Pleistocene Volcanism in the Anahim Volcanic Belt, West-Central British Columbia

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2014-10-24 A Second North American Hot-spot: Pleistocene Volcanism in the Anahim Volcanic Belt, west-central British Columbia

Kuehn, Christian

Kuehn, C. (2014). A Second North American Hot-spot: Pleistocene Volcanism in the Anahim Volcanic Belt, west-central British Columbia (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/25002 http://hdl.handle.net/11023/1936 doctoral thesis

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UNIVERSITY OF CALGARY

A Second North American Hot-spot: Pleistocene Volcanism in the Anahim Volcanic Belt,

west-central British Columbia

Christian Kuehn

A THESIS

SUBMITTED TO THE FACULTY OF GRADUATE STUDIES

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE

DEGREE OF DOCTOR OF PHILOSOPHY

GRADUATE PROGRAM IN GEOLOGY AND GEOPHYSICS

CALGARY, ALBERTA

OCTOBER, 2014

Abstract

Alkaline and peralkaline magmatism occurred along the Anahim Volcanic Belt (AVB), a 330 km long linear feature in west-central British Columbia. The belt includes three felsic shield volcanoes, the Rainbow, Ilgachuz and Itcha ranges as its most notable features, as well as regionally extensive cone fields, lava flows, dyke swarms and a pluton. Volcanic activity took place periodically from the Late Miocene to the Holocene. A systematic decrease in the ages of individual centres from the western part of the AVB to its eastern end is interpreted as the effect of a hot-spot underlying the Interior Plateau of British Columbia. Other hypotheses for the existence of the AVB include regional extension, a plate edge/slab window effect along the northern edge of the subducted Juan de Fuca/Explorer plates, and a fracture propagating west to east. In this study, I first summarise existing works to provide a context for AVB volcanism.

Then I report new whole-rock geochemical data and 40Ar/39Ar age determinations for two previously little-studied cone fields around Satah Mountain and Baldface Mountain in the central part of the AVB. Individual volcanic centres in these fields are generally small in extent and volume and most have been heavily modified by glacial erosion. These centers are compositionally heterogeneous but overall the lavas erupted in either field are similar to those erupted from the larger Itcha Range shield volcano nearby. Rock types include minor alkali basalts and basanites (44−52 wt% SiO2), but more evolved trachyandesites, trachytes and phonolites (59−64 wt% SiO2) are the most abundant lithologies. Timing of volcanism in the

Satah Mtn. field is constrained by 11 40Ar/39Ar ages which indicate volcanism between 2.21 and

1.43 Ma; in the Baldface Mtn. field, seven age data indicate volcanism from 2.52 to 0.91 Ma.

The data further indicate that volcanic activity in these fields was, at least partially, coeval with the Itcha Range. These new data provide additional support for the mantle plume/hot-spot

ii hypothesis, the only hypothesis that accounts for both the (per)alkaline character of AVB magmatism and the linear age-succession of volcanic centres.

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Acknowledgements

Firstly, I would like to thank Bernard Guest for his willingness to take me on as a PhD student after my first supervisor had left and to find a project that would be of interest to the both of us.

Thanks, Bernard, for your patience and constant encouragement and jumping into “the financial

I’m looking at the Department and Graduate Studies in particular. What a poor performance by either entity.

breach” when no one else would (i.e., in nine out of ten cases).

To Kelly Russell, I extend similar thanks for his unwavering support, especially during and after my defense, and for seeing and believing in the worth of my work (since I rarely did).

From my supervisory and examination committee, I thank Mike Wieser and especially Rajeev

Nair for their constructive comments and interest in my thesis. Further thanks for their roles and

Despite the latter being quite unprofessional in her role as an examiner, in addition to being underhanded and manipulative. Go home, Jen.

advice go to Catherine Hickson and Jen Cuthbertson.

On the technical and analytical side, I thank the staffs at the Trace Element Analytical Labora- tory (McGill University, Montréal), at the Peter Hooper GeoAnalytical Lab (Washington State

University, Pullman, WA) and at the Mineralogisches Institut (Albert-Ludwigs-Universität,

Freiburg i. Br.) as well as Lorraine Bloom for her help with the thinst section photography and If only the Department could and would finally invest in bringing its preparation facility into the 21 century…

Mickey Horvath for helping with sample preparation.

To Jeff “Apple” Benowitz at the University of Alaska-Fairbanks, I offer a triple “Hooray!

Hooray! Hooray!” for his exemplary work on the Ar-Ar age determinations, unceasing encouragement and good humour throughout the past three years. Should we meet again, drinks will be on me!

To Will Matthews I extend my thanks for his generous help in producing impeccable GIS maps and for always interesting/intriguing comments, some of which had unintended consequences!

Without my field assistants, I would have gone insane (at best) or “gone dead” (at worst) during field work in 2010-12. So to Hazel Jenkins, Stephen Ainsworth and Lincoln Hanton my sincere thanks for not only being willing to help me and become, essentially, glorified porters of volcanic rocks, but also for being such incredibly good sports in dealing with frugal food and accommodations, heat/rain/cold/difficult terrain, myriads of bugs and one moody German… I would also like to acknowledge the invaluable, generous and selfless help of Lori and Chris

Schmid (and “Spud”) of Alexis Creek (B. C.), for providing local information and assistance during field work on the Chilcotin Plateau. I will continue to pay it forward! Thanks also go to the

BC Forest Service and the Tsi Del Del Tsilhqot’in First Nation for assistance during field work.

The debts of gratitude that I owe my friends here in Calgary and back home in Germany are endless and it feels wrong having to limit myself to a few scant lines here, but alas! On the

Canadian side, I say “Thank You” to Carmen most especially, to Vikki & Kenny (and family), to

Adar & Oren, to Keith, and last, but certainly not least, to my good friend Scott. On the German side, I say “Danke schön!” to Buddi & Steffi, to Ulli, to Justus & Agi, to Benny, to both Matze

M.s and to Brigitte and Dieter for their patience, comfort and infinite encouragement. And

Johannes, Ingrid and Petra belong here, too. And the entire Kühn and Juli families. And my

Chörli! The list is sooo long…

Finally, to my Mama and Papa, I will say my thanks and so much more in person.

Dedication

Dedicated to my indomitable stubbornness to see things through that I’ve started, with all the good, bad and ugly this usually entails. And to my parents for their never-ending patience, support and worries about their volcano-obsessed son! And in the place of honour, I dedicate this work to my Aunt Heidi (†) who unknowingly helped start my fascination with volcanoes 25 years ago but then very knowingly supported me without fail. How I wish that she could have been around to see this endeavour come to a good end…

Table of Contents

Abstract ...... ii Acknowledgements ...... iv Dedication ...... vi Table of Contents ...... vii List of Tables ...... x List of Figures and Illustrations ...... xi List of Symbols, Abbreviations and Nomenclature ...... xiv Epigraph ...... xv

CHAPTER ONE: INTRODUCTION ...... 16 1.1 Thesis Overview ...... 16 1.2 Volcanic activity in western Canada ...... 18 1.3 Volcanotectonic association of volcanic fields and provinces in British Columbia ...... 23

CHAPTER TWO: PREVIOUS WORK ...... 27 2.1 The western part of the Anahim Volcanic Belt ...... 29 2.2 The central part of the Anahim Volcanic Belt ...... 32 2.2.1 Rainbow Range and Anahim Peak ...... 35 2.2.1.1 Geological Overview ...... 35 2.2.1.2 Stratigraphy and petrography ...... 38 2.2.1.3 Geochemistry ...... 39 2.2.1.4 Timing of activity ...... 42 2.2.2 Ilgachuz Range ...... 43 2.2.2.1 Geological Overview ...... 43 2.2.2.2 Stratigraphy and petrography ...... 47 2.2.2.3 Geochemistry ...... 52 2.2.2.4 Timing of activity ...... 54 2.2.3 Itcha Range ...... 55 2.2.3.1 Geological Overview ...... 55 2.2.3.2 Stratigraphy and petrography ...... 58 2.2.3.3 Geochemistry ...... 61 2.2.3.4 Timing of activity ...... 63 2.3 The eastern part of the Anahim Volcanic Belt ...... 64 2.3.1 Basement rocks and their relation to the AVB ...... 64 2.3.2 Nazko Cone ...... 67 2.4 Origin of AVB volcanoes ...... 73

CHAPTER THREE: THE SATAH MOUNTAIN AND BALDFACE MOUNTAIN VOLCANIC FIELDS: PLEISTOCENE VOLCANISM IN THE ANAHIM VOLCANIC BELT, WEST-CENTRAL BRITISH COLUMBIA, CANADA ...... 77 3.1 Abstract ...... 77 3.2 Introduction ...... 78 3.3 Geologic Setting ...... 86

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3.3.1 Study areas ...... 88 3.3.1.1 The Satah Mountain Volcanic Field ...... 90 3.3.1.2 The Baldface Mountain Volcanic Field ...... 97 3.3.1.3 Other centres ...... 100 3.4 Petrography ...... 108 3.4.1 Rock description ...... 108 3.4.2 Thin section petrography ...... 108 3.5 Samples and analytical methods ...... 115 3.5.1 Whole-rock geochemical analysis ...... 115 3.5.2 40Ar/39Ar age data ...... 118 3.6 Results ...... 127 3.6.1 Geochemistry ...... 127 3.6.1.1 Major elements ...... 127 3.6.1.2 Trace elements ...... 136 3.6.1.3 Rare earth elements ...... 143 3.6.2 40Ar/39Ar dating ...... 146 3.7 Discussion ...... 152 3.7.1 Timing of volcanic activity ...... 152 3.7.2 Correlation between age and geochemistry ...... 156 3.7.3 Volcanotectonic controls ...... 158 3.8 Conclusion ...... 162

CHAPTER FOUR: VOLCANOTECTONIC CONTROLS ON THE ANAHIM VOLCANIC BELT ...... 164 4.1 Abstract ...... 164 4.2 Introduction ...... 166 4.3 The four main hypotheses ...... 173 4.3.1 The Mantle Plume Hypothesis ...... 173 4.3.2 The Continental Rifting Hypothesis ...... 181 4.3.2.1 Felsic shield volcanoes in East Africa ...... 181 4.3.2.2 The Northern Cordilleran Volcanic Province ...... 184 4.3.3 The Plate-Edge Effect and Slab Window Hypotheses ...... 188 4.3.3.1 The case of the Yellowstone hot-spot track ...... 194 4.3.4 The Propagating Fracture Hypothesis ...... 195 4.4 So how and where does the Anahim Volcanic Belt fit in? ...... 200 4.4.1 The age-succession of AVB volcanic centres ...... 200 4.4.1.1 Oceanic and continental hot-spots ...... 205 4.4.1.2 Continental Rifting – East African Rift and Northern Cordilleran Volcanic Province ...... 207 4.4.1.3 Plate Edge Effect - Alert Bay Volcanic Belt ...... 207 4.4.1.4 Propagating Fracture - The Canary Islands ...... 208 4.4.1.5 Could a fracture, propagating or not, be applied to the Satah Mtn. volcanic field? ...... 208 4.4.2 Geophysical data ...... 211 4.4.2.1 Heat flow data ...... 211 4.4.2.2 Aeromagnetic data ...... 213

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4.4.2.3 Gravity data ...... 215 4.4.3 Can geochemistry provide a clue? ...... 218 4.4.3.1 Assessment of OIB affinity of AVB lavas ...... 224 4.4.3.1.1 Individual assessment of volcanotectonic settings ...... 228 4.4.3.1.2 Oceanic and continental hot-spots ...... 238 4.4.3.1.3 Continental Rifting - East African Rift and Northern Cordilleran Volcanic Province ...... 241 4.4.3.1.4 Plate edge effect - The Alert Bay Volcanic Belt and Yellowstone...... 245 4.4.3.1.5 Propagating fracture - The Canary Islands ...... 246 4.5 Interpretation and Conclusion ...... 247

CHAPTER FIVE: THESIS SUMMARY ...... 253

REFERENCES ...... 257

APPENDICES ...... 276 A1 Samples Locations (relates to chapter 3.3.1) ...... 276 A2 Original XRF data (relates to chapter 3.5.1) ...... 280 A3 Original 40Ar/39Ar geochronology data (relates to chapter 3.5.2) ...... 314

List of Tables

Table 1 Mineral compositions of olivines, pyroxenes and feldspars for the four major Rainbow Range lava types ...... 41

Table 2 Mineral compositions of olivines, pyroxenes and feldspars for the four major Ilgachuz Group units and the late-stage Flank basalt ...... 53

Table 3 Representative XRF (major and trace elements) analyses of Neogene and Quater- nary volcanic rocks from the Baldface Mountain and Satah Mountain Volcanic Fields ...... 115

Table 4 Rare earth element concentration (in ppm) for mafic lavas of two BMVF and three SMVF centres ...... 118

Table 5 40Ar/39Ar analyses of the Satah Mtn. Volcanic Field (SMVF), Baldface Mtn. Volcanic Field (BMVF) and other volcanic centres (O)...... 121

Table 6 Liquidus temperature and water content in selected samples of the rock types determined ...... 132

Table 7 Overview of age, geochemistry, isotope data (where available) for AVB centres and select non-AVB centres ...... 201

Table 8 Overview of present-day plate motion data for the SRP/Y and AVB ...... 204

Table A9 Sample locations for BMVF, SMVF and other centres ...... 277

Tables A10 XRF whole-rock raw data (major and trace elements), rare earth elements contents for selected samples and mineral norms (incl. Mg# and differentiation index [D.I.])...... 283

Table A11 40Ar/39Ar analyses from volcanic centres in the Baldface Mountain (BMVF), Satah Mountain Volcanic Fields (SMVF) and other centres (O)...... 315

Tables A12 Raw data, release spectra for 39Ar, Ca/K and Cl/K ratios and isochron diagrams for 24 homogeneous whole rock separates from the Satah and Baldface Mountain Volcanic Fields, west-central British Columbia ...... 320

List of Figures and Illustrations

Figure 1 Index map of Anahim Volcanic Belt (AVB) in west-central British Columbia...... 20

Figure 2 Location map showing the National Topographic Maps Series (NTS) grids covering the central AVB and the current study areas ...... 28

Figure 3 Location map for the western part of the AVB...... 30

Figure 4 Location map (coloured hill-shade DEM) for the central and eastern part of the AVB ...... 32

Figure 5 Satellite image (Landsat) of the Rainbow Range ...... 36

Figure 6 Satellite image (Landsat) of the Ilgachuz Range ...... 45

Figure 7 Satellite image (Landsat) of the Itcha Range ...... 56

Figure 8 The central and southern parts of the Itcha Range as seen from a small volcanic centre in the Baldface Mountain Volcanic Field (BMVF) 20 km to the East ...... 58

Figure 9 Schematic stratigraphy column for the eastern-most part of the Satah Mtn. Volcanic Field ...... 66

Figure 10 Views of Nazko Cone ...... 69

Figure 11 Oblique aerial views of Nazko Cone ...... 71

Figure 12 Schematic and generalized diagrams for the evolution of the AVB shield volcanoes...... 75

Figure 13 Location map of select Neogene and Quaternary volcanic centres in British Columbia ...... 82

Figure 14 Detailed location map of the SMVF and sample locations therein ...... 84

Figure 15 Detailed locations map of the BMVF and sample locations therein ...... 85

Figure 16 Photographic survey of field work study areas (SMVF, BMVF) ...... 104

Figure 17 Thin section photomicrographs of SMVF and BMVF lavas ...... 111

Figure 18 40Ar/39Ar age spectra for seven samples from the Baldface Mtn. Volcanic Field, 11 samples from the Satah Mtn. Volcanic Fields) and six older and/or non-AVB affiliated centres ...... 125

Figure 19 Plot of total alkalis vs. silica (TAS) of new SMVF (blue rhombs) and BMVF data (red squares) ...... 128

Figure 20 Harker diagrams showing variation in major element and selected trace element abundances versus SiO2 for SMVF and BMVF lavas...... 134

Figure 21 Harker variation diagrams for SMVF and BMVF lavas based on rock types ...... 137

Figure 22 Alumina saturation diagram for SMVF and BMVF lavas and those of outlying (other centres) ...... 141

Figure 23 Multi-element, primitive mantle-normalized spider diagram for two mafic SMVF and three mafic BMVF lavas ...... 142

Figure 24 Chondrite-normalized rare earth element concentrations for selected mafic samples from the SMVF and BMVF ...... 144

Figure 25 Distribution of volcanic centres in the SMVF and BMVF for which 40Ar/39Ar ages were determined in this study ...... 147

Figure 26 Overview of ranges of ages of AVB centres from W to E and comparison with other volcanic centres in western Canada ...... 150

Figure 27 Plot of composition (as a function of SiO2 content) and age for SMVF and BMVF centres ...... 155

Figure 28 Diagram illustrating P-wave velocity model for AVB region ...... 161

Figure 29 Geological map of the central and eastern Anahim Volcanic Belt (AVB). Inset shows location of area in west-central British Columbia (red box) ...... 169

Figure 30 Digital elevation model of the central AVB ...... 171

Figure 31 Index map of the major islands of the Hawaiian archipelago ...... 175

Figure 32 Schematic plot showing the apparent decrease in age (K-Ar) of plutonic and volcanic centres of the AVB ...... 179

Figure 33 Schematic overview of select Neogene−Quaternary volcanic centres in the Northern Cordilleran Volcanic Province (NCVP) ...... 185

Figure 34 Schematic diagram of the current tectonic settings of SW British Columbia, including important volcanic belts ...... 189

Figure 35 Schematic location map of the Canary Islands ...... 196

Figure 36 Schematic diagram illustrating the “batch” model assumed for the Canary Islands ...... 198

Figure 37 Schematic NNW-SSE cross-section from the Itcha Range along Satah Ridge to illustrate the "melt batch model" applied to the SMVF ...... 210

xii

Figure 38 Heat flow map for B. C...... 212

Figure 39 Aeromagnetic map of Interior or British Columbia, covering parts of the central and eastern AVB ...... 214

Figure 40 Map of part of the central and eastern AVB with underlying gravity contours ...... 217

Figure 41 TAS diagrams for lavas observed in the Anahim Volcanic Belt and compared to other volcanotectonic settings ...... 219

Figure 42 Alumina saturation diagrams of AVB and non-AVB centres ...... 221

Figure 43 Cr/Y discrimination diagram for mafic rocks from the SMVF and BMVFand selected mafic lavas from the Ilgachuz and Itcha ranges ...... 223

Figure 44 Nb vs. Nb/U discrimination diagrams for AVB and non-AVB mafic lavas...... 226

Figure 45 Rare earth element (REE) diagrams for AVB mafic lavas ...... 229

Figures 46 REE patterns for mafic lavas from several volcanic fields/regions (and different volcanotectonic settings) compared to AVB data ...... 230

Figures 47 Multi-element and mantle-normalized concentrations of trace and incompatible elements from mafic AVB lavas compared with those of different volcanotectonic settings...... 235

Figures A48 Release spectra for 39Ar, Ca/K and Cl/K ratios and isochron diagrams for 24 homogeneous whole rock separates from the Satah and Baldface Mountain Volcanic Fields, west-central British Columbia ...... 320

xiii

List of Symbols, Abbreviations and Nomenclature

Abbreviation Definition

ABVB Alert Bay Volcanic Belt

Ar-Ar Argon-Argon (method for age determination)

AVB Anahim Volcanic Belt

AOB Alkali olivine basalt

BMVF Baldface Mountain Volcanic Field

CC Continental crust (with modifiers as necessary)

D.I. Differentiation index

EAR East African Rift

EM Enriched mantle

GVB Garibaldi Volcanic Belt

K/Ar Potassium-Argon (method for age determination)

MER Main Ethiopian Rift

N-MORB Normal Mid-Oceanic Ridge Basalt

NCVP Northern Cordilleran Volcanic Province

OIB Ocean Island Basalt

OLG Ootsa Lake Group

REE Rare earth element

SMVF Satah Mountain Volcanic Field

SRP/Y Snake River Plain/Yellowstone

TLMC Tatla Lake Metamorphic Complex

XRF X-ray fluorescence (analytical method)

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Epigraph

One equal temper of heroic hearts,

Made weak by time and fate, but strong in will

To strive, to seek, to find, and not to yield.

- Ulysses (68–70), Alfred, Lord Tennyson

Chapter One: Introduction

1.1 Thesis Overview

This study synthesises existing knowledge about the Anahim Volcanic Belt (AVB) and presents new geochemical and geochronological data from two fields of volcanic cones: the Satah

Mountain and Baldface Mountain volcanic fields (SMVF, BMVF). These fields are in close spatial proximity to the Itcha Range shield volcano and while the former field was briefly mentioned in a Ph.D. thesis (CHARLAND 1994), the present work is the first systematic study of either volcanic field.

Chapter Two (p. 27) summarizes previous works on the AVB and provides information on the stratigraphy, geochemistry and evolution of the belt’s three parts and individual centres therein. Furthermore, other major volcanic regions in western Canada are briefly described to provide a framework for understanding volcanic activity in the AVB. An edited version of this chapter will eventually be submitted to the Canadian Journal of Earth Sciences in 2015.

Chapter Three (p. 77) presents my own field observations and data yielded from analyses of rock samples my field assistants and I collected during three field seasons on the Chilcotin

Plateau. Whole-rock XRF geochemical data and new 40Ar/39Ar age determinations are presented to assess and corroborate the association of the SMVF and BMVF with the AVB. Additional samples were collected from outside these two fields and are presented where suitable as well.

This chapter, in a shortened form, has been submitted to the Bulletin of Volcanology for consideration for publication (as KUEHN ET AL. 2014 OR 2015). It is currently in the revision stage and was co-authored by Dr. Bernard Guest (Department of Geology and Geophysics,

University of Calgary), Dr. Kelly Russell (Department of Earth and Ocean Sciences, University

16 of British Columbia) and Dr. Jeff Benowitz (Geochronology Lab, University of Alaska at

Fairbanks). The roles of the authors were as follows: Apart from undertaking field work and sample collection, I prepared the rock samples for XRF and Ar-Ar analyses, both of which were conducted outside of the University of Calgary. The data from these analyses were then reduced, visualised and interpreted by myself. Drs. Guest and Russell provided guidance and comments on the layout, interpretation of results, clarified ambiguities in early drafts and helped “straighten out” the manuscript. Dr. Benowitz performed the Ar-Ar analyses and provided comments on my interpretation of the data. Any remaining errors remain my own.

Chapter Four (p. 164) is an assessment of the various hypotheses proposed for the existence and evolution of the AVB. Each hypothesis is accompanied by a description of at least one volcanic region on Earth that is associated with that respective hypothesis. Finally, these hypotheses are assessed in light of how, if at all, they can account for the geochemical, geochronological and volcanotectonic characteristics observed in the AVB. I plan to submit an edited version of this chapter to either Geology or GSA Bulletin in the first half of 2015.

Chapter Five (p. 253) provides a summary of this thesis, followed by the References. The appendices (p. 276) include information on the locations of each sample that was used in this study and provide the original XRF geochemistry and geochronology data (including tables and figures). Selections of these samples (either as hand samples, crushings or analytical powders) are retained in the collection of the Department of Geology and Geophysics at the University of

Calgary. Cross-references within this thesis are indicated for chapters and sub-chapters

(abbreviated “cf. ch.” throughout).

1.2 Volcanic activity in western Canada

Western Canada is part of the Pacific Ring of Fire (SOUTHER 1977, 1990; FRANCIS &

OPPENHEIMER 2003), yet it is rarely perceived as such as no major volcanic eruptions have taken place since the first European explorers arrived in the region in the late 18th century

(SUTHERLAND BROWN 1969). However, over 100 individual volcanic centres, distributed over the Yukon Territory and especially British Columbia (B. C.), have been active during the

Neogene and Quaternary (e.g., SOUTHER 1977, 1990; HICKSON 1987, 1990; SOUTHER ET AL.

1987; GREEN ET AL. 1988; EDWARDS & RUSSELL 1999, 2000; this study). This volcanic activity occurred either in the form of geographically isolated, short-lived centres or large, multi-stage volcanic complexes. These centres are arranged into distinct belts or volcanic provinces and provide a “Canadian link” between the better-known Cascade Range volcanoes of the western

United States and those in Alaska (SOUTHER 1977, 1990; HICKSON 1990; FRANCIS &

OPPENHEIMER 2003).

The Anahim Volcanic Belt (AVB) of west-central B. C. comprises a multitude of volcanic landforms, including dykes, plutons (SOUTHER 1977; 1986), complex shield volcanoes (BEVIER

1978, 1981; BEVIER ET AL. 1979; CHARLAND ET AL. 1993, 1995; CHARLAND 1994; SOUTHER &

SOUTHER 1994), regionally extensive fields of largely monogenetic tephra cones, associated lava flows and eroded remnants of these (SOUTHER ET AL. 1987; this study). The AVB extends ~330 km in WSW-ENE direction from Milbanke Sound on the west coast of B. C. across the Chilcotin

Plateau to Nazko Cone, 80 km west of Quesnel (Fig. 1). The width of the belt is less well- defined and ranges from 25 to 60 km along its trend. Outside of the shield volcanoes that rise above the treeline, rock exposures are discontinuous and often small in size. These exposures are made more ambiguous due to the large-scale modification of the landscape that occurred

18 during repeated episodes of glaciation during the Neogene and Quaternary which left behind an extensive cover of glacial till.

The AVB is located at ~52º latitude (Fig. 1) and extends from islands on the Pacific coast near

Bella Bella across the Coast Mountains and onto the Chilcotin Plateau (SOUTHER 1986). The belt is located between Neogene subduction-related volcanism to the south (SOUTHER 1977,

1990; GREEN ET AL. 1988), extension-related volcanism of Pleistocene and Holocene ages to the east (HICKSON & SOUTHER 1984; HICKSON 1987), and generally extension-related volcanism in the northern parts of the province (EDWARDS & RUSSELL 1999; 2000; EDWARDS ET AL. 2002,

2011). Spatially and temporally associated with AVB are plateau basalts of the Chilcotin Group that form a thin, albeit extensive veneer over much of the interior of B. C. (BEVIER 1983A/B;

MATHEWS 1989; ANDREWS & RUSSELL 2008). Unlike these areas, the AVB cuts across the dominantly NW-SE structural grain of British Columbia at a high angle. Where the AVB intersects the Coast Mountains, the latter attain somewhat lower elevations than to the north and the south (ANDREWS, PERS. COMM. 2012). Original mapping of the area was done by TIPPER

(1969, 1971).

The remote location of the AVB has likely contributed to the low number of previous studies.

However, comprehensive studies were carried out on the belt’s three large shield volcanoes: the

Rainbow Range (BEVIER 1978, 1981), the Ilgachuz Range (SOUTHER & SOUTHER 1994) and the

Itcha Range (CHARLAND 1994; CHARLAND ET AL. 1993, 1995). The western and eastern parts of the AVB were studied in the mid-1980s (SOUTHER 1986; SOUTHER ET AL. 1987). No historic activity has taken place in the belt, with the last eruption at an AVB centre having taken place some 7,200 years BP at Nazko Cone, the youngest AVB centre (SOUTHER ET AL. 1987). The most recent event was an earthquake swarm in the vicinity of that centre in 2007–2008 which

19 was interpreted as magma injection into the lower crust (CASSIDY ET AL. 2011). There are currently no indications of renewed activity in the area; however, future eruptions could possibly occur at or in the vicinity of Nazko Cone (HICKSON ET AL. 2009).

The origin and evolution of the AVB is not completely understood. The belt’s linear arrangement, predominantly alkaline to peralkaline geochemistry and an apparent linear decrease in ages from west to east have long been interpreted as being due to a mantle plume underlying this part of western North America (e.g., SOUTHER 1977, 1986; BEVIER ET AL. 1979).

Figure 1 Index maps. (Top) Location of Anahim Volcanic Belt (AVB) and Milbanke

Sound cones in west-central British Columbia. Red box outlines extent of enlarged area.

(Bottom) Overview of the AVB. Red triangles denote major centres in the AVB, red dashed circles approximate location and extent of present study areas. Grey squares identify regionally important settlements. The western part of the AVB includes centres west of the Coast Mountains: the Bella Bella dyke swarms; the alkaline King Island pluton on the eponymous island (cf. Fig. 3 as well). Postglacial centres given for reference are Kitasu Hill

/ Milbanke Sound cones (not individually shown), but these are likely not associated with the AVB. East of the Coast Mountains, the central part of the AVB includes the Rainbow

Range, the Ilgachuz Range, and the Itcha Range with the associated SMVF to the south and BMVF to the east, respectively (not shown individually; cf. Figs. 11, 12 and 13). The eastern part of the AVB is centered on Nazko Cone. Courses of Chilko, Chilcotin and

Fraser rivers given for reference.

Figure 1

The generation and ascent of mantle-derived melts through the overriding North American continental plate then led to the creation of multiple centres that, while being spatially and temporally distinct, share a common evolution (BEVIER AT AL. 1979; CHARLAND 1994; SOUTHER

& SOUTHER 1994). Other hypotheses for the belt’s evolution include continental rifting to explain the presence of continental alkaline and peralkaline volcanoes (TIPPER 1969; SOUTHER

1977); fracturing of the North American plate and the underlying lithosphere above the northern edge of the subducting Juan de Fuca/Explorer plates (BEVIER ET AL. 1979; ARMSTRONG ET AL.

1985); presence of a slab window allowing mantle material to upwell and cause melt generation in the wake of a now subducted plate (THORKELSON 1996; EDWARDS & RUSSELL 2000; JAMES ET

AL. 2011; THORKELSON ET AL. 2011); finally, a propagating fracture due to regional stress regimes and existing crustal zones of weakness, similar to what was once proposed for the

Canary Islands (ANGUITA & HERNÁN 1975, 2000).

1.3 Volcanotectonic association of volcanic fields and provinces in British Columbia

Based on their respective volcanotectonic, spatial and temporal associations, Neogene and Qua- ternary volcanic centres in western Canada have been grouped into several distinct domains, which are briefly summarised below. Please see ch. 4 for a more detailed discussion on the volcano-tectonic regimes controlling the evolution of these volcanic fields and provinces.

 Pemberton and Garibaldi Volcanic Belts (PVB, GVB; SOUTHER 1990): Both of

these are related to subduction off the south-west coast of B. C. and are considered the

northerly extension of the Cascades volcanic arc (GREEN ET AL. 1988). Volcanic centres

and related plutons in the PVB are predominantly Oligocene and Late Miocene in age

and show a calc-alkaline affinity. The belt is thought to be related to the subduction of

the then-existing Farallon Plate, which had largely been subducted under North America

by the late Pliocene (SOUTHER 1990). The Neogene to Quaternary GVB became the

“successor” of the PVB when the remnants of the Farallon Plate were reorganized into

the smaller Juan de Fuca and Explorer plates (GREEN ET AL. 1988). The Juan de Fuca

plate is currently being subducted under the North American plate whereas the smaller

Explorer plate is being overridden by North America (RIDDIHOUGH 1984; ROHR &

FURLONG 1995). GVB centres were active at different points in time, with overall

activity commencing in the Middle Pliocene and continuing at different centres for

varying amounts of time during much of the Pleistocene. The most recent activity at Mt.

Meager is dated at ~2,350 years BP (HICKSON ET AL. 1999).

 Potentially related to the subduction of the Juan de Fuca plate is the Late Miocene

to Pliocene Alert Bay Volcanic Belt (ABVB) on northern Vancouver Island

(ARMSTRONG ET AL. 1985; SOUTHER 1990). Here, a dichotomy of an older period of calc- alkaline magmatism and a later, more alkaline period is observed. The timing of activity in the ABVB is thought to be connected to the reconfiguration of the Pacific-Farallon-

Juan de Fuca/Explorer plate system and is interpreted as a surface expression of the descending edge of the Juan de Fuca plate (ARMSTRONG ET AL. 1985). See ch. 4.3.3 for a detailed assessment of this volcanotectonic setting.

 The Chilcotin Group basalts (BEVIER 1983A/B; MATHEWS 1989; DOHANEY 2009) comprise extensive plateau basalts of Late Oligocene (25−19 Ma) to predominantly

Miocene (10−6 Ma) and Pliocene (3−2 Ma) ages in the interior of B. C. The Chilcotin

Group basalts unconformably overlie older rocks affiliated with the Stikinia, Cache Creek and Quesnellia terranes (BEVIER 1983A). These basalts were presumably erupted from fissures and/or central vents from low shields that are aligned along a northwesterly trend, paralleling the PVB (BEVIER 1983A). The Chilcotin basalts are contemporaneous with both that belt and, to a lesser extent, the earliest activity in the GVB. The same applies to the AVB (BEVIER ET AL. 1979) which the Chilcotin basalts in part or fully underlie along their northwestern extent. Early mapping assigned both AVB and

Chilcotin Group rocks to the same category (TIPPER 1969), but subsequent works

(BEVIER 1983A/B; MATHEWS 1989) separated the AVB rocks from the Chilcotin basalts.

These basalts have a distinct transitional geochemical signature and their setting is thought to be in a back-arc basin above the subducted Farallon and subducting Juan de

Fuca plates (BEVIER 1983A).

 The generally extension-related Northern Cordilleran Volcanic Province (NCVP;

EDWARDS & RUSSELL 1999, 2000), formerly called Stikine volcanic belt (SOUTHER

1990), includes large and long-lived centres such as the Mt. Edziza-Spectrum Range complex (SOUTHER ET AL. 1984), Hoodoo Mountain (EDWARDS ET AL. 2002) and Level

Mountain (HAMILTON 1981), as well as extensive fields of small, monogenetic cones, tuyas and associated lava flows (EDWARDS ET AL. 2011). It is thought that the extensional and/or transtensional tectonic regime controlling the NCVP is related to the rifting of the

NW continental margin of North America (ENGEBRETSON ET AL. 1985) and has been compared to the Basin and Range province of the western United States (EDWARDS &

RUSSELL 1999). The repeated movement of the Queen Charlotte triple junction off the west coast of B. C. and parallel to the continental margin of North America since the

Miocene is interpreted to have led to a change in the region’s stress regime from compressional to extensional (EDWARDS & RUSSELL 1999, 2000). Scattered volcanism in the Yukon and eastern Alaska denotes the northwestern limit of the NCVP.

 The Wells Grey−Clearwater volcanic field in east-central B. C. comprises Pleisto- cene and Holocene volcanic rocks that record at least two episodes of activity during times of glaciation (HICKSON & SOUTHER 1984; HICKSON 1987; HICKSON ET AL. 1995).

Volcanic landforms include small tephra cones, tuyas, valley-filling lava flows and associated breccias of predominantly basaltic composition. Many of these exhibit features of subglacial and/or subaqueous eruptions (e.g., pillow lavas, hyaloclastite breccias). The

Wells Grey−Clearwater field is located between the Interior Plateau to the west and the

Columbia Mountains to the east. Volcanic activity is interpreted to be the result of crustal extension which initiated decompression melting. Faults, also due to extension, then provided these melts with ascent pathways to the surface (HICKSON 1987; HICKSON

ET AL. 1995).

A previous suggestion (BEVIER ET AL. 1979; ROGERS 1981) that this area could be the

easternmost expression of AVB volcanism has since been disproven (HICKSON 1987), as

both the trajectory of an AVB hot-spot track and the necessary vector for movement of

the North American plate do not align with the southeasterly location of the Wells

Grey−Clearwater field. Short-lived eruptions were small in volume and geographically

scattered (HICKSON ET AL. 1995), similar to what is reported in the present study for the

SMVF and BMVF (cf. ch. 3).

Volcanic activity in British Columbia during the Neogene and Quaternary outside of these belts and fields took place in the form of scattered and short-lived eruptions. Examples of the latter can be found in areas around Quesnel Lake (SOUTHER 1990; this study); the Iskut-Unuk cones and at Tseax Cone near Aiyansh at the southern end of the NCVP (350 km to the northwest of the AVB). These latter examples were the loci of the most recent eruptions of

Canadian volcanoes (SUTHERLAND BROWN 1969; HAUKSDOTTIR ET AL. 1994). Due to the activity of many of these centres being coeval with repeated episodes of Cordilleran glaciation

(SOUTHER 1990; HICKSON ET AL. 1995; EDWARDS & RUSSELL 2011; ROED ET AL. 2013), features displaying the interaction of lava and water and/or ice and extensive glacial modification of older centres are found in most volcanic areas of B. C.

Chapter Two: Previous Work

The study area in the Anahim Volcanic Belt is covered by National Topographic Map Series

(NTS) grid 093C (Fig. 2). The area is located in the Chilcotin Plateau (formerly referred to as the Fraser or Interior Plateau), a remote and sparsely populated part of west-central British

Columbia. The volcanic centres of the SMVF studied for this work are covered by NTS sheets

093C/02 (Chantslar Lake), 07 (Satah Mountain), and 10 (Downton Creek); for centres of the

BMVF, also sheets 093C/09 (Clusko River), 15 (Kushya River) and 16 (Toil Mountain).

Outliers of these fields continue into other areas of the 093C grid, but only a few were studied in detail (mainly in sheet 093C/08, Chezacut) due to inaccessibility (cf. ch. 3).

A summary of the main parts of the AVB follows, which is divided into a western part (the

Bella Bella and Bella Coola regions), the central part (including the three main shield volcanoes and present study areas) and an eastern part (the Nazko Cone area; Figs. 1 through 4). Only a few authors have studied this area and the pioneering works of Jack Souther (SOUTHER 1977,

1986; SOUTHER ET AL. 1987; SOUTHER & SOUTHER 1994), Mary Lou Bevier (BEVIER 1978, 1981,

1989; BEVIER ET AL. 1979) and Anne Charland (CHARLAND 1994; CHARLAND ET AL. 1993, 1995) form the basis of the following descriptions. These include summaries of the stratigraphy, petrology, geochemistry and ages of the rocks of the respective AVB centres. At the time of writing, these works are the most substantial sources of information on these volcanoes, leading to extensive and repeated citations of them in this chapter.

Figure 2 Location map showing the National Topographic Maps Series (NTS) grids covering the central AVB and the current study areas. (Modified using data provided by

GEOGRATIS, Department of Natural Resources Canada [2014]. Contains information licensed under the Open Government Licence – Canada.)

2.1 The western part of the Anahim Volcanic Belt

Subvolcanic and plutonic rocks that outcrop on the coasts of and on several islands in the Bella

Bella region are considered to be the westernmost locations of magmatic activity in the AVB

(SOUTHER 1986; 1990). Rock types include alkali basalts, hawaiites, trachytes, comendites and rhyolites in subvolcanic dykes, syenite in the King Island pluton and associated rhyolitic breccias elsewhere. The bimodal geochemistry and petrography of the rocks is similar to the eruptive rocks in the central and eastern parts of the AVB (see the following chapters).

On Swindle, Price and Nathan islands to the northwest of Bella Bella (Fig. 3), volcanic centres were later defined as the Milbanke Sound cones (SOUTHER 1986, 1990). With the exception of Kitasu Hill, a 240 m high pyroclastic cone on Swindle Island, most of these individual centres are very heavily eroded and not much of them is left but rhyolitic breccias and flows. Lithic clasts in these breccias suggest that volcanic activity was explosive. A post-glacial age is assumed for the Milbanke Sound cones (SOUTHER 1990), thus making an association with the AVB belt, other than spatial, very unlikely.

On Athlone, Shearwater, Campbell and Denny islands (Fig. 3), small eruptive centres exist in addition to a multitude of dykes that outcrop on the shorelines of these islands. These dykes occur as two distinct swarms on Athlone and Dufferin Island and Campbell and Denny Island, respectively. Orientation of the dykes in each swarm is very uniform, with the former (Gale

Passage swarm) having an average trend of ~020º and the latter (Bella Bella swarm) of ~170º

(SOUTHER 1986). In either swarm, the dykes are predominantly planar and vertical and based on observed cross-cutting relationships appear to have been emplaced in two stages: early felsic dykes cut by later, more mafic dykes. An extrapolation of the two trends to the north indicates a common source at depth that lies on the trend of the proposed AVB hot-spot. At 14.5 to 12.5

Ma, the mid-Miocene ages of these rocks are the oldest recorded for the AVB (SOUTHER 1986; cf. ch. 3.6).

Figure 3 Location map for the western part of the AVB; Bella Bella townsite for reference (cf. Fig. 1). Red triangles denote the Milbanke Sound cones (not all of which have yet been officially named). Red stipples on Athlone, Shearwater and Campbell islands schematically indicate the two dyke swarms exposed on the shores of these islands

(GS−Gale passage swarm, BB−Bella Bella swarm). The King Island pluton is discontinuously exposed on Denny Island and central King Island. Geology modified from

SOUTHER (1990) and MASSEY ET AL. (2005).

The King Island pluton is discontinuously exposed on Denny and King Islands between Bella

Bella and Bella Coola (Fig. 3). The pluton extends over 40 km in a northeasterly direction across the dominant NW-SE trend of the Coast Mountains. It consists of alkaline to peralkaline, coarse-grained syenite which grades into a granite that contains an abundance of sodic minerals

(aegirine, arvfedsonite). It is indicated that the granite formed from the syenite by fractionation

(SOUTHER 1986), with the granite forming a cupola on top of the syenite. Open cavities indicate emplacement at shallow depth (2–5 km). Uplift occurred after the Late Miocene on the order of

<1 km at the coast and up to 4 km in the vicinity of the pluton, exhuming the hypabyssal and plutonic rocks in the region (PARRISH 1983; SOUTHER 1986). Chemically, the syenite of the King

Island pluton is identical with trachytes observed in the dyke swarms farther west. This is also the case for the sodic granite and the comendites and rhyolites. Close geochemical similarities exist with the various alkaline rocks from the Rainbow and Ilgachuz ranges in the central AVB, indicating a common source and/or petrogenesis for all of these rocks. The age of the King

Island pluton is constrained by three K-Ar dates to a period from 13 to 10.3 Ma, indicating a decrease in age from the volcanic centres and dyke swarms to the west (SOUTHER 1986).

2.2 The central part of the Anahim Volcanic Belt

The central AVB includes the three large shield volcanoes (the Rainbow, Ilgachuz and Itcha ranges) and regionally extensive cone fields (Fig. 4). The general Anahim Lake area was mapped at 1:253,440 scale by the Geological Survey of Canada in the late 1960s (TIPPER 1969,

1971). Outside of the three shield volcanoes and the Coast Mountains to the west, coverage of bedrock in the Chilcotin Plateau by glacial drift is generally extensive (10 m minimum thickness;

ANDREWS & RUSSELL 2008) and, together with dense vegetation, often limits outcrops to topographical highs and/or river valleys. MIHALYNUK ET AL. (2008, 2009), however, point out

Figure 4 Index map (coloured hill-shade DEM) for the central and eastern part of the

AVB. Highway 20, Anahim Lake, Chezacut and Chilanko Forks townsites given for reference. Coast Mountains (highest relief) occupy western part of area. Rivers include the Atnarko, Tahyseco and Dean rivers, which drain west into the Pacific Ocean, and the

Chilko and Chilcotin rivers, which drain east into the Fraser River. Red triangles denote major volcanic edifices. Present study areas around Satah and Baldface Mtn. have central peaks in red, smaller centres in orange. Grey triangles denote other mountains mentioned in the text. KM−King Mountain, AP−Anahim Peak, P. Ck.−Punkutlaenkut Creek,

WT−Whitetop Mtn., NH−North Hill, TM−Toil Mtn., MD−Mt. Dent, MS−Mt. Sheringham,

RT−Redtop Mtn. Nazko Cone is the sole mapped volcanic centre of the eastern AVB.

(Digital topography map modified using DEM data provided by GEOGRATIS, Department of Natural Resources Canada [2014]. Contains information licensed under the Open

Government Licence – Canada.)

Figure 4

33 that outcrops are more widespread than previously thought, but these are still of small size and rarely continuous. The earlier geological map was in part compiled and inferred from aerial photographs (GHENT, PERS. COMM. 2011) that, while sensu latiore correct, could not provide detailed information, especially where contacts between different units are concerned. Smaller scale maps of the shield volcanoes (BEVIER 1978; CHARLAND 1994; SOUTHER & SOUTHER 1994) have since been produced and more recently, regional mapping at 1:50,000 scale and accompanying studies of the respective geology, geochronology and mineralization were undertaken for the Chezacut (MIHALYNUK ET AL. 2008) and Chilanko Forks areas (MIHALYNUK

ET AL. 2009) that border the present study areas to the east and southeast (Fig. 4).

The bedrock under the central and eastern part of the AVB is inferred to be part of the predominantly volcanic Middle Jurassic Hazelton Group (andesites and basalts) and the Eocene

Ootsa Lake Group (OLG; TIPPER 1969; MIHALYNUK ET AL. 2008, 2009). Above these strata, the flat-lying plateau basalts of the Chilcotin Group underlie large areas of the central and eastern

AVB as well. It had been noted by several authors (e.g., TIPPER 1969; SOUTHER 1986; SOUTHER

& SOUTHER 1994) that contacts were very difficult to identify due to limited exposures and petrographical similarity between AVB rocks and the Chilcotin Group, with which the former

“merge imperceptibly” (SOUTHER 1986; p. 896). However, more recent mapping along newly established logging roads and aided by aerial photography revealed more rock exposure while also recognizing that cover by the Chilcotin basalts is less extensive than previously thought

(MIHALYNUK ET AL. 2009; DOHANEY 2009). While a few older centres affiliated with the OLG were studied and sampled in this study (cf. ch. 3.2.1.3 and 3.5.2), no actual contacts between

AVB volcanic rocks and either Chilcotin basalts or older units could be identified. AVB rocks

34 are thought to extend under the Quaternary cover into the area NW of Chilanko Forks

(MIHALYNUK ET AL. 2009).

To the west of the Rainbow Range, the Coast Mountains consist of a complex assortment of largely plutonic and metamorphic rocks of Mesozoic and Eocene ages (GEHRELS ET AL. 2009).

At their eastern extent these are likely to be partially covered by lavas from the Rainbow Range.

Slight tilting of the Chilcotin basalts at their westernmost extent indicates continuing uplift of the

Coast Mountains since the Miocene (MATHEWS 1989). However, the Rainbow Range appears not to have been affected by this, possibly due to its more easterly location and younger age; furthermore, no faulting is evident there (BEVIER 1978).

2.2.1 Rainbow Range and Anahim Peak

2.2.1.1 Geological Overview

The Rainbow Range is the westernmost of the three large shield volcanoes of the central AVB

(BEVIER 1978; 1981). The volcano rises ~1,300 m above the Chilcotin Plateau and reaches an elevation of 2,495 m at Tsitsutl Peak (Fig. 5). The range consists of a dissected central part,

2 which is roughly circular in shape and covers an area of ~900 km (BEVIER ET AL. 1979). Early mapping of the area (TIPPER 1969) shows the Rainbow Range overlying Late Miocene to

Pliocene volcanics that have since been assigned to the Chilcotin Group (BEVIER 1983A/B;

MATHEWS 1989). Eocene and Mesozoic volcanics in turn underlie these rocks. The centre of the actual shield is complex and highly eroded. The varicoloured nature of the exposed rocks is taken as evidence of hydrothermal alteration (BEVIER, PERS. COMM. 2012). A south-western

“spur”, west of Macedo Peak and around Mt. MacKenzie (Fig. 5), appears to consist of similarly

35 multicoloured rocks and several stacked flow units along eroded valley walls, similar to the central part of the Rainbow Range. This spur might already overlie the most easterly parts of the

Coast Mountains, but no actual contacts have been mapped in that area. Aerial photographs indicate the Tahyseco River valley might be the westernmost extent of rocks from the Rainbow

Range, but the area has not yet been mapped in detail (Fig. 5; cf. Bella Coola geological map by

HAGGART ET AL. [2006]). About 10 km to the NE of Tsitsutl Peak lies Anahim Peak, an isolated,

1,897 m high erosional remnant of a volcanic plug, covering some 12 km2 in area.

The Rainbow Range was studied in the late 1970s (BEVIER 1978, 1981: BEVIER ET AL. 1979), with most of its northern flank and Anahim Peak mapped. The central part south of Tsitsutl Peak and Beef Trail Creek, the western part around Taiataeszi Peak and the entire southern flank including Beef Peak, Macedo Peak and Mt. MacKenzie remain unstudied, but appear stratigraphically more complicated, possibly due to erosion, than the volcano’s northern flank. Rock types are also more diverse, with the central part appearing to consist in parts of a hydrothermally altered dome complex (BEVIER, PERS. COMM. 2012).

Figure 5 Satellite image (Landsat) of the Rainbow Range, showing the circular shield, the south-western “spur” around Mt. MacKenzie and Anahim Peak to the NE of the volcano. Peaks mentioned in the text are highlighted. The Tahyseco River valley at the photo’s left-hand edge is thought to be the approximate western extent of volcanic rocks.

Note broad glacial valleys radiating from the central parts of the volcano. The Chilcotin

Highway is visible at lower right. Image source: GOOGLE EARTH (2013A).

Figure 5

126º W 125º 45’ W

52º 46’ N

Anahim Pk. Tsitsutl Peak

Taiataeszi Pk. Tahyseco River Beef Pk .

Macedo Pk. Mt. MacKenzie 52º 36’ N

9 km

2.2.1.2 Stratigraphy and petrography

The volcanic rocks of the Rainbow Range are of an alkaline to mildly peralkaline and evolved nature. The unmapped central complex of domes, flows and intrusions are hydrothermally altered, as peralkaline rocks are highly susceptible to weathering and/or leaching processes

(BEVIER 1978). The varicoloured rocks give the range its name (SOUTHER 1977). The northern flank of the volcano was mapped in detail (BEVIER 1978), with the incised glacial valleys allowing for a comprehensive study of the volcano’s internal structure. An 845 m thick succession of gently outward dipping flows include (in stratigraphic order):

 Comenditic trachytes†, with individual flows of 30–60 m in thickness and up to 2 km in

length. Mildly porphyritic (5–10%) with phenocrysts of anorthoclase and hedenbergite.

 Mugearite flows of 1–4 m in thickness and intercalated breccias and air fall deposits.

Porphyritic (10–25%) with phenocrysts of plagioclase, olivine and clinopyroxene.

 Comendite, the most voluminous unit on the northern flank (constituting 75% of the suc-

cession). Flows of 30–60 m thickness and up to 3 km in length. Up to 10% phenocrysts of

either a sanidine+hedenbergite or sanidine+hedenbergite+fayalite+arfvedsonite assemblage.

 Hawaiite, erupted onto the comendite unit in the late stages of activity (similar to the Itcha

Range; see below). The hawaiites appear as plugs, dykes and flows of up to 10 m in thick-

ness. Highly porphyritic with up to 15% olivine, plagioclase and clinopyroxene phenocrysts.

† Mugearite is an alkaline, oligoclase-bearing variety of basaltic trachyandesite (cf. LEMAÎTRE ET AL. 1992), whereas a hawaiite is an olivine-bearing alkaline trachybasalt (cf. CHARLAND 1994). Comendites and pantellerites are alkaline (Na-rich) varieties of rhyolite, containing sodic feldspars (sanidine) and/or sodic pyroxenes (aegirine/acmite) and amphiboles (arfvedsonite/katophorite).

 Trachyte, described only from Anahim Peak. These rocks contains up to 10% of calcic

plagioclase and pyroxenes.

Anahim Peak, 10 km to the NE of the Rainbow Range, is a 1,897 m high erosional remnant of a trachytic plug and multiple flanking lava flows. These lavas were emplaced into a white rhyolite, which is thought to be lithologically identical to the Eocene Ootsa Lake Group, and a volcanogenic sandstone which is believed to be sourced from Rainbow Range rocks (BEVIER

1978). Anahim Peak consists of seven hawaiite flows with a cumulative thickness of 335 m.

Their original extent is unknown, but their coarser-grained nature might indicate they were ponded during cooling. A final episode of activity emplaced a trachytic plug into the hawaiite flows. Unlike lavas from the Rainbow Range, xenoliths (both volcanic and crustal) occur in the rocks erupted from Anahim Peak (BEVIER 1978, 1981).

2.2.1.3 Geochemistry

Volcanic rocks from the Rainbow Range exhibit a compositional bimodality between mafic alkaline rocks and felsic peralkaline ones. While alkaline lavas are present at many volcanic centres in western Canada, this bimodal characteristic is unique to the AVB (cf. SOUTHER ET AL.

1984; SOUTHER & SOUTHER 1994; CHARLAND 1994). The felsic lavas are the most voluminous rocks in the Rainbow Range and comprise pantellerites and comendites. A gap in SiO2 content

(between 56.3 and 64.8 wt%) is comparable to data from the Itcha Range (CHARLAND ET AL.

1995) and new data from the SMVF and BMVF (this study). The late-stage hawaiites have lower SiO2 (48.8−50.6 wt%) and total alkali contents (4.5−5.8 wt% Na2O+K2O), but higher

MgO, Fe, TiO2 and CaO than the comendites and comenditic trachytes (64.8−71.6 wt% SiO2,

8.9−11.6 wt% Na2O+K2O; BEVIER 1978).

Despite the silicic nature of these lavas (up to 71 wt% SiO2), their fluidity was high enough

(10 to 30 times less viscous than calc-alkaline rhyolites; BEVIER 1978) to allow flows to travel several kilometres downslope at a very low angle, thus leading to the construction of a shield volcano. Characteristically, these oversatured peralkaline rocks (comendite, pantellerites) and the mineral phases contained therein have high Na, K and Fe3+ contents vs. low Al, Ca and Mg, which inhibits polymerization of silica tetrahedra, leading to lower viscosity (cf. SCHMINCKE &

SWANSON 1967; SCHMINCKE 1974; BEVIER 1978; DINGWELL ET AL. 1985).

Olivine in the Rainbow Range comendites is predominantly fayalitic; in the mugearites and hawaiites, the olivines are more forsteritic. Calcic pyroxenes dominate, with Mg-rich diopsides occurring in the hawaiites, and (sodic) hedenbergites in comenditic trachytes and comendites.

Groundmass pyroxenes of acmitic (Na-rich) composition are chemically distinct from these phenocrysts and indicate the peralkaline nature of the erupted lavas. Sodic amphiboles only occur in the peralkaline silicic rocks, with arfvedsonite being the amphibole characteristic of such rocks. Equally characteristic is the presence of late-stage aenigmatite in the comenditic trachytes and comendites. Feldspars exist as sanidine in the comendites, anorthoclase in the comenditic trachytes and labradorite (± andesine) in the mugearites and hawaiites and oligoclase in the Anahim Peak trachyte. Table 1 (next page) briefly summarizes the main phenocrysts phases found in Rainbow Range lavas.

Table 1 Mineral compositions of olivines, pyroxenes and feldspars for the four major

Rainbow Range lava types (compiled from BEVIER [1978]).

Rock type Olivine Pyroxene Feldspar labradorite, minor Hawaiite forsterite (Fo68-71) diopsidic augite andesine labradorite, minor Mugearite Forsterite (Fo69) augite andesine Comenditic trachyte - hedenbergite anorthoclase

Comendite Fayalite (Fa95) hedenbergite sanidine

The origin of oversaturated, peralkaline lavas is commonly thought to be dominated by fractional crystallization of alkali feldspar from an alkali olivine basalt during residence of such melts in a crustal magma chamber (e.g., SOUTHER & HICKSON 1984; EDWARDS ET AL. 2002).

Continuing fractional crystallization progressively drives the composition of the remaining liquid and newly-forming crystals towards peralkalinity. Other processes such as anatexis and assimilation of crustal rocks, fluid transfers are also involved; a combination of any or all of these processes is proposed to be the most dominant process (MACDONALD ET AL. 2008). Often, a suite of petrogenetically related mafic and felsic lavas are found at the same volcano (WEBB &

WEAVER 1975; SELF & GUNN 1976; WEAVER 1977; SOUTHER ET AL. 1984; MACDONALD ET AL.

2008; GIORDANO ET AL. 2014). Feldspar fractionation and the presence of a volatile phase

(water, halogens) also appear to be important factors in the derivation of felsic magmas from mafic melts. Degrees of crystallization necessary for the genesis of evolved melts range between

70 and 90%. Commonly, small-scale and small-volume eruptions of more evolved magmas take place towards the end of a shield volcano’s activity (as seen in the shield volcanoes on Hawai’i or the Canary Islands; cf. FREY ET AL. 1990; SCHMINCKE 1982).

The mafic and felsic lavas of the Rainbow Range are interpreted to have been derived from the same parent magma (BEVIER 1978). The associated magma chamber was large and long- lived enough to allow continuous fractional crystallization and even compositional zoning of the stored magmas. Repeated retrieval of these magmas, each “batch” with a somewhat unique geochemical fingerprint, explains the close spatial and temporal association between mafic and felsic lavas. A melt generation model (BEVIER 1978) established a sequence of hawaiite− mugearite−comenditic trachyte−comendite as the most accurate one. However, this does not agree with the field observations of hawaiites constituting the final magmas to be erupted. The presence of a zoned magma chamber from which different melts were extracted at different times and/or eruption of fresh, mantle-derived batches of mafic magmas that then differentiated for different amounts of time in the chamber might explain this apparent contradiction.

Rainbow Range rocks are similar in major and trace element contents and 87Sr/86Sr ratios to

(per)alkaline rocks from other volcanic centres, such as Mt. Edziza in northern British Columbia

(SOUTHER ET AL. 1984; SOUTHER ET AL. 1984) and felsic volcanoes in the East African Rift

87 86 (WEBB & WEAVER 1975; WEAVER 1977). Initial ratios for Sr/ Sr range from 0.7031−0.727

(BEVIER 1989).

2.2.1.4 Timing of activity

The duration of volcanic activity in the Rainbow Range and at Anahim Peak and is constrained by four K-Ar ages from three units on the volcano’s northern flank and one from Anahim Peak

(BEVIER 1978). Due to this stratigraphically restricted coverage, the oldest rocks may not yet have been identified. The lowest comenditic trachyte unit mapped yielded the oldest age for the

Rainbow Range (8.7 ± 0.3 Ma). The overlying comendite and hawaiite units give ages of 7.2 ±

0.3 Ma and 7.9 ± 0.3 Ma, respectively. The stratigraphically lowest hawaiite flow from Anahim

Peak gives an age of 6.7 ± 0.3 Ma, thus indicating activity there took place some 500 ka after activity in the Rainbow Range had presumably ceased. Age determination using the 87Rb/86Sr whole-rock isochron technique yields an age of 8.6 ± 0.3 Ma, which agrees well with K-Ar ages and suggests no crustal contamination of Rainbow Range magmas (BEVIER 1989).

2.2.2 Ilgachuz Range

2.2.2.1 Geological Overview

The Ilgachuz Range is situated ca. 30 km ENE of the Rainbow Range (NTS 093C/11

[Christensen Creek] and 14 [Carnlick Creek]). This composite shield volcano rises about 1,200 m above the surrounding Chilcotin Plateau (peak at Far Mountain, 2,433 m), is elliptical in shape and extends ca. 30 km in NW-SE direction and ca. 20 km in W-E direction (SOUTHER 1986;

SOUTHER & SOUTHER 1994; Fig. 6). Like the Rainbow Range, this shield volcano exhibits a ra- dial drainage system and was extensively modified by glacial action, especially during the Fraser glaciation, which may have covered the entire volcano (SOUTHER & SOUTHER 1994). The western side of the range has been eroded by a glacier that once occupied the Dean River valley, leading to truncated spurs and a steep escarpment. Three major valleys (Festuca Creek in the northwest, Carnlick Creek in the northeast and Pan Creek in the East) dissect the central part of the volcano and show well-developed floodplains and steep valley walls typical of glacial erosion. Additional post-glacial erosion modified the volcano even further. Still, as with the

Rainbow Range, the Ilgachuz Range retains a general shield-like morphology and includes a hydrothermally altered complex of domes, crests and erosional remnants at its centre.

The repeated glaciations left deposits of varying thickness that mantle the lower parts of the volcano and cover most of the underlying igneous, volcaniclastic and metamorphic rocks of

Mesozoic ages. These are, in part, correlative with rocks of the Hazelton Group and are thought to belong to the Stikine terrane (SOUTHER & SOUTHER 1994). Porphyritic intrusions, flat-lying rhyolites and associated breccias of the Eocene Ootsa Lake Group unconformably overlie these older rocks. In turn, these Eocene rocks are unconformably overlain by basalts of the Neogene

Chilcotin Group (BEVIER 1983A/B; MATHEWS 1989). Two small outcrops of Mesozoic basement rocks in the eroded centre of the volcano indicate that the basal flows of the Ilgachuz Range unconformably overlie those Mesozoic rocks. Conversely, Ilgachuz lavas are thought to more or less conformably overlie the Chilcotin basalts (SOUTHER & SOUTHER 1994). However, no actual contacts between these basalts and lavas of Rainbow, Ilgachuz or Itcha affinity have been observed.

