Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
DSpace
UBCV
Harris, Martin Alexander
Master of Science - MSc
University of British Columbia
The focus of this thesis is Cracked Mountain Volcano, located in the Garibaldi volcanic belt (GVB), of southwestern British Columbia, Canada. This study investigates the physical and petrochemical evolution of Cracked Mountain. Field mapping, lithostratigraphy, petrography, geochemistry, and thermodynamics were used to model: i) the eruptive sequence, style, duration, and paleoenvironment, ii) the causes of petrochemical variation and the P-T-H2O contents for the Cracked Mountain magmas. The major findings show that Cracked Mountain has a glaciovolcanic origin. We find lapilli tuffs consistent with a phreatomagmatic (i.e. explosive) origin, followed by intrusions (dykes, peperites) and effusions (pillows, sheet-lavas), indicating a transitional eruptive style. Paleomagnetic directions record a single-pole direction (i.e. monogenetic eruption). The edifice morphology indicates syn-eruptive confinement by a paleo-ice sheet that was  850 m thick, capable of holding a ‘leaky’ paleolake system with a maximum of ~0.36 km3 of water. The glaciovolcanic (40Ar/39Ar) age of ~400 ka represents an important record of the Cordilleran Ice sheet (CIS) in southwestern BC during the mid-Pleistocene. Petrographically, Cracked Mountain volcanic rocks comprise two unique suites: i) an olivine-plagioclase phyric (OP) assemblage and ii) an olivine-plagioclase-augite phyric (OPA) assemblage. Thermodynamic modeling based on Rhyolite-MELTS (Gualda and Ghiorso, 2015) reveals that these differences in phenocryst assemblage require distinct storage conditions before the eruption. OP magma must have been stored at depths less than 6 km (<2 kbar) and temperatures of 1240-1155 ̊ C. In contrast, OPA magmas crystallized at depths between 7-9 km (~2-2.5 kbar) at 1250-1150 ̊ C. Both magmas contained ≤ 0.5 H2O wt.% in their respective systems. Incompatible elements show no significant chemical differences between the two petrographic suites, indicating a singular melt source. Detailed analysis of variations in major element compositions with Pearce Element Ratios (PER) suggests that the two distinct petrographic assemblages (OP and OPA) can be explained by crystal fractionation within different systems before the eruption. Subsequent mixing likely occurred during transport and eruption. Cracked Mountain provides clear evidence for a single eruption tapping multiple magma chambers stored at different crustal depths thereby indirectly informing on the connectivity of crustal stored magmas in the Garibaldi volcanic belt.
PHYSICAL AND CHEMICAL EVOLUTION OF CRACKED MOUNTAIN GLACIOVOLCANO, SW BRITISH COLUMBIA by Martin Alexander Harris B.Sc., The University of Oregon, 2017 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Geological Sciences) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) December 2021 © Martin Alexander Harris, 2021 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the thesis entitled: PHYSICAL AND CHEMICAL EVOLUTION OF CRACKED MOUNTAIN GLACIOVOLCANO, SW BRITISH COLUMBIA Submitted by Martin Alexander Harris in partial fulfillment of the requirements for the degree of Master of Science in Geological Sciences. Examining Committee: James K. Russell, Professor, Department of Earth, Ocean, and Atmospheric Sciences, UBC Supervisor Dominique Weis, Professor, Department of Earth, Ocean, and Atmospheric Sciences, UBC Supervisory Committee Member Lucy Porritt, Lecturer and Research Associate, Department of Earth, Ocean, and Atmospheric Sciences, UBC Supervisory Committee Member Lee Groat, Professor, Department of Earth, Ocean, and Atmospheric Sciences, UBC Additional Examiner iii Abstract The focus of this thesis is Cracked Mountain Volcano, located in the Garibaldi volcanic belt (GVB), of southwestern British Columbia, Canada. This study investigates the physical and petrochemical evolution of Cracked Mountain. Field mapping, lithostratigraphy, petrography, geochemistry, and thermodynamics were used to model: i) the eruptive sequence, style, duration, and paleoenvironment, ii) the causes of petrochemical variation and the P-T-H2O contents for the Cracked Mountain magmas. The major findings show that Cracked Mountain has a glaciovolcanic origin. We find lapilli tuffs consistent with a phreatomagmatic (i.e. explosive) origin, followed by intrusions (dykes, peperites) and effusions (pillows, sheet-lavas), indicating a transitional eruptive style. Paleomagnetic directions record a single-pole direction (i.e. monogenetic eruption). The edifice morphology indicates syn-eruptive confinement by a paleo-ice sheet that was  850 m thick, capable of holding a ‘leaky’ paleolake system with a maximum of ~0.36 km3 of water. The glaciovolcanic (40Ar/39Ar) age of ~400 ka represents an important record of the Cordilleran Ice sheet (CIS) in southwestern BC during the mid-Pleistocene. Petrographically, Cracked Mountain volcanic rocks comprise two unique suites: i) an olivine-plagioclase phyric (OP) assemblage and ii) an olivine-plagioclase-augite phyric (OPA) assemblage. Thermodynamic modeling based on Rhyolite-MELTS (Gualda and Ghiorso, 2015) reveals that these differences in phenocryst assemblage require distinct storage conditions before the eruption. OP magma must have been stored at depths less than 6 km (<2 kbar) and temperatures of 1240-1155 ̊ C. In contrast, OPA magmas crystallized at depths between 7-9 km (~2-2.5 kbar) at 1250-1150 ̊ C. Both magmas contained ≤ 0.5 H2O wt.