Rocks ...... 28 3.6 Hypabyssal Rocks ...... 33 Chapter 4: Geochemistry ...... 35 4.1 Major Element Oxides ...... 35 4.2 Trace Elements ...... 40 4.3 Group 2 Intrusion Suite Modelling ...... 43 4.4 Isotope Geochemistry ...... 45 4.4.1 6180/ 613c Carbonate Discrimination ...... 45 4.4.2 40~r/39~rThermochronology ...... 46 Chapter 5: Metamorphism ...... 48 5.1 MI: Seafloor-Hydrothermal Metamorphism ...... 50 5.2 M2: Regional Metamorphism. Greenstone Amphibolite ...... 50 5.3 M2: Contact Metamorphism. Hornfels/Amphibolite ...... 52 5.4 Geothermobarometery ...... 53 5.4.1 Hornblende Barometry ...... 55 5.4.2 Plagioclase-HornblendeThermometry ...... 59 5.4.3 Results ...... 60 Chapter 6: Structure...... 62 6.1 Dl- Northeast Directed. Dextral Compression ...... 65 6.2 D2- Northwest Directed Compression...... 66 6.3 D3- South/Southeast Extension. Dextral ...... 66 6.4 D4- North-South Dextral. Transverse Shears ...... 69 6.5 D5- Regional Uplift and Tilting ...... 69 6.6 Other ...... 69 Chapter 7: Tectonic Synthesis And Discussion ...... 70 7.1 Comparison of Nootka and Regional Wrangellia Stratigraphy ...... 70 7.2 Triassic: 230-200 Ma ...... 76 7.3 Jurassic: 200-168 Ma ...... 76 7.4 Jurassic: 168 Ma to Eocene ...... 77 7.5 Eocene-Oligocene ...... 78 Conclusions ...... 79 Reference List ...... -81 Appendices ...... -85 Appendix A- Nootka Island Rock Catalog ...... 86 Appendix B- Major and Trace Element Data ...... 88 Appendix C- whole-~ock40~r/39~r Data ...... 92 Appendix D- Maps ...... 95

vii LIST OF FIGURES

Figure 2.1: Simplified regional map showing the locations of the Wrangellia Terrane ...... 4

Figure 3.1: Photomicrographs of selected Nootka volcanic rocks ...... 15

Figure 3.2: Outcrop showing numerous flows (to 20 cm) of amgydaloidal basalts from Group 2b ...... 19

Figure 3.3: Photomicrographs of selected Nootka Island metasedimentary rocks ...... 21

Figure 3.4: Escalante conglomerate, Carmanah Group ...... 25

Figure 3.5: Gently southwest dipping. broadly folded siltstones with lenticular sandstones on Beano Beach. Hesquiat Formation. Carmanah Group ...... 27

Figure 3.6: Photomicrographs and photographs of selected Nootka intrusions...... 32

Figure 3.7: An example of crosscutting relationships among three intrusive lithologies ...... 34

Figure 4.1: Total alkalis versus silica for the Nootka Island. non- sedimentary lithotypes (LeBas. 1986) ...... 36

Figure 4.2: AFM diagram for Nootka rocks ...... 37

Figure 4.3: MnO.TiO2.P2O5. major-element tectonic discrimination diagram (Mullen. 1985) ...... 37

Figure 4.4: Fenner diagrams for Nootka Island rocks ...... 39

Figure 4.5: MORB-normalized trace element plot displaying the major non- sedimentary lithotypes on Nootka Island ...... 41

Figure 4.6: La/Nb trace element ratio plot for Wrangellia volcanics ...... 42

Figure 4.7: La/Nb trace element ratio plot for Nootka Island samples...... 42

Figure 4.8: La vs . Nb plot of the Group 2 granite. intermediate. and hornblende gabbro series intrusions...... 44

viii Figure 4.9: ZrjCe vs . LajNb plot of the Group 2 granite. intermediate. and hornblende gabbro series intrusions...... 44

Figure 4.10: 6"0/ 613c isotope discrimination plot ...... 45

Figure 4.11: 40Arj30Ar. whole-rock plateau ages for three aphyric basalts from Nootka Island ...... 47

Figure 5.1: Map of relative metamorphic grades on Nootka Island ...... 49

Figure 5.2. Xenoliths in a tonalite from station SC04052 ...... 51

Figure 5.3: Hornblende barometry for Nootka Island ...... 57

Figure 5.4: Magmatic epidote. sample SC04072 ...... 58

Figure 5.5: Magmatic epidote phase diagram for a tonalite ...... 59

Figure 5.6: Geothermobarometry and PT diagram for select Nootka Island samples ...... 61

Figure 6.1: Equal-area stereonet plots...... 63

Figure 6.2: Block diagram showing the deformation of Nootka Island rocks ...... 64

Figure 6.3: Dynamic amphibolites ...... 65

Figure 6.4: Northwestern extent of the Nuchatl shear ...... 67 Figure 6.5. Late stage hydrothermal fluids ...... 68

Figure 7.1: Timeline of the Nootka Island tectonics...... 72

Figure 7.2: Tectonic synthesis of the formation of Nootka Island. Devonian to late Triassic period...... 73

Figure 7.3: Tectonic synthesis. early to mid Jurassic period...... 74

Figure 7.4: Tectonic synthesis. mid Jurassic period to Oligocene epoch ...... 75

LIST OF TABLES

Table 5.1. Calculated Ca-rich amphibole formulae and resulting thermobarometry ...... 54 LIST OF ABBREVIATIONS

Mineral Abbreviations (Kretz, 1983): Bt Biotite Cal Calcite Chl Chlorite Ale3 Augite Czo Chnozoisite EP Epidote Grs Grossular Garnet Hbl Hornblende 0r Orthoclase Feldspar Mag Magnetite Pl Plagioclase PY Pyrite Qtz Quartz Wo Wollastonite Zo Zoisite

Other Abbreviations: CPC Coast Plutonic Complex WCC Westcoast Crystalline Complex OIT Ocean lsland Tholeiite MORB Mid-Ocean Ridge Basalt N-MORB Normal Mid-Ocean Ridge Basalt E-MORB Evolved Mid-Ocean Ridge Basalt OlAB Ocean lsland Arc Tholeiite IAT lsland Arc Tholeiite CAB Calc-alkaline Basalt OCA OceanicIContinental Andesi tes Fe* Total Fe Content f -02 Oxygen Fugacity CHAPTER 1 : INTRODUCTION

This thesis investigates the geology and tectonics of the Nootka lsland region. Nootka lsland lies on the western seaboard of Vancouver lsland on the continental shelf with a convergent plate boundary to its west. It is considered a metamorphosed portion of Wrangellia, an exotic terrane that formed part of the Insular belt after accreting to the North American continent during the Jurassic (Figure 2.1).

Provided with this work is a 1:110,000 scale detailed geologic map of the region with a stratigraphic column and schematic cross section (Appendix D; a fold-out located as the last page of this document),block diagram showing different episodes of deformation, and tectonic models (Figure 6.2 and Figure 7.1 -Figure 7.4). Field reconnaissance consisted of two two-week periods during the summers of 2004 and 2005. Accessibility is by a skeletal system of logging roads and around the island by seacraft. A large portion of the island contains dense vegetation, steep slopes, and is generally impenetrable.

The Nootka lsland area lies within the central area of the 1:50,000 Topographic Mapsheet 92E, Surveys and Mapping Branch, of the Department of Energy and Mines Resources. Supplementing data are a shaded digital elevation model (DEM and aeromagnetics map (Appendix D) provided by the BC MapPlace website developed for public use by the Government of British Columbia Ministry of Energy, Mines, and Petroleum Recources, using data sourced from Warner Miles, Government of Canada, Natural Resources Canada, Geological Survey of Canada-Ottawa, and Bruce Mackenzie, Geosense Consulting-Nelson, British Columbia.

The primary focus of this project is to examine the stratigraphy, structure, petrochemistry, and metamorphism of the Nootka lsland portion of the Westcoast Crystalline Complex (WCC). In addition to geological field studies, geochemical analyses and petrographic studies were conducted on most lithotypes. Three basalts were selected for 40~r/39~rdating and a carbonate was selected for 13~/180analysis. A secondary motive was to compare the rocks for similarities with adjacent Wrangellian material and place the genesis of Nootka Island into a regional context. Consequently, surveys in the Nootka Island region support the refinement of the WCC terminology to reflect protolith stratigraphy. This approach allows a qualitative comparison to regional Wrangellia rocks and a more comprehensive understanding of the structure and timing in the district. CHAPTER 2: GEOLOGIC SETTING

The northwestern margin of North America was formed in a complex history of magmatism, sedimentation, metamorphism and deformation. Comprising the outermost portion of the area are three exotic terranes. The Wrangellia terrane (Figure 2.1) lies on the eastern-most side of the belt, thrust westward over the Pacific Rim and Crescent terranes (Monger and Price, 2002). Wrangellia is the best exposed and exists within an accreted package that forms a bridge between the Juan de Fuca and Explorer Plates subducting on the west, and the Coast Plutonic Complex to the east.

Wrangellia strata, to which those of Nootka Island are to be compared, comprises strata from three major volcanic episodes in the Devonian, Triassic, and Jurassicin addition to a Pennsylvanian amalgamation with the smaller Alexander terrane (Gardner et at., 1988). The major volcanic episodes are separated by inter-episodic volcaniclastic and marine sedimentation. The oldest, the ocean-island arc (Sicker Group) formed on existing oceanic crust followed by marine sedimentation of limestone and calc-arenites of the Buttle Lake Group. Later, Karmutsen volcanics of the Vancouver Group erupted over the Sicker and Buttle Lake Groups as a homogeneous and voluminous succession of basalts followed by deposition of limestone and other sediments that form the remaining Vancouver Group stratigraphy- the Quatsino and Parson Bay Formations. Shortly before accretion, the third and last episode of arc activity formed the Talkeetna and Bonanza Group volcanic rocks with the Jurassic lsland Intrusions forming the roots of the system during the early-mid Jurassic.

During the Cretaceous, pericratonic sediments of the Nanaimo Group were deposited between Wrangellia and the Coast Plutonic Complex to the east. Eocene magmatism resulted in the Flores volcanics and associated Clayoquot intrusions (Massey, 1995; Madsen et al., 2006). Ocean-margin sedimentary rocks of the Carmanah Group were layed unconformably on the western flank of Wrangellia during the Eocene-Oligocene. Contact and regional metamorphism of the Wrangellian assemblage produced greenstones, greenschists, hornfelses, and amphibolites, revealed in strata that once folded into depth and now lie exhumed at the surface in various locations along the western coastline of Vancouver Island- called the Wescoast Crystalline Complex (WCC) (Muller et al., 1981). Abundant north- and northwest-directed faults and fault zones also dissect Wrangellia resulting from its convergence with North America and later underthrusting of younger material. The accretion of the Pacific Rim and Crescent terranes, unconsolidated melanges and ophiolites that were thrust under Wrangellia demonstrate the westward relocation of the active convergent margin after docking of the Wrangellia terrane to the continental margin of North America. (Clowes et at., 1987).

Figure 2.1: Simplified regional map showing the locations of the Wrangellia Terrane. Not shown on this map but also located within the Insular Belt are the Pacific, Crescent, and Alexander Terranes. This map compiles interpretations from Clift et al. (2005), DeBari et al. (1999), Yorath et al., (1999), and from Monger and Price (2002). The geologic setting described herein concentrates on previous studies most relevant to the Nootka lsland map area. Investigation of Wrangellian rocks began with Clapp (1912) on southern Vancouver Island. A regional study commenced during a Geological Survey of Canada mapping project of Vancouver lsland conducted primarily by Muller (1977) and a 1:250,000 mineral-potential and mapping survey of the Nootka Sound region area by Muller, Cameron, and Northcote (1981). Other studies contributing a significant portion of information to this study are works on the Karmutsen basalts by Barker et al. (1989) and more southerly on Vancouver lsland by Massey (1995); of the Bonanza-Jurassic arc genesis (DeBari et al., 1999); and of the northerly Talkeetna Formation by Clift et al. (2005a, b). Seismic images transecting Vancouver lsland produced during the LITHOPROBE project exposed prominent markers and horizons in the crust below Vancouver Island, and provided a detailed geologic map surrounding the Alberni area (Yorath et al., 1985, Clowes et al., 1987; Yorath et al., 1999).

2.1 Wrangellia

Composing Wrangellia are three successions of sub-aqueous and subaerial volcanics that accreted to an overriding plate and were unconformably capped with Cretaceous and Tertiary calcareous and terrigeneous sediments (Isachsen 1987). The extent of Wrangellia along the northwestern coast of North America is shown in Figure 2.1. The oldest recognized volcanics, the Sicker Group, display island-arc signatures, are Devonian in age (Massey, 1995)) and are primarily andesitic to dacitic volcanic and volcaniclastic rocks (Muller, 1977). Deposited above these basalts are Carboniferous and Permian limestones and sediments of the Saint Mary, Fourth Lake, and Mount Mark Formations in the Buttle Lake Group. Karmutsen volcanic rocks of tholleiitic pillows and flood basalts to basaltic-andesites were deposited on top of the Buttle Lake Group. The Karmutsen is the lowest unit of the overlying late-Triassic Vancouver Group, situated below the Quatsino, Parson Bay, and Sutton Formations (Barker et al., 1989).

Arc-like volcanism of Jurassic Talkeetna and Bonanza Groups yielded sub-alkaline and calc-alkaline, basalt-basaltic andesite extrusive flows and a more felsic areal component (Clift, 2005a-b; Muller et at., 1981). Contemporaneous gabbros-tonalites- granites of the Jurassic lsland Intrusive Suite intruded mid-upper crustal Sicker, Karmutsen, and lower-most Bonanza Groups, are considered the co-magmatic source for the extrusive Bonanza counterparts (DeBari et al., 1999). Development of the Westcoast Crystalline Complex (WCC) was postulated during the emplacement of the Jurassic lsland Intrusive Suite, an irregular belt of heterogeneous amphibolite and greenschist assemblages, extending along the west coast of Vancouver lsland (Muller et al., 1981). Field relationships and geochemistry suggest that the Jurassic lsland Intrusions metamorphosed the surrounding hosts and formed a suite of contact meta- sediment and contact meta-volcanic products; thus, the WCC was regarded as roots to the extrusive component of the Jurassic arc by lsachsen (1987) and DeBari et al. (1999). Mesoscopic details of the WCC, however, remain largely unstudied.