Early mapping (TIPPER 1969) divided the Ilgachuz Range into just two Cenozoic units which were combined with coeval rocks that were later assigned to the Chilcotin Group (BEVIER

1983A). The distinction between the flat-lying basalts of the Chilcotin Group and the overlying

Ilgachuz Range rocks, particularly for distal flows at the edge of the volcanic edifice, is, as has been noted, difficult by the lack of exposed contacts and led TIPPER (1969) to suggest that they are both coeval and coextensive. It has since been proven that AVB and Chilcotin Group rocks have distinct petrographical, geochemical and petrological attributes (BEVIER 1981; 1983A/B;

SOUTHER 1986).

Figure 6 Satellite image (Landsat) of the Ilgachuz Range. Blue triangles denote peaks that are referred to in the text. Note truncation of the volcanic edifice and escarpment on the western edge of the volcano as well as large glacial valleys (1 = Festuca Creek, 2 =

Carnlick Creek, 3 = Pan Creek). Rocks of Ilgachuz affinity outcrop outside the NE and SE boundaries of the photo. Dean River is at the western (left) edge of image, paralleling forest service road. (Image source: GOOGLE EARTH 2013B)

Figure 6

2.2.2.2 Stratigraphy and petrography

Detailed mapping of the Ilgachuz Range (SOUTHER & SOUTHER 1994) led to recognition of a complex evolution of the volcano during the Late Miocene and Early Pliocene. These authors established the Ilgachuz Group for intrusive, extrusive and related volcaniclastic rocks; this group was sub-divided into four formations and 20 map units. An additional two units for the later stages of activity were mapped in the eastern part of the volcano. Rocks of units close to the centre of the volcano have experienced extensive and likely repeated hydrothermal alteration.

A synopsis of the most stratigraphically important units follows‡. Please refer to Figure 5 for the locations of mentioned place names. (Note that unless indicated otherwise, all observations, data and interpretations referred to in this chapter come from SOUTHER & SOUTHER (1994). The various formations referred to herein are delineated by these authors based on the formations’ place in the overall stratigraphy and their individual petrographic and geochemical characteristics.)

The basement underlying the Ilgachuz Range consists of volcanic and metamorphic rocks of

Mesozoic ages (Hazelton Group), metamorphic and plutonic rocks of the Eocene Tatla Lake

Metamorphic Complex (TLMC; FRIEDMAN & ARMSTRONG 1988) and the Neogene Chilcotin basalts (TIPPER 1969; SOUTHER & SOUTHER 1994). Unconformably overlying most of these strata, lavas and associated breccias of the Dean River formation form the basal, elliptical

Ilgachuz shield that was constructed during the first stage of activity. This formation was likely erupted from a set of vents near the centre of the volcano and consists of weathered comendite

‡ For a full description, see SOUTHER & SOUTHER (1994), pp. 17-52, and the accompanying geological map

(1845A).

47 and comenditic trachyte flows and minor breccias that are exposed along the outer perimeter of the Ilgachuz Range and within the deeply incised glacial valleys. The minimum thickness of this formation is 300 m, with individual flows along the western escarpment and Carnlick Creek being 15 to 30 m thick although some flows reach 150 m in thickness. Columnar jointing, basal and top breccias are common features. The comendites and comenditic trachytes are holocrystalline and moderately porphyritic, with unzoned alkali feldspars being by far the most abundant phenocryst phase. Hedenbergitic clinopyroxenes and fayalitic olivine make up the remaining phenocrysts. The groundmass is similarly dominated by feldspar laths. Sodic pyroxenes and amphiboles are further components and indicate the alkaline character of these rocks. The extent and volume of lavas of the Dean River formation, together with a lack of compositional variation, are interpreted that these lavas were erupted in a rapid fashion from a magma reservoir that did not experience much evolution (SOUTHER & SOUTHER 1994).

Flows, domes, and their intrusive equivalents of the Carnlick Creek Volcanics conformably overlie the older Dean River Volcanics. Early explosive and voluminous effusive eruptions of rhyolites were followed by intrusion and eruption of trachytes (SOUTHER & SOUTHER 1994).

Rocks from the Carnlick Creek Formation underlie and/or build most of the prominent peaks in the central, southern and eastern parts of the Ilgachuz Range. Most of these, such as Pipe Organ

Mtn., Mizzen Mtn., Carnlick Mtn. or Calliope Mtn. (Fig. 6) are considered to be eruptive centres of the Carnlick Creek Formation (SOUTHER & SOUTHER 1994). This formation was subdivided into eight map units that are expressed as a “shield and dome facies” and/or an “intracaldera facies”. The former include thick flows (over 300 m in overall thickness), domes and pyroclastics that built a second shield on top of the existing Dean River basal shield, especially in the northern part of the Range. The intracaldera facies includes multiple subaerial tephra deposits

48 that can be found up to 25 km to the NE of the Ilgachuz Range. In its central part, epiclastic deposits (consisting in part of Dean River comendites that were reworked by debris flows and/or landslides) as well as lacustrine tuffs and fluvial volcaniclastics were laid down in and in close proximity to a central caldera that formed either before or during the early stages of eruptions.

A complex intracaldera facies was deposited in a ca. 5 km wide depression in the centre of the

Ilgachuz shield. This caldera was likely caused by the large erupted volume of Dean River volcanics that created a void in a shallow magma chamber and subsequent collapse of the then existing summit (SOUTHER & SOUTHER 1994). Several episodes of volcanic activity took place in and along the rim of the caldera, filling it with rhyolite domes and comendite flows, some of which spilled over the caldera rim. Intercalated flows and pyroclastic deposits indicate that volcanic activity likely took place at numerous individual centres in a somewhat synchronous fashion. At some point, possibly during a period of glaciation, ponded water formed a lake into

3 which large amounts of vitric, lacustrine tuff (~2 km ; SOUTHER 1984) were deposited. This fine grained, glassy tuff exhibits thin beds with graded and crossbedded laminations and is intercalated with volcaniclastic deposits, lapilli and breccias. The presence of large amounts of glass and lapilli suggests the eruption of this tuff took place during times of glaciation (SOUTHER

& SOUTHER 1994). The latest stage of activity led to voluminous trachyte flows of up 150 m in thickness (SOUTHER 1986) that were also ponded and overlaid most of the older deposits.

Compositionally, the older units of the Carnlick Creek formation are comendites (Mizzen

Mtn.), whereas younger ones are comenditic trachytes, trachytes (Pipe Organ Mtn.) or phonolites. While spatially and temporally distinct, the individual units are broadly similar in their petrographical and geochemical attributes. The older rhyolites and comendites are porphyritic

(10−40%), with sanidine, hedenbergite and aenigmatite being the major phenocryst phases.

Fayalitic olivine and sodic pyroxenes and amphiboles make up the groundmass. Younger comendites are often aphyric and show flow banding. Phenocrysts in the comenditic trachytes and trachytes are pre-dominantly anorthoclase, with minor sodic pyroxenes and amphiboles.

Coarse-grained (<30 cm) and glassy outer breccias are common for most of these units. The late-stage trachytes were erupted as two petrographically and mineralogically distinct lithologies at Pipe Organ Mtn., Mt. Scot and Go-around Mtn., respectively. The former overlie the comendites and are even more porphyritic (30−50%) with sanidine, anorthoclase and sodic oligoclase being the main phenocryst phases. The high content of phenocrysts, both in the erupted lavas and related intrusions indicate emplacement as a highly viscous orthocumulate

(SOUTHER & SOUTHER 1994). Some of the comendites and trachytes were also emplaced as subvolcanic intrusions.

The upper shield of the Ilgachuz Range is made up of the Arnica Lake Volcanics. This unit comprises remnants of flows that cap the central peaks. It disconformably rests on the Carnlick

Creek formation in the centre and the Dean River formation at the shield’s periphery. Arnica

Lake flows were erupted relatively shortly after the eruption of the Carnlick Creek rocks, as the latter were only locally eroded to any large degree. The Arnica Lake formation is up to 335 m thick. Individual flows range between 20 and 150 m in thickness and appear to have been erupted from a central source area. Extrapolation from the outward-dipping flows points to a source built on top of the caldera at a former summit of the Ilgachuz Range that has since been destroyed by erosion (SOUTHER & SOUTHER 1994).

The geochemistry and mineralogy of the Arnica Lake Volcanics share much with the preceding units. Both extrusive and intrusive rocks are uniformly porphyritic comendites and pantellerites with up to 30% phenocrysts (anorthoclase and sanidine, sodic pyroxenes and

50 amphiboles). Like the Dean River and Carnlick Creek volcanics, olivine is almost purely fayalitic in composition. The large amounts of comenditic obsidian point to a rapid chilling of feeder dykes and outer flow margins. No significant change in texture or mineralogy is observed between thin and thick flows.

Rocks assigned to the Dean River, Carnlick Creek and Arnica Lake formations comprise the main, predominantly comenditic shield of the Ilgachuz Range. Overlying these, especially in the northern, eastern and southern parts of the Range and capping many of the higher peaks (e.g., Far

Mtn.), are units of the Tundra Mountain Volcanics. Predominantly of an alkali basaltic composition, these rocks form a thin mantle and have been subdivided by SOUTHER & SOUTHER (1994) into four map units. A late stage rhyolite of limited extent and small volume around the Range’s highest peak, Far Mtn., and Go-around Mtn. in the southern part appears to be coeval with the basalts. This rhyolite is thought to represent a residual felsic magma that had remained from earlier periods of activity. A well-preserved feeder dyke on the northern side of Festuca Creek also belongs to this formation.

Eruption of basaltic rather than rhyolitic magmas began about 1 Ma after the onset activity in the Ilgachuz Range (see ch. 2.2.2.4 below). The lowermost members of the Tundra Mountain formation unconformably overlie the older units, possibly indicating the removal of older lavas by erosion. The thicknesses of the formation’s map units range between 35 and 150 m and it mainly exists as remnant flows, pyroclastic breccias and necks. The presence of scoria indicates fire fountaining during eruptive periods. The early basalts and trachybasalts are similar to the older comendites in that they are porphyritic with calcic and/or sodic plagioclase, forsteritic olivine and minor calcic augites being the phenocrysts phases. Later-stage basalts form a mono- tonous succession of thin pāhoehoe flows that are predominantly aphyric with a uniform

51 mineralogy dominated by labradorite and minor olivine. The coeval rhyolite unit is similar in geochemistry and mineralogy to the alkaline rocks of earlier eruptive episodes. Rocks of the

Tundra Mountain formation appear to have erupted from multiple vents both to the north-west and east of the volcano’s centre. A final, late-stage eruption of basalts built a small pyroclastic cone on the eastern flank of Mizzen Mtn, presumably during the Late Pliocene or even the

Pleistocene (SOUTHER & SOUTHER 1994).

2.2.2.3 Geochemistry

As with the other two shield volcanoes of the AVB, whole rock geochemistry of the Ilgachuz

Range show a markedly bimodal distribution with a mafic (45-52 wt% SiO2) and a felsic suite

(59-76 wt% SiO2). These rocks are nepheline normative and quartz normative, respectively.

Rocks of the upper shield (the Tundra Mountain Formation described above) and the late-stage basalts make up the entirety of the mafic suite, with the majority of the units plotting as trachybasalts/hawaiites in a total alkali vs. silica (TAS) diagram (LE MAÎTRE ET AL. 1992; see ch. 3.5.1 for a comparison plot with new data from this study). Trace element plots (SOUTHER & SOU-

THER 1994, p. 61) show considerable overlap between the mafic and felsic suites. Additionally, by and large constant LILE ratios also indicate a petrogenetical link between the two rock series insofar as a common parental magma is concerned. Discriminant plots based on minor element data from the mafic and felsic suites strongly indicate a within-plate setting (Figs. 69 and 70 in

SOUTHER & SOUTHER [1994]). The felsic suite also has the distinct peralkaline character typical for the centres in the west and central part of the AVB (BEVIER 1978, 1981: SOUTHER 1986;

CHARLAND ET AL. 1995). Mineral chemistry analyses of olivines, pyroxenes and feldspars show a similar bimodal distribution between early, felsic rocks and later, more mafic rocks (Table 2).

Table 2 Mineral compositions of olivines, pyroxenes and feldspars for the four major

Ilgachuz Group units and late-stage Flank basalt (modified from SOUTHER & SOUTHER

1994).

Formation name Olivine Pyroxene Feldspar (Mafic/Felsic) exclusively sanidine, Dean River (F) fayalitic (

fayalitic (Fo5-35) to Diopsidic augite, Tundra Mtn. (M) labradorite forsteritic (Fo55-78) hedenbergite

Flank basalt (M) forsteritic (

Lead and strontium isotope data are consistent with data from other AVB centres (BEVIER

1989). The initial Pb and Sr values are low (87Sr/86Sr = 0.7031−0.7042) and characteristic of a depleted mantle source. However, the high isotopic ratios preclude a MORB source and suggest an affinity with a source that is linked with seamounts and oceanic islands in the northeast

Pacific Ocean. A final eruption of basalt during the Quaternary in the eastern part of the

Ilgachuz Range is suggested to be connected to a deeper source that supplied magma that was less depleted than any of the preceding ones.

Whatever the primary source of the magmas, there is evidence that basaltic magmas, possibly initiated by a mantle plume (BEVIER ET AL. 1979), ascended along deep fractures and then pooled at the lower crust where they led to partial melting of the surrounding rocks (SOUTHER &

SOUTHER 1994). Subsequently, ascending melts created a shallow magma chamber from which

53 comenditic lavas of the Dean River formation erupted and build the first, basal shield. Once this magma chamber was established, continuing fractional crystallization created ever more highly differentiated magmas that were then erupted as geochemically distinct batches as the Carnlick

Creek and Arnica Lake Formations. Injections of fresh magma from the lower crustal reservoir replenished and modified the content of the shallow magma chamber (SOUTHER & SOUTHER

1994). Occasionally, these fresher (and more mafic) magmas manage to “punch through”, resulting in small-volume basaltic eruptions during times of generally felsic magmatism.

Eventually, a more voluminous batch of basaltic magma was tapped from underneath the fractionated low-crustal reservoir and erupted in the Early Pliocene to produce the Tundra

Mountain Formation. The motion of the North American Plate to the southwest eventually cut off magma supply from this reservoir, causing volcanic activity in the Ilgachuz Range to wane and, after the small-scale eruption of (primary?) mantle-sourced basalt on the Range’s east flank, to cease altogether at ~4 Ma (SOUTHER & SOUTHER 1994).

2.2.2.4 Timing of activity

Volcanic activity in the Ilgachuz Range commenced ~600 ka after the final periods of activity in the Rainbow Range and Anahim Peak (SOUTHER 1986). A set of 22 K-Ar dates were produced

(SOUTHER & SOUTHER 1994) from ten of the units mapped by these authors. These age data give a range from 6.1 ± 0.2 Ma for rocks of the Carnlick Creek Formation to 4.0 ± 0.6 Ma for the

Tundra Mountain Formation. Somewhat incongruously, ages for Dean River comendites range from 5.7 ± 0.1 Ma to 5.1 ± 0.1 Ma, which is at odds with their place at the bottom of the stratigraphy established by SOUTHER & SOUTHER (1994). However, this could be due to some of the former samples containing excess atmospheric argon, thus yielding older ages. For the stratigra-

54 phically highest Tundra Mountain Formation, results for the various basaltic units range from 5.6 to 4.9 ± 0.2 Ma, with the sole rhyolitic unit giving the youngest age (4.0 ± 0.6 Ma). This too appears to contradict the presumably coeval eruption of the basalts of the Tundra Mountain formation and the rhyolite. A whole-rock Rb-Sr isochron regression yields an age of 6.6 ± 0.7 Ma

(BEVIER 1989). While this is older than any of the K-Ar ages, it is still within error of those ages. The consistency between the Rb-Sr date also indicates lack of contamination of Ilgachuz magmas by crustal rocks.

Overall, 17 out of 22 Ilgachuz ages fall into a period between 5.5 and 4.9 Ma, thus indicating a relatively short period of high activity during the Late Miocene and Early Pliocene, with few, if any, extensive dormant periods (SOUTHER & SOUTHER 1994). The overall construction of the

Ilgachuz Range took around 2 Ma, similar to the Rainbow and Itcha ranges (SOUTHER 1986; see below). This indicates slightly longer “lifetimes” than other hot-spot affiliated volcanoes such as those on Hawai’i (e.g., MOORE & CLAGUE 1992), La Réunion (e.g., OEHLER ET AL. 2008) or the

Canary Islands (e.g., PARIS ET AL. 2005). See ch. 4 for a discussion of this difference.

2.2.3 Itcha Range

2.2.3.1 Geological Overview

The Itcha Range is the easternmost shield volcano in the AVB, located ~30 km ESE of the centre of the Ilgachuz Range. Extending some 16 km in N-S direction and 18 km in WNW-ESE direction, the volcano covers an area of ~ 300 km2 and rises some 700 m above the surrounding plateau to 2,427 m at Mt. Downton in its central part (Figs. 7, 8). The Itcha Range is the smallest of the three central volcanoes and also the least “shield-like” due to a predominance of

55 overlapping and coalescing domes (STOUT & NICHOLLS 1983; CHARLAND ET AL. 1993, 1995;

CHARLAND 1994). The range also is the most heavily modified by erosion, lacking the shield- like appearance of the Rainbow and Ilgachuz ranges; however, some craters and cinder cones appear to have survived glacial modification, especially on the eastern flank of the volcano.

Furthermore, there is evidence for faulting in the Itcha Ranges (TIPPER 1969; CHARLAND ET AL.

1993) that is reportedly lacking in the other two shield volcanoes (BEVIER 1978; SOUTHER &

SOUTHER 1994).

Volcanic activity in the Itcha Range lasted from the Late Pliocene to around the Middle

Pleistocene (SOUTHER 1986). Unlike the Rainbow and Ilgachuz ranges, the Itcha Range has two associated areas of coeval activity outside of the actual central volcano in form of regionally extensive cone fields to the south and east, respectively: the Satah Mountain Volcanic Field

(SMVF) which extends along a NNW-SSE trending ridge for ~40 km; and the Baldface

Mountain Volcanic Field (BMVF) 20 km to the east (this study). See ch. 3 for a detailed description and discussion of these two fields.

Figure 7 Satellite image (Landsat) of the Itcha Range with three major peaks highlighted. Note irregular shape of the volcanic edifice and young reddish cinder cones on the northeastern and southeastern flanks (image source: GOOGLE EARTH 2013C).

Figure 7

125º W 124º 50’ W

Mt. 52º 45’ N Fukawi

Itcha Mtn.

Mt. Downton

52º 40’ N

5 km

2.2.3.2 Stratigraphy and petrography

Mapping of the volcanic edifice produced a detailed stratigraphy (CHARLAND ET AL. 1993;

CHARLAND 1994) that is similar to that of both the Rainbow and Ilgachuz ranges. A summary of this stratigraphy follows; for complete descriptions and discussion, please refer to CHARLAND

(1994). Basement rocks belong, as farther west, to the Mesozoic, Eocene and Neogene strata discussed previously. These crop out in the deeply eroded centre of the volcano. The Itcha

Range experienced repeated glaciations, some of them contemporaneous with volcanic activity

(CHARLAND ET AL. 1993). Glacial drift and colluvial deposits cover large tracts of the volcano and the areas between it and the BMVF and SMVF. Dense forests and extensive swamps and muskeg further limit rock exposures and obscure the actual extent of Itcha rocks (Fig. 8).

D I

Figure 8 The central and southern parts of the Itcha Range as seen from a small volcanic centre in the Baldface Mountain Volcanic Field 20 km to the East. DMt.

Downton, IItcha Mtn. Note general lack of shield-like morphology, young, reddish- coloured cinder cones on southern flank (on left), broad glacial valley (facing towards viewer) and dense boreal forests between the volcano and the BMVF.

The basal shield is composed of thick trachytic, phonolitic and rhyolitic flows. Two periods of activity have their own distinct geochemical characteristics, with the earlier eruptive product being slightly nepheline normative and the latter more highly nepheline normative or quartz normative. The trachytes are aphyric and were erupted both as relatively fluid flows and/or domes with associated volcanogenic breccias. Minor basaltic flows are intercalated into this sequence and might again indicate small batches of basaltic magmas punching through the felsic magmas and being erupted synchronously with them (CHARLAND ET AL. 1995). As with the

Ilgachuz Range, most of the volcanic activity seems to have been located near the centre of the shield (CHARLAND 1994).

Subsequent volcanic activity changed in character from effusive to more explosive. During this stage, more porphyritic trachytes were erupted in the northern and southern parts of the volcano, mostly in the form of thin lava flows and pyroclastic material. This material was subsequently reworked and is intercalated with later lava flows. Following this episode, the later-stage quartz trachytes and trachytes were erupted as small domes, plugs and intrusions, perhaps indicating an increase in viscosity of the magmas. These later lavas are porphyritic, with alkali feldspars (sanidine) being the dominant phenocryst phase; fayalitic olivines and clinopyroxenes (aegirine) are minor constituents. Of note is a scoriaceous breccia that includes xenoliths from the underlying volcanic basement rocks and older metamorphic rocks (CHARLAND

1994). Trachytic to phonolitic subvolcanic intrusions and thick flows (up to 100 m in thickness and possibly emplaced as down-slope creeping coulees) form the most voluminous unit of the felsic shield-building stage. These rocks comprise large parts of the central and western parts of the volcano where flows directly and unconformably overlie the pre-Itcha lithologies. Towards the end of the shield stage, eruption of a unique, megacrystic trachyte with a high content (<

25%) of plagioclase, olivine and clinopyroxene phenocrysts took place on the western flanks of the volcano.

As in the case of the Ilgachuz Range, the final stages of volcanic activity in the Itchas involved more mafic rocks of a basanitic or alkali basaltic composition that unconformably overlie the basal shield (CHARLAND ET AL. 1995). The basanites contain more (up to 16.5 wt%) normative nepheline than the alkali basalts. The latter were further subdivided into aphyric or plagioclase-phyric hawaiites and porphyritic alkali-olivine basalts (AOB) that are hypersthene- normative and contain forsteritic olivine, plagioclase and even quartz as phenocrysts. The AOBs also often carry a wide range of igneous and lithic xenocrysts and xenoliths. The hawaiites are defined by CHARLAND ET AL. (1995) as having andesine feldspar in their norm and MgO contents in excess of 5 wt%. In a setting interpreted as similar to the Ilgachuz Range, eruption of these mafic lavas predominantly took place in the eastern half of the volcanic edifice from numerous monogenetic cinder cones and/or fissures. Some of these are well-preserved and are conspicuous due to their reddish colour, possibly caused by subsequent oxidation (Figs. 7, 8).

Pillow lavas and hyaloclastite breccias are evidence of both subaqueous and/or subglacial eruptions (CHARLAND 1994); K/Ar ages for lavas of this most recent period of activity overlap with a regional glaciation in the Middle Pleistocene (MATHEWS & ROUSE 1986). Both ‘a’a and pāhoehoe flow morphologies have been identified, with individual flows being of smaller thicknesses (<30 m) than their felsic counterparts.

The hawaiites are more extensive than the AOBs and were erupted in the early stages of mafic activity, their eruption loci often in existing structures in the central and southeastern parts of the volcano. The AOB were erupted both coevally with and after eruption of the hawaiites. The latest stage of activity produced small basanitic flows that contain conspicuous mantle xenoliths

(STOUT & NICHOLLS 1983). Of note is the presence of two sets of fractures that cut the volcanic edifice: one set trends between 010 to 330º, the other between 055 to 090º (TIPPER 1969;

CHARLAND 1994). The orientation of the first set is similar to the orientation of the morphological high many centres in the SMVF are located on (cf. ch. 3.2.1). Unlike the Rainbow and

Ilgachuz ranges, the centre of the Itcha Range appears to not have been affected by pervasive, post-eruptive hydrothermal alteration (CHARLAND ET AL. 1993).

2.2.3.3 Geochemistry

Rocks of the Itcha Range show many similarities with those of the Rainbow and Ilgachuz ranges.

None of them are primary melts and the same bimodality between early, voluminous and more felsic rocks, and later, more mafic and less voluminous rocks can be observed, with the same

Daly Gap (between 52 and 59 wt% SiO2) separating them (CHARLAND ET AL. 1993; CHARLAND

1994). This trait and intercalated mafic units within the early-stage felsic rocks indicate the existence of a petrogenetical link between these suites. A major difference, however, is that rocks from the Itcha Range are generally more undersaturated in silica (<69 wt% SiO2 overall), especially those of the mafic suite (<44.2 wt% SiO2; CHARLAND ET AL. 1995), than those from the Rainbow and Ilgachuz ranges. The peralkaline comendites and pantellerites of those ranges are missing in the Itcha Range. The majority of Itcha rocks have agpaiitic indices† identifying these rocks as metaluminous (CHARLAND ET AL. 1993; cf. ch. 4.4.3). Trace element data and ratios show both good correlations of the felsic rocks with other AVB centres. Rare earth

† The agpaiitic index refers to the alkali over aluminum ratio (Na+K/Al) of a given rock. Rocks with a ratio >1 are considered peralkaline, those with a ratio of <1 metaluminous.

61 element profiles show similarly strong fractionation patterns of these elements in the mafic and felsic suites of the Itcha Range, with higher enrichment of the light and heavy rare earth elements (LREE, HREE) in the felsic rocks (CHARLAND 1994).

In addition to fractional crystallization, petrogenesis of the felsic rocks of the Itcha Range requires some kind of crustal component in order to explain certain REE patterns and ratios

(CHARLAND 1994), despite Pb and Sr isotope data suggesting the opposite (BEVIER 1989). Initial

87Sr/86Sr ratios determined for the mafic Itcha lavas range from 0.7028 to 0.7034, for the felsic ones from 0.7031 to 0.7061 (CHARLAND ET AL. 1993), showing overlap with ratios determined for other centres in the AVB (BEVIER 1989). When age correction is applied to the felsic rocks, their initial ratios become impossible to tell from the mafic ones. Together with the parallel REE profiles, this further indicates that the felsic and mafic magmas are petrogenetically related.

High-pressure crystal fractionation that explains the genesis of the mafic rocks (especially the hawaiites) is common to some of the other alkaline volcanic complexes in western Canada such as Mt. Edziza (SOUTHER ET AL. 1984) or Level Mtn. (HAMILTON 1981) and does not necessarily require assimilation of crustal rocks (CHARLAND ET AL. 1995). The trace element patterns of the mafic suite are similar to those from other intraplate alkaline volcanoes (SUN & MCDONOUGH

1989).

A two-trend evolution in the later stages of activity towards both silica oversaturation and undersaturation could be explained by the tapping of either different and/or compositionally distinct parts of a shallow magma chamber or smaller, isolated batches that evolved along individual differentiation paths (cf. figures on p. 138 of CHARLAND ET AL. 1993). The evolution from AOBs to increasingly smaller volume basanites fits into this picture both within the framework of the other two large central volcanoes and the AVB as a whole (SOUTHER ET AL.

1987; see ch. 2.3.2 below). The undersaturated nature of the basanites is interpreted to indicate genesis of magma at decreasing degrees of partial melting and/or the magma being sourced from a distinct, deeper and less depleted mantle source (SOUTHER ET AL. 1987).

2.2.3.4 Timing of activity

The age of the Itcha Range is constrained by seven K-Ar dates (SOUTHER 1986) that indicate that activity commenced at ~3.5 Ma. Construction of the basal shield lasted between 300 and 500 ka, similar to the Ilgachuz Range (SOUTHER & SOUTHER 1994). Unlike at that volcano, a period of volcanic quiescence lasting ~900 ka followed in the Itcha Range (CHARLAND 1994). The late- stage mafic eruptions appear to have taken place over an extended period from 2.2 to 0.8 Ma, which also is unusually long when compared to either the Rainbow or the Ilgachuz Ranges. A well-preserved basanitic cinder cone in the central part of the volcano has been suggested to be as young as the basanitic Nazko Cone farther east (CHARLAND ET AL. 1993; see next chapter).

The evolution from felsic to mafic and increasingly silica-undersaturated magmatism in addition to an apparent eastward shift of activity within the Itcha Range could be a function of the decrease in and eventual ceasing of magma generation due to the underlying reservoir/conduit being cut off by the movement of the North American plate by the hot-spot

(CHARLAND ET AL. 1995). This, again, mirrors the evolution of the Ilgachuz Range as well as many other hot-spot affiliated volcanic systems around the world, such as Hawai’i or the Snake

River Plain/Yellowstone hot-spot (e.g., MOORE & CLAGUE 1992; JAMES ET AL. 2011).

2.3 The eastern part of the Anahim Volcanic Belt

The extent of Quaternary volcanic activity east of the Itcha Range is not well defined. The

Baldface Mountain Volcanic Field, situated some 20 km to the east, lies directly on the trend of the proposed hot-spot (this study). That field comprises numerous tephra cones, lava flows of largely unknown origin and extent and erosional remnants of both. Please see chapters 3.3 and

3.6 for a detailed discussion of the BMVF’s field relations, geochemistry and geochronology.

2.3.1 Basement rocks and their relation to the AVB

Farther east and southeast of the BMVF the terrain becomes more rugged. This area around

Redtop Mtn., Toil Mtn., Mt. Dent and Mt. Sheringham (Fig. 4) is mapped as part of the Eocene

Ootsa Lake Group (OLG) which comprises rhyolites, dacites with minor andesites and/or basalts and their associated volcanogenic sediments (TIPPER 1969). A more recent study by

MIHALYNUK ET AL. (2008) better defined the geology of the area (NTS 093C/09, Chezacut) and parts of the OLG were re-assigned to underlying Mesozoic strata of the Stikine terrane (Fig. 9).

These latter strata largely consist of basaltic and andesitic flows at the bottom of the succession and various, partially volcanogenically derived, clastic sedimentary rocks at its top. The maximum thickness of this succession is estimated to be up to 1,500 m; tilting, folding and low-grade metamorphism took place after the emplacement, but preceded Eocene volcanic activity

(MIHALYNUK ET AL. 2008). On Luck Mtn. (cf. Fig. 4), east of the flats that border the SMVF, various volcano-sedimentary strata of Mesozoic age are exposed (TIPPER 1969; MIHALYNUK ET

AL. 2008).

Lavas and associated sedimentary rocks of the OLG extensively underlie NTS 093C/09

(Chezacut) and surrounding areas. The calc-alkaline lavas of the Group are pre-dominantly basaltic to dacitic in character and extend from the north under the Chilcotin Plateau. This sequence of lavas and volcanogenic rocks reaches a potential maximum thickness of 3,800 m

(MIHALYNUK ET AL. 2008). Reported dates range from 53 to 44 Ma (palynological dates:

40 39 GRAINGER ET AL. 2001; Ar/ Ar dates: METCALFE ET AL. 1997). Lithologically identical rocks of Oligocene age are reported from the area as well (TIPPER 1969), but are not mentioned in the more recent study (MIHALYNUK ET AL. 2008).

Figure 9 Schematic stratigraphy column for the eastern-most part of the SMVF, in the vicinity of Luck Mtn. (cf. Fig. 4). Note the generally low thickness of Chilcotin Group basalts; their paleo-valley filling character is also schematically indicated. Eocene and Meso- zoic strata are cut off by unconformities (highly simplified from MIHALYNUK ET AL. [2008]).

AVB strata pinch out to the east (Fig. 9) and contacts with underlying units at the eastern end of the study area are somewhat conjectural due to lack of actual surface outcrops as the bedrock is covered by hummocky moraine deposits. This area does not show much relief and is inter-

66 preted, together with the deposition of moraines, to have been shaped during the retreat of ice at the end of the last glaciation (TIPPER 1969, 1971). Contacts between Neogene and older rocks are generally thought to be unconformable and were mapped using a combination of gravity, aeromagnetic and glaciogenic data (MIHALYNUK ET AL. 2008, 2009; MIHALYNUK, PERS. COMM.

2013). These authors also report high-angle reverse faulting in AVB flows in the NE part of the present study area which are interpreted as (un)loading effects during and/or after glaciation. No such features were observed during field work for this study (see ch. 3.3.1).

The terrain to the east becomes more elevated and rugged. The rocks at surface in this area are largely of Eocene and Mesozoic ages and in places overlain by the Chilcotin basalts

(MIHALYNUK ET AL. 2008).

2.3.2 Nazko Cone

The eastern terminus of the proposed Anahim hot-spot is thought to be Nazko Cone (52º 55.7’ N,

123º 43.9 W; NTS 093B/13, Marmot Lake) and its vicinity (HICKSON 1987; SOUTHER ET AL.

1987). Nazko Cone is a 120 m-high polygenetic pyroclastic cone that is presently being used as a rock quarry (Fig. 10). SOUTHER ET AL. (1987) describe a minimum of three subglacial and subaerial episodes of activity during the Quaternary. The oldest of these episode produced a basanitic lava flow dated at 0.340 ± 0.003 Ma (K-Ar age; SOUTHER ET AL. 1987) and 0.333 ±

0.005 Ma (40Ar/39Ar age; this study). The second episode occurred subglacially, possibly during the Fraser Glaciation during the Late Pleistocene (SOUTHER ET AL. 1987). The most recent episode built the present pyroclastic cone and produced two low-volume lava flows as well as a fallout deposit within 5 km of the cone (Fig. 11). No radiometric ages exist for lavas from the second episode. However, the third episode was confined by radiocarbon dating of peat that is

67 intercalated with the tephra fallout that gave an age of 7,200 years BP (SOUTHER ET AL. 1987:

HICKSON ET AL. 2009). Based on these ages, activity lasted for over 300 ka. After the third, short-lived episode, Nazko Cone has remained inactive during the remainder of the Holocene.

The centre is located close to lavas of the Late Miocene Cheslatta Lake suite of Chilcotin Group basalts (DOHANEY 2009), but the relationship of Nazko lavas with underlying units is currently unknown. RUSSELL (PERS. COMM. 2011) reported that a large number of previously unknown volcanic centres exist in the vicinity south and west of Nazko Cone. While the affiliation of these centres is unclear as they have yet to be studied in detail (HICKSON, PERS. COMM. 2014), it appears that many of these centres are, in fact, part of the Baldface Mtn. volcanic field. An extensive lava flow (>15 km long) has been recognized 15 km to the west of Nazko Cone (HICK-

SON ET AL. 2009); no source has yet been found, but a postglacial age is assumed for this flow.

Nazko lavas are more alkaline and undersaturated in composition than other rocks of the AVB or Chilcotin basalts (BEVIER 1983A). They all are nepheline normative and are classified as basanites, with SiO2 contents of 43−48 wt% and alkali (Na+K) contents of 5.31−8.48 wt%

(SOUTHER ET AL. 1987; cf. ch. 4.4.2). The second and third episodes are more primitive and undersaturated (up to 9.3 wt% MgO compared to 5.8 wt% during the first eruptive episode), with lower SiO2 contents by ~5 % and alkalis by ~3% compared to the first episode. Considering the small overall volume of erupted material (less than 1 km3), this might indicate small-scale, compositional changes in a heterogeneous magma source. In comparison, basalts of the Chilcotin

Group which underlie the area have slightly higher SiO2 contents (up to 10 wt% more), and even lower alkali contents. These more undersaturated Nazko lavas might indicate a magma source that is deeper and/or less depleted than those for other AVB centres (SOUTHER ET AL. 1987).

This is similar to the evolution towards more undersaturated magmas in the Ilgachuz and Itcha ranges (SOUTHER & SOUTHER 1994; CHARLAND ET AL. 1995).

The most recent geologic activity anywhere in the AVB was an earthquake swarm that occurred in October 2007, at 52º 52.5’ N and 124º 2.5’ W, about 20 km SW of Nazko Cone

(HICKSON ET AL. 2009; CASSIDY ET AL. 2011). This swarm was located in a heretofore seismically inactive region of the Nechako Basin. Eight earthquakes (MW 2.3–2.9) were followed by over 1,000 microearthquakes, most of which were located at a depth of 25–35 km and within a 5 km radius. Spasmodic bursts associated with the earthquake swarm indicated the breaking of rock by moving magma; this has been interpreted as injection of magma at mid- crustal levels (CASSIDY ET AL. 2011). Apart from this episode, there are currently no indications of renewed volcanic activity in the area (HICKSON ET AL. 2009).

Figure 10 (Top) View east on Nazko Cone. The vegetated area and the red edge on the right are part of the cone that was built during the third eruptive stage, which also produced the black scoria deposit that is being mined in the foreground.

(Bottom) Detail of the fallout deposit. Note bomb to the left of person and horizons with larger scoriae.

Figure 10

Figure 11 (Top) Oblique aerial view of Nazko Cone (view towards the NE). Blue triangle at left denotes location of geochron sample (N-1-2, 0.333 ± 0.005 Ma; see ch. 3.5) from flow of the first eruptive period in the Late Pleistocene. Note pink rocks at the centre of the cone that is used as a rock quarry and ogives (pressure ridges) on lava flow in the foreground. Image source: GOOGLE EARTH (2013D).

(Bottom) Coloured aerial view indicating products of the three eruptive episodes: Basanite flow from first episode (blue, overlain by scoria from third episode); subglacial mound from second episode (pink), largely modified by mining; pyroclastic cone (green), lava flows (yellow) and fallout deposit (orange) from third eruptive episode in the Holocene.

Scale bar at bottom left indicates 200 m. Image source: GOOGLE EARTH (2013D). Geology modified from SOUTHER ET AL. (1987).

Figure 11

2.4 Origin of AVB volcanoes

Volcanic rocks of AVB affiliation, as well as other large volcanic centres in western Canada, such as Mt. Edziza or Level Mtn. (SOUTHER 1977; HAMILTON 1981; SOUTHER ET AL. 1984) are predominantly alkaline in character. While this “trait” is generally and broadly indicative of a within-plate setting, it can suggest either a hot-spot associated with a mantle plume source or a rifting-related source (WEBB & WEAVER 1975; WEAVER 1977; BEVIER ET AL. 1979; SOUTHER

1986). There are only few areas worldwide that exhibit continental peralkaline volcanism. The

Turkana region of the East African Rift and AVB are the only two instances where felsic shield volcanoes developed (WEBB & WEAVER 1975; WEAVER 1977; CHARLAND ET AL. 1993). In western Canada, the (per)alkaline rocks of the Mt. Edziza-Spectrum Range complex in northern

British Columbia were erupted in a setting of crustal extension (SOUTHER ET AL. 1984; EDWARDS

& RUSSELL 1999, 2000). As at other large central volcanoes in an intraplate settings,

(per)alkaline rocks are commonly erupted in small volumes late in the life of a volcano (e.g.,

FREY AT AL. 1990).

Conversely, the Rainbow, Ilgachuz and Itcha ranges each erupted large amounts of felsic magmas which were followed by late-stage eruptions of small volumes of more primitive magmas (Fig. 12). Of these, hawaiites are the volumetrically predominant rock type, as they are in most alkaline volcanic provinces of an intraplate setting (CHARLAND ET AL. 1995). As noted earlier, volcanic activity at each of the three shield volcanoes lasted approximately 2 Ma

(SOUTHER 1986), a relatively short amount of time when compared to the longevity of, for example, Mt. Edziza (SOUTHER 1992; also cf. ch. 4). Together with the younging progression of ages from west to east along the trend of the AVB, this gives credence to the postulated hot-spot being responsible for magmatic activity (BEVIER ET AL. 1979). A previously suggested

73 relationship between AVB rocks and the coeval Chilcotin Group basalts (TIPPER 1969), largely based on their spatial proximity and petrographic similarity, has been rejected in light of the clear differences in their respective field relations, geochemistry, geographical extent and volcanotectonic settings, with the Chilcotin basalts having been attributed to a distinct back-arc setting

(BEVIER 1983A/B; MATHEWS 1989; DOSTAL ET AL. 2008). A more in-depth discussion of this topic follows in ch. 4.

The processes that lead to the generation of alkaline and peralkaline magmas are highly complex and no single process can explain the degrees of differentiation seen in such systems.

Fractional crystallization, low-volume partial melting, contamination by crustal rocks assimilated during the ascent of the magmas, the presence of volatile phases or any combination of these all can play a role (SOUTHER ET AL. 1984; CHARLAND 1994; SOUTHER & SOUTHER, 1994; FAURE

2001).

As mentioned before, movement of the North American plate over a potential mantle plume during the Neogene and Quaternary could explain the progressively younger ages determined for

AVB centres. The Itcha Range is situated about 30 km to the ESE of the centre of the Ilgachuz

Range and slightly south of the W-E trend of the proposed hot-spot (~253º; see ch. 3.6). This variation, however, is within widths proposed for observed hot-spot tracks (HICKSON 1987). The distances between both the Ilgachuz and Itcha ranges and the Itcha Range and Nazko Cone 80 km to the east agree within error with the velocity of the North American plate during the Neo- gene (between 2.0 and 3.3 cm/yr; e.g., BEVIER ET AL. 1979; GRIPP & GORDON 2002; MERCIER ET

AL. 2009). This further agrees with the amount of time that passed (~500 ka) between the last activity in the Ilgachuz Range and the first in the Itcha Range.

Figure 12 Schematic and generalized diagrams for the evolution of the AVB shield volcanoes. (Modified from SOUTHER & SOUTHER [1994].)

(A) A heat source in the mantle (potentially mantle plume-fed) generates basaltic magmas at the boundary between mantle and crust. Through differentiation and potential crustal melting and assimilation, more felsic magmas begin to form a cupola on top of the basalts; due to their greater buoyancy, these felsic magmas eventually begin to ascend through the crust. (An older and already extinct shield volcano is depicted on the left. Movement of the North American Plate is from right to left.)

(B) The felsic magmas form a shallow magma chamber (where differentiation is continuing) and eventually erupt at the surface, constructing a felsic basal shield.

(C) After voluminous amounts of felsic lavas have been erupted, the top of the shallow magma collapses, creating a caldera. Occasionally, fresh mafic magmas manage to ascend and erupt, leading to intercalated felsic and mafic units.

(D) Eruption of more evolved rocks is eventually being followed by rise and eruption of mafic melts.

(E) Eruption of alkaline mafic lavas (from lower crustal reservoir of basaltic magmas) forms a thin veneer on top of the previous felsic shield.

(F) Final eruptions of undersaturated lavas (hawaiites, basanites) build small cinder cones and lava flows on eastern flanks of shield. Activity wanes and eventually ceases through to disconnect from heat source/mantle plume. Volcanic activity may commence after several

100 ka farther to the east.

Figure 12

Chapter Three: The Satah Mountain and Baldface Mountain Volcanic Fields:

Pleistocene volcanism in the Anahim Volcanic Belt, west-central British Columbia, Canada

3.1 Abstract

A large number of small volcanic centres and erosional remnants thereof exist in the Satah

Mountain and Baldface Mountain Volcanic Fields (SMVF, BMVF) in the Chilcotin Plateau, west-central British Columbia, Canada. The SMVF and BMVF are spatially associated with the

Anahim Volcanic Belt (AVB), a linear feature of alkaline to peralkaline plutonic and volcanic centres of Miocene to Holocene ages. These centres are mostly small in size and homogeneous in composition; however, stratigraphic relationships between individual centres are obscured because of extensive Quaternary cover. The origin of the AVB is contentious with the passage of a hot-spot being the most widely accepted hypothesis. New whole-rock 40Ar/39Ar age data

(n=24) are presented for 11 individual SMVF centres (~2.21 to ~1.43 Ma), 7 for the BMVF

(~3.91 to ~0.91 Ma) and 6 outside of these fields (mostly Eocene). Of these last centres, only

Nazko Cone is affiliated with the AVB. The age ranges for the SMVF and BMVF are largely coeval with the Itcha Range suggesting that, in addition to a close spatial and geo-chemical relationship, they are contemporaneous with Itcha volcanism. The location of these volcanic fields fits well into the postulated AVB hot-spot track. Whole-rock chemical compositions

(n=59) of volcanic rock samples from these fields suggest a strong geochemical affinity to the nearby Itcha Range shield volcano. Trace element and REE patterns suggest a mantle source of

AVB lavas, similar to ocean island basalts (OIB). Eruption rates in the SMVF were high enough to build an elongated ridge that deviates from the E-W trend of the AVB by almost 90º. This deviation might reflect the mechanisms and processes facilitating magma ascent through the lithosphere in a tectonically complex region, and possibly hot-spot track variability.

3.2 Introduction

Continental hot-spot volcanic rocks provide an opportunity to sample and study the subcontinental lithosphere and asthenosphere (e.g., BEVIER 1989; RICHARDS ET AL. 1989; DERUELLE

ET AL. 2007). Only two continental hot-spots are documented in North America: the well-known

Yellowstone hot-spot in Wyoming (e.g., PIERCE & MORGAN 1992; JAMES ET AL. 2011) and the

Anahim hot-spot in British Columbia (e.g., SOUTHER 1977, 1986). Both of these apparent hot- spot tracks are consistent with a 2−3 cm/yr rate and direction of movement of the North

American plate (MINSTER ET AL. 1974; HICKSON 1987; GRIPP & GORDON 2002). However, the interpretation of the Anahim Volcanic Belt (AVB) is contentious, with interpretations ranging from continental rifting to a mantle plume/hot-spot (BEVIER ET AL. 1979) to plate-edge/slab window effects (THORKELSON ET AL. 2011). In this paper, we provide new field observations, geochemistry and geochronology data that are used to test and, in the end, support the hot-spot interpretation for the AVB.

The AVB in west-central British Columbia (B. C.) is a ~330 km long, E-W trending line of volcanic and plutonic centres at around 52º N (Fig. 13a). The AVB is composed of alkaline and peralkaline dyke swarms, shield volcanoes and regionally extensive fields of tephra cones, ranging in age from Miocene in the west to Quaternary at its eastern end (SOUTHER 1977, 1986;

BEVIER 1978, 1981; BEVIER ET AL. 1979; STOUT & NICHOLLS 1983; SOUTHER ET AL. 1987;

SOUTHER & SOUTHER 1994; CHARLAND 1994; CHARLAND ET AL. 1993, 1995). The AVB is located in the remote, densely forested and largely inaccessible Chilcotin Plateau, making field work challenging. Previous research on the AVB is limited.

Previous work defines three components of the AVB. The western segment is exposed on islands in the Bella Bella region and comprises the oldest rocks (Middle Miocene) including

78 erosional remnants of cones, flows, dykes and associated breccias (SOUTHER 1990). An alkaline pluton is also associated with the belt and is exposed on King Island in the eastern part of this segment (SOUTHER 1986). The central segment (Fig. 13b) consists of three large shield volcanoes: the Rainbow Range (BEVIER 1978, 1981), Ilgachuz Range (SOUTHER & SOUTHER 1994), and Itcha Range (CHARLAND ET AL. 1993, 1995; CHARLAND 1994). The Itcha Range is also associated with two extensive cone fields centered on Satah Mountain and Baldface Mountain, respectively (Fig. 13b; CHARLAND 1994; this study). The eastern segment includes only Nazko

Cone, which is considered the current location of the AVB hot-spot (SOUTHER ET AL. 1987;

HICKSON ET AL. 2009). The last eruption at an AVB centre occurred at Nazko Cone ~7,200 years

BP (SOUTHER ET AL. 1987). An earthquake swarm (ML < 3) in late 2007 in the vicinity of that centre has been interpreted as an injection of magma into the lower crust (CASSIDY ET AL. 2011).

Finally, volcanic rocks in the vicinity of Quesnel Lake and seismicity near Kinbasket Lake were previously suggested to be associated with the AVB (ROGERS 1981). However, this association has since been refuted (HICKSON & SOUTHER 1984; HICKSON 1987).

The AVB is located east of the triple junction between the Juan-de-Fuca/Explorer, Pacific and

North American plates. The overall tectonic configuration between these plates has remained relatively constant since the Middle Miocene; however, the Queen Charlotte triple junction has changed its location several times during this time (RIDDIHOUGH 1977, 1984; MADSEN ET AL.

2006). These motions of the triple junction caused a stress regime change from a compressional to transtensional across B. C. (ENGEBRETSON ET AL. 1985). This change is hypothesized to have influenced Neogene-Quaternary volcanism in the B. C. interior (EDWARDS & RUSSELL 1999,

2000).

The AVB is one of several Neogene-Quaternary volcanic belts in B. C. (Fig. 13a). The

Miocene Pemberton and Quaternary Garibaldi volcanic belts to the south are aligned subparallel to the continental margin and are interpreted as related to subduction of the Juan-de-

Fuca/Explorer plates (SOUTHER 1977; BEVIER 1983A/B; GREEN ET AL. 1988). In northern B. C., the Northern Cordilleran Volcanic Province (NCVP) is interpreted to be related to regional transtension (SOUTHER 1977; EDWARDS & RUSSELL 1999, 2000). The AVB, which is located north of the edge of the subducting Juan de Fuca/Explorer plates, is unique in that it runs west to east and nearly perpendicular to major geomorphological, structural and tectonic elements of the

Canadian cordillera that are predominantly trending NW-SE (BEVIER 1989).

The hot-spot interpretation for the AVB is primarily based on the linear decrease of ages from west to east along the trend of the belt, its linear orientation and, to a lesser degree, the alkaline to peralkaline character of the rock types (SOUTHER 1977, 1986; BEVIER ET AL. 1979). This has led to the inference of the existence of a mantle plume underlying this part of the North

American plate. Recent tomographic modeling (MERCIER ET AL. 2009) shows a low-velocity zone beneath the AVB. Euler pole modelling by HICKSON (1987) showed alignment with then existing plate motion constructions, also supporting the hot-spot hypothesis. The Anahim hot- spot would have been interacting with the North American plate since the Middle Miocene. Any prior record that might have existed in form of oceanic volcanic centres/seamounts on the

Farallon/Juan de Fuca plates has presumably been subducted under North America and lost.

Continental alkaline magmatism is often associated with rifting and hot-spots. Examples include the East African Rift (e.g., WEBB & WEAVER 1975; WEAVER 1977; CHOROWICZ 2005;

GIORDANO ET AL. 2014), the Cameroon Line (DERUELLE ET AL. 2007), the Rhine Graben and

Massif Central in Europe (DOWNES 1987; WILSON & DOWNES 1992), or the Northern Cordilleran

Volcanic Province of northern British Columbia (EDWARDS & RUSSELL 1999, 2000). The geochemistry of the AVB is distinctly alkaline to peralkaline, supporting either hot-spot or rift settings.

This study focuses on two volcanic fields situated in the central part of the AVB, the Satah

Mountain Volcanic Field (SMVF) and Baldface Mountain Volcanic Field (BMVF) and their relationship to the AVB (Figs. 14, 15). However, we also briefly present new data for Nazko

Cone which marks the eastern limit of the AVB (SOUTHER ET AL. 1987) and for Pleistocene volcanic rocks exposed near Quesnel Lake, an area once postulated to have a connection to the

40 39 AVB hot-spot (SOUTHER 1977; ROGERS 1981). Our new geochemical data and Ar/ Ar age determinations are integrated with published data from other AVB centres to produce a single coherent database that constrains the processes and mechanisms responsible for magmatism in this part of western Canada. Specifically, these data are used to test the hypothesis that the volcanic edifices defining the AVB represent, in fact, the trace of a second continental hot-spot under North America.

Figure 13 (A) Location of select Neogene and Quaternary volcanic centres in British

Columbia (modified from EDWARDS & RUSSELL [2000]). Abbreviations: PVB−Pemberton

Volcanic Belt, GVB−Garibaldi Volcanic Belt, EP−Explorer Plate, JdFP−Juan de Fuca

Plate. Enlargement of Anahim Volcanic Belt (AVB) and prominent centres therein:

1−Bella Bella dyke swarms; 2−King Island pluton; 3−Rainbow Range; 4−Ilgachuz Range;

5−Itcha Range; 6−Satah Mountain Volcanic Field (SMVF); 7−Baldface Mountain Volcanic

Field (BMVF); 8−Nazko Cone.

(B) Location of Satah Mountain (SMVF) and Baldface Mountain Volcanic Fields (BMVF) in the central AVB. Triangles denote central peaks of Satah Mtn., Baldface Mtn. and Red- top Mtn., respectively. Also note difference of morphology of the Itcha Range as compared to the older and deeply dissected edifices of the Rainbow and Ilgachuz ranges.

TLMC−Tatla Lake Metamorphic Complex.

Figure 13

Figure 14 Detailed location map of the SMVF and sample locations therein. Dashed lines denote approximate NNW-SSE trend of aligned centres on Satah Ridge (light blue) and E-W trend of cones northeast of Punkutlaenkut Lake (orange).

Figure 15 Detailed locations map of the BMVF and sample locations therein. (Blue arrows indicate direction of flow for the Chilcotin River and Moore Creek.)

3.3 Geologic Setting

The Satah Mountain and Baldface Mountain Volcanic Fields (Figs. 13b, 14, 15) are located in the central part of the AVB. The AVB extends from the Pacific coast through the Coast

Mountains and onto the Chilcotin Plateau in west-central British Columbia. The northernmost parts of the SMVF around Satah Mountain were included in a study by CHARLAND (1994) and are described as “(…) trachytic domes (…) overlain by remnants of mafic cinder cones and lava flows”. The central part of the AVB east of the Coast Mountains consists of three large and complex shield volcanoes: the Rainbow, Ilgachuz and Itcha ranges. Previous studies focussed mainly on the stratigraphy, geochemistry and petrogenesis of the magmas erupted at each volcano. Volcanic activity at each of these ranges lasted ~2 Ma (SOUTHER 1986): Late Miocene

(Rainbow Range and Anahim Peak; BEVIER 1978), latest Miocene and Early Pliocene (Ilgachuz

Range; SOUTHER & SOUTHER 1994) and Pliocene to Early Pleistocene (Itcha Range; BEVIER ET

AL. 1979). Similar durations of activity for individual volcanoes and/or volcanic fields are reported for Neogene and Quaternary centres along the Yellowstone hot-spot track (PIERCE &

MORGAN 1992).

The basement rocks beneath the central AVB belong to the Devonian to Jurassic Stikine terrane (MIHALYNUK ET AL. 2009) which is composed of an assemblage of metamorphic, plutonic, volcanic and volcaniclastic successions (Hazelton Group). Overlying this terrane are volcanic and volcaniclastic rocks of Eocene age (Ootsa Lake Group; TIPPER 1969; MIHALYNUK

ET AL. 2008, 2009). Basalts of the Neogene to Quaternary Chilcotin Group unconformably overlie these older strata, forming an extensive, though thin veneer on the Interior Plateau

(BEVIER 1983A/B; ANDREWS & RUSSELL 2008; MIHALYNUK ET AL. 2008). These basalts are of transitional geochemistry and have been associated with back-arc volcanism related to the

subduction of the Juan de Fuca plate that took place during the Late Oligocene, Miocene and early Pleistocene (BEVIER 1983A/B). Rocks of the AVB are thought to conformably overlie these older sequences and in places to “imperceptibly merge” with the Chilcotin basalts (TIPPER 1969).

In the study area, no contacts between these were found. Additionally, neither Chilcotin Group basalts nor AVB rocks show signs of folding (MIHALYNUK ET AL. 2009), although reverse faulting associated with glaciation has been noted (cf. CLAGUE & JAMES 2002). There is also little evidence of historic seismicity related to tectonics (CASSIDY ET AL. 2011), suggesting that the area is tectonically stable.

Geochemistry of AVB centres is alkaline to peralkaline, with associated rocks ranging from oversatured, highly evolved phonolites and rhyolites in the western and central parts to more undersaturated lavas that erupted in the Rainbow, Ilgachuz and Itcha ranges and at the eastern terminus of the AVB, Nazko Cone (SOUTHER ET AL. 1987). The three central volcanoes share a similar evolution, with an early shield-building stage with repeated eruptions of large volumes of predominantly felsic magmas that became progressively more varied. Despite their high SiO2 contents (in excess of 60 wt% SiO2), these lavas remained fluid enough to build a felsic shield

(SCHMINCKE 1974; BEVIER 1978). In the final stages of activity in the Ilgachuz and Itcha ranges, small volumes of more mafic lavas (hawaiites and basanites) built small cinder cones and capping flows on their eastern flanks (SOUTHER & SOUTHER 1994; CHARLAND ET AL. 1995). In the Rainbow Range, only small erosional necks remain of this final phase (BEVIER 1978).

Based on this diverse range of lava compositions and, more importantly, an apparently linear decrease in ages from west to east, SOUTHER (1977) proposed a mantle plume as the cause of

AVB magmatism (also see SOUTHER 1986; BEVIER 1978). Work by HICKSON (1987) on Euler pole further corroborated this hypothesis. Other volcanotectonic models include continental

rifting (BEVIER ET AL. 1979); a plate-edge effect and/or slab window leading to magma ascent along the northern edge of the subducting Juan de Fuca plate (THORKELSON 1996; THORKELSON

ET AL. 2011); or a propagating crack controlled by stress fields related to large-scale plate tectonics of western North America (BEVIER ET AL. 1979; also see ch. 4). Isotopic studies of Pb and Sr systems indicate the presence of sub-oceanic mantle under central British Columbia

(BEVIER 1989).

3.3.1 Study areas

The Satah Mountain Volcanic Field (52º 28.2’ N / 124º 41.4’ W; Fig. 14) forms a ~40 km by 20 km long NNW-SSE trending ridge (“Satah Ridge”), a notable deviation from the overall E-W trend of the AVB. Numerous conical structures connect the SMVF to the Itcha Range, 25 km

NNW of Satah Mountain. The extent of the field to the south is unconstrained. It is likely that flows from the SMVF extend east and west of the ridge into hummocky lowlands that are covered with glaciofluvial deposits (TIPPER 1971; MIHALYNUK ET AL. 2008).

The Baldface Mountain Volcanic Field (52° 45.6’ N / 124° 31.8’ W; Fig. 15) lies ~25 km east of the Itcha Range and covers an area of ~400 km2. Its actual extent is difficult to define, as only a small number of centres in the vicinity of Baldface Mountain could be accessed for sampling.

Numerous conical structures to the north and east were identified and mapped based on their lithology, appearance and distribution as Late Miocene to Pliocene volcanics (TIPPER 1969), a broad descriptor which at that time included both the flat-laying plateau basalts and lavas from all AVB centres. Later studies assigned the plateau basalts to the Chilcotin Group (BEVIER

1983A/B) and individual cone-shaped centres to the AVB (BEVIER 1978; SOUTHER & SOUTHER

1994; CHARLAND 1994).

Neither the SMVF nor BMVF appear to have been affected by folding and/or faulting.

However, the trend of Satah Ridge (light-blue line; Fig. 14) and the trend of a line of four cones north of Punkutlaenkut Creek (orange line) in the field’s northern part correspond to two sets of fracture systems in the central Itcha Range that trend between 330º and 010º and 055º to 090º, respectively (TIPPER 1969; CHARLAND ET AL. 1993). The ridge rises on average 200 m above the surrounding flats and appears somewhat asymmetrical in cross-section, with a steeper western flank and a gentler eastern flank, maybe an effect of erosion caused by glacial advances coming from the Coast Mountains to the west and southwest (TIPPER 1971; JACKAMAN & SACCO 2014).

The flats west of the ridge lie on average ~1,300 m, whereas in the East they average ~1,225 m.

Prior to field work, the existing geological maps (TIPPER 1969, 1971) and aerial photographs were used to identify potentially suitable centres for sampling. A number of centres that were selected for this study could not be accessed, but nonetheless a reasonable geographical coverage was achieved with 18 sample locations in the SMVF and eight in the BMVF. In the former, an area of ~420 km2 was covered to determine the lithologies of individual centres and whether any correlations could be made between location, geochemistry and age of these centres. Many of the centres have informal names in the local Tsilhqot’in language (e.g., “Satah” meaning “Of the

Sun and Moon”) and will hereafter be referred to by their sampling designations.