% in their respective systems. Incompatible elements show no significant chemical differences between the two petrographic suites, indicating a singular melt source. Detailed analysis of variations in major element compositions with Pearce Element Ratios (PER) suggests that the two distinct petrographic assemblages (OP and OPA) can be explained by crystal fractionation within different systems before the eruption. Subsequent mixing likely occurred during transport and eruption. Cracked Mountain provides clear evidence for a single eruption tapping multiple magma chambers stored at different crustal depths thereby indirectly informing on the connectivity of crustal stored magmas in the Garibaldi volcanic belt. iv Lay Summary Glaciovolcanism is the interaction between volcanoes and glaciers. Southwestern British Columbia (SWBC) hosts an active volcanic system known as the Garibaldi volcanic belt. Over the past 1 million years, cycles of continental-scale ice sheets have advanced and retreated across SWBC. However, each subsequent glacial cycle destroys much of the evidence of a past cycle. In this thesis, a particular volcano called Cracked Mountain is studied in detail due to its glaciovolcanic origin. From the shape, thickness, rock types, and eruptive age, we recover the paleo ice dimensions in the localized area of SWBC at the exact time of the eruption. Additionally, we investigate the mineral and chemical data of the Cracked Mountain rocks, which provide a window into the magma chamber conditions for this volcano. A key finding of this thesis is that a thick ice sheet (~850 m) covered part of SWBC ~400 thousand years ago. v Preface This thesis comprises an introduction, a conclusion, and two research chapters. The latter are presented in a manuscript format for publication in peer-reviewed international geoscience journals. Chapter 2 has already been submitted, while Chapter 3 is a draft manuscript being prepared for submission. Both manuscripts are co-authored by my supervisor, Dr. Kelly Russell who guided my research focus and provided editorial feedback. Chapter 2 includes several other co-authors that provided expertise in topics relevant to the research. I have included a list of contributions from each of these co-authors below. Both research chapters in this thesis are designed as stand-alone manuscripts, but they are linked by a common theme of focusing on Cracked Mountain eruptive processes. In both chapters, I use the presence of glaciovolcanic deposits as my evidence to present the full eruptive story. The chapters are meant to build on each other, but due to overlap in the study setting, some background and introductory information are repeated. A version of Chapter 2 has been submitted to an international journal and is currently under review as Harris, M., Russell J.K., Barendregt, R., Porritt., L.A., Wilson, A. Explosive Glaciovolcanism at Cracked Mountain Volcano, Garibaldi Volcanic Belt, Canada. I conducted the field mapping, lithostratigraphy, geochemical, petrographic analyses, supported and guided by Dr. Russell. The writing is all my original work, and the co-authors were used to guide my interpretations based on their expertise. Dr. Barendregt was involved in paleomagnetic sampling in the field and subsequent analyses at the University of Lethbridge. Discussions with Dr. Barendregt were extremely insightful and he was heavily involved in the interpretation of paleomagnetic data. Dr. Porritt assisted in the field and aided my interpretations of the fragmental lithofacies present at Cracked Mountain. Dr. Wilson provided much of the background information for Cracked Mountain, including preliminary maps, hand samples, thin sections, and major and trace elemental geochemistry. All co-authors were involved in the editorial process before manuscript submission. vi Table of Contents Abstract ......................................................................................................................................... iii Lay Summary ............................................................................................................................... iv Preface .............................................................................................................................................v Table of Contents ......................................................................................................................... vi List of Tables ..................................................................................................................................x List of Figures .............................................................................................................................. xii Acknowledgements .................................................................................................................... xiv Chapter 1: Introduction ................................................................................................................1 1.1 Importance of Glaciovolcanism ...................................................................................... 2 1.2 Research Goals................................................................................................................ 2 1.3 Scope of Thesis and Outline ........................................................................................... 3 1.3.1 Physical Volcanology of Cracked Mountain .............................................................. 4 1.3.2 Petrological and Chemical Volcanology of Cracked Mountain ................................. 5 1.3.3 Conclusions and Implications of Study ...................................................................... 5 Chapter 2: Explosive Glaciovolcanism at Cracked Mountain Volcano, Garibaldi Volcanic Belt, Canada ...................................................................................................................................7 2.1 Introduction ..................................................................................................................... 