Sedimentary rocks of the Cretaceous-age Nanaimo Group unconformably overlie the entire section, visible along the eastern edges of Vancouver lsland (Mustard et al., 1995). The youngest rocks in the region are the Tertiary Flores volcanics, co- magmatic Catface intrusions, and locally derived Eocene and Oligocene Carmanah sediments. The Catface intrusions further divide into the older 60-45 Ma Clayoquot and 47-38 Ma Mt. Washington suites (Massey, 1995). Bodies of these intrusions were not found in the study area. Conglomerate, siltstone, and sandstone beds of the Carmanah Group lie parallel to the NW-SE trend of Vancouver lsland across the western-most portion of the study area and are gently westward-dipping (Cameron, 1980).

General north-westward movement of Wrangellia is apparent from paleomagnetics and biogeography. Permian Rugose coral biogeography places Wrangellia 5000 * 1000 km off the west of the North American craton, near 300' E longitude (Belasky and Runnegar, 1994). Cretaceous-age paleomagnetics indicate the northern portion of Wrangellia rotated 15' CCW, was at moderate paleolatitudes with the coast of British Columbia (Stamatakos et al., 2001), and travelled together no more than 2000 km northward to its present day state (Mustard et al., 1995, Enkin et al., 2001).

2.1.1 Sicker Group; Devonian

The nomenclature for strata within the Sicker Group has vaned through time, but recently has settled to reflect more regional sections and acceptance among researchers. The Sicker Group refers to the products of a calk-alkaline arc above oceanic crust in the Devonian. The Duck Lake Formation comprises pillowed and massive basaltic flows (Massey, 1991) and is the lowest strata within the group. Overlying these flows is the Nitinat Formation of augite-phyric agglomerates, tuffs, tuff-breccias, pillowed flows and discontinuous inter-beds of sandstone and minor volcaniclastic rocks. A complete section for the Nitinat Formation has yet to be re- constructed. Lastly, volcaniclastic rocks of the McLaughlin Ridge Formation (Yorath et al., 1999) conformably overlie all prior strata and likely represent interfingering of local volcanic sources. Variations within the McLaughlin Ridge Formation include pebbly grit, sandstones, cherty siltstones, and argillites.

The formations in the Sicker Group are laterally variable. Exposures are largely contained within the Cowichan Anticlinorium on Vancouver lsland and may or may not be correlative with the substrate forming the Westcoast Crystalline Complex located distally westward (DeBari et al., 1999). Rocks of this group formed the basement for the overlying carbonate sediments of the Permian Buttle Lake Group.

2.1.2 Buttle Lake Group; Carboniferous-Permian

Carbonates and clastics of late Paleozoic age, termed the Buttle Lake Group, are visible on Vancouver lsland in small southerly outcrops and as displaced slivers in various locations along the western portion of Vancouver Island. From the lowermost stratigraphical unit upward are the Fourth Lake, Mount Mark, and Saint Mary Lake Formations recently named by Yorath et al. (1999). The Fourth Lake formation conformably overlies Sicker Group rocks and contains small beds of siliceous argilUtes, minor grey limestone, chert, and green sandstones. The sandstones are petrochemically similar to the rocks of the underlying McLaughlin Ridge Formation. Capping these are massive, bioclastic, well-bedded limestones of the Mount Mark Formation. The Mount Mark Formation forms a substantial body that is internally consistent and up to 300 meters thick. The Saint Mary Lake Formation that represents the top of the Buttle Lake strata was previously considered the thinnest unit (Yorath et al., 1999) but may vary to greater thicknesses at other locations on Vancouver Island (Marshall et al., 2005). The primary components of this formation are, like the Fourth Lake, thin-small rythmic beds of sandstone and shale. 2.1.3 Vancouver Group; Triassic

The late Triassic Karmutsen volcanic rocks, Quatsino limestones, and Parson Bay and Sutton sediments of the Vancouver Group were deposited over the existing Wrangellian substrate. The Karmutsen Formation is laterally equivalent with the Nikolai Greenstone in the northern extent of WrangelIia (Yorath et a[., 1999). It includes a massive pile (up to 6000 meters thick) of pillow basalts and flows. The Karmutsen volcanic rocks demonstrate remarkable chemical and petrographic homogeneity (Barker et al., 1989). Individual flows characterize the whole, have a uniform tholeiitic signature, and frequently contain glomerophenocrysts of plagioclase. Because of their voluminous nature, E-Morb, and plume-like chemistry, one modern analogue for Karmutsen volcanism may be the Ontong-Java oceanic plateau (Sun et al., 1979; Yorath et al., 1999).

Toward the end of Triassic volcanism, minor limestones and volcaniclastic rocks became intercalated with the Karmutsen. The oldest of the intercalations is the Quatsino Formation of weakly bedded, fossiliferous limestone that grades upward into flaggy limestone. This unit varies in thickness but extends to 300 meters in the type area of Quatsino Sound. The next formation in sequence is the Parson Bay Formation and may reflect a change from turbulent shelf carbonate deposition to a deeper water environment (Carlisle and Susuki, 1974). Within the Parson Bay Formation, lower argillites, greenish arenites, and thin limestones grade upward to arenites. The youngest of the Vancouver Group sedimentary rocks are flaggy limestones and fine- grained clastic sediments that lie within the Sutton Formation. The Sutton Formation may be time equivalent to the Parson Bay Formation (Yorath et al., 1999). 2.1.4 Bonanza Group/Talkeetna Volcanics; Jurassic

All of the units deposited during the Jurassic in the southern portion of Wrangellia are currently assigned to the Bonanza Group and represent an emerging calc-alkaline to sub-alkaline arc. The Talkeetna arc in the northern portion of Wrangellia is also calc- alkaline and of Jurassic age. Minor differences exist in the geochemistry and stratigraphy of the two arcs but both overly older Wrangellian strata and together represent the final volcanism during Wrangellia's existence as an exotic terrane (Clift et al., 2005b).

The Bonanza Group is an incompletely-defined package of mostly emergent, effusive volcanic rocks and minor discontinuous beds of volcaniclastic and other sedimentary rocks (DeBari et al., 1999). The volcanics range from basalt to rhyolite and are frequently plagiophyric. Subdivisions within the Bonanza Group correlate poorly among exposures due to the high degree of lateral heterogeneity. The most common facies appearing throughout the Bonanza arc is the Klanawa Creek Facies that extends to 2000 meters in thickness and grades from basal basalt flows and tuffs to dacite and rhyolite (Yorath et al., 1999).

The Talkeetna Volcanics are similar to the Bonanza but present more exposures of amygdaloidal and pillowed flows, carry frequent intercalations of volcaniclastic strata, and contain lesser amounts of rhyolites and dacites (Clift et al., 2005b). The whole of Talkeetna strata are heterogeneous and type sections are, as in many volcanic arcs, only locally applicable.

2.1.4.1 Island Intrusions; Jurassic

The Jurassic Island Intrusions are a suite of mafic to intermediate plutonic rocks on Vancouver lsland that share similar geochemistry with and are the likely parent magmas to the Bonanza volcanics (DeBari et al., 1999). Pulses of plutonism were initially mafic, subsequently generating intermediate melts of diorite to granodiorite composition. DeBari et al. (1999) recognized two main pulses of Jurassic plutonism on Vancouver Island: the first one yielding some of the WCC rocks south of Nootka lsland and diorites and other mafic intrusions at 190 Ma; the second resulting in more intermediate and felsic intrusions between 170 and 165 Ma. These intrusions are usually course-grained and are evident throughout the entire section of Pre-Cretaceous Wrangellia on Nootka Island. Phenocrysts include biotite, hornblende, quartz, plagioclase, and orthoclase. Exposures of the intrusions weather greyish white.

2.1.5 Westcoast Crystalline Complex; Jurassic

The Westcoast Crystalline Complex (WCC; Muller et al., 1981) is an assemblage of metamorphosed rocks that trend parallel to the west coast of Vancouver lsland and include Nootka Island. Metamorphic grades span greenschist, hornblende hornfels, and lower amphibolite. WCC rocks poorly correlate within the complex. Muller et al. (1981 ) attributed subsequent Jurassic plutonism to concomitant granitization as a by- product of the WCC, induced by regional metamorphism.

This study shows that Jurassic plutonism existed prior to, during, and after regional metamorphism, the latter being probably synonymous with accretion and generating what is exposed on Nootka lsland and the Westcoast Crystalline Complex. This study also provides evidence that on Nootka lsland the WCC includes Bonanza and Karmutsen strata, in addition to Sicker Group (Isachsen, 1987; DeBari et al., 1999).

Problems with WCC characterization include its geochemical similarities to many Wrangellia rocks: WCC protoliths include volcanics from the Talkeetna and Bonanza Groups, mafic-intermediate members of the Jurassic lsland Intrusions, the Nitinat Formation of the Sicker Group, and the Wark-Colquitz gneiss. DeBari et al. (1999) showed that the WCC is similar in age and chemistry to rocks from the Bonanzallsland Intrusions that formed the Jurassic volcanoplutonic arc. 2.1.6 Carmanah Group; Eocene-Oligocene

The Carmanah Group is an assemblage of three sedimentary formations: the Escalante, Hesquiat, and Sooke. These were deposited during the Eocene and Oligocene epochs. The Carmanah sedimentary rocks exist as continuous small exposures along the western coast of Vancouver Island. Rock types comprise conglomerates, then siltstones and sandstones topped by conglomerates, derived from the underlying Wrangellian strata. The Carmanah Group is exposed on Nootka Island and is described further in Chapter 3. CHAPTER 3: NOOTKA ISLAND

3.1 Geology

Nootka lsland represents a small portion of the WCC in southern Wrangellia, as one of the islands along the western coastline of Vancouver lsland in British Columbia (Appendix D). The geology of Nootka lsland includes a widespread igneous suite that intrudes massive beds of fine-grained volcanic rocks with inter-bedded successions of carbonate and siliciclastic rocks. Volcaniclastic and sedimentary sequences are laterally discontinuous or variable. Most rocks have been subjected to greenschist- grade pressures and temperatures. Largely, the strata, intrusions, and metamorphism are of Jurassic age and overlap the apex of orogenic-scale compression. Following deformation, late-stage basalt dykes and extension further disrupted the strata.

Current geography of the island reflects past glacial activity and mass wasting. Outcrops are visible along coastlines and inland, where active logging has removed vegetation to expose the earth. Recent landslides and mass wasting surfaces also expose the surficial geology. Outcrops are rarely larger than 5.0 square meters, and weather dark maroon-brown, brown-yellow, and/or white. Hand specimens typically exhibit alteration, recrystallization, metasomatism, or shearing. Where protolith identification is possible, the lack of a complete section limits correlation among different exposures to structural and geochemical association.

3.2 Unit Definitions and Nomenclature

This work uses new nomenclature for the Nootka lsland rocks (protoliths) and intrusions. Lithotype descriptions of rocks from Nootka lsland denote first-order variations (volcanic, sedimentary, plutonic) that are further divided according to individual units or facies and by geochemistry (Chapter 4). Samples from the various lithologies are numbered according to their station number (Appendix A), were selected for purity, removed of their weathered surfaces, thin sectioned, and submitted for geochemical analysis (Appendix B). The volcanic and plutonic rocks on Nootka lsland are divided into three primary groups. Sample numbers that relate to each group are represented in the appendices and throughout the text. Supporting data for these group headings are developed. Group 1 includes the oldest package of volcanic rocks and is probably Triassic in age. These are basaltic rocks and are correlated with the Karmutsen Formation. Group 2 includes the younger (Jurassic) basalts and their associated plutonic equivalents, possibly correlative with the Bonanza Group volcanics and their associated Jurassic lsland Intrusions. Group 2b is a stratigraphihc subset of Group 2 that was discovered after the primary divisions were established. It includes an anorthosite and thin flows of basalts that lie at and intercalated within the contact between volcanic Groups 1 and 2.

3.3 Volcanic Rocks

The volcanic rocks of Nootka lsland are herein divided into three lithotypes. Group 1 contains hyaloclastites with rare amygdules and metamorphosed calcareous xenoliths. Group 2 includes a pillowed flow, amygdaloidal basalts, plagiophyric basalt and basaltic andesites, ash-fall and lapilli tuffs. Group 2b, an amygdaloidal subset of Group 2, appears at boundary between Groups 1 and 2 and is further distinguished using trace element geochemistry (Chapter 4).

3.3.1 Group I (new), Tglv

The Group 1 lithotype contains hyaloclastites, with rare horizons containing incorporated exotic material now visible as oblong clasts of chlorite and epidote up to 5.0 cm long. Rare horizons contain small percentages of zeolite, quartz, calcite, and/or plagioclase-filled amygdules. All varieties are green in outcrop, have undergone extensive regional metamorphism with significant chlorite replacement and weather various browns, greens, and white. 3.3.1.1 Hyaloclastite

The Group 1 basalts are characterized by curvilinear glass shards suspended in monomict breccia that is common in environments when an extruded basalt autobrecciates upon contact with a body of water (McPhie et al., 1993). This shard- rich unit is laterally extensive and lacks rotated blocks and an adjacent coherent component. Therefore, this unit and others within the Nootka Island region that contain similar textures are interpreted as hyaloclastites that erupted into a body of water instead of brecciating at the forefront of a flow that began subaerially.