Most of the sampled sites in the SMVF and BMVF are eroded remnants of former tephra cones, domes, plugs and lava flows (Fig. 16). In the SMVF, only Satah Mtn. (1,921 m; Fig. 16a) and Mt. Punkutlaenkut (1,908 m) are larger edifices. Satah Mtn. has two summits: the western summit is flat-topped and the eastern appears to retain the morphology of a cone with a small summit crater (~180 m in diameter) that is breached on its southwestern rim. These two centres stand between 300 and 400 m in relief over the surrounding plateau. A rough estimate of their

post-erosion volume is ~600 * 106 m3 for Mt. Punkutlaenkut (based on a cone) and ~170 * 106 m3 for the western part of Satah Mtn. (based on a conic section). For a list of all sample locations, please refer to appendix A1 (p. 276).

3.3.1.1 The Satah Mountain Volcanic Field

The SMVF extends some 40 km from the southern flanks of the Itcha Range to, presumably, just north of Chantslar Lake and the Tatla Lake Metamorphic Complex of Mesozoic metamorphics and Eocene intrusives (MIHALYNUK ET AL. 2009; Fig. 13b). No contacts were identified in the field at this time and the southern extent of the field is not yet defined. At the field’s northern edge, a chain of four cones (labeled “9”, “10”, “11”, “12”) north of Punkutlaenkut Creek are parallel to the strike of E-W trending normal faults in the Itcha Range 15 km to the north (Fig. 14; also cf. Fig. 29). From there, the approximately 25 km long, N-S-trending ridge includes Satah

Mtn. and seven other centres (labeled “MM”, “NTB”, “TB”, “TC”, “16”, “3”, “19”). Five other centres (“JH”, “CH”, “SL”, “TL”, “5”, “6”) are located a few kilometres outside of this ridge.

Morphologically, the flat tops of the western part of Satah Mtn. and of Sugarloaf Mtn. in the southwestern part of the study area are in part reminiscent of tuyas (EDWARDS ET AL. 2011). It is likely that the entire area is covered by lava flows of various origins, but outcrop is patchy and extensively covered in glaciofluvial deposits that contain abundant volcanic material of potentially local, but largely unknown affiliation (JACKAMAN & SACCO 2014). Only on morphological highs and along some valleys incised by rivers do in situ outcrops exist. Larger rivers, such as the Chilcotin River, have cut through the Neogene volcanics into the underlying

Eocene and Mesozoic strata (MIHALYNUK ET AL. 2008). Present-day creeks with steep valley sides (e.g., Punkutlaenkut and Palmer Creek) are deemed too small to have cut through hard

volcanic rocks themselves and are interpreted to be successors of former, more vigorous glacial meltwater channels (cf. TIPPER 1971; JACKAMAN & SACCO 2014). Satah Ridge constitutes a drainage divide: the eastern flanks drain into the Chilcotin River and eventually the Fraser River, whereas the western flanks drain and flow west into the Dean River. There is evidence for a glacial lake east of Satah Ridge in the Chezacut area during the last Ice Age (MIHALYNUK ET AL.

2009).

Tephra and unconsolidated red scoria exist in disconnected patches throughout the study area.

It is likely that this material was erupted from various centres at different times, but most of it appears to have been removed and/or redistributed by glaciers, leaving more resistant flow units behind. Rounded sandstone and gneiss erratics of up to 1 m in size are found on some centres, indicating that these were overtopped by ice during one or several of the regional glaciations during the Pleistocene and Holocene (TIPPER 1971; MATHEWS & ROUSE 1986; HICKSON 1987;

EDWARDS ET AL. 2011; ROED ET AL. 2013).

Below follows a description of SMVF centres (Fig. 16). Most of these were accessed and sampled during field work (2010−2012).

 Centre “9”: At the eastern end of a chain of four or five cones running E-W north of

Punkutlaenkut Creek. Almost circular, with a diameter of ~1.7 km. Elevation/

prominence: 1,673 m / 145 m. At top crater-like depression (~340 m in diameter). In situ

outcrop and felsenmeer on northern and southern slopes.

 Centre “10”: Not studied in detail, 2.5 km west of centre “9”. Irregularly shaped, ~1.7 by

1.75 km. Base elevation / height from base: 1,724 m / 162 m.

 Centre “11”: Not studied in detail, 1.4 km north-east of centre “12”. Conical shape with

flat top, ~1.7 by 1.9 km. Base elevation / height from base: 1,726 m / 192 m.

 Centre “12”: Western end of this chain of cones, 2.5 km northeast of Lake Punkutlaenkut.

1.5 by 1.7 km, with a crescent-shaped central part (900 by 520 m). Base elevation / height

from base: 1,736 m / 188 m.

 Centre “MM”: 4 km north of Satah Mtn. Cupola-shaped, 1.3 by 1.1 km. Base elevation /

height from base: 1,687 m / 172 m. At top crater-like depression, but this appears to be an

erosional effect. Edifice appears to consist of two parts: an oval-shaped lower unit

(elongated NE-SW) and an upper, circular-shaped part that rises ~50 m over the lower

unit. Massive units forming cliffs and felsenmeers on all but the northern flanks. Platey-

weathering flows in central depression produce a “pinging” sound characteristic of

phonolites when hit with a rock hammer (cf. similar description in SOUTHER & SOUTHER

[1994], p. 47). Several thin lava flows (1−2 m) outcrop in cliffs on the eastern side. On

the northern flank, a few blocks of tuffaceous breccia are observed (but are not in situ.)

 Centre “U”: A small outcrop of a weathered lava flow in a hill-side 3 km NW of Satah

Mtn. Minimum thickness of ~5 m, as lower contacts obscured by scree.

 Mt. Punkutlaenkut (sample designation “CM”): 7 km WNW of Satah Mountain. Second-

largest edifice in the SMVF, ~2.9 by 3.2 km. Base elevation / height from base: 1,908 m

/ 334 m. Some scattered scoria on the summit and SW flank indicated by red colour of

outcrop. No remnant of a crater/eruptive centre. What appear to be remnants of

individual thin flows outcrop at the top of the mountain, some of them highly vesiculated.

Cliff of platey-weathering lava flows (thickness ~10 m) on the northern flank that appear

to dip towards the summit.

 Satah Mountain (“SM”): Double-peaked, eastern and western cone at equal elevation of

1,921 m (Fig. 16a). The volcano rises some 400 m above the surrounding terrain; a

younger, 50 m-high scoria cone sits on the volcano’s northern flank and is conspicuous by

the vivid red colour of its scoriaceous rocks (Fig. 16b). A small saddle between the two

peaks and the southeastern flanks are covered with vesiculated and poorly sorted red

scoria and pumice (<10 cm in size). This thin (1 m?) scoria layer appears to be overlain

by lava flows on the west cone. The west cone features a flat top rimmed by a cliff

(40−50 m in height) of large blocks of vesiculated lavas, often with columnar jointing,

that dip inward. The east cone appears to have retained a crater (~180 m in diameter, ~25

m deep) which appears breached on its southwest rim. Tabular-weathering lavas, distinct

in appearance from the lavas on the west cone, are exposed along this rim and dip inward

at 20 to 40º. A lava flow exposed on the east cone’s lower flank contains what appears to

be volcanic “dropstones” (<5 cm in diameter). On the north flank of the east cone, three

flow units are exposed that each measure ~10 m in thickness. The felsenmeers covering

most of the upper flanks consists of unsorted blocks, ranging from a couple of tens of

centimetres in size to up to five metres; some of these scree slopes exhibit downslope

movement in form of a slow-moving debris flow. Of note are rounded blocks of gneiss

(<1 m in diameter) that are randomly distributed on the flat top of the west cone.

 Centre “6”: Located 6 km SE of Satah Mtn. A ridge-like edifice, 2.2 by 1.3 km in size.

Its long axis appears to parallel the trend of the Satah ridge. A small swampy lake is lo-

cated in a depression at the northern end of the centre. Base elevation / height from base:

1,593 m / 179 m. Rocks again exhibit weathering into tabular slabs, of which some in the

southern parts of the centre appear to be dipping sub-vertically. No scoria was observed.

 Centre “NTB” (Fig. 16c): About 4 km SSW of Satah Mtn. Almost perfect cone with a

basal diameter of ~1 km and a flat top. Base elevation / height from base: 1,855 m / 240

m. Along the top rim, concentric fractures of 1−2 m in width might indicate either

cooling cracks of a solidifying plug in a former volcano’s vent or gravity-induced settling

(slope angle of 30−40º). Rock type is the same everywhere on the cone, forming a

prominent “arc” on southwestern slope and a 15−20 m high cliff around the base. No

scoria layers were observed.

 Centre “TB”: Separated from “NTB” by a small creek in a U-shaped valley (250 m wide).

Despite the two centres’ close proximity, they have distinctly different lithologies (see ch.

3.5 below). Centre is elliptical with a long axis in NNE-SSW direction; 1.7 by 1.5 km.

Base elevation / height from base: 1,894 m / 289 m. Cliffs and felsenmeere on all sides.

On the upper flanks, there are six erosional remnants that appear to be small dykes; these

dip towards the centre of the edifice at ~40º. Lavas weather into slabs that again produce

a ringing sound when struck with a hammer. Possible small outcrop of underlying,

strongly foliated basement rocks on the northern valley side (the geological map of the

area [TIPPER 1969] also indicates presence of Mesozoic basement rocks 3 km to the NW

of this centre).

 Centre “2C”: About 2 km south of “TB”, this centre was not studied in detail and appears

to be shaped by the headwaters of Palmer Creek, with a wedge of the edifice between two

arms pointing east. Base elevation / height from base: 1,718 m / 181 m. Aerial

photography indicates presence of red scoria (?) on southern flanks. Cliffs of up 50 m in

height and felsenmeers are partially overgrown by forests. The centre is of notably lesser

elevation than centres “TB” to the north and “16” to the south.

 Centre “16”: Located 3.5 km due south of centre “TB”. Dimensions of central structure

are somewhat difficult to determine due to dense vegetation cover (estimate of 2 by 1.8

km) and undulating terrain. The centre appears to be form a roughly circular rise that on

its west side terminates in 10 to 20 m high cliffs. On the cone’s south flank, a ~1.3 km-

long ridge appears to be a remnant of a thick (30−40 m) lava flow that extends for about

1.5 km at least (Fig. 16i). South of the centre, logging in the 1990s has exposed lava

flows that may have flowed for several kilometres to the south and southeast. The

topography is very likely parallel to the dip surfaces of these lava flows. Individual lava

flows are visible and may be as much as 5 m or more in thickness, but no close-up

observation was possible. In the headwaters of Palmer Creek, up to 100 m of these and

underlying lavas are exposed, but no detailed observation of them have been carried out at

this time.

 Centre “3” (Fig. 16j): A small circular centre, 1.3 by 1.2 km, 4 km due west of centre

“16”. Base elevation / height from base: 1,665 m / 120 m. Small patches of red scoria

outcrop on the south-western flank and are overlain by more massive flows that form

cliffs of up to 20 m in height. Cooling/settling cracks are several metres wide and up to

20 metres deep and seem to break parallel to columnar cooling surfaces in the lava.

Centre has appearance of a cone breached on its western side.

 Centre “19”: Prominent cone in the southwestern part of the SMVF, 3.5 km SW of centre

“16”. The central cone measures ~1.9 by 1.7 km. Base elevation / height from base:

1,754 m / 309 m. Part of a broad swell (6.5 by 3.8 km), presumably flows that appear to

preferentially have flowed towards the west. Prominent cliffs on the cone’s north flank

might be remnants of flows with individual thicknesses between 20 and 40 m. No large,

conical structures exist between this centre and Sugarloaf Mtn., 12 km to the SSW.

 Centre “5”: On the eastern edge of the SMVF study area, this centre is similar in

dimension (1.4 by 1.2 km) and shape to centre “3”. Base elevation / height from base:

1,399 m / 88 m. Massive cliffs of columnar lavas on the centre’s perimeter and platey-

weathering flows in its centre that dip south at ~10º. Of note are boulders of dark,

vesiculated and olivine-bearing basalts (< 2 m in diameter) that are scattered on the cone

and that are in stark contrast to the cone’s lighter rocks. The remnant of a blocky lava

flows extends for ~400 m just north of the cone (source unknown).

 Centre “CH”: A small “knoll” about 0.47 by 0.4 km in size at the south end of a 1.5 km,

NE-SW trending ridge of lava flows. Base elevation / height from base: 1,531 m / 72 m.

This small size indicates a plug or neck of a monogenetic centre. A columnar-jointed lava

cap overlies a hyaloclastite-pillow breccia unit (Fig. 16f/g), indicating a change from a

subaqueous to a subaerial environment during the presumably short-lived eruption. The

columns are 20−30 cm in diametre and several metres long/high. They are aligned

vertical to subhorizontal with tops of the columns generally perpendicular to the surface of

the neck. The columns are truncated at the top, indicating subsequent erosion by glaciers.

A knoll of similar shape and dimension is located 1.75 km east of this centre (not studied).

No notable structures exist south or east of here.

 Centre “SL” (for Sugarloaf Mtn.): Sugarloaf Mtn. is a prominent structure in the

southwestern part of the SMVF, 12 km SSW of centre “19”. Sugarloaf Mtn., not studied

in detail due to access problems, is almost circular (1.3 by 1.1 km), and notable for its flat

top surrounded by cliffs on all sides. Base elevation / height from base: 1,742 m / 164 m.

Sample location for this centre is a small knoll 2.2 km NNE of the actual summit, a cliff in

an eroded hillside. The cliff is massive and ~40 m in thickness. No scoria was observed.

The forest service road 4.5 km north of “SL” near Turbo Lake (Fig. 14) is built on the

surface of lava flows; a sample (TL-1) was taken from what is thought to be an in situ

location (see appendix A1 below for details).

 Centre “JH” (for Jorgensen Hill): On the far southeastern edge of the SMVF study area,

14 km SE of “CH”, this centre is a small crescent-shaped “welt” (1.7 by 0.8 km) with only

a small cliff outcrop on its upper SW rim. Base elevation / height from base: 1,335 m / 77

m. The exposed cliff is ~10 m in thickness, but its lower contact is obscured by scree. A

small patch of red tuff exist on the south flank but is literally restricted to eroded soil

under a tree root. North, east and south of “JH”, the glaciofluvial flats extend for tens of

kilometers without any notable features. Flows from this centre have dips of ~20º to the

north and southeast, respectively MIHALYNUK ET AL. (2009).

 Centre “GR” (for Grizzly Mountain): See ch 3.2.1.3 below.

3.3.1.2 The Baldface Mountain Volcanic Field

The Baldface Mountain Volcanic Field (BMVF) with its eponymous central peak is located some 22 km NE of Mt. Downton in the Itcha Ranges (Figs. 6, 16d/h) and 33 km NNE of Satah

Mtn. Centres affiliated with the BMVF might extend to the Moore Creek area, 15 km to the SE of Baldface Mtn. and are located close to rocks of the Eocene Ootsa Lake Group. The field lacks the elongated arrangement of SMVF and it is likely that a number of conical structures to the north and east of the BMVF centres studied here are also of AVB affiliation (cf. also TIPPER

1969). The youngest AVB centre, Nazko Cone, is located 44 km to the northeast of the BMVF.

Additional volcanic centres and a post-glacial (?) lava flow have recently been discovered between the BMVF and Nazko Cone (HICKSON ET AL. 2009), but at time of writing have not been further investigated (HICKSON, PERS. COMM. 2014).

Rock exposures are even patchier in this field than in the SMVF, with most centres lacking the cliff-like exposures of volcanic rocks that was observed in the other field. This may be due to the fact that, during the last glaciation, the Anahim Lobe sourced from the Coast Mountains stopped short of the BMVF (TIPPER 1971). This may also explain the presence of at least one largely unmodified tephra cone (“CC”; see below). Quaternary cover in the region exists as basal tills, both as till veneers (<2 m in thickness and conforming to the underlying topography) on elevated terrain and/or individual cones and till blankets (> 2 m in thickness or masking some of the variations in the underlying topography). Locally, the tills also incorporates volcanic rocks of both Anahim and/or Chilcotin Group affinity (cf. SACCO ET AL. 2014).

 Baldface Mountain (designated “BF”): Baldface Mountain sits at the western edge of an

hourglass-shaped morphologic height with a long axis trending NE-SW (~3.5 by 3 km).

The south, west and north slopes are all steep-sided and bare, likely giving the mountain

its name (Fig. 16d). Elevation / prominence: 1,798 m / 188 m. The scree is platey-

weathering slabs of aphyric, phonolitic lava. No scoria was observed.

 Centre “BF-K”: A small pile (210 by 170 m) on the south flank of Baldface Mtn., 1 km

from the actual summit. It appears to be the (eruptive?) centre of a low shield. Elevation /

prominence: 1,683 m / 34 m (over surface of shield). The exposed lava is highly

porphyritic (<25%), with feldspar phenocrysts exclusively.

 Centres “25A/25B”: These two centres, ~4 km to the SW of Baldface Mtn., are almost

identical in shape and dimensions. Both are ~1.6 by 1.6 km, with basal perimeters of ~5

km. Elevation / prominence of north cone (25A): 1,657 m / 145 m; of south cone (25B):

1,636 m / 124 m. No actual outcrop was found was 25A. On 25B, in situ outcrop is

limited to two small banks of olivine- and feldspar-bearing lava (<5 m in length, <1 m

thick) on the upper east flank of cone. Abundant red scoria, vesicular blocks (<0.5 m in

diameter) and spindle-shaped volcanic bombs cover the lower eastern and southern flanks.

 Centres “26A/26B”: 3.9 km SE of Baldface Mtn., this centre has two distinct low

summits that form a N-S trending compound structure. Overall dimensions are ~4.7 by

3.5 km. The individual central structures are almost circular in shape, with crescent-

shaped/breached upper parts (open to the west for 26A, open to the east for 26B). At

“26A”, only a small erosional remnant of a vesicular lava flow (~5 m thick) is exposed.

At “26B”, weathered lavas crop out in breach of the summit and eroded valley on the

north side as well as a 20 m high cliff on summit. Elevation / prominence of north cone

(26A): 1,716 m / 134 m; of south cone (26B): 1,683 m / 101 m.

 Centre “26C”: Small conical structure 2 km SE of centre 25, sitting on another low

shield. Not studied in detail, but taken to be source of (several?) lava flows that are ex-

posed on surface and next to old forest service road that runs around the southern base of

the cone. Large blocks (up to 1 m in diameter) of lava moved during logging and building

of service road are interpreted to be “near crop” (cf. MIHALYNUK ET AL. 2008, 2009). At

eastern end of low shield, 2 km south of centre 26B, a small vesicular lava flow is exposed

that preserves some original textures such as pāhoehoe ropey surfaces.

 Whitetop Mountain: Proved inaccessible on foot, not studied in detail. Almost circular in

shape, ~1 km in diameter. Elevation / prominence: 1,543 m / 110 m. Outcrop on upper

part of cone and on eroded west flank.

 Centre “Moore Creek” (designated “C-O”): Lava flow exposed on sides of Moore Ck.

Valley, 15−20 m in thickness. Lateral extent of the flow is unknown as the lava is

overlain by Quaternary ablation till (SACCO ET AL. 2014). Source of the flow is also

unknown. The geological map (TIPPER 1969) shows a fault at or very close to this

location (cf. Fig. 29). This flow may not be affiliated with the AVB (see ch. 3.5.2 for a

discussion of this possibility).

 Centre “CC”: 14 km SE of Baldface Mtn., this centre is the one apparently unmodified

(?) centre studied. This cinder cone (1.1 by 1.2 km) retains a crater, ca. 70 m deep, that is

breached on its northern rim and ringed by an agglutinated spatter ramp (up to 30 m high).

This ramp is dense in its lower parts, but frothy and brittle at the top (Fig. 16h). Red

scoria covers the crater floor, most of it less than 10 cm in size and poorly sorted. On

south and southeast flank, remnants of aphyric and vesicular lava flows are exposed.

Elevation / prominence: 1,568 m / 153 m. In shape and dimension, this centre is similar to

Nazko Cone (SOUTHER ET AL. 1987) and pyroclastic cones of postglacial age in the Wells

Gray – Clearwater area (HICKSON & SOUTHER 1984).

3.3.1.3 Other centres

In an attempt to define the extent of both the SMVF and BMVF, volcanic centres at the edges of either field were studied to determine their geochemistry and ages. If these would be similar to, say, the more northerly parts of the SMVF, then the southern extent of that field could be better

100

defined. This was also done because the geological map for the area (Anahim Lake; TIPPER

1969) did not really distinguish between the many conical structures observed in the central

AVB. Tipper (1969) assigned almost all of these cones as “Late Miocene and/or Pliocene basalts and andesite”.

Additionally, fresh rock samples were retrieved from Nazko Cone to confirm the age of its first eruption (cf. SOUTHER ET AL. 1987). One volcanic centre on the northern shore of Quesnel

Lake was sampled for geochemistry and age determination to investigate the formerly postulated hypothesis of this area being at the eastern end of the AVB (cf. ROGERS 1981). Unfortunately, accessibility remained a problem, with a wet 2011 summer leading to flooding, washed-out roads and over-grown vegetation. No mapping could be carried out, and even collection of rock samples was problematic. A description of centres that were accessed and sampled follows below. For discussion of geochemistry and geochronology data, please see ch. 3.6 below.

 Centre “Grizzly Mountain” (designated “GR”): A steep-sided and irregular-shaped dome

(1.4 by 1.1 km) on the south shore of Chantslar Lake. Massive blocks of crystal-rich

andesite/dacite, often with flow banding in the more glassy portions. Rounded gneiss and

granite erratics (< 50 cm) are scattered on the top of the centre. In its lower parts that are

less steep, more mafic and vesiculated lava outcrops. Just south of Grizzly Mtn. is

another “knoll” with cut-off columns (cf. centre “CH” above) that are angled 30−40º from

the vertical. (Note: 40Ar/39Ar analysis yielded an Eocene age for “GR”. As a

consequence, this centre is not affiliated with the AVB.)

 Redtop Mountain (“RT”): An eroded volcano 36 km east of Satah Mtn. Affiliated with

the Eocene Ootsa Lake Group, which at Redtop Mtn. consists mainly of hornblende-

101

bearing dacite and rhyolite flows (MIHALYNUK ET AL. 2008). Not affiliated with any AVB

activity.

 Chezacut Road (“CRD”): A small road-side outcrop of a lava flow, also affiliated with

the Ootsa Lake Group. Mapped as vitreous black dacite (unit “EOdh”; MIHALYNUK ET

AL., 2009). Not affiliated with any AVB activity.

 Nazko Cone (samples designed “N-1-2, N-3-1, N-Bomb”): A small cinder cone 75 km

west of Quesnel and 55 km NE of Baldface Mtn., Nazko Cone is considered the youngest

AVB volcano and approximately at the present location of the hot-spot (SOUTHER ET AL.

1987). See ch. 2.1.6 for a fuller description (Figs. 10, 11). The central post-glacial cone

is about 900 by 730 m in size and is currently used as a quarry for porous scoria. Base

elevation / height from base: 1,240 m / 120 m. After episodes of activity in the Late

Pleistocene and during a period when the area was glaciated, the current cinder cone, an

associated olivine basalt flow (length of <2 km) and an airfall deposit were dated to a

short episode of fire-fountaining at around 7,200 BP (SOUTHER ET AL. 1987).

 Abbott Creek Cone (designated “AC” and “X” for a xenolith-rich lava flow): A NW-SE

trending ridge (6.5 by 2.5 km, elevation 1,645 m) crowned by a small cinder cone (1.6 by

1.3 km; 140 m high), located in a south-facing valley in the Cariboo Mountains on the

north shore of Quesnel Lake (Fig. 13a). In a small quarry on the south flank, lava flows

(5−10 m thick) outcrop that retain original ropey flow top structures (pāhoehoe).

Vesiculated basalt pillows are also present, indicating subaqueous or subglacial

emplacement. These flows presumably rest on top of a thin (~2 m) unit of palagonitized

tuff that appears to dip southward at low angle. This unit is exposed 1.6 km east of the

quarry along the forest service road that skirts around the southern end of the ridge. Both

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the tuff and the lavas are likely unconformably overlaying basement rocks of the

Kootenay terrane (LOGAN ET AL. 2010), exposures of which exist further east along that

forest service road (identified as Devon to Carboniferous orthogneiss [MASSEY ET AL.

2005]). In elevation, the basements rocks are only 24 m below the level of the quarry.

The cinder cone itself could not be accessed. A soil study (SANBORN & SMITH 2010)

found volcanic breccia and in situ basalt between 0.5 and 1 m depth on the cone. About 5

km SE and downslope of the cone, logging has exposed basaltic lava flows over several

hundred metres. Minimum thickness of these flows, which are thought to have a source

on Abbott Creek Cone, is 5 m. These flows are of note for their spectacular inclusion of

abundant mantle xenoliths (Fig. 16k), some of which are 40 cm in diameter!

 Quesnel Lake Quaternary Volcanics (designated “QV”): On the geological map for the

area (LOGAN ET AL. 2010), five small exposures of Quaternary volcanic rocks are indi-

cated in the immediate vicinity of Quesnel Lake. One location on the shore directly south

of the lake’s centre could not be confirmed during field work. Within the area of pre-

sumed these Quaternary volcanic rocks, small outcrops of bluish volcanic rock are

exposed along a forest service road. 40Ar/39Ar yielded a Mesozoic age of these rocks. No

correlation whatsoever exists between AVB rocks and volcanic rocks in the Quesnel Lake

area.

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Figure 16 Photographic survey of field work study areas (SMVF, BMVF)

(A) Panoramic view of Satah Mtn. from the south. Relief of volcano above the

surrounding plateau surface is ~300 m. Note flat top of western summit, possibly an

effect of glacial erosion.

(B) Small tephra cone on the north flank of Satah Mtn. Four E−W aligned cones in the

middle distance and Ilgachuz and Itcha ranges in the far distance. View NW.

(D) View of Baldface Mtn. Bare scree slopes on western and southern flanks

presumably gave the mountain its name.

(E) Platey-weathering trachytic lava flow at centre “16”.

(F) Pillow lavas in a hyaloclastite-pillow breccia at centre “CH”. Hammer is 40 cm.

(G) Same hyaloclastite-pillow breccia as if (F), overlain by trachybasaltic lava flow.

Height of exposure is ~15 m. Barely visible at right are angled columns.

(H) Crater of centre “CC” in the BMVF. Centre is unmodified by glacial erosion.

Depth of crater is ~70 m. Red scoria and blocks from spatter rim litter the crater

floor.

(I) Massive lava flow south centre “16”, showing hackly (?) jointing. Estimated thick-

ness of flow is ~20 m.

(J) Cliff around the top of centre “3”, ~20 m high. Fractures in lava parallel the

perimeter of the cone and appear concentric, possibly a consequence of cooling.

(K) Pleistocene basanite flow from Abbott Creek Cone (Quesnel Lake), containing

abundant mantle xenoliths. Pacific tree frog (5 cm long) for scale.

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Figure 16 A

105

Figure 16 continued C D

E F

G H

106

Figure 16 continued

I J

107

3.4 Petrography

3.4.1 Rock description

Sampled lavas of the SMVF and BMVF range from basanites to phonolites, with trachytes representing more than half of all samples. Trachytes and trachyandesites commonly weather into stacks of thin (~10 cm) individual slabs with orange-brown weathering rinds (Fig. 16e).

Vesicularity and amount of phenocrysts visible in hand specimen varies from one location to another and sometimes even within few metres at a single location. On Satah Mtn., light-grey slabs outcrop on the eastern summit, while the western summit is crowned by a 50 m high cliff of almost black, vesiculated lava columns. At centre “CH”, a small neck about 200 m in diameter and 50 m high, a hyaloclastite-pillow breccia unit is overlain by columnar basalt (Fig.

16f/g), indicating a change from a subaqueous to a subaerial environment during eruption. An extremely fine-grained groundmass and lack of phenocrysts indicates rapid cooling of the erupted lavas at this centres. Otherwise, few individual lava flows were identified; south of centre “16”, individual flows reach several metres in thickness, are grey to red-brown and highly vesiculated. A trachybasaltic flow to the SW of that centre is ~20 m high and exhibits complex

(hackly?) jointing patterns (Fig. 16i).

3.4.2 Thin section petrography

The majority of the rocks sampled are holocrystalline (Fig. 17) with varying degrees of vesicularity and phenocryst content (or lack thereof). Alkali feldspar, plagioclase, pyroxene, olivine and small (0.5 mm) equant grains of oxides are the most common phenocrysts, sometimes visible with the naked eye. These phenocrysts show a wide range of habits, with the

108

larger ones usually being more euhedral than smaller grains. Euhedral alkali feldspars are of tabular habit, both as isolated phenocrysts and laths in the groundmass. Plagioclase is sometimes present as both phenocrysts and xenocrysts of up 5 mm in size, exhibiting lamellar and polysynthetic twinning and embayment of grain boundaries. Olivine and clinopyroxenes form phenocrysts (~1 cm in diameter), microphenocrysts and tiny crystallites in the groundmass of most trachytes, indicating late-stage crystallization (Fig. 17e). Alteration of olivine to iddingsite is common.

Centre “NTB” (Fig. 16c) has the coarsest-grained trachytic lavas of any centre (Fig. 17f), with simple-twinned, euhedral sanidine and tartan-twinned anorthoclase phenocrysts (~1 cm). Minute grains of quartz show up in the more felsic lavas (centres “NTB”, Satah Mtn.). Rocks from

Satah Mtn. are the most porphyritic rocks studied, with up to 40% phenocrysts of plagioclase and anorthoclase, some of which exhibit sieve texture (Fig. 17g). Nepheline is usually restricted to the groundmass and intergrown with sanidine, but does form small, hexagonal crystals in a few of the more alkaline lavas. Pleochroic sodic pyroxene (aegirine-augite?) and possibly amphibole

(arfvedsonite?) are visible as small anhedral flakes in many of the trachytes (Fig. 17h).

Trachytic texture is widespread with small aligned feldspar laths in flow alignment (often in distinct domains) and set in a pilotaxitic groundmass (Fig. 17f). In the phonolites, all phenocrysts are feldspars (sanidine).

The alkaline olivine basalts and basanites of the BMVF are medium to dark grey in colour.

These rocks are aphyric to sparsely porphyritic (510%), with holocrystalline to cryptocrystalline groundmasses (Fig. 17a). Olivine, clinopyroxenes and alkali feldspars are the predominant phenocrysts. One hawaiitic flow in the BMVF (centre 26C, Fig. 17b) contains rounded, partly resorbed plagioclase. Intersertal and seriate textures are common in these rocks,

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as are large, flattened vesicles. In contrast, hawaiites at SMVF centres “3” and “JH” are almost black, aphyric and glassy.

In the SMVF, scoria deposits are rare and are confined to patchy outcrops on some centres

(Satah Mtn., Mt. Punkutlaenkut, centres “2C”, “MM”, “16” and “JH”) where they are overlain by lavas and thus were partially protected from erosion. The scoria is highly vesiculated and oxidized to a red-brown colour. The glassy bubble walls contain euhedral to anhedral clinopyroxenes and feldspars (0.1−0.5 mm). Brilliant red scoria and small bombs (<20 cm) were only found on centres “25B” and “CC” in the BMVF (Fig. 16h).

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A B

Figure 17 Thin section photomicrographs of SMVF and BMVF lavas (all XPL unless noted otherwise).

(A) Basalt from BMVF centre “26B”. Subhedral olivine phenocrysts (ol) in a matrix of alkali feldspar (kfs), pyroxene (cpx), olivine (ol) and Fe-oxides (ox). Irregular grey patches are vesicles. Slight flow alignment of feldspar microlites is discernable in centre and upper left of figure.

(B) Hawaiite from BMVF centre “26C”. Olivine phenocrysts in a slightly coarser-grained groundmass (as compared to A) consisting of kfs laths (showing subparallel alignment), ol, possibly nepheline (ne), pyroxenes and oxides.

111

Figure 17 continued

C D

(C) Trachybasalt from massive flow at SMVF centre “16”. Rounded and partially resorbed plagioclase (plag) xenocryst exhibiting lamellar twinning. Smaller olivine phenol- crysts and microphenocrysts (ol) in upper part of figure. Groundmass is dominated by kfs laths, ol, cpx and ox.

(D) Same sample with a subhedral ol phenocryst showing zoning and resorption features

(left and right of smaller cpx grain). Smaller plag and opx phenocrysts appear colourless.

Fine-grained groundmass consists of kfs laths and microlites, ol, possibly cpx and ox.

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Figure 17 continued E F ac?

(E) Basaltic trachyandesite (almost hawaiitic) from SMVF centre “CH”. Subhedral ol and cpx appear as phenocrysts and microphenocrysts. Microcrystalline groundmass consists of kfs, ol, cpx and Fe-oxides. There is very little alignment of the kfs microlaths.

(F) Trachytic sample from SMVF centre “NTB”. Holocrystalline groundmass of kfs laths

(sanidine) show strong flow alignment. Dark grains in lower right are oxides, and a few scattered, colourful (red, yellowish) grains of cpx. Greenish, anhedral crystal of sodic pyroxene acmite (acmite? [ac]) left of centre.

113

Figure 17 continued G H

(G) Porphyritic benmoreite from west cone of Satah Mtn. (sample “SM-W”). Large plag phenocryst showing sieve texture and slight alteration along cracks (brown colours).

Intergranular groundmass consists of plag and kfs laths, cpx and oxides.

(H) Trachyte sample from SMVF centre “19” (PPL). Rock is aphanitic with a pilotaxitic texture. Groundmass consists of sanidine laths (± ne), small oxides grains and conspicuous green acmite flakes and possibly brown amphibole.

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3.5 Samples and analytical methods

3.5.1 Whole-rock geochemical analysis

In this paper, we report new whole-rock analyses (n=59) for 20 individual SMVF centres (41 analyses), seven BMVF centres (10 analyses) and six outlying centres (8 analyses). A representative selection for SMVF and BMVF centres is given in Table 3. Whole-rock X-ray fluorescence and LOI analyses were carried out on whole-rock samples from unaltered rock chips at the

Trace Element Analytical Laboratories, McGill University, Montreal, and at the Geoanalytical

Laboratory at Washington State University, Pullman, WA. Major elements and trace elements

(Ni, Cr, Sc, V, Ba, Rb, Sr, Zr, Y, Nb, Ga, Cu, Zn, Pb, La, Ce, Th, Nd, U) are reported at pre- cisions of 2σ. Rare earth elements were analyzed at McGill University using the ICP-MS method, but as only five mafic samples were analysed (Table 4), results should be treated with caution and are likely not representative of either the SMVF or BMVF. Total Fe2O3 was determined by XRF analysis and FeO contents by volumetric titration at McGill University and the Institute for Mineralogy-Geochemistry, University of Freiburg i. Br. (Germany), following the procedures outlined by WILSON (1955).

For full data tables, procedures and detection limits please refer to appendix A2 (p. 280).

next two pages

Table 3 Representative XRF (major and trace elements) analyses of Neogene and

Quaternary volcanic rocks from the Baldface Mountain (25B-1-2 to CC-1-1) and Satah

Mountain Volcanic Fields (2C-1-1 to TB-1-2). Major elements in wt%, trace elements in ppm. (Note: A dash (-) indicates an element that was not determined during analysis, a zero (0) below detection limit.)

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Table 3

BALDFACE MOUNTAIN VOLCANIC FIELD SATAH MOUNTAIN VOLCANIC FIELD Sample 25B-1-2 26A-1-3 26C-1-3 BF-1-3 CC-1-1 2C-1-1 3-1-4 6-2-3 9-1-2 12-2-1 Basaltic tra- Rock type trachybasalt basanite hawaiite phonolite trachybasalt phonolite phonotephrite trachyte trachyte chyandesite Centre 25B 26A 26C Baldface CC 2C 3 6 9 12 Latitude 52º43.27’N 52º44.18’N 52º42.41’N 52º45.46’N 52º38.45’N 52º24.82’N 52º23.85’N 52º25.79’N 52º32.0’N 52º32.02’N Longitude 124º33.14’W 124º29.24’W 124º29.56’W 124º31.83’W 124º26.58’W 124º42.45’W 124º45.71’N 124º37.09’W 124º43.09’W 124º47.96’W SiO2 47.69 43.60 49.14 59.45 45.31 59.34 50.91 51.44 63.41 60.83 TiO2 3.06 3.50 2.35 0.25 3.22 0.13 2.32 1.50 0.21 0.57 Al2O3 16.53 14.04 15.58 18.86 16.49 16.71 16.41 17.80 16.55 17.05 Fe2O3 6.82 13.15 3.63 4.04 13.64 3.72 4.60 5.86 2.48 3.75 FeO 5.49 0.61 7.67 1.70 0.00 2.30 7.53 5.47 3.28 2.90 MnO 0.17 0.18 0.17 0.12 0.17 0.21 0.21 0.16 0.17 0.20 MgO 4.61 8.81 6.70 0.25 3.71 0.02 3.20 2.01 0.02 0.41 CaO 8.12 8.92 7.56 1.45 7.99 0.91 5.72 4.02 1.08 1.89 Na2O 4.54 3.92 3.81 7.67 4.07 8.68 5.54 6.23 6.93 6.14 K2O 1.35 1.62 2.08 5.15 1.63 4.85 2.37 2.86 5.32 5.79 P2O5 0.96 0.74 0.60 0.14 0.65 0.03 1.12 1.19 0.04 0.18 LOI 0.00 0.43 0.00 1.06 3.72 1.09 -0.53 0.66 0.04 0.14 Trace 0.25 0.26 0.26 0.20 0.20 0.43 0.25 0.25 0.21 0.17 Total 99.59 99.78 99.55 100.34 100.80 98.42 99.65 99.45 99.74 100.02 Ni 43 165 140 1 38 3 0 0 0 0 Cr 62 176 302 2 77 3 0 0 0 0 Sc 15 18 15 1 17 0 12 0 0 11 V 189 208 168 3 206 3 64 29 13 17 Ba 496 451 727 468 388 9 698 668 24 407 Rb 53 29 23 95 24 233 35 120 43 79 Sr 985 883 650 90 786 3 782 3 1160 33 Zr 266 273 223 677 240 2208 365 1166 427 673 Y 27 25 22 20 26 158 41 36 28 48 Nb 51 54 37 104 42 316 54 147 66 93 Ga 22 24 23 36 24 71 25 44 21 36 Cu 32 44 78 7 61 5 10 37 19 21 Zn 121 124 85 187 79 462 460 81 165 147 Pb 3 2 3 9 4 26 4 12 6 3 La 38 36 30 68 - 203 47 - - - Ce 86 83 47 134 58 404 104 113 129 137 Th 3 4 4 10 3 32 4 16 7 9 Nd 47 45 35 45 - 169 61 - - - U 4 3 1 1 0 12 3 0 2 0

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Table 3 continued

SATAH MOUNTAIN VOLCANIC FIELD Sample 16-6-1 16-7-1 CH-2-1 CM-4-3 JH-1-3 SM-1-3 SM-L-1 SM-W-4 TB-1-2 trachy- Basaltic tra- basaltic tra- trachy- Rock type hawaiite trachyte trachybasalt trachyte trachyte andesite chyandesite chyandesite andesite Centre 16 16 CH Mt. Punkut. JH Satah Mtn. Satah Mtn. Satah Mtn. TB Latitude 52º23.49’N 52º23.64’N 52º20.37’N 52º29.61’N 52º16.54’N 52º28.58’N 52º28.56’N 52º28.38’N 52º25.71’N Longitude 124º41.62’W 124º42.04’W 124º40.03’W 1247.67’W 124º29.15’W 124º41.37’W 124º41.04’W 124º41.99’W 124º42.17’W SiO2 48.91 56.72 50.64 59.28 48.71 50.00 60.68 54.40 61.01 TiO2 2.41 0.90 2.13 0.74 2.80 2.30 0.36 1.46 0.17 Al2O3 16.34 16.68 15.57 17.08 16.97 16.84 17.69 17.70 17.70 Fe2O3 11.01 7.19 2.64 3.03 4.93 4.91 4.41 4.14 3.48 FeO 0.35 1.16 7.18 4.41 7.48 6.08 1.39 5.10 2.22 MnO 0.17 0.21 0.16 0.20 0.19 3.98 0.14 0.18 0.21 MgO 6.20 0.80 6.06 0.67 4.02 0.18 0.19 1.80 0.08 CaO 7.89 2.47 6.92 2.31 6.18 7.12 1.11 4.88 1.26 Na2O 3.85 5.55 4.20 6.00 5.17 4.53 6.22 5.29 7.24 K2O 1.51 4.93 3.11 5.50 1.79 1.74 5.61 3.55 5.35 P2O5 0.71 0.46 0.62 0.33 0.86 0.81 0.10 0.97 0.04 LOI 1.04 2.86 0.54 0.13 0.00 0.88 1.40 0.00 0.92 Trace 0.21 0.20 0.25 0.14 0.23 0.21 0.19 0.29 0.25 Total 100.60 100.13 100.02 99.82 99.33 100.16 99.49 99.76 99.93 Ni 103 0 109 0 0 25 2 0 0 Cr 139 12 179 0 0 58 5 0 0 Sc 16 11 16 0 0 13 6 13 0 V 166 15 157 13 119 145 9 45 12 Ba 466 840 588 182 691 641 119 1575 0 Rb 20 59 43 72 35 20 99 36 140 Sr 671 189 621 15 820 587 40 580 20 Zr 192 490 339 633 323 256 920 319 1409 Y 23 40 25 57 31 26 51 33 102 Nb 32 68 52 88 50 40 123 49 216 Ga 23 33 23 37 22 24 40 27 52 Cu 33 19 33 9 29 49 7 27 18 Zn 120 124 119 177 103 90 192 105 267 Pb 3 7 2 10 5 2 10 4 16 La 27 - 40 - 41 33 74 - - Ce 59 100 88 148 70 72 170 61 270 Th 3 7 5 9 5 3 9 5 21 Nd 32 - 43 - 47 40 68 - - U 2 0 2 2 1 1 3 2 5

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Table 4 Rare earth element concentration (in ppm) for mafic lavas of two BMVF and three SMVF centres. For analytical procedures and detection limits, please refer to appendix A2.

Sample 26C-1-3 C-O-1 16-C-B2 JH-1-3 SM-1-3 Centre 26C Moore Ck. 16 Jorgensen Hill Satah Mtn. bas. trachy- Rock type hawaiite basalt trachybasalt trachybasalt andesite La 30.2 21.7 25.3 40.6 33.4 Ce 64.2 48.0 55.0 87.7 71.9 Pr 8.2 6.3 7.1 11.1 9.2 Nd 34.9 27.4 31.8 47.5 39.9 Sm 7.3 6.1 7.0 9.7 8.6 Eu 2.8 2.3 2.5 3.2 3.3 Gd 6.7 5.8 6.6 8.7 7.9 Tb 0.9 0.8 0.9 1.2 1.1 Dy 4.9 4.4 4.9 6.9 5.9 Ho 0.8 0.8 0.9 1.2 1.0 Er 2.1 1.9 2.2 3.0 2.7 Tm 0.3 0.3 0.3 0.4 0.3 Yb 1.5 1.4 1.6 2.4 2.1 Lu 0.2 0.2 0.3 0.3 0.3

3.5.2 40Ar/39Ar age data

A total of 24 individual lava samples were collected for age dating (Table 5; Fig. 18) with the aim to establish a good areal coverage of the SMVF and BMVF and sample the various lithologies of volcanic centres therein. Of these, seven were collected in the BMVF, 11 in the

SMVF, and six in areas that are either established as being part of the AVB (such as Nazko

Cone, one sample) or were thought to be potentially associated with the AVB (five samples; cf. ch. 3.2.1.3). None of these five investigatory samples were eventually determined to be associated with the AVB (see the discussion below). Ideally, the same sample was used for both age determination and XRF geochemical analysis. Where this was not possible, another sample from the same location/flow unit was used. 118

Analyses were performed on holocrystalline, homogeneous whole-rock and phenocryst-free chips (crushed and sieved to 1−0.5 mm size fraction). The samples and standards were wrapped in aluminium foil and loaded into aluminium cans of 2.5 cm diameter and 6 cm height. The samples were irradiated in position 5c of the uranium enriched research reactor of McMaster

University in Hamilton, ON (Canada), for 0.75 megawatt-hours.

Upon their return from the reactor, the sample and monitors were loaded into 2 mm diameter holes in a copper tray that was then loaded in an ultra-high vacuum extraction line. The monitors were fused, and samples heated, using a 6-watt argon-ion laser following the technique described in LAYER ET AL. (1987) and BENOWITZ ET AL. (2013). Argon purification was achieved using a liquid nitrogen cold trap and a SAES Zr-Al getter at 400 ºC. The samples were analyzed in a

VG-3600 mass spectrometer at the Geophysical Institute, University of Alaska Fairbanks. The

Ar isotopes measured were corrected for system blank and mass discrimination, as well as Ca, K and Cl interference reactions following procedures outlined in MCDOUGALL & HARRISON

(1999). Typical full-system 8 min. laser blank values (in moles) were generally 2×10-16 mol

40Ar, 3×10-18 mol 39Ar, 9×10-18 mol 38Ar and 2×10-18 mol 36Ar, which are 10–50 times smaller than the sample/standard volume fractions. Correction factors for nucleogenic interferences

39 37 during irradiation were determined from irradiated CaF2 and K2SO4 as follows: ( Ar/ Ar) Ca =

7.06×10-4, (36Ar/37Ar) Ca = 2.79×10-4 and (40Ar/39Ar) K = 0.0297. Mass discrimination was mo- nitored by running calibrated air shots. The mass discrimination during these experiments was

1.5% per mass unit. While doing the experiments, calibration measurements were made on a weekly to monthly basis to check for changes in mass discrimination with no significant variation seen during these intervals. Calculation of ages is based on the parameters of STEIGER

119

AND JÄGER (1977) and reported at ± 1σ level. The integrated age is the age given by the total gas measured and equals a K-Ar age.

Raw data and isochron plots, where available, for all analyses can be found in appendix A3 on p. 314)

120

Table 5 40Ar/39Ar analyses of the Satah Mtn. Volcanic Field (SMVF), Baldface Mtn. Volcanic Field (BMVF) and other volcanic centres (O) in central British Columbia.

Integrated Plateau Age Plateau Isochron Age Sample Affiliation Isochron Information Age (Ma) (Ma) Information (Ma) 6 of 9 fractions 6 of 8 fractions, J1 39 40 36 25B-1-2 BMVF 2.38 ± 0.046 2.43 ± 0.051 83.1% Ar release 2.45 ± 0.12 Ar/ Ari = 294.8 ± 11.5 MSWD = 0.31 MSWD = 0.34 9 of 11 fractions 8 of 11 fractions, J2 1.37 ± 0.053 26A-1-3 BMVF 1.58 ± 0.048 1.37 ± 0.046* 44.7% 39Ar release 40Ar/36Ar = 296.8 ± 5.9 See note 1 i MSWD = 0.82 MSWD = 0.94 10 of 11 fractions 10 of 11 fractions, J1 39 40 36 26C-1-1 BMVF 0.91 ± 0.026 0.91 ± 0.028 99.3% Ar release 0.94 ± 0.035 Ar/ Ari = 293.8 ± 3.7 MSWD = 1.41 MSWD = 1.49 5 of 8 fractions 5 of 8 fractions, J2 39 40 36 BF-1-3 BMVF 2.42 ± 0.027 2.37 ± 0.026 88.7% Ar release 2.33 ± 0.037 Ar/ Ari = 329 ± 29.6 MSWD = 0.42 MSWD = 0.11 5 of 8 fractions BF-K-2 BMVF 2.50 ± 0.024 2.52 ± 0.025 90.3% 39Ar release See note 2 J2 MSWD = 0.12 7 of 8 fractions 7 of 8 fractions, J1 39 40 36 C-O-1 BMVF(?) 3.94 ± 0.053 3.91 ± 0.054 99.3% Ar release 3.96 ± 0.097 Ar/ Ari = 290.8 ± 19.0 MSWD = 1.11 MSWD = 1.18 5 of 9 fractions 5 of 9 fractions, J1 39 40 36 CC-2-1 BMVF 2.34 ± 0.043 2.22 ± 0.038 84.8% Ar release 2.17 ± 0.12 Ar/ Ari = 308.1 ± 39.0 MSWD = 1.03 MSWD = 1.24 6 of 8 fractions 6 of 8 fractions, J2 39 40 36 3-2-2 SMVF 1.91 ± 0.034 1.94 ± 0.031 92.6% Ar release 1.94 ± 0.071 Ar/ Ari = 300.1 ± 27.9 MSWD = 0.86 MSWD = 0.97 8 of 10 fractions 9 of 10 fractions, J1 39 40 36 9-1-1 SMVF 1.95 ± 0.014 1.95 ± 0.015 98.8% Ar release 1.94 ± 0.015 Ar/ Ari = 281.5 ± 69.1 MSWD = 1.22 MSWD = 1.33 121

Table 5 continued

Integrated Plateau Age Plateau Isochron Age Sample Affinity Isochron Information Age (Ma) (Ma) Information (Ma) 9 of 10 fractions 9 of 10 fractions, J1 39 40 36 12-2-3 SMVF 1.67 ± 0.015 1.66 ± 0.014 99.3% Ar release 1.66 ± 0.030 Ar/ Ari = 297.2 ± 16.9 MSWD = 0.95 MSWD = 1.06 8 of 12 fractions 8 of 12 fractions, J1 39 40 36 16-6-1 SMVF 1.75 ± 0.016 1.77 ± 0.015 87.7% Ar release 1.78 ± 0.032 Ar/ Ari = 290.0 ± 11.2 MSWD = 0.21 MSWD = 0.20 7 of 10 fractions 7 of 10 fractions, J1 39 40 36 CH-2-1 SMVF 1.43 ± 0.020 1.43 ± 0.019 95.7% Ar release 1.46 ± 0.063 Ar/ Ari = 283.4 ± 29.9 MSWD = 0.30 MSWD = 0.31 7 of 8 fractions CM-4-2 SMVF 1.96 ± 0.021 1.96 ± 0.021 99.6% 39Ar release See note 3 J2 MSWD = 0.86 9 of 10 fractions 9 of 10 fractions, J1 39 40 36 JH-1-5 SMVF 2.19 ± 0.030 2.21 ± 0.029 98.8% Ar release 2.22 ± 0.085 Ar/ Ari = 294.0 ± 28.1 MSWD = 0.91 MSWD = 1.01 7 of 14 fractions 7 of 14 fractions, J2 39 40 36 SL-1-4 SMVF 2.23 ± 0.021 2.18 ± 0.023 73.9% Ar release 2.20 ± 0.038 Ar/ Ari = 267.3 ± 57.4 MSWD = 0.16 MSWD = 0.15 8 of 10 fractions 8 of 10 fractions, J1 39 40 36 SM-L-1 SMVF 1.83 ± 0.015 1.83 ± 0.014 98.6% Ar release 1.85 ± 0.014 Ar/ Ari = 273.8 ± 29.6 MSWD = 0.88 MSWD = 0.88 7 of 10 fractions 7 of 10 fractions, J1 39 40 36 SM-W-1 SMVF 1.67 ± 0.026 1.72 ± 0.023 95.5% Ar release 1.70 ± 0.035 Ar/ Ari = 298.5 ± 4.9 MSWD = 0.75 MSWD = 0.77 8 of 10 fractions 8 of 10 fractions, J1 39 40 36 TB-1-1 SMVF 1.73 ± 0.017 1.74 ± 0.016 96.5% Ar release 1.77 ± 0.022 Ar/ Ari = 269.8 ± 18.2 MSWD = 1.19 MSWD = 1.04

122

Table 5 continued

Integrated Plateau Age Plateau Isochron Age Sample Affinity Isochron Information Age (Ma) (Ma) Information (Ma) 9 of 10 fractions 9 of 10 fractions, J1 39 40 36 N-1-2 O (AVB) 0.34 ± 0.003 0.333 ± 0.005 95.7% Ar release 0.33 ± 0.006 Ar/ Ari = 298.5 ± 1.9 MSWD = 2.26 MSWD = 1.87 8 of 13 fractions 175.96 ± QV-1-1 O (LQ) 172.9 ± 1.49 94.7% 39Ar release See note 4 J1 2.37* MSWD = 2.74 4 of 7 fractions 4 of 7 fractions, J1 39 40 36 X-7 O (LQ) 0.18 ± 0.008 0.174 ± 0.007 64.5% Ar release 0.18 ± 0.006 Ar/ Ari = 292.2 ± 13.6 MSWD = 0.06 MSWD = 0.07 6 of 8 fractions CRD- O (OLG) 53.08 ± 0.48 54.85 ± 0.68 89.6% 39Ar release See note 5 J2 1-1 MSWD = 1.74 3 of 10 fractions GR-2-1 O (OLG) 47.52 ± 0.32 50.68 ± 0.48 52.0% 39Ar release See note 6 J1 MSWD = 0.76 6 of 8 fractions RT-1-3 O (OLG) 48.74 ± 0.47 51.39 ± 0.97* 75.1% 39Ar release See note 7 J2 MSWD = 3.56

Analytical notes: Ages determined using standard TCR-2 (sanidine) with an age of 27.87 Ma (LANPHERE & DALRYMPLE 2000).

Bold ages denote most robust and preferred age. An asterisk (*) next to a plateau age denotes a weighted average age if not all criteria for a true plateau age have been met. Ages given at ± 1σ. For all samples, the initial 40Ar/36Ar ratio is ± 2σ of the present-day atmospheric value (295.5). Irradiation parameter J is indicated by J1 = 8.001e-05 ± 2.250e-07 and J2 = 1.043e-04 ± 5.854e-07 (i.e. two individual sets of analyses). MSWD = mean square weighted deviates.

123

Note 1: Integrated, isochron and weighted average ages are within error, which indicates

minimum alteration and/or loss.

Note 2: No isochron age determination was possible because of the homogeneous

radiogenic content of the release.

Note 3: No isochron age determination was possible because of the evidence of loss.

Note 4: No true plateau age was produced (MSWD ≤ 2.5). Integrated (172.9 ± 1.49 Ma)

and the weighted average age (175.96 ± 2.37 Ma) are not within error. Weighted

average age is preferred due to evidence of minor loss in the low temperature/less

retentive step-heat releases.

Note 5: Integrated (53.08 ± 0.48 Ma) and the weighted average age (54.85 ± 0.52 Ma) are

broadly within error. Weighted average age is preferred due to evidence of minor

loss in the low temperature/less retentive step-heat releases.

Note 6: Integrated age (47.52 ± 0.32 Ma) and plateau age (50.68 ± 0.48 Ma) are not

within error. Plateau age is preferred as the most robust age due to evidence of

minor loss in the low temperature/less retentive step-heat releases.

Note 7: No true plateau age was produced (MSWD ≤ 2.5). Integrated (48.74 ± 0.47 Ma)

and the weighted average age (51.39 ± 0.97 Ma) are not within error. Weighted

average age is preferred due to evidence of minor loss in the low temperature/less

retentive step-heat releases.

124

Figure 18 40Ar/39Ar age spectra (given at 1σ level) for 7 samples from the Baldface Mtn.

Volcanic Field (25B-1-2 through CC-2-1), 11 samples from the Satah Mtn. Volcanic Fields

(3-2-2 through TB-1-1) and six older and/or non-AVB affiliated centres (N-1-2 through RT-

1-3). Consecutive fractions that cumulatively released over 50% of 39Ar are coloured in blue. These plateau ages are preferred and represent the crystallization age of the given rock sample. (Cf. Table 3 and data repository [appendix A3] for more information and isochron diagrams.)

125

Figure 18 continued

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3.6 Results

3.6.1 Geochemistry

Major, trace and rare earth element compositions of SMVF and BMVF lavas are reported in

Tables 3 and 4 and visualized in figures 19, 20 and 21.

3.6.1.1 Major elements

Plotted on a TAS major element diagram where SiO2 serves as a differentiation index (Fig. 19) cf. LE MAÎTRE ET AL. 1992), lavas from the SMVF and BMVF occur in a bimodal suite of mafic affinity (basanites to trachybasalts with overall 44−52.5 wt% SiO2) and felsic affinity (trachytes and phonolites; overall 59−64.3 wt% SiO2). While alkali contents and, to a lesser degree, aluminum (Al2O3) contents increase with increasing SiO2, MgO, Fe2O3, CaO, TiO2 and P2O5 contents decrease. Such variations are consistent with fractional crystallisation of olivine, clinopyroxene, oxides, feldspars (at approximately 55 wt% SiO2) and apatite (cf. GOURGAUD &

VINCENT 2004).

Major element correlation based on sample location (Figs. 20) shows that most BMVF lavas are slightly more primitive (44−49.4 wt% SiO2; 3.9-9 wt% MgO) than SMVF lavas (48.3−52.5 wt% SiO2, 2−7.7 wt% MgO). Two samples from Baldface Mtn. are exceptions in that they plot of trachytes and phonolites, respectively. These diagrams (Fig. 20) also show that BMVF and

SMVF samples form separate populations as a function of their respective SiO2 contents. BMVF centres are generally more primitive, with higher MgO, Fe2O3 (tot.), TiO2 and CaO contents and lower Na2O, K2O (and also Zr and Pb) contents than SMVF centres. SMVF data plot as two clusters that appear to roughly correlate with the position of centres within the field (Fig. 20).

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Figure 19 (A) Plot of total alkalis vs. silica of new SMVF (blue rhombs) and BMVF data (red squares), showing the bimodal distribution into distinct mafic and felsic suites.

Other centres sampled in this study are given as well (yellow triangles). Diagram based on specifications of LE MAÎTRE ET AL. (1992); dashed line is the boundary between alkaline and subalkaline fields (IRVINE & BARAGAR 1971).

(B) Same data plotted with existing data for other AVB centres and volcanic centres in close spatial relation. Sources for selected existing data: Rainbow Range (BEVIER 1978);

Ilgachuz Range (SOUTHER & SOUTHER 1994); Itcha Range and Satah* (CHARLAND 1994);

Nazko Cone (SOUTHER ET AL. 1987); Wells Gray–Clearwater (HICKSON & SOUTHER 1984);

Chilcotin (BEVIER 1983A).

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Figure 19

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One cluster (48.3−52.5 wt% SiO2) mainly comprises smaller centres in the southern half of the field whereas the other cluster (56.9−64.3 wt% SiO2) includes all centres north of Palmer Creek and the larger centres (“16”, “19”) of the southern half. The northern cluster is low in MgO (all under 1.5 wt%) and high in K2O (4.6−5.8 wt%) compared to the southern cluster. Contents of

Al2O3 are restricted between 14 and 19 wt%.

A few intermediate samples from Satah Mtn. plot as trachyandesites and are more closely related to the more highly evolved felsic cluster (Fig. 19a). SMVF samples overlap with those reported by CHARLAND (1994) and generally, there is good overlap between our data and existing data from the Rainbow, Ilgachuz and Itcha ranges (Fig. 19b; cf. BEVIER 1978;

CHARLAND 1994; SOUTHER & SOUTHER 1994). The total alkali content of mafic BMVF lavas is more restricted compared to the SMVF (4.4−6 wt% vs. 4.2-9.4 Na2O+K2O). Overall, total alkali contents range from 4.2−14 wt%; all samples but one (LF-16-2-1) plot in the alkaline field as defined by IRVINE & BARAGAR (1971). SMVF and BMVF basalts and trachybasalts have elevated alkali content (up to 7 wt% Na2O+K2O) and are predominantly of sodic affinity (Fig.

21). The most Mg-rich basalts contain ~9 wt% MgO).

The patterns observed for SMVF and BMVF lavas overlap and, by and large, follow the trends of existing geochemistry data from the Rainbow Range (BEVIER 1978), Ilgachuz Range

(SOUTHER & SOUTHER 1994) and Itcha Range (CHARLAND 1994; indicated by grey areas in Figs.

21). The ‘Daly gap’ of intermediate compositions is somewhat more strongly expressed in lavas from the three shield volcanoes. Our data include four trachyandesitic samples (benmoreites) from the SMVF that fall in this gap, thus somewhat ‘blurring’ the bimodal pattern of SMVF lavas. SMVF and BMVF lavas also contain ~0.5 wt% more P2O5 than rocks from the three shield volcanoes.

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The outlying, non-AVB centres show distinctly different geochemical characteristics.

Samples were analysed from older centres “GR” (dacite/trachyte) and “LM” (basaltic andesite) to the south and east, respectively, of the SMVF; together with centres “RT” (andesite) and

“CRD” (subalkaline trachyte), these data plot outside of both SMVF and BMVF cluster.