7 2.2 Geological Background .................................................................................................. 9 2.3 Cracked Mountain Physiography and Morphology ...................................................... 10 2.4 Volcanic Lithofacies ..................................................................................................... 12 2.4.1 Volcaniclastic ............................................................................................................ 12 vii 2.4.2 Coherent .................................................................................................................... 20 2.5 Lithofacies Associations ............................................................................................... 24 2.5.1 Lithofacies Associations A ....................................................................................... 25 2.5.2 Lithofacies Associations B ....................................................................................... 27 2.5.3 Lithofacies Associations C ....................................................................................... 29 2.5.4 Lithofacies Associations D ....................................................................................... 29 2.6 Chemistry and Petrography........................................................................................... 30 2.6.1 Petrography ............................................................................................................... 30 2.6.2 Geochemistry ............................................................................................................ 32 2.7 Geochronometry ........................................................................................................... 36 2.7.1 Radiogenic 40Ar /39Ar Results ................................................................................... 36 2.7.2 Paleomagetic Methods and Results .......................................................................... 36 2.8 Discussion ..................................................................................................................... 41 2.8.1 A Glaciovolcanic Eruption Within an Englacial Lake ............................................. 41 2.8.2 Explosive Onset to Glaciovolcanic Eruption ............................................................ 42 2.8.3 Model for CM eruption ............................................................................................. 44 2.8.4 Paleoenvironmental Reconstruction ......................................................................... 50 2.9 Summary ....................................................................................................................... 54 Chapter 3: The Magmatic Origins of Cracked Mountain: Evidence for Cryptic Tapping of Two Magma Chambers During a Monogenetic Eruption .......................................................55 3.1 Introduction ................................................................................................................... 56 3.2 Geological Background ................................................................................................ 57 3.3 Cracked Mountain Volcano .......................................................................................... 58 viii 3.3.1 Morphology............................................................................................................... 58 3.3.2 Geology ..................................................................................................................... 59 3.4 Petrological Results ...................................................................................................... 61 3.4.1 Petrography ............................................................................................................... 61 3.4.2 Major and Trace Element Geochemistry .................................................................. 63 3.4.3 EMP mineral compositions ....................................................................................... 71 3.5 Paleomagnetic Results .................................................................................................. 73 3.6 Discussion ..................................................................................................................... 76 3.6.1 Isobaric Crystallization Models of CM Magmas ...................................................... 76 3.6.2 Origin of Chemical Variations in CM Samples ........................................................ 79 3.6.3 Temperature and H2O Constraints for CM Magmas ................................................ 85 3.6.4 Storage, Transport, and Eruptive Model for CM ...................................................... 87 3.6.5 Implications for Monogenetic Volcanoes ................................................................. 90 3.7 Summary ....................................................................................................................... 92 Chapter 4: Conclusion .................................................................................................................93 4.1 Physical Volcanology of Cracked Mountain ................................................................ 94 4.2 Petrological and Chemical Volcanology of Cracked Mountain ................................... 95 4.3 Future Implications of Study ........................................................................................ 