All hyaloclastites are from the center of Nootka Island, 50-120 metres northeast of Crawfish Lake (Appendix D). These rocks are aphyric, hackly, greenish to dark-gray basalts with infrequent, medium-grained pyrite and plagioclase (Figure 3.1A). Best displayed by sample SC04022, petrographic microscopy reveals a fine-grained breccia comprising lithic clasts of glass and plagioclase suspended in a clast-supported groundmass. Lithic clasts range from rounded to angular. Small (<0.2 mm) grains of hornblende, plagioclase, and chlorite comprise the glass. All minerals were overprinted by secondary chlorite and calcite and calcic plagioclase amygdules were overprinted by prehnite, pumpellyite, and epidote. Palagonitic alteration of glass fragments is common. Rare 0.5 mm oblong lithics comprise fine quartz grains and secondary chlorite blades. Rare clots of brown material may have been organic matter incorporated into the flow. Figure 3.1: Photomicrographs of selected Nootka volcanic rocks. Photos are in approximate stratigraphic order from top-bottom, A-B-C-D-F-E. (A) Greenstone Group 1 hyaloclastite (SC04022). Brown stain in top left is a palagonite clay. (B) Amygdaloidal Group 2b basalt, later chloritized (5~04064). (C) Group 2b basalt with sericitized plagioclase and aligned hornblendes, amphibolite facies, retrograde chlorite. (D) Amphibolite-facies, plagiophyric Group 2 basalt. Plagioclase grains are highly sericitized and hornblendes are granoblastic. (E) Lapilli tuff, Group 2. Chlorite is syntaxial with calcite. (F) Possible pillow breccia: skeletal plagioclase laths, groundmass, and chlorite stains (black) suspend plagioclase and augite phenocrysts. 3.3.2 Amygdaloidal Flows

Station(s): SC04013, SC04064

Two amygdaloidal samples present within Group 1 were discovered at the top of the Group 1 stratigraphy. One sample was thin-sectioned (Figure 3.16). In hand sample, these display a similar appearance to the hyaloclastites of this group. These rocks contain chlorite and glass, and, include rounded amygdules of a prehnite, epidote, and pumpellyite.

3.3.3 Group 2 (new), Jg2v

The Group 2 lithotype contains a varied sequence of amygdaloidal flows, plagiophyric basalts, lapilli tuffs, and other minor basalts of unknown nature as enclaves or variously affected by local intrusions. Group 2 rocks, like those of Group 1, are also greenschists but exhibit less green coloration in outcrop and a lower degree of chloritization and sericitization of plagioclase. Group 2 outcrops weather black, brown, maroon, rarely green, and with or without white specks from the amygdules and plagioclase phenocrysts.

3.3.3.1 Plagiophyric Basalt

Station(s): SC05085, SC05088

Appearing in numerous small locations around Nootka Island, plagiophyric basalt is the most abundant style of all exposed basalts. Flow thickness is a minimum of 30 cm and the widest continuous section is 5.0 m. Typically visible as a porphyritic black basalt that weathers black and minor green, the most striking characteristic is its (up to 15%) concentration of

In thin sections, the plagioclase is bimodal in size (.05 mm and 3.0 mm) and commonly sericitized (Figure 3.1 D). Finely-crystalline plagioclase laths form 50% of the surrounding groundmass with 30% hornblende, 10%chlorite, 5% biotite, 3% quartz, 1% hypersthene, and

3.3.3.2 Pillow Basalt

Station: SC05076

Sample SC05076 represents a unit that dips 70 degrees to the southwest and is located the in the northwestern-most exposure of Nootka Island, north of Nuchatlitz Inlet (Appendix D). The sampled outcrop lies below other outcrops of pillow basalts, and above a minor vesiculated layer that exhibits a tops-up attitude.

Equal amounts of subhedral augite and subhedral plagioclase phenocrysts comprise 30%of the total mineralogy (Figure 3.1F). The phenocrysts, ranging from 2.0 to 50 mm, occasionally display low integrity; ie., their crystalline structure surrounds other material. Sericitized plagioclase laths, minor grains of augite, uralitized augite, and interstitial blue chlorite form the groundmass with minor opaques and palagonite. The small (< 0.5 mm), rounded masses of palagonite form < 2.0 % of the rock and are enclosed within the groundmass. Together, the palagonite, uralitized augite, interstitial chlorite, and sericitized plagioclase suggest incipient hydration during genesis, perhaps from below a pillow-forming flow.

3.3.3.3 Lapilli Tuff

Station(s): SCOW 06, SC05107

These samples were taken from the Hecate Channel, across the inlet north of Nootka Island. Both sampled locations dip at -50 degrees to the southwest and have good integrity with little metamorphism. Weathered surfaces differentially expose lapilli from the matrix, having a jagged, rough gray-and-black appearance.

Containing various sizes of angular plagioclase fragments up to 0.5 cm, this rock is dominantly (35%)volcanic ash with 30% plagioclase lapilli, 25% interstitial and replacement chlorite, 9% interstitial quartz and calcite, and

3.3.4 Group 2b (new), Jg2bv

This group is petrographically identical to the amygdaloidal unit of Group 2 and contains multiple, small, amygdaloidal flows and lesser amounts of plagiophyric basalt (Figure 3.1 C). Mesoscopically, however, it contains similarities with both Groups 1 and 2: greenschist alteration to the degree of Group 1, and plagiophyric nature akin to Group 2. Where the flows are exposed, they lie at or near the base of the Group 2 strata as flows and shallow level sills that intruded the Ewart and Crawfish groups and underlying Group 1 hyaloclastites. Their geochemistry separates them from the bulk of Group 2 basalts and is discussed in Chapter 4.

3.3.4.1 Amygdaloidal Flows

Station: SC05091

In outcrop, this unit is a dark green basalt, with a hackly or dusty appearance on fresh surfaces, that forms small sections of numerous flows ranging from 20 cm to 3.0 m thick (Figure 3.2). Exposures are, but not limited to, between the Crawfish and Ewart Lakes (SC04091), in the Gunpowder Valley north and west of Crawfish Lake, and found as abundant, large ~2.0meter diameter blocks of angular to sub-angular debris south of Nuchatlitz Inlet, north of Ewart Lake (SC04064). In the Gunpowder valley, this unit steeply dips 70" to the southwest, lying between an aphyric unit containing epidote nodules and a unit supporting numerous, sub-rounded phenocrysts of plagioclase.

Amygdules are equant to oblong and flattened, vary up to 1.5 cm in size, and are uniformly scattered throughout individual flows. An example of this unit is found at SC04064, dominantly greenschist-facies mineralogy, and SC05091, of presumably primary extrusive mineralogy containing magnetite, plagioclase, quartz, and hornblende. All amygdaloidal flows contain up to 30% amygdules of quartz, prehnite, pumpellyite, sericitized plagioclase, andlor epidote; and, a vitrophyric groundmass comprised of -50% small laths of hornblende or chlorite. Magnetite and ilmenite are frequently concentrated in and around the amygdules that do not contain plagioclase. The matrix exhibits a bedding-parallel flow fabric that deflects around the amygdules and contains little to no evidence of crystal deformation. Higher percentages of zeolite in the amygdules coincide with increase of matrix chloritization and overprinting of original flow fabric.

Figure 3.2: Outcrop showing numerous flows (to 20 cm) of amgydaloidal basalts from Group 2b.

3.4 Sedimentary Rocks

The sedimentary rocks on Nootka Island represent two time intervals. The oldest units, of probable late Triassic age, comprise a lower package of limestones (Crawfish group) and an upper package of sedimentary rocks that internally range upward from calcarenites to siltstones and sandstones (Ewart group). The volume of the sediments does not equate to those observed regionally, suggesting that the depositional environment on Nootka Island was different, or that the overlying and more massive beds have been eroded away to expose an uncomformable surface on which the Group 2 volcanics were deposited. The youngest sedimentary units- Eocene and Oligocene in age- are the youngest observed lithified rocks. They overlap the western margin of Nootka Island and include conglomerates, sandstones, and siltstones that were formed in a marine setting (Cameron, 1980).

3.4.1 Crawfish group (new), TCI

Stations: SC04013105092, SC04035-36, SC04043-44, SC05078-9, SC05092

The Crawfish group is a collection of metamorphosed limestones and rare disseminated skarns. Their formation represents a marine environment and regional subsidence of the Group 1 basalt strata that forms the basal exposures in the Nootka Island region. To the west of the Nuchatl shear, outcrops of the limestones lie adjacent to the Ewart group and have similar structural attitudes. On the east of the shear, the only indicated occurrence of the Crawfish group exists- in similar stratigraphic position- were metamorphosed into large calcite veins and a small skarn in a contact aureole near station SC04052.

In the locations where structural features are intact (SC040131092, 035, 043, 079)) flaggy, gray-dark gray ~0.5m beds and >2.0 cm laminae reveal textures of very-coarse to fine sand-size, well-sorted, euhedral calcite grains. Limestones of the Crawfish group appear to grade, over -10.0 m, into finer-grained, laminated, calc-silicates. Primary units may have been pure limestone that graded locally into a calc-arenite.

In thin section, calcite grains range from microspar to equant and blocky, and are present alongside minor carbonate matter, dolomite, diopside, and clinozoisite varying in amounts among different laminae. Most samples contain thin tectonic (short, non- suture-like) stylolites sub-parallel to axial cleavage. Samples SC04013 and SC05092 display the least recrystallization but contain no fossils, or relicts of former depositional environment, such as conodonts (for which they were tested). Figure 3.3: Photomicrographs of selected Nootka Island metasedimentary rocks. Photos are in approximate stratigraphic order from bottom-top: F-E-C-D-B-A. (A) Metamorphosed lithic arkose with plagioclase, magnetite, and hornblende

porphyroclasts- -- that cut primary cross-bedding, from the Boston Point facies, Ewart group (SC04084). (B) A quartz and pyrite vein that cuts a metasiltstone (argillite) of the SiltISand facies, Ewart group (SC0401 IB). (C) Cryptorythmic calc-argillites, lower SiltISand facies (SC04087). (D) Foliated argillite from the middle SiltISand facies (SC04082). (E) Metamorphosed calc-silicate from the EwartICrawfish boundary (SC04012). (F) Open-system garnet -wollastonite contact metamorphic assemblage in Crawfish group sample (SC04036). Within contact aureoles, the unit becomes boudined, finer-grained, and/ or skarn-like. Sample KO4036 displays porphyroblasts of grossular garnet with wollastonite- these phase relationships suggest of amphibolite facies contact metamorphism (Figure 3.3F). Penetrative fabric in this sample is non-existent, probably overprinted by retrograde crystallization. Frequently, skarn rocks have bleached zones around thin veins and are rarely brecciated.

3.4.2 Ewart group (new), TEss/TEbp

Stations: SCO4Oll B, SC04082B, SC05087, SC04083, SC04012, SC05087, SC05084A-B

This group is a package of siliceous sedimentary rocks, divided into three separate facies, together exposed in discontinuous lenses on Nootka Island. From between the southern tip of Ewart Lake and Crawfish Lake, this group strikes northwest along the western flank of a plunging sycline, to exposures on the east side of Crawfish Lake, through to Bajo Creek.

Exposures of similar orientation strike from the Spanish Islands to Boston Point, Kendrick Inlet, Gunpowder Main, and a small outcrop on the southeast side of the Nuchatlitz Inlet (Map- Appendix D).

The rythmic beds of the Ewart group contain quartz, hornblende, plagioclase, and occasionally biotite grains and smaller minor diopside, and clinozoisite. Magnetite grain concentrations in sandstones delineate original bedding. Penetrative fabrics in this unit form small angles to original bedding, accompanied by hornblende porphyroclasts throughout, and garnet porphyroblasts near the base.

3.4.2.1 Laurie Redbed facies

Station: SC04037 (no sample taken)

This is a subdivision, perhaps correlative with nomenclature from Yorath et al. (1999)) termed the Redbed Creek Facies, applied to describe two individual outcrops on Nootka Island. This facies is a 5.0 meter horizon of faintly-bedded fine maroon silts that are lateral in strike to the Ewart SiltISand facies and represent lithified tuffs oxided in a marine environment. Due to the greater volume of the SiltISand facies compared to the Laurie Redbed type of rock, this facies is mentioned here for the sole purpose of informing future researchers but is not developed further within this study.

One outcrop is located at Bajo Creek near the western coast, adjacent to a contact skarn further to the west. Laterally-discontinuous bedding is represented by slight changes in maroon color and grain size with homogenous microcrystalline matrix and rare faint bed traces. The second exposure of this sedimentary facies is centered in the northern island near the Inside Passage of the Nuchatlitz Inlet, inland from Blowhole Bay, with an unknown structural attitude. The nature of the outcrops suggests quiet and shallow-water deposition occurring intermittently with arc activation.

3.4.2.2 Silt/Sand facies, TEss

Stations: SC04011 B, SC04012, SC04083, SC05082B, SC05087

The aluminous, garnet-bearing samples SC04012 and SC05083 contain medium grains of plagioclase, secondary apatite, quartz, calcite, and clinozoisite, and irregular garnet porphyroblasts. Bedding or laminations are disrupted and discontinuous in both hand sample and thin section; fabrics resulting from metamorphism. Station SC04012 is near the contact of the Ewart and Crawfish groups, station SC04083 lies in the Spanish Islands, flanking Nootka on the southeast in Nootka Sound. These two samples likely reflect metasomatism between the Ewart and underlying Crawfish groups during metamorphism.

Sample SC04011 B is uniformly red-gray rock from a facies that dips 53 degrees to the northeast; it is an example of the finest-grained facies of the Ewart group. This siltstone is well-sorted with grain sizes ranging from 0.01 mm to 0.2 mm (Figure 3.38). Quartz subdomains and pyrite veins indicate this is metamorphosed/recrystallized, comprised of 30% quartz, 25% rounded plagioclase grains, 15%biotite and 15%chlorite parallel to bedding, 5% small angular detrital amphibole, 5% magnetite, ilmenite, and pyrite, and 5% other opaque matter.

Similar to the previous sample, SC05087 outcrops southwest along Crawfish Lake along strike from SC04011 B and exhibits similar structural attitude. Mesoscopically, however, the outcrop displays rhythmic beds and laminations of alternating fine, well- sorted wacke within medium, moderately sorted arenite, respectively (Figure 3.3C). Modal mineralogy is similar to SC04011 B but with a relative 10%increase in chloritization, 5% increase of both magnetite and sub-rounded hornblende, and lack of pyrite. Metamorphism of this sample suggests metasomatic influx or re-mobilization of carbonate that created porphyroblasts of clinozoisite in the wacke laminae. Metamorphic foliation is sub-parallel to original bedding, evidenced by the wackelarenite layering and magnetite concentrations within individual laminae.

Sample SC05082B is correlative with the other samples in this facies, exhibiting marked increase in quartz (50%), poorer sorting, plagioclase porphyroblasts up to I.Omm, better-defined laminae by both quartz, biotite, and magnetite concentrations, and slight grading within individual layers (Figure 3.3D). Shearing of this sample deflected fabrics around plagioclase porphyroblasts and recrystallized quartz in resulting pressure shadows.