On a K2O vs. Na2O diagram (Fig. 21) the BMVF data form a cluster that overlaps with the southern SMVF cluster. Rocks from these fields plot in the Na-series or K-series fields; the northern SMVF and Baldface Mtn. data plot in the K-series field exclusively. On a Nb- normalised Zr vs. Ba discrimination plot, SMVF/BMVF and existing AVB data are indicate to be related to an OIB and/or enriched mantle (EM1) source area (see ch. 4 for an in-depth discussion of this topic).

On a peralkalinity plot (Fig. 22), the SMVF and BMVF data show considerable scatter. All of the BMVF and most of the SMVF data are of metaluminous affinity, but some SMVF lavas are shown as peralkaline. Agpaiitic indices (Na+K/Al) range from 0.51 to 0.97 for the BMVF and

0.53 to 1.17 for the SMVF (samples from the other centres are plotted but no further considered here), with the highest values from SMVF trachytes and phonolites and indicating the peralkaline nature of these rocks. Estimates of liquidus temperatures and H2O contents for representative samples were calculated using an Excel spreadsheet are given (Table 6). For the mafic samples

(basanite, basalt, trachybasalt), the high liquidus temperatures of up to 1,325 °C are in agreement with values reported in the literature (cf. GREEN & RINGWOOD 1967); H2O contents are very low, almost dry (max. 0.33 wt%), which agrees well with experimentally determined values for basaltic and basanitic melts at low pressure (GREEN 1969). For the felsic samples (trachytes, phonolites), the calculated temperatures are on high side, but temperatures as high as 1050 °C

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have been experimentally determined for phonolites (cf. MANLEY 1992). H2O contents fall in the lower end of experimentally determined values (cf. WHITTINGTON ET AL. 2001).

Table 6 Liquidus temperature and water content in selected samples of the rock types determined. (Bsn = basanite, bas = basalt, trb = trachybasalt, bas. trad. = basaltic trachyandesite, tra = trachyte, pho = phonolite). These numbers were arrived at using an

Excel-based CIPW calculation programme developed by K. Hollocher, Union College,

Schenectady, NY (USA). The original template can be accessed at http://minerva.union.edu/hollochk/c_petrology/other_files/norm4.xls.

Sample Rock type Liquidus (ºC) H2O (wt%) 26A-1-3 bsn 1325 0.14 N-3-1 bsn 1330 0.13 C-O-1 bas 1289 0.18 LF-16-2-1 bas 1232 0.33 25B-1-2 trb 1256 0.26 26C-1-3 trb 1225 0.35 LF-5-1 trb 1215 0.39 CC-2-1 trb 1255 0.26 3-1-4 bas. trad. 1199 0.45 SM-1-3 bas. trad. 1201 0.44 5-1-5 tra 951 2.23 MM-1-4 tra 1019 1.61 SM-3-2 tra 1041 1.42 2C-1-3 pho 1018 1.63 BF-1-3 pho 1033 1.49

In terms of CIPW normative mineralogy, 22 of the overall 43 SMVF samples are nepheline normative (maximum 14 wt% nepheline); 17 are hypersthene normative (maximum 12.5 wt% hypersthene). Some transitional samples have very small amounts of either Hy or Ne. Of these samples, 13 are also quartz normative and seven acmite normative (<11.8 wt%). The acmite

(sodic pyroxene) is indicated in six trachytic and phonolitic samples from centres “2C”, “CM”,

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“MM” and “U”, the latter three of which are in close proximity to one another in the northern part of the SMVF. Sodic amphiboles are indicated in thin section, but no microprobe work was performed to ascertain this observation. In addition to the occurrence of acmite, the ferriferous character of the trachytes (5.2 < Fe2O3 < 9.5 wt%) is characteristic of peralkaline lavas

(GOURGAUD & VINCENT 2004). Only five SMVF trachybasalt samples have over 5 wt% MgO and are thus classified as hawaiites (cf. CHARLAND ET AL. 1995). Out of 11 BMVF samples, seven are nepheline normative; three hypersthene normative; and one quartz normative.

Differentiation indices (D.I.) for mafic BMVF lavas range from 55−66, for felsic lavas from

51−92. For SMVF mafic lavas, the D.I. range from 57−70, for felsic lavas 63−88 (see appendix

A2 for individual values). Fourteen samples, predominantly trachytes, show normative quartz, but often only in traces (maximum 2.8 wt% SiO2). Interestingly, the majority of centres with qtz-normative lavas are located in the southern part of the SMVF. While two trends between a dominant trachyte−phonolite series and a volumetrically subordinate qtz-trachyte−rhyolite series have been noted in the nearby Itcha Range (CHARLAND ET AL. 1993), no such trends are evident in the SMVF or BMVF due to the lack of rhyolites in either field.

Even when plotted on just the TAS diagram (Fig. 19a), the outlying centres show distinctly different geochemical characteristics. Samples were analysed from older centres “GR” (dacite/ trachyte) and “LM” (basaltic andesite) to the south and east, respectively, of the SMVF; together with centres “RT” (andesite) and “CRD” (subalkaline trachyte), these data plot outside of both

SMVF and BMVF cluster. We, therefore, regard them as not affiliated with the AVB at all; a fact that is all the more obvious and self-explanatory considering their Eocene ages (see below).

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Figure 20 Harker diagrams showing variation in major element and selected trace element abundances versus SiO2. These diagrams discriminate the data based on field affinity. Blue rhombs: SMVF; red squares: BMVF; green triangles: Satah Mountain samples. Note that the SMVF data is divided into a southerly cluster defined by lower SiO2 values (<52.5 wt%) and a more northerly cluster (more than 57.7 wt%); the circles in the

Fe2O3 plot indicate this.

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Figure 20

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3.6.1.2 Trace elements

Distribution of selected trace elements versus Zr considered as a differentiation index, are plotted in Figs. 21 (cf. Table 3). High-field-strength elements (HFSE; e.g., U, Y, Th, Zr) behave incompatibly with increasing SiO2, and show elevated contents in the more felsic lavas (e.g. centres “MM”, “TB”, “2C”). Analyses from trachytic phonolitic SMVF centres “2C” and “U” show conspicuous enrichment in Zr (~2,500 ppm) and Pb (25 and 28 ppm), although similarly high values were reported for phonolites from the Itcha Range (CHARLAND ET AL. 1993). Rb/Zr ratios show considerable overlap between mafic lavas (0.078−0.135) and more felsic ones

(0.095−0.155), indicating a common source/parental magma (CHARLAND ET AL. 1995).

The southern SMVF cluster and BMVF data show moderate and strong enrichment in Sr over the northern SMVF cluster. The BMVF exhibits scattered, but generally much higher Ni contents (43−184 ppm) than SMVF centres; the majority of SMVF centres with elevated Ni levels (up to 162 ppm) are from lavas in the southern part of the field. These values are comparable to those reported from the Ilgachuz (SOUTHER & SOUTHER 1994) and Itcha ranges

(CHARLAND 1994), and also to data reported from the Tibesti, Chad (GOURGAUD & VINCENT

2004). This is another indication that these AVB basalts do not represent primitive magmas

(which have <400 ppm Ni; cf. SATO 1977). Correlations between incompatible elements Rb, Sr,

Nb, Th and Zr (Figs. 20, 21) define a relatively linear evolution from the mafic lavas to the felsic ones. Such correlations may be related to fractional crystallisation, for example of zircon (Zr) and feldspar (Sr) (cf. GOURGAUD & VINCENT 2004).

In a multi-element spider diagram (Fig. 23a), basalts and trachybasalts from the SMVF and

BMVF exhibit moderate negative anomalies of Rb and Th, and moderate positive anomalies of

Ba, K and Pb. Such anomalies may reflect fractionation of K-feldspars and plagioclase, but the

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lack of a strongly negative Ba or K anomaly (as commonly observed in trachytes and phonolites) likely reflects that no extensive fractionation of feldspars did occur. Our data exhibit patterns that are comparable in shape and steepness (Fig. 23a) to mafic lavas from the Ilgachuz and Itcha ranges (SOUTHER & SOUTHER 1994; CHARLAND 1994). Slight enrichment of SMVF and BMVF lavas is observed for some MREE and HREE. The overall patterns for mafic AVB lavas (Fig.

23b) again follow closely that of an average OIB (SUN & MCDONOUGH 1989), corroborating a hot-spot/plume affinity of these magmas. Plotting AVB mafic lavas on a Nb-normalised Ba vs.

Zr discrimination diagram (Fig. 21) also indicates an OIB affinity, and possibly an enriched mantle (EM1) source region. Source regions affiliated with primitive mantle, N-MORB or exclusive to continental crust domains can be excluded. However, the slight positive anomalies for Ba, K and Pb mentioned above correlate to similar spikes in the average composition of crustal domains (RUDNICK & FOUNTAIN 1995) and may yet indicate small degrees of crustal contamination of these mafic melts during ascent and/or storage in the crust.

Figure 21 Harker variation diagrams based on rock types. Major element oxides given in wt%, selected trace elements in ppm. Grey areas denote compositions of lavas from the

Rainbow, Ilgachuz and Itcha ranges (data from BEVIER [1978], SOUTHER & SOUTHER

[1994] and CHARLAND [1994]). No Pb data existed for AVB centres prior to this study.

Na2O vs. K2O indicated predominant sodic or potassic character of SMVF and BMVF lavas. Zr/Nb vs. Ba/Nb discrimination diagram indicates affiliation of AVB lavas with an

OIB and/or EM1 source.

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Figure 21

138

Figure 21 continued

139

Figure 21 continued

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Figure 22 (A) Alumina saturation diagram for SMVF and BMVF lavas and those of outlying (other centres), indicating predominantly metaluminous character of these rocks

(symbols as in Figure 19a).

(B) Same diagram, but based on TAS-determined rock types and without non-AVB centres

(symbols as in Figure 21).

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Figure 23 (A) Multi-element, primitive mantle-normalized spider diagram for two mafic SMVF and three mafic BMVF lavas (normalization values from SUN & MCDONOUGH

[1989]). Pink-shaded field denotes mafic lavas from the Ilgachuz Range (SOUTHER &

SOUTHER [1994]), blue-shaded field mafic lavas from the Itcha Range (CHARLAND [1994]).

(B) Spider diagram comparing AVB data (yellow, pink and blue shaded fields) with average values for LCC, MCC, UCC, OIB, E-MORB and N-MORB. Abbreviations and data sources given in Fig. 24 below. 142

3.6.1.3 Rare earth elements

Rare earth elements were measured for a few select samples of the more SMVF and BMVF mafic lavas. Chondrite-normalized REE patterns (Fig. 24a) show that samples from Satah Mtn. and Jorgensen Hill (SM-1-3, JH-1-3) are slightly more enriched than those from either the southern part of the SMVF (16-C-B2) or the BMVF (26C-1-3; C-O-1, which also is discordant).

The first two SMVF samples show substantial LREE enrichment (100 to 150 times, likely controlled by olivine and pyroxene) and less HREE enrichment (~10 times). Fractionation between LREE and HREE is moderate ((La/Yb)n = 10.2−14.3); for mafic lavas from the

Ilgachuz and Itcha ranges, the ratio is 7.4−18.7 (SOUTHER & SOUTHER 1994) and 9.3−12.0

(CHARLAND 1994), respectively.

The REE pattern for SMVF and BMVF mafic lavas are similar to those reported from the

Ilgachuz and Itcha ranges (Fig. 24b; SOUTHER & SOUTHER 1994; CHARLAND 1994), all of which follow the OIB pattern (SUN & MCDONOUGH 1989) more closely than those of continental crust

(RUDNICK & FOUNTAIN 1995). These patterns are characteristic of intra-plate continental basalts

(GOURGAUD & VINCENT 2004). No Eu anomaly exists for SMVF, BMVF or Itcha mafic lavas

(but is well expressed in the felsic lavas of the AVB; cf. CHARLAND 1994, SOUTHER & SOUTHER

1994). We interpret this as an indicator that no significant fractionation of plagioclase and/or alkali feldspar occurred in these SMVF and BMVF lavas, as indicated by the absence of even more highly evolved comendites or pantellerites.

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Figure 24 (A) Chondrite-normalized rare earth element concentrations for selected mafic samples from the SMVF (SM, 16-C, JH,) and BMVF (26C, C-O). Normalization values from SUN & MCDONOUGH (1989).

(B) Chondrite-normalized REE rare earth element concentrations from present study

(yellow shaded area) compared with mafic lavas from the Ilgachuz (dotted outline; data from SOUTHER & SOUTHER [1994]) and Itcha ranges (dashed outline; data from CHARLAND

[1994]). Plotted as lines are average REE concentrations for the lower, middle and upper continental crust (LCC, MCC, UCC; data from RUDNICK & FOUNTAIN [1995]), as well as average OIB (ocean island basalt) and N-MORB (mid-ocean ridge basalt) concentrations

(data from SUN & MCDONOUGH [1989]). The AVB data fit the OIB line the best.

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Figure 24

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3.6.2 40Ar/39Ar dating

Nineteen samples had integrated, plateau and isochron ages that were within error, indicating minimal alteration and/or loss of argon (Table 5; Fig. 18). One sample (26A-1-3) has integrated, weighted average age and isochron ages that were within error, likewise indicating minimal alteration. Four samples that yielded Eocene or Mesozoic ages show signs of argon loss. The plateau ages are preferred because of their higher precision and/or high atmospheric content of the initial gas release for most of the samples. These ages are therefore interpreted to be representative of when these rocks were erupted (Table 5; Fig. 18). Figure 25 shows the SMVF and BMVF centres and some of the outlying centres that were dated during this study.

Of these six outlying centres that were sampled, three are in the vicinity of the study areas

(GR-2-1, RT-1-3, CRD-1-1) and yielded Eocene ages; one sample from Nazko Cone (N-1-2) confirmed an existing K-Ar age of this centre’s first episode of Quaternary activity at ~0.33 Ma

(cf. 0.340 ± 0.003 Ma [SOUTHER ET AL. 1987]). A sample (X-7) from a basanite flow originating at Abbott Creek Cone indicates younger volcanic activity (~0.17 Ma) in the Quesnel Lake area, which overlaps with a date yielded from another, unnamed volcanic centre 13 km NE of Abbott

40 39 Creek Cone (0.17 Ma; HICKSON 1990). A Ar/ Ar age of 0.35 ± 0.01 Ma is reported from the lava flow exposed in the quarry on the SW flank of this centre (KELMAN, unpubl. data), which may indicate that volcanic activity at Abbott Creek Cone lasted for at least 180 ka. Conversely, a sample (QV-1-1) from a roadside outcrop on the south shore of Quesnel Lake, taken from a small area mapped as “Quaternary volcanics” (LOGAN ET AL. 2010), yielded a Jurassic age.

These two samples are clearly part of both a younger and a much older episode of volcanic activity, respectively, and thus unrelated to any AVB rocks.

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Figure 25 Distribution of volcanic centres in the SMVF and BMVF for which 40Ar/39Ar ages were determined in this study. Red triangles denote Pleistocene ages, orange triangle a Pliocene age (C-0-1), and yellow triangles (GR-2-1, RT-1-3) Eocene non-AVB ages. Base map constructed using DEM data provided by GEOGRATIS (Department of Natural Re- sources Canada, 2014. Contains information licensed under the Open Government Licence

– Canada). Ages keyed to Table 5.

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A plot of these ages (Fig. 26a) with existing data for the AVB and other major Neogene and

Quaternary volcanic centres in B. C. shows that eruptive episodes in the SMVF and BMVF are coeval with activity in the nearby Itcha Range. SMVF ages are confined to a relatively short period of time of ~0.78 Ma in the Early Pleistocene, during which eruptions were taking place along the entire length of the field. Initial volcanic activity in the SMVF took place after activity in the Itcha Range had been ongoing for ~1 Ma (SOUTHER 1986). Our data show no clear trend of activity in the field migrating in any given direction. However, the more southerly centres

“Jorgensen Hill” and “SL” yield slightly older ages than centres in the northern part of the field, with “JH” yielding the oldest SMVF age at 2.21 ± 0.03 Ma (sample JH-1-4). Samples taken from the western (SM-W-1) and eastern summits (SM-L-1) of Satah Mtn. indicate minimum duration of activity at this centre of ~0.16 Ma. A breached scoria ring on the north flank of

Satah Mtn. (Fig. 16b) is interpreted to be younger than the main edifice due to it appearing largely unmodified by later glacial erosion. Two centres (“9” and “12”) at the opposite ends of the small E-W trending chain of cones at the northern edge of the SMVF show a younging trend towards the west, but this interpretation should be treated with caution as no data from the two centres (“10”, “11”) in the middle is available. The youngest SMVF centre, “CH” (1.43 ± 0.02

Ma), is also the smallest in height and volume; somewhat frustratingly, its location in the southern part of the SMVF is between two of the oldest centres of the field.

The seven ages obtained for BMVF centres also indicate a temporal overlap with activity in the Itcha Range. Six samples define a period of activity of ~1.6 Ma that both precedes and post- dates activity in the SMVF by several 100 ka. The oldest age (BF-K-2, 2.52 ± 0.02 Ma), comes from a small trachyte “knob” just south of Baldface Mtn. However, the data obtained from Bald- face Mtn. itself is only slightly younger (BF-1-3, 2.37 ± 0.03 Ma) and the close proximity

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between the two centres might indicate that these are part of a larger centre or single period of activity. The youngest sample (26C-1-1, 0.91 ± 0.03 Ma) comes from a basaltic flow some 6 km to the southeast of Baldface Mtn. One sample (C-O-1) from a basalt flow close to the eastern reaches of mapped AVB units yields a somewhat incongruously old Pliocene age (3.91 ± 0.053

Ma), similar to the oldest rocks known from the Itcha Range and/or the Chilcotin Group basalts

(BEVIER 1983B). The source of that flow is currently unknown.

The Eocene ages yielded by three samples (GR-2-1, RT-1-3, CRD-1-1) indicate, in addition to their spatially distinct locations and lithologies, an affiliation of these outlying centres with the

Ootsa Lake Group described by TIPPER (1969) and MIHALYNUK ET AL. (2008, 2009). This succession of basaltic to dacitic flows and associated volcanogenic sediments reaches between

500 and 1,000 m in thickness in the study areas. Our ages for centres “RT” and “CRD” are consistent with those published in MIHALYNUK ET AL. (2009).

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Figure 26 (A) Overview of ranges of ages of AVB centres from W to E. Results from present study are highlighted in red. Dashed lines indicate uncertainty for oldest age data.

For comparison, periods of activity at other volcanic fields and provinces in British

Columbia are given as well. It is evident that activity of non-AVB centres is much-longer lived. (Note that continuous lines do not represent continuous activity.) BB−Bella Bella dyke swarms, KI−King Island pluton, RR−Rainbow Range, IR−Ilgachuz Range,

ITR−Itcha Range, SMVF−Satah Mtn. Volcanic Field, BMVF−Baldface Mtn. Volcanic

Field, NC−Nazko Cone, ACC−Abbott Creek Cone, CGB−Chilcotin Group basalts,

ED/SR−Mt. Edziza-Spectrum Range, GVB−Garibaldi Volcanic Belt (existing data compiled and modified from BEVIER [1983B], SOUTHER [1986]; SOUTHER ET AL. [1984,

1987]; GREEN ET AL. [1988]; SOUTHER & SOUTHER [1994]).

(B) Age-distance plot for AVB centres based on existing K-Ar ages and new Ar/Ar ages for

SMVF and BMVF. Distances are measured from central location in the Bella Bella dyke swarms to other locations. Horizontal error bars take extent of individual centres and locations into account. Dashed lines outline age-distance progression of a hot-spot track for the North American plate moving at 2 cm/yr (blue) or 3 cm/yr (red). Symbols as in Figure

19b.

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Figure 26 A

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3.7 Discussion

The new whole-rock geochemistry and geochronology data obtained from the SMVF and BMVF suggest that volcanic activity in these fields was coeval with activity in the nearby Itcha Range

(SOUTHER 1986; CHARLAND ET AL. 1993; 1995). Both fields consist of monogenetic centres and a few larger (and likely polygenetic) centres, but periods of activity here clearly were more geographically scattered, of shorter duration and considerably less voluminous than in the Itcha

Range. This style of individual eruptions from multiple centres that are spatially and temporally scattered and that were generally of low volume is similar to that of the Wells Grey-Clearwater volcanic province (HICKSON & SOUTHER 1984; HICKSON 1987).

3.7.1 Timing of volcanic activity

Of the 18 40Ar/39Ar dated samples collected from the SMVF and BMVF, 16 fall into a period ranging from ~2.5 to ~1.4 Ma, with one older and one slightly younger outlier in the BMVF

(Table 5; Figs. 18, 25 & 26b). Activity in the latter field appears to have started some 0.3 Ma earlier and lasted between 0.08 and 0.54 Ma longer than in the SMVF (based on the youngest age data from a single flow). During the same time period (2.2−0.8 Ma), activity in the Itcha

Range had entered its second, more mafic stage (CHARLAND ET AL. 1993; 1995). In relation to the other AVB centres with established ages (SOUTHER 1986; SOUTHER ET AL. 1987), and considering the potentially hot-spot related decrease in ages from west to east, these new age data for the SMVF and, in particular, the BMVF appear to coincide with where one would expect them to be, both spatially and chronologically. The movement of the North American Plate since the Neogene over a stationery mantle plume at the currently accepted velocity of 2−3 cm/yr

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(BEVIER ET AL. 1979; SOUTHER ET AL. 1987; GRIPP & GORDON 2002; MERCIER ET AL. 2009) during the timespan allotted could conceivably lead to new magmatic activity at progressively more easterly locations. The BMVF is situated some 22 km to the east of the Itcha Range and broadly coincides with a position of a hot-spot roughly 1 Ma after initial activity in the Itcha

Range. Nazko Cone, itself situated some 80 km to the NE of the Itcha Range, also appears to be consistent with this model in terms of the trend of the proposed hot-spot and distance to the Itcha

Range and BMVF (HICKSON 1987; SOUTHER ET AL. 1987).

A plot of age vs. distance (Fig. 26b), based on existing K-Ar and new 40Ar/39Ar data indicates that AVB centres fall along paths of a hot-spot migrating at 2−3 cm/yr. We assume a “ground zero” at the Bella Bella dykes (average age ~13.2 Ma; SOUTHER 1986). All AVB centres east of this location are at distances from “ground zero” that agree with the timings of magmatism and volcanic activity at the respective centres. K-Ar ages from the Rainbow Range (BEVIER ET AL.

1979) are slightly older, possibly due to excess argon in those samples. Data from the Itcha

Range (SOUTHER 1986), relative velocity calculations (HICKSON 1987) and our SMVF and

BMVF data suggest a slowing down of the average hot-spot motion during the Upper Pliocene and Pleistocene; however, age data from Nazko Cone (SOUTHER ET AL. 1987; this study) does correlate with the motion of the North American plate (~2.5 cm/yr; MINSTER ET AL. 1974;

MADSEN ET AL. 2006) and motion data for the Yellowstone hot-spot (~2.7 cm/yr at an azimuth of

241º ± 24 º; GRIPP & GORDON 2002). Euler pole calculations and subsequent position of potential hot-spot trends by HICKSON (1987) also indicate consistency with the mantle plume/hot-spot hypothesis. Now considered unrelated to the AVB, small-scale Quaternary volcanic activity at Quesnel Lake might be the result of leaky normal or transform faults that provided ways for magma ascent, similar to the Wells Grey-Clearwater area (HICKSON 1987).

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Concurrently with volcanism in the central AVB, other centres in B. C. were erupting. In the

Upper Miocene, the earliest activity at the eventual Mt. Edziza-Spectrum Range complex is recorded (SOUTHER ET AL. 1984; EDWARDS & RUSSELL 1999). The Chilcotin Group basalts erupted several times since the Middle Miocene (BEVIER 1983B; Fig. 26a). In the Early

Pleistocene, subduction-related volcanic activity in southwestern B. C. led to the inception of the

Garibaldi Volcanic Belt (GREEN ET AL. 1988). It is evident (Fig. 26a) that none of the AVB centres have the same longevity, both in terms of overall duration of activity and repeated activity at one locality, as some of these other volcanic belts and provinces (e.g., Mt. Edziza).

There is no clear trend especially within the SMVF that indicates initiation of volcanic activity at one particular location and then migrating from there. There is also no discernable correlation between the age of individual centres and their respective geochemistry. However, in the BMVF, the more evolved rocks tend to be older than the mafic rocks, but the divide between them is small and within error (Fig. 27). One of the oldest centres in the SMVF (“JH”, 2.21 ±

0.029 Ma) erupted hawaiitic lavas which is somewhat at odds with observation from the Ilgachuz

(SOUTHER & SOUTHER 1994) and Itcha ranges (STOUT & NICHOLLS 1983; CHARLAND ET AL.

1993) where hawaiites are part of the final stages of activity. However, in both cases the amount of erupted mafic magma was insignificant compared to the large volumes of the earlier, felsic magmas. We interpret the spatially and temporally scattered activity in the SMVF as a result of individual batches of melt of different compositions ascending and erupting at the surface at

“random” times (also see ch. 4.4.3).

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Figure 27 Plot of composition (as a function of SiO2 content) and age for SMVF and

BMVF (minus outlier C-O-1 and non-AVB centres). While a slight trend of younger and more primitive rocks exists in the BMVF, no such trend can be seen for the SMVF.

Symbols as in Figure 19. (Note: Error bars for these data are so small that they do not show up in the diagram. See Table 5 for error values for these ages.)

The BMVF ages are from centres that are both spatially and chronologically in close proximity (apart from the Pliocene “outlier”, C-0-1), thus possibly indicating coeval activity at individual centres. An apparent lack of activity between ~2.2 and ~1.4 Ma as well as ages appearing to cluster around ~2.4 Ma may be due to the poor spatial coverage of the data, with five out of seven samples coming from centres within a few kilometres of each other. Sample

CC-2-1 (2.22 ± 0.04 Ma) is from a well-preserved tephra cone 14 km to the ESE of Baldface

Mtn. and again indicates coeval activity in different areas of the field. The older BMVF centres

155 erupted somewhat more evolved rocks, e.g. trachytes and phonolites at Baldface Mtn., the largest edifice in the field (Fig. 27). Unlike in the SMVF, however, the youngest dated rocks from the

BMVF are hawaiites (26C-1-1) and basanites (26A-1-3) which appear to have been erupted

~0.65 Ma after the trachytes and phonolites.

The latest volcanic activity in the BMVF may also have been occurring during or shortly after a period of major regional glaciation in central British Columbia during the Early Pleistocene

(MATHEWS & ROUSE 1986). It is likely that most, if not all, of the then existing volcanic centres in the SMVF and BMVF (and the AVB in general) were affected and modified by this glaciation.

3.7.2 Correlation between age and geochemistry

Both in the shield volcanoes and the AVB as a whole, there appears to be a trend towards less evolved and more undersaturated rocks with time (SOUTHER ET AL. 1987; CHARLAND ET AL.

1995). Nazko Cone, the youngest AVB centre, erupted basanites exclusively (SOUTHER ET AL.

1987), possibly indicating the tapping of a magma source that was deeper and/or less depleted than sources for the Rainbow, Ilgachuz and Itcha ranges, and the SMVF and BMVF. No such trend is apparent in rocks analysed in the present study, but this could simply be a function of the small quantity of data.

The roughly linear arrangement of centres in the SMVF paralleling the orientation of faults in the Itcha Range is similar to the alignment of monogenetic cones in the Chichinautzin Volcanic

Field of central Mexico. That field is thought to be linked to a fault system which may have provided ways for small batches of magma to ascend (ARCE ET AL. 2013). Another analogue for the AVB in general, and the SMVF in particular, might be found in the Chaîne des Puys, an area

156 of continental alkaline volcanism in the Massif Central of central France (DOWNES 1987). This chain of Pleistocene and Holocene centres is comparable to the SMVF in its extent (ca. 40 by 10 km), type of volcanic edifices (trachytic domes, Strombolian cinder cones), and association with an existing central volcano, Mont-Dore (CONDOMINES 1997). The Massif Central is thought to be underlain by a small-scale mantle plume, which may also have induced (or at least assisted) continental rifting (GRANET ET AL. 1995). There is also a strong similarity between AVB geochemistry and that of the Chaîne des Puys, with two series of magma series (silica-undersaturated basanite−tephrite−phonolite vs. a partially silica-saturated alkali basalt–trachyandesite– trachyte−rhyolite series) observed for either location (DOWNES 1987; CHARLAND 1994). The tectonic setting of the Massif Central and its youngest member, the Chaîne des Puys, is largely controlled by an N-S trending graben system that was established in the Oligocene. Similar to the central volcanoes of the AVB, activity at Mont-Dore consisted of two distinct phases lasting some 1.5 Ma (DOWNES 1987).

Erupted magma volumes from SMVF and BMVF centres were several magnitudes lower than in the shield volcanoes. It is hard to quantify how much material was erupted and then removed during periods of glaciation. That presumably small batches of (highly) evolved melts were able to ascend and erupt to form both monogenetic and polygenetic centres could be explained with the aforementioned low viscosity of these lavas due to increased de-polymerization of silica tetrahedra, which is characteristic for alkaline lavas (and containing F and/or Cl; SCHMINCKE &

SWANSON 1967; SCHMINCKE 1974; BEVIER 1978; DINGWELL ET AL. 1985; CHARLAND 1994).

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3.7.3 Volcanotectonic controls

A relationship between the SMVF and BMVF and the nearby Itcha Range is suggested by spatial, temporal and geochemical similarities. The alignment of Satah Ridge parallel to normal faults in that range as well as the presence of small conical structures between the SMVF and the

Itcha Range suggest that magma ascent was likely controlled by faults that allowed migration of magmas away from the Itcha Range, where activity was more highly localized over a longer period of time (CHARLAND ET AL. 1993, 1995). The lack of voluminous phonolites or rhyolites in the SMVF and BMVF indicates that their magmas did not differentiate to the same degree as those of the three shields (BEVIER ET AL. 1979). No fault scarps were observed during sample collection, possibly due to thick Quaternary cover. The Satah Ridge spatially coincides with an area of increased gravity (RIDDELL 2006), which probably indicates that the ridge is the product of repeated volcanic eruptions and piling up of lava flows in this area (see ch. 4.4.2).

Conversely, neither the Rainbow nor the Ilgachuz ranges feature associated extensive volcanic fields in their immediate vicinity, which may indicate the lack of similar fracture systems associated with either volcano. Despite the Chilcotin Group basalts reaching their greatest areal extent in the vicinity of the central AVB, it is unlikely that the SMVF and/or

BMVF ever were a source area for these basalts. Moreover, despite the petrographic similarity between Chilcotin Group and AVB rocks, the former are distinctly different in their geochemistry, eruption ages and interpreted tectonic settings (BEVIER 1983A/B; cf. ch. 4.4.3).

The location and Neogene motion of the Queen Charlotte triple junction does not provide a clear explanation for the location and kind of alkaline magmatism observed in the AVB. A tectonically somewhat comparable situation at the Mendocino and Rivera triple junctions off the coast of California led to Neogene volcanism onshore. However, that volcanism lacks both the

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(per)alkaline character of AVB rocks and a comparable linear decrease in ages (JOHNSON &

O’NEIL 1984).

An alternate explanation for the AVB is that it is the result of a plate-edge effect

(THORKELSON 1996; THORKELSON ET AL. 2011). The AVB is located north of the northern edge of the subducting Juan de Fuca/Explorer slab (AUDET ET AL. 2008) and appears to lie at an acute angle to that subducted plate at depth (BEVIER ET AL. 1979). Poloidal and toroidal flow of upwelling asthenospheric material around the subducting plate could cause melting of the slab edge (SOUTHER ET AL. 1987; AUDET ET AL. 2008), similar to what has recently been proposed for the Yellowstone hot-spot (JAMES ET AL. 2011). Furthermore, the interaction of upwelling asthenosphere with the overriding plate could lead to crustal attenuation (AUDET ET AL. 2008).

These processes could potentially lead to magma generation and if subsequently rifting is induced at the Earth’s surface, ascent ways for these magmas could be generated.

On northern Vancouver Island, the Late Miocene to Pliocene Alert Bay Volcanic Belt

(ABVB) has been proposed to be the product of such a volcanotectonic regime (ARMSTRONG ET

AL. 1985). However, that belt is located almost exactly above and parallel to the edge of the subducting Juan de Fuca/Explorer plate whereas the AVB is over 100 km lateral distance from the

NE trend of the slab edge at depth; at no time during the Neogene or Quaternary did the subducting slab underlie the AVB (RIDDIHOUGH 1977; EDWARDS & RUSSELL 2000). Lavas of the

ABVB have a distinct, subalkaline signature compared to the AVB’s alkaline lavas. This model would also struggle to give an explanation for the eastward migration of activity in the AVB.

Based in part on the alkaline geochemistry of AVB rocks and in part on the linear decrease in ages from west to east, the main mechanism driving magmatic activity in the belt is postulated to be a mantle plume (e.g., SOUTHER 1977, 1986; BEVIER ET AL. 1979). Incipient activity in both

159 the AVB (in the Bella Bella region) and the Chilcotin basalts in the Middle Miocene coincide with increased uplift in the Coast Mountains in the area, which could have been caused by the passage of such a hot-spot (MERCIER ET AL. 2009). Recent tomographic studies of western Ca- nada using P and S velocity models by these authors have revealed a low-velocity anomaly under west-central British Columbia with its centre near Nazko Cone and extending to a depth of ~400 km (Fig. 28). This anomaly is imaged along strike of the AVB, underlying the central part of the

AVB and also an area east of Nazko Cone. Low-velocity zones are recognized beneath other hot-spots and paralleling their tracks and such zones are now thought to be associated with these hot-spots’ source areas (including the Yellowstone hot-spot track; cf. JAMES ET AL. 2011). The existence of such a low-velocity zone under the AVB further corroborates the hot-spot/mantle plume theory driving magmatism along this belt (MERCIER ET AL. 2009).

Measured in a straight line from the Bella Bella dyke swarms to Nazko Cone, the AVB track has an azimuth of ~253º and a length of ~315 km, a distance over which AVB centres record

~13.2 Ma of volcanic activity. This then yields an average motion of the North American plate over a potential mantle plume of ~2.38 cm/yr. The average AVB azimuth yielded by GPS data is 248.1° and the average motion of North America is 1.98 cm/yr (cf. ch. 4.4.1). This would theoretically require AVB centres to record close to 16 Ma of magmatic activity, but this value is broadly within error and also depends on the assumption that the Bella Bella region is indeed the westernmost locality of the AVB. The actual oldest K/Ar date for the Bella Bella dykes is 14.5

Ma (BEVIER 1989).

These AVB data agree (within error) with those from MINSTER & JORDAN (1978) for the

Yellowstone hot-spot (azimuth of 240 ± 20º, velocity of 2.4 cm/yr) and those of GRIPP &

GORDON (2002; azimuth of 249.5 ± 10.7°, velocity of 2.68 ± 0.78 cm/yr; again cf. ch. 4.4.1).

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Together, these two independent hot-spot tracks corroborate the hypothesis of a present-day movement of North America of ~2.5 cm/yr in a southwesterly direction.

Figure 28 Diagram illustrating P-wave velocity model (modified from MERCIER ET AL.

[2009]). Cross-section is oriented WSW-ENE. Colours indicate P wave perturbation: blue

+2%, red -2%. Note zone of low velocity (down to ~400 km depth) under-lying central and eastern AVB as well as an area farther east. Conduits underneath AVB centres are stylized with lighter colours indicating an older age. The surface topography is smoothed and exaggerated 50 times. AVB volcanic centres include RR – Rainbow Range, ILG – Ilgachuz

Range, IR – Itcha Range, BMVF – Baldface Mtn. volcanic field, NC – Nazko Cone. NAP –

North American Plate; solid arrow schematically indicates westward motion of NAP.

Dashed arrow schematically indicates subduction of Juan de Fuca plate (blue wedge directly above the arrow; note that the slab is not actually underlying the AVB!).

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3.8 Conclusion

The Satah Mountain and Baldface Mountain Volcanic Fields comprise over three dozen individual volcanic centres. The majority of these centres have been substantially modified by glacial action, removing much of the original pyroclastic material. There are indications that volcanism occurred during periods of glaciation. The SMVF is located on a ridge that is parallel to existing normal faults in the nearby Itcha Range shield volcano. An area of elevated gravity broadly coincides with the extent of this ridge and is likely the result of repeated eruption of lava flows along a 20−25 km long zone. The BMVF lacks such a linear alignment of centres, but is located on the surface trend of the proposed hot-spot underlying the interior of British Columbia. As such, the BMVF provides a link between the Itcha Range and Nazko Cone 80 km to the east, assumed to be the current location of the Anahim hot-spot.

This paper presents the first 40Ar/39Ar ages for both the SMVF and BMVF, which indicate contemporaneous activity in these fields and the Itcha Range. These age data are confined in duration to ~1.6 Ma in the Early Pleistocene (from ~2.52 to 0.91 Ma) and considering the generally small dimensions of most centres, activity was likely episodic and short-lived (larger structures such as Satah Mtn., Baldface Mtn. and Mt. Punkutlaenkut excluded). Our data also indicate no close relationship between the timing of activity and the geochemistry of the erupted lavas. However, the age data and the location of the two cone fields agree with the vector of

North America plate motion over a potential mantle plume since the Neogene. As a consequence, the AVB, though spatially separated, is temporally and geometrically linked to the better-known Yellowstone hot-spot 1,400 km to the SE. The presence of two hot-spot tracks on the same continent and their general agreement with each other provides a unique tool in assessing and testing the motion of North America. In the AVB, magmatism has produced

162 heterogeneous lavas ranging from undersaturated basanites to more highly evolved trachytes, phonolites, rhyolites and their alkaline and peralkaline differentiates. The overlap of existing regional geochemical and geochronological data with ours, in addition to the similarities with the

Yellowstone hot-spot and a recently discovered low-velocity zone underlying the Chilcotin

Plateau, offers additional support for the hypothesis of magmatism along the AVB being driven by a mantle plume.

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Chapter Four: Volcanotectonic controls on the Anahim Volcanic Belt

4.1 Abstract

Alkaline and peralkaline magmatism occurred along the Anahim Volcanic Belt (AVB) in west- central British Columbia. The belt comprises plutonic, hypabyssal and volcanic centres of Mio- cene to Holocene ages that linearly decrease in age from west to east. To account for this, a mantle plume has been suggested to underlie the Interior Plateau of British Columbia, creating a hot-spot track at the surface. The WSW-ENE trend of the AVB is in agreement with that of the better-known Yellowstone hot-spot in the United States. Both hot-spot tracks define Neogene motion of the North American plate in a southwesterly direction at ~2.5 cm/yr. However, the alkaline to peralkaline affinities of AVB rocks make sole attribution to a hot-spot difficult, as they could also be the result of continental rifting. The AVB’s location close to the northern edge of the subducted Juan de Fuca/ Explorer plates has led to the hypothesis of the belt being the result of a slab window or a plate-edge effect, with mantle flow around the plate edge leading to magma generation at depth and potential crustal attenuation at the surface. A slab window regime could create alkaline magmas similar to the ones from the AVB but it cannot satisfactorily account for the linear decrease of ages along the belt. A fourth hypothesis evokes the eastward propagation of a fracture across western British Columbia as the driving mechanism for magmatism in the AVB. New XRF geochemistry and 40Ar/39Ar data from two AVB cone fields corroborate the hot-spot hypothesis in part. In this study, I assess these four hypotheses in regards to their respective geochemical and geochronological attributes in order to find out if any one of them or a combination can account for the origin and evolution of the AVB. Trace element and REE patterns suggest an ocean island basalt (OIB) affinity of AVB lavas, but again,

164 there is a wide overlap with alkaline lavas generated in a rift setting. However, an exclusively crustal source of AVB magmas and/or input from subduction of the Juan de Fuca plate to the south can be ruled out.

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4.2 Introduction

Even to a non-geologist, the linear arrangement of centres in the Anahim Volcanic Belt (AVB), with its E-W trend that cuts across the dominant NW-SE structural grain of western North

America, is notable (Figs. 29, 30; also cf. Figs. 1 & 13). What could cause this? The linear decrease in age of volcanic and plutonic centres from west to east along the AVB (SOUTHER 1977,

1986; this study) fits well with the hypothesis of a hot-spot track that was created by the southwesterly movement of the North American continental plate over a mantle plume during the

Neogene and Quaternary (BEVIER ET AL. 1979). All AVB centres share similarities in their geochemical signatures, which are defined by a bimodal distribution of mafic and felsic rocks, a lack of rocks of intermediate composition, and a generally alkaline or even peralkaline character

(BEVIER 1978, 1981; SOUTHER 1986; CHARLAND 1994). Dykes, erosional remnants of cones, flows and associated volcanogenic sediments on the Pacific coast in the vicinity of Bella Bella and an alkaline pluton on Denny and King islands to the east have been proposed to constitute the “root zone” of Anahim magmatism that has been exposed at surface by the uplift of the Coast

Mountains of several kilometres during the Neogene (PARRISH 1983; SOUTHER 1986; cf. Fig. 3).

One of the unique features of the AVB is the presence of three felsic shield volcanoes in the belt’s central part. The Rainbow, Ilgachuz and Itcha ranges are large volcanic edifices with complex evolutions that, while individual in detail, share many similarities (BEVIER 1978, 1981:

SOUTHER 1986; SOUTHER & SOUTHER 1994; CHARLAND ET AL. 1993, 1995; CHARLAND 1994; cf.

Fig. 12). During the early stages of activity, large volumes of felsic lavas (trachytes, phonolites and their peralkaline differentiates) built basal shields. During subsequent activity, generally felsic lavas were erupted that became more compositionally varied with time, indicating differentiation of magmas in shallow magma chambers beneath the volcanoes (BEVIER 1981;

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CHARLAND ET AL. 1993; SOUTHER & SOUTHER 1994). The final stages of activity at each of the shield volcanoes saw the eruption of small volumes of more primitive lavas that built small cinder cones and flows. The composition of these more mafic lavas is basanitic to hawaiitic, indicating that small batches of melt reached the surface without much differentiation (STOUT &

NICHOLLS 1983; CHARLAND ET AL. 1995).

The Itcha Range is associated with two volcanic fields ‒the Satah Mtn. (SMVF) and Baldface

Mtn. volcanic fields (BMVF)‒ that comprise dozens of small, largely monogenetic cones and erosional remnants of domes, necks and flows (cf. ch. 3 and Figs. 13b, 14, 15; this study). Many centres in the SMVF are aligned along a NNW-SSE trending high (“Satah Ridge”) that is

(sub)parallel to normal faults in the Itcha Range (TIPPER 1969, CHARLAND 1994; Fig. 29). The

BMVF, situated ~20 km east of the Itcha Range, is located on the E-W trend of the proposed hot- spot track. Both fields feature rocks with a bimodal distribution and alkaline affinities; trachybasalts and trachytes are the prevalent rock types. Either field lacks the highly evolved comendites or pantellerites found in the three shield volcanoes (CHARLAND ET AL. 1993, 1995; this study). 40Ar/39Ar age data indicate that Pleistocene and Pliocene activity in the SMVF and

BMVF was largely coeval with volcanic activity in the Itcha Range, with the majority of these fields’ age data falling between 2.4 and 1.4 Ma. The youngest age (0.91 Ma) from a single hawaiitic flow in the BMVF is largely coeval with final activity in the Itcha Range and precedes activity at Nazko Cone, the youngest AVB centre, by ~600 ka (SOUTHER ET AL. 1987; this study).

The NNW-SSE orientation of Satah Ridge may partly be controlled by existing fracture systems/fault in the area. The geology map (Fig. 29), as well as the official geological map for

British Columbia (MASSEY ET AL. 2005), shows the Yalakom fault and its splays to the SW of the central AVB. An extensional fault terminating the Tatla Lake Metamorphic Complex on its

167 northern side (Fig. 29; cf. FRIEDMAN & ARMSTRONG 1988) appears to have an orientation similar to the one of Satah Ridge, but as the fault is covered by and does not displace younger Chilcotin and/or AVB lavas, it cannot be stated with certainty that a relationship between the fault and

Satah Ridge exists. The Dean River valley 30 km west of the SMVF trends NNW-SSE and parallels the northernmost extent of the Yalakom fault, too (cf. Figs. 29, 30). The geological map of B. C. (MASSEY ET AL. 2005) suggests that this fault, which is covered by alluvium, continues NW-wards between the Rainbow and Ilgachuz ranges and may have acted as a zone of weakness (between the Coast Mountains to the west and the Chilcotin Plateau to the east). This zone eventually became the location of the Dean River valley, which was further widened by the passage of glaciers. The cover of younger volcanic rocks, colluvium and alluvium is widespread throughout the Chilcotin Plateau (cf. ANDREWS & RUSSELL 2008; DOHANEY 2009) and may cover existing faults, especially if these remained largely inactive during the later Neogene and

Quaternary. However, this fact does not disprove the existence of such faults and the role they may have played in controlling melt ascent and geometry of conduits in the central AVB.

Basalts of the Chilcotin Group underlie the AVB in most places. While these basalts are both coeval with as well as chemically and isotopically similar to AVB rocks, they have a distinct transitional character. They were erupted during the Miocene and Pliocene in a back-arc setting related to subduction of the Juan de Fuca plate (BEVIER 1983A/B).

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Figure 29 Geological map of the central and eastern Anahim Volcanic Belt (AVB).

Inset shows location of area in west-central British Columbia (red box). Anahim Lake,

Tatla Lake, Chezacut and Nazko townsites are given for reference. Green shades denote rocks of Neogene ages, yellow and orange shades Paleogene or older. “Cenozoic undifferentiated rocks” in darker pink denote late-stage lavas of the Itcha Range and the

SMVF and BMVF. Note the Chilcotin Group basalts have their greatest extent in the vicinity of the AVB. White dashed lines running through the northern and central parts of the SMVF indicate presumed E-W and NNW-SSE trending faults, the northern one of which is parallel to E-W faults in the nearby Itcha Range. RR‒Rainbow Range,

AP‒Anahim Peak, ILG‒Ilgachuz Range, IR‒Itcha Range, SMVF‒Satah Mtn. Volcanic

Field, BMVF‒Baldface Mtn. Volcanic Field, NC‒Nazko Cone. (Modified using data for polygons provided by GEOGRATIS, Department of Natural Resources Canada [2014].

Contains information licensed under the Open Government Licence – Canada.)

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Figure 29

Yalakom fault and splays

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Figure 30 Digital elevation model of the central AVB. Inset shows location of area in west-central British Columbia (red box). Anahim Lake townsite and Highway 20 (purple line running through centre of figure) given for reference. Coast Mountains to the west are of higher elevation than the three shield volcanoes, which rise up to 2,495 m in the Rainbow

Range. Note incision of Dean River valley (black dashed line) between Rainbow and

Ilgachuz ranges. SMVF centres are mainly located on a NNW-SSE trending ridge that is associated with the Itcha Range shield volcano. RR−Rainbow Range, ILG−Ilgachuz

Range, IR−Itcha Range, SMVF−Satah Mtn. Volcanic Field, BMVF−Baldface Mtn.

Volcanic Field. (Modified using data for polygons provided by GEOGRATIS, Department of

Natural Resources Canada [2014]. Contains information licensed under the Open

Government Licence – Canada.)

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Figure 30

Dean River valley

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4.3 The four hypotheses

The remote location of the AVB resulted in relatively few detailed studies of its rocks and evolution (cf. BEVIER ET AL. 1979; BEVIER 1981; SOUTHER 1986; SOUTHER ET AL. 1987; SOUTHER

& SOUTHER 1994; CHARLAND ET AL. 1993, 1995; KUEHN ET AL. IN REVIEW). Based in part on the

AVB’s alkaline geochemistry, but more importantly on the linear decrease in ages from west to east, the presence of a mantle plume under the Interior Plateau of British Columbia has been a favoured hypothesis for many decades to explain the presence of the belt (cf. SOUTHER 1977;

BEVIER ET AL. 1979; ROGERS 1981).

Below, this hypothesis will be assessed in light of existing data, together with three other hypotheses that have been put forward. This includes general comparisons with other volcanic areas in the world where similar volcanotectonic processes have been recognized.

4.3.1 The Mantle Plume Hypothesis

Mantle plumes have been evoked as the main mechanism driving volcanic activity, particularly in intraplate settings (e.g., WILSON 1963, 1973; RICHARDS ET AL. 1989). Magmatism related to mantle plumes produces rocks that are diverse in composition and, in conjunction with plate tectonics, can result in hot-spot tracks of volcanic and/or plutonic centres that exhibit a distinct progression of ages. Many island chains in the Pacific and Atlantic oceans have been associated with mantle plumes and hot-spots since the idea first gained traction in the 1960s. On these islands, shield volcanoes are often the most prominent product of volcanic activity.

While shield volcanoes exist in several locations and tectonic settings, they are especially recognized from oceanic islands such as Iceland (e.g. ROSSI 1996), Hawai’i (e.g., LOCKWOOD &

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LIPMAN 1987; FREY ET AL. 1990), La Réunion (e.g., OEHLER ET AL. 2008), the Comoros Islands

(e.g., NOUGIER ET AL. 1986), the Azores (e.g., SELF & GUNN 1976; MUNGALL & MARTIN 1995) and the Canary Islands (e.g., ANGUITA & HERNÁN 1975, 2000; SCHMINCKE 1982; PARIS ET AL.

2005). Continental shield volcanoes are less common, but can occur in rift settings (see next chapter), in transitional ocean-to-continent settings (e.g., the Cameroon line [DERUELLE ET AL.

2007]) or as intraplate volcanoes (e.g., the Tibesti massif in the central Sahara [GOURGAUD &

VINCENT 2004; PERMENTER & OPPENHEIMER 2007]).

In the case of the AVB, the three shield volcanoes are its most notable feature. They are the largest edifices anywhere in the belt and tower over the surrounding Chilcotin Plateau and are renowned for their colourful rocks. The main distinction between these and other shield volcanoes is that on oceanic islands, basaltic rocks ‒both of tholeiitic and alkaline affinities‒ are far more dominant than felsic ones (CLAGUE 1987). Most of the locations mentioned above are thought to be affiliated with mantle plumes and to constitute hot-spot tracks at the surface (e.g.,

WILSON 1963, 1973). In the following section, Hawai’i will briefly be used as an example for shield volcanoes on oceanic islands.

The best-known shield volcanoes in the Hawaiian chain (Mauna Loa and Mauna Kea on

Hawai’i, Haleakalā on Maui) are volumetrically enormous edifices with volumes of several

10,000 km3 and total heights from the seafloor of ~10 km. Their shields are built almost exclusively (>95% volume) of thin pāhoehoe flows of tholeiitic or alkali olivine basalts. Usually for Hawaiian (and also Canarian) volcanoes, an early shield-building stage, which lasts for several 100 ka, is followed, after a hiatus, by small-scale eruptions of more alkaline rocks that build cinder cones and flows (CLAGUE 1987; FREY ET AL. 1990). Summit calderas are common as well as linear rift zones associated with the larger central volcanoes (LOCKWOOD & LIPMAN

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1987; CARRACEDO 1994). On Hawai’i, the majority of recent volcanic activity has taken place along these rift zones (cf. the by now 31-year long Pu’u O’o eruption in the East Rift zone on

Hawai’i [HELIKER ET AL. 2003]). Continuous movement of the Pacific plate over the proposed mantle plume has generated a chain of islands that increase in age towards the northwest, with

Hawai’i being the island closest to the current location of the hot-spot under the Lōʻihi seamount

(CLAGUE 1987; CLAGUE & DALRYMPLE 1988; Fig. 31).

Figure 31 Index map of the major islands of the Hawaiian archipelago. Numbers in brackets indicates oldest determined age of each island (CLAGUE & DALRYMPLE 1988). Red star denotes current location of Hawai’i hot-spot at Lōʻihi seamount. Triangles denote major volcanoes; red indicates active volcano currently in its basaltic shield stage, yellow dormant volcano in its alkaline post-shield stage, and black assumed extinct. HA−Haleakalā,

KO−Kohala, MK−Mauna Kea, HU− Hualālai, ML−Mauna Loa, KI−Kīlauea, LO−Lōʻihi.

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Other island chains or archipelagos such as the Azores, Galápagos or Canary Islands are associated with mantle plumes/hot-spots as well (WILSON 1973). However, all of these are more complicated in their tectonic settings and evolutions than Hawai’i, which is located in the middle of the Pacific oceanic plate. The Azores are located close to and across the Mid-Atlantic ridge

(SELF & GUNN 1976; MUNGALL & MARTIN 1995) and the Galápagos Islands close to a triple junction between the Nazca, Cocos and Pacific plates (BEHN ET AL. 2004). Lastly, the Canary

Islands are situated close to the edge of the African plate and are believed to be tectonically linked onshore to the Atlas Mountains in Morocco (ANGUITA & HERNÁN 1975, 2000;

CARRACEDO 1994, 1999; see below). Differences in geochemistry, temporal and spatial distribution of volcanic activity, among others, are a function of these different tectonic settings, despite a similar “underlying” process (in form of a mantle plume) driving, or at least contri- buting to, magmatism at the surface.

While tholeiitic and alkaline basalts are by far the most dominant rock types on oceanic islands of an intraplate setting, alkaline and peralkaline felsic rocks occur as well. Comenditic trachytes, comendites, phonolites and pantellerites have been described from Iceland, the Azores and other Atlantic islands, where they are often spatially and temporally associated with mildly alkaline basalts, hawaiites and/or mugearites (e.g., BAKER 1974: SELF & GUNN 1976; ROSSI

1996). In the majority of these locations, felsic volcanism follows basaltic volcanism and often is of a more explosive nature due to the higher viscosity and/or volatile content of the felsic magmas (SELF & GUNN 1976). Furthermore, the locations mentioned above are close to or directly above the Mid-Atlantic ridge or located on submarine plateaux, both of which again indicate a more complex volcanotectonic regime (BAKER 1974) than the rather straightforward interaction between a mantle plume penetrating oceanic crust as in the case of Hawai’i.

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In stark contrast to the Hawaiian shield volcanoes, the evolution of the AVB shields is almost the complete opposite. The initial shield-building stage, during which large volumes of felsic lavas (trachytes, phonolites, rhyolites) erupt, is followed by a later stage of more mafic volcanic activity (basanites, alkali olivine basalts; BEVIER 1978, 1981; SOUTHER & SOUTHER 1994;

CHARLAND ET AL. 1995). In the Ilgachuz Range, a summit caldera existed during the later stages of the shield-building phase, indicating the presence of a shallow magma chamber that collapsed after eruption of the voluminous felsic magmas (SOUTHER & SOUTHER 1994). There, as well as in the Rainbow and Itcha ranges, volcanic activity appears to preferentially have taken place at a central location; rift zones as observed on Hawai’i or the Canary Islands are absent†. Only the late-stage mafic eruptions took place at individual cones away from the centres of the AVB volcanoes, although modification of the volcanoes by glaciers has left few original structures intact (SOUTHER & SOUTHER 1994; CHARLAND ET AL. 1995).

The AVB is located in a geologically and tectonically complex region (e.g., TIPPER 1969;).

Whereas the Hawaiian Islands are built on “just” an oceanic plate, the AVB is located on continental crust that is heterogeneous in composition and complex in its assembly (cf. BEVIER ET

AL. 1979; MONGER ET AL. 1982). In rocks of the Rainbow Range, BEVIER (1981) found no evidence of crustal contamination in the comenditic lavas. However, rocks from dyke swarms that are considered the western part of the AVB on the Pacific coast and from the Itcha Range are interpreted to have experienced small amounts of crustal contamination (STOUT & NICHOLLS

1983; SOUTHER 1986; BEVIER 1989; CHARLAND ET AL. 1993). Crystal fractionation and differentiation of volatile-rich primitive melts in shallow magma chambers under the AVB shield

† Rift systems are commonly a function of the size of shield volcanoes, with the larger examples (such as those on

Hawai’i or the Canary Islands) developing rift systems (cf. CARRACEDO 1994).

177 volcanoes (SOUTHER & SOUTHER 1994) are thought to be the main mechanisms responsible for the generation of the voluminous felsic lavas there. These magma chambers are similar to the ones described from oceanic islands (e.g. Socorro Island in the east Pacific; BAKER 1974). In either case, the chambers are sourced from a deeper, possibly fixed source. In the chamber, the magmas differentiate, with the evolving felsic melts forming a cupola on top of the less buoyant mafic material (SOUTHER 1986). In both oceanic and continental settings, comendites and/or comenditic trachytes are more abundant than more highly evolved pantellerites, possibly a function of shorter residence times in a magma chamber which does not allow for sufficient levels of differentiation to be attained.

As mentioned earlier, the main argument for a mantle plume/hot-spot underlying the AVB is the evident and linear decrease in rock ages as one moves east from the Pacific coast onto the

Chilcotin Plateau. K-Ar age data (SOUTHER 1986) established the progressive younging of volcanic and plutonic centres (Fig. 32). Two dyke swarms and a pluton in the Bella Bella region are of Middle Miocene ages. The three shield volcanoes were active during the Late Miocene to early Pliocene (Rainbow Range/Anahim Peak [BEVIER 1981], Ilgachuz Range [SOUTHER &

SOUTHER 1994]) and Pliocene to Early Pleistocene (Itcha Range [SOUTHER 1986]). The Satah

Mtn. and Baldface Mtn. volcanic fields are predominantly of Pleistocene ages (this study, cf. ch.

3.5.2), and Nazko Cone is Late Pleistocene to Holocene in age (SOUTHER ET AL. 1987). The locations and distances between these centres are in agreement with the motion vector of the

North American plate since the Miocene (HICKSON 1987; GRIPP & GORDON 2002; MERCIER ET

AL. 2009). The hot-spot trend of the AVB (azimuth ~253º) is within error of the trend established for the Yellowstone hot-spot (azimuth 241° ± 23.8°; GRIPP & GORDON 2002; cf.

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BRANDON & GOLES [1988] for a discussion of the two tracks in relation to motion of the North

American plate).

Figure 32 Schematic plot showing the apparent decrease in age (K-Ar) of plutonic and volcanic centres of the AVB (modified from SOUTHER [1986]). Compare with Fig. 26.

Other continental alkaline shield volcanoes that are interpreted to be linked to a mantle plume/hot-spot include the Tibesti Mountains and the associated Emi Koussi “shield-like” volcano in the central Sahara (Libya/Chad border region; GOURGAUD & VINCENT 2004;

PERMENTER & OPPENHEIMER 2007). Activity at Emi Koussi has been occurring since the Early

Pleistocene (2.4 Ma); 40Ar/39Ar age data confine a period of volcanic activity of ~1.1 Ma

(GOURGAUD & VINCENT 2004) which is shorter, but broadly comparable with the individual

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“lifespans” of each of the AVB shield volcanoes (SOUTHER 1986). The geochemistry of the lavas erupted at Emi Koussi is bimodal and alkaline, with a saturated and an undersaturated series and a compositional gap between 44 and 54 wt% SiO2. Crystal fractionation explains the petrogenesis of either series, but crustal contamination is thought necessary to account for the Si- saturated suite. Comenditic trachytes occur as ignimbrites and lava flows. These and phonolitic domes and pyroclastics are overlain by less voluminous basaltic lavas (GOURGAUD & VINCENT

2004), again similar to the AVB shields.

Regional uplift of the Tibesti area and the bimodal geochemistry contribute to a mantle plume being considered as the most likely cause for volcanic activity at this location. It is notable that, unlike in the AVB, activity at the Tibesti/Emi Koussi complex is more centralised, with no clear age-successive progression in any specific direction. Given the slow motion of the African plate

(0.8 mm/yr in a generally northwesterly direction; PERMENTER & OPPENHEIMER 2007), this should come as no surprise. This also explains the enormous size (100,000 km2 in area; ~4,000 km2 for Emi Koussi alone) and high elevation of the Tibesti/Emi Koussi complex (peaks over

3,000 m; relief of up to 1,500 m; GOURGAUD & VINCENT 2004), as repeated eruptions in a spatially confined region built volcanic edifices close to and/or on top of one another. In comparison, the AVB shield volcanoes are between 200 and 400 km2 in area, up to 370 km3 in volume (BEVIER 1981) and reach a maximum elevation of 2,495 m in the Rainbow Range. The

Chilcotin Plateau in the vicinity of the shields lies at an average elevation of 1,200−1,500 m

(TIPPER 1969, 1971), so the relief of the Rainbow, Ilgachuz and Itcha ranges is comparable to that of the Tibesti complex.