96 Bibliography .................................................................................................................................99 Appendices ..................................................................................................................................109 Appendix A: Additional Whole-Rock Geochemical Data ...................................................... 109 A.1 Whole-Rock Major and Trace Geochemical Compositions for Cracked Mountain Samples ............................................................................................................................... 109 ix A.2 Whole-Rock Major and Trace Geochemical Compositions for Mount Meager Volcanic Complex Samples ................................................................................................ 113 Appendix B: Radiogenic 40Ar/39Ar Data ............................................................................... 118 B.1 40Ar/39Ar Results for Cracked Mountain Sample MH-19-055 ............................... 118 B.2 40Ar/39Ar Results for Additional MMVC Samples ................................................. 128 Appendix C: Paleomagnetic Data .......................................................................................... 138 Appendix D: Electron-Microprobe Analyses for Cracked Mountain Samples ..................... 140 D.1 Olivine Analyses ..................................................................................................... 140 D.2 Plagioclase Analyses ............................................................................................... 148 D.3 Clinopyroxene Analyses ......................................................................................... 157 Appendix E: Isotope Geochemistry ...................................................................................... 162 E.1 Methods................................................................................................................... 162 E.2 Results ..................................................................................................................... 163 x List of Tables Table 2.1: Codes, descriptions, approximate edifice volume, and interpretations of Cracked Mountain Volcanic Lithofacies..................................................................................................... 14 Table 2.2: Summary of distributions, descriptions, and interpretations of lithofacies associations at Cracked Mountain .................................................................................................................... 26 Table 2.3: Representative whole-rock major (wt. %) and rare earth (ppm) element compositions of Cracked Mountain volcanic rocks ............................................................................................ 35 Table 3.1: Petrographic summary of Cracked Mountain volcanic lithofacies .............................. 62 Table 3.2: Whole-rock major (wt. %) element compositions and normative mineralogy of Cracked Mountain volcanic rocks ............................................................................................... .66 Table 3.3: Trace (ppm) element compositions of Cracked Mountain volcanic rocks .................. 69 Table 3.4: Paleomagnetic analyses ............................................................................................... 75 Table 3.5: Thermodynamic summary of Cracked Mountain volcanic rocks ................................ 84 Table A1: Whole-rock major (wt. %) and rare earth (ppm) element compositions of additional Cracked Mountain volcanic rocks .............................................................................................. 110 Table A2: Whole-rock major (wt. %) and rare earth (ppm) element compositions of additional Mount Meager volcanic complex rocks ...................................................................................... 114 Table B1: Complete heating steps of Ar/Ar geochronological analysis of Cracked Mountain sample MH-19-055 .................................................................................................................... 119 Table B2: Ar/Ar summary table for Mount Meager volcanic complex rocks ............................ 129 Table C1: Paleomagnetic analyses.............................................................................................. 139 xi Table D1: Electron microprobe major element (wt %) analyses of Cracked Mountain olivine minerals ....................................................................................................................................... 141 Table D2: Electron microprobe major element (wt %) analyses of Cracked Mountain plagioclase minerals ....................................................................................................................................... 149 Table D3: Electron microprobe major element (wt %) analyses of Cracked Mountain clinopyroxene minerals ............................................................................................................... 158 Table E1: Nd, Sr, Hf, and Pb isotope ratios for Mount Meager volcanic samples ..................... 163 xii List of Figures Figure 2.1: Location and geological setting of Cracked Mountain volcano ................................... 8 Figure 2.2: Geology of Cracked Mountain volcano ..................................................................... 11 Figure 2.3: Physiographic setting of Cracked Mountain volcano................................................. 17 Figure 2.4: Field photos of Cracked Mountain lapilli tuffs .......................................................... 19 Figure 2.5: Field photos of Cracked Mountain peperitic intrusions ............................................. 21 Figure 2.6: Field photos of Cracked Mountain peperites ............................................................. 23 Figure 2.7: Field photos of Cracked Mountain tuff breccias ........................................................ 