3.4.2.3 Boston Point facies, TEbp

Station: SC05084

This subdivision within the Ewart group contains quartz, plagioclase, hornblende, biotite, chlorite, and magnetite as its dominant mineralogy (Figure 3.3A). Individual laminae, from 1-3.0 cm, have quartz, plagioclase, hornblende, or biotite as their dominant constituents. Frequently, as the sediments are commonly overprinted and metamorphosed, older hornblende grains grew new rims and range up to 2.0 mm in crystal size with increasing grade (also indicated by quartz mobilization into pressure shadows around the new hornblende porphyroblasts). Plagioclase grains are rounded and almost completely sericitized, displaying only shadows of former cleavage and twinning. Rare structural fabrics are incongruous to bedding- magnetite and biotite serve to delineate former bedding planes. Though metamorphism has affected this sample, evidence for a sedimentary origin of the protolith exists in minor bed truncations forming consistent 'concave-up' younging directions- indicating this unit is not overturned. Figure 3.4: Escalante conglomerate, Carmanah Group, Nootka Island (SC04042). Clast descriptions clockwise from top left: hornblende gabbro; chlorite-rich greenstone; carbonate; amphibolite; and center, anorthosite. The matrix is detrital composite of hornblende, biotite, quartz, plagioclase, chlorite, magnetite, and minor calcite.

3.4.3 Carmanah Group- Eocene to Oligocene, ECe/OCh/OCs

On Nootka Island, the Carmanah Group strikes parallel to the western coast (Geolgic Map, Appendix D) and unconformably overlies older stratigraphy. These rocks dip -30" southwest. The base of the Carmanah group is obscured by vegetation, and the the top of the Carmanah is covered by deposits of colluvial debris, glacial diamicts, and extends away from the island under ocean water.

3.4.3.1 Escalante Formation, ECe

Station: SC04042

In the Beano Creek area, a homogenous package of conglomerates representing the lowest formation of the Carmanah Group dips 20" to the southwest. The thickness of the Escalante Formation is approximately 50 metres on Nootka Island but ranges in thickness elsewhere (Muller, 1981; Cameron, 1980). It is poorly-moderately sorted, matrix-supported (60%),comprises rounded clasts up to 5.0 cm, and is upright (Figure 3.4). A slight fining-upward sequence exists in one 0.5 meter-thick bed. The lithics within the conglomerate represent all of the lithologies from Nootka Island in addition to a maroon-colored porphyritic rhyolite that has thus far been unobserved in the immediate area.

3.4.3.2 Hesquiat Formation, OCh

Station: SC04080

Resting conformably above the Escalante Formation, the Hesquiat Formation contains a lower member of finer-grained conglomerate underlying an upper member of well- bedded siltstones containing frequent sandstone lenses. The conglomerate exhibits better sorting, more silty matrix, and smaller lithics than those of the underlying Escalante Formation.

The upper member of the Hesquiat, the siltstones, forms the thickest sedimentary package of the Carmanah Group (Figure 3.5). Many laminae and beds comprise this formation, ranging from 1.0 cm to 0.5 meters thick, and expose iron concretions up to 3.0 cm wide along the bedding surfaces that appear to crosscut primary textures. Intermittent, oblong sandstone lenses exposed in perpendicular planes to bedding in the siltstones are up to 4.0 meters in length. The sand lenses form anastomosing structures on the bedding planes, otherwise dominated by hummocky bed sets. This relationship suggests the Hesquiat Formation was deposited in a shallow-dipping, low- energy environment, as a tidal flat or shallow marine shelf during a transgression of sea level between deposition of the Escalante and Sooke Formations (Cameron, 1980).

3.4.3.3 Sooke Formation, OCs

A sample of the Sooke Formation was not retrieved from the field; however, a small exposure exists on the southwest coastline of Nootka Island in the breaker zone off Bajo Point and forms the underwater reef systems to the west. Past research (Muller, 1980) on the Sooke Formation describes conglomerates and sandstones, similar to the Escalante Formation, suggesting a regression. Figure 3.5: Gently southwest dipping, broadly folded siltstones with lenticular sandstones on Beano Beach, Hesquiat Formation, Carmanah Group. Plutonic rocks constitute over 50% of the exposures on Nootka Island. They have highly variable textures and chemistries. Crosscutting relationships reveal a temporal trend from hornblende gabbros to hornblende diorites, diorites, tonalites, granodiorites, and lastly, granites. Co-existing in proximal age with the hornblende gabbros are a layered hornblende crystal fractionate and a cumulate anorthosite. Their geochemistry and lateral gradations tolfrom adjacent hornblende gabbros suggest they are chronologically contemporaneous with the earliest intrusions. The youngest observed magmatism on Nootka Island is represented by series of pyrite- bearing basalt dykes that appear to radiate from larger plutonic bodies.

Many intrusions contain abundant aphyric and phaneritic xenoliths, xenolith screens, en-echelon tension gashes and other mixing fabrics at their boundaries. Agmatites, quartz veins and migmatites are common in contact aureoles.

Contacts among the various intrusive lithologies nearly always suggest pre- crystallization mixing. In most cases, more silicic intrusives crosscut the more mafic varieties; though, rarely do hornblende diorites exhibit chilled margins against diorites thus indicating a coeval evolution. Geochemical relationships among all of the various suites are discussed in Chapter 4.

To facilitate descriptions within the plutonic suite, the plutonic rocks of Nootka Island are divided into six units. These are hypabyssal rocks, crystal fractionates, anorthosites, and three 'series' named after their most voluminous component. 'Hornblende gabbros' describes intrusions with over 30% hornblende and less than 5.0% quartz (hornblende gabbros and hornblende diorites). 'Intermediates' are those with 10-3096 hornblende and >5.0%quartz (hornblende diorites, diorites, and tonalites). Lastly, 'granites' refer to the intrusions with ~5.0%hornblende, and relatively high proportions of potassium feldspar (granodiorites and granites). 3.5.1.1 Hornblende Gabbro Series, (new) Jg2ihg

Stations: SCO4Ol9.1, SC04070, SC05090, SC05095, SCO5lO0, SCO5lO2

This is the most widespread suite of intrusions on Nootka Island. Outcrops of hornblende gabbro appear both isolated and along the margins of younger intrusions.

The contacts between hornblende gabbros and other intrusions exhibit ductile, brittle, veined and permeated gradations. Contacts with non-intrusive stratigraphy were rarely identified due to ground cover and small outcrop sizes. However, two contacts between basalt and a hornblende gabbro were observed, and revealed a gradational, agmatitic-like veining and permeation of the gabbroic fluids into the basalt resulting in hornblende hornfels metamorphism of the former- hardly recognizable in hand specimen because both contain plagioclase and hornblende as their dominant minerals.

Frequently seriate, hornblende gabbros display abundant 'pegmatitic segregations'. These zones exhibit an increase in grain sizes (up to 3.0 cm average) with euhedral hornblendes suspended in a subhedral plagioclase matrix. Where these pegmatitic segregations occur, the plagioclase is white, not the common gray. Occasionally these pegmatitic segregations also contain crystals of epidote, quartz, and microcline- the involvement of these minerals are discussed in Chapter 6.

Ranging from 1.0 mm to 1.0 cm, modal mineralogies are equally hornblende and gray plagioclase with <10 % in total of biotite, apatite, quartz, hypersthene, magnetite, ilmenite, pyrite and rutile in decreasing order (Figure 3.6E). Hornblende contents vary from 35 to 50%. Most hornblende grains are oikocrystic. Alteration minerals in this suite are chlorite, actinolite, sericite and muscovite after plagioclase, and uralite after minor biotite and pyroxene. Penetrative fabrics within the hornblende gabbros are parallel to the bedding within country rock. Nearly half of all hornblende gabbros exhibit cumulate textures, displaying hornblende oikocrysts from 1.0 cm to 2.0 cm in size that enclose euhedral chadocrysts of plagioclase, to 1.0 mm. Some of the cumulates (SC04070) comprise 70% hornblende oikocrysts up to 3.0 cm at their widest, and have minor uralitized clinopyroxenes with rare chlorite and bladed actinolite crystals along grain boundaries. 3.5.1.2 Hornblende Crystal Fractionate

Stations: SC04037

The occurrence of a well developed cumulate obtained from the Bajo Creek valley (SC04037)- a hornblende crystal fractionate- indicates that crystal settling may have been a significant process in the formation of the early intrusions. This hornblende crystal fractionate is named due to a 90% concentration of unbent planar hornblende crystals up to 6.0 cm that exhibit planar layering that 'dips' to the southwest- parallel to local bedding attitude (Figure 3.6F).

3.5.1.3 Anorthosite, (new) Jg2bia

Station: SC04071

Sample SC04071 is an anorthosite located 0.5 km south of the Plumper Main Line logging road at the junctions of Beano and Bajo Creeks, 1.0 km from SC04070, and 2.0 km from sample SC04037 (Map- Appendix D). It contains oikocrysts of both hornblende and plagioclase (Figure 3.6C). Hornblende oikocrysts are up to 1.0 cm in size and frequently altered to actinolite, together comprising 30% of the modal mineralogy. The abundance of hornblende may indicate that this anorthosite was derived as a leuco-gabbro (John Moore, personal communication). Individual plagioclase grains are <0.5 cm on the long axis, randomly oriented, euhedral, twinned, un-zoned, and embayed within larger (<2.0 cm) plagioclase oikocrysts of similar nature. Little secondary alteration- sericitization- of the plagioclase is evident.

3.5.1.4 Intermediate Series, (new) Jg2ii

Stations: SC04019.2, SC04086

Tonalites, quartz diorites, diorites, and hornblende diorites comprise the bulk of intrusive exposures on Nootka Island. These intrusions are usually adjacent to and cut hornblende gabbros. Intrusions in the intermediate series appear as stocks and plutons surrounded by minor agmatite veins and trondjhemite dykes. They lie in mesozonal contact with country rock, and occasionally contain planar fabrics in accordance to the regional trend. Enclaves and xenoliths within the intermediate series intrusions are derived from other intrusions of the intermediate series, hornblende gabbros, and basalts from Groups 1 and 2. The xenoliths exhibit brittle and ductile behaviour, with or without recrystallization at the margins of entrained volcanic pieces. Also, quenched mafic inclusions present within this series suggest that these intermediate intrusive phases existed co-magmatically at various stages of cooling.

The crystal sizes of the minerals in this series vary from fine to coarse, the latter being granoblastic (Figure 3.68 and D). The coarse varieties record regional planar fabrics well. PLagioclase is the most abundant mineral (40-80%)followed by quartz (5.0-30%)and together comprise 70-90%of the minerals in this series. Other minerals are hornblende with rare biotite and sphene.

3.5.1.5 Granite Series, (new) Jg2ig

Stations: SC04031 B, SC04024

The granites and granodiorites of Nootka Island are coarsely crystalline and equigranular. Intrusions of the granite series are exposed in the northern and central portions of Nootka Island. They lie in epizonal contact with the surrounding country rock, having crisper contacts and lower temperatures within contact aureoles. The Granite series also entrains fewer xenoliths than the other series. Brittle faults and fractures frequently bound and cut the granites. Alteration of the granites is evident as 'bleached' halos around grain boundaries, cloudy quartz, and weathered micas.

Quartz and plagioclase are equally abundant and compose 60-70%of the minerals in this series (Figure 3.6A and B). Where present, K-feldspar crystals range up to 15%and are euhedral. The remaining minerals are (in decreasing order) biotite, hornblende, muscovite, and pyrite, totalling 10%. Approximately 3.0% of the rock is magnetite and 2.0% of the rock is apatite, sphene, and other opaques. Figure 3.6: Photomicrographs and photographs of selected Nootka intrusions. Photos are in approximate temporal order (bottom-top) F/E/C-DIB-A. (A) Coarse grained granite (SC04024). (B) Chilled margin of granite intrusive with a tonalite (SCO4031b). (C) Anorthosite (SC04071), displaying slight foliation from bottom left- top right. Hornblende is rare and oikokrystic, plagioclase grains are fresh and unaltered. (D) Co-mingling textures are common at boundaries among intermediate and mafic intrusions. Here, schlieren formed at the contacts between a tonalite and a hornblende diorite. Hammer for scale, (E) Cumulate texture in a hornblende gabbro with sericitized plagioclase laths. (F) Hand sample of a layered crystal fractionate of hornblendes. 3.6 Hypabyssal Rocks

3.6.1.1 Basalt Dykes

Stations: SC04019.3, SC04047, SC04053-55, SC05078

Basalt dykes are common on Nootka Island and exhibit pairs up to 0.5 meters wide. They are all steeply dipping; most dykes can be traced along their strike to the nearest intrusion. Sample SC04078- a sill- lies in intrusive contact within the Crawfish group, parallel to bedding. Basalt dykes are ubiquitously fresh and cut most folds, intrusives, structures, and stratigraphy (Figure 3.7). In thin section, the basalt dykes are aphyric with varying amounts of hornblende and plagioclase, with actinolite, 1.O-5.0 % euhedral pyrite, and rare phenocrysts of olivine (SC04053). Rarely the dykes are altered, contain chlorite, or are cut by other dykes or veinlets. One basalt dyke contains partially-digested granite xenoliths up to 2.0 cm in diameter and may indicate its emplacement after crystallization of earlier Jurassic granites. Figure 3.7: An example of crosscutting relationships among three intrusive lithologies. (A) Brittle xenoliths of a hornblende gabbro in a tonalite (B). (C) The two pristine, aphyric, basalt dykes that cut the tonalite were sampled and age dated (SCO4O 19.3). CHAPTER 4: GEOCHEMISTRY

A usefulness of geochemical analyses is to quantitatively distinguish and characterize the different lithotypes of Nootka Island. Inductively-coupled plasma analysis mass- spectrometery (ICP-MS), X-ray fluorescence spectrometry (XRF), and instrumental neutron activation analysis (INAA) were used to record the major and trace element abundance at ACTLABS (Toronto, ON) and ALS Chemex (Vancouver, BC). Chemical analyses of 23 rocks from Nootka island are listed in Appendix B. Regional data sets from Yorath et al. (1999)) Massey (1995)) and Barker (1989) are used for comparison. Data from the more northerly Talkeetna volcanics (Clift et. al., 2005a) are used in the trace elements subsection.

Loss-on-ignition values (LOI) for all analyzed samples from Nootka Island vary from 0.47%-4.2%. Two samples were run as duplicates and used to evaluate data quality (mafic volcanic: SC04022, SC04022b; and granodiorite: SC04024 and SC04024b). The standard deviations for each element in the samples and their percentages relative to the element concentrations are listed in Appendix B.