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4.3.2 The Continental Rifting Hypothesis

4.3.2.1 Felsic shield volcanoes in East Africa

While rocks of (per)alkaline composition do occur in small quantities in otherwise basaltic shield volcanoes, it has been noted (CHARLAND 1994; CHARLAND ET AL. 1993, 1995) that the AVB is one of only three known instances of continental felsic shield volcanoes, or more specifically, shield volcanoes with an early shield-building stage in which felsic lavas dominate, followed by a late-stage and volumetrically minor mafic stage. Other locations of such volcanoes are the

Turkana and Gregory Rift regions, Kenya, which are part of the East African Rift (EAR; WEBB

& WEAVER 1975; WEAVER 1977). Alkaline basalts and peralkaline felsic lavas also occur elsewhere in the EAR and Main Ethiopian Rift (MER; CLASS ET AL. 1994; MACDONALD ET AL.

1995; CHOROWICZ 2005; GIORDANO ET AL. 2014)

These EAR volcanoes are Plio- to Pleistocene and Quaternary in age and share general similarities regarding morphology, structural and lithological characteristics (WEBB & WEAVER 1975;

2 WEAVER 1977). The volcanoes reach up to 600 km in size and reliefs of several hundred metres above the surrounding rift floor, comparable to the AVB shields (BEVIER 1981; SOUTHER &

SOUTHER 1994; CHARLAND 1994). Individual periods of activity range from 0.5 to 2 Ma (WEBB

& WEAVER 1975), again similar to the Rainbow, Ilgachuz and Itcha ranges (SOUTHER 1986).

The composition of these EAR volcanoes is bimodal and predominantly peralkaline trachytic

(58‒67 wt% SiO2) and, as in the AVB, subordinate mafic lavas (hawaiites and basanites, < 5% in volume) occur in the final stages of activity (WEAVER 1977). The compositional gap between the mafic and felsic members of such a suite exists in most rift settings (SOUTHER ET AL. 1984;

GIORDANO ET AL. 2014) and both BAKER (1974) and WEAVER (1977) note the general lack of

181 intermediate lavas in both oceanic and continental settings. This has been interpreted as a function of the high crystal content and consequent higher viscosity of intermediate lavas, thus inhibiting their ascent and eventual eruption (cf. PECCERILLO ET AL. 2003; MACDONALD ET AL.

2008).

The peralkaline nature of the EAR trachytic lavas allows them to remain fluid enough to construct shields (cf. BEVIER 1978), even though elsewhere, the trachytes built domes and thick flows. Similarly, effusive and explosive periods occurred repeatedly. Central source zones and stratiform flanks are reported, with those central zones comprising thick flows, plugs and dykes, similar to the AVB shields (BEVIER 1981; SOUTHER & SOUTHER 1994; CHARLAND ET AL. 1993).

The dyke swarms generally parallel the region’s structural NE-SW trend and are thought to be the main eruptive conduits (WEBB & WEAVER 1975), rather than individual craters or cones, as observed in the AVB. The trachytic shield volcanoes of Quaternary age in the Gregory Rift of

Kenya also feature summit calderas, the collapse of which is thought to have occurred at the end of the shield-building phase after voluminous eruptions of trachytes (WEAVER 1977), similar to the AVB’s Ilgachuz Range (SOUTHER & SOUTHER 1994). Seven volcanoes in the South Turkana region record overall ~4 Ma of volcanic activity (WEBB & WEAVER 1975). Their close linear alignment in space is, crucially, not reflected by a temporally linear arrangement as is the case with the AVB (see below).

The volcanotectonic setting of the EAR shield volcanoes is closely related to and controlled by the active tectonics of the East African Rift (CHOROWICZ 2005). The volcanoes are located close to the western escarpment of the rift and dyke swarms and fissures are often subparallel to its trend. Basaltic eruptions during the Holocene are interpreted to be result of both simple pulling apart of the rift floor and of fault-related fissures (WEAVER 1977), indicating

182 synchroneity of eruptive and faulting events. The relationship between early-stage trachytes and late-stage mafic lavas is explained with the presence of shallow-level magma chambers under the volcanoes in which melts differentiated into trachytes, whereas the basalts come from deeper source areas that were accessed during periods of extension (WEAVER 1977).

A similar scenario has been postulated for the AVB shield volcanoes, even though the role of extension is much less clear there (BEVIER ET AL. 1979; SOUTHER & SOUTHER 1994). No normal faults paralleling the trend of the AVB have been mapped in the area (TIPPER 1969; MASSEY ET

AL. 2005; MIHALYNUK ET AL. 2008, 2009). This does not necessarily mean that such faults do not exist; it is possible that the extensive Quaternary cover on the Chilcotin Plateau masks them

(ANDREWS & RUSSELL 2008). The alignment of many SMVF centres on a ridge that extends from the Itcha Range and is subparallel to a set of ~N-S trending normal faults in that range

(CHARLAND 1994) strongly suggests the presence of further faults in the subsurface (cf. ch. 3.2,

Figs. 14, 29). Such fractures/faults may have been established before the passage of the Anahim hot-spot. These faults could potentially be affiliated with the larger Yalakom fault, a high-angle transform fault along which predominantly dextral slip has been occurring from the Late

Cretaceous into the Eocene (MILLER 1988; UMHOEFER & SCHIARRIZA 1996). The Eocene Tatla

Lake Metamorphic Complex is bounded at its southwestern edge by the Yalakom fault and at its northern extent by an extensional fault whose strike appears to be trending N-S before it disappears under younger AVB and Chilcotin strata (Fig. 29; cf. FRIEDMAN & ARMSTRONG

1988).

It is furthermore conceivable that the intersection of the hot-spot with existing faults in the area where the Itcha Range and SMVF would eventually develop “activated” those faults and turned them into conduits for magmas (cf. NGAKO ET AL. 2006). The smaller size of SMVF

183 centres could be a function of increasing distance from that intersection and heat source (now the location of the Itcha Range) and/or smaller amounts of melts being generated and able to ascend to the surface.

4.3.2.2 The Northern Cordilleran Volcanic Province

Located closer to the AVB is the Northern Cordilleran Volcanic Province (NCVP; formerly Sti- kine Volcanic Belt [SOUTHER 1977]) in the northwestern part of British Columbia. The NCVP extends into the Yukon and eastern Alaska and comprises a large number of volcanic centres of

Neogene to Quaternary ages (EDWARDS & RUSSELL 2000; EDWARDS ET AL. 2002, 2011; Fig. 33).

The NCVP extends over an area of 1,200 by 400 km and is generally aligned to a N-S trend. In an area bounded by the Tintina and Denali faults, dozens of volcanic centres comprise large and long-lived central volcanoes as well as regionally extensive fields of tuyas (subglacial volcanoes), cinder cones, lava flows and eroded remnants thereof (EDWARDS & RUSSELL 1999).

Compositions of lavas from the NCVP are mostly alkaline to peralkaline and show a similar bimodal distribution with mafic and felsic clusters, similar to the AVB and the EAR volcanoes.

However, evolved rocks (phonolites, trachytes, rhyolites and their peralkaline counterparts) make up less than 30% of all volcanic rocks and are restricted to the larger central volcanoes such as the Mt. Edziza‒Spectrum Range complex, Hearts Peak, Level Mtn. and Hoodoo Mtn.

Smaller and geographically scattered monogenetic centres erupted less evolved lavas, with most compositions plotting in the basalt, trachybasalt, basanite and foidite fields of the TAS diagram

(EDWARDS & RUSSELL 2000).

Level Mtn. and the Mt. Edziza-Spectrum Range complex are the largest volcanic edifices in the NCVP, with cumulative “lifetimes” in excess of 5 Ma (HAMILTON 1981; SOUTHER ET AL.

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Figure 33 Schematic overview of select Neogene−Quaternary volcanic centres in the

Northern Cordilleran Volcanic Province (NCVP). Long-lived central volcanoes are outlined, smaller and/or monogenetic centres denoted by triangles. Traces of Denali and

Tintina faults confine area of volcanic activity in the Neogene and Quaternary. Double- lines indicated locally important graben structures; arrows indicate direction of extension.

(Modified from EDWARDS & RUSSELL [1999, 2000]).

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3 1984; SOUTHER 1992; cf. ch. 3.6.2 above). In terms of volume (~860 km ), Level Mtn. alone is more than twice as large (HAMILTON 1981) as any of the AVB shields, an indicator of long-lived volcanic activity at that volcano that did not migrate in any direction over time. Both Level Mtn. and Mt. Edziza consist of broad shields (or plateaus) of basaltic lavas onto which more evolved rocks were erupted, an obvious difference to the felsic shield stages of the Rainbow, Ilgachuz and Itcha ranges. In the case of Mt. Edziza, five magmatic cycles are recognized that moved from erupting mafic lavas early on to later stages of felsic magmatism (SOUTHER 1992). Trace element data for the mafic rocks indicate an OIB-type mantle source, as do isotope ratios for all

NCVP rocks. No strong signal of crustal contamination is evident in the mafic lavas and

EDWARDS & RUSSELL (2000) interpret them to be asthenospherically sourced.

As with all volcanic belts in western Canada, the NCVP is linked to the overall tectonic regime of the Pacific Northwest, with the configuration and interaction of the Pacific, Juan de

Fuca/Explorer and North American plates being the controlling mechanisms (ENGEBRETSON ET

AL. 1985; CHARLAND 1994; EDWARDS & RUSSELL 1999). Based on the predominantly alkaline and peralkaline lavas erupted in the NCVP, multi-directional migration of volcanic activity from the centre of the province, a lack of seismicity, high heat flow (cf. ch. 4.4.2), and good correlation of extensional periods in the region with overall extension between the North

American and Pacific plates, the volcanotectonic setting for the NCVP is interpreted to be extensional to transtensional (SOUTHER 1977; EDWARDS & RUSSELL 2000). Changes from a compressional to an extensional regime in the Late Miocene (~ 11 Ma) were followed by an increase in NCVP magmatism and the amount of magmas erupted (EDWARDS & RUSSELL 1999,

2000; a similar regime is thought to influence volcanism in the Canary Islands, discussed in ch.

4.3.4 below).

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Despite the current compressive (and/or transpressive) regime along the western margin of

North America, Holocene magmatism in the NCVP has been continuing (SUTHERLAND BROWN

1969; HICKSON 1990; HAUKSDÓTTIR & RUSSELL 1994); this is attributed to accommodation of stresses by local extension (EDWARDS & RUSSELL 1999). Normal faults trending NNW-SSE in the southern and central parts of the NCVP (Fig. 33) are thought to have been active from the

Miocene to the Pliocene and are an indicator of the extensional nature of the region’s tectonic regime (EDWARDS & RUSSELL 2000). Alternatively (and additionally), a slab window has been suggested to be located and widening at depth beneath western British Columbia since the

Oligocene (THORKELSON ET AL. 2011), allowing upwelling of the asthenosphere and subsequent decompressional melt generation and crustal attenuation (see next chapter).

The earliest volcanic NCVP activity occurred in the Early Miocene (EDWARDS & RUSSELL

1999). Level Mtn. and Mt. Edziza were the loci of repeated eruptions since that time, respectively, with activity lasting into the Quaternary (SOUTHER ET AL. 1984). During the

Pleistocene and Holocene, activity took place throughout the entire NCVP, with more recent activity concentrated in the southern part of the belt (EDWARDS & RUSSELL 2000). Despite this spatio-temporal relationship of NCVP volcanism, there does not appear to be a linear, unidirectional progression in ages along the axis of the NCVP. Rather, initial volcanism in the central part of the volcanic province (at Level Mtn.) migrated both north and south with time.

Such a pattern is also in agreement with the slab window model as a widening window could account for multi-directional propagation of magmatism (EDWARDS & RUSSELL 1999). It is possible to explain the Neogene evolution of the NCVP with a combination of slab window formation and spreading beneath the NCVP and events related to the plate-tectonic configuration in the Pacific Northwest.

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The small and isolated cones of the Iskut-Unuk area and Tseax Cone and flow near Aiyansh

(Fig. 33) constitute the youngest NCVP centres, with the Lava Fork centre of the former area the

th location of the last eruption of a Canadian volcano in the late 18 century (SUTHERLAND BROWN

1969; HAUKSDÓTTIR & RUSSELL 1994; HICKSON, PERS. COMM. 2014). South and southeast of here, there are no more Neogene volcanic centres until one reaches the northernmost exposures of the Chilcotin Group and the AVB shield volcanoes, over 350 km away.

4.3.3 The Plate-Edge Effect and Slab Window Hypotheses

The AVB is situated ~100 km lateral distance north of the subducted edge of the Juan de

Fuca/Explorer plates (Fig. 34). These two young oceanic plates are remnants of the former

Farallon plate which had been subducted under North (and South) America by the Oligocene

(SCHMID ET AL. 2002; MADSEN ET AL. 2006). The ongoing oblique subduction of the Juan de

Fuca/Explorer plate pair at the Cascadia subduction zone is complicated by these plates’ young age and consequent high buoyancy. The maximum distance between the Juan de Fuca spreading ridge and the trench is ~430 km off the coast of Oregon; at its northern end off the west coast of

Vancouver Island, the spreading ridge itself is being subducted, creating in the process the Queen

Charlotte triple junction (RIDDIHOUGH 1977, 1984). As a consequence, the smaller Explorer plate is thought to have decoupled from the Juan de Fuca plate and is now being passively overridden by the southwest-ward moving North American continental plate (AUDET ET AL.

2008). The Juan de Fuca plate continues its active subduction with ENE-trending vector at ~4.5 cm/yr (ROHR & FURLONG 1995; SIGLOCH & MIHALYNUK 2013). The “capture” of the Explorer plate by North America stopped active subduction of the plate at ~5 Ma (ROHR & FURLONG

1995); this occurred ~10 Ma after initial AVB magmatism, but before volcanic activity in the

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Figure 34 Schematic diagram of the current tectonic settings of SW British Columbia, including important volcanic belts: Anahim (red triangles) and Alert Bay (orange triangles) volcanic belts, and Garibaldi/Cascade arc (yellow triangles). Red arrow denotes direction of subduction, blue shaded field indicates approximate subducted Juan de

Fuca/Explorer slab down to 200 km. Black dashed lines with numbers indicate position and depth (in km) of the top of subducting Juan de Fuca/Explorer plates. Large arrows indicate relative dextral motion along the Queen Charlotte transform fault, smaller arrows the Juan de Fuca spreading ridge(s). Cascadia SZ‒Cascadia subduction zone,

EP‒Explorer plate, JdFP‒Juan de Fuca plate, NAP‒North American plate. (Modified from AUDET ET AL. [2008]).

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Itcha Range, SMVF and BMVF. It is unclear what effect this stop of subduction might have had on volcanic activity in the AVB, if any. (Note: I will keep referring to the subducting Juan de

Fuca/Explorer plates below, even though subduction of the Explorer plate has ended. During the evolution of the AVB in the Miocene, however, that subduction was still ongoing.)

The configuration of the plates in the region and the general position of the triple junction has essentially remained the same since the Middle Eocene (CHARLAND 1994; MADSEN ET AL. 2006;

AUDET ET AL. 2008). At no point during this time was the area of the AVB underlain by a subducting slab (RIDDIHOUGH 1977, 1984), even though the geometry of the subducted slab at depth since the Middle Miocene allows for this scenario (MADSEN ET AL. 2006). The presence of suboceanic mantle underlying the AVB has been indicated by Pb and Sr isotopic studies (BEVIER

1989). The lack of a subducted slab underlying the AVB could be a result of the slab window potentially existing under the NCVP and expanding with time towards the south (THORKELSON

1996; EDWARDS & RUSSELL 2000; THORKELSON ET AL. 2011; see previous chapter). This is significant as the presence of a subducting oceanic plate might have impeded or entirely prevented the rise of hot plume material through the mantle to the surface (OBREBSKI ET AL.

2010; JAMES ET AL. 2011). While a slab window would have allowed such material to rise after the cessation of subduction, it has been noted elsewhere (HOLE ET AL. 1991) that the timing of such a sequence of events would have been quite coincidental.

The plate-edge effect is related to the slab window effect and thus both of these hypotheses are assessed together (the plate-edge effect obviously being a spatially more restricted phenol- menon). It is postulated that toroidal and poloidal flow of hotter mantle material around the edge(s) or front of a subducting slab or upwelling of mantle material through a slab window can initiate decompressional melting in the overlying mantle wedge and/or at the base of the

190 lithosphere (HOLE ET AL. 1995; THORKELSON ET AL. 2011). If crustal attenuation also takes place as a consequence, or the region above the upwelling zone has already experienced crustal thinning, magmas would be provided a way to ascend to the surface. As a consequence, this could lead to volcanic activity that would be geochemically similar to an extension-related setting. As mentioned above, the NCVP in northern B. C. has been postulated to be linked to slab window-related extension that began in the Early Miocene (EDWARDS & RUSSELL 1999,

2000). The current southern edge of this slab window is projected roughly parallel to the trend of the AVB and within 100 km lateral distance to the north (THORKELSON 1996; THORKELSON ET

AL. 2011). The recent study of AUDET ET AL. (2008) on the fate of the Explorer plate and the position of the northern edge of the subducted plate south of the AVB indicate that this slab window could have, in fact, a slightly larger extent to the south (cf. THORKELSON ET AL. 2011 and their Fig. 3d).

Alkaline magmas have been attributed to slab window formation and are thought to have risen rapidly to the surface with little compositional change (HOLE ET AL. 1995). These authors also convincingly argue that re-ordering of a plate-tectonic configuration and resulting changes in subduction can account for alkaline magmatism. The collision and subsequent subduction of the

Farallon spreading ridge in the Cascadia subduction zone is interpreted to be such a re-ordering, with the creation of a triple junction and slab window under western B. C. being the consequence. Studies from Antarctica and Baja California (HOLE ET AL. 1995) and the NCVP

(EDWARDS & RUSSELL 1999, 2000) indicate that several millions of years pass between creation and/or passage of a slab window at depth and initiation of volcanic activity at the surface. Dis- continuous volcanic activity can persist at a location for several tens of millions of years after the

191 creation of a slab window. However, in both the Antarctic and Baja California cases, alkaline mafic rocks occur exclusively; no felsic rocks have been recognized (HOLE ET AL. 1995).

While no subduction-related volcanism in B. C. occurs north of the subducted edge of the

Juan de Fuca/Explorer plates (AUDET ET AL. 2008), the short Alert Bay Volcanic Belt (ABVB) on northern Vancouver Island is closely related to the subduction of the Juan de Fuca/Explorer plates in time and space (ARMSTRONG ET AL. 1985; Fig. 34). (The Quaternary to Holocene

Silverthrone and Franklin Glacier volcanic fields on the B. C. mainland lie on the extension of the ABVB’s strike, but are also considered to constitute the extreme NW edge of the Pemberton and Garibaldi Volcanic Belt [cf. GREEN ET AL. 1988; HICKSON 1990]). The ABVB is located almost exactly over and parallels the northern edge of the subducting Juan de Fuca/Explorer plates (RIDDIHOUGH 1977).

Volcanic activity along this belt occurred during the Neogene and exhibits a calc-alkaline and calc-alkaline-to-tholeiitic signature characteristic of subduction-related volcanism (such as the

Garibaldi Volcanic Belt north of Vancouver or Cascade Range volcanism in the US). A NE- ward decrease in ages from Late Miocene to Late Pliocene along the ABVB across northern

Vancouver Island is accompanied by a change from mafic to felsic magmatism (48 to 74 wt%

SiO2; ARMSTRONG ET AL. 1985). Centres are small and composed of basalt, andesite, dacite and rhyolite and are predominantly of subalkaline affinity. Two phases of activity occurred during the Late Miocene and Pliocene, with most of the activity as indicated by K-Ar age data confined to a period of ~2.2 Ma during the Pliocene (ARMSTRONG ET AL. 1985). Also of note is that only little subduction-related volcanism in southern B. C. was taking place during the period of

ABVB activity; volcanic activity of the Pemberton Volcanic Belt had begun to peter out at ~7

Ma (GREEN ET AL. 1988). Subduction-related activity later resumed in the Garibaldi Volcanic

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Belt (cf. ch. 1.3) at ~2 Ma (BEVIER ET AL. 1979; GREEN ET AL. 1988) and is considered to be ongoing, even though no historic eruptions have taken place at any of the belt’s volcanoes.

While a spatially linear arrangement of volcanic centres (sub)parallel to the descending slab- edge at depth can be attained in a plate-edge setting (BEVIER ET AL. 1979; JAMES ET AL. 2011) , the question remains of how to achieve a temporal arrangement, i.e. the linear decrease of volcanic rocks as observed in the AVB. Assuming toroidal flow of mantle material around the northern (and NE-SW trending) edge of the Juan de Fuca/Explorer plates, the upwelling of asthenospheric material and, more importantly, melt generation and ascent would need to occur in a region that has a similar orientation. But does melt generation take place in a temporally linear fashion, too? Does flow around the plate edge take place simultaneously at any given point along that edge, or at discrete locations? To achieve the west-to-east decrease in AVB rock ages, toroidal flow and subsequent melt generation would have to start at a relative more westerly and shallower position along the plate edge, then cease and resume at a more easterly and deeper point and so on (an unlikely scenario). And in case of a slab window, which would become larger with time (cf. EDWARDS & RUSSELL 2000), one should not expect the spatially and temporally linear alignment of volcanic centres as observed in the AVB. Rather, a spatial alignment might be (sub)parallel to the trailing edge of the subducted plate. If upwelling of the asthenosphere “follows” that trailing edge, parallel and progressively younger chains of volcanoes should be the case. However, no such chains exist in western B. C.

The ABVB on northern Vancouver Island appears to confirm that a temporal linearity can be produced by plate-edge magmatism, despite volcanic activity being spatially and temporally more restricted (ARMSTRONG ET AL. 1985) than that of the AVB. Other studies (HOLE ET AL.

1991, 1995) do not indicate a “switch-on/switch-off” nature of plate-edge/slab window magma-

193 tism in such a way that would account for a temporally restricted period of activity in one location that than resumes at another location (either parallel to the plate edge or perpendicular to it).

Rather, a study of slab window related volcanism on the Antarctic Peninsula (HOLE ET AL. 1995) indicates activity can and does resume at previously established volcanic centres millions of years after initial activity at those centres. This, too, is not observed in the AVB.

4.3.3.1 The case of the Yellowstone hot-spot track

A recent study of the Yellowstone hot-spot track (JAMES ET AL. 2011) argues for that track’s existence and development being due to a plate-edge effect as well. Fragmentation of the edge of the subducted Farallon plate and a “gap” in that plate led to mantle flow around the leading edge and the fragmented sides of the subducted slab. This slab underlies the Snake River

Plain/Yellowstone (SRP/Y) track in its entirety, and its along-strike edge is parallel to the northern extent of the SRP/Y track (JAMES ET AL. 2011). The slab gap is at depth of 400−500 km and is parallel and located slightly to the NW of the track. A case is made that upper mantle upwelling through that slab gap causes subsequent melt generation. This, in addition to a trench retreat, the continuing descent and subhorizontal subduction of the oceanic Farallon plate at depth would be able to “mimic” a mantle plume-like setting. Magmas generated from such a setting would be comparable to hot-spot/OIB magmas (in case of Yellowstone, a subduction signature also is indicated in the basalts; see cf. 4.4.3 below) and the continuing motion of the overlying North American plate could then generate a hot-spot track at the surface (JAMES ET AL.

2011). Similarly, mantle upwelling on a scale comparable to mantle plumes has been suggested to occur during onset and early stages of subduction. The Farallon slab at depth is considered

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(OBREBSKI ET AL. 2010; JAMES ET AL. 2011) to block direct ascent of a potential mantle plume and associated magmas.

These ideas would certainly merit application to the AVB as well, considering that belt’s proximity to the northern edge of the subducting Juan de Fuca/Explorer plates, especially during the periods of high volcanic activity in the Miocene and Pliocene. In the case of the AVB, however, the slab gap (which might be considered equivalent to a slab window) is located right underneath the hot-spot track, and not at distance from it (THORKELSON ET AL. 2011). There is also no remnant slab imaged at depth under southern B. C. as in case of the Farallon plate and

Yellowstone. JAMES ET AL. (2011) indicate that such a remnant slab might need to be located at a certain depth (400 to 600 km) in order to initiate and/or allow mantle upwelling around the slab’s edges. In case of the AVB, the slab edge of the Juan de Fuca/Explorer plates would be well above such depths (Figs. 28, 34; cf. AUDET ET AL. 2008).

4.3.4 The Propagating Fracture Hypothesis

A fourth hypothesis briefly mentioned, but not further investigated, by BEVIER ET AL. (1979) is that of lithospheric fracturing. A similar process of a propagating fracture has been postulated for another volcanic chain potentially related to a mantle plume/hot-spot: the Canary Islands. In the following section, this location will be described before a comparison with the AVB is made.

The Canary Islands are a 400 km-long chain of seven volcanic islands in the Atlantic Ocean at

~28° N, between 100 and 500 km off the coast of Morocco (ANGUITA & HERNÁN 1975;

SCHMINCKE 1982; CARRACEDO 1994, 1999; Fig. 35). The islands span the transition from oceanic to continental lithosphere and record volcanic activity from Early Miocene to Recent times (PARIS ET AL. 2005). Because of the archipelago’s chain-like arrangement, a mantle plume

195 was again proposed to be the driving mechanism for volcanic activity. However, the picture might not be quite as straightforward.

Figure 35 Schematic location map of the Canary Islands. Numbers in brackets indicate the oldest dated rocks on each island and red stars indicate notable historic eruptions. The islands are grouped into three zones: a “shield stage” to which the youngest islands, La

Palma and El Hierro, belong; a “hiatus stage” of no Quaternary activity; and a

“rejuvenated stage” of volcanic activity that follows the hiatus stage. Blue dashed lines indicate rift zones along which the majority of Holocene activity has taken place.

(Modified from CARRACEDO [1994] and PARIS ET AL. [2005].)

196

The Canary Islands are located close to the edge of the African continental plate which, as has been noted above, is considered almost completely stationary (CARRACEDO 1994). There is a general age progression towards the west where the youngest islands are located, but large effusive eruptions in the 18th century on the easternmost island, Lanzarote, dilute the picture of a straight east-to-west age progression. Three stages of volcanic activity (or lack thereof) are recognized: a shield-building stage, followed by a hiatus stage lasting 3‒8 Ma (ANGUITA &

HERNÁN 1975) which, in turn, is followed by a “rejuvenated” stage (PARIS ET AL. 2005; Fig. 35).

Multiple cycles of activity saw volcanic eruptions on all but one of the islands during the Qua- ternary. Volcanic edifices comprise complex and long-lived central volcanoes, calderas and dyke swarms as well as clusters of vents and cones that are aligned along rift zones, similar to those of Hawai’i. Similarly, compositions of lavas range, once again, from mafic (basanites, tholeiitic and olivine basalts) erupted in the earlier, shield-building stage to more highly evolved ones (trachytes, phonolites) during the rejuvenated stage (SCHMINCKE 1982; ABLAY ET AL. 1998).

Volcanic activity in the Canarian archipelago has been associated with another mantle plume/hot-spot (WILSON 1973, among many others), the activity of which has been described as

“waning” (CARRACEDO 1994). As shown in figure 35, eruptions have taken place within the past

300 years at the opposite ends of the chain, over 400 km apart, a distance greater than the extent of the AVB. As a possible explanation, the crustal conditions beneath the islands are interpreted in such a way as to have influenced the potential hot-spot so that ascending magmas spread laterally. Potentially further influenced by a fracture system that tectonically connects the

Canary Islands to the Atlas Mountains of Morocco, it is thought that instead of a single fixed plume of hot material a number of mechanically separate and chemically distinct batches of melt

(which are linked to the plume nonetheless) ascend through the lithosphere, reaching the surface

197 at different locations and times (ANGUITA & HERNÁN 2000; Fig. 36). The longevity of the volcanic activity in the Canary Islands (upwards of 20 Ma; CARRACEDO 1994) is a function of their near stationary location since the Late Oligocene (PERMENTER & OPPENHEIMER 2007). A low-velocity zone similar to the one described under west-central B. C. (MERCIER ET AL. 2009) is also present in close proximity to the Canary Islands (CARRACEDO 1994), which again would favour the mantle plume/hot-spot hypothesis.

Figure 36 Schematic diagram illustrating the “batch” model proposed for the Canary

Islands. Individual batches of melt are being generated by a deeper heat source (not shown) and ascend through the asthenosphere. Light red batches are still ascending, red ones are linked to recently active volcanism, and green potentially inactive batches associated with “hiatus stage” islands and yellow ones with “rejuvenated stage” islands.

H−El Hierro, LP−La Palma, G−La Gomera, T−Tenerife, GC−Gran Canaria,

F−Fuerteventura, LZ−Lanzarote. (Modified from ANGUITA & HERNÁN [2000].)

198

In light of the seeming contradiction of a hot-spot track developing on/very close to a largely stationary plate, an alternative in form of a westward propagating fracture has been proposed to account for the temporal non-linearity of volcanism on the islands (ANGUITA & HERNÁN 1975).

Such a fracture in the lithosphere would be able to draw from asthenospheric melts and the general west-ward propagation of this fracture (or fracture system) could lead to progressively younger islands in that direction without shutting off the already existing magma conduits on the older and more easterly islands (ANGUITA & HERNÁN 2000; cf. ch. 4.4.3 below).

Furthermore, fracture propagation and eruptive cycles on the islands are similar to tectonic processes in the Atlas Mountains in NW Africa. Tensional periods during orogeny in these mountains overlap with or are followed by periods of intense volcanic activity in the Canary

Islands. Periods of compression close the conduits; cessation of volcanic activity lags behind by several millions of years. North-easterly trends in the arrangement of the islands and in early dyke swarms are close to trends recognized in the Atlas Mountains (ANGUITA & HERNÁN 1975).

Unlike the Hawaiian archipelago, where hot-spot activity and plate motion occur at a relatively steady state, a fracture model can also account for different age-distance relationships between individual islands by allowing for irregular propagation of that fracture, both spatially and temporally. However, CARRACEDO (1999) has pointed out that a propagating fracture would be unlikely to cross the boundary between continental and oceanic lithosphere and prefers a mantle plume as the “underlying” mechanism that drives volcanism in the Canary Islands. In their work on the Yellowstone hot-spot, JAMES ET AL. (2011) also note that a propagating rift can lead to a hot-spot track without the presence of deep mantle plume.

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4.4 So how and where does the Anahim Volcanic Belt fit in?

Below I address the similarities and differences between the AVB and the volcanoes or volcanic belts/provinces/complexes used as examples for different tectonic settings in the previous sec- tions above. The two main aspects to be discussed are the age-succession and geochemistry of erupted lavas. For more information about non-AVB volcanoes, please refer to the works cited.

4.4.1 The age-succession of AVB volcanic centres

Each of the four hypotheses outlined in the previous chapter addresses certain geological aspects of the AVB (summarised in Table 7). For many previous authors, the preferred explanation for the belt’s existence has been the passage of a mantle plume/hot spot under west-central British

Columbia (SOUTHER 1977; BEVIER ET AL. 1979; BEVIER 1981; HICKSON 1987; BRANDON &

40 39 GOLES 1988). Newer geochemistry and Ar/ Ar age data for the SMVF and BMVF corroborate those findings or, at the very least, are not in contradiction of them (this study). The presence of a low-velocity zone that is closely aligned with the extent of the AVB also supports the hot-spot hypothesis (MERCIER ET AL. 2009; cf. ch. 3.7.3). Lastly, the orientation and length of the belt (~253°, ~330 km) broadly agrees with the observed one of the Snake River

Plain/Yellowstone hot-spot track in the United States (~241 ± 23.8°, ~550 km; cf. GRIPP &

GORDON 2002). Both define WSW to SW-ward motion of the North American plate since the

Miocene at 2‒3 cm/yr. Additionally, present-day GPS data (HS3-NUVEL1A) broadly corroborate the vectors for both tracks: 1.98 cm/yr at ~248° (AVB) and 2.69 cm/yr at ~250°

(Yellowstone; UNAVCO 2014). Table 8 gives an overview of HS3-NUVEL1A GPS data for each for several AVB centres and coeval SRP/Y centres.

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Table 7 Overview of age, geochemistry, isotope data (where available) for AVB centres and select non-AVB centres discussed in chapter 4.3. Sources and abbreviations after the table.

Volcanic Age(s) of Isotope Linear progression centre/ volcanic Geochemistry ratios Tectonic setting Sources of ages? 87 86 belt/province centres ( Sr/ Sri) Mafic and felsic 14.5−10.3 Ma dyke swarms, 0.70352 – Western AVB 1, 2 (K-Ar) alkaline pluton 0.7232 (sye, gra) Early felsic stage Potentially a hot- Rainbow 8.7−6.7 Ma 0.7032 – (com, pan), late Yes. Unidirectional spot sourced by a 1, 2 Range (AVB) (K-Ar) 0.7040 mafic stage (haw) decrease from ~14 Ma mantle plume. Early felsic stage at western end of AVB Other settings can Ilgachuz 6.1−4 Ma 0.70308 – (com, tra), late to Recent (7200 BP) at only partially 2, 3 Range (AVB) (K-Ar) 0.70425 mafic stage (aob) Nazko Cone. Activity account for alka- Early felsic stage at the shield volcanoes line magmatism Itcha Range 3.5−1.1 Ma (tra, pho, rhyo), is not synchronous. 0.7029 – and unidirectional 1, 2, 4 (AVB) (K-Ar) late mafic stage 0.7033 age-succession. (haw, bsn, aob) 0.33 Ma − Nazko Cone Basanites, minor 0.70288 – 7,200 BP 5 (AVB) phonotephrite 0.70295 (K-Ar, 14C) Back-arc setting Two periods at Transitional, Chilcotin 0.7031 ± 7 – related to sub- 10–6 Ma and (sub)alkaline No 20, 21 Basalts 0.7038 ± 2 duction of Juan de 3–2 Ma basalts Fuca plate Yes. Centres get (8 Ma) Subalkaline younger from SW to Alert Bay 0.7030 – 4.7 – 2.5 Ma basalt, andesite, NE, but belt is of short Plate-edge 22 Volcanic Belt 0.7037 ± 1 (K-Ar) dacite length of period of activity.

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Table 7 continued

Volcanic Age(s) of Isotope Linear progression centre/ volcanic Geochemistry ratios Tectonic setting Sources of ages? belt/province centres (87Sr/86Sr) Earliest activity Dominantly al- Partially. Initial acti- at 20 Ma. Cen- kaline basalts, ha- vity at centre of vol- Northern tral volcanoes of waiites, also ne- Extensional and/or canic province, which Cordilleran Miocene to Ho- phelinites, per- 0.7026 – transtensional, 23, 24, then spread non- Volcanic locene ages. alkaline felsic la- 0.7039 region underlain 25, 26 unidirectionally in Southern NCVP vas in long-lived by a slab window Province both northerly and Pleistocene to central volcanoes southerly directions. Recent (18th c.) (tra, pho, com) Predominantly Partially. General trachytic (>90% progression parallel to South Turkana 6–2 Ma in volume), pan- trend of rift, but - Continental rift 6 (EAR) (K-Ar) tellerites, minor jumping between basalts, if any centres. Predominantly None apparent. Vol- Main Late Pleistocene felsic lavas (tra, canoes are spatially 0.7039 ± 7 – Continental rift 7 Ethiopian Rift to Recent rhyo), very minor aligned along 0.7063 ± 7 and mantle plume mafic lavas (bas) EAR/Afar trends. Miocene to None apparent. Acti- Tibesti Vol- Felsic lavas (tra, Pliocene, vity moved W to E and Continental canic Complex pho), younger - 8, 9 2.4–1.3 Ma back, some centres hot-spot alkaline basalts (TVC) (Emi Koussi) erupted coevally. Yes. Unidirectional to Pliocene to NW due to motion of Overwhelmingly Recent Pacific plate over basaltic (>95% in (main islands), Hawaiian hot-spot at 0.7031 – Oceanic 10, 11, Hawai’i volume), late- Hawai’i itself ~9.5 cm/yr. 0.7042 hot-spot 12 stage alkaline late Pleistocene Synchronous activity volcanism (tra) to Recent on and between individual islands.

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Table 7 continued

Volcanic Age(s) of Isotope Linear progression centre/ volcanic Geochemistry ratios Tectonic setting Sources of ages? belt/province centres (87Sr/86Sr) Mafic lavas (bas), Partially. Islands east on some islands of Mid-Atlantic Ridge Hybrid of oceanic (per)alkaline increase in age away hot-spot and 5.1 Ma to 0.7034 ± 8 – 13, 14, Azores lavas (tra, pho, from the ridge. The divergent plate Recent (1957) 0.7052 ± 1 15, 16 com, pan, up to two islands west of the boundary (Mid- 50% in total ridge are of Late Atlantic Ridge) volume) Pleistocene age. Early stages Yes. Ages of gener- mainly basaltic, Potentially hybrid ally decrease from east Varied but also with between oceanic ~20 Ma to to west, but activity between 17, 18, Canary Islands felsic lavas (tra, hot-spot (pre- Recent (2012) has taken place at both individual 19 pho); late stages ferred) and pro- ends of the archipelago islands of activity follow pagating fracture in historic times. similar pattern

Sources: 1−SOUTHER (1986); 2−BEVIER (1989); 3−CHARLAND (1994); 4−SOUTHER & SOUTHER (1994); 5−SOUTHER ET AL.

(1987); 6−WEBB & WEAVER (1975); 7−GIORDANO ET AL. (2014); 8−GOURGAUD & VINCENT (2004); 9−PERMENTER & OPPENHEIMER

(2007); 10−STILLE ET AL. (1986); 11−CLAGUE & DALRYMPLE (1988); 12−CARRACEDO (1999); 13−SELF & GUNN (1976); 14−FERAUD

ET AL. 1980; 15−DAVIES ET AL. (1989); 16−MUNGALL & MARTIN (1995); 17−SCHMINCKE (1982); 18−CARRACEDO (1994); 19−PARIS ET

AL. (2005); 20−BEVIER (1983A); 21−BEVIER (1983B); 22−ARMSTRONG ET AL. (1985); 23−SOUTHER ET AL. (1984); 24−EDWARDS &

RUSSELL (2000); 25−EDWARDS ET AL. (2002); 26−EDWARDS ET AL. (2011). Abbreviations: sye−syenite, gra−granite, bas−basalt, bsn−basanite, haw−hawaiite, aob−alkali olivine basalt, tra−trachyte, pho−phonolite, rhyo−rhyolite, com−comendite, pan−pantellerite.

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Table 8 Overview of present-day plate motion data for the SRP/Y and AVB (UNAVCO 2014). Speed, azimuth values and vectors were calculated using GPS data (based on the HS3-NUVEL1A model; cf. GRIPP & GORDON [2002]); the program for calculating these values can be found at http://www.unavco.org/software/geodetic-utilities/plate-motion-calculator/plate- motion-calculator.html. All localities are in reference to the North American plate (and in relation to the hot-spot framework).

Latitude Longitude Speed Azimuth (°, N Vel. E Vel. Locality (N) (W) (cm/yr) cw from N) (cm/yr) (cm/yr) Silver City Rhyolite 43° 1.93’ 116° 52.14’ 2.66 251.2 -0.86 -2.52

Chalk Hills 42° 43.89’ 115° 46.61’ 2.69 251.12 -0.87 -2.55

Goose Creek 42° 12.78’ 113° 55.55’ 2.75 251.01 -0.89 -2.6 Grassy Cone 43° 27.25’ 113° 34.9’ 2.69 250.46 -0.90 -2.53 Middle Butte 43° 29.42’ 112° 44.27’ 2.7 250.31 -0.91 -2.54 Mud Lake 43° 53.27’ 112° 23.89’ 2.68 250.09 -0.91 -2.52 Mesa Falls 44° 7.62’ 111° 28.42’ 2.68 249.86 -0.92 -2.51 Mallard Lake 44° 29.67’ 110° 46.46’ 2.67 249.6 -0.93 -2.50 Yellowstone Resurgent Dome Sour Creek Snake River Plain/ SnakeRiver 44° 39.64’ 110° 24.09’ 2.67 249.48 -0.94 -2.50 Resurgent Dome Average 2.69 250.34 Bella Bella 52° 12.84’ 128° 14.1’ 1.96 249.18 -0.70 -1.83 King Island 52° 9.14’ 127° 45.82’ 1.97 249.07 -0.70 -1.84 Rainbow Range 52° 43.45’ 125° 46.83’ 1.97 248.1 -0.73 -1.83 Anahim Peak 52° 45.43’ 125° 37.57’ 1.97 248 -0.74 -1.82 Ilgachuz Range 52° 45.73’ 125° 18.45’ 1.97 247.9 -0.74 -1.83

Belt Itcha Range 52° 42.39’ 124° 51.06’ 1.98 247.82 -0.75 -1.84 Satah Mtn. 52° 28.58’ 124° 41.35’ 2.0 247.94 -0.75 -1.85 Baldface Mtn. 52° 45.6’ 124° 31.94’ 1.98 247.69 -0.75 -1.83

Anahim Volcanic Nazko Cone 52° 55.7’ 123° 43.96’ 1.99 247.3 -0.76 -1.83 Average 1.98 248.1

Sources: SRP/Y locations from ARMSTRONG ET AL. (1975) and CHANG ET AL. (2007). For AVB, this study.

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One question that arises in case of an Anahim hot-spot is whether there ever were any older expressions of its activity west of where the oldest rocks and centres of the belt are located on the

Pacific coast on islands in the vicinity of Bella Coola (dyke swarms, the King Island pluton;

SOUTHER 1986; cf. ch. 2.1). Bathymetric mapping indicates no seamounts on the continental shelf in the area to the west of Bella Coola (CRAWFORD ET AL. 1995). If any pre-Miocene centres did exist, they would have been submarine, as the location of the continental margin of North

America was still to the north-east of its present location. Based on this assumption, any older submarine volcanoes would have been built on the Farallon/Juan de Fuca oceanic plates. As this plate was by then already subducting in a generally easterly direction under North America

(RIDDIHOUGH 1977, 1984; ENGEBRETSON ET AL. 1985), any evidence of such edifices would presumably have been subducted with the plate, leaving no trace of them. However, Eocene volcanic rocks in western Washington and Oregon that have been associated with the then position of the Yellowstone hot-spot are interpreted to be seamounts that were accreted to western North America during subduction (BRANDON & GOLES 1988). However, the lack of similarly accreted volcanic rocks at or close to the western end of the AVB might simply indicate that no such seamounts existed in the region to begin with.

4.4.1.1 Oceanic and continental hot-spots

In case of the examples used for hot-spot volcanism, an oceanic island chain like Hawai’i exhibits unambiguous evidence for unidirectional, SE to NW age-succession of volcanoes and islands initiated by a mantle plume/hot-spot and subsequently being carried away by the motion of the Pacific plate (Fig. 31). The combination of high velocity of the Pacific plate (~9.5 cm/yr) and high eruption rates result in volcanic islands that grow rapidly (within a few 100 ka) and

205 move away from the location of the hot-spot (within a few millions of years; CLAGUE 1987;

CLAGUE & DALRYMPLE 1988). Island chains or archipelagoes in tectonically more complex settings, such as the Azores or Canary Islands, show age successions as well, but are often lacking the unidirectional aspect. In a striking difference to the AVB, volcanic activity in each of these three locations is partially coeval, i.e. older volcanoes are either still active while a younger centre commences activity (e.g., Hawai’i) or activity resumes at an older centre after a prolonged hiatus (e.g., Canary Islands).

Continental hot-spot volcanism can show either unidirectional age-successions (e.g., Snake

River Plain/Yellowstone; PIERCE & MORGAN 1992; JAMES ET AL. 2011) or more diffuse patterns of migrating activity (e.g., Tibesti Volcanic Complex; PERMENTER & OPPENHEIMER 2007). In both cases, controlling factors are (1) the relative motion of the continental plate moving over the mantle plume/hot-spot (to the SW at 2−3 cm/yr in case of Yellowstone and the North American plate; almost no motion in case of the Tibesti and the African plate); and (2) the structure and composition of that continental plate. While a detailed appraisal of the latter is beyond the scope of this study, it is important to note that the western part of the North American plate is a complex collage of terranes composed of a variety of volcanic, metamorphic and sedimentary rocks (MONGER ET AL. 1982). The long history of subduction off the west coast of the continent and the “fate” of the subducted plates is also likely to influence plume-sourced magmatic activity at the surface: the presence of a subducted plate at depth might act as a barrier for ascending plume material (cf. OBREBSKI ET AL. 2010).

Interaction of a mantle plume with (thick) continental crust of heterogeneous composition is invariably different than that of a plume that rises under oceanic crust, both in regard to the time a plume might need to penetrate the crust (including potential ponding at the base of the crust),

206 retention time in magma chambers and contamination of mantle-sourced magmas by assimilation of crustal rocks (SOUTHER & SOUTHER 1994). The final composition(s) of erupted magmas and the amount of erupted material are direct consequences of these different settings.

4.4.1.2 Continental Rifting – East African Rift and Northern Cordilleran Volcanic Province

The volcanoes mentioned in the East African Rift (EAR) are controlled, again quite unambi- guously, by the extension taking place along that rift. In the Afar region of Ethiopia, the rift is additionally underlain by a mantle plume, as trace element and isotope data indicate (GIORDANO

ET AL. 2014), resulting in a prodigious amount of volcanic activity in the region. Many of the volcanoes in the EAR show spatial alignment parallel to the trend of the rift and in some cases, volcanic activity can show some elements of migration (WEBB & WEAVER 1975). However, it again is missing the overall unidirectional component seen in Hawai’i or the AVB.

A similar pattern is indicated for the NCVP in northern B. C., with initial volcanic activity in the middle of that volcanic province subsequently spreading towards both the north and south

(EDWARDS & RUSSELL 1999, 2000). Quaternary activity has taken place throughout the NCVP

(EDWARDS ET AL. 2002, 2011), with the most recent eruptions happening in the southern part of it

(SUTHERLAND BROWN 1969; HICKSON 1990).

4.4.1.3 Plate Edge Effect - Alert Bay Volcanic Belt

This small volcanic belt on Vancouver Island is interpreted to be related to a plate-edge effect along the northern edge of the subducting Juan de Fuca/Explorer plates (ARMSTRONG ET AL.

1985). While this example can partially account for a spatially and temporally linear alignment

207 of volcanic centres, the belt is small in length (less than 100 km) and shows uneven distribution of timings of volcanic activity. Moreover, the ABVB is situated almost directly atop and parallel to the subducted plate edge (Fig. 34), whereas the AVB is located ~100 km to the north and at an acute angle to that edge. For a similar scenario at Yellowstone, JAMES ET AL. (2011) suggested that a plate edge (or slab fragmentation) effect can lead to a hot-spot like age-succession of volcanic centres at the surface.

4.4.1.4 Propagating Fracture - The Canary Islands

Finally, as an example of oceanic islands in a tectonically complex setting, the Canary Islands exhibit certain aspects of hot-spot volcanism. The seven islands as a whole show a definite progression towards younger ages of their respective first activity from east to west. Volcanic activity does not show a similar unidirectional succession, with the most notable eruptions in historic times taking place, in chronological order, on Tenerife (central location in the archipelago),

Lanzarote (eastern part), and La Palma and El Hierro (the westernmost and therefore youngest islands; PARIS ET AL. 2005; cf. Fig. 35). This particular spatio-temporal relationship of volcanic activity is currently interpreted to be due to a plume-sourced asthenospheric reservoir from which separate melt batches rise to the surface at different times and locations (ANGUITA &

HERNÁN 2000).

4.4.1.5 Could a fracture, propagating or not, be applied to the Satah Mtn. volcanic field?

Here, there perhaps appears to be a similarity to what is observed in the AVB: the SMVF south of the Itcha Range exhibits a similar pattern of localized volcanic activity, with individual

208 centres having erupted chemically distinct magmas at different points in time and space (this study; cf. ch. 3). One obvious difference between the Canary Islands on one hand and the AVB and the SMVF and the other is the scope of magmatism and its longevity (~20 Ma) of the former versus the 14 Ma of volcanic activity in the latter. However, the propagating fracture model and local extension suggested for the Canary Islands might, on a smaller scale, be comparable to the faults/fractures suggested to both link the SMVF with the Itcha Range and to have provided pathways for magmas to ascend (CHARLAND 1994; this study).

The genesis and ascent of melts under the Canary Islands is, as outlined above, somewhat controversial. However, one interpretation of chemically distinct batches (or “blobs”) of melt reaching the surface at different times and locations (cf. Fig. 36) may have some applicability in regards to explaining the location and evolution of the Satah Mtn. volcanic field. Conduits for melt ascent in the Canary Islands are linked to either a propagating fracture and/or localized extension (ANGUITA & HERNÁN 2000). While field evidence for similar features in the central

AVB in general and the SMVF in particular is currently lacking, it seems not unlikely that a similarly “local” regime might exist there, as the orientation of Satah Ridge parallel to faults in the nearby Itcha Range implies (CHARLAND 1994; this study).

Figure 37 schematically and in highly simplified fashion shows how the “melt batch” model of the Canary Islands might be applied to the SMVF and the Itcha Range during a period of volcanic activity in both locations. A pre-existing fracture system (or, more broadly, a zone of weakness) may have been re-activated by the passage of the proposed Anahim hot-spot. Where the centre of this hot-spot intersected with that zone of weakness, the Itcha Range began to develop. The zone of weakness extended some tens of kilometres towards the south and along it, small batches of heterogeneous magmas migrated both laterally and upwards. A “mature

209 plumbing system” with separate levels of small magma chambers is thought to exist under the

Itcha Range as well (CHARLAND ET AL. 1993; Fig. 37). Melts, which did not include the most highly evolved magmas seen elsewhere in AVB, then individually reached the surface at distinct times and locations in the SMVF. These locations, however, were aligned in a relatively narrow

“band” and the volcanic eruptions were preferentially taking place in or close to that band, building Satah Ridge over a period of at least 800 ka (cf. ch. 3.6.1).

N S

Figure 37 Schematic NNW-SSE cross-section from the Itcha Range along Satah Ridge

(incl. centres “11”, “NTB”, “TB” to centre “CH” at the field’s southern end). The location of the AVB hot-spot during the Pliocene and Pleistocene is supposed to be under the Itcha

Range (its lateral extent as illustrated here is conjectural). Small batches of compositionally distinct magmas migrate along and ascend through pre-existing faults and fractures connecting the Itcha Range with the SMVF (parallel to cross-section). These magmas might further form local, cupola-shaped shallow magma chambers (cf. CHARLAND ET AL.

[1995]) and erupt at distinct times and locations. More evolved magmas are indicated by lighter red tones.

210

The lack of another large volcanic centre east of the Itcha Range may indicate the absence of other fractures or zone of weaknesses in the eastern part of the AVB. Neither the Rainbow nor

Ilgachuz ranges have regional cone fields associated with them, which may also indicate lack of existing fractures at those volcanoes. Since both these shield volcanoes are larger and more shield-like than the Itcha Range, an assumption might be made that hot-spot activity was still stronger when these volcanoes were developing. Another possible explanation is that some sort of fractures or fault did (and do?) exist at, or rather under, the Rainbow and Ilgachuz ranges.

These might be splays of the nearby Yalakom fault (MILLER 1988; UMHOEFER & SCHIARRIZA

1996) and be covered by younger and alluvial deposits.

It is conceivable that a combination of hot-spot passage or local extension, with both pre- existing faults and ones that only developed because of the presence of a hot-spot in close proximity, might explain the existence and development of the AVB. The available geochemistry data allow for both a hot-spot and/or a rift setting, while geophysical data remain ambivalent (see below). Further studies, including detailed mapping in the vicinity of the Satah

Mtn. and Baldface Mtn. volcanic fields, may help shed additional light on the volcanotectonic regime that controlled (and perhaps still controls) the Anahim Volcanic Belt.

4.4.2 Geophysical data

4.4.2.1 Heat flow data

Heat flow data for British Columbia (MAJOROWICZ & OSADETZ 2008) indicate no unusually high heat flow for the southern Nechako Basin where the AVB crosses it (Fig. 38). The area’s heat flow ranges from 70 to 80 mW/m2 and follows the overall NW-SE oriented structural grain of

211

2 the region. Heat flow measurements 110 km SE of Satah Mtn. yielded 68 mW/m (BENTKOWSKI

2 & LEWIS 1994); borehole measurements 7 km east of Nazko Cone yielded 58−81 mW/m at a depth of 150 m (FAIRBANK & FAULKNER 1992). Areas of elevated heat flow in B. C.

(MAJOROWICZ & OSADETZ 2008) are aligned with the NCVP (EDWARDS & RUSSELL 1999), the northern part of the Garibaldi Volcanic Belt (GREEN ET AL. 1988) and the southeastern part of the province, indicating those regions’ more recent geological (and also volcanic) activity.

Figure 38 Heat flow map for B. C. Red triangles − major AVB centres. Black square −

Vancouver. NCVP−Northern Cordilleran Volcanic Province, GVB−Garibaldi Volcanic

Belt. (Modified from MAJOROWICZ & OSADETZ [2008].)

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4.4.2.2 Aeromagnetic data

A new 2014 survey of the Interior of B. C. included acquisition of new aeromagnetic data. As the survey is still in progress, the data have not yet been integrated with other geology and geochemistry data. A preliminary map produced from aeromagnetic data (AEROQUEST AIRBORNE &

GEOSCIENCE BC 2014) covers the central and eastern parts of the AVB (Fig. 39).

High-resolution aeromagnetic data have been used to delineate individual lava flows both at the Earth’s surface and under younger cover (cf. FINN & MORGAN 2002). However, in case of the AVB, a large-scale (along the length of the belt) assessment based on aeromagnetic data is both beyond the scope of this thesis and the preliminary status of the data used for the map in

Fig. 39 (no reports have yet been published on these new data). In the part of the SMVF that was covered in the 2014 survey, steep gradients between low and high aeromagnetic values exist over very short distances. Several spatially confined and circular areas of high value do coincide with the location of individual SMVF centres at the surface. The same is the case of a few centres in the BMVF, and for Nazko Cone. An area of exceptionally high aeromagnetic values and flat aeromagnetic topography underlies older Eocene volcanics east of the BMVF; this area also features notably low gravity contours. The overlying terrain is of slightly higher elevation and more rugged appearance than other parts of the Chilcotin Plateau, but an assessment of why this might be is not possible at this time.

213

Figure 39 Aeromagnetic map of Interior or British Columbia, covering parts of the central and eastern AVB (the Ilgachuz and Itcha ranges are part of a provincial reserve and were not included in the 2014 TREK project survey). Important AVB centres and select SMVF and BMVF centres study indicated by white and black triangles (the change in colour is for better visibility only). (Modified from AEROQUEST AIRBORNE & GEOSCIENCE BC [2014].)

214

4.4.2.3 Gravity data

Figure 40 shows part of the central and eastern AVB for which gravity data exist (RIDDELL

2006). No particular E-W or WSW-ENE oriented areas of elevated gravity contours (indicating the presence of large amounts of volcanic rocks) parallel to the trend of the AVB can be discerned. Rather, distinct areas of differing gravity are located close to one another and without any particular patterns.

The location and extent of Satah Ridge largely coincides with an area of elevated gravity; however, values abruptly drop off east of the ridge and the Itcha Range, with most of the BMVF underlain by an area of lower gravity. This area of low gravity continues eastward, again indicating the lack of dense volcanic rocks in the region between the BMVF and Nazko Cone. The latter location again coincides with a locally restricted area of higher gravity. The area underlying the Ilgachuz and Itcha ranges does not show any particularly elevated gravity, which is unusual as one should expect the piled-up amount of lavas to influence the local gravity field, resulting in positive anomalies. However, this could be due to presence of the Chilcotin basalts in the immediate vicinity of these shield volcanoes, leading to a lack of contrast in the gravity contours of the volcanoes and the plateau basalts surrounding those (LINES, PERS. COMM. 2014).

The elevated gravity values under Satah Ridge may be an indication of preferential intrusion

(?) and eruption of magmas along a proposed NNW-SSE fracture zone that is thought to connect the SMVF with the Itcha Range (cf. CHARLAND 1994). Gravity is not affected by surface erosion to any large degree, and depicts underlying processes. Despite it being a topographic high, the amount of lavas erupted along Satah Ridge (and potentially removed by the glaciers after the

SMVF developed ~2.5 Ma ago) by themselves probably would not be sufficient to have an effect

215 on gravity measurements without the additional presence of intrusions/remnant magma chambers in the subsurface (cf. the previous chapter and Fig. 37).

It is beyond the scope of this study to find an explanation for the particular gravity patterns (or lack thereof) underlying the central and eastern AVB. One focus of future studies should be on the geophysical characteristics of the Chilcotin Plateau and to tie them into the volcanotectonics of the AVB. The ongoing TREK study of Geoscience BC will doubtlessly produce high- resolution maps and large amounts of aeromagnetic and gravity data that will be tremendous assets for future studies of the AVB.†

† The TREK project was started by Geoscience BC in 2013/14 and continues to collect geochemical and geophysical data which at the time of writing was accessed at http://www.geosciencebc.com/s/TREK.asp.

216

Figure 40 Map of part of the central and eastern AVB with underlying gravity contours

(modified from RIDDELL [2006]). Note NNW-SSE trending drop in gravity just east of the

Itcha Range and SMVF (itself of distinctly elevated gravity); generally low gravity in the vicinity of the BMVF; and slightly elevated gravity underlying Nazko Cone. No E-W trending pattern parallel to the trend of the AVB can be discerned, nor are the Ilgachuz and Itcha ranges underlain by high gravity areas. The area of high gravity west of Puntzi

Lake correlates to Late Jurassic Chilanko Igneous Complex (tonalite, intrusive grano- diorite; cf. MIHALYNUK ET AL. 2009), which is unrelated to any AVB activity or structures.

217

4.4.3 Can geochemistry provide a clue?

Table 7 summarises pertinent geochemical, geochronological and isotope data from the AVB and selected volcanoes or volcanic regions mentioned in the assessment of the four hypotheses above. In this chapter, AVB data will be compared to geochemistry data (major, trace and rare earth elements) from non-AVB lavas.

AVB lavas plotted on a total alkali vs. silica diagram (LE MAÎTRE ET AL. 1992) show both the general overlap of lavas from individual centres and their differences (Fig. 41a; data from

BEVIER [1978], SOUTHER ET AL. [1987], CHARLAND [1994], SOUTHER & SOUTHER [1994], this study). The bimodal suite of mafic and felsic rocks with a gap in intermediate compositions is well expressed for the three shield volcanoes; data for the SMVF and BMVF partially mirror that arrangement. The main difference between the data from these two fields and those from the nearby shield volcanoes is that no rhyolitic and/or pantelleritic rocks are presently recognized in the SMVF and BMVF, and only a small number of centres in these fields erupted peralkaline lavas (Figs. 41a, 42a; cf. ch. 3.5). Figures 41b and 42b overlay geochemistry data from non-

AVB volcanic centres with AVB data, highlighting similarities and differences, respectively.

A Cr vs. Y diagram (Fig. 43) used for discriminating basalts based on their arc, MOR or intraplate settings shows that AVB alkaline basalt predominantly plot in the intraplate basalt field, despite considerable scatter in the Cr contents of the rocks plotted. Based on their respective Cr contents (all below 300 ppm), none of the AVB basalts are considered primitive melts (cf. TUREKIAN 1963). SMVF and BMVF mafic lavas plot towards the upper end of AVB basalts from the Itcha and Ilgachuz ranges for which Cr and Y contents are available (CHARLAND

1994; SOUTHER & SOUTHER 1994), possibly indicating that the former are of a slightly more primitive characters.

218

Figure 41 (A) TAS diagram (after LE MAÎTRE ET AL. 1992) for lavas observed in the

Anahim Volcanic Belt. Alkaline boundary after IRVINE & BARAGAR (1971). Orange circles − Rainbow Range (BEVIER 1978), violet squares − Ilgachuz Range (SOUTHER &

SOUTHER 1994), green triangles − Itcha Range (CHARLAND 1994), blue rhombs − Satah

Mtn. volcanic field (this study), red rhombs − Baldface Mtn. volcanic field (this study), yellow cross-squares − Nazko Cone (SOUTHER ET AL. 1987).