24 Figure 2.8: Field photos of Cracked Mountain effusive lavas ...................................................... 28 Figure 2.9: Photomicrographs showing textures of Cracked Mountain volcaniclastic lithofacies ....................................................................................................................................................... 31 Figure 2.10: Whole-rock geochemical plots of Cracked Mountain volcanic rocks ..................... 33 Figure 2.11: Stereographic plots of magnetic remanence directions for Cracked Mountain volcanic rocks ............................................................................................................................... 38 Figure 2.12 Eruptive model for Cracked Mountain volcano ........................................................ 46 Figure 2.13: Paleoclimate glacial reconstruction at the time of Cracked Mountain eruption ...... 49 Figure 2.14: Cracked Mountain age relationship with global marine isotope record ................... 53 Figure 3.1: Location, geological setting, and sample distribution for Cracked Mountain volcano....................................................................................................................................................... 57 Figure 3.2: Photomicrographs of Cracked Mountain coherent lithofacies ................................... 60 Figure 3.3: Major (XRF) and trace elemental (ICP-MS) compositions for whole-rock samples from Cracked Mountain volcano .................................................................................................. 64 xiii Figure 3.4: Incompatible element ratios versus Mg# for Cracked Mountain volcanic rocks ....... 65 Figure 3.5: Electron microprobe analyses of CM mineral compositions ..................................... 72 Figure 3.6: Stereographic plot of mean paleomagnetic data for Cracked Mountain volcanic rocks....................................................................................................................................................... 76 Figure 3.7: Phase portraits for Cracked Mountain volcanic samples ........................................... 78 Figure 3.8: Conserved element geochemical diagrams for Cracked Mountain volcanic rocks .... 80 Figure 3.9: Pearce element ratio (PER) assemblage tests for one and two mineral phases for Cracked Mountain volcanic rocks ................................................................................................ 82 Figure 3.10: Pearce element ratio (PER) assemblage tests for three mineral phases for Cracked Mountain volcanic rocks ............................................................................................................... 83 Figure 3.11: Combined PER and thermodynamic chemical models for Cracked Mountain volcanic rocks ............................................................................................................................... 86 Figure 3.12 Storage, transport, and eruptive model for Cracked Mountain magmas ................... 89 Figure B1: 40Ar /39Ar geochronometry for samples from Cracked Mountain Volcano ............. 127 Figure B2.1: Geologic map and sample locations for Mount Meager volcanic complex rocks that have undergone Ar/Ar age determinations ................................................................................. 130 Figure B2.2: 40Ar /39Ar plateau diagrams for Mount Meager volcanic complex samples ........ 133 Figure B2.3: 40Ar /39Ar inverse-isochron diagrams for Mount Meager volcanic complex samples..................................................................................................................................................... 134 Figure B2.4: Paleoclimate glacial reconstruction for the MMVC within the last 500 ka .......... 136 Figure C1: Stereographic plot and google earth imagery of Cracked Mountain paleomagnetic site 1................................................................................................................................................... 138 Figure E1: Isotope data versus ages for Mount Meager volcanic complex samples .................. 164 xiv Acknowledgments I would like to thank my supervisor, Kelly Russell for all the time, energy, and money he has provided to make this project possible. From day one, he has supplied me with a fascinating project that played on my strengths while also challenging me to learn new skills. The passion Kelly brings to all volcanology discussions is inspiring, and I am forever grateful to have had the opportunity to work with him. I would like to thank all my current and former VPL lab mates that helped me throughout my time at UBC, particularly: Amy Ryan, Alex Wilson, David Sasse, Mu Li, and Katherine Landoni. A special thanks to Sophie Leiter, Lindsey Abdale, Annie Borch, for their assistance in the field and their helpful revisions on numerous drafts of writing. Thanks to Mahmud Mohammad for his extensive help in the field. Thanks to Rene Barendregt for his help with all things paleomagnetic. Without all these helping hands, my work would not have been possible. Thanks to my co-supervisors Lucy Porritt and Dominique Weis. You have both been very kind and insightful each time I reached out to talk, and I greatly appreciate all your help. Lastly, this research was supported by the National Resources of Canada (NRCan) Research Affiliate Program for the Geothermal Energy Project, Mount Meager. Special thanks to Dr. Steve Grasby of NRCan for all his help organizing field campaigns and funding analytical methods. 