Of the major oxides, SO2, A1203, and MgO, and NaO have the largest standard deviations at 0.74%) 0.12%) 0.12%) and 0.1 1%. 34 trace elements were analyzed- the standard deviations were all less than 1.0%. However, the standard deviations as normalized to total concentration of each trace element yielded total concentration variability of 13.3, 8.92, 9.69, and 30.5% in elements Co, Cr, Ni, and Pb, respectively.

4.1 Major Element Oxides

The major element chemical plots show the general geochemical character of Nootka Island rocks. On the total alkalis vs. silica (TAS) diagram of Le Bas et al. (1986), Groups 1, 2, and 2b are principally contained within the basalt field (Figure 4.1 ). Groups 1 and 2b display tight clusters in the center of the basalt field whereas the rocks of Group 2 exhibit a wider compositional array. Three samples of the Group 2 rocks, correlating with the intrusions from the granite series, fall outside of the main basalt cluster in the dacitic and rhyolitic composition fields. Group 1 rocks display another tight cluster in the tholeiitic field, situated to the right of the tholeiiticlcalc-alkaline trend line on an AFM diagram (Figure 4.2). Group 2b also lies on the tholeiitic side of the trend line but is more distributed and surrounds the Group 1 cluster. Both of these distributions overlap the Karmutsen basalt fields of Yorath et al. (1999) and Massey (1995a-b). Group 2 displays a calc-alkaline trend with some outliers that fall within the domains created by Groups 1 and 2b. The calc- alkaline trend of the Group 2 rocks overlaps both of the Karmutsen and Bonanza fields.

On a Mn0-P205-Ti02diagram (Figure 4.3), useful for describing tectonic affinities (Mullen, 1983), Group 1 displays a tight distribution in the MORB field that also ecompasses the Karmutsen basalts of Yorath et al. (1999) and Massey (1995). Group 2b lies in the upper left portion of the IAT field separate from the Sicker, Karmutsen, or Bonanza groups. Group 2, Bonanza, and Sicker rocks overlap and are widely distributed, covering portions of the lower IAT field, upper CAB field, and left side of the OIB field.

Figure 4.1 : Total alkalis versus silica for the Nootka Island, non-sedimentary lithotypes (LeBas, 1986). Figure 4.2: AFM diagram for Nootka rocks. Shaded fields represent data from Yorath et al. (1999).

Figure 4.3: Mn0-Ti02-P205,major-element tectonic discrimination diagram (Mullen, 1985). Shaded fields represent data from Yorath et al. (1999). Using MgO as a proxy for the degree of magma evolution (because most Nootka rocks have a basaltic composition), Fenner diagrams display the relationships among the various major-element oxides (Figure 4.4). Ti02, K20, &03, and P2O5have varied relationships with respect to MgO, whereas FeO* and CaO increase with increasing MgO content. It is unclear whether the spread in distributions pertains to secondary alteration, wherein variability of the fluid-mobile K20, and less frequently Ti02, within an altered rock suppresses their petrogenetic significance (Pearce, 1982). However, the genesis and character of Nootka Island rocks can be further evaluated by trace elements, which are less susceptible to alteration. Figure 4.4: Fenner diagrams for Nootka Island rocks. 4.2 Trace Elements

The trace-element geochemistry of the Nootka Island lithotypes is useful in understanding petrogenesis as many trace elements are less mobile during alteration, and, they help to distinguish differences in tectono-magmatic environments (arcs, mid-ocean ridges, plumes). This discrimination is possible as elemental contributions within fluids drawn from a subducting slab will be different that those from a mantle wedge below an arc or a spreading ridge (Pearce, 1984, Clift et al., 2005a).

Figure 4.5 is a MORB-normalized multi-element diagram (Pearce, 1984) on which different petrologic units of Nootka Island are displayed in ratio to those element concentrations typical of a mid-ocean ridge basalt standard (Sun & McDonnough, 1989). The diagram contains the fluid-mobile trace elements on the left from Sr to Th (LILE- the large-ion lithophile elements), and fluid-immobile elements on the right from Ta to Yb (HFSE- the high field strength elements). The diagram is arranged such that incompatibility of elements in mafic igneous systems increases toward the center of the diagram (toward Th and Ta).

Group 1 has low relief E-MORB-like curves (Figure 4.5) typically of a MORB-like basalt that contains higher abundances of fluid-mobile trace elements. Group 2 displays a typical arc-like pattern, slightly enriched in the LILE compared to the HFSE. Group 2b rocks are similar to Group 2 but exhibit considerable depletion of the elements Ce to Sm. It is concluded that the low values reflect actual element abundances and are not the result of incomplete dissolution, or another analytical problem, because separate samples produced the same patterns measured in separate assays.

The small range exhibited by Group 1 indicates derivations from a homogeneous parent that remained unaltered throughout sourcing. The trace element patterns of Group 2 suggest formation above subducting crust. It is not likely that the Group 2b rocks were depleted after cooling, but rather sourced from a reservoir that was either previously depleted in Nb, Ce, P, Zr, Hf, and Sm, or derived at the onset of the anatexis responsible for Group 2 magmatism prior to significant contribution from the mantle wedge. Using LaINb as an indicator of tectonic affinity, Group 1 plots mainly in the N- MORBIE-MORB and Karmutsen fields (Figure 4.6 and 4.7). The clustering of Group 2b near the origin of the diagram indicates derivation from a depleted source or a high degree of partial melting relative to typical arc magmas. Group 2 is located near Group 2b and displays an oblong pattern trending toward the Group 2b cluster. This relationship may reflect a shared source for the Groups 2 and 2b, and a continuing increase in trace-element concentration during fractionation.

I I I I I I I I I I I I I I r

r --+ , Bonanza (avg)

Figure 4.5: MORB-normalized trace element plot displaying the major non-sedimentary lithotypes on Nootka Island, using normalization values from Pearce (1984). Figure 4.6: LaINb trace element ratio plot for Wrangellia volcanics. The dashed field in lower left represents the range of all lithotypes from Nootka Island. Data from Yorath et al. (1999), Barker (1989) Massey (1995a-b), and estimated for the Talkeetna from Clift et al. (2005a).

Figure 4.7: LaINb trace element ratio plot for Nootka Island samples. 4.3 Group 2 Intrusion Suite Modelling

Multiple sequences of intrusions are observed on Nootka Island. Field observations support a sequence of hornblende gabbro, hornblende diorite, diorite, tonalite, granodiorite, and granite intrusions followed by basalt dykes. The comingling contacts among the intrusions and the similarity of trace element ratios of the intrusions to the Group 2 volcanics suggest they may be cornagmatic.

Thorough modelling of the chemical variations among a diverse suite of intrusions is typically complex because geochemistry reflects both the source for the intrusions and a magmatic history involving melting and crystallization as well as mixing and assimilation (Frost et. a[., 2001 ).

To form a simple model that tests for plausible consanguinity (common magma lineage), the three primary intrusion series within Group 2 were evaluated. La and Ce were used because of their fluid-mobile compatible nature relative to Nb and Zr. In a closed-system environment, ratios among these elements should remain the same although their total concentrations should increase with increased fractionation (Pearce, 1984).

The linear distribution of the three series on Figure 4.8 indicates that a limited amount of open-system behavior occurred (and contaminated the source). A regression line drawn through the points passes through the origin and does not cross any tectonic affinity boundaries, indicating possible consanguinity.

To further test their consanguinity, a plot of LaINb vs ZrICe is used (Figure 4.9). As both of the ratios should remain constant through fractionation (Thorkelson, 2001), variations among the sample distributions indicate possible contamination from introduced fluids. As displayed in Figure 4.9, the samples are not evenly distributed, indicating possible contamination of the series though how much is unclear. As shown by Figure 4.6 and Figure 4.7, however, the density of La and Nb concentrations for the Nootka Island Group 2 and Group 2b rocks forms a tighter cluster than those for any of the other Wrangellia igneous units. This illustrates that a shared source among all of the Jurassic lithotypes on Nootka Island is plausible (Li et al., 2004). Granites

Figure 4.8: La vs. Nb plot of the Group 2 granite, intermediate, and hornblende gabbro series intrusions.

Granites o Intermediates H6l:(ja66ros

Figure 4.9: ZrICe vs. LaINb plot of the Group 2 granite, intermediate, and hornblende gabbro series intrusions. 4.4 Isotope Geochemistry

4.4.1 6180/ 613c Carbonate Discrimination

The carbonate strata within the Crawfish group (sample SC04092) were analyzed by Dan Marshall at Carleton University, Ottowa, Canada, for 61 801 61 3C isotopes and compared with regional Wrangellia carbonate strata. The isotopes, plotted on Figure 4.10, fall within broad fields of both the Parson Bay and Quatsino Formations of the late Triassic. This aligns well with previous researcher's assumptions that the carbonates exposed within the 'Westcoast Crystalline Complex' may be analogous to the Quatsino Formation (Yorath et al., 1999). However, caution must taken in 6180 analysis, because it is highly susceptible to retrograde fluid flow and may be transferred into or out of the system (Young, 1993). Because these carbonates were elevated to amphibolite grade metamorphism, and the effects of metamorphism on 61 80 and 61 3C concentrations are unknown, the trajectory of the 61801 613C ratio is unclear and the 61 801 61 3C values of the Crawfish group require further investigation.

Figure 4.10: 6180/ 6I3cisotope discrimination plot showing likeness of a Crawfish group carbonates (sample SCO4Ol2- black) to limestone from the Triassic Quatsino Formation (light gray). The Crawfish group sample could also be correlative with minor carbonates in the Parsons Bay Formation (dark gray), but there are not enough values for accurate constraint. Three samples were selected for potassium-argon geochronology and analyzed using the whole-rock 40~r/39~rmethod by Thomas Ullrich at UBC, Vancouver, Canada(Figure 4.11 ; data listed in Appendix C). The group was comprised of a hyaloclastite from Group 1 (SC04022), an aphyric basalt from Group 2 (SC04031), and a hypabyssal dyke (SC04019.3). Sample SC04022 (altered) yielded a whole-rock plateau age of 158 + 2.5 Ma. The Group 2 basalt SC04031 contained excess argon and revealed no reliable plateau age. Sample SC04019.3 yielded good plateaus and a crystallization age of 168 5.5 Ma.

Acting as a lower age boundary for deformation and metamorphism, the unaltered sample of SC04019.3 contained the least altered grains of hornblende and plagioclase in thin section. This dyke and others in the hypabyssal suite represent the youngest observed Jurassic rocks, crosscutting most structures and other units including the Group 1 basalt represented by sample SC04022. The age of the dykes and their emplacement- at 168 Ma- indicate their presence after the peak of deformation. The hyaloclastite (SC04022)- at -1 58 Ma- underwent at least one thermal resetting resulting from regional greenschist-grade metamorphism indicated by the mineralogy and degree of recrystallization. This method of isotope geochronology is not always capable of discriminating multiple thermal episodes. Sample SC04031 displays the poorest isotopic trend and an age inconsistent with geologic constraints. This is possibly due to local interference from a granite pluton, altering the amount of 40~rin the sample. u 20 40 60 80 100 Cumulative 39grPercent Figure 4.1 1 :40Ar/30Ar, whole-rock plateau ages for three aphyric basalts from Nootka Island. CHAPTER 5: METAMORPHISM

The omnipresence of greenstones on Nootka Island indicates that pre-existing strata were buried and regionally metamorphosed. Metamorphism became dynamic near contemporaneous shears and reached higher temperatures within contact aureoules.

Two metamorphic domains are displayed on Nootka Island, are juxtaposed by the Nuchatl shear (Figure 5.1). Regional metamorphic grades are highest on the west side of the shear, and form a visible gradient on the east side of the shear with from higher grades in the south than in the north. Contact metamorphism exists throughout the island but is most distinct where intrusions contacted rocks of lower metamorphic grades. Almost all outcrops on Nootka Island display some amounts of retrograde chloritization.

On the west side of the Nuchatl shear, the rocks reached upper greenschist or lower amphibolite regional metamorphic facies at pressure of approximately 3.2 kbar. Contact metamorphism is recorded locally by hornblende-plagioclase themometry at approximately 720•‹C. Across the Nuchatl shear to the east, the regional metamorphic grade reached pressures of approximately 2 kbar with contact metamorphic temperatures ranging from approximately 680•‹C to 700•‹C in the south. Regional metamorphism to the northwest of the Beaver Creek Thrust was sub-greenschist, with contact metamorphism occuring locally in the vicinity of intrusions.

Seafloor-hydrothermal metamorphism of the lower strata existed first. Shortly afterward, regional metamorphism occurred and was likely associated with large deformational events and widespread plutonism. Hydrothermal alteration exploited brittle features during the last metamorphic activity, approaching the end of regional metamorphism and afterwards during extensional uplift (Figure 6.5). - - Fsuh UndsRnMl -A - i'hr~sFaun Approximate -Extenslorial Fault - r - EulenstonalFault, Inferred

\\v... DynarnlcAmph~bollte, Fohated

Lower Amphibolite ornblende Hornfels

Figure 5.1: Map of relative metamorphic grades on Nootka Island. Size of dots indicates increased metamorphic grades, from 0.0 kbar (light shade) to 3.5 kbar (dark- amphibolite). The individual thermobarometric results are shown beneath each sample locality. 5.1 MI: Seafloor-Hydrothermal Metamorphism

Stations: SC04022, SC04064

Early hydrothermal metamorphism is evident within the Group 1 basalts that is not evident within other lithotypes in the Nootka Island region. The metamorphism is expressed by: (1) de-watering rinds around the Group 1 xenoliths within hornblende- diorite intrusives (Figure 5.2)) and (2)) low metamorphic grade zeolite assemblages that overprint calcic plagioclase amygdules within the Group 1 volcanic rocks.

Sample SC04022, a hyaloclasite that shows partly complete hydration to chlorite (90%) and lesser palagonitic clays (Figure 3.1A), contains metamorphosed, previous vitric shards that were composed of fine-grained plagioclase and hornblende. Chloritization of the groundmass displays no foliation. Sample SC04064, like SC04022, is mostly chloritized but contains amygdules filled with calcic plagioclase and quartz that are overprinted by prehnite, pumpellyite, and epidote.

This style of alteration suggests that seawater infiltrated the Group 1 rocks, perhaps while they were still hot (McPhie et al., 1993). Starkley and Frost (1990) described this style of alteration for Karmutsen basalts on Vancouver Island, where hydrothermal metamorphism permeated amygdaloidal flows to trigger the formation of zeolite and epidote assemblages.