(B) TAS diagram for lavas of non-AVB volcanic centres/belts discussed in ch. 4.3. Grey fields indicate AVB data from Fig. 41a. Dark blue rhombs − Emuruangogolak volcano

(northern Kenya rift; WEAVER 1977), red rhombs − Main Ethiopian Rift volcanoes

(GIORDANO ET AL. 2014), dark-grey squares − Alert Bay volcanic belt (Vancouver Island;

ARMSTRONG ET AL. 1985), purple squares – Chilcotin Group basalts (BEVIER 1983A), olive triangles − NCVP (Mt. Edziza [SOUTHER ET AL. 1984] and Hoodoo Mtn. [EDWARDS ET AL.

2002]), light green triangles − NCVP Tuya field (EDWARDS ET AL. 2011), purple crosses −

Canary Islands (ABLAY ET AL. 1998), orange circles − Terceira Island (Azores; MUNGALL &

MARTIN 1995), blue squares − Hawai’i (CLAGUE 1987; COUSENS ET AL. 2003), yellow squares − Tibesti Volcanic Complex (Chad; GOURGAUD & VINCENT 2004).

219

Figure 41

220

Figure 42 Alumina saturation diagrams of AVB and non-AVB centres. Data sources as in Fig. 41.

(A) Alumina saturation diagram of AVB alkaline lavas. Symbols as in Fig. 19. Note that peralkaline rocks are predominantly, but not exclusively, found in the three large shield volcanoes.

(B) Alumina saturation diagram for select alkaline lavas of non-AVB centres (East African

Rift, Alert Bay volcanic belt, NCVP [Hoodoo Mtn. and Tuya Field], Canary Islands,

Azores, Hawai’i, Tibesti and Chilcotin group basalts). Grey field indicates AVB data.

Symbols as in Fig. 41b.

221

Figure 42 A

222

Figure 43 Cr/Y discrimination diagram (modified from PEARCE [1982]) for mafic rocks from the SMVF and BMVF (this study) and selected mafic lavas from the Ilgachuz and

Itcha ranges (data from SOUTHER & SOUTHER [1994] and CHARLAND [1994]). Despite considerable scatter in Cr contents, the majority of the mafic lavas plot in the within-plate basalt fields.

223

4.4.3.1 Assessment of OIB affinity of AVB lavas

To further assess the source regions of AVB lavas, Nb/U ratios (HOFMANN ET AL. 1986) were plotted for SMVF, BMVF and mafic lavas from the Itcha Range (Fig. 44a). A REE pattern diagram (Fig. 45) and a multi-element spider diagram (Fig. 47a) for AVB lavas (mafic lavas from the SMVF and BMVF, as well as the Ilgachuz and Itcha ranges) have been presented and are also discussed in ch. 3.5.1 (p. 115). Elevated contents of niobium have been observed in many ocean island basalts as compared to MORBs or the continental crust. The diagram shows that there is considerable scatter for the SMVF and BMVF lavas (which include both mafic and felsic lavas from these fields). However, some of the mafic and many of the trachytic lavas fall in the OIB field. The most highly evolved rocks found in the two fields (phonolites) have higher

Nb contents (up to 360 ppm), and therefore plot outside of the OIB field. Several of the more mafic lavas (e.g., trachybasalts, basaltic trachyandesites) have lower Nb/U ratios (14−28) and plot between the OIB and two continental crust domains. This may potentially be an indication of some crustal contamination in these mafic rocks. Conversely, mafic lavas (hawaiites, basanites) from the Itcha Range (CHARLAND 1994) almost exclusively plot in a nicely constrained area in the OIB field (no applicable trace element data exist for the Rainbow and

Ilgachuz ranges), strongly indicating their OIB affinity. It is conceivable that for the SMVF and

BMVF, their more weakly expressed bimodality and general lack of explicitly mafic rocks

(basanites, basalts) are responsible for the scatter observed in their Nb/U ratios.

When comparing AVB rocks with those from other continental hot-spot and rift settings for which Nb and U data are reported (Tibesti and the MER and EAR, respectively; Fig. 44b), two things can be seen: (1) Mafic lavas from the Tibesti (GOURGAUD & VINCENT 2004) partially plot in the OIB field, but also outside it as a result of lower Nb/U ratios or higher Nb contents, similar

224 to the SMVF and BMVF patterns observed (Fig. 44a). (2) Lavas from the bimodal Gedemsa and

Fanta ‘Ale volcanoes in the MER show excellent fit in the OIB field, likely a consequence of the signature of the Afar mantle plume (enriched mantle) that underlies the MER and contributes to the high magmatic activity in the region (GIORDANO ET AL. 2014). (3) Alkaline mafic lavas from the EAR (Huri Hills; CLASS ET AL. 1994) show a very similar distribution to

MER lavas. The source region of these EAR lavas has been postulated to be in lithospheric mantle, tapped by rifting, although a plume component is likely as well. A similar “in between” position of AVB lavas between an OIB and enriched mantle (EM1) source is indicated by a

Ba/Nb diagram (Fig. 21).

The difficulty of telling plume-sourced lavas apart from those affiliated with continental rifting can be clearly seen (cf. BEVIER ET. 1979). If anything, the Nb/U diagram allows to clearly refute the affiliation of AVB lavas with either a MORB source, primitive mantle or exclusive continental crust domain (cf. HOFMANN ET AL. 1986). Using existing mafic lava samples from the Rainbow and Ilgachuz ranges and re-analysing them to acquire additional Nb and U data to further corroborate the OIB affinity indicated by the mafic Itcha lavas (Fig. 44a) might help in making this interpretation more robust.

225

Figure 44 Nb vs. Nb/U discrimination diagrams for AVB and non-AVB mafic lavas.

(A) SMVF and BMVF data from present study. Symbols as in Fig. 21 (additional red triangles indicate mafic Itcha Range lavas [CHARLAND 1994], as these are the only existing

AVB data for which U contents were determined). Dashed lines indicate Nb/U ratio (47 ±

10) of mantle. Dots and fields indicate distinct domains of Nb/U ratios: PM−primitive mantle, MORB−mid-oceanic ridge basalt, CLM−continental lithospheric mantle,

OIB−ocean island basalt, LCC−lower continental crust, ACC−average continental crust,

UCC−upper continental crust. (Modified using values from HOFMANN ET AL. [1986] and

SIMS & DEPAOLO [1997].)

(B) Comparison of AVB data from Fig. 44a (grey field) with rocks from the Main Ethio- pian Rift (MER1−Gedemsa volcano, MER2−Fanta ‘Ale volcano; GIORDANO ET AL. 2014), the East African Rift (EAR; CLASS ET AL. 1994) and Tibesti (GOURGAUD & VINCENT 2004).

226

Figure 44 A

227

4.4.3.1.1 Individual assessment of volcanotectonic settings

In this section, the different volcanotectonic settings suggested for the AVB and introduced in ch. 4.3 will be assessed using select REE (Figs. 45 and 46) and trace element geochemistry (Fig.

47) from these settings. The focus will be on continental hot-spots vs. continental rift settings.

Diagrams are shown first (pp. 228−237), followed by the interpretations. To see through crustal contamination as best as possible, only data from mafic rocks (i.e., the least differentiated) are used to compare geochemical patterns of AVB lavas with those of non-AVB provenance.

228

Figure 45 Rare earth element (REE) diagrams for mafic lavas from the SMVF and

BMVF (yellow shaded field; this study), as well as from the Ilgachuz (dotted outline) and

Itcha ranges (dashed outline; data from SOUTHER & SOUTHER [1994] and CHARLAND

[1994], respectively). LCC, MCC, UCC average compositions from RUDNICK & FOUNTAIN

(1995); chondrite normalization values and average values for OIB and N-MORB from

SUN & MCDONOUGH (1989). For individual SMVF and BMVF REE patterns, see ch

3.6.1.3. In the following figures, all AVB data are combined into one grey-shaded field.

229

Figures 46 REE patterns for mafic lavas from several volcanic fields/regions (and different volcanotectonic settings) compared to AVB data (grey shaded field). Average

OIB shown as pink line (based on SUN & MCDONOUGH 1989).

(A) Apple-green shaded field: Yellowstone (HILDRETH ET AL. 1991).

(B) Yellow shaded field: Tibesti (GOURGAUD & VINCENT 2004).

(D) Pink shaded field: Gedemsa and Fanta Ale volcanoes of the Main Ethiopian Rift

(MER) in the East African Rift (EAR; GIORDANO ET AL. 2014).

(E) Light-blue shaded field: Silali volcano in the Gregory Rift region of EAR

(MACDONALD ET AL. 1995).

(F) Dark-blue shaded field: Huri Hills, northern Kenya (EAR; CLASS ET AL. 1994).

(G) Northern Cordilleran Province (NCVP). Teal shaded field: Hoodoo Mtn. phono-

lites; single teal line: single basalt sample (EDWARDS & RUSSELL 2002); three light-

blue lines: Mt. Edziza (SOUTHER & HICKSON 1984).

230

Figure 46 A

231

Figure 46 continued C

232

Figure 46 continued E

233

Figure 46 continued G

234

Figures 47 Multi-element and mantle-normalized concentrations of trace and incompatible elements from mafic AVB lavas compared with those of different volcanotectonic settings. In diagrams 47b through 47g, combined AVB data from 47a is visualised as an underlying grey field. (Due to insufficient data, no comparison plots could be made for the

NCVP). Pink line: average OIB (SUN & MCDONOUGH 1989). Sources for data used for comparison are the same as in Figs. 45 and 46.

(A) AVB data. Yellow shaded field: SMVF and BMVF rocks (this study); pink shaded

field: Ilgachuz Range; blue shaded field: Itcha Range.

(B) Yellowstone.

(D) Azores.

(E) Gedemsa and Fanta Ale volcanoes (MER).

(F) Silali volcano in the Gregory Rift region of EAR.

(G) Dark-blue shaded field: Huri Hills (northern Kenya).

(H) Alert Bay Volcanic Belt (partial data only; ARMSTRONG ET AL. [1985]).

235

Figure 47 A

236

Figure 47 continued D

237

Figure 47 continued G

4.4.3.1.2 Oceanic and continental hot-spots

As outlined above, oceanic hot-spot volcanism is overwhelmingly basaltic in character. In the

case of Hawai’i, a decrease in magma supply with increasing distance from the location of the

hot-spot is followed by eruption of more alkaline basalts and/or evolved rocks (cf. FREY ET AL.

1990). This usually occurs after a hiatus and these late-stage lavas are volumetrically sub-

ordinate to the preceding basaltic shield stages (CLAGUE 1987). This trend towards more

238 alkaline compositions is indicated in Figure 41b, with trachytes being the dominant evolved rock type on Hawai’i. Compared with other ocean islands, the range of volcanic rocks on Hawai’i is quite restricted. Conversely, the Azores, Galapágos, Cape Verde and Canary islands erupted a

87 86 wider variety of rocks (COUSENS ET AL. 2003; SELF & GUNN 1976; SCHMINCKE 1982). Sr/ Sr ratios of Hawaiian centres are more restricted in range (0.7031–0.7042; STILLE ET AL. 1986) than those from the AVB shield volcanoes (0.7029–0.7116; BEVIER 1989; Table 7). The high ratios for rocks from the western AVB could indicate either contamination of their magmas by assimilation of underlying crust with high radiogenic Sr content; more extensive differentiation in magma chambers than that proposed for the shield volcanoes; or exclusive melting of crustal rocks (BEVIER 1989).

 Yellowstone: The Yellowstone hot-spot led to voluminous eruptions of bimodal lavas

since the Miocene (PIERCE & MORGAN 1992). REE patterns for Yellowstone basalts (Fig.

46a; n=22) indicate a wide range of REE enrichment: LREE are 30 to 130 times enriched

over chondrite, HREE 10 to 30 times. A deep mantle contribution to these mafic magmas

is thought likely (HILDRETH ET AL. 1991), but the more complex continental crust

underlying the SRP/Y area contributes to final REE patterns through contamination as

well. This may help explain the wider range of REE contents in Yellowstone basalts and

lower LREE enrichment as compared to the AVB rocks. The pattern of the LREE is

closer to average values established for the upper and mid-continental continental crust

(UCC; MCC; cf. RUDNICK & FOUNTAIN 1995). A trace-element spidergram (Fig. 47b)

shows only partial overlap with AVB data; most notable is a large negative Nb anomaly.

This is interpreted to be due to a remnant subduction signature and would corroborate a

239

recent study (JAMES ET AL. 2011) that postulates the old oceanic Farallon plate underlying

the SRP/Y at a depth of several hundred kilometres. Other than this anomaly, the

Yellowstone pattern is flatter than the AVB’s, with slightly less enrichment of compatible

elements and slight enrichment of the more incompatible elements. On a whole, trace

element enrichment over primitive mantle is less than 80 times and generally similar to an

UCC or MCC pattern (RUDNICK & FOUNTAIN 1995).

 Tibesti: Data from the Tibesti Volcanic Complex again exhibit a bimodal distribution

(Fig. 41b). However, the mafic end of the suite is more strongly undersaturated than all

AVB rocks save the basanites reported from Nazko Cone (SOUTHER ET AL. 1987). The

felsic end is dominated by phonolites and trachytes (GOURGAUD & VINCENT 2004); some

minor rhyolites are present in the form of ignimbrites (these do not show up in the TAS

diagram above due to lack of such XRF whole-rock data supplied by these authors). The

Tibesti rocks show considerable overlap with AVB rocks in terms of peralkalinity (Fig.

42b). REE patterns for mafic Tibesti lavas (yellow shaded field; Fig. 46b) are based on a

small number of samples (n=4). REE contents and the resulting pattern are interpreted as

indicative of an upper mantle origin (GOURGAUD & VINCENT 2004). Overlap with AVB

data is very good; Tibesti lavas are slightly more enriched (10 to 20 times) than AVB

lavas in the LREE, whereas for MREE and HREE, the patterns are almost identical.

Compared with average values (SUN & MCDONOUGH 1989), the Tibesti data also follow

the OIB the closest. A trace element spidergram (Fig. 47c) shows a few differences. The

more compatible elements (Rb, Ba etc.) show similar abundances and patterns, but Tibesti

mafic lavas are slightly depleted in K, P and more incompatible elements than the AVB.

Trace element patterns are generally slightly lower than the average OIB curve (SUN &

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MCDONOUGH 1989), and notably so with the incompatible elements. Here, enrichment is

less than 5 times over primitive mantle.

 Azores: On the TAS diagram (Fig. 41b), data from the Azores shows a bimodal

distribution that appears somewhat skewed towards the more felsic end. Most rocks are of

a metaluminous affinity, with only very few peralkaline samples (Fig. 42b). REE patterns

of mafic rocks from the Azores (n=44; FLOWER ET AL. 1976; WHITE ET AL. 1979; Fig. 46c)

are very similar in slope to AVB data, but slightly more enriched (LREE are strongly

enriched at 100 to 360 times over chondrite, HREE up to 35 times) than the AVB.

Especially the LREE are more enriched than MORBs erupted elsewhere along the Mid-

Atlantic Ridge (WHITE ET AL. 1979). Fractionation is moderate to high (La/Ybn =

7.8−17.1). The REE pattern once again follows the average OIB line the closest (SUN &

MCDONOUGH 1989). The trace element spidergram (Fig. 47d) shows an unusual positive

U anomaly, and smaller negative anomalies for K and P. Generally, the Azores pattern

follows the slope of average OIB line; the more incompatible elements are slightly

enriched compared to the AVB pattern (up to 10 times over primitive mantle [AVB 5

times]). In addition to decompressional melting at the Mid-Atlantic Ridge, a plume

component is proposed in the mafic lavas of the Azores to account for the high abundance

of LIL trace elements (WHITE ET AL. 1979).

4.4.3.1.3 Continental Rifting – East African Rift and Northern Cordilleran Volcanic Province

 Similar to the AVB shields, the trachytic shield volcanoes in the Turkana region of the

EAR exhibit comparable degrees of peralkalinity (Fig. 42b), leading them to have

comenditic and/or pantelleritic affinities. Normative acmite (aegirine) in EAR trachytes

241

reaches up to 20 wt% (WEAVER 1977), compared to only 3.5−11 wt% in AVB rocks

(BEVIER 1978; CHARLAND 1994; this study); normative quartz for EAR reaches up to 12%

(in trachytes; WEAVER 1977), in AVB rocks up to 30 wt% (in Ilgachuz rhyolites;

SOUTHER & SOUTHER 1994). Maximum normative quartz in BMVF lavas is a meagre

0.68 wt% (trachyte), in SMVF lavas 2.8 wt% (also trachyte; this study; cf. ch. 3.5). No

trace element data for these volcanoes exist.

 Gedemsa and Fanta ‘Ale, two Quaternary shield volcanoes located in the Main Ethiopian

Rift (MER) close to the Afar region in the northern part of the EAR, feature bimodal

volcanism heavily weighted towards the felsic spectrum (trachytes, rhyolites and their

peralkaline counterparts; Fig. 41b). 87Sr/86Sr ratios of the MER volcanoes are similar to

AVB data (BEVIER ET AL. 1979; Table 7). A comparison of the peralkaline character of

either region show some overlap in the peralkaline field (Na+K / Al > 1), but EAR rocks

are slightly more peralkaline than their AVB counterparts (Fig. 42b). Available data

indicate that metaluminous rocks are rare in the two areas used for comparison (South

Turkana region [WEAVER 1977], MER [GIORDANO ET AL. 2014]).

REE patterns for alkaline basalts from different regions of the EAR and MER (CLASS ET

AL. 1994: MACDONALD ET AL. 1995; GIORDANO ET AL. 2014] generally show good

agreement with one another on one hand, and the AVB on the other (Figs. 46d-f).

Fractionation is high in alkaline basalts (n=25) from the Huri Hills, Kenya (La/Ybn =

5.9−23.1), low in basalts (n=15) from Silali volcano, Gregory Rift (La/Ybn = 4.5−5.3),

and at two volcanoes (n=24) in the MER (La/Ybn = 5.6−8.5). The MER pattern (Fig. 46d)

parallels the average OIB line and shows the most overlap with the AVB pattern. The

Huri Hills and Silali patterns (Figs. 46e/f) behave much the same, with differences mostly

242

in the LREE and MREE, which are less enriched than the AVB lavas. Trace element spi-

dergrams (Figs. 47e-g) also show many similarities with the AVB spidergram (Fig. 47a),

outside of a similar negative P anomaly in all three datasets and slightly higher enrichment

in the more incompatible elements. The rift setting for all three examples is well-

established, but both the Huri Hills (CLASS ET AL. 1994) and especially the MER

volcanoes have plume components in their magmas (GIORDANO ET AL. 2014), as the close

alignment with the average OIB pattern indicates.

 The larger central volcanoes (Mt. Edziza, Hoodoo Mtn.) of the NCVP have a bimodal

distribution of lava compositions that is broadly similar to the AVB (Fig. 41b). In case of

the Mt. Edziza-Spectrum Range complex, however, a cyclicity of volcanic activity is

recognized (SOUTHER ET AL. 1984). Each of these cycles started with mafic lavas

(alkaline basalts) and culminated in the eruption of oversaturated peralkaline felsic lavas

(comendites, pantellerites). In the AVB shield volcanoes, no such cyclicity has been

observed, despite the presence of minor mafic units intercalated in the early stages of

felsic volcanism (CHARLAND 1994; SOUTHER & SOUTHER 1994). The cycles of volcanic

activity at Mt. Edziza are indicated to have lasted between 0.2 and 2 Ma each, which is

comparable to the entire “life time” of each of the AVB shield volcanoes (SOUTHER 1986;

BEVIER ET AL. 1989). This might indicate a more stable setting for the NCVP central

volcanoes with a long-lived source area at depth that has remained localized since the Late

Miocene (SOUTHER ET AL. 1984). Phonolitic lavas are generally rarer than trachytic or

rhyolitic ones, both in the NCVP and AVB. Hoodoo Mtn. in the southern part of the

NCVP is the only volcano that erupted large volumes of phonolites (EDWARDS ET AL.

2002). In the AVB, phonolites are described from the Itcha Range (CHARLAND ET AL.

243

1993), two small volcanic centres in the SMVF and one in the BMVF (this study; cf. ch.

3.6). In terms of peralkalinity, the Hoodoo Mtn. phonolites are all of peralkaline affinity,

whereas the Tuya Field lavas are all metaluminous basalts and basanites (Figs. 41b, 42b;

cf. EDWARDS ET AL. 2011). Mt. Edziza lavas plot bimodally as both metaluminous and

peralkaline, with good overlap of the more evolved comendites with those of the AVB.

REE data for the NCVP are few (n=11) and only those of the larger volcanoes are

considered here. Even these data come with a small caveat, as data for Hoodoo Mtn.

included only one single basalt sample (heavy teal line in Fig. 46g). That sample has a

REE pattern very similar to AVB mafic lavas (especially those from the Ilgachuz Range).

The teal-shaded field are all felsic Hoodoo Mtn. lavas and clearly indicate a separate

pattern for REE in those lavas, with a significant negative Eu anomaly (likely due to

feldspar fractionation) and generally much higher enrichments in REE (LREE 400 to 600

times over chondrite, HREE 60 to 90 times). The Edziza patterns (shown as three blue

lines) show erratic patterns that are more aligned with average N-MORB or UCC lines.

(Note: No trace element spidergrams could be constructed for NCVP volcanic centres due

to lack of applicable data.)

 Co-extensive and coeval with the AVB, the Chilcotin Group basalts require another brief

mention. It is clear from looking at the TAS plot (Fig. 41b) that these transitional basalts

plot almost completely outside the AVB data. Their subalkaline character alone (though

close to the dividing line of IRVINE & BARAGAR [1971], hence the term “transitional”) sets

them apart from AVB mafic lavas (cf. BEVIER 1983A/B), despite petrographic and isotopic

similarities. These basalts entirely plot in the metaluminous field of the peralkalinity

diagram in Fig. 42b.

244

4.4.3.1.4 Plate edge effect - The Alert Bay Volcanic Belt and Yellowstone

To the south of the Anahim belt, the Alert Bay Volcanic Belt on Vancouver Island, while showing similarities in terms of age-successive volcanism, is chemically quite different. The predominantly subalkaline and peraluminous character of ABVB lavas is in marked contrast with the alkaline and peralkaline lavas of the AVB (Figs. 41b, 42b; ARMSTRONG ET AL. 1985). ABVB lavas of intermediate compositions such as andesites or dacites have no equivalents in the AVB

(BEVIER 1981; CHARLAND ET AL. 1993). No REE data for the ABVB have yet been reported, but a spidergram based on partial trace element data (ARMSTRONG ET AL. 1985) shows a lack of overlap with AVB data, especially in Sr, Zr, and Y contents (Fig. 47h)

In case of the Snake River Plain/Yellowstone hot-spot track being caused by slab edge fragmentation and mantle upwelling (JAMES ET AL. 2011), it must be noted that the volcanotectonic setting is more complex than for the AVB. The thick crust and the presence of continental lithospheric mantle underneath the SRP/Y region is thought to have contaminated magmas to such a degree that any plume signature would have been lost. The multi-element spidergram (Fig. 47b) for Quaternary Yellowstone basalts (HILDRETH ET AL. 1991) shows a distinct negative Nb anomaly considered characteristic for subduction-related magmas (cf.

BRIQUEU ET AL. 1984; KELEMAN ET AL. 1993) which might confirm the presence at depth of the subducted Farallon slab and its interaction with upwelling mantle around it (JAMES ET AL. 2011).

In the AVB basalts, no such Nb anomaly exists (Fig. 47a); this would further corroborate the postulated lack of a subducting slab underlying western B. C. since the Miocene (cf. RIDDI-

HOUGH 1984; EDWARDS & RUSSELL 1999, 2000; THORKELSON ET AL. 2011).

245

4.4.3.1.5 Propagating fracture - The Canary Islands

The geochemical data used for the Canary Islands indicates overlap with AVB data only at the mafic end of the suite (Fig. 41b). Canary Islands mafic rocks are more alkali-rich than equivalent AVB rocks, resulting in more tephritic and phonotephritic compositions. Only two

SMVF centres plot in the phonotephrite field of the TAS diagram, and even these plot close to the boundaries with the basaltic trachyandesite and basanite fields, respectively (this study; cf. ch. 3.6). Overall, the trend of the Canary Islands suite is more alkali-rich than any trends described for AVB volcanoes (CHARLAND 1994), with phonolites the dominant evolved rock type. Comparing peralkaline affinities show that Canarian lavas are less peralkaline than AVB ones but show overlap in the more metaluminous rocks (Fig. 42b).

246

4.5 Interpretation and Conclusion

The Anahim Volcanic Belt in west-central British Columbia records Neogene and Quaternary magmatism along a 330 km long, roughly E-W trending narrow area extending from the Pacific coast through the Coast Mountains onto the Chilcotin Plateau. In the western part of the AVB, uplift in the Coast Mountains and subsequent erosion have exposed intrusive and plutonic rocks of Middle and Late Miocene ages (SOUTHER 1986). In the central AVB, volcanic activity ranging in age from Late Miocene to Early Pleistocene resulted in the development of three complex shield volcanoes and, in case of one of them, associated cone fields. The eastern part of the belt is currently and solely defined by a small cinder cone, Nazko Cone, which erupted in the

Late Pleistocene and Holocene (SOUTHER ET AL. 1987).

Similar to the more extensive Northern Cordilleran Volcanic Province in the northwestern part of B. C. and other intraplate volcanoes, AVB rocks show a distinct bimodal chemistry.

However, unlike the former volcanic province, where alkaline mafic rocks dominate, the most abundant rocks in the AVB are alkaline to peralkaline felsic ones. Most notable is the presence of three felsic shield volcanoes, which makes west-central B. C. one of only a handful of locations in the world where such volcanoes exist. Each of the AVB shield volcanoes was active for ~2 Ma (including periods of dormancy) and consists of a basal, mostly trachytic to comenditic shield into which are intercalated minor units of both more mafic and more highly differentiated lavas. Late-stage activity was of alkaline mafic character. The small volumes of hawaiites, alkaline basalts and basanites that were erupted during this late stage might indicate the waning of activity as the volcanoes become disconnected from the magma source at depth.

Unlike the larger Mt. Edziza-Spectrum Range complex in the NCVP, no repeated cycles of activity and no progression from mafic towards more evolved rocks within such a cycle is

247 observed in the AVB shield volcanoes (SOUTHER & HICKSON 1984; SOUTHER ET AL. 1984).

Trace element and isotope systematics indicate a mantle source for the AVB magmas similar to

OIBs, but none of them are original mantle melts. Storage of these melts in shallow magma chambers under the volcanoes allowed for extensive fractional crystallization to take place that progressively drove the composition of the remaining magmas towards ever more alkaline and eventually peralkaline levels (BEVIER 1978; CHARLAND 1994). Some amount of contamination through assimilation of crustal rocks is indicated for centres in the western AVB and felsic rocks of the Itcha Range (BEVIER 1989; CHARLAND 1994). Repeated injections of more primitive magmas from a deeper source might conceivably have caused eruptions of evolved melts already in these magma chambers. Sometimes, such felsic eruptions were accompanied by coeval eruptions of small amounts of these fresh melts that either got entrained in the larger volume of felsic magma or that managed to rapidly make it through the chamber. In either case, these more primitive melts would presumably have not had much time to differentiate. The late-stage mafic volcanism is interpreted to be the result a similar scenario of or due to the tapping of a deeper and/or less depleted source area (SOUTHER & SOUTHER 1994). This pattern towards progressively less depleted and/or more undersaturated magmas is recognized both within each individual shield volcano and the AVB as a whole (CHARLAND ET AL. 1995).

While ages for the oldest rocks of the Rainbow and Itcha ranges in particular have not yet been determined (the central and southern parts of the Rainbow Range still await mapping in detail), the overall succession of ages from Middle Miocene in the western AVB to Holocene at its eastern terminus is by now well established (SOUTHER 1986; this study). Age data for the three shield volcanoes indicate that each of them was active for ~2 Ma, which is similar to other continental shield volcanoes around the world (e.g., in the East African Rift or the Tibesti), but

248 longer than the Hawaiian shield volcanoes. Volcanic activity was likely taking place at relatively central locations, but the complex stratigraphy of particularly the Ilgachuz and Itcha ranges suggests that eruptions also occurred away from the centre of the shields. The final mafic eruptions at these volcanoes seem to have preferentially taken place at cones and/or fissures on their respective eastern flanks, possibly another expression of volcanic activity progressing eastward in both time and space.

The SMVF, despite its N-S alignment within the general E-W trend of the AVB, has geochemical similarities with the Itcha Range and, perhaps more importantly, the ages determined for the field’s periods of volcanic activity during the Early and Middle Pleistocene

(Gelasian and Calabrian) are in agreement with its spatial location. The BMVF exhibits comparable geochemical and geochronological similarities. Moreover, the BMVF neatly fits into the hot-spot hypothesis insofar as its location east of the Itcha Range coincides with where successive volcanic activity along the AVB would be expected to have taken place. Nazko

Cone, the youngest AVB centre, also fits into this scheme, but one question that remains is why there appear to be no notable volcanic centres, either in form of a young central volcano or another cone field, between it and the BMVF.

Of the four main hypotheses put forward, the hot-spot hypothesis continues to best fit the available data and field observations. Continental rifting, with or without the presence of a slab window at depth, can account for the presence of spatially and temporally associated mafic and felsic rocks, both in a larger area and in a single volcano. Decompressional melting of mantle asthenosphere can occur in continental rifts, but does not necessarily require the presence of either a slab window (as in case of the NCVP) or a mantle plume (EDWARDS & RUSSELL 2000).

However, continental rifting is often initiated or assisted by the presence of a mantle plume. The

249 existence of the Azores or Iceland is attributed to the combination of a spreading ridge and a mantle plume; together with inducing thermal buoyancy in the surrounding oceanic crust, the subsequent large-scale melt generation is the main reason why these islands actually exist.

However, the linear age-succession of volcanic centres that is the most notable defining feature of the AVB, is mostly missing from these locations. There is also no real evidence in the AVB of E-W trending normal faults that one would expect to see as a result of such extension.

A plate-edge effect, as demonstrated for the Alert Bay Volcanic Belt on northern Vancouver

Island (ARMSTRONG ET AL. 1985), appears unlikely to be able to have initiated and maintained volcanic activity of the kind seen in the AVB, despite a similar scenario having recently been proposed for the Yellowstone hot-spot (JAMES ET AL. 2011). Trace element patterns for Yellow- stone basalts show a significant Nb anomaly, which is common for a subduction setting and therefore might corroborate a plate edge/slab fragmentation for that volcanic province. How- ever, a strong argument has been made for a slab window underlying western Canada and migration of the southern edge of that slab window since the Miocene to the south (EDWARDS ET

AL. 1999, 2000; THORKELSON ET AL. 2011). Asthenospheric upwelling could well account for generation of alkaline melts and cause crustal attenuation, resulting in magmatism at the surface.

However, this model, too, does not provide an explanation for the unidirectional decrease in ages along the Anahim belt. Shouldn’t one expect to see multiple similarly linear volcanic belts in the wake of the passing slab window, belts that should also be parallel to one other? This question remains to be addressed.

A propagating fracture similar to the one proposed for the Canary Islands could both initiate decompressional melting of asthenospheric mantle and also help to explain a spatial progression of activity, but fails to explain the pattern of activity in the AVB shield volcanoes. After

250 initiation of activity, each of the shields remained active (in a discontinuous fashion) for roughly

2 Ma. No overlap in activity is indicated between the Rainbow, Ilgachuz and Itcha ranges, respectively. In fact, the only overlap of volcanic activity anywhere in the belt exists between the Itcha Range and the Satah and Baldface Mountain volcanic fields. The last volcanic activity in the central part of the AVB is dated at 0.8 Ma in the Itcha Range (BEVIER 1989). Nazko Cone last erupted 7,200 years BP but despite an overall period of activity of ~0.34 Ma, it never made past a cinder cone stage (SOUTHER ET AL. 1987), or it has not yet done so.

The effect of local and pre-existing structures (faults, crustal fractures) on the development of the AVB as whole and the SMVF in particular is difficult to assess, yet probable. The cover of the Chilcotin Plateau by a veneer of Chilcotin Basalts (which are coeval and co-extensive with

AVB lavas) and glacial till masks the underlying bedrock and any faults that may exist in the region. The important Yalakom fault (and its off-shoots) to the southwest of the SMVF are in close spatial proximity to the central AVB and may have played a role in controlling the location and distribution of eventual AVB volcanoes. It is also possible that an interaction and intersection of a passing mantle plume with existing local faults actually allowed magmas to rise to the surface.

In the end, there remain a number of question marks for the evolution of the Anahim Volcanic

Belt. The continental hot-spot model still offers the best explanation for the (per)alkaline nature of Anahim magmatism and, it bears repeating, the clear linear progression of ages from old in the west to young in the east. The fact that the Itcha Range is the smallest of the three Anahim shield volcanoes and the lack of another large volcanic edifice east of the central part of the AVB may indicate waning activity of such a hot-spot. An earthquake swarm in late 2007, however, indicates that magmatic activity in the AVB due to this hot-spot may not yet be at an end

251

(CASSIDY ET AL. 2011). Lastly, and in a larger context, the AVB is similar in geometry to the

Yellowstone hot-spot in the northwestern United States and both could be of use to further assess the movement of North America since the Miocene.

Despite the Anahim belt being a challenging area to work in, it may prove worthwhile for future studies to investigate the oldest rocks in the Rainbow and Itcha Ranges and to refine existing ages from the western part of the AVB with newer methods. There, the Milbanke Sound cones, despite their post-glacial age which appears unrelated to this part of the AVB, require more in-depth studies to assess their volcanotectonic affiliation (which may well be unrelated to the AVB). Complete mapping of the central and southern parts of the Rainbow Range is yet to be undertaken. The same goes for large parts of the Satah and Baldface Mountain volcanic fields and mapping them in detail may help to establish the stratigraphic relationship(s) of the latter two fields. Doing so would further define the extent of lavas from these fields as well as the

AVB as a whole. Thus, it may be possible to find evidence of faults between the Itcha Range and SMVF or general E-W trending faults that would prove that local extension, whether influenced by a hot-spot or not, might indeed have played a role in the development of the belt.

252

Chapter Five: Thesis Summary

This study on the Anahim Volcanic Belt in west-central British Columbia combines a synopsis of previous works with original research providing all-new geochemistry and geochronology data for the Satah Mountain and Baldface Mountain volcanic fields, two heretofore little-studied cone fields in the vicinity of the Itcha Range shield volcano. The main goals of my research were to (1) investigate these two volcanic fields and put them into context within the AVB; and

(2) to provide and investigate additional data to assess the hot-spot hypothesis proposed to explain the origin and evolution of the AVB itself. Challenging field conditions prevented a complete coverage of the SMVF and BMVF areas, but samples retrieved from overall 27 individual locations provide a reasonable foundation for the present geological study.

Volcanic activity in the SMVF mainly occurred along a 200 m high, N-S trending ridge

(“Satah Ridge”) that extends from the Itcha Range to the north, but a few centres lie outside of this ridge. Quaternary cover masks stratigraphic relationships both between individual centres and basement rocks and repeated glacial modification of many centres left few primary features and/or once-existing pyroclastic deposits behind. Subglacial and/or subaqueous volcanism is indicated by the presence of pillow lavas, hyaloclastite breccias and subvertical to horizontal lava columns at one, possibly, two centres. Distribution, small extent and heterogeneous composition of individual centres suggest that volcanic activity in the SMVF was sporadic and restricted in duration. A possible way to explain this pattern would be that separate batches of chemically distinct magmas reached the surface at different times and locations. The orientation of Satah

Ridge and a linear alignment of several centres therein are parallel to normal faults in the nearby

Itcha Range, suggesting that volcanic activity in the SMVF may have at least partially been controlled by faulting and/or regional extension.

253

As with other AVB centres, a bimodal suite of mafic and felsic rocks is recognized in the

SMVF. Alkaline basalts and trachybasalts (48.3−51.3 wt% SiO2) are dominated by trachytes and a few phonolites (59-63.6 wt% SiO2), with only a few rocks of intermediate composition.

Mafic lavas are aphanitic to aphyric and appear very fresh. More alkaline felsic lavas are more porphyritic and often moderately weathered due to the susceptibility of Na and K to leaching.

Alkaline feldspar (sanidine, anorthoclase), plagioclase, clinopyroxenes, olivine and Fe-oxides are the dominant phenocryst phases and in some of the alkaline trachytes, green sodic pyroxenes

(aegirine/acmite) occur. Trachytic texture with flow aligned feldspar microlites is common.

Lavas from BMVF centres are slightly more undersaturated than SMVF lavas or those from the shield volcanoes (44−49.4 wt% SiO2). Alkaline olivine basalts and basanites are more abundant than evolved rocks (one trachyte, one phonolite, both 60 wt% SiO2). The alkaline olivine basalts are conspicuous by the presence of large, flattened vesicles. No peralkaline rocks were found in the SMVF and BMVF as opposed to the large shield volcanoes. Otherwise, the bimodal distribution and rock types described from the two cone fields is similar to other AVB centres.

BMVF centres appear to have been less affected by the last advance of glaciers from the Coast

Mountains than SMVF centres; a number of centres appear largely unmodified in their morphology and have retained pyroclastics deposits considered to be associated with those centres.

All new 40Ar/39Ar age data determined for eleven SMVF and seven BMVF centres indicate that volcanic activity in these fields was largely coeval with that in the Itcha Range. The SMVF data define a period of volcanic activity from 2.21 ± 0.03 Ma to 1.43 ± 0.02 Ma in the Early

Pleistocene. No clear migration of volcanic activity from one centre in any direction is indicated by these data. The BMVF data indicate that volcanic activity there lasted from 2.52 ± 0.02 Ma to 0.91 ± 0.03 Ma, i.e. it preceded activity in the SMVF by ~300 ka and also lasted ~500 ka

254 longer. A Pliocene age from the southeastern edge of the BMVF might have been determined for a flow affiliated with the Chilcotin Group basalts rather than the AVB; this flow also has chemistry similar to that of the Chilcotin basalts.

In the framework of an Anahim hot-spot, these new age data for the SMVF and BMVF are spatially and temporally located where one would expect them to be: in the vicinity of the Itcha

Range, and both of them younger than all but the latest lavas from that shield volcano. The increasing undersaturation of lavas in the AVB, both at individual volcanoes and overall along the belt, suggests a waning heat and/or melt source or the tapping of deeper melt regions. The presence of exclusively basanitic lavas at Nazko Cone, the easternmost and youngest AVB volcano, corroborates this assumption.

An overall assessment of potential volcanotectonic mechanisms responsible for a linear volcanic belt with alkaline to peralkaline chemistry included: (1) the aforementioned presence of a mantle plume under west-central British Columbia since the Miocene, creating a hot-spot track at the surface through the southwesterly motion of the North American Plate, similar to the

Yellowstone hot-spot in the northwestern United States; (2) continental rifting and/or regional extension, recognized in other parts of western Canada and the world for driving alkaline magmatism and volcanism (e.g., in the Northern Cordilleran Volcanic Province or the East

African Rift); (3) a plate edge and/or slab window effect (or possibly a combination of both processes) related to the subduction of the Juan de Fuca/Explorer plates offshore B. C., leading to mantle flow around the subducted plate edge/through the slab window and causing attenuation of the overlying crust and potentially alkaline magmatism; and (4) a fracture propagating west to east across west-central B. C. and the Chilcotin Plateau, providing magmas generated by decompressional melting paths to ascend.

255

Of these hypotheses, the hot-spot hypothesis has been favoured by authors working on the

AVB from early on. Unfortunately, yet expectedly, the geochemical data remain ambivalent as to a definite answer to the “hot-spot vs. not-spot” question. The present work supports the hot- spot hypothesis, because it best explains both the alkaline nature of AVB magmatism and the linear decrease in ages. Alkaline magmatism is observed in many hot-spot settings, both in continental and oceanic intra-plate regimes. Expression of this kind of magmatism is strongly influenced by interaction of hot up-welling material with the overlying plate and the motion vector, if any, of that plate as it moves over the –presumably stationary– mantle plume. The succession of younger centres in the AVB from east to west is similar to that observed on many oceanic islands (such as Hawai’i) and the age-distance relationship of AVB centres agree with the motion of the North American plate since the Middle Miocene of 2−3 cm/yr in a westerly to southwesterly direction. This vector is within error of the one established for the better-known

Yellowstone hot-spot track.

Future work on the AVB is warranted, though it may be many years before the area piques someone’s interest again. Detailed mapping of the SMVF and BMVF as a whole, not just of individual centres (which was only cursorily done for this study) should help in establishing stratigraphic relationships between individual centres as well as with the underlying basement rocks

(likely to be Chilcotin group basalts and/or Eocene volcanic rocks). Field observations indicate the presence of additional small centres between the Itcha Range and the SMVF and BMVF, respectively, and in the vicinity of the latter cone field especially. New age determinations would also help to better establish periods of activity in the Rainbow Range and, to a lesser degree, the Itcha Range. Further studies of trace element and isotope systematics of AVB lavas may provide additional evidence for the presence of a mantle plume under west-central B. C.

256

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Appendices

A1 Samples Locations (relates to chapter 3.3.1)

All the samples used for geochemical and geochronological analyses that were collected during three field seasons (July/August 2010, July/August 2011, July 2012) are listed below, grouped by their affiliation and sorted in alpha-numerical order (Table A9). Samples identifiers are somewhat inconsistent, but for the most part directly refer to the preliminary labels used for identifying centres prior to field work: the first set of numbers/letters refers to the centre, the second to a specific location at that centre, and the third to the sample number taken at the location (e.g., “SM-W-4” = Satah Mtn. - western cone - sample 4). A sample designated “SM-

W-2” would have been taken from exactly the same location and would have been used as

“back-up” for additional sample material. Likewise, “CH-2-1” refers to centre “CH”, location 2, first sample. Note that only samples used for actual analyses are listed.

Sample locations are given as latitude/longitude (degrees, decimal minutes), with approximate elevation (GPS measurements; elevation error between 5−10 m). Affiliation refers to location in the Baldface Mountain Volcanic Field (BMVF), Satah Mountain Volcanic Field (SMVF), or other centres (O; LQ = Quesnel Lake Volcanics, AVB = other Anahim Volcanic Belt centres,

OLG = Ootsa Lake Group: M = Mesozoic). Additional notes are included where applicable and unless specified otherwise, samples are in situ material taken from the volcanic edifice/cinder cone/outcrop itself. A check mark () indicates whether XRF and/or 40Ar/39Ar analyses were performed on any given sample.

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Table A9 Sample locations for BMVF, SMVF and other centres

Sample Affiliation Latitude Longitude Elevation Notes XRF Ar/Ar

25B-1-2 BMVF 52° 43.27’ N 124° 33.14’ W 1,618 m  

26A-1-3 BMVF 52° 44.18’ N 124° 29.24’ W 1,686 m Flow (?)  

26B-1-3 BMVF 52° 43.68’ N 124° 29.09’ W 1,657 m Flow 

26C-1-1  BMVF 52° 42.41’ N 124° 29.56’ W 1,483 m Flow 26C-1-3 

26C-2-1 BMVF 52° 42.07’ N 124° 32.29 ‘W 1,490 m Flow (?) 

BF-1-3 BMVF 52° 45.43’ N 124° 31.86’ W 1,709 m  

BF-K-2 BMVF 52° 44.94’ N 124° 31.95’ W 1,683 m Neck (?)  

C-O-1 BMVF (?) 52° 39.54’ N 124° 22.99’W 1,381 m Flow  

CC-1-1 BMVF 52° 38.46’ N 124° 26.58’ W 1,552 m Spatter 

CC-2-1 BMVF 52° 38.18’ N 124° 26.70’ W 1,470 m Cinder “ramp”  

2C-1-1 duplicate  SMVF 52° 24.82’ N 124° 42.45’ W 1,591 m 2C-1-3 

3-1-4 SMVF 52° 23.85’ N 124° 45.71’ W 1,656 m 

3-2-2 SMVF 52° 23.70’ N 124° 46.01’ W 1,599 m  

5-1-5 SMVF 52° 22.47’ N 124° 33.93’ W 1,376 m 

5-2-3 SMVF 52° 22.50’ N 124° 34.12’ W 1,394 m 

6-1-1A SMVF 52° 25.81’ N 124° 36.89’ W 1,529 m 

6-2-3 SMVF 52° 25.79’ N 124° 37.09’ W 1,547 m 

9-1-1  SMVF 52° 32.00’ N 124° 43.09’ W 1,650 m 9-1-2 

12-1-4 SMVF 52° 32.20’ N 124° 47.95’ W 1,714 m 

12-2-1  SMVF 52° 32.02’ N 124° 47.96’ W 1,691 m 12-2-3 

16-1A-2 SMVF 52° 22.36’ N 124° 40.02’ W 1,500 m Flow (?) 

16-1B-3 SMVF 52° 22.37’ N 124° 40.01’ W 1,506 m Flow (?) 

16-6-1 SMVF 52° 23.49’ N 124° 41.62’ W 1,639 m Flow  

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Table A9 continued

16-7-1 SMVF 52° 23.64’ N 124° 42.04’ W 1,755 m 

16-9-6 SMVF 52° 22.34’ N 124° 39.99’ W 1,476 m Flow 

16-C-B2 SMVF 52° 23.30’ N 124° 41.28’ W 1,576 m Flow (?) 

19-1-5 SMVF 52° 22.43’ N 124° 43.89’ W 1,619 m 

19-2-3 SMVF 52° 22.89’ N 124° 44.43’ W 1,598 m Flow 

CH-1-1 SMVF 52° 20.35’ N 124° 39.97’ W 1,508 m Small plug,  subglacial (?) CH-2-1 SMVF 52° 20.37’ N 124° 40.03’ W 1,519 m 

CM-4-2  SMVF 52° 29.61’ N 124° 47.67’ W 1,877 m CM-4-3 

JH-1-3 

JH-1-5 SMVF 52° 16.54’ N 124° 29.15’ W 1,317 m Small plug 

JH-1-6 

LF-1-1 SMVF 52° 25.41’ N 124° 39.49’ W 1,497 m Flow 

LF-5-1 SMVF 52° 22.88’ N 124° 34.13’ W 1,311 m Blocky flow 

LF-16-2-1 SMVF 52° 23.09’ N 124° 41.71’ W 1,581 m Flow 

LF-17-1-1 SMVF 52° 21.36’ N 124° 39.67’ W 1,439 m Flow 

MM-1-4 SMVF 52° 30.57’ N 124° 42.27’ W 1,668 m 

MM-2-2 SMVF 52° 30.55’ N 124° 42.13’ W 1,662 m 

NTB-1-4 SMVF 52° 26.26’ N 124° 42.41’ W 1,697 m Dome (?) 

Dome (?)  NTB-2-1 SMVF 52° 26.46’ N 124° 42.48’ W 1,837 m Duplicate 

SL-1-4 SMVF 52° 17.49’ N 124° 47.38’ W 1,579 m  

SM-1-3 SMVF 52° 28.58’ N 124° 41.37’ W 1,908 m 

SM-3-2 SMVF 52° 28.50’ N 124° 41.46’ W 1,904 m Flow (?) 

SM-L-1 SMVF 52° 28.56’ N 124° 41.04’ W 1,801 m Flow (?)  

SM-W-1  SMVF 52° 28.58’ N 124° 41.36’ W 1,908 m SM-W-4 

SMN-1-2 SMVF 52° 28.73’ N 124° 41.77’ W 1,807 m Spatter Ring 

TB-1-1 SMVF 52° 25.71’ N 124° 42.17’ W 1,867 m 

278

Table A9 continued

TB-1-2 SMVF 52° 25.71’ N 124° 42.17’ W 1,867 m 

TB-2-2 SMVF 52° 25.88’ N 124° 42.59’ W 1,753 m 

TL-1 SMVF 52° 18.88’ N 124° 48.17’ W 1,497 m Flow 

U-1-2 SMVF 52° 29.64’ N 124° 43.49’ W 1,613 m Flow (?) 

AC-2-3 O (LQ) 52° 35.39’ N 121° 8.42’ W 1,272 m Flow, younger 

CRD-1-1 O (OLG) 52° 27.75’ N 124° 4.41’ W 1,071 m Flow, older  

GR-2-1 O (OLG) 52° 07.90’ N 124° 35.45’ W 1,407 m Plug, older  

LM-1-4 O (M) 52° 27.81’ N 124° 18.88’ W 1,199 m Flow (?), older 

N-1-2 O (AVB) 52° 55.95’ N 123° 44.79’ W 1,062 m Flow  

N-3-1 O (AVB) 52° 55.39’ N 123° 44.63’ W 1,067 m Flow 

N-Bomb O (AVB) 52° 55.85’ N 123° 44.20’ W 1,109 m Scoria/Bomb 

QV-1-1 O (M) 52° 30.43’ N 121° 04.66’ W 845 m Mesozoic 

RT-1-3 O (OLG) 52° 27.90’ N 124° 09.74’ W 1,247 m Flow (?), older  

X-3 Flow, younger,  O (LQ) 52° 34.90’ N 121° 05.94’ W 957 m w/ mantle X-7 xenoliths 

279

A2 Original XRF data (relates to chapter 3.5.1)

Below are listed (Tables A10) the reduced data from the whole-rock XRF analyses carried out on samples from the Satah Mountain (SMVF) and Baldface Mountain Volcanic Fields (BMVF). A superscript “1” indicates that the sample was analyzed at the Trace Element Analytical

Laboratory at McGill University, Montréal (Canada), in 2011; a superscript “2” indicates the

Geochemistry Laboratory at Washington State University, Pullman (USA), in 2013. FeO contents were calculated by titration at McGill University (2011) and the Institut für Mineralogie und Geochemie, Albert-Ludwigs-Universität, Freiburg i. Br. (Germany; 2013). Titration procedures follow the ones established by WILSON (1955).

Major elements concentrations are given as oxides in weight percent, trace element and rare earth element data in ppm. “LOI” is loss (or rarely, gain) on ignition. As there are differences in instruments, procedures and detection limits between McGill and Washington State University, parameters for each set of analyses is provided below.

Respective normative mineralogies (given in wt%), Mg# (molar ratio of Mg/(Mg + Fe2+)) and differentiation indices (D.I.; (Qz+Or+Ab+Ne)/Total) were calculated using a Excel spread-sheet programmed by K. Hollocher, Union College, Schenectady, NY (USA). The original template can be accessed at http://minerva.union.edu/hollochk/c_petrology/other_files/norm4.xls.

McGill University samples

Analyses were obtained with a Phillips PW 2440 XRF-spectrometer system using 32 mm diameter fused beads that were prepared with a lithium tetraborate flux (sample:flux ratio of 1:5).

These yielded concentrations of the major elements Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K and P as well as trace elements Ba, Ce, Co, Cr, Cu, Ni, Sc, V and Zn. Trace elements Ga, Nb, Pb, Rb, Sr,

280

Th, U, Y and Zr were determined on 40 mm diameter pressed pellets, using 10 gr of sample powder with 2 gr Hoechst (Clariant) Wax C Micropowder. Accuracy for silica is within 0.5%, for all other major and trace elements within 1%. Rare earth element analysis (marked with an asterisk * in the tables below) was done with a Perkin Elmer Elan 6100 DRCplus ICP-MS, using lithium metaborate fused beads. Analytical procedures are summarized in a PDF created by Dr.

William Minarik (accessible at http://eps.mcgill.ca/~minarik/geochem/GeoLab/XRF%20

ANALYTICAL%20PROCEDURE.pdf.)

Detection limits (in ppm, based on three times the background σ values) for XRF analyses of major and trace elements are as follows:

Major elements Trace elements

Si 60 Mg 95 Ba 12 Ni 3 Ga 1 Th 1

Ti 25 Ca 15 Ce 15 Sc 10 Nb 0.3 U 1

Al 120 Na 35 Co 10 V 7 Pb 1 Y 1

Fe 25 K 25 Cr 10 Zn 2 Rb 1 Zr 1

Mn 25 P 35 Cu 2 Sr 1

Detection limits for REE using ICP-MS (in ppm, based on three times the background σ values):

Y 0.05 Pr 0.005 Gd 0.005 Er 0.005 Th 0.02

Ba 0.3 Nd 0.005 Tb 0.005 Tm 0.005 U 0.02

La 0.05 Sm 0.005 Dy 0.005 Yb 0.005

Ce 0.05 Eu 0.005 Ho 0.005 Lu 0.005

281

Washington State University samples

Analyses were obtained with a ThermoARL Advant’XP sequential XRF-spectrometer system using 32 mm diameter beads fused at 1,000° C that were prepared with a di-lithium tetraborate flux (sample:flux ratio of 1:2). Fused beads are re-ground and refused. Analyses yielded concentrations of the major elements Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K and P as well as trace elements Ni, Cr, Sc, V, Ba, Rb, Sr, Zr, Y, Nb, Ga, Cu, Zn, Pb, La, Ce, Th, Nd, U, Bi and Cs.

Sample preparation and analytical procedures are described in JOHNSON ET AL. (1999).

Detection limits for XRF analyses of major and trace elements are as follows (major elements in wt%, normalised, trace elements in ppm, both based on two times the background σ values):

Major elements Trace elements

Si 0.19 Mg 0.073 Ni 3.5 Rb 1.7 Ga 2.7 Ce 7.9 Cs 5.1

Ti 0.012 Ca 0.043 Cr 3 Sr 4.6 Cu 7.4 Th 1.6

Al 0.082 Na 0.036 Sc 1.6 Zr 3.9 Zn 3.3 Nd 4.3

Fe 0.18 K 0.015 V 5 Y 1.2 Pb 2.6 U 2.7

Mn 0.002 P 0.003 Ba 11.7 Nb 1.2 La 5.7 Bi 2

Mineral abbreviations in the following table:

Qtz = quartz, Or = orthoclase, Ab = albite, An = anorthite, Ne = nepheline, Di = diopside,

Ac = acmite, Wo = wollastonite, Hy = hypersthene, Ol = olivine, Cr = chromite, Mt = magnetite,

Hem = hematite, Ilm = ilmenite, Ap = apatite, Zr = zircon, Sph = sphene.

282

Tables A10 XRF whole-rock data (major and trace elements), rare earth elements contents for selected samples and mineral norms (incl. Mg# and differentiation index [D.I.]).