1 Chapter 1: Introduction Glaciovolcanism is the interaction between volcanoes and ice in all of its forms including snow, firn, and meltwater (Kelman et al., 2002; Smellie, 2006; Russell et al., 2014). Glaciovolcanoes span the globe but most studies have been focused on the polar regions (Antarctica, Iceland, and British Columbia) (Smellie and Edwards, 2016). Glaciovolcanic eruptions are unique in that they 1) produce distinct edifices and lithofacies compared with subaerial eruptions (Jakobsson and Gudmundsson, 2008; Edwards et al., 2015; Smellie and Edwards, 2016), 2) their morphology and lithofacies successions directly reflect their eruption environment (i.e. ice-impoundment, subglacial, supraglacial, or subaerial) (Kelman et al., 2002; Smellie, 2007; Russell et al., 2014), and 3) they provide a land-based record of the paleoclimate at the time of the eruption (Mee et al., 2006; Edwards et al., 2015; Wilson and Russell, 2018; Wilson et al., 2020). Southwest British Columbia has an extensive history of waxing and waning continental ice sheets throughout the Pleistocene (Clague, 2009; Clague and Ward, 2011). The Garibaldi volcanic belt (GVB) is the northern extension of the active Cascade volcanic arc, which extends up from Glacier Peak, Washington, USA to Silverthrone British Columbia, Canada (Roddick and Souther, 1987; Green et al., 1988; Hildreth, 2007). The GVB hosts numerous glaciovolcanic landforms (Mathews, 1952; Lawrence et al., 1984; Roddick and Souther, 1987; Kelman et al., 2002; Wilson and Russell, 2017, 2018; Wilson et al., 2019). This thesis investigates Cracked Mountain, a glaciovolcanic landform within the Mount Meager Volcanic Complex (MMVC), located in the GVB (Wilson and Russell, 2018). 2 1.1 Importance of Glaciovolcanism The field of glaciovolcanism has grown in recent decades (Russell et al., 2014) namely due to their impact as a geological hazard (i.e. 2010 Eyjafjallajökull, Icelandic eruption) (Dellino et al., 2012; Barsotti et al., 2020), and the insight they provide on paleo-environments. It is important to study records of glaciovolcanism because they preserve a record of their eruptive environment through their morphologies, lithofacies, and stratigraphic successions (Kelman et al., 2002; Smellie, 2007; Russell et al., 2014). Where dated, (commonly 40Ar/39Ar or K-Ar techniques) glaciovolcanoes provide localized and empirical evidence for the presence, absence, and extent of paleo-ice that in turn, can be used to reconstruct paleoclimates (e.g., Smellie, 2018; Wilson et al., 2020). Volcanic eruptions have been shown to have major impacts on global climate (e.g., Sigl et al., 2015; Aubry et al., 2016), and volcanism triggered by ice-sheet growth and decay has also been suggested (e.g., Grove, 1974; Carrivick et al., 2009). These studies have led to investigations and modeling of the causal linkages between volcanic eruptions and glaciers and the role that glacial loading and unloading of the crust may play in modulating volcanism. (e.g., Wilson and Russell, 2020; Guillot and Ponce, 2021). 1.2 Research Goals This thesis examines Cracked Mountain volcano in the southwest flank of the Mount Meager Volcanic Complex, BC. Cracked Mountain was chosen in part because of its unique geology, where the volcano is built of subaqueous style volcanic deposits constrained in an alpine environment. Since no body of water presently exists and no physical barriers are capable of hosting a paleo lake, the only feasible explanation for the occurrence of subaqueous deposits at Cracked Mountain is that of a glaciovolcanic origin (e.g., Kelman et al., 2002; Smellie, 2007; 3 Edwards et al., 2009), thus informing on the paleoclimate at the time of the eruption. Additionally, the Cracked Mountain volcano is dissected by cracks expressed along the surfaces at all elevations cutting into the interior of the volcano down to 40 metres in some locations. This morphological exposure of the internal volcanic lithofacies allows for an in-depth study of the eruptive sequence, which has enabled this thesis to provide the first detailed volcanological study of the Cracked Mountain glaciovolcano. The objective of this thesis is to inform on the physical and chemical evolution of the Cracked Mountain volcano. My forensic reconstruction of the volcanic evolution of Cracked Mountain is based on field mapping and stratigraphy, petrography, geochemistry, and thermodynamic modeling. These data sets are used to constrain pre-eruptive crustal storage conditions and eruption processes. The broader implications of this study include 1) establishment of the paleoenvironment of SWBC during the mid-Pleistocene, 2) documentation of an explosive onset to the Glaciovolcanic eruption, in contrast to conventional tuya eruptive models (e.g., Smellie, 2007; Edwards et al., 2015; Smellie and Edwards, 2016), and 3) providing new insights into the connections between crustal storage and eruptions of monogenetic volcanoes. 1.3 Scope of Thesis and Outline I use my investigation of Cracked Mountain and the Mount Meager Volcanic Complex to answer the following questions, broadly divided into two domains: Physical Volcanology: 1. What were the eruptive sequence, style, and duration for the Cracked Mountain volcano? 4 2. What can we learn about the paleoenvironment at the time of the Cracked Mountain eruption? Petrologic and Chemical Volcanology: 1. What are the causes of petrological and chemical variations for the Cracked Mountain lavas? 2. What were the P-T-H2O conditions for the pre-eruptive Cracked Mountain magmas, and what does that tell us about the magma chamber dynamics? 