5.2 M2: Regional Metamorphism, Greenstone Amphibolite

Nootka Island rocks that are pre to syn- intrusion of the Group 2 granite series magmas exhibit a minimum metamorphic grade consistent with the lower greenschist facies (Figure 3.18). Higher grade metamorphic rocks appear to the west of the Nuchatl shear; the lowest grade metamorphic rocks outcrop east of the Nuchtal shear and north of the Beaver Creek thrust. The degree of metamorphism varies with stratigraphy, affecting rocks that existed at depth and those surrounding the mafic- intermediate intrusions to a higher degree. The uppermost volcanic stratigraphy of Group 2 exhibits very Little evidence of metamorphism, mainly minor chlorite and calcite precipitation in cavities that may not be related to M2. xe 5.2. Xenoliths in a tonalite from station SC04052. The Group I xenoliths exhibit a green color (chlorite) derived from prior sea-floor metamorphism. They produced 'de-watering' zones around them comprising larger crystals that resulted from increased local water contents as water was released from the xenoliths during entrainment and heating. The Group 2 xenolith, demonstrating its plagiophyric and amygdaloidal character, does not have a 'de-watering' zone.

Regionally metamorphosed volcanic rocks appear green-black and form rough surfaces when broken. Chlorite overprints prehnite, pumpellyite, and epidote, comprising amygdules and alteration products after volcanic groundmass. Alteration styles in sedimentary rocks vary with composition but include chlorite after biotite, and quartz precipitation and mobilization. Where evident, fabrics derived during this metamorphic event are parallel to bedding except along the western coastline of the island where the fabrics penetrate and have destroyed other textures. Some of the mafic to intermediate intrusions also experienced greenschist grade. Alteration styles, in addition to chloritization, include seriticitization of plagioclase. The intermediate series rarely contains alteration of hornblende, but commonly has sericitized plagioclase crystals. The granite series intrusions only display oxidized biotites and chloritization along microfractures. Constraining the timing of regional metamorphism is difficult. Of all xenoliths, those exhibiting prior metamorphism comprise less than 20%. However, this does indicate that some regional metamorphic assemblages proceeded or were contemporaneous with the bulk of Jurassic magmatism. Higher levels in the stratigraphy exhibit less greenschist alteration and likely underwent a shorter duration of regional metamorphism, at lower pressures and temperatures or not at all, locally showing only alteration by hydrothermal fluids and contact metamorphism in the vicinity of igneous intrusions.

5.3 M2: Contact Metamorphism, Hornfels/Amphibolite

Stations: SC05052, SC05072

Country rocks were contact-metamorphosed into the hornblende-hornfels and lower amphibolite temperatures as xenoliths, enclaves, or at marginal contact with intrusions. Paralleling the pattern of regional metamorphism, contact metamorphism reached the highest grades at lowest stratigraphical levels. Aureoles around the intermediate series exhibit the widest degree of textures and comprise the majority of contact-metamorphic exposures. Within these zones, structures range from ductile to brittle and agmatitic to veined. Contact rocks of the granite series are brittle, veined, rarely permeated, and reach greenschist grades.

Chlorite may be straight or bent, and exhibits dis-equilibrium crystal structures. Plagioclase grains are almost completely sericitized, and hornblende crystals have patchy pleochroism with broad ranges of interference colors interpreted to be re- organization of the crystal structure. Within zones of contact- amphibolitizationlhornblende hornfels, hornblendes display euhedral growth rims and are in places poikiloblastic.

Xenoliths of previously chloritized material exhibit 'de-watering' margins, wherein prograde metamorphism of the chlorite-rich clasts expelled volatiles into the surrounding matrix that locally increased water contents of the magma and formed hornblende and plagioclase (Figure 5.3). Other contact relations are younger rims of hornblende and plagioclase growths around older crystal cores on edges of xenoliths or country rock (SC04052) and indicate hornblende hornfels metamorphic facies. 5.4 Geothermobarometery

The plagioclase-hornblende geothermometer of Holland and Blundy (1994) provided approximate ranges of metamorphic temperatures for two amphibolites (SC05077, SC05088), a xenolith (SC04052)) and a hornblende-hornfels grade contact rock (SC04072) from Nootka Island. Geobarometers are lacking in the rocks from Nootka Island, however, pressures were estimated using the stability field of magmatic epidote (SC04072), and both aluminium and sodium contents in hornblende (Brown, 1976; Hollister et al., 1987; Johnson and Rutherford, 1989; Schmidt, 1992, Anderson and Smith 1995).

Electron-microprobe analysis by Dan Marshall at CRPGICNRS, Nancy, France, provided data from adjacent hornblende and plagioclase crystals. Albite and anorthite components were estimated using direct ratios of Ca to Na + K. Amphibole formulae were calculated based on 23 0 (+OH+CL+F) (Anderson and Smith, 1995, Blundy and Holland, 1990). The formulae were then normalized to 13 cations of Si+Ti+Fe+Mn+Mg and approximated ~e~'through charge balancing to provide the best approximation for Ca-hornblendes (Essene, 1989; Cosca et al., 1991), listed in Table 5.1. All samples are edenitic hornblendes with an average weight fractions of Fe*l(Fe*+Mg) equal to 0.36 and ~gl(~g+~e")between 0.63 and 0.75.

These amphibole formulae assume fixed crystallographic site preferences for the cations (Cosca et al., 1991; Brown, 1976). The tetrahedral configuration used is

Si>Aliv>Ti>o, where q represents site vacancies, possibly increasing proportionately to Ti (Hollister et al., 1987). The other cation arrangements are Alvi>Ti>Mn>Mg>Fein MI- M3 sites, Fe>Ca>Nain M4, and Na>K in the A site. The charge imbalances were then corrected to estimate ~e~'by assuming ~e~'equal to the inverse proportion of cation excess multiplied by double of the number of oxygens (Cosca et al., 1991). Table 5.1: Calculated Ca-rich amphibole formulae and resulting thermobarometry assuming 13=Si+Ti+Fe+Mn+Mg cations, 23 0, and using charge balance for ~e~' estimation. Refer to text for details. Normalized cations Si Ti A1 Cr ~e~+ ~e~+ Mn Mg Ca Na K Fe3+/Fez+ Fe*/Mg M~/F~'+ Total Pressure (k 6ar): \- , IAH- Anderson & Smith (1995) I 2.059 2.497 3.343 3.1551 9 AH- Schmidt (1 992) I 2.094 2.542 3.875 3.675 9 AH- Johnson and Rutherford (1989) I 1.076 1.474 2.659 2.481

AH- Hollister et a1 (1987) P( +/- I. 0 kbar) = -4.76 + 5.64 ~l(total) NH- Brown (1 976) I 2.260 2.131 3.231 2.952

, , Average Pressure I 1.755 2.092 3.301 3.085 Temperature ("C): at 0 kbar 699 713 730 749 at 5 kbar 661 677 706 716 at 10 kbar 623 641 682 685 at 15 kbar 585 604 659 651 at Averaged Pressure 680 700 720 720 5.4.1 Hornblende Barometry

The four aluminium-in-hornblende (AH) barometers used in this study rely on the edeniteltschermakite components of plagioclase and hornblende, where Ca, Na, and Al partitioning are largely controlled by pressure, and Al is the essential pressure indicator. An additional hornblende barometer from Brown (1976)- referred to as the NH or crossite barometer- relies on the amount of Na in the M4 site to indicate pressure of metamorphism. Early theoretical AH barometry (Hammarstrom and Zen, 1986; Hollister et al., 1987) was improved by requiring a buffered assemblage (Johnson and Rutherford, 1989) and further experimentation (Schmidt, 1992; Anderson and Smith, 1995; Ague, 1997). Early attempts at AH barometry failed to consider the distribution of Al as dependent on temperature (Holland and Blundy, 1994). Likewise, early attempts by Johnson and Rutherford (1989) considered the assemblage in the presence of fluid phases but this rendered their barometer only useful for temperatures greater than the wet solidus of granite. Subsequent calibrations of the barometer accounted for this problem and became more robust over a greater range of temperatures: Anderson and Smith (1995) modified Schmidt's (1992) work to eliminate a fluid phase, thereby extending the union of pressure, hornblendes, and aluminium over a wide range of temperatures and becoming the most likeable candidate for this study.

Ague (1997) verified the reliability of Johnson and Rutherford's (1989) barometer at higher temperatures and Schmidt's (1992) at lower temperatures. Using a solidlsolid reaction of quartz-mica-hornblende-two feldspars, Ague (1997) eliminated the dependency on f02and found general agreement among his and other researcher's barometers.

Regardless of the barometer used, their application to metamorphic assemblages requires assumption that the hornblende formed under relatively dry and buffered conditions (Ague, 1997). Constraining fluid activities are essential in dictating whether metamorphic hornblendes make appropriate barometers and the fluid parameters of Nootka Island metamorphism are not well known. It is possible that the hornblendes in the metamorphosed Nootka rocks were internally buffered by the plagioclase, magnetite, and titanite present in the assemblage, though the latter two are present in very marginal amounts.

Anderson and Smith (1995) suggest three restrictions on the application of hornblende barometry. (1) Hornblendes that have been buffered appropriately have a lower limit

of Fe3'/ (Fe2'+Fe3') = 0.25, and a value of Fe*/ (Fek+Mg)between 0.40 and 0.60. Higher ratios of Fea/ (Fe^+Mg)indicate significant Fe3'-~l,i exchange and a defective barometer. (2) Samples without titanite and K-feldspar may still be likely candidates for geobarometry because neither significantly alters pressure determinations. (3) Samples failing either of the above should use additional barometers to verify pressures.

The Nootka lsland hornblendes have lower Fe*/ (Fe*+Mg)values than Anderson and Smith (1995) recommend, from 0.31-0.38, but the values are considered too low to allow for Fe3'-~l,i exchange. The Nootka lsland hornblendes have an acceptable range of Fe3'/ (Fe2'+Fe3') for analyses, from 0.25 to 0.50. These levels of Fe2' Fe3' suggest that amphibolite metamorphism occurred in an environment with acceptable f-O2 levels for AH barometry.

Figure 5.3 displays the results from four aluminium-in-hornblende barometers and the additional crossite barometer (NH) of Brown (1976) using data from Table 5.1. Relative agreement exists among all of the barometers and indicates greater pressures on the western side of Nootka lsland compared to those in the east. In the author's opinion, the barometer of Anderson and Smith (1995) is most accurate in accordance with their barometer's sensitivity to temperature variations and having eliminated dependencies upon fluid phases. )Indkrson d~mith(1995) + Schmdt (1992) Johnson oZ ~utheford(1989) A Kolihkter et al(1987) Brown (1976) Figure 5.3: Hornblende barometry for Nootka Island. Adjusting Brown's barometer (arrow) yields a lower Na-Hbl estimate for sample SC04052 if assuming vacancies are introduced with excess TiOz. Samples are arranged from west (left) to east (right) across the Nuchatl shear.

The NH barometry values lie within error margins of those that use aluminum. NH barometry of sample SC04052, however, produced an anomalous value, probably due to its excess titanium. Adjusting the barometer regarding an assumption of a 1:10 integration of vacancies with substitution of Ti for Aliv in the tetrahedral site (Hollister et al., 1987) produced more accurate results. The adjustment had minimal effect on the calculated pressures for samples SC04072, SC05077, and 5C05088, but lowered the estimate for 5C04052 by 1.0 kbar. A relationship between increased Ti concentration within metamorphosed hornblendes has been recognized for other Ca-rich hornblendes from Vancouver Island (Terabayashi, 1993).

5.4.1.1 Magmatic Epidote

Magmatic epidote was previously thought to be an indicator of high-pressure environments, but is now recognized at lower pressures in the presence of elevated f- O2 (Figure 5.5; Bird and Helgeson, 1980). For example, a solidus tonalite can grow epidote at pressures in excess of 3.0 kbar in a system where f-O2 is buffered by a solidus magnetitelhematite exchange (Schmidt and Poli, 2004; Figure 5.5). Introduced C-0-H-Sfluids at an intrusion margin can also result in a higher oxygen fugacity at Low pressures and allow for epidote crystallization. Common mineral assemblages that contain magmatic epidote are plagioclase, hornblende, biotite, microcline, and quartz, where the timing of epidote in the crystallization sequence is delayed at low pressures (Schmidt and Poli, 2004).

There are two distinct observed settings of magmatic epidote on Nootka Island. The first, indicated by sample SC04072, is present at the margin of an unaltered tonalite near the contact with metamorphosed Group 1 basalts. The crystallization sequence was plagioclase, hornblende, epidote, and lastly quartz, placing epidote growth late at high fugacities and pressures somewhere below 5.0 kbar (Schmidt and Poli, 2004; Figure 5.5). AH and NH barometry on this sample suggests pressures as low as 1.4 kbar (see Section 5.5.3 below), indicating the system must have had, or developed, high oxygen fugacities to stabilize epidote crystallization or carried the epidote from deeper levels in the crust.

Figure 5.4: Magmatic epidote, sample SC04072. Temperature ('c) Figure 5.5: Magmatic epidote phase diagram for a tonalite, modified from Schmidt and Poli (2002). Shaded region corresponds to the phase assemblage in sample SC04072. Arrow shows motion of stability field in presence of increased O2 fugacity (see text).

The second setting for magmatic epidote lies within pegmatitic segregations formed in many of the hornblende gabbros from Nootka Island (Series 1). The mineral assemblage in these settings is almost entirely hornblende, plagioclase, and epidote. The variance within and random occurrence of the pegmatitic segregations precludes any reliable determination of pressure, temperature or f-02.

5.4.2 Plagioclase-Hornblende Thermometry

Temperatures for the Nootka metamorphic rocks were calculated using the HB-PLAG program developed by Tim Holland following the work of Holland and Blundy (1994). They tested the temperature solutions from this method against 215 natural mineral pairs that had well-constrained temperatures and pressures by other methods and quote errors of +/- 40' Celsius. The intent of the analysis is to use chemistries of co- existing hornblende and plagioclase crystal pairs to estimate temperatures for crystal formation by observing Ca and Na exchanges at different temperatures. Generation of temperature solutions depends on, for this study, the edenite + (4) quartz = tremolite + albite equilibrium, because richterite is a minor phase of all Nootka metamorphic hornblendes (Holland and Blundy, 1994).