Sample 25B-1-22 Rock type trachybasalt Sample 26A-1-32 Rock type basanite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 47.69 Qtz 0.00 SiO2 43.60 Qtz 0.00

TiO2 3.06 Or 8.25 TiO2 3.50 Or 9.81

Al2O3 16.53 Ab 37.46 Al2O3 14.04 Ab 25.76

Fe2O3 6.82 An 19.90 Fe2O3 13.15 An 15.33 FeO 5.49 Ne 1.04 FeO 0.61 Ne 4.47 MgO 4.61 Di 10.77 MgO 8.81 Di 11.56 MnO 0.18 Ac 0.00 MnO 0.18 Ac 0.00 CaO 8.12 Hy 0.00 CaO 8.92 Hy 0.00

Na2O 4.54 Ol 4.58 Na2O 3.92 Ol 11.72

K2O 1.35 Cr 0.01 K2O 1.62 Cr 0.04

P2O5 0.96 Mt 9.43 P2O5 0.74 Mt 0.00 LOI 0.56 Hem 0.35 LOI 0.43 Hem 13.24

Trace tot. 0.25 Ilm 5.83 Trace tot. 0.26 Ilm 1.68 Total 100.16 Ap 2.22 Total 99.78 Ap 1.74 Zr 0.06 Zr 0.06 Trace elements (ppm) Total 99.90 Trace elements (ppm) Total 99.89

Rb 53 Mg# 60.0 Rb 29 Mg# 96.3 Sr 985 D.I. 66.7 Sr 883 D.I. 55.4 Ba 496 Ba 451 Nb 51 Nb 54 Zr 266 Zr 273 Y 27 Y 25 Sc 15 Sc 18 V 189 V 208 Cr 62 Cr 176 Ni 43 Ni 165 Co - Co - Cu 32 Cu 44 Zn 121 Zn 124 Th 3 Th 4 Pb 3 Pb 2 Ga 22 Ga 24 U 4 U 3

Rare earth elements (ppm) Rare earth elements (ppm)

La 38 La 36 Ce 86 Ce 83 Nd 47 Nd 45 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

283

Sample 26B-1-32 Rock type basalt Sample 26C-1-31 Rock type hawaiite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 47.28 Qtz 0.00 SiO2 49.14 Qtz 0.00

TiO2 2.64 Or 5.56 TiO2 2.35 Or 12.64

Al2O3 15.25 Ab 33.88 Al2O3 15.58 Ab 31.08

Fe2O3 5.31 An 20.85 Fe2O3 3.63 An 18.49 FeO 6.62 Ne 0.00 FeO 7.67 Ne 1.10 MgO 7.67 Di 12.89 MgO 6.70 Di 11.91 MnO 0.16 Ac 0.00 MnO 0.17 Ac 0.00 CaO 8.49 Hy 0.22 CaO 7.56 Hy 0.00

Na2O 3.90 Ol 11.88 Na2O 3.81 Ol 13.43

K2O 0.90 Cr 0.04 K2O 2.08 Cr 0.06

P2O5 0.73 Mt 7.76 P2O5 0.60 Mt 5.29 LOI 0.51 Hem 0.00 LOI 0.00 Hem 0.00

Trace tot. 0.24 Ilm 5.05 Trace tot. 0.26 Ilm 4.48 Total 99.70 Ap 1.71 Total 99.55 Ap 1.39 Zr 0.04 Zr 0.04 Trace elements (ppm) Total 99.90 Trace elements (ppm) Total 99.91

Rb 25 Mg# 67.4 Rb 23 Mg# 60.9 Sr 783 D.I. 60.3 Sr 650 D.I. 63.3 Ba 429 Ba 674 Nb 32 Nb 37 Zr 196 Zr 223 Y 22 Y 21 Sc 19 Sc 15 V 185 V 168 Cr 208 Cr 302 Ni 156 Ni 140 Co - Co 38 Cu 49 Cu 78 Zn 119 Zn 85 Th 2 Th 4 Pb 2 Pb 3 Ga 23 Ga 23 U 2 U 0

Rare earth elements (ppm) Rare earth elements (ppm)*

La 27 La 30.2 Tb 0.9 Ce 65 Ce 64.2 Dy 4.9 Nd 36 Pr 8.2 Ho 0.8 Sm - Nd 34.9 Er 2.1 Eu - Sm 7.3 Tm 0.3 Tb - Eu 2.8 Yb 1.5 Ho - Gd 6.7 Lu 0.2 Yb - Lu -

284

Sample 26C-2-12 Rock type basalt Sample BF-1-32 Rock type phonolite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 47.64 Qtz 0.00 SiO2 59.45 Qtz 0.00

TiO2 2.44 Or 8.95 TiO2 0.25 Or 30.85

Al2O3 14.35 Ab 26.11 Al2O3 18.86 Ab 49.96

Fe2O3 4.15 An 19.38 Fe2O3 4.04 An 2.24 FeO 7.10 Ne 1.36 FeO 1.7 Ne 7.75 MgO 8.92 Di 17.95 MgO 0.25 Di 1.34 MnO 0.16 Ac 0.00 MnO 0.12 Ac 0.00 CaO 9.22 Hy 0.00 CaO 1.45 Hy 0.00

Na2O 3.30 Ol 14.07 Na2O 7.67 Ol 0.00

K2O 1.48 Cr 0.07 K2O 5.15 Cr 0.00

P2O5 0.55 Mt 6.05 P2O5 0.14 Mt 5.18 LOI -0.34 * Hem 0.00 LOI 1.06 Hem 0.50

Trace tot. 0.24 Ilm 4.65 Trace tot. 0.20 Ilm 0.47 Total 99.21 Ap 1.27 Total 100.34 Ap 0.32 Zr 0.04 Zr 0.13 Trace elements (ppm) Total 99.90 Trace elements (ppm) Total 99.78

Rb 23 Mg# 69.1 Rb 95 Mg# 20.7 Sr 689 D.I. 55.8 Sr 90 D.I. 90.8 Ba 347 Ba 468 Nb 37 Nb 104 Zr 232 Zr 677 Y 22 Y 20 Sc 23 Sc 1 V 221 V 3 Cr 344 Cr 2 Ni 184 Ni 1 Co - Co - Cu 45 Cu 7 Zn 115 Zn 187 Th 4 Th 10 Pb 2 Pb 9 Ga 22 Ga 36 U 1 U 1

Rare earth elements (ppm) Rare earth elements (ppm)

La 27 La 69 Ce 61 Ce 134 Nd 31 Nd 45 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

285

Sample BF-K-22 Rock type trachyte Sample C-O-11 Rock type basalt

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 59.04 Qtz 0.68 SiO2 44.56 Qtz 0.00

TiO2 0.50 Or 29.03 TiO2 3.68 Or 7.86

Al2O3 18.44 Ab 51.64 Al2O3 15.35 Ab 26.91

Fe2O3 3.75 An 9.04 Fe2O3 7.81 An 24.55 FeO 2.47 Ne 0.00 FeO 5.39 Ne 0.00 MgO 0.50 Di 0.00 MgO 6.53 Di 12.17 MnO 0.17 Ac 0.00 MnO 0.20 Ac 0.00 CaO 2.22 Hy 2.21 CaO 8.68 Hy 5.94

Na2O 5.95 Ol 0.00 Na2O 3.00 Ol 3.62

K2O 4.79 Cr 0.00 K2O 1.26 Cr 0.00

P2O5 0.27 Mt 5.52 P2O5 0.53 Mt 7.59 LOI 1.12 Hem 0.00 LOI 2.63 Hem 2.81

Trace tot. 0.24 Ilm 0.97 Trace tot. 0.21 Ilm 7.20 Total 99.46 Ap 0.65 Total 99.83 Ap 1.27 Zr 0.15 Zr 0.03 Trace elements (ppm) Total 99.89 Trace elements (ppm) Total 99.95

Rb 84 Mg# 26.6 Rb 17 Mg# 68.3 Sr 349 D.I. 90.4 Sr 773 D.I. 59.3 Ba 635 Ba 363 Nb 111 Nb 31 Zr 692 Zr 177 Y 29 Y 19 Sc 3 Sc 17 V 4 V 273 Cr 2 Cr 142 Ni 1 Ni 80 Co - Co 45 Cu 9 Cu 53 Zn 135 Zn 78 Th 9 Th 3 Pb 8 Pb 3 Ga 29 Ga 21 U 5 U 0.6

Rare earth elements (ppm) Rare earth elements (ppm)*

La 71 La 21.7 Tb 0.8 Ce 133 Ce 48.0 Dy 4.4 Nd 53 Pr 6.3 Ho 0.8 Sm - Nd 27.4 Er 1.9 Eu - Sm 6.1 Tm 0.3 Tb - Eu 2.3 Yb 1.4 Ho - Gd 5.8 Lu 0.2 Yb - Lu -

286

Sample CC-1-11 Rock type trachybasalt Sample CC-2-12 Rock type trachybasalt

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 45.31 Qtz 0.00 SiO2 47.20 Qtz 0.00

TiO2 3.22 Or 10.23 TiO2 3.21 Or 8.95

Al2O3 16.49 Ab 26.08 Al2O3 16.69 Ab 30.88

Fe2O3 13.64 An 22.03 Fe2O3 4.10 An 21.37 FeO 0.0 Ne 5.74 FeO 8.08 Ne 3.56 MgO 3.71 Di 12.14 MgO 4.51 Di 13.12 MnO 0.17 Ac 0.00 MnO 0.16 Ac 0.00 CaO 7.99 Hy 0.00 CaO 8.40 Hy 0.00

Na2O 4.07 Ol 13.61 Na2O 4.29 Ol 8.36

K2O 1.63 Cr 0.03 K2O 1.47 Cr 0.01

P2O5 0.65 Mt 2.06 P2O5 0.62 Mt 6.02 LOI 3.72 Hem 0.00 LOI 0.53 Hem 0.00

Trace tot. 0.22 Ilm 6.38 Trace tot. 0.21 Ilm 6.15 Total 100.82 Ap 1.58 Total 99.47 Ap 1.46 Zr 0.04 Zr 0.04 Trace elements (ppm) Total 99.92 Trace elements (ppm) Total 99.92

Rb 24 Mg# 37.5 Rb 25 Mg# 49.9 Sr 786 D.I. 64.1 Sr 786 D.I. 64.8 Ba 388 Ba 385 Nb 42 Nb 40 Zr 240 Zr 242 Y 26 Y 25 Sc 17 Sc 18 V 206 V 129 Cr 142 Cr 61 Ni 80 Ni 43 Co 43 Co - Cu 61 Cu 36 Zn 79 Zn 124 Th 3 Th 3 Pb 24 Pb 2 Ga 24 Ga 24 U 0.0 U 1

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 29 Ce 58 Ce 60 Nd - Nd 34 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

287

Sample 2C-1-12 (d) Rock type phonolite Sample 2C-1-31 Rock type phonolite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 59.34 Qtz 0.00 SiO2 59.41 Qtz 0.00

TiO2 0.13 Or 29.37 TiO2 0.14 Or 29.84

Al2O3 16.71 Ab 45.21 Al2O3 16.93 Ab 41.05

Fe2O3 3.72 An 0.00 Fe2O3 3.82 An 0.00 FeO 2.30 Ne 8.28 FeO 2.65 Ne 10.68 MgO 0.02 Di 3.93 MgO 0.04 Di 4.10 MnO 0.21 Ac 8.88 MnO 0.22 Ac 10.73 CaO 0.91 Hy 0.00 CaO 0.92 Hy 0.00

Na2O 8.68 Ol 1.45 Na2O 8.45 Ol 2.24

K2O 4.85 Cr 0.00 K2O 4.95 Cr 0.00

P2O5 0.03 Mt 1.07 P2O5 0.04 Mt 0.28 LOI 1.09 Hem 0.00 LOI 1.05 Hem 0.00

Trace tot. 0.43 Ilm 0.25 Trace tot. 0.42 Ilm 0.27 Total 98.42 Ap 0.07 Total 99.04 Ap 0.09 Zr 0.46 Zr 0.51 Trace elements (ppm) Total 99.57 Trace elements (ppm) Total 99.79

Rb 233 Mg# 1.5 Rb 238 Mg# 2.6 Sr 3 D.I. 82.9 Sr 2 D.I. 81.6 Ba 9 Ba 3 Nb 316 Nb 360 Zr 2208 Zr 2501 Y 158 Y 152 Sc 0 Sc 0 V 3 V 11 Cr 3 Cr 0 Ni 3 Ni 0 Co - Co 0 Cu 5 Cu 4 Zn 462 Zn 425 Th 32 Th 30 Pb 26 Pb 28 Ga 71 Ga 74 U 12 U 10

Rare earth elements (ppm) Rare earth elements (ppm)* (not used)

La 203 La 205.9 Tb 4.9 Ce 404 Ce 410.7 Dy 30.0 Nd 169 Pr 46.6 Ho 5.8 Sm - Nd 169.9 Er 16.1 Eu - Sm 33.7 Tm 2.2 Tb - Eu 2.2 Yb 14.4 Ho - Gd 28.5 Lu 2.0 Yb - Lu -

288

Sample 3-1-42 Rock type basaltic Sample 3-2-22 Rock type basaltic trachyandesite trachyandesite Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 50.91 Qtz 0.00 SiO2 51.08 Qtz 0.00

TiO2 2.32 Or 14.30 TiO2 2.28 Or 14.53

Al2O3 16.41 Ab 41.49 Al2O3 16.41 Ab 41.96

Fe2O3 4.60 An 12.46 Fe2O3 4.64 An 12.39 FeO 7.53 Ne 2.87 FeO 7.45 Ne 2.55 MgO 3.20 Di 6.75 MgO 3.12 Di 6.58 MnO 0.21 Ac 0.00 MnO 0.21 Ac 0.00 CaO 5.72 Hy 0.00 CaO 5.70 Hy 0.00

Na2O 5.54 Ol 8.21 Na2O 5.51 Ol 8.04

K2O 2.37 Cr 0.00 K2O 2.42 Cr 0.00

P2O5 1.12 Mt 6.66 P2O5 1.15 Mt 6.71 LOI -0.53 Hem 0.00 LOI -0.45 Hem 0.00

Trace tot. 0.25 Ilm 4.41 Trace tot. 0.25 Ilm 4.31 Total 99.65 Ap 2.59 Total 99.77 Ap 2.66 Zr 0.07 Zr 0.07 Trace elements (ppm) Total 99.81 Trace elements (ppm) Total 99.80

Rb 35 Mg# 43.1 Rb 37 Mg# 42.7 Sr 782 D.I. 71.1 Sr 776 D.I. 71.4 Ba 698 Ba 710 Nb 54 Nb 55 Zr 365 Zr 374 Y 41 Y 41 Sc 12 Sc 12 V 64 V 53 Cr 0 Cr 0 Ni 0 Ni 3 Co - Co - Cu 10 Cu 14 Zn 160 Zn 160 Th 4 Th 5 Pb 4 Pb 5 Ga 25 Ga 28 U 3 U 3

Rare earth elements (ppm) Rare earth elements (ppm)

La 47 La 49 Ce 104 Ce 105 Nd 61 Nd 58 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

289

Sample 5-1-51 Rock type trachyte Sample 5-2-32 Rock type trachyte

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 63.89 Qtz 2.24 SiO2 59.31 Qtz 0.00

TiO2 0.25 Or 30.49 TiO2 0.50 Or 33.17

Al2O3 15.64 Ab 52.23 Al2O3 16.99 Ab 51.33

Fe2O3 2.88 An 0.00 Fe2O3 4.72 An 1.67 FeO 3.25 Ne 0.00 FeO 2.14 Ne 1.64 MgO 0.07 Di 4.11 MgO 0.39 Di 2.15 MnO 0.18 Ac 5.42 MnO 0.19 Ac 0.00 CaO 0.99 Hy 3.08 CaO 1.89 Wo 1.63

Na2O 6.86 Ol 0.00 Na2O 6.42 Hy 0.00

K2O 5.13 Cr 0.00 K2O 5.48 Ol 0.00

P2O5 0.05 Mt 1.49 P2O5 0.18 Cr 0.00 LOI 0.26 Hem 0.00 LOI 1.04 Mt 6.14

Trace tot. 0.20 Ilm 0.47 Trace tot. 0.20 Hem 0.57 Total 99.65 Ap 0.12 Total 99.68 Ilm 0.97 Zr 0.25 Ap 0.42 Trace elements (ppm) Total 99.90 Trace elements (ppm) Zr 0.12 Total 99.78 Rb 130 Mg# 3.7 Rb 69 Sr 7 D.I. 85.0 Sr 68 Mg# 24.7 Ba 24 Ba 621 D.I. 87.8 Nb 162 Nb 87 Zr 1236 Zr 583 Y 27 Y 49 Sc 0 Sc 10 V 15 V 2 Cr 0 Cr 3 Ni 0 Ni 2 Co 0 Co - Cu 16 Cu 5 Zn 214 Zn 178 Th 19 Th 6 Pb 15 Pb 8 Ga 46 Ga 37 U 3 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 67 Ce 103 Ce 133 Nd - Nd 63 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

290

Sample 6-1-1A2 Rock type phonotephrite Sample 6-2-31 Rock type phonotephrite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 51.30 Qtz 0.00 SiO2 51.44 Qtz 0.00

TiO2 1.52 Or 17.10 TiO2 1.50 Or 17.43

Al2O3 17.48 Ab 48.65 Al2O3 17.80 Ab 46.10

Fe2O3 6.94 An 10.90 Fe2O3 5.86 An 11.60 FeO 4.05 Ne 3.22 FeO 5.47 Ne 4.24 MgO 1.93 Di 0.83 MgO 2.01 Di 0.18 MnO 0.17 Ac 0.00 MnO 0.16 Ac 0.00 CaO 3.98 Hy 0.00 CaO 4.02 Hy 0.00

Na2O 6.35 Ol 3.17 Na2O 6.23 Ol 5.84

K2O 2.79 Cr 0.00 K2O 2.86 Cr 0.00

P2O5 1.21 Mt 9.37 P2O5 1.19 Mt 8.60 LOI 0.92 Hem 0.62 LOI 0.66 Hem 0.00

Trace tot. 0.28 Ilm 2.94 Trace tot. 0.25 Ilm 2.89 Total 98.92 Ap 2.85 Total 99.45 Ap 2.78 Zr 0.09 Zr 0.24 Trace elements (ppm) Total 99.74 Trace elements (ppm) Total 99.90

Rb 45 Mg# 46.0 Rb 120 Mg# 39.5 Sr 1185 D.I. 79.9 Sr 3 D.I. 79.4 Ba 628 Ba 668 Nb 66 Nb 147 Zr 435 Zr 1166 Y 28 Y 36 Sc 4 Sc 0 V 19 V 29 Cr 1 Cr 0 Ni 4 Ni 0 Co - Co 16 Cu 18 Cu 37 Zn 118 Zn 81 Th 5 Th 16 Pb 5 Pb 12 Ga 21 Ga 44 U 3 U 0

Rare earth elements (ppm) Rare earth elements (ppm)

La 60 La - Ce 121 Ce 113 Nd 61 Nd - Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

291

Sample 9-1-21 Rock type trachyte Sample 12-1-42 Rock type trachyte

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 63.41 Qtz 0.04 SiO2 59.65 Qtz 0.00

TiO2 0.21 Or 31.56 TiO2 0.75 Or 33.62

Al2O3 16.55 Ab 55.65 Al2O3 16.85 Ab 45.50

Fe2O3 2.48 An 0.00 Fe2O3 2.39 An 2.29 FeO 3.28 Ne 0.00 FeO 4.50 Ne 2.06 MgO 0.02 Di 4.87 MgO 0.55 Di 5.77 MnO 0.17 Ac 2.78 MnO 0.19 Ac 0.00 CaO 1.08 Hy 2.21 CaO 2.16 Hy 0.00

Na2O 6.93 Ol 0.00 Na2O 6.07 Ol 2.91

K2O 5.32 Cr 0.00 K2O 5.59 Cr 0.00

P2O5 0.04 Mt 2.22 P2O5 0.27 Mt 3.49 LOI 0.04 Hem 0.00 LOI -0.27 Hem 0.00

Trace tot. 0.21 Ilm 0.40 Trace tot. 0.20 Ilm 1.44 Total 99.74 Ap 0.09 Total 98.90 Ap 0.63 Zr 0.09 Zr 0.12 Trace elements (ppm) Total 99.91 Trace elements (ppm) Total 99.83

Rb 43 Mg# 1.1 Rb 69 Mg# 17.8 Sr 1160 D.I. 87.3 Sr 76 D.I. 85.5 Ba 24 Ba 688 Nb 66 Nb 77 Zr 427 Zr 556 Y 28 Y 42 Sc 0.0 Sc 12 V 13 V 3 Cr 0.0 Cr 2 Ni 0.0 Ni 3 Co 0.0 Co - Cu 19 Cu 8 Zn 165 Zn 169 Th 7 Th 6 Pb 6 Pb 7 Ga 21 Ga 34 U 2 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 57 Ce 129 Ce 124 Nd - Nd 56 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

292

Sample 12-2-11 Rock type trachyte Sample 16-1A-21 Rock type trachyandesite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 60.83 Qtz 0.00 SiO2 57.41 Qtz 0.63

TiO2 0.57 Or 34.46 TiO2 1.06 Or 27.68

Al2O3 17.05 Ab 50.46 Al2O3 16.97 Ab 47.67

Fe2O3 3.75 An 1.67 Fe2O3 4.83 An 7.25 FeO 2.9 Ne 0.91 FeO 3.65 Ne 0.00 MgO 0.41 Di 5.31 MgO 1.13 Di 3.65 MnO 0.20 Ac 0.00 MnO 0.22 Ac 0.00 CaO 1.89 Wo 0.05 CaO 3.22 Hy 2.44

Na2O 6.14 Hy 0.00 Na2O 5.56 Ol 0.00

K2O 5.79 Ol 0.00 K2O 4.59 Cr 0.00

P2O5 0.18 Cr 0.00 P2O5 0.62 Mt 7.05 LOI 0.14 Mt 5.45 LOI 0.39 Hem 0.00

Trace tot. 0.17 Hem 0.00 Trace tot. 0.23 Ilm 2.03 Total 100.02 Ilm 1.08 Total 99.88 Ap 1.44 Ap 0.42 Zr 0.09 Trace elements (ppm) Zr 0.13 Trace elements (ppm) Total 99.93 Total 99.94 Rb 79 Rb 55 Mg# 35.6 Sr 34 Mg# 20.1 Sr 308 D.I. 83.2 Ba 407 D.I. 87.5 Ba 1069 Nb 93 Nb 60 Zr 673 Zr 432 Y 48 Y 42 Sc 11 Sc 0 V 17 V 20 Cr 0.0 Cr 11 Ni 0.0 Ni 0 Co 0.0 Co 0 Cu 21 Cu 17 Zn 147 Zn 127 Th 9 Th 7 Pb 3 Pb 5 Ga 36 Ga 33 U 0.0 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La - La - Ce 137 Ce 90 Nd - Nd - Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

293

Sample 16-1B-31 Rock type trachyte Sample 16-6-12 Rock type hawaiite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 58.39 Qtz 0.21 SiO2 48.91 Qtz 0.00

TiO2 0.86 Or 31.17 TiO2 2.41 Or 9.16

Al2O3 16.81 Ab 49.55 Al2O3 16.34 Ab 33.41

Fe2O3 4.96 An 4.31 Fe2O3 11.01 An 22.09 FeO 3.02 Ne 0.00 FeO 0.35 Ne 0.00 MgO 0.81 Di 4.20 MgO 6.20 Di 4.37 MnO 0.22 Ac 0.00 MnO 0.17 Ac 0.00 CaO 2.50 Hy 0.51 CaO 7.89 Hy 10.09

Na2O 5.78 Ol 0.00 Na2O 3.85 Ol 2.38

K2O 5.17 Cr 0.00 K2O 1.51 Cr 0.03

P2O5 0.42 Mt 7.25 P2O5 0.71 Mt 0.00 LOI 0.82 Hem 0.00 LOI 1.04 Hem 11.06

Trace tot. 0.20 Ilm 1.63 Trace tot. 0.21 Ilm 1.10 Total 99.96 Ap 0.97 Total 100.60 Ap 1.65 Zr 0.10 Zr 0.04 Trace elements (ppm) Total 99.90 Trace elements (ppm) Sph 4.51 Total 99.89 Rb 68 Mg# 32.4 Rb 20 Sr 156 D.I. 85.2 Sr 671 Mg# 96.9 Ba 794 Ba 466 D.I. 64.7 Nb 74 Nb 32 Zr 511 Zr 192 Y 46 Y 23 Sc 0 Sc 16 V 16 V 166 Cr 0 Cr 139 Ni 0 Ni 103 Co 0 Co - Cu 10 Cu 33 Zn 139 Zn 120 Th 7 Th 3 Pb 6 Pb 3 Ga 35 Ga 23 U 0 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 27 Ce 107 Ce 59 Nd - Nd 32 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

294

Sample 16-7-11 Rock type trachyandesite Sample 16-9-62 Rock type trachyte

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 56.72 Qtz 0.81 SiO2 60.44 Qtz 1.40

TiO2 0.90 Or 30.32 TiO2 0.66 Or 30.90

Al2O3 16.68 Ab 48.62 Al2O3 15.75 Ab 50.32

Fe2O3 7.19 An 5.70 Fe2O3 4.76 An 0.71 FeO 1.16 Ne 0.00 FeO 4.21 Ne 0.00 MgO 0.80 Di 2.78 MgO 0.36 Di 7.70 MnO 0.21 Ac 0.00 MnO 0.25 Ac 0.00 CaO 2.47 Hy 0.75 CaO 2.28 Hy 0.09

Na2O 5.55 Ol 0.00 Na2O 5.98 Ol 0.00

K2O 4.93 Cr 0.00 K2O 5.22 Cr 0.00

P2O5 0.45 Mt 1.86 P2O5 0.24 Mt 6.89 LOI 2.86 Hem 6.11 LOI 0.14 Hem 0.00

Trace tot. 0.20 Ilm 1.77 Trace tot. 0.15 Ilm 1.25 Total 100.12 Ap 1.09 Total 100.44 Ap 0.56 Zr 0.10 Zr 0.10 Trace elements (ppm) Total 99.91 Trace elements (ppm) Total 99.92

Rb 59 Mg# 55.1 Rb 64 Mg# 13.3 Sr 190 D.I. 85.5 Sr 26 D.I. 83.3 Ba 840 Ba 276 Nb 69 Nb 65 Zr 490 Zr 493 Y 40 Y 46 Sc 11 Sc 15 V 15 V 2 Cr 12 Cr 2 Ni 0 Ni 1 Co 0 Co - Cu 19 Cu 6 Zn 124 Zn 197 Th 7 Th 6 Pb 7 Pb 7 Ga 34 Ga 32 U 0 U 1

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 57 Ce 100 Ce 126 Nd - Nd 64 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

295

Sample 16-C-B22 Rock type trachybasalt Sample 19-1-52 Rock type trachyte

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 48.35 Qtz 0.00 SiO2 59.93 Qtz 2.38

TiO2 2.54 Or 7.65 TiO2 0.43 Or 30.34

Al2O3 16.06 Ab 32.71 Al2O3 15.49 Ab 51.37

Fe2O3 3.96 An 21.62 Fe2O3 5.83 An 0.52 FeO 8.08 Ne 0.56 FeO 3.24 Ne 0.00 MgO 6.67 Di 11.72 MgO 0.12 Di 2.36 MnO 0.17 Ac 0.00 MnO 0.25 Ac 0.00 CaO 8.34 Hy 0.00 CaO 2.25 Wo 3.16

Na2O 3.92 Ol 13.44 Na2O 6.07 Hy 0.00

K2O 1.27 Cr 0.03 K2O 5.06 Ol 0.00

P2O5 0.70 Mt 5.73 P2O5 0.13 Cr 0.00 LOI -0.67 Hem 0.00 LOI 0.59 Mt 8.54

Trace tot. 0.20 Ilm 4.81 Trace tot. 0.18 Hem 0.00 Total 99.59 Ap 1.62 Total 99.57 Ilm 0.82 Zr 0.03 Ap 0.30 Trace elements (ppm) Total 99.92 Trace elements (ppm) Zr 0.12 Total 99.91 Rb 17 Mg# 59.5 Rb 69 Sr 650 D.I. 62.5 Sr 26 Mg# 6.1 Ba 385 Ba 325 D.I. 84.6 Nb 28 Nb 82 Zr 175 Zr 591 Y 24 Y 68 Sc 19 Sc 7 V 184 V 2 Cr 135 Cr 2 Ni 108 Ni 2 Co - Co - Cu 41 Cu 4 Zn 120 Zn 227 Th 3 Th 7 Pb 2 Pb 7 Ga 23 Ga 35 U 1 U 2

Rare earth elements (ppm)* Rare earth elements (ppm)

La 25.3 Tb 0.9 La 74 Ce 55.0 Dy 4.9 Ce 159 Pr 7.1 Ho 0.9 Nd 79 Nd 31.8 Er 2.2 Sm - Sm 7.0 Tm 0.3 Eu - Eu 2.5 Yb 1.6 Tb - Gd 6.6 Lu 0.3 Ho - Yb - Lu -

296

Sample 19-2-32 Rock type trachyte Sample CH-1-11 Rock type basaltic trachyandesite Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 59.16 Qtz 0.12 SiO2 50.17 Qtz 0.00

TiO2 0.54 Or 30.59 TiO2 2.13 Or 17.27

Al2O3 15.30 Ab 49.46 Al2O3 15.47 Ab 29.11

Fe2O3 3.90 An 0.80 Fe2O3 2.92 An 16.37 FeO 5.40 Ne 0.00 FeO 7.20 Ne 1.89 MgO 0.26 Di 9.67 MgO 6.28 Di 13.00 MnO 0.28 Ac 0.00 MnO 0.17 Ac 0.00 CaO 2.58 Hy 2.00 CaO 7.36 Hy 0.00

Na2O 5.76 Ol 0.00 Na2O 3.75 Ol 12.43

K2O 5.07 Cr 0.00 K2O 2.85 Cr 0.01

P2O5 0.18 Mt 5.74 P2O5 0.60 Mt 4.28 LOI 0.52 Hem 0.00 LOI 0.45 Hem 0.00

Trace tot. 0.18 Ilm 1.04 Trace tot. 0.25 Ilm 4.08 Total 99.13 Ap 0.42 Total 99.60 Ap 1.41 Zr 0.10 Zr 0.06 Trace elements (ppm) Total 99.94 Trace elements (ppm) Total 99.91

Rb 66 Mg# 7.8 Rb 38 Mg# 60.9 Sr 49 D.I. 81.0 Sr 588 D.I. 64.6 Ba 498 Ba 621 Nb 72 Nb 55 Zr 508 Zr 322 Y 59 Y 25 Sc 11 Sc 15 V 3 V 162 Cr 2 Cr 273 Ni 2 Ni 159 Co - Co 33 Cu 4 Cu 56 Zn 192 Zn 82 Th 5 Th 6 Pb 6 Pb 4 Ga 32 Ga 24 U 2 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La 66 La - Ce 128 Ce 75 Nd 72 Nd - Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

297

Sample CH-2-12 Rock type basaltic Sample CM-4-31 Rock type trachyte trachyandesite Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 50.64 Qtz 0.00 SiO2 60.56 Qtz 2.85

TiO2 2.13 Or 18.75 TiO2 0.43 Or 30.80

Al2O3 15.57 Ab 28.38 Al2O3 15.28 Ab 49.83

Fe2O3 2.64 An 13.91 Fe2O3 7.85 An 0.00 FeO 7.18 Ne 4.19 FeO 1.63 Ne 0.00 MgO 6.06 Di 13.13 MgO 0.08 Di 0.43 MnO 0.16 Ac 0.00 MnO 0.27 Ac 3.06 CaO 6.92 Hy 0.00 CaO 1.91 Hy 0.00

Na2O 4.20 Ol 12.06 Na2O 6.28 Ol 0.00

K2O 3.11 Cr 0.04 K2O 5.18 Cr 0.00

P2O5 0.62 Mt 3.84 P2O5 0.12 Mt 4.89 LOI 0.54 Hem 0.00 LOI 0.13 Hem 3.44

Trace tot. 0.25 Ilm 4.06 Trace tot. 0.15 Ilm 0.82 Total 100.02 Ap 1.44 Total 99.87 Ap 0.28 Zr 0.07 Zr 0.13 Trace elements (ppm) Total 99.87 Trace elements (ppm) Total 99.95

Rb 43 Mg# 60.1 Rb 72 Mg# 8.0 Sr 621 D.I. 65.2 Sr 15 D.I. 83.5 Ba 588 Ba 182 Nb 52 Nb 88 Zr 339 Zr 634 Y 25 Y 57 Sc 16 Sc 0 V 157 V 13 Cr 179 Cr 0 Ni 109 Ni 0 Co - Co 0 Cu 33 Cu 9 Zn 119 Zn 177 Th 5 Th 9 Pb 2 Pb 10 Ga 23 Ga 37 U 2 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La 40 La - Ce 88 Ce 148 Nd 43 Nd - Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

298

Sample JH-1-31 Rock type trachybasalt Sample JH-1-62 Rock type trachybasalt

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 48.71 Qtz 0.00 SiO2 49.49 Qtz 0.00

TiO2 2.80 Or 10.93 TiO2 2.89 Or 11.66

Al2O3 16.97 Ab 38.70 Al2O3 17.02 Ab 38.46

Fe2O3 4.93 An 17.07 Fe2O3 4.66 An 16.25 FeO 7.48 Ne 3.30 FeO 7.47 Ne 3.52 MgO 4.02 Di 6.21 MgO 4.06 Di 6.71 MnO 0.19 Ac 0.00 MnO 0.19 Ac 0.00 CaO 6.18 Hy 0.00 CaO 6.23 Hy 0.00

Na2O 5.17 Ol 9.06 Na2O 5.32 Ol 8.88

K2O 1.79 Cr 0.01 K2O 1.94 Cr 0.00

P2O5 0.86 Mt 7.19 P2O5 0.89 Mt 6.73 LOI 0.00 Hem 0.00 LOI -0.20 Hem 0.00

Trace tot. 0.22 Ilm 5.36 Trace tot. 0.24 Ilm 5.47 Total 99.32 Ap 2.02 Total 100.20 Ap 2.06 Zr 0.06 Zr 0.06 Trace elements (ppm) Total 99.91 Trace elements (ppm) Total 99.80

Rb 35 Mg# 48.9 Rb 35 Mg# 49.2 Sr 820 D.I. 70.0 Sr 862 D.I. 69.9 Ba 620 Ba 632 Nb 50 Nb 50 Zr 323 Zr 331 Y 30 Y 33 Sc 0 Sc 11 V 119 V 107 Cr 0 Cr 0 Ni 0 Ni 4 Co 28 Co - Cu 29 Cu 18 Zn 103 Zn 141 Th 3 Th 3 Pb 5 Pb 4 Ga 22 Ga 24 U 1 U 2

Rare earth elements (ppm)* Rare earth elements (ppm)

La 40.6 Tb 1.2 La 40 Ce 87.7 Dy 6.9 Ce 90 Pr 11.1 Ho 1.2 Nd 51 Nd 47.5 Er 3.0 Sm - Sm 9.7 Tm 0.4 Eu - Eu 3.2 Yb 2.4 Tb - Gd 8.7 Lu 0.3 Ho - Yb - Lu -

299

Sample LF-1-12 Rock type basaltic Sample LF-5-12 Rock type trachybasalt trachyandesite Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 49.81 Qtz 0.76 SiO2 50.32 Qtz 0.00

TiO2 2.34 Or 13.31 TiO2 2.11 Or 12.15

Al2O3 16.15 Ab 40.77 Al2O3 15.41 Ab 31.95

Fe2O3 7.32 An 15.86 Fe2O3 3.13 An 17.58 FeO 5.55 Ne 0.00 FeO 8.20 Ne 0.85 MgO 3.09 Di 4.19 MgO 7.26 Di 12.07 MnO 0.26 Ac 0.00 MnO 0.18 Ac 0.00 CaO 6.07 Hy 6.57 CaO 7.41 Hy 0.00

Na2O 4.73 Ol 0.00 Na2O 3.93 Ol 15.50

K2O 2.19 Cr 0.00 K2O 2.01 Cr 0.04

P2O5 1.34 Mt 10.71 P2O5 0.54 Mt 4.51 LOI 0.80 Hem 0.00 LOI -0.44 Hem 0.00

Trace tot. 0.24 Ilm 4.48 Trace tot. 0.24 Ilm 3.97 Total 99.89 Ap 3.10 Total 100.30 Ap 1.25 Zr 0.07 Zr 0.04 Trace elements (ppm) Total 99.82 Trace elements (ppm) Total 99.91

Rb 36 Mg# 49.8 Rb 22 Mg# 61.2 Sr 765 D.I. 70.7 Sr 509 D.I. 62.5 Ba 657 Ba 781 Nb 54 Nb 30 Zr 357 Zr 191 Y 45 Y 24 Sc 13 Sc 19 V 44 V 155 Cr 0 Cr 200 Ni 4 Ni 161 Co - Co - Cu 11 Cu 37 Zn 182 Zn 119 Th 5 Th 2 Pb 3 Pb 3 Ga 26 Ga 21 U 2 U 0

Rare earth elements (ppm) Rare earth elements (ppm)

La 46 La 24 Ce 106 Ce 58 Nd 60 Nd 31 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

300

Sample LF-16-2-12 Rock type basalt Sample LF-17-1-12 Rock type trachyandesite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 48.26 Qtz 1.24 SiO2 57.47 Qtz 0.00

TiO2 2.23 Or 5.72 TiO2 1.06 Or 28.65

Al2O3 14.64 Ab 27.65 Al2O3 16.44 Ab 47.91

Fe2O3 7.71 An 22.71 Fe2O3 3.82 An 5.56 FeO 4.29 Ne 0.00 FeO 4.47 Ne 0.00 MgO 7.55 Di 14.36 MgO 1.08 Di 4.58 MnO 0.17 Ac 0.00 MnO 0.23 Ac 0.00 CaO 8.90 Hy 12.45 CaO 3.03 Hy 3.38

Na2O 3.15 Ol 0.00 Na2O 5.61 Ol 0.61

K2O 0.94 Cr 0.04 K2O 4.72 Cr 0.00

P2O5 0.47 Mt 8.07 P2O5 0.60 Mt 5.61 LOI 0.97 Hem 2.26 LOI 0.63 Hem 0.00

Trace tot. 0.18 Ilm 4.29 Trace tot. 0.23 Ilm 2.03 Total 99.46 Ap 1.11 Total 99.39 Ap 1.41 Zr 0.03 Zr 0.09 Trace elements (ppm) Total 99.93 Trace elements (ppm) Total 99.83

Rb 17 Mg# 75.8 Rb 68 Mg# 30.0 Sr 497 D.I. 57.3 Sr 258 D.I. 82.1 Ba 258 Ba 947 Nb 21 Nb 63 Zr 156 Zr 439 Y 24 Y 47 Sc 20 Sc 12 V 193 V 11 Cr 181 Cr 0 Ni 152 Ni 1 Co - Co - Cu 44 Cu 9 Zn 120 Zn 189 Th 2 Th 6 Pb 2 Pb 5 Ga 21 Ga 31 U 0 U 1

Rare earth elements (ppm) Rare earth elements (ppm)

La 20 La 57 Ce 44 Ce 122 Nd 25 Nd 63 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

301

Sample MM-1-41 Rock type trachyte Sample MM-2-22 Rock type trachyte

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 59.75 Qtz 0.00 SiO2 60.51 Qtz 0.00

TiO2 0.30 Or 28.66 TiO2 0.19 Or 29.49

Al2O3 16.35 Ab 44.70 Al2O3 16.33 Ab 44.80

Fe2O3 4.27 An 0.00 Fe2O3 4.97 An 0.00 FeO 3.04 Ne 7.38 FeO 1.77 Ne 6.88 MgO 0.25 Di 5.60 MgO 0.04 Di 4.58 MnO 0.21 Ac 8.99 MnO 0.22 Ac 11.81 CaO 1.35 Hy 0.00 CaO 1.06 Hy 0.00

Na2O 7.98 Ol 1.71 Na2O 8.25 Ol 0.22

K2O 4.78 Cr 0.00 K2O 4.91 Cr 0.00

P2O5 0.06 Mt 1.77 P2O5 0.03 Mt 1.40 LOI 0.86 Hem 0.00 LOI 1.05 Hem 0.00

Trace tot. 0.31 Ilm 0.57 Trace tot. 0.31 Ilm 0.36 Total 99.51 Ap 0.14 Total 99.64 Ap 0.07 Zr 0.34 Zr 0.30 Trace elements (ppm) Total 99.86 Trace elements (ppm) Total

Rb 154 Mg# 12.6 Rb 149 Mg# 3.8 Sr 38 D.I. 80.7 Sr 7 D.I. 81.2 Ba 15 Ba 13 Nb 252 Nb 218 Zr 1666 Zr 1481 Y 122 Y 113 Sc 0 Sc 1 V 18 V 1 Cr 21 Cr 2 Ni 0 Ni 2 Co 0 Co - Cu 17 Cu 3 Zn 352 Zn 403 Th 24 Th 19 Pb 19 Pb 19 Ga 59 Ga 58 U 6 U 3

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 163 Ce 321 Ce 306 Nd - Nd 141 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

302

Sample NTB-1-41 Rock type trachyte Sample NTB-2-12 (d) Rock type trachyte

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 62.51 Qtz 0.00 SiO2 62.06 Qtz 0.00

TiO2 0.49 Or 34.50 TiO2 0.49 Or 33.44

Al2O3 17.10 Ab 53.47 Al2O3 16.78 Ab 54.78

Fe2O3 2.15 An 1.04 Fe2O3 2.20 An 0.22 FeO 3.24 Ne 0.00 FeO 3.17 Ne 0.23 MgO 0.36 Di 4.67 MgO 0.34 Di 5.30 MnO 0.14 Ac 0.00 MnO 0.15 Ac 0.00 CaO 1.52 Hy 0.12 CaO 1.48 Hy 0.00

Na2O 6.31 Ol 1.51 Na2O 6.46 Ol 1.23

K2O 5.82 Cr 0.00 K2O 5.59 Cr 0.00

P2O5 0.16 Mt 3.12 P2O5 0.16 Mt 3.22 LOI 0.00 Hem 0.00 LOI 0.13 Hem 0.00

Trace tot. 0.19 Ilm 0.93 Trace tot. 0.20 Ilm 0.93 Total 99.99 Ap 0.37 Total 99.21 Ap 0.37 Zr 0.19 Zr 0.19 Trace elements (ppm) Total 99.92 Trace elements (ppm) Total 99.91

Rb 101 Mg# 16.5 Rb 113 Mg# 15.9 Sr 53 D.I. 89.0 Sr 46 D.I. 88.7 Ba 291 Ba 224 Nb 100 Nb 108 Zr 950 Zr 931 Y 37 Y 42 Sc 0 Sc 6 V 13 V 5 Cr 0 Cr 2 Ni 0 Ni 2 Co - Co - Cu 20 Cu 6 Zn 131 Zn 176 Th 11 Th 11 Pb 10 Pb 10 Ga 39 Ga 39 U 3 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 69 Ce 111 Ce 141 Nd - Nd 60 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

303

Sample NTB-2-41 Rock type trachyte Sample SL-1-42 Rock type trachyte

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 62.04 Qtz 0.28 SiO2 62.97 Qtz 2.33

TiO2 0.48 Or 34.38 TiO2 0.39 Or 32.74

Al2O3 16.96 Ab 53.11 Al2O3 17.01 Ab 54.32

Fe2O3 2.75 An 1.19 Fe2O3 4.24 An 1.28 FeO 2.67 Ne 0.00 FeO 1.10 Ne 0.00 MgO 0.38 Di 4.90 MgO 0.41 Di 2.20 MnO 0.13 Ac 0.00 MnO 0.11 Ac 0.00 CaO 1.61 Hy 0.55 CaO 1.36 Wo 0.67

Na2O 6.24 Ol 0.00 Na2O 6.40 Hy 0.00

K2O 5.76 Cr 0.00 K2O 5.50 Ol 0.00

P2O5 0.16 Mt 4.02 P2O5 0.15 Cr 0.00 LOI 0.48 Hem 0.00 LOI 0.22 Mt 2.77

Trace tot. 0.20 Ilm 0.91 Trace tot. 0.22 Hem 2.34 Total 99.86 Ap 0.37 Total 100.08 Ilm 0.74 Zr 0.19 Ap 0.35 Trace elements (ppm) Total 99.90 Trace elements (ppm) Zr 0.18 Total 99.92 Rb 101 Mg# 20.1 Rb 102 Sr 60 D.I. 89.0 Sr 59 Mg# 39.9 Ba 295 Ba 455 D.I. 90.7 Nb 103 Nb 116 Zr 987 Zr 864 Y 44 Y 54 Sc 0 Sc 6 V 17 V 5 Cr 0 Cr 2 Ni 0 Ni 2 Co 0 Co - Cu 21 Cu 7 Zn 131 Zn 194 Th 12 Th 10 Pb 10 Pb 9 Ga 38 Ga 35 U 3 U 4

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 82 Ce 147 Ce 165 Nd - Nd 74 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

304

Sample SM-1-31 Rock type basaltic Sample SM-3-21 Rock type trachyte trachyandesite Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 50.00 Qtz 0.00 SiO2 59.28 Qtz 0.00

TiO2 2.30 Or 10.69 TiO2 0.74 Or 32.96

Al2O3 16.84 Ab 39.65 Al2O3 17.08 Ab 46.80

Fe2O3 4.91 An 19.79 Fe2O3 3.03 An 3.09 FeO 6.08 Ne 0.00 FeO 4.41 Ne 2.29 MgO 3.98 Di 8.03 MgO 0.67 Di 5.24 MnO 0.18 Ac 0.00 MnO 0.20 Ac 0.00 CaO 7.12 Hy 3.68 CaO 2.31 Hy 0.00

Na2O 4.53 Ol 4.45 Na2O 6.00 Ol 2.82

K2O 1.74 Cr 0.01 K2O 5.50 Cr 0.00

P2O5 0.81 Mt 7.22 P2O5 0.33 Mt 4.41 LOI 0.88 Hem 0.00 LOI 0.00 Hem 0.00

Trace tot. 0.21 Ilm 4.43 Trace tot. 0.23 Ilm 1.41 Total 100.16 Ap 1.90 Total 99.78 Ap 0.76 Zr 0.06 Zr 0.13 Trace elements (ppm) Total 99.91 Trace elements (ppm) Total 99.91

Rb 20 Mg# 53.8 Rb 73 Mg# 21.3 Sr 587 D.I. 70.1 Sr 103 D.I. 85.1 Ba 641 Ba 980 Nb 40 Nb 95 Zr 256 Zr 698 Y 26 Y 46 Sc 13 Sc 0 V 145 V 17 Cr 58 Cr 0 Ni 25 Ni 0 Co 27 Co 0 Cu 49 Cu 0 Zn 90 Zn 143 Th 3 Th 11 Pb 2 Pb 8 Ga 24 Ga 34 U 1 U 2

Rare earth elements (ppm)* Rare earth elements (ppm)

La 33.4 Tb 1.1 La Ce 71.9 Dy 5.9 Ce 117 Pr 9.2 Ho 1.0 Nd Nd 39.9 Er 2.7 Sm Sm 8.6 Tm 0.3 Eu Eu 3.3 Yb 2.1 Tb Gd 7.9 Lu 0.3 Ho Yb Lu

305

Sample SM-L-12 Rock type trachyte Sample SM-W-41 Rock type trachyandesite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 60.68 Qtz 0.79 SiO2 54.40 Qtz 0.00

TiO2 0.36 Or 33.84 TiO2 1.46 Or 21.69

Al2O3 17.69 Ab 53.88 Al2O3 17.70 Ab 45.49

Fe2O3 4.41 An 3.62 Fe2O3 4.14 An 13.13 FeO 1.39 Ne 0.00 FeO 5.10 Ne 0.00 MgO 0.19 Di 0.86 MgO 1.80 Di 3.57 MnO 0.14 Ac 0.00 MnO 0.18 Ac 0.00 CaO 1.11 Hy 0.08 CaO 4.88 Hy 0.13

Na2O 6.22 Ol 0.00 Na2O 5.29 Ol 4.75

K2O 5.61 Cr 0.00 K2O 3.55 Cr 0.00

P2O5 0.10 Mt 3.96 P2O5 0.93 Mt 6.02 LOI 1.40 Hem 1.77 LOI 0.00 Hem 0.00

Trace tot. 0.19 Ilm 0.70 Trace tot. 0.29 Ilm 2.77 Total 99.49 Ap 0.23 Total 100.16 Ap 2.25 Zr 0.19 Zr 0.06 Trace elements (ppm) Total 99.92 Trace elements (ppm) Total 99.86

Rb 99 Mg# 19.3 Rb 37 Mg# 38.6 Sr 40 D.I. 92.1 Sr 580 D.I. 80.3 Ba 119 Ba 1575 Nb 123 Nb 49 Zr 920 Zr 319 Y 51 Y 33 Sc 6 Sc 13 V 9 V 45 Cr 5 Cr 0 Ni 2 Ni 0 Co - Co 14 Cu 7 Cu 27 Zn 192 Zn 105 Th 9 Th 5 Pb 10 Pb 4 Ga 40 Ga 27 U 3 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La 74 La - Ce 170 Ce 61 Nd 68 Nd - Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

306

Sample SMN-1-22 Rock type basaltic Sample TB-1-21 Rock type trachyte trachyandesite Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 51.73 Qtz 0.00 SiO2 61.01 Qtz 0.00

TiO2 1.93 Or 11.35 TiO2 0.17 Or 32.03

Al2O3 15.22 Ab 33.49 Al2O3 17.5 Ab 52.91

Fe2O3 4.36 An 17.79 Fe2O3 3.48 An 0.00 FeO 6.43 Ne 0.00 FeO 2.22 Ne 4.37 MgO 6.29 Di 12.35 MgO 0.08 Di 3.44 MnO 0.17 Ac 0.00 MnO 0.21 Ac 0.93 CaO 7.36 Hy 10.49 CaO 1.26 Wo 0.90

Na2O 3.91 Ol 3.34 Na2O 7.24 Hy 0.00

K2O 1.89 Cr 0.04 K2O 5.35 Ol 0.00

P2O5 0.43 Mt 6.32 P2O5 0.04 Cr 0.00 LOI 0.19 Hem 0.00 LOI 0.92 Mt 4.64

Trace tot. 0.20 Ilm 3.67 Trace tot. 0.25 Hem 0.00 Total 100.11 Ap 1.00 Total 99.73 Ilm 0.32 Zr 0.06 Ap 0.09 Trace elements (ppm) Total 99.90 Trace elements (ppm) Zr 0.28 Total 99.91 Rb 38 Mg# 63.6 Rb 140 Sr 444 D.I. 62.6 Sr 20 Mg# 6.0 Ba 405 Ba 0 D.I. 89.3 Nb 42 Nb 216 Zr 282 Zr 1409 Y 27 Y 103 Sc 18 Sc 0 V 152 V 12 Cr 181 Cr 0 Ni 120 Ni 0 Co - Co 0 Cu 43 Cu 18 Zn 118 Zn 267 Th 6 Th 21 Pb 4 Pb 16 Ga 23 Ga 52 U 3 U 5

Rare earth elements (ppm) Rare earth elements (ppm)

La 33 La - Ce 68 Ce 270 Nd 32 Nd - Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

307

Sample TB-2-22 Rock type trachyte Sample TL-12 Rock type trachybasalt

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 60.90 Qtz 0.00 SiO2 49.22 Qtz 0.00

TiO2 0.16 Or 32.21 TiO2 2.45 Or 10.51

Al2O3 17.61 Ab 55.40 Al2O3 15.79 Ab 29.08

Fe2O3 5.21 An 0.11 Fe2O3 1.88 An 19.38 FeO 0.69 Ne 3.14 FeO 9.55 Ne 2.60 MgO 0.06 Di 0.32 MgO 6.64 Di 13.19 MnO 0.19 Ac 0.00 MnO 0.17 Ac 0.00 CaO 1.11 Wo 1.98 CaO 8.11 Hy 0.00

Na2O 7.14 Hy 0.00 Na2O 3.95 Ol 16.28

K2O 5.38 Ol 0.00 K2O 1.74 Cr 0.03

P2O5 0.04 Cr 0.00 P2O5 0.63 Mt 2.71 LOI 1.07 Mt 2.41 LOI -0.52 Hem 0.00

Trace tot. 0.26 Hem 3.62 Trace tot. 0.24 Ilm 4.63 Total 99.82 Ilm 0.30 Total 99.85 Ap 1.46 Ap 0.09 Zr 0.03 Trace elements (ppm) Zr 0.30 Trace elements (ppm) Total 99.90 Total 99.88 Rb 142 Rb 19 Mg# 55.3 Sr 3 Mg# 13.3 Sr 611 D.I. 61.6 Ba 0 D.I. 90.9 Ba 737 Nb 226 Nb 29 Zr 1474 Zr 183 Y 99 Y 23 Sc 0 Sc 19 V 12 V 185 Cr 0 Cr 159 Ni 0 Ni 124 Co 0 Co - Cu 20 Cu 42 Zn 259 Zn 122 Th 22 Th 2 Pb 16 Pb 2 Ga 53 Ga 21 U 5 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 29 Ce 277 Ce 58 Nd - Nd 31 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

308

Sample U-1-22 Rock type phonolite Sample AC-2-32 Rock type basanite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 58.93 Qtz 0.00 SiO2 44.81 Qtz 0.00

TiO2 0.14 Or 29.08 TiO2 3.14 Or 11.66

Al2O3 16.43 Ab 46.74 Al2O3 14.40 Ab 19.68

Fe2O3 5.94 An 0.00 Fe2O3 3.86 An 14.72 FeO 0.85 Ne 7.04 FeO 9.61 Ne 8.86 MgO 0.05 Di 0.27 MgO 6.81 Di 17.60 MnO 0.25 Ac 10.47 MnO 0.18 Ac 0.00 CaO 0.89 Wo 1.71 CaO 8.33 Hy 0.00

Na2O 8.31 Hy 0.00 Na2O 4.27 Ol 13.39

K2O 4.77 Ol 0.00 K2O 1.90 Cr 0.03

P2O5 0.02 Cr 0.00 P2O5 0.82 Mt 5.68 LOI 1.78 Mt 3.28 LOI 0.89 Hem 0.00

Trace tot. 0.48 Hem 0.24 Trace tot. 0.29 Ilm 6.06 Total 98.84 Ilm 0.27 Total 99.31 Ap 1.92 Ap 0.05 Zr 0.07 Trace elements (ppm) Zr 0.52 Trace elements (ppm) Total 99.67 Total 99.67 Rb 255 Rb 46 Mg# 55.8 Sr 5 Mg# 9.2 Sr 964 D.I. 54.9 Ba 8 D.I. 82.9 Ba 594 Nb 339 Nb 69 Zr 2529 Zr 339 Y 179 Y 25 Sc 1 Sc 15 V 2 V 190 Cr 3 Cr 157 Ni 5 Ni 116 Co - Co - Cu 5 Cu 48 Zn 451 Zn 147 Th 31 Th 6 Pb 25 Pb 3 Ga 75 Ga 25 U 8 U 3

Rare earth elements (ppm) Rare earth elements (ppm)

La 237 La 51 Ce 483 Ce 98 Nd 196 Nd 47 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

309

Sample CRD-1-12 Rock type trachyte Sample GR-2-11 Rock type dacite/trachyte

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 63.53 Qtz 19.43 SiO2 66.01 Qtz 24.42

TiO2 0.74 Or 22.24 TiO2 0.76 Or 23.41

Al2O3 15.83 Ab 33.50 Al2O3 15.42 Ab 32.79

Fe2O3 2.52 An 15.26 Fe2O3 4.68 An 9.90 FeO 1.67 Ne 0.00 FeO 0.32 Ne 0.00 MgO 1.11 Di 1.35 MgO 0.54 Di 0.00 MnO 0.05 Ac 0.00 MnO 0.03 Ac 0.00 CaO 3.82 Hy 2.22 CaO 2.43 Hy 1.37

Na2O 3.79 Ol 0.00 Na2O 3.75 Ol 0.00

K2O 3.59 Cr 0.00 K2O 3.80 Cr 0.00

P2O5 0.30 Mt 3.50 P2O5 0.30 Mt 0.00 LOI 1.61 Hem 0.17 LOI 1.99 Hem 4.76

Trace tot. 0.22 Ilm 1.44 Trace tot. 0.26 Ilm 0.76 Total 98.78 Ap 0.72 Total 100.29 Ap 0.72 Zr 0.04 Zr 0.09 Trace elements (ppm) Total 99.87 Trace elements (ppm) Total 99.91

Rb 117 Mg# 54.2 Rb 69 Mg# 74.8 Sr 476 D.I. 90.4 Sr 400 D.I. 90.5 Ba 1041 Ba 1338 Nb 10 Nb 15 Zr 220 Zr 403 Y 14 Y 34 Sc 8 Sc 0 V 101 V 76 Cr 6 Cr 41 Ni 8 Ni 0 Co - Co - Cu 25 Cu 53 Zn 65 Zn 57 Th 11 Th 7 Pb 10 Pb 11 Ga 18 Ga 17 U 4 U 3

Rare earth elements (ppm) Rare earth elements (ppm)

La 30 La - Ce 57 Ce 40 Nd 26 Nd - Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

310

Sample LM-1-41 Rock type basaltic andesite Sample N-1-22 Rock type basanite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 53.19 Qtz 12.90 SiO2 47.74 Qtz 0.00

TiO2 0.78 Or 10.68 TiO2 2.50 Or 15.58

Al2O3 15.38 Ab 24.61 Al2O3 15.36 Ab 23.83

Fe2O3 6.26 An 26.14 Fe2O3 4.06 An 10.96 FeO 1.47 Ne 0.00 FeO 8.03 Ne 10.36 MgO 3.96 Di 9.85 MgO 6.51 Di 13.58 MnO 0.14 Ac 0.00 MnO 0.18 Ac 0.00 CaO 7.67 Hy 5.99 CaO 7.02 Hy 0.00

Na2O 2.64 Ol 0.00 Na2O 5.08 Ol 12.42

K2O 1.65 Cr 0.00 K2O 2.61 Cr 0.03

P2O5 0.19 Mt 3.14 P2O5 1.05 Mt 5.86 LOI 6.62 Hem 4.53 LOI 0.30 Hem 0.00

Trace tot. 0.21 Ilm 1.58 Trace tot. -0.25 Ilm 4.71 Total 100.16 Ap 0.49 Total 100.19 Ap 2.41 Zr 0.01 Zr 0.09 Trace elements (ppm) Total 99.92 Trace elements (ppm) Total 99.83

Rb 32 Mg# 82.8 Rb 42 Mg# 59.1 Sr 545 D.I. 74.3 Sr 1056 D.I. 60.7 Ba 525 Ba 534 Nb 2 Nb 71 Zr 76 Zr 410 Y 15 Y 27 Sc 19 Sc 13 V 181 V 143 Cr 145 Cr 171 Ni 50 Ni 116 Co 23 Co - Cu 432 Cu 36 Zn 39 Zn 130 Th 2 Th 6 Pb 5 Pb 4 Ga 16 Ga 22 U 0 U 3

Rare earth elements (ppm) Rare earth elements (ppm)

La - La 52 Ce 15 Ce 115 Nd - Nd 50 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

311

Sample N-3-12 Rock type basanite Sample N-Bomb2 Rock type basanite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 43.51 Qtz 0.00 SiO2 43.98 Qtz 0.00

TiO2 3.89 Or 12.50 TiO2 3.81 Or 12.38

Al2O3 13.80 Ab 9.46 Al2O3 13.77 Ab 11.98

Fe2O3 2.88 An 14.85 Fe2O3 4.35 An 14.59 FeO 10.50 Ne 11.70 FeO 9.00 Ne 10.30 MgO 9.02 Di 21.22 MgO 9.41 Di 20.65 MnO 0.18 Ac 0.00 MnO 0.18 Ac 0.00 CaO 9.24 Hy 0.00 CaO 9.18 Hy 0.00

Na2O 3.67 Ol 16.75 Na2O 3.69 Ol 14.66

K2O 2.08 Cr 0.03 K2O 2.08 Cr 0.04

P2O5 0.74 Mt 4.19 P2O5 0.73 Mt 6.28 LOI -0.44 Hem 0.00 LOI -0.47 Hem 0.00

Trace tot. 0.26 Ilm 7.39 Trace tot. 0.26 Ilm 7.20 Total 99.33 Ap 1.69 Total 99.97 Ap 1.69 Zr 0.06 Zr 0.06 Trace elements (ppm) Total 99.84 Trace elements (ppm) Total 99.83

Rb 28 Mg# 60.5 Rb 28 Mg# 65.1 Sr 835 D.I. 48.5 Sr 796 D.I. 49.3 Ba 397 Ba 380 Nb 56 Nb 55 Zr 289 Zr 290 Y 25 Y 26 Sc 20 Sc 20 V 263 V 263 Cr 169 Cr 183 Ni 167 Ni 183 Co - Co - Cu 46 Cu 57 Zn 124 Zn 127 Th 4 Th 4 Pb 1 Pb 2 Ga 23 Ga 22 U 2 U 3

Rare earth elements (ppm) Rare earth elements (ppm)

La 39 La 38 Ce 81 Ce 79 Nd 41 Nd 42 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

312

Sample RT-1-32 Rock type andesite Sample X-32 Rock type basanite

Major elements (wt%) Normative mineralogy (wt%) Major elements (wt%) Normative mineralogy (wt%)

SiO2 58.20 Qtz 14.47 SiO2 45.20 Qtz 0.00

TiO2 0.88 Or 12.00 TiO2 2.56 Or 9.80

Al2O3 15.80 Ab 29.76 Al2O3 13.84 Ab 21.95

Fe2O3 2.64 An 22.55 Fe2O3 4.82 An 14.75 FeO 3.19 Ne 0.00 FeO 7.83 Ne 6.75 MgO 4.01 Di 2.69 MgO 10.07 Di 14.78 MnO 0.11 Ac 0.00 MnO 0.19 Ac 0.00 CaO 5.70 Hy 11.63 CaO 7.73 Hy 0.00

Na2O 3.34 Ol 0.00 Na2O 4.00 Ol 17.83

K2O 1.88 Cr 0.01 K2O 1.59 Cr 0.09

P2O5 0.42 Mt 3.97 P2O5 0.80 Mt 7.06 LOI 3.41 Hem 0.00 LOI -0.05 Hem 0.00

Trace tot. 0.26 Ilm 1.73 Trace tot. 0.33 Ilm 4.92 Total 99.84 Ap 1.00 Total 98.96 Ap 1.85 Zr 0.04 Zr 0.06 Trace elements (ppm) Total 99.85 Trace elements (ppm) Total 99.84

Rb 85 Mg# 69.1 Rb 38 Mg# 69.6 Sr 581 D.I. 78.8 Sr 889 D.I. 53.3 Ba 1134 Ba 725 Nb 13 Nb 70 Zr 221 Zr 308 Y 20 Y 24 Sc 16 Sc 15 V 124 V 155 Cr 88 Cr 381 Ni 39 Ni 287 Co - Co - Cu 41 Cu 39 Zn 93 Zn 121 Th 10 Th 6 Pb 10 Pb 3 Ga 18 Ga 21 U 4 U 2

Rare earth elements (ppm) Rare earth elements (ppm)

La 36 La 54 Ce 67 Ce 105 Nd 31 Nd 48 Sm - Sm - Eu - Eu - Tb - Tb - Ho - Ho - Yb - Yb - Lu - Lu -

313

A3 Original 40Ar/39Ar geochronology data (relates to chapter 3.5.2)

Below is listed information from 40Ar/39Ar determinations conducted at the Geochronology

Laboratory at the University of Alaska, Fairbanks (USA). The analyses were done in two instalments, the first in August 2012, and the second in January 2013. For sample preparation and data acquisition, see ch. 3.5.2 (p. 118). Table A11 again summarizes the age data; the full raw data (Tables A12), age spectra, Ca/K and Cl/K ratios and isochron plots (where available) for each individual sample are given farther down (Figs. A48). For the age spectra, consecutive fractions used for plateau age calculation are coloured in blue; for calculation of isochron ages, chosen fractions are indicated by red data points and circles.

314

Table A11 40Ar/39Ar analyses from volcanic centres in the Baldface Mountain (BMVF), Satah Mountain Volcanic Fields

(SMVF) and other centres (O).

1) Affiliation: BMVF = Baldface Mtn. Volcanic Field, SMVF = Satah Mtn. Volcanic Field, O = other centres (AVB = Anahim

Volcanic Belt, LQ = Quesnel Lake, OLG = Ootsa Lake Group).

2) Integrated age is the age given by the total gas measured (equivalent to a K-Ar age). All samples were analyzed against UAF

Geochronology Laboratory standard TCR-2 (27.87 Ma). Ages are reported at ±1σ

3) Preferred age. An asterisk (*) next to a plateau age denotes a weighted average age, as not all criteria for a true plateau age

have been met. See notes.

4) Plateau age is defined by three or more consecutive gas fractions that represent at least 50% of the total gas release and that are

within 2σ of each other (MSWD = Mean Square Weighted Deviation; should be <2.5).