1.3.1 Physical Volcanology of Cracked Mountain Chapter 2 of this thesis addresses the physical volcanological evolution of Cracked Mountain. The data used in this chapter comes from field mapping, lithostratigraphy, petrography, paleomagnetic analysis, and geochronological analysis. The chapter presents detailed lithofacies associated with the transitional (i.e. explosive, intrusive, and effusive) eruptive style. The outcomes of this chapter allow us to model the sequence of events for the eruption. The results of the paleomagnetic analyses constrained the duration, and we present our new 40Ar/39Ar results for the absolute age of the eruption. Lastly, we use the edifice morphology and surrounding topography to model the paleo-ice dimensions in the localized Garibaldi volcanic belt at the time of the Cracked Mountain eruption. The overarching importance of this chapter is founded on the reconstruction of a detailed eruptive sequence that took place in a climate that differs greatly from the one we live in today. Thus, the physical volcanological study of Cracked Mountain can be used as a land-based climate proxy, which, if combined with other paleoclimate data (e.g., ice-cores, glacial deposits, glaciovolcanoes), can help us better understand past cycles of climate change. 5 1.3.2 Petrological and Chemical Volcanology of Cracked Mountain Chapter 3 of this thesis addresses the petrochemical evolution of the Cracked Mountain magmatic system. The data used in this chapter comes from petrography, and major, trace, and mineral chemistry. This chapter includes a detailed discussion on phase equilibria models using both Pearce Element Ratio analysis and Rhyolite-MELTS. The outcomes of these petrochemical models establish pre-eruptive storage conditions (i.e. pressure-temperature-water conditions of the magmas at the time of crystallization) and inform on the magmatic plumbing for Cracked Mountain. While there have been prior studies on the melt sources for the Garibaldi volcanic belt (GVB) (e.g., (Green and Sinha, 2004; Mullen and Weis, 2013, 2015; Mullen et al., 2017), few have focused in detail on the upper crustal conditions. Thus, the recovery of magma chamber dynamics at Cracked Mountain volcano has broader implications for the understanding of continental volcanic arcs (i.e. Cascades), and particularly for monogenetic systems. 1.3.3 Conclusions and Implications of Study Chapter 4 of this thesis presents a summary of findings for this study. Here, I explore the wider implications of each of the themes addressed above, relating to the physical volcanological study of a glaciovolcanic eruption within the mid-Pleistocene and the petrochemical recovery of the magma chambers that fed the Cracked Mountain eruption. Lastly, I review additional thesis data, such as new 40Ar/39Ar ages and Pb, Nd, Sr, and Hf isotopic ratios for MMVC samples. Throughout this thesis project, widespread mapping, sampling, and subsequent analyses were conducted on several ancillary volcanic occurrences within the localized MMVC. Although this additional data does not directly relate to the study and investigation of Cracked Mountain 6 volcano, I use the concluding chapter to discuss how these data may be used in future studies that aim to build upon the Cracked Mountain story and expand to the regional Garibaldi volcanic belt. 7 Chapter 2: Explosive Glaciovolcanism at Cracked Mountain Volcano, Garibaldi Volcanic Belt, Canada 2.1. Introduction The Garibaldi Volcanic Belt (GVB) is the northern segment of the Cascade Volcanic Arc (Roddick and Souther, 1987; Green et al., 1988; Hildreth, 2007). Garibaldi belt volcanic deposits range from Pleistocene to Holocene in age and result from subduction of the Juan de Fuca plate beneath the North American Plate (Roddick and Souther, 1987; Green et al., 1988; Hildreth, 2007). Southwest British Columbia has a protracted history of multiple glaciations, with cycles of advancing and retreating continental ice sheets throughout the Pleistocene (Clague, 2009; Clague and Ward, 2011). As a result, the GVB hosts numerous glaciovolcanic landforms. Prior studies concerning glaciovolcanism have focused on the Mount Garibaldi volcanic field (e.g., Mathews, 1952; Wilson et al., 2019), the Mount Cayley volcanic field (e.g., Kelman et al., 2002; Kelman, 2005), the Mount Meager volcanic complex (MMVC) (e.g., Wilson and Russell, 2017, 2018), the Salal Glacier volcanic complex (e.g., Lawrence et al., 1984; Wilson and Russell, 2018), and the Bridge River volcanic field (e.g., Roddick and Souther, 1987; Wilson and Russell, 2018). Cracked Mountain is a ~0.18 km3 basaltic volcano situated on the southern flank of the MMVC and originally identified by Read (1979) as part of the Mosaic Assemblage. Here, we present a new dataset including a map of volcanic lithofacies, petrographic and geochemical characteristics of the deposits, geochronometric (40Ar /39Ar) age estimates, and paleomagnetic directions of all lithofacies. Collectively, these data inform on the physical volcanological evolution of the Cracked Mountain (CM) volcano. Our analysis shows CM to have a 8 glaciovolcanic origin (Kelman et al., 2002; Smellie, 2007; Edwards et al., 2009) involving sustained eruption within an englacial lake. The lithofacies and their stratigraphic relationships indicate an explosive eruption onset dominated by phreatomagmatic activity that transitioned to effusive eruption expressed by intrusions and lavas. We use the geometry of the CM edifice (i.e. shape and size) and the distribution of lithofacies to reconstruct the eruptive history of the glaciovolcanic edifice and the minimum distribution of the enclosing paleo-ice sheet. Our findings contribute to a larger story of glaciovolcanism within the GVB and understanding the paleoclimate of SW British Columbia. 