5.4.3 Results

Figure 5.6 displays the results from Nootka Island thermobarometric analyses. The linear, pressure-independent hornblende-plagioclase thermometers after Holland and Blundy (1994) are shown as vertical bars. Overlying these are approximate pressures derived by hornblende barometry. The PT ranges given by both hornblende analyses align well with predicted range of magmatic epidote pressure estimates.

Thermobarometry of Nootka rocks indicates maximum temperatures near 700-720" Celsius and averages of 3.2 and 2.2 kbar, west and east of the Nuchatl shear, respectively. Because the metamorphic rocks comprise surface deposits as well as intrusions, exposed strata must have been buried to approximately 9 km. Furthermore, the youngest involved strata are of Jurassic age and cut by a basalt dyke that cooled at 168 Ma. An approximate counter-clockwise PT path for Nootka metamorphism starts at low pressure with rising temperatures during intrusion of the hornblende gabbros, followed by higher pressures resulting from burial by deformation, then relaxation of both pressure and temperature during uplift and exhumation. This type of path is concurrent with regional arc metamorphism in a collision-zone setting and is consistent with determinations from the study area (Bucher and Frey, 2002). Temperature "~ekius Figure 5.6: Geothermobarometry and PT diagram for select Nootka Island samples. Vertical fields are from hornblende-plagioclase thermometry and the horizontal dashes constrain barometry averages. Also shown are magmatic epidote stability field and counter-clockwise path (arrow) displaying collisional arc magmatism. CHAPTER 6: STRUCTURE

The regional structure of Vancouver lsland trends northwesterly as expressed by faults, folds, and elongate intrusions. Anticlinoria control the stratigraphy exposing the oldest material in their cores and within south-central Vancouver Island. Nootka lsland geology, as the northern-most portion of the Westcoast Crystalline Complex, compliments the regional north-northwest trend.

On outcrop, parasitic folds are useful indicators of the larger features. Brittle features like fractures and joints often overprint early fabrics from ductile strain along axial planes. The earliest deformation produced tight folds, the axis of which being largely parallel with bedding. Other features on the island are more localized, surround intrusions, and probably resulted from the 'room problem' (Winter, 2001) and strain partitioning around cooled intrusions during translation.

At least five episodes of deformation are likely to have affected Nootka lsland rocks. The first four episodes created the most visible effects on Nootka lsland and are displayed in Figure 6.1 and Figure 6.2. The first episode (Dl) created tight northwest- southeast trending folds and an inferred major thrust fault to the west of Nootka Island. S1 foliations are sub-parallel to bedding (So) except near the southwest, where So disappears and motion indicators suggest Nootka rocks were on the footwall of major dextral thrust fault. The second event (Dz) refolded the earlier strata into elongate dome-and-basin Fz interference patterns and uplifted blocks along reverse faults. D3 represents relaxation in the crust as oblique extension and contains the most dominant shear zone on Nootka Island: the Nuchatl shear. Steep D4 dextral shears further dismembered small portions of Nootka Island. Figure 6.1 : Equal-area stereonet plots illustrating the history of Nootka Island deformation. Dl displays bedding and S1 foliations. D2 shows reverse faults, the axial planes for the F2 folds are assumed to be parallel. Three measurements for the Nuchatl shear and one from a chlorite schist (SC05089) are shown in D3. D4 represents vertical planes and late dextral shearing. Figure 6.2: Block diagram showing the deformation of Nootka Island rocks: white, gray, and dark gray represent Group 2 and 2b, Group 1, and basement strata, respectively. The black arrows indicate direction of principal stress. At Dl, the model is located on the footwall side of a thrust, shown here in approximate location (see text). D4 shows the orientation of late dextral transverse shears. This block is later uplifted and tilted to the northeast during D5. Scale is general- block heights are roughly equivalent to 10 kilometres. 6. I Dl- Northeast Directed, Dextral Compression

The oldest and most widespread episode of deformation involved most of the strata on Nootka Island, exluding some of the intermediate series intrusions, the granite series intrusions, and other strata 168 Ma and younger. This event created penetrative fabrics that trend along the western coastline and indicate compression to the northwest, corresponding with M2 metamorphism. Dl is likely related to regional docking-related deformation observed elsewhere on Vancouver lsland where thickening of the crust resulted in folding, metamorphism, and detachment of the Nootka Island rocks from the underlying crust (Yorath et al., 1999).

The Dl event indicates that rocks exposed along the western margin were proximal to a zone of intense deformation. Tight folds (F,) produced by the Dl event, since re- folded into a dome-and-basin pattern by D2, have vertical to steep axial planes that generally align with S1 fabrics. The S1 fabrics are most penetrative along the western margin of Nootka Island where they overprint older textures. Two examples of this fabric are samples SC05077, from the western coastline, and SC0401 IA, located 2.0 kilometers eastward across an F1 anticline (Figure 6.3; Appendix D). The metamorphic textures include S, C, and C' fabrics defined by hornblende porphyroblasts and quartz crystallization in pressure shadows.

Figure 6.3: Dynamic amphibolites indicating regional deformation. Orientation of the photos is looking to the northwest. Samples are SC05077 (left) and SC04011 (right). C and C' fabrics are visible in SC05077. Fabrics in SC04011 are less visible and less pervasive due to its location more distal from the deformation. Inset displays dotted lines that match broken cleavage traces resulting from brittle, sinistral rotation that occurred after the Dl event. 6.2 DZ- Northwest Directed Compression

The second episode of deformation was directed to the northwest, though the presence of some east-west striking features suggests transition and overlap of Dl and D2. Results from the second episode of deformation are broad folds, reverse faults, and an elongate dome-and-basin fold interference pattern throughout Nootka Island from refolding of all prior strata. D2 lacks a corresponding S2, probably due to its gentle character.

F2 folds strike approximately northeast-southwest and are open and asymmetric. Their fold axis are sub-horizontal as indicated by rare F2 axial cleavages. The fold axes parallel a thrust fault that occurred toward the end of D2 and cuts most F2 folds. The fault, the Beaver Creek thrust, is only directly exposed on the hillside north of the Kendrick lnlet and at the mouth of Gunpowder valley as a band of iron-stained sheared rock. More numerous indicators of the thrust fault are thin fault planes that display thrusting motion and dip from 20- 40•‹SW. Other accompanying features are increased concentration of fractures, shift of lithotype locations across the fault plane, and preferential erosion. Where visible, the thrust displays a brittle, anastomosing, and brecciated character with a throw of 400 meters or less determined by the proximity of displaced features.

It is likely that the D2 event represents a change from orogen-orthogonal to orogen- oblique compression, reflecting transition in the east from a convergent margin to a dextrally transverse one. Two basalt dykes that cut a D2 fault west of the Tahsis lnlet limit timing of this event. The dykes are mesoscopically identical to sample SC04019.3, restricting local D2 deformation to approximately 168.0 Ma or older.

6.3 D3- South/Southeast Extension, Dextral

The third episode of deformation (D3)developed the Nuchatl shear and flanking greenschists (SC05089; Figure 6.4). It was oblique extensional, affected all Jurassic and older rocks on Nootka Island. It is traceable for the majority of its strike, both in the field and on aeromagnetic maps. The Nuchatl shear is a brittle fault/cataclasite (Muller, 1980; Ramsay, 1987) that strikes 320" northwest and juxtaposes the lower portion of an F1 fold on the west containing the highest grade of metamorphic rocks with the upper portion of the same fold containing slightly lower metamorphic grades on the east. It vanes from vertical to northeast dipping, averaging 50" and up to 70 meters in width. Slickensides within the shear zone indicate dextral, normal movement with a rake of 40" southwest. Supporting this dextral motion are sigmoidal quatz boudins in flanking phyllite schists most visible at station SC05089.

Figure 6.4: Northwestern extent of the Nuchatl shear at the mouth of the Nuchatlitz Inlet. Sub-vertical green epidote veins and lenticular zones within the shear are easily exploited by erosion and form abundant voids along coastal exposures. Figure 6.5. Late stage hydrothermal fluids caused epidotization along fracture sets, seen here in a plagiophyric Group 2 basalt north and east of Crawfish Lake near SC04072.

The amount of displacement along the Nuchatl shear is not evident from field observations. However, indications for displacement do exist when restoring the southwestern and northeastern portions. From Figure 6.2, the two prominent F2 folds in the map view become aligned sub-vertically, placing the southwestern portion beneath the southeastern side. This geometric alignment also agrees with the expected increase of metamorphic grade with depth, wherein rocks of the southwestern portion underwent the highest metamorphic pressures. Assuming this reconstruction, the Nuchatl shear had 15 kilometers of displacement along rake with a heave of 12 kilometers. Given that the barometry of the amphibolites to the west indicate only 3.2 kbar +/- 0.6, approximately equal to 9 kilometers depth, the two are in general agreement. Hydrothermal fluids related to this event exploited joints and fractures parallel to the Nuchatl shear. They are best visible as epidote alteration aureoles around fracture and joint sets (Figure 6.5). Occasionally, hydrothermal fluids are expressed as individual epidote/calcite/chlorite veins that wander through the country rock within and to the southwest of the Nuchatl shear. These veins cut Dl and D2 features, strike northwest-southeast, and may have resulted from decompression of meteoric fluids during extension and uplift.

6.4 D4- North-South Dextral, Transverse Shears

The D4 features cut all stratigraphy on Nootka Island. They are expressed as strike-slip shears and are flanked by Mode 1 calcite veins (Ramsay, 1987). The shears are dextral, striking north-south with less than 1.0 kilometre of displacement by field evidence. The calcite veins strike generally east-west and dip steeply. The displacement of Carmanah Group sediments at D4 tension shears and dissection by the calcite veins confine development and motion of the D4 features to late Oligocene.

6.5 D5- Regional Uplift and Tilting

D5 may be coeval with D4, as uplift and deformation of the Carmanah Group sediments, formerly deposited in a submarine setting. Gentle folds within the Carmanah sediments indicate northeast-directed compression. Thickening of the Carmanah sediments southerly along the coastline indicate an ancient basin that now lies exposed along the western and southern flanks of Vancouver Island, perhaps in response to subduction-related processes (Yorath et al., 1999). The tilting is probably in the range of a few degrees; more research is needed to constrain this motion.

6.6 Other

Many small veins, shears, and fractures exist on Nootka Island. Two northwest- southeast striking shears, trending north-northwest and located on the eastern side of the Nuchatl shear, appear to have little displacement along them. They cut D2 features but are themselves cut by D3. These may be correlative with the overlap of Dl and D2, wherein northeast-directed compression of Dl existed after the initiation of D2. CHAPTER 7: TECTONIC SYNTHESIS AND DISCUSSION

This chapter provides an annotated timeline of the genesis of Nootka lsland as it relates to the surrounding regions. Considered herein are the stratigraphic, geochemical, structural, and genetic relations that tie the formation of Nootka lsland and Wrangellia from the Triassic through active volcanoplutonism in the early Jurassic to obduction to the North American continent (Figure 7.1 to Figure 7.4).

7.1 Comparison of Nootka and Regional Wrangellia Stratigraphy

Though Group 1 lacks the distinguishing plagioclase glomerocrysts present in most lithofacies of the Karmutsen Group, both display a tholeiitic and MORB-like signature. The overall nature of LlLE and HFSE of the Group 1 rocks additionally indicate that Group 1 is equivalent to the Karmutsen Formation.

The Group 2 volcanics display an island arc-tholeiite to calc-alkaline array of basalts, correlative with either the Devonian Sicker or Jurassic BonanzaITalkeetna volcanic rocks. An absence of regional metamorphism in the upper strata of Group 2, and superposition of Group 2 over Group 1 suggest that Group 2 is correlative with the adjacent Jurassic BonanzaITalkeetna volcanic rocks rather than the Devonian Sicker Group.

As discussed in Chapter 5, the three series of intrusions are co-magmatic and co- genetic with the Group 2 strata. The intrusions show arc-like signatures, span Dl- the most recent duration of intense deformation and metamorphism (Chapter 4 and Figure 7.1), and thus are likely equivalent to the other Jurassic arc-related intrusions of the Jurassic lsland Intrusive Suite (Muller, 1981; Yorath et al., 1999; DeBari et al., 1999) and form a Jurassic volcanoplutonic arc with the Group 2 volcanics.

The elements of Nootka lsland that have a more tentative correlation with adjacent Wrangellia are the Group 2b strata and its anomalous anorthosite (SC04071). Strata of Group 2b overlie Group 1, are intercalated among the upper most Triassic Ewart and Crawfish groups, and lie at the base of the overlying Group 2 volcanics. Though they display depletion in the HFSE relative to other Wrangellia and local rocks, the defining characteristics of the Group 2b units- plagiophyric textures and LlLE concentrations that parallel regional strata- indicate they may be the formative base of the Group 2 volcanics. The Group 2b rocks were perhaps derived from the first impulse of crustal anatexis during initiation of the Jurassic arc before involvement of fluids from the mantle wedge.

The overall concentrations of LlLE and HFSE within Groups 2 and 2b are lower than any other volcanic group in Wrangellia; the closest are those of the Talkeetna volcanics (Clift et al., 2005a, b). The lower LlLE concentrations in Groups 2 and 2b indicate less of a contribution from a slab-generated source than for the BonanzaITalkeetna arcs. The lower concentrations of the HFSE within Groups 2 and 2b indicate sourcing from a mantle depleted in the HFSE relative to the mantle source for the BonanzaITalkeetna arc magmatism. The reasons for this relationship is not yet understood.

The sediments of the Ewart and Crawfish groups also display an apparent relationship to the uppermost components of the Triassic Vancouver Group, principally due to stratigraphic controls and loosely supported by the isotope analysis in Figure 4.10. Together, their deposition, position, and style represent a marine environment, spanning the time of quiescence between volcanic episodes (Crawfish group and SiltISand facies) to the initiation of Jurassic magmatism- indicated by the volcanoclastics within the Boston Point facies. Thus these units may be correlative with the late-Triassic Quatsino and Parson Bay Formations (Yorath et. al., 1999). I! M5 -4 .2. ; Late Triassic Ear5 Jurassic NifiJurassic Eocene/Ofigocene A 2Q0 168 158 54 I ,, Z I I d. 3 V' 0 Z/ancouver Group @onanzaflafketna % @gionacActivity rr wcc Tr r m z o -group 2 Z/okanics Cannanah Group group 26 ShallFhws % ~okanismand - -P Sedmentatwn -Ewart group Crawfish group k3 a Group 1 QasaCts r?m 2 gn - - 3. ,#northosite? granite Series p Intermedzate .Yeries Plutonism

-- (Dl (D2 (D3 5442 Netamorphism Ear4 to Late Triassic

...... - ...... Vancouver..._ ...... _.._._ Group.... I . .