5) Present-day atmospheric 40Ar/36Ar ratio is 295.5

315

Table A11

Integrated Plateau Plateau Isochron Isochron or other Sample Affiliation1 Age (ka)2 Age (ka)3 Information4 Age (ka) Information5 6 of 9 fractions 6 of 9 fractions 39 40 36 25B-1-2 BMVF 2383 ± 46 2426 ± 51 83.1% Ar release 2450 ± 115 Ar/ Ari = 294.8 ± 11.5 MSWD = 0.31 MSWD = 0.34 8 of 11 fractions 8 of 11 fractions 1368 ± 53 26A-1-3 BMVF 1578 ± 48 1373 ± 46* 44.7% 39Ar release 40Ar/36Ar = 296.8 ± 5.9 See note 1 i MSWD = 0.82 MSWD = 0.94 10 of 11 fractions 10 of 11 fractions 39 40 36 26C-1-1 BMVF 908 ± 26 913 ± 28 99.3% Ar release 937 ± 35 Ar/ Ari = 293.8 ± 3.7 MSWD = 1.41 MSWD = 1.49 5 of 8 fractions 5 of 8 fractions 39 40 36 BF-1-3 BMVF 2425 ± 27 2368 ± 26 88.7% Ar release 2332 ± 37 Ar/ Ari = 329 ± 29.6 MSWD = 0.42 MSWD = 0.11 5 of 8 fractions BF-K-2 BMVF 2502 ± 24 2520 ± 25 90.3% 39Ar release See note 2 - MSWD = 0.12 7 of 8 fractions 7 of 8 fractions 39 40 36 C-O-1 BMVF(?) 3939 ± 53 3909 ± 54 99.3% Ar release 3964 ± 97 Ar/ Ari = 290.8 ± 19.0 MSWD = 1.11 MSWD = 1.18 5 of 9 fractions 5 of 9 fractions 39 40 36 CC-2-1 BMVF 2343 ± 43 2216 ± 38 84.8% Ar release 2165 ± 119 Ar/ Ari = 308.1 ± 39.0 MSWD = 1.03 MSWD = 1.24 6 of 8 fractions 6 of 8 fractions 39 40 36 3-2-2 SMVF 1913 ± 34 1936 ± 31 92.6% Ar release 1979 ± 36 Ar/ Ari = 300.1 ± 27.9 MSWD = 0.86 MSWD = 0.97 9 of 10 fractions 9 of 10 fractions 39 40 36 9-1-1 SMVF 1949 ± 14 1949 ± 15 98.8% Ar release 1943 ± 15 Ar/ Ari = 281.5 ± 69.1 MSWD = 1.22 MSWD = 1.33

316

Table A11 continued

Integrated Plateau Plateau Isochron Isochron or other Sample Affiliation1 Age (ka)2 Age (ka)3 Information4 Age (ka) Information5 9 of 10 fractions 9 of 10 fractions 39 40 36 12-2-3 SMVF 1669 ± 15 1659 ± 14 99.3% Ar release 1661 ± 30 Ar/ Ari = 297.2 ± 16.9 MSWD = 0.95 MSWD = 1.06 8 of 12 fractions 8 of 12 fractions 39 40 36 16-6-1 SMVF 1755 ± 16 1772 ± 15 87.7% Ar release 1785 ± 32 Ar/ Ari = 290.0 ± 11.2 MSWD = 0.21 MSWD = 0.20 7 of 10 fractions 7 of 10 fractions 39 40 36 CH-2-1 SMVF 1435 ± 20 1435 ± 19 95.7% Ar release 1464 ± 63 Ar/ Ari = 283.4 ± 29.9 MSWD = 0.30 MSWD = 0.31 7 of 8 fractions CM-4-2 SMVF 1962 ± 21 1958 ± 21 99.6% 39Ar release See note 3 - MSWD = 0.86 9 of 10 fractions 9 of 10 fractions 39 40 36 JH-1-5 SMVF 2187 ± 30 2206 ± 29 98.8% Ar release 2221 ± 85 Ar/ Ari = 294.0 ± 28.1 MSWD = 0.91 MSWD = 1.01 7 of 14 fractions 7 of 14 fractions 39 40 36 SL-1-4 SMVF 2234 ± 21 2178 ± 23 73.9% Ar release 2196 ± 38 Ar/ Ari = 273.8 ± 29.6 MSWD = 0.16 MSWD = 0.88 8 of 10 fractions 8 of 10 fractions 39 40 36 SM-L-1 SMVF 1835 ± 15 1833 ± 14 98.6% Ar release 1848 ± 18 Ar/ Ari = 295.3 ± 11.0 MSWD = 0.88 MSWD = 0.77 7 of 10 fractions 7 of 10 fractions 39 40 36 SM-W-1 SMVF 1667 ± 26 1724 ± 23 95.5% Ar release 1697 ± 35 Ar/ Ari = 298.5 ± 4.9 MSWD = 0.75 MSWD = 0.77

317

Table A11 continued

Integrated Plateau Plateau Isochron Isochron or other Sample Affiliation1 Age (ka)2 Age (ka)3 Information4 Age (ka) Information5 8 of 10 fractions 9 of 10 fractions 39 40 36 TB-1-1 SMVF 1729 ± 17 1740 ± 16 96.5% Ar release 1772 ± 22 Ar/ Ari = 269.8 ± 18.2 MSWD = 1.19 MSWD = 1.00 9 of 10 fractions 9 of 10 fractions 39 40 36 N-1-2 O (AVB) 337 ± 3 333 ± 5 95.7% Ar release 326 ± 6 Ar/ Ari = 298.5 ± 1.9 MSWD = 2.26 MSWD = 1.87 8 of 13 fractions 172898 ± 175960 ± QV-1-1 O (LQ) 94.7% 39Ar release See note 4 --- 1494 2373* MSWD = 2.74 4 of 7 fractions 4 of 7 fractions 39 40 36 X-7 O (LQ) 183 ± 8 174 ± 7 64.5% Ar release 184.5± 60 Ar/ Ari = 292.2 ± 13.6 MSWD = 0.06 MSWD = 0.07 6 of 8 fractions CRD-1-1 O (OLG) 53078 ± 482 54852 ± 684 89.6% 39Ar release See note 5 --- MSWD = 1.74 3 of 10 fractions GR-2-1 O (OLG) 47518 ± 319 50683 ± 477 52.0% 39Ar release See note 6 --- MSWD = 0.76 6 of 8 fractions 51388 ± RT-1-3 O (OLG) 48744 ± 471 75.1% 39Ar release See note 7 --- 968* MSWD = 3.56

318

Note 1: 26A-1-3: Integrated, isochron and weighted average ages are within error, indicating minimum alteration and/or loss.

Note 2: BF-K-2: No isochron age determination was possible because of evidence of loss.

Note 3: CM-4-2: No isochron age determination was possible because of the homogeneous radiogenic content of the release.

Note 4: QV-1-1: No true plateau age was produced (MSWD ≤2.5). Integrated (172.9 ± 1.49 Ma) and the weighted average age

(175.96 ± 2.37 Ma) are not within error. Weighted average age is preferred due to evidence of minor loss in the low

temperature/less retentive step-heat releases. No isochron age determination was possible because of evidence of loss.

Note 5: CRD-1-1: Integrated (53.08 ± 0.48 Ma) and the weighted average age (54.85 ± 0.52 Ma) are broadly within error.

Weighted average age is preferred due to evidence of minor loss in the low temperature/less retentive step-heat

releases. No isochron age determination was possible because of the homogeneous radiogenic content of the release

and evidence of loss.

Note 6: GR-2-1: Integrated age (47.52 ± 0.32 Ma) and plateau age (50.68 ± 0.48 Ma) are not within error. The plateau age is

preferred as the most robust age due to evidence of minor loss in the low temperature/less retentive step-heat releases.

No isochron age determination was possible because of the homogeneous radiogenic content of the release.

Note 7: RT-1-3: No true plateau age was produced (MSWD ≤2.5). Integrated (48.74 ± 0.47 Ma) and the weighted average age

(51.39 ± 0.97 Ma) are not within error. Weighted average age is preferred due to evidence of minor loss in the low

temperature/less retentive step-heat releases. No isochron age determination was possible because of evidence of loss.

319

Tables A12 and Figures A48

Raw data, release spectra for 39Ar, Ca/K and Cl/K ratios and isochrones for 24 homogeneous whole rock separates from the

Satah and Baldface Mountain Volcanic Fields, west-central British Columbia. Steps used in plateau age determination are shaded blue and indicated by beams. Fractions used for isochron age determinations are coloured red.

25B-1-2 BMVF J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 5.14 41.15422 1.69095 0.44827 0.01787 0.0854 0.00358 61.27777 0.82277 0.03281 0.00343 0.00029 15.92938 1.46337 2297.92 210.97 B 600 24.94 34.72898 0.99056 0.63561 0.01842 0.06006 0.00168 50.99398 1.16679 0.03383 0.00334 0.00024 17.01238 0.86161 2454.05 124.2 C 900 43.49 31.7705 0.97339 0.93456 0.02738 0.05074 0.00143 46.99907 1.71593 0.0503 0.00395 0.00023 16.83404 0.8381 2428.34 120.82 D 1500 64.87 29.82783 0.80142 1.30714 0.03613 0.04509 0.00124 44.3535 2.40064 0.06641 0.00447 0.00019 16.59695 0.6838 2394.16 98.57 E 2000 74.67 31.11262 0.59477 1.56383 0.02887 0.0487 0.00132 45.88232 2.87259 0.05309 0.00551 0.00019 16.83997 0.56849 2429.19 81.95 F 2500 83.46 40.6058 0.47147 2.05724 0.02775 0.07935 0.00123 57.37011 3.78024 0.05106 0.00877 0.00022 17.32273 0.49927 2498.78 71.97 G 3000 88.3 65.652 0.72853 3.02769 0.03085 0.1689 0.0046 75.6751 5.5673 0.05685 0.01488 0.00038 15.99678 1.38853 2307.64 200.18 H 5000 95.38 112.7665 1.14122 6.47501 0.06231 0.33455 0.00409 87.21625 11.93534 0.11538 0.0239 0.00033 14.4782 1.13502 2088.7 163.65 I 9000 100 114.8399 1.66306 7.21498 0.11137 0.34017 0.00583 87.03462 13.30629 0.20644 0.02742 0.00073 14.96184 1.60208 2158.43 230.98 Integrated n=9 44.38155 0.40993 1.87669 0.01627 0.09478 0.00088 62.79756 3.44804 0.02993 0.00751 0.00011 16.52188 0.31839 2383.34 46.39

320

Tables A12 and Figures A48 continued

26A-1-3 SMVF J = 1.043e-04 ± 5.854e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 400 14032 107.36815 1.52533 0.10969 0.00227 0.3279 0.00552 90.26026 0.20127 0.00416 0.00082 0.00029 10.45529 1.05637 1965.86 198.52 B 600 37.96 62.15616 0.90609 0.18657 0.00359 0.17905 0.00311 85.13876 0.34238 0.00659 0.0006 0.00017 9.23398 0.61199 1736.33 115.02 C 800 55.37 45.53795 0.65964 0.37189 0.00641 0.12585 0.00232 81.65057 0.68255 0.01178 0.00049 0.00013 8.3527 0.49763 1570.69 93.54 D 1000 67.06 28.1893 0.55839 0.68005 0.01188 0.06966 0.00155 72.90097 1.24839 0.02183 0.00061 0.00011 7.63465 0.53601 1435.72 100.76 E 1250 73.68 17.53347 0.25439 1.07562 0.01697 0.03372 0.00089 56.41518 1.97512 0.03119 0.00058 0.00016 7.6348 0.30567 1435.74 57.46 F 1500 78.28 15.54535 0.21506 1.23198 0.01981 0.02735 0.00113 51.42769 2.26247 0.03641 0.00058 0.00019 7.54288 0.35574 1418.47 66.87 G 2000 83.4 16.92215 0.25756 1.44439 0.02043 0.03309 0.00106 57.18714 2.65296 0.03757 0.00071 0.00013 7.23954 0.33857 1361.44 63.65 H 2500 87.84 14.39875 0.1871 1.69981 0.02472 0.02579 0.00132 52.06244 3.12267 0.04546 0.00126 0.00015 6.89647 0.40219 1296.95 75.61 I 3000 91.12 16.5656 0.17022 1.88676 0.02175 0.03501 0.00198 61.61801 3.46656 0.04001 0.00136 0.0003 6.35529 0.59308 1195.21 111.5 J 5000 97.6 53.87134 1.05949 5.44908 0.10303 0.16027 0.00365 87.12794 10.0369 0.19051 0.0045 0.00028 6.95731 1.13248 1308.39 212.9 K 9000 100 45.81505 0.76678 6.46747 0.10644 0.13183 0.00293 83.91616 11.9214 0.1971 0.00651 0.00033 7.39785 0.84151 1391.2 158.19 Integrated n=11 49.80064 0.27748 1.05329 0.00738 0.14034 0.00103 83.14951 1.93408 0.01357 0.00106 0.00007 8.39289 0.24998 1578.24 47.81

321

Tables A12 and Figures A48 continued

26C-1-1 BMVF J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 0.7 340.784 9.83383 1.78341 0.06029 1.15044 0.04033 99.72243 3.27645 0.11091 0.04812 0.00337 0.94702 10.5073 136.7 1516.6 B 600 10.55 105.741 1.06414 1.04455 0.01729 0.33531 0.00489 93.65035 1.91803 0.03178 0.01811 0.00064 6.71726 1.08587 969.37 156.66 C 800 26.25 43.04634 0.59279 0.57249 0.00794 0.12542 0.00186 86.04426 1.05086 0.01458 0.00813 0.00027 6.00572 0.58002 866.71 83.68 D 1000 39.53 30.18457 0.3636 0.42207 0.00496 0.08257 0.00117 80.798 0.77466 0.00911 0.00486 0.00021 5.79207 0.36578 835.88 52.78 E 1200 50.07 24.31522 0.2214 0.38167 0.00389 0.05912 0.00076 71.80864 0.7005 0.00714 0.0038 0.00023 6.84827 0.2353 988.27 33.95 F 1500 59.98 20.66313 0.12143 0.39832 0.00282 0.04757 0.00091 67.97136 0.73107 0.00517 0.00346 0.00012 6.61047 0.28009 953.96 40.41 G 2000 70.3 17.65713 0.1353 0.47834 0.00576 0.0385 0.00068 64.32005 0.87799 0.01057 0.0033 0.00012 6.29159 0.21944 907.95 31.66 H 2500 78.57 17.52491 0.10611 0.62445 0.0048 0.03759 0.00103 63.20455 1.14629 0.00882 0.00405 0.00016 6.44029 0.311 929.41 44.87 I 3000 85.91 18.86163 0.08745 0.82779 0.00953 0.04203 0.00083 65.58905 1.51977 0.01751 0.00475 0.00016 6.48404 0.25002 935.72 36.07 J 5000 95.57 27.84369 0.15733 2.28339 0.02325 0.07464 0.00079 78.62533 4.19648 0.04279 0.00792 0.00014 5.95476 0.2308 859.36 33.3 K 9000 100 29.83574 0.19846 3.13701 0.02164 0.07887 0.00148 77.32811 5.76876 0.03988 0.01085 0.00022 6.77261 0.44052 977.35 63.55 Integrated n=11 36.85013 0.12758 0.86273 0.0036 0.10357 0.00058 82.92672 1.58396 0.00662 0.00706 0.00009 6.29029 0.17693 907.77 25.65

322

Tables A12 and Figures A48 continued

BF-1-3 BMVF J = 1.043e-04 ± 5.854e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 0.0077 123.49026 1.74866 1.55558 0.02264 0.35687 0.00868 85.31259 2.85742 0.04163 0.03588 0.00104 18.15311 2.54861 3411.87 478.56 B 1000 0.0321 92.83452 1.53642 0.14585 0.00383 0.25754 0.00393 81.99045 0.26764 0.00702 0.05193 0.00095 16.71546 1.33898 3141.9 251.46 C 1500 0.1128 40.82144 0.69531 0.07593 0.00157 0.0887 0.00138 64.23975 0.13933 0.00288 0.04374 0.00079 14.58801 0.5769 2742.32 108.37 D 2000 0.349 16.62932 0.29644 0.06447 0.00104 0.01265 0.00025 22.47823 0.1183 0.0019 0.04064 0.00075 12.86891 0.27136 2419.37 50.98 E 2500 0.5688 13.30987 0.22351 0.05184 0.00093 0.00254 0.0002 5.60861 0.09512 0.00171 0.04221 0.00077 12.5358 0.22528 2356.79 42.33 F 3000 0.7094 13.29446 0.21197 0.0638 0.00109 0.00259 0.00031 5.73213 0.11706 0.00201 0.03764 0.0006 12.50497 0.22464 2351 42.21 G 5000 0.9665 13.27245 0.23979 0.13477 0.00247 0.00272 0.00016 5.98512 0.24731 0.00454 0.02208 0.00046 12.45134 0.23731 2340.92 44.59 H 9000 1 15.0349 0.18577 0.46455 0.00585 0.0087 0.00127 16.88496 0.85267 0.01073 0.01026 0.00029 12.47568 0.41 2345.49 77.03 Integrated n=8 19.15389 0.13966 0.10754 0.00081 0.02111 0.00019 32.56455 0.19734 0.00149 0.03526 0.00029 12.89746 0.12353 2424.74 26.9

323

Tables A12 and Figures A48 continued

BF-K-2 BMVF J = 1.043e-04 ± 5.854e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 0.53 81.87329 1.10288 0.21182 0.00901 0.24566 0.00823 88.67679 0.38871 0.01654 0.01614 0.00139 9.26871 2.34505 1742.86 440.74 B 1000 2.86 37.30029 0.45002 0.11026 0.00321 0.08767 0.00224 69.48552 0.20233 0.00589 0.00336 0.00026 11.37382 0.66944 2138.46 125.79 C 1500 9.69 19.89418 0.22056 0.05031 0.00106 0.0232 0.00067 34.4971 0.09231 0.00195 0.00117 0.00009 13.01228 0.26581 2446.31 49.94 D 2000 21.94 15.96328 0.20823 0.04157 0.00084 0.00861 0.00041 15.94819 0.07627 0.00155 0.0006 0.00006 13.39286 0.22463 2517.81 42.2 E 2500 37.83 14.90545 0.20775 0.0395 0.00067 0.00525 0.00033 10.40765 0.07247 0.00124 0.00045 0.00005 13.32791 0.21915 2505.6 41.17 F 3000 51.34 14.39285 0.18693 0.03848 0.0006 0.00346 0.00031 7.09105 0.07061 0.0011 0.00032 0.00008 13.34501 0.20179 2508.82 37.91 G 5000 79.77 14.40562 0.23905 0.04369 0.00073 0.00333 0.00015 6.82867 0.08016 0.00134 0.0004 0.00006 13.39465 0.23529 2518.14 44.2 H 9000 100 15.00338 0.23976 0.12029 0.00181 0.00495 0.00021 9.69916 0.22074 0.00331 0.00052 0.00006 13.52251 0.23526 2542.16 44.2 Integrated n=8 16.06018 0.10253 0.06045 0.00043 0.00923 0.00013 16.98682 0.11092 0.0008 0.00065 0.00003 13.30798 0.1006 2501.86 23.54

No isochron determination possible

324

Tables A12 and Figures A48 continued

C-0-1 BMVF (?) J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 400 0.71 327.9532 12.87696 4.03756 0.18095 0.92252 0.05211 83.02914 7.42954 0.33392 0.11494 0.00808 55.8106 11.7622 8038.25 1690.3 B 800 7.57 55.90602 1.84719 2.5635 0.08574 0.10747 0.00588 56.45712 4.71221 0.15789 0.06408 0.00252 24.37431 2.09181 3514.97 301.36 C 1200 27.64 33.36803 0.94006 1.37259 0.03987 0.0242 0.00182 21.11141 2.52095 0.0733 0.02864 0.00088 26.32568 0.98806 3796.08 142.33 D 1600 42.55 32.49425 0.53659 0.94575 0.01604 0.01596 0.00219 14.29145 1.73647 0.02946 0.01635 0.00051 27.8435 0.81473 4014.7 117.34 E 2200 0.6023 32.60537 0.40253 0.75804 0.00963 0.01961 0.00195 17.59603 1.39164 0.0177 0.00888 0.00033 26.85804 0.6841 3872.76 98.54 F 3000 74.16 33.46046 0.24796 0.95648 0.00882 0.01855 0.00235 16.1638 1.7562 0.01621 0.00685 0.00042 28.04604 0.72889 4043.87 104.98 G 5000 94.74 38.95101 0.29711 4.55079 0.03428 0.04083 0.00171 30.03401 8.37699 0.0633 0.01451 0.00047 27.31955 0.55291 3939.24 79.64 H 9000 100 51.16937 0.4442 4.98061 0.04817 0.07602 0.00548 43.12451 9.17099 0.08901 0.01661 0.00112 29.18867 1.63777 4208.43 235.86 Integrated n=8 38.84533 0.27184 2.0887 0.01384 0.03963 0.00095 29.72933 3.83814 0.02547 0.01978 0.00027 27.31632 0.35778 3938.77 52.71

325

Tables A12 and Figures A48 continued

CC-2-1 BMVF J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 1.09 292.869 11.40466 1.76868 0.06929 0.87916 0.0305 88.66529 3.24935 0.12746 0.00749 0.00182 33.23401 10.4197 4790.92 1500.08 B 600 11.43 57.16881 1.84429 1.30516 0.03949 0.12496 0.00355 64.43646 2.39701 0.0726 0.00114 0.00029 20.33944 1.54188 2933.59 222.21 C 900 30.37 27.31048 0.92018 1.16209 0.03721 0.03813 0.00124 40.94795 2.13402 0.06839 0.00046 0.00014 16.12311 0.80114 2325.85 115.49 D 1500 65.52 20.17571 0.43211 1.11812 0.03144 0.01809 0.00046 26.07318 2.05321 0.05778 0.00058 0.00008 14.90509 0.35012 2150.25 50.48 E 2000 81.52 20.28103 0.48982 1.26029 0.03133 0.01645 0.00047 23.48891 2.31451 0.05759 0.00134 0.00011 15.50834 0.45233 2237.22 65.21 F 2500 90.63 20.79966 0.52557 1.5237 0.04139 0.01789 0.00062 24.84788 2.79879 0.0761 0.00278 0.00016 15.6259 0.48423 2254.17 69.81 G 3000 96.2 23.04447 0.53317 1.94366 0.04739 0.02844 0.0011 35.82563 3.57124 0.08719 0.00516 0.00021 14.78991 0.53967 2133.64 77.81 H 5000 98.53 47.80002 1.20193 5.91054 0.15704 0.08614 0.00363 52.26238 10.89049 0.29056 0.01903 0.00071 22.90006 1.33359 3302.57 192.15 I 9000 100 27.18712 0.51518 3.07326 0.0637 0.04231 0.00326 45.10671 5.65128 0.11739 0.00817 0.00056 14.94006 1.03683 2155.29 149.49 Integrated n=9 29.31309 0.35241 1.39915 0.01705 0.04459 0.00057 44.59764 2.56978 0.03135 0.00181 0.00007 16.23975 0.29538 2342.67 43.09

326

Tables A12 and Figures A48 continued

3-2-2 SMVF J = 1.043e-04 ± 5.854e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 1.17 73.3992 1.31597 0.6034 0.01667 0.20999 0.01364 84.50498 1.10763 0.03062 0.06667 0.00169 11.37347 4.03141 2138.39 757.52 B 1000 7.44 44.03227 0.37329 0.55787 0.00621 0.12145 0.00408 81.4549 1.02401 0.0114 0.04886 0.00059 8.16354 1.22092 1535.13 229.49 C 1500 14.68 22.14869 0.28093 0.51786 0.00765 0.03955 0.00283 52.63961 0.95055 0.01405 0.0393 0.00051 10.47948 0.85696 1970.4 161.04 D 2000 22.93 15.42394 0.24184 0.55389 0.00959 0.0189 0.00209 35.98841 1.01672 0.01762 0.03218 0.00058 9.85796 0.64789 1853.6 121.76 E 2500 32.59 14.03008 0.15463 0.52053 0.00649 0.01469 0.00203 30.69401 0.95545 0.01192 0.0282 0.00031 9.70668 0.61524 1825.17 115.63 F 3000 43.72 13.43276 0.14097 0.46003 0.00605 0.01191 0.00137 25.96944 0.84437 0.0111 0.0196 0.00034 9.92559 0.4218 1866.31 79.27 G 5000 80.17 13.32211 0.16544 0.5383 0.00666 0.00973 0.00048 21.30616 0.98807 0.01223 0.01529 0.00028 10.46429 0.20322 1967.55 38.19 H 9000 100 14.9022 0.15721 0.81084 0.01002 0.01473 0.00073 28.82663 1.48863 0.01841 0.01168 0.00019 10.59134 0.24769 1991.42 46.55 Integrated n=8 17.15763 0.08938 0.5837 0.00341 0.02371 0.00053 40.62437 1.07146 0.00627 0.02214 0.00015 10.17402 0.16838 1913 33.41

327

Tables A12 and Figures A48 continued

9-1-1 SMVF J = 8.001e-05 ± 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 0.19 29.7398 1.78608 0.11971 0.06147 0.09148 0.03663 90.95061 0.21967 0.11281 0.00779 0.00482 2.68881 10.762 388.08 1553.14 B 600 5.46 15.55271 0.40183 0.01627 0.00243 0.00476 0.00141 9.0568 0.02985 0.00446 0.00088 0.00021 14.11728 0.57034 2036.66 82.23 C 900 33.45 13.64934 0.13129 0.01025 0.0004 0.00133 0.00024 2.87622 0.0188 0.00074 0.00047 0.00005 13.228 0.14825 1908.44 21.38 D 1200 55.21 13.58716 0.06094 0.00766 0.00042 0.00055 0.00039 1.19702 0.01405 0.00077 0.00056 0.00007 13.39524 0.1311 1932.55 18.9 E 1500 68.55 14.00374 0.06353 0.00743 0.00128 0.00095 0.00057 2.0136 0.01364 0.00234 0.00046 0.0001 13.69273 0.1796 1975.45 25.9 F 2000 77.96 13.16196 0.04955 0.03043 0.00095 -0.00147 0.00089 -3.32153 0.05583 0.00175 0.00057 0.00013 13.56875 0.26637 1957.57 38.41 G 2500 84.88 12.93619 0.0503 0.23301 0.00265 -0.00233 0.00135 -5.47816 0.4276 0.00486 0.00156 0.00021 13.61578 0.40173 1964.35 57.93 H 3000 88.94 12.08334 0.10034 0.22138 0.0049 -0.00848 0.00204 -20.9388 0.40626 0.00899 0.00139 0.00039 14.57981 0.61518 2103.35 88.7 I 5000 95.04 12.70193 0.08625 0.44136 0.0039 -0.00243 0.00116 -5.94505 0.8101 0.00716 0.00216 0.0002 13.42979 0.35372 1937.53 51 J 9000 100 12.93689 0.07505 0.1541 0.00288 -0.00159 0.00174 -3.7477 0.28279 0.00528 0.00127 0.00021 13.39237 0.51917 1932.14 74.86 Integrated n=10 13.56207 0.04581 0.06918 0.00048 0.00017 0.00025 0.33713 0.12693 0.00089 0.00079 0.00004 13.48741 0.08716 1945.84 13.71

328

Tables A12 and Figures A48 continued

12-2-3 SMVF J = 8.001e-05 ± 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 0.74 62.65634 0.62596 0.10039 0.01993 0.14133 0.01264 66.67131 0.18422 0.03658 0.01877 0.00135 20.87412 3.73186 3010.64 537.79 B 600 8.9 21.85581 0.38964 0.06103 0.00204 0.03373 0.00104 45.65001 0.11199 0.00374 0.00906 0.00029 11.863 0.42964 1711.6 61.96 C 900 24.26 15.43888 0.24729 0.0394 0.00116 0.01354 0.00064 25.9362 0.0723 0.00213 0.00962 0.00024 11.41294 0.28195 1646.69 40.66 D 1200 42.6 14.87096 0.16555 0.03459 0.00098 0.01235 0.00055 24.56322 0.06347 0.00181 0.01127 0.00018 11.19604 0.21502 1615.41 31.01 E 1500 57.59 14.28552 0.11092 0.03653 0.00115 0.00982 0.00056 20.32681 0.06703 0.00211 0.01196 0.00015 11.35836 0.19046 1638.82 27.47 F 2000 71.05 13.86006 0.06629 0.04196 0.0011 0.00764 0.00062 16.29846 0.07698 0.00202 0.01082 0.00015 11.57656 0.19191 1670.29 27.68 G 2500 84.1 13.83705 0.06599 0.09153 0.00214 0.00695 0.00063 14.81202 0.16796 0.00392 0.00788 0.00011 11.76297 0.19569 1697.17 28.22 H 3000 91.85 14.73758 0.05684 0.17273 0.0037 0.00962 0.00088 19.23732 0.31698 0.0068 0.00521 0.00011 11.87993 0.26587 1714.04 38.34 I 5000 97.62 16.05427 0.09951 0.40421 0.00577 0.01548 0.00139 28.33261 0.74188 0.01059 0.00314 0.00016 11.48767 0.41697 1657.47 60.13 J 9000 100 19.32885 0.18151 0.43565 0.00711 0.0283 0.00352 43.1461 0.7996 0.01305 0.00345 0.00045 10.9757 1.04528 1583.63 150.75 Integrated n=10 15.68783 0.06172 0.08828 0.0007 0.01386 0.00027 26.11524 0.16199 0.00129 0.00937 0.00007 11.5697 0.09597 1669.3 14.61

329

Tables A12 and Figures A48 continued

16-6-1 SMVF J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 0.46 193.502 6.46546 1.79016 0.06902 0.63547 0.02015 96.9825 3.28886 0.12696 0.05728 0.00268 5.84541 6.60034 843.58 952.3 B 600 3.41 60.60315 1.43763 1.80281 0.03908 0.16666 0.00348 81.05829 3.31213 0.0719 0.03117 0.00077 11.48828 1.27554 1657.56 183.95 C 900 13.61 25.13246 0.51854 1.32413 0.02747 0.04402 0.001 51.38609 2.43188 0.0505 0.01221 0.00029 12.21487 0.47658 1762.34 68.73 D 1200 31.18 18.16992 0.2621 0.91553 0.01703 0.01958 0.00039 31.47294 1.68096 0.03129 0.0051 0.00015 12.43901 0.20339 1794.66 29.33 E 1500 48.38 16.68961 0.31156 0.72097 0.01329 0.01516 0.00038 26.52617 1.32355 0.02441 0.00339 0.00012 12.24692 0.28388 1766.96 40.94 F 1800 61.9 16.189 0.18967 0.67524 0.0095 0.01335 0.0003 24.05982 1.23956 0.01745 0.0035 0.00011 12.27726 0.18518 1771.34 26.7 G 2000 72.45 16.24915 0.1745 0.71855 0.00719 0.01352 0.00026 24.25947 1.3191 0.01321 0.00429 0.00012 12.29095 0.1672 1773.31 24.11 H 2200 79.46 16.83265 0.17178 0.80973 0.01093 0.01577 0.00048 27.32967 1.48659 0.02008 0.00572 0.00013 12.21776 0.20069 1762.76 28.94 I 2500 85.54 18.28173 0.19306 0.96679 0.01031 0.02044 0.00034 32.65737 1.77515 0.01895 0.00882 0.00017 12.29981 0.18142 1774.59 26.16 J 3000 91.11 20.93534 0.19217 1.42884 0.01274 0.03022 0.00049 42.15649 2.62437 0.02343 0.01475 0.00025 12.10479 0.2085 1746.47 30.07 K 5000 97.61 31.49042 0.32461 3.93056 0.0359 0.06829 0.00076 63.11521 7.2321 0.06623 0.03468 0.00039 11.63655 0.27969 1678.94 40.34 L 9000 100 43.40051 0.69724 6.83946 0.10309 0.11047 0.00246 73.96994 12.61038 0.191 0.0611 0.00105 11.34428 0.813 1636.79 117.25 Integrated n=12 21.75621 0.11615 1.26349 0.00668 0.03274 0.00022 44.05251 2.3204 0.01228 0.01031 0.00007 12.16631 0.10205 1755.34 15.52

330

Tables A12 and Figures A48 continued

CH-2-1 SMVF J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 0.27 123.1488 5.98207 2.00374 0.13902 0.43121 0.0389 103.3615 3.6818 0.2558 0.05084 0.00947 -4.14448 9.87242 -598.35 1425.54 B 600 2.82 43.73648 0.74298 0.82144 0.0255 0.11964 0.00458 80.73093 1.5081 0.04684 0.03446 0.001 8.42678 1.45338 1215.99 209.65 C 900 14.03 17.21205 0.31692 0.45852 0.00976 0.02502 0.0012 42.80738 0.84159 0.01792 0.01656 0.00045 9.83022 0.41961 1418.42 60.52 D 1200 36.14 13.75993 0.19433 0.36053 0.0064 0.01292 0.00055 27.60004 0.66168 0.01176 0.01182 0.00023 9.94322 0.22926 1434.72 33.07 E 1500 58.55 13.2287 0.17302 0.33085 0.0044 0.01114 0.00057 24.74233 0.60721 0.00807 0.00968 0.00017 9.93559 0.22646 1433.62 32.66 F 2000 75.15 13.87106 0.14786 0.38488 0.00488 0.01276 0.00079 27.00356 0.7064 0.00896 0.00911 0.00023 10.10646 0.26414 1458.26 38.1 G 2500 84.83 14.07323 0.10337 0.4908 0.00479 0.01423 0.00148 29.65963 0.90085 0.0088 0.00799 0.00022 9.88171 0.44531 1425.85 64.23 H 3000 91.94 14.94045 0.09729 0.59149 0.00596 0.01563 0.00152 30.63943 1.08576 0.01095 0.00776 0.00044 10.34651 0.45567 1492.89 65.72 I 5000 98.5 17.09602 0.15184 1.68555 0.02011 0.02646 0.00252 44.9989 3.09644 0.03699 0.01222 0.00049 9.39787 0.74848 1356.06 107.96 J 9000 100 20.40065 0.23526 2.53171 0.03484 0.01824 0.00667 25.43524 4.65366 0.06415 0.01512 0.00108 15.21679 1.98499 2195.19 286.18 Integrated n=10 15.53601 0.07895 0.53373 0.00296 0.01898 0.0004 35.88232 0.9797 0.00543 0.01152 0.00011 9.94604 0.1325 1435.13 19.53

331

Tables A12 and Figures A48 continued

CM-4-2 SMVF J = 1.043e-04 ± 5.854e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 0.37 47.20962 1.23286 0.21783 0.01864 0.10833 0.01002 67.81316 0.39974 0.03422 0.00422 0.00145 15.18806 3.09336 2855.03 581.03 B 1000 4.2 14.70879 0.16577 0.04838 0.00156 0.01272 0.00097 25.57316 0.08877 0.00286 0.00124 0.00015 10.92555 0.31644 2054.23 59.46 C 1500 10.41 11.97969 0.11749 0.03628 0.00132 0.0044 0.00064 10.86154 0.06658 0.00243 0.00086 0.00011 10.65231 0.21893 2002.88 41.14 D 2000 17.76 11.48785 0.11923 0.0327 0.00103 0.00303 0.00056 7.7938 0.05999 0.00188 0.00089 0.00008 10.56537 0.20065 1986.54 37.71 E 2500 26.87 11.19195 0.13412 0.0346 0.00102 0.00246 0.00049 6.48249 0.06349 0.00187 0.00084 0.00006 10.43891 0.19349 1962.78 36.36 F 3000 36.85 10.95635 0.13588 0.05134 0.00117 0.00216 0.00033 5.8016 0.09421 0.00215 0.00083 0.00007 10.2931 0.16309 1935.38 30.65 G 5000 73.5 11.05057 0.19665 0.08779 0.00137 0.00241 0.00013 6.39532 0.16109 0.00252 0.00083 0.00006 10.31669 0.19393 1939.81 36.44 H 9000 100 11.2223 0.18672 0.14374 0.00239 0.00266 0.00019 6.92134 0.26377 0.00438 0.00094 0.00007 10.41898 0.18877 1959.03 35.47 Integrated n=8 11.46454 0.09173 0.08586 0.00076 0.00342 0.00012 8.76504 0.15756 0.00139 0.00089 0.00003 10.43321 0.09416 1961.71 20.84

No isochron determination possible

332

Tables A12 and Figures A48 continued

JH-1-5 SMVF J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 0.19 247.7355 35.76156 1.13449 0.34378 0.89969 0.17196 107.2908 2.0833 0.6318 0.28577 0.04442 -18.07423 33.8315 -2610.9 4890.61 B 600 2.59 51.44472 1.07805 1.01483 0.03544 0.12372 0.00925 70.94477 1.86341 0.06513 0.34612 0.00836 14.94947 2.7207 2156.65 392.26 C 900 12.31 22.92745 0.28167 0.74944 0.01097 0.02657 0.00198 34.01307 1.37584 0.02015 0.20072 0.00244 15.11753 0.63131 2180.88 91.02 D 1200 28.41 20.26436 0.1703 0.62187 0.00728 0.01846 0.0013 26.71205 1.14156 0.01337 0.15152 0.00184 14.83609 0.40958 2140.3 59.05 E 1500 38.78 21.29702 0.18682 0.5664 0.00778 0.02262 0.00192 31.20989 1.03968 0.01429 0.11229 0.00125 14.63567 0.5824 2111.4 83.97 F 2000 49.29 21.41106 0.14993 0.60837 0.00804 0.02233 0.00204 30.62301 1.11675 0.01477 0.07732 0.00087 14.84013 0.61419 2140.88 88.55 G 2500 54.73 20.82169 0.25245 0.62936 0.01368 0.01496 0.00331 21.01193 1.1553 0.02513 0.06138 0.00121 16.43051 0.99949 2370.17 144.09 H 3000 59.26 21.15432 0.2454 0.67583 0.02088 0.01649 0.00477 22.80676 1.24064 0.03835 0.04834 0.00151 16.31458 1.42575 2353.45 205.54 I 5000 85.7 21.39219 0.13099 1.45371 0.01033 0.01992 0.00063 26.98685 2.67009 0.01899 0.02564 0.00042 15.61347 0.21206 2252.38 30.57 J 9000 100 20.82426 0.14454 1.66251 0.01575 0.01864 0.00198 25.83019 3.05406 0.02896 0.0219 0.00049 15.44144 0.59568 2227.58 85.88 Integrated n=10 22.38079 0.06853 1.00921 0.00419 0.02442 0.00067 31.91434 1.85308 0.00769 0.08796 0.00044 15.22876 0.2046 2196.91 30.14

333

Tables A12 and Figures A48 continued

SL-1-4 SMVF J = 1.043e-04 ± 5.854e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 0.61 75.83794 1.81779 0.11795 0.00407 0.22488 0.00568 87.64588 0.21644 0.00747 0.00151 0.00052 9.36622 1.91054 1761.18 359.07 B 1000 7.15 13.96555 0.3684 0.05774 0.00168 0.00851 0.00035 18.01098 0.10595 0.00308 0.00043 0.00007 11.42633 0.34686 2148.33 65.18 C 1500 23.81 12.43714 0.20518 0.04421 0.00085 0.00293 0.00012 6.95239 0.08113 0.00155 0.00029 0.00005 11.54519 0.19558 2170.66 36.75 D 1750 36.3 12.14838 0.29619 0.03874 0.00095 0.00181 0.00013 4.39897 0.07108 0.00174 0.00031 0.00006 11.5859 0.29202 2178.31 54.87 E 2000 47.79 12.13486 0.29406 0.03728 0.00094 0.00199 0.00012 4.83648 0.06841 0.00172 0.00025 0.00007 11.52 0.28864 2165.93 54.24 F 2250 58.54 12.16788 0.28783 0.03643 0.00091 0.0018 0.00013 4.34533 0.06684 0.00166 0.00028 0.00006 11.61104 0.28385 2183.03 53.33 G 2500 67.53 12.32329 0.28995 0.03701 0.00089 0.00211 0.00016 5.03683 0.06791 0.00164 0.00029 0.00006 11.67469 0.28645 2194.99 53.82 H 2750 74.51 12.60124 0.28584 0.03834 0.00088 0.00264 0.00017 6.17843 0.07034 0.00161 0.00037 0.00007 11.79514 0.28107 2217.63 52.81 I 3000 80.73 13.04038 0.29386 0.0428 0.00106 0.00335 0.00021 7.57891 0.07853 0.00194 0.00044 0.00008 12.02497 0.28876 2260.81 54.26 J 3500 87.24 14.12553 0.32644 0.08699 0.00197 0.00582 0.00029 12.14838 0.15963 0.00362 0.00051 0.00008 12.38418 0.31786 2328.3 59.72 K 4000 92.74 15.91215 0.37579 0.14915 0.00321 0.01006 0.00039 18.64547 0.2737 0.0059 0.00057 0.00009 12.92246 0.35608 2429.43 66.9 L 4500 96.45 17.12551 0.3588 0.2354 0.00505 0.0125 0.00043 21.488 0.43199 0.00926 0.00061 0.00008 13.4245 0.33989 2523.75 63.85 M 5000 98.73 18.05817 0.34627 0.24924 0.00521 0.0144 0.00078 23.48985 0.4574 0.00956 0.0008 0.00013 13.79604 0.38161 2593.55 71.69 N 9000 100 30.83881 0.59465 0.49384 0.01112 0.05447 0.00166 52.11264 0.90645 0.02042 0.00105 0.00017 14.75882 0.63704 2774.4 119.66 Integrated n=14 13.70238 0.09253 0.06813 0.00047 0.00607 0.00007 13.08289 0.12501 0.00087 0.00038 0.00002 11.88447 0.08758 2234.41 20.69

334

Tables A12 and Figures A48 continued

SM-L-1 SMVF J = 8.001e-05 ± 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 0.1 380.3909 13.6041 0.12423 0.08123 1.26381 0.09012 98.18207 0.22797 0.14906 -0.0032 0.00896 6.91531 24.2319 997.94 3495.91 B 600 1.41 69.37868 2.33783 0.1159 0.00883 0.18667 0.00972 79.52574 0.21267 0.0162 0.00405 0.00111 14.19985 2.836 2048.57 408.91 C 900 13.25 16.80731 0.35747 0.03648 0.00109 0.01439 0.00068 25.32293 0.06694 0.00199 0.00059 0.00012 12.52935 0.36765 1807.69 53.02 D 1200 44.87 13.22913 0.15911 0.02404 0.00042 0.0025 0.00019 5.58042 0.04411 0.00076 0.00034 0.00006 12.46305 0.16417 1798.13 23.67 E 1500 62.58 13.08887 0.11661 0.02204 0.00089 0.00086 0.00039 1.93964 0.04045 0.00163 0.00034 0.00007 12.80607 0.16298 1847.59 23.5 F 2000 74.12 13.55606 0.12705 0.02814 0.00113 0.00225 0.00048 4.90311 0.05164 0.00208 0.0006 0.00009 12.8634 0.18797 1855.86 27.11 G 2500 78.99 13.1021 0.08715 0.07308 0.00161 0.00131 0.0013 2.91735 0.1341 0.00295 0.00105 0.00026 12.69169 0.39369 1831.1 56.77 H 3000 83.96 13.46118 0.07229 0.18358 0.00277 0.00136 0.00151 2.87064 0.33689 0.00508 0.00239 0.0002 13.0476 0.45218 1882.42 65.2 I 5000 97.02 13.82368 0.05115 0.20747 0.00184 0.00328 0.00064 6.9102 0.38073 0.00337 0.00237 0.00012 12.84267 0.19451 1852.87 28.05 J 9000 100 12.42914 0.07042 0.18709 0.00355 -0.00388 0.00233 -9.36966 0.34333 0.00652 0.00174 0.00038 13.56302 0.69095 1956.74 99.63 Integrated n=10 14.83897 0.07512 0.06608 0.00048 0.0071 0.00024 14.12911 0.12125 0.00087 0.00089 0.00004 12.71745 0.09945 1834.81 15.24

335

Tables A12 and Figures A48 continued

SM-W-1 SMVF J = 8.001e-05 ± 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 0.07 1337.483 255.3334 0.88617 0.40552 4.96006 1.00015 109.5832 1.62701 0.74501 0.04011 0.027 -128.2509 98.7029 -18608 14395.36 B 600 0.53 409.1827 10.00932 0.63715 0.04834 1.45265 0.05127 104.9008 1.16961 0.08878 0.01058 0.00537 -20.06093 11.3593 -2898.1 1642.34 C 900 4.46 59.43725 0.67689 0.41989 0.00888 0.17363 0.00478 86.30495 0.77068 0.01631 0.00345 0.0004 8.13831 1.37218 1174.37 197.94 D 1200 21.26 17.64284 0.09147 0.27853 0.00293 0.01924 0.00106 32.1451 0.51116 0.00537 0.00156 0.00011 11.95373 0.32026 1724.68 46.18 E 1500 41.25 14.81014 0.10485 0.23672 0.00437 0.0096 0.0009 19.06285 0.43443 0.00803 0.00124 0.00015 11.96487 0.28174 1726.29 40.63 F 2000 63.64 25.3411 0.1952 0.22716 0.00252 0.04672 0.00084 54.46582 0.41687 0.00463 0.00154 0.00011 11.52719 0.27432 1663.17 39.56 G 2500 78.96 28.42371 0.24303 0.24533 0.003 0.05653 0.00134 58.76369 0.45023 0.0055 0.00238 0.00021 11.71067 0.40655 1689.63 58.63 H 3000 86.93 34.822 0.31247 0.33539 0.00473 0.07563 0.00235 64.152 0.61554 0.00868 0.00532 0.00023 12.4753 0.69257 1799.9 99.87 I 5000 96.48 39.14992 0.25519 1.26151 0.01246 0.0904 0.00205 68.01888 2.31677 0.02291 0.01954 0.00038 12.52225 0.61377 1806.67 88.51 J 9000 100 70.55208 0.78223 2.4914 0.03335 0.1963 0.00475 81.96117 4.57943 0.06142 0.03343 0.00077 12.74385 1.29221 1838.62 186.34 Integrated n=10 30.07393 0.08605 0.43859 0.00206 0.0627 0.0006 61.54803 0.805 0.00379 0.00491 0.00008 11.55618 0.17844 1667.35 26.16

336

Tables A12 and Figures A48 continued

TB-1-1 SMVF J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 2.11 205.33158 2.77222 0.36443 0.00693 0.2976 0.00419 42.82013 0.66885 0.01273 0.00545 0.0005 117.4216 2.57577 21956.06 478.71 B 1000 10.42 289.70686 5.15927 0.47792 0.0061 0.22152 0.00323 22.58334 0.87721 0.01121 0.00288 0.00021 224.3341 4.8873 41717.31 898.42 C 1500 22.58 306.41259 5.35304 0.53194 0.00628 0.03024 0.00078 2.90257 0.9764 0.01152 0.00148 0.00009 297.6017 5.31708 55135.85 970.18 D 2000 37.38 305.7998 5.29342 0.44375 0.00492 0.00654 0.00055 0.62019 0.81447 0.00903 0.00132 0.00006 303.969 5.28927 56297.29 964.48 E 2500 54.87 301.01229 5.31193 0.35048 0.00451 0.00459 0.00036 0.44105 0.64324 0.00828 0.00149 0.00008 299.7293 5.30783 55524.02 968.28 F 3000 71.82 294.96694 5.26311 0.30131 0.00412 0.00421 0.00038 0.4129 0.55297 0.00756 0.00192 0.00008 293.782 5.25904 54438.75 959.96 G 5000 95.89 292.49514 5.11985 0.31308 0.00381 0.00434 0.0004 0.42927 0.57458 0.007 0.00399 0.00007 291.2744 5.11644 53980.97 934.17 H 9000 100 286.84831 5.12353 0.43063 0.0068 0.00756 0.00223 0.76645 0.79039 0.01249 0.00789 0.00026 284.7069 5.15578 52781.46 941.98 I 5000 95.89 292.49514 5.11985 0.31308 0.00381 0.00434 0.0004 0.42927 0.57458 0.007 0.00399 0.00007 291.2744 5.11644 53980.97 934.17 J 9000 100 286.84831 5.12353 0.43063 0.0068 0.00756 0.00223 0.76645 0.79039 0.01249 0.00789 0.00026 284.7069 5.15578 52781.46 941.98 Integrated n=10 295.76549 2.10585 0.3832 0.00189 0.03221 0.00032 3.20741 0.70331 0.00347 0.0026 0.00004 286.3278 2.08922 53077.59 481.53

337

Tables A12 and Figures A48 continued

N-1-2 AVB J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 400 4.34 59.3993 0.2497 0.32439 0.00248 0.19132 0.0012 95.17894 0.59535 0.00456 0.03496 0.0003 2.8629 0.28944 413.21 41.77 B 600 15.46 19.64212 0.05595 0.32655 0.00143 0.05822 0.00025 87.58951 0.59931 0.00262 0.02553 0.0001 2.43456 0.0667 351.39 9.63 C 800 30.66 10.02134 0.04121 0.27043 0.00168 0.02575 0.00017 75.92622 0.4963 0.00308 0.02058 0.00015 2.40583 0.04505 347.24 6.5 D 1000 45.3 7.03863 0.02235 0.2527 0.00126 0.01598 0.00014 67.0834 0.46376 0.00232 0.0187 0.00011 2.30751 0.04292 333.06 6.19 E 1200 57.39 5.16117 0.02401 0.27238 0.0025 0.00968 0.00016 55.31726 0.49988 0.00459 0.01785 0.00017 2.29332 0.04918 331.01 7.1 F 1600 70.84 4.94883 0.01812 0.31734 0.00184 0.00886 0.00013 52.70967 0.5824 0.00337 0.01691 0.00014 2.3268 0.04094 335.84 5.91 G 2200 82.25 5.45453 0.02168 0.43601 0.00286 0.01087 0.00011 58.56525 0.80026 0.00526 0.01597 0.00011 2.24846 0.03522 324.53 5.08 H 3000 89.76 6.86116 0.0194 0.91624 0.00501 0.01562 0.0003 66.45193 1.68226 0.0092 0.01861 0.00014 2.29331 0.0883 331.01 12.74 I 5000 96.21 10.55816 0.09127 3.67164 0.03012 0.02985 0.00037 80.91306 6.75448 0.05556 0.04348 0.00039 2.0148 0.11621 290.81 16.77 J 9000 100 10.20048 0.12901 3.82769 0.04522 0.02793 0.00047 78.03895 7.04232 0.08343 0.04676 0.00066 2.23968 0.15953 323.27 23.02 Integrated n=10 10.81132 0.01493 0.70522 0.00209 0.02879 0.00008 78.3782 1.29463 0.00385 0.02245 0.00006 2.33235 0.02276 336.64 3.42

338

Tables A12 and Figures A48 continued

QV-1-1 O (LQ) J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 250 0.24 595.4153 324.5183 -0.4166 2.11784 1.6149 1.03629 80.15592 -0.76417 3.88367 -0.0508 0.07723 118.114 176.483 16969.55 25236.54 B 500 0.71 669.4562 221.4569 -0.09927 0.97442 0.5201 0.35243 22.95949 -0.18214 1.78768 -0.0382 0.04408 515.6934 193.475 72944.91 26821.24 C 750 1.68 543.6692 97.55011 1.38535 0.59548 0.20675 0.16861 11.21701 2.54441 1.09477 -0.0115 0.02604 483.1321 99.5324 68425.32 13832.66 D 1000 3.07 946.7 119.9401 1.32008 0.42556 0.26877 0.12349 8.37819 2.42443 0.78231 0.00968 0.01836 868.1658 115.606 121157.7 15603.66 E 1250 5.28 1215.534 119.442 0.43157 0.28675 0.31654 0.08601 7.69251 0.79212 0.52647 0.0047 0.00881 1122.343 112.887 155142.6 14952.31 F 1500 8.36 1291.008 59.76619 0.56881 0.15484 0.18645 0.05136 4.2642 1.04411 0.28435 0.00249 0.00673 1236.425 59.2279 170190.3 7779.82 G 2000 19.98 1319.705 25.27461 0.33549 0.04534 0.06638 0.01728 1.48424 0.61573 0.08324 0.00151 0.00181 1300.397 25.4372 178573.7 3325.79 H 2500 56.79 1246.876 14.67098 0.53864 0.01532 0.01959 0.00448 0.46066 0.98871 0.02813 0.00183 0.00101 1241.575 14.6761 170866.6 1927.03 I 3000 70.91 1273.33 31.5614 2.7008 0.08257 0.04176 0.01296 0.95163 4.96507 0.15208 0.01932 0.00207 1263.594 31.6173 173755.5 4144.86 J 3500 79.62 1392.733 32.92359 5.82621 0.17672 0.0903 0.01591 1.88138 10.73446 0.32694 0.07579 0.00333 1372.148 32.917 187930.5 4281.47 K 4000 87.62 1371.596 40.81783 4.39954 0.15446 0.10515 0.02113 2.23892 8.09772 0.28517 0.07079 0.00488 1345.037 40.6503 184400.8 5297.69 L 5000 96.98 1309.716 34.08953 3.66567 0.11817 0.05752 0.01629 1.27474 6.74345 0.21795 0.04909 0.00237 1296.347 34.1839 178044.1 4470.68 M 9000 100 1340.219 80.44006 7.66169 0.55055 0.10938 0.04259 2.3647 14.13463 1.02121 0.0531 0.0089 1315.616 80.4099 180562.5 10501.61 Integrated n=13 1275.891 10.83522 2.11281 0.0293 0.07059 0.0058 1.62124 3.8825 0.05393 0.02194 0.00093 1257.052 10.8308 172897.8 1494.28

No isochron determination possible

339

Tables A12 and Figures A48 continued

X-7 O (LQ) J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 6.99 25.7604 0.30327 0.56366 0.00901 0.0843 0.00125 96.63569 1.03465 0.01654 0.13168 0.00186 0.86601 0.3739 125 53.97 B 1000 26.11 11.53021 0.05131 0.3593 0.00339 0.03494 0.00028 89.52766 0.65944 0.00622 0.10565 0.00056 1.20468 0.08133 173.89 11.74 C 1500 41.66 9.18929 0.05716 0.3531 0.00287 0.02696 0.00028 86.65809 0.64805 0.00527 0.0847 0.00051 1.22237 0.08707 176.44 12.57 D 2000 54.72 9.60213 0.10002 0.45803 0.00555 0.02837 0.00028 87.17302 0.8407 0.01018 0.065 0.00072 1.22825 0.08534 177.29 12.32 E 3000 71.48 9.86346 0.12187 1.15214 0.01304 0.02963 0.00038 88.08128 2.11574 0.02397 0.05026 0.00063 1.17302 0.12349 169.32 17.82 F 5000 93.1 9.27437 0.15558 2.91978 0.04704 0.02735 0.00051 84.81165 5.36847 0.08667 0.05267 0.00086 1.40702 0.16663 203.09 24.05 G 9000 100 9.67764 0.25978 2.88909 0.07498 0.0272 0.00069 80.83342 5.31193 0.13815 0.05253 0.00148 1.85297 0.22452 267.45 32.4 Integrated n=7 11.01326 0.05321 1.24732 0.0093 0.03322 0.00018 88.44762 2.29069 0.01709 0.0745 0.00035 1.26998 0.05652 183.31 8.17

340

Tables A12 and Figures A48 continued

CRD-1-1 O (OLG?) J = 1.043e-04 ± 5.854e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 2.11 205.33158 2.77222 0.36443 0.00693 0.2976 0.00419 42.82013 0.66885 0.01273 0.00545 0.0005 117.4216 2.57577 21956.06 478.71 B 1000 10.42 289.70686 5.15927 0.47792 0.0061 0.22152 0.00323 22.58334 0.87721 0.01121 0.00288 0.00021 224.3341 4.8873 41717.31 898.42 C 1500 22.58 306.41259 5.35304 0.53194 0.00628 0.03024 0.00078 2.90257 0.9764 0.01152 0.00148 0.00009 297.6017 5.31708 55135.85 970.18 D 2000 37.38 305.7998 5.29342 0.44375 0.00492 0.00654 0.00055 0.62019 0.81447 0.00903 0.00132 0.00006 303.969 5.28927 56297.29 964.48 E 2500 54.87 301.01229 5.31193 0.35048 0.00451 0.00459 0.00036 0.44105 0.64324 0.00828 0.00149 0.00008 299.7293 5.30783 55524.02 968.28 F 3000 71.82 294.96694 5.26311 0.30131 0.00412 0.00421 0.00038 0.4129 0.55297 0.00756 0.00192 0.00008 293.782 5.25904 54438.75 959.96 G 5000 95.89 292.49514 5.11985 0.31308 0.00381 0.00434 0.0004 0.42927 0.57458 0.007 0.00399 0.00007 291.2744 5.11644 53980.97 934.17 H 9000 100 286.84831 5.12353 0.43063 0.0068 0.00756 0.00223 0.76645 0.79039 0.01249 0.00789 0.00026 284.7069 5.15578 52781.46 941.98 Integrated n=8 295.76549 2.10585 0.3832 0.00189 0.03221 0.00032 3.20741 0.70331 0.00347 0.0026 0.00004 286.3278 2.08922 53077.59 481.53

No isochron determination possible

341

Tables A12 and Figures A48 continued

GR-2-1 OLG J = 8.001e-05 +/- 2.250e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 300 1.33 116.947 2.70835 0.53199 0.01544 0.24752 0.00954 62.5205 0.9765 0.02836 0.00598 0.00112 43.83648 3.18645 6316.67 458.35 B 600 4.50 199.8668 5.16298 0.46145 0.01168 0.12807 0.00449 18.91832 0.84697 0.02145 0.00267 0.00051 162.0841 4.75728 23246.22 677.92 C 900 10.99 311.9791 5.54725 0.34606 0.00507 0.06184 0.00126 5.84889 0.63512 0.00931 0.00202 0.00023 293.7756 5.47914 41915.42 772.74 D 1200 22.16 337.757 5.32963 0.24603 0.00293 0.02184 0.00065 1.90532 0.45151 0.00537 0.00158 0.00013 331.3501 5.32845 47206.92 749.29 E 1500 34.45 341.1708 5.33342 0.22999 0.0019 0.01429 0.0006 1.23193 0.42207 0.00348 0.0017 0.00016 336.9932 5.33476 48000.28 749.85 F 2000 49.28 359.9047 5.66207 0.2171 0.00178 0.0089 0.00059 0.72617 0.39842 0.00326 0.00266 0.00012 357.3165 5.66355 50854.63 794.8 G 2500 68.21 361.4521 5.63088 0.18608 0.00188 0.00415 0.00039 0.33538 0.34148 0.00345 0.00293 0.00011 360.2576 5.6322 51267.33 790.22 H 3000 86.41 353.4379 5.51496 0.1713 0.00197 0.00913 0.00045 0.75908 0.31435 0.00362 0.00411 0.0001 350.768 5.51573 49935.41 774.45 I 5000 97.26 377.5302 5.9292 0.1982 0.00333 0.1401 0.0013 10.96252 0.36372 0.00611 0.01551 0.00031 336.1639 5.91219 47883.71 831.06 J 9000 100 490.2333 8.38032 0.22159 0.00703 0.56542 0.00691 34.08028 0.40666 0.01291 0.03105 0.00079 323.1914 8.09191 46059.28 1138.61 Integrated n=10 348.3095 2.07121 0.22609 0.00093 0.05005 0.00033 4.24157 0.41491 0.0017 0.00491 0.00006 333.5605 2.06856 47517.71 319.34

No isochron determination possible

342

Tables A12 and Figures A48 continued

RT-1-3 O (OLG?) J = 1.043e-04 ± 5.854e-07 Power Cumulative Atm. Age ± 1σ ID 40Ar/39Ar ± 37Ar/39Ar ± 36Ar/39Ar ± 40 Ca/K ± Cl/K ± 40Ar*/39K ± (mW) 39Ar (%) Ar (ka) (ka) (%) A 500 5.91 448.67225 7.22016 0.28171 0.00431 1.01847 0.01501 67.07658 0.51699 0.00791 0.03215 0.00103 147.7379 5.89892 27581.62 1092.91 B 1000 24.91 493.42887 6.63347 0.38308 0.00397 0.85369 0.00815 51.12142 0.70309 0.00729 0.03712 0.00067 241.2318 5.9224 44820.89 1086.83 C 1500 50.64 419.51064 5.49167 0.68129 0.00614 0.49763 0.00466 35.04147 1.25067 0.01128 0.03033 0.00049 272.6198 5.09164 50571.77 931.4 D 2000 72.45 350.61388 4.55641 0.94208 0.00917 0.23852 0.00256 20.0819 1.72973 0.01684 0.01909 0.00029 280.3668 4.36182 51988.33 797.27 E 2500 84.42 319.07359 4.59154 1.01128 0.01188 0.12367 0.00158 11.4283 1.85689 0.02184 0.01101 0.00019 282.7846 4.39878 52430.22 803.83 F 3000 92.49 303.84661 4.21589 1.11497 0.01365 0.08164 0.00143 7.91037 2.04743 0.02509 0.00885 0.00023 280.0044 4.11773 51922.1 752.68 G 5000 98.98 288.16377 4.04764 2.07425 0.02523 0.0578 0.00177 5.86878 3.81155 0.04643 0.0137 0.00029 271.6221 3.99854 50389.24 731.52 H 9000 100 283.50638 3.0451 4.70318 0.0599 0.06939 0.0072 7.09634 8.65845 0.11065 0.0182 0.00074 264.238 3.64167 49037.85 666.73 Integrated n=8 388.96499 2.26106 0.86413 0.00372 0.42821 0.00196 32.51535 1.58653 0.00683 0.02403 0.0002 262.6319 2.1101 48743.78 471.37

No isochron determination possible

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