Figure 7.2: Tectonic synthesis of the formation of Nootka Island, Devonian to late Triassic period. Ear6y Jurassic - 200 Na 7-

Figure 7.3: Tectonic synthesis of the formation of Nootka Island, early to mid Jurassic period. Late Jurassic - Cretaceous

--- Coast Hitonic Compks

Eocene- Ofigocene

Figure 7.4: Tectonic synthesis of the formation of Nootka Island, mid Jurassic period to Oligocene epoch. 7.2 Triassic: 230-200 Ma

In the late Triassic, basalts of the Karmutsen Formation effused onto the older island arc and sediments of the Sicker and Buttle Lake Groups. They constructed a massive pile of homogenous flows, forming a wide expanse of recognizable facies that extends the length of the Wrangellia exotic terrane. Near the top of the sequence and close to the end of the Karmutsen volcanism, in the study area, the frequency of the flows slowed. Minor lenses of sediment began to develop, and in some instances are encompassed within the flows themselves as chloritized and epidotized nodules/xenoliths. Minor amounts of palagonite clays are also observed. Quenching of some flows resulted in formation of hyaloclastites and later seawater infiltration resulted in widespread chlorite alteration (MI). Glass shards, internal brecciation, and chlorite characterize the textures and alteration products of local Group 1 basalts.

The end of the Triassic volcanism is marked by the accumulation of Vancouver Group limestones and sediments (Quatsino and Parson's Bay Formations). Locally, these units have a thin and distinct character (Crawfish and Ewart groups). In sequence, the environment underwent a transition upward from carbonate (Crawfish group) to silicic (Ewart group). Within the Ewart group the sediment size coarsened upwards. Individual units from bottom to top include: the cryptorythmic calc-argillites and upper silts of the SiltISand facies, the volcanogenic sands of the Boston Point facies, and possibly a few anomalous beds of the maroon tuffs of the Laurie Redbed facies.

7.3 Jurassic: 200-168 Ma

This time interval includes the bulk of intrusions, flows, and metamorphism present on Nootka Island. Care is taken to separate out the individual events though many overlap. Age relationships for the initiation and cessation of most events are imprecise. Four primary events happened during this time interval: 1 ) formation of the Group 2/2b volcanoplutonic arc resulting from nearby subducting material, 2) Dl deformation and Mz orogenic metamorphism, 3) emplacement of the granite series intrusions, 4) D2 deformation and hypabyssal dyke activity. Early in the Jurassic is the first pulse of calc-alkaline magma (DeBari et al., 1999), formed above subducting crust, that reached the surface and intruded into and over the Crawfish and Ewart group sediments. The plutonic equivalent for the Group 2b strata was an anorthosite, likely co-existing with or fractionated from the hornblende gabbro and intermediate series intrusions of Group 2. Flows and tuffs of Group 2 continued to accumulate on the surface.

Affecting all rocks of Group 1, 2b, the hornblende gabbro series, and some of the Group 2 strata, was a large north-west directed thrust fault (Dl) west of Nootka lsland that placed all of Nootka lsland at lower crustal levels and produced tight northwest- trending folds. Sustained temperatures (720' C), pressures (2.5-3.2 kbar), and arc activity of the intermediate series intrusions induced regional and contact metamorphism (amphibolite-hornfels). This event may be representative of regional obduction to the North American plate and detachment from the underlying crust- the style of folding that affected Nootka lsland rocks compliments the regional trend of Vancouver lsland a significant northwestward portion of Wrangellia.

Continuing Group 2 arc magmatism resulted in the granite series intrusions that overprinted Dl and D2 features, intruding into Group 2 extrusive flows and lithic tuffs at elevations in the crust unaffected by regional metamorphism. The second pulse of Jurassic magmatism recognized by DeBari et al. (1999), from 170 to 165 Ma, correlates well with the relative timing of the granite series intrusions observed on Nootka Island.

The direction and intensity of regional compression changed during the emplacement of the granite series to a northward-directed compression (D2)that uplifted the southern portion of Nootka lsland and created the Beaver Creek thrust. Numerous basalt dykes punctuated the end of the deformation: one of the basalt dykes at Beaver Creek (SC04019.3) was 40/39~rgondated at 168 +I-5.5 Ma.

7.4 Jurassic: 168 Ma to Eocene

Jurassic volcanoplutonic activity on Nootka lsland had ended by this time though elevated temperatures continued, evidenced by the thermally reset 158 +I-2.5 40/39~rgondate of the Group 1 hyaloclastite (SC04022). The most significant feature that developed during this time was the Nuchatl shear (D3)that occurred in response to regional extension. The Nuchatl shear, a major northwest-southeast striking, oblique-slip shear zone, juxtaposed an upper-crust section on the eastern half of Nootka Island against a lower-crust section on the west. Accompanying the movement along the shear was formation of greenschists and syn-tectonic tension gashes.

7.5 Eocene-Oligocene

The deposition of the Carmanah Group sediments constitutes the sedimentation within the Eocene and Oligocene epochs. These units strike along the western coast of Nootka Island and rest unconformably over older strata. The Carmanah Group contains a lower formation of conglomerates (Escalante), a middle formation of siltstones (Hesquiat), and a capping sequence of conglomerates (Sooke Formation). This group was deposited in a marine environment and represents local transgressive high stand (Cameron, 1980).

Oligocene or later uplift resulted in gentle folding and exposure of these marine sediments, possibly due to regional tilting to the northeast. Further dissection of the sediments and underlying rocks consisted of north-south striking shears. CONCLUSIONS

The observations and research undertaken as part of this study suggest that Nootka lsland formed in a setting similar to that described for the adjacent exotic Wrangellia terrane. However, due to limited outcrop exposures revealing contact relationships, Nootka lsland stratigraphy retains an informal description-based nomenclature until further research provides additional comprehension.

The Group 1 strata that form the base of the exposed rock on Nootka lsland are likely a discontinuous upper portion of the Vancouver Group: plateau basalts of the Karmutsen Volcanics with minor beds of marine sedimentary rocks. The volcanoplutonic rocks of Groups 2 and 2b share arc-like trace element signatures and concentrations similar to the Bonanza and Talkeetna arcs that formed during the early Jurassic period. Depletion of the immobile elements within Group 2b lithotypes relative to the overlying Group 2 volcanic rocks suggest arc magmatism commenced with melts that lacked a mantle-derived component. Continued subduction and volcanoplutonic activity resulted in the Group 2 rocks containing contributions from both the crust and the mantle. Similarily, major oxide concentrations within the Group 2 and 2b rocks trend from island arc theoleiites to calc alkaline, respectively.

Data derived during this research suggests that the Nootka lsland portion of the Westcoast Crystalline Complex involves deformed Triassic to Jurassic coherent and clastic rocks. Deformation and metamorphism of these rocks reached 720' Celsius and 3.2 kbar as measured by hornblende-plagioclase thermometry and Al and Na-in- hornblende geobarometry. Penetrative fabrics in the deformed strata are most pervasive in the areas containing the highest metamorphic grade, both trending along the western coastline. These fabrics are refolded by D2 folds and cut by basalt dykes that together constrain timing of deformation and metamorphism to 168 and 158 Ma, respectively. This deformation likely happened during convergence of the exotic Wrangellia terrane to the North American continental margin. A melange, formed at depth along the western margin, originated during compression and subsequent detachment of the Nootka lsland rocks Rocks emplaced to 3.0 km during this compression were translated northward, evidenced by the D2 event, and exposed along the Nuchatl shear during collapse of the thickened pile. Postdating Oligocene Carmanah Group sedimentation was an episode of compression that produced brittle shearing, folding, tilting, and uplift. This Latter event may have resulted from addition of the Pacific Rim and Cresent terranes to the lnuslar accretionary package. REFERENCE LIST

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78 Plagiophyric Basalt Sill x 78 Green Calc-Argillites wl Basalt Dyke 78 Carbonates-Limestones, Orange & Gray 79 Limestones 80a-c Spanish Islands Argillites, sands 8 1 AmphiboliteIGneiss Mesosome x 82 Assorted Metasediments +I- Garnet x 82 Tonalite 82 Sheared Basalt Dyke 84 Boston Point Metasediments x

Appendix B- Major and Trace Element Data

Sample Easting Northing FeO MnO CaO SC04013 657943 5506500 10.56325 0.182 9.73 SCO4Ol9.l 664786 551 1065 7.58756 0.143 9.44 SCO4Ol9.2 664784 551 1063 1.58224 0.014 1.48 SCO4Ol9.3 664785 551 1064 9.1 4283 0.1 7 7.93 SC04022A 660444 5508802 11.I 1 I64 0.159 10.57 SCO4022B 660445 5508803 11.0577 0.159 10.59 SC04024A 658038 5509394 2.741 95 0.084 2.55 SCO4024B 658039 5509395 2.697 0.082 2.52 SC04031 660889 551 5400 9.39455 0.159 5.85 SC04047 661 779 5504364 9.1698 0.146 7.22 SC04061 660224 5509331 7.53362 0.136 9.25 SC04070 667049 55041 21 9.5294 0.179 10.27 SC04071 665500 5502973 5.53784 0.082 14.66 SC05076 646100 5521 000 9.83506 0.2 9.68 SC05077 648200 5509450 8.8281 8 0.1 7 9.03 SC05078 663100 5499200 8.61 242 0.15 9.15 SC05081 672050 5496100 9.92496 0.2 11.22 SC05085 666000 551 1900 8.66636 0.14 9.06 SC05086 658850 5505800 7.65948 0.1 3 8.06 SC05088 658270 5505500 9.73617 0.24 5.98 SC05091 657950 5506505 6.60765 0.1 10.44 SC05102 671000 5506600 10.6981 0.1 7 11.73 SCO5105 660444 5508802 11.3274 0.1 7 10.65 SCO5106 666500 5525200 12.35226 0.24 8.84 Sample SCO4O 13 SC04019.1 SCO4Ol9.2 SCO4Ol9.3 SC04022A SC04022B SC04024A SC04024B SC04031 SC04047 SC04061 SC04070 SC04071 SC05076 SC05077 SC05078 SC05081 SC05085 SC05086 SC05088 SC05091 SC05102 SC05105 SC05106 Sample SC04013 SC04019.1 SC04019.2 SC04019.3 SC04022A SC04022B SC04024A SC04024B SC04031 SC04047 SC04061 SC04070 SC04071 SC05076 SC05077 SC05078 SC05081 SC05085 SC05086 SC05088 SC05091 SCO5lO2 SC05105 SC05106 Error Analysis, Using Samples SC04022, SC04024, and Duplicates

Si02 Ti02 A1203 FeOT MnO MgO CaO Na20 K20 P205 AverageStdDev 0.74 0.01 0.12 0.09 0.01 0.12 0.03 0.11 0.02 0.01 % of Whole 0.28 0.39 0.48 0.76 0.85 0.05 0.49 0.15 7.98 2.44

Ba Be Ce Co Cr Cs Cu Dy Er Eu Ga Gd Average Std Dev 11.04 0.00 2.35 12.76 70.30 0.02 25.32 0.22 0.14 0.06 0.49 0.29 % of Whole 0.37 0.00 5.81 13.30 8.92 1.884 1.88 1.95 0.78 1.49 2.78 2.38

Hf Ho La Lu Nb Nd Ni Pb Pr Rb Sc Sm Average Std Dev 0.08 0.04 0.90 0.02 0.06 0.88 2.66 2.67 0.23 0.84 0.91 0.19 % of Whole 2.57 0.64 5.03 1.45 1.35 4.95 9.69 30.50 4.67 1.69 0.56 2.70

\o k Sr Ta Tb Th Tm U V Y Yb Zn Zr AverageStdDev 5.32 0.01 0.03 0.15 0.03 0.01 79.37 1.09 0.09 20.12 7.03 % of Whole 0.86 1.37 0.24 1.19 0.83 0.69 2.13 3.87 1.22 3.72 3.83 Appendix C- Whole-Rock "~r/~'~rData

Laser Isotope Ratios Power(%) 40Arl39Ar O/040Ar atm

96.3 85.77 74.47 67.77 31 55 25.36 22.72 34.59 51.39

Volume 39ArK = Integrated Date =

Volumes are 1E-13 cm3 NPT Neutron flux monitors: 28.02 Ma FCs (Renne et al., 1998) Laser Isotope Ratios Power(%) 40Ar139Ar 37Arl39Ar 36Ar139Ar CalK CllK Oh40Ar atm f 39Ar 40Ar*/39ArK Age

J = Volume 39ArK = Integrated Date =

Volumes are 1E-13 cm3 NPT Neutron fiux monitors: 28.02 Ma FCs (Renne et al., 1998) Laser Isotope Ratios Power(%) 40Ar139Ar %40Ar atm f 39Ar

Volume 39ArK = Integrated Date =

Volumes are 1E-13 cm3 NPT Neutron flux monitors: 28.02 Ma FCs (Renne et al., 1998) Appendix D- Maps

Figure B. 1 Nootka Island Field Locations This shaded digital elevation model (DEM) was built using ArcGlS and base raster data on BC MapPlace website developed for public use by the British Columbia Ministry of Energy, Mines, and Petroleum Resources. Original data is the work of Bruce Mackenzie, Geosense Consulting, Nelson, British Columbia. Figure B, 2 Nootka Island Aeromagnetism The aeromagnetic data to which the Mootka Geology is compared is provided by the BC MapPlace website, developed for pub& lase by the British Columbia Ministry of Energy, Mines, and Petroleum Resources, Prom data prodded by Warner Miles of Government of Canada, Natural Resources Canada, Geologkal Survey of Canada-Ottawa. Figure B. 3 (Followin# page). Geologic Map of Nootka Island. -- Unconformrtd' ~eologicNap dVootka IsCand ---.Contact, Inferred ...... Contact. Projected tHAntiform .. -, .- . . Fault. Undefined .Wrters - A - - Thrust Fault. Approximate; ----- Extensional Fault ;' 0 2, 500 5,000 10,OOO -I-. Extensional Fault, Inferred L