9 Figure 2.1: Location and geologic setting of Cracked Mountain volcano. A) Map of the Cascade volcanic arc in the USA and Canada (i.e. Garibaldi volcanic belt (GVB)) (modified from Mullen and Weis, 2013; Wilson and Russell, 2017). B) Undivided geological map of MMVC distribution of Mt. Meager volcanic deposits (MV), basement (Bu) throughout the region (Woodsworth, 1977; Read, 1979; Harris and Russell, 2021). The youngest MMVC eruption, 2350 B.P. Pebble Creek Formation (PcF) (Hickson et al., 1999; Stewart et al., 2008) is differentiated from other MMVC volcanics. Cracked Mountain (CM) is situated south of the main MMVC (Wilson and Russell, 2018; Harris and Russell, 2021). 2.2 Geological Background The Mount Meager volcanic complex is situated 160 km north of Vancouver in SW British Columbia (Fig. 2.1) and is one of eight major centres and volcanic fields comprising the GVB (Fig. 2.1A). Recent GVB geochemical and petrological studies show increases in melt alkalinity and a decrease in slab-derived signatures moving northward in the GVB (Green and Sinha, 2004; Mullen and Weis, 2013). In particular, the MMVC, Salal Glacier volcanic complex, and Bridge River volcanic field show a heightened primitive signature compared to the southward GVB and the High Cascade volcanoes. These findings suggest that the Nootka Fault, located Northwest of the Bridge River cones (Fig. 2.1A), may mark the terminus of the Juan de Fuca subduction where a window between the Juan de Fuca and Northward Explorer plate allows upwelling of asthenospheric melts under the northernmost GVB centres (Mullen and Weis, 2013). The MMVC (Fig. 2.1B) contains Pleistocene to Holocene basalt to rhyolite overlying basement igneous and metamorphic rocks of the Coastal Plutonic complex (Fig. 2.1B) (Woodsworth, 1977; Read, 1979; Green et al., 1988). The MMVC is also host to the youngest GVB eruptive deposits, namely the 2350 B.P. Pebble Creek formation (Hickson et al., 1999; Stewart et al., 2008). Intermediate to felsic lavas are dominant within the Mount Meager Massif, however, localized mafic centres are present in the north (Lillooet Ridge and River), west 10 (Mosaic Ridge), and southwest (Cracked Mountain and Elaho Valley) regions of the volcanic complex (Fig. 2.1B) (Read, 1979, 1990; Harris and Russell, 2021). The ages of the Mosaic Ridge basalts and Elaho Valley basaltic andesites are ~90 and 140 ka respectively (Woodsworth, 1977; Green et al., 1988). 2.3 Cracked Mountain Physiography and Morphology The Cracked Mountain volcano unconformably overlies basement granodiorite (Bg) and schist (Bs) of the Gambier and Cadwallader Groups respectively (Fig. 2.2A) (Read, 1979). The volcanic deposits form a slightly asymmetric, NE-SW trending ~250 m thick ridge that is ~1,300 m long and ~1,000 m wide. The summit of CM rises to 1,650 m above sea level (a.s.l.) and the margins reach elevations as low as 1,250 m (Fig. 2.2A). Cracked Mountain is surrounded by steep valleys of the Meager Creek and Elaho River tributaries to the north and west respectively (Fig. 2.3). Extensional cracks dissect the entirety of CM (Figs. 2.2A; 2.3A), ranging from 0.5 to > 20 m in width and up to 30 m in depth. The fractures form parallel clusters that commonly trend perpendicular to the downslope direction. All CM lithofacies are offset and displaced by cracks. No glacial deposits (i.e. till, erratics) are found within cracks, suggesting a post-eruptive and post-glacial origin. The shape and surface features of CM show evidence of glacial enveloping and scouring. The present-day surface is littered with cobble to boulder-sized granitic erratics and some locations have been smoothed and striated in a SW direction. These findings show that post-eruption Cordilleran Ice Sheets have reached elevations greater than the summit of CM. The margins of CM are cliffs up to 40 m high, which is unusually thick for basaltic lava (e.g., Edwards et al., 2015). We interpret this morphology to be a result of syn-eruptive glacial 11 12 Figure 2.2: Geology of Cracked Mountain. A) Geologic map showing the distribution of CM volcanic lithofacies. Dyke location and orientations are shown in red; extensional cracks are shown in black. The volcanic edifice unconformably overlies basement granodiorites (Bg) and mica-schists (Bs). Black-numbered dots show locations of representative stratigraphic logs (B, C). B) Graphic logs showing volcanic stratigraphy at various locations and elevations (black numbered dot) within the map area (depicted in Figs. 2.2A). Lithologies are depicted with various patterns and symbols while corresponding map units are shown in the same colours as Fig. 2.2A. Red lines shown in map units represent intruding dykes observed within the lithologies of the graphic logs. confinement and subsequent erosion. There is no evidence of ice-abutment in the form of laterally facing, hackly, or irregular jointed lavas (e.g., Lescinsky and Fink, 2000; Kelman et al., 2002) suggesting that the outermost CM margins result from post-eruptive glacial erosion rather than reflecting primary lava-ice contact surfaces. 2.4 Volcanic Lithofacies We recognize 10 CM lithofacies (Table 2.1) that include both volcaniclastic and coherent lithofacies. All volcanic deposits are olivine and plagioclase porphyritic and differ only in their groundmass textures ranging from holocrystalline, hypocrystalline, and quenched. The terminology used to describe grain size and componentry of volcaniclastic rocks is after White and Houghton (2006). 2.4.1 Volcaniclastic CM lapilli tuffs (Lt1-2) (Table 2.1) form the stratigraphically lowest (Fig. 2.2B) lithofacies. Observed thicknesses range from 0.5 m to < 6 m. Lt1 is massive, moderately- to poorly sorted, and is observed throughout the CM edifice from its base to its summit (Fig. 2.2A; 13 2.4A). Lt1 is comprised of dense and blocky to highly vesiculated and cuspate vitric juveniles and contains 5- 35% lapilli-sized clasts supported in a vitric ash matrix. Lt1 is commonly intruded by dykes (Ld1-2) and mingled with peperitic lobes (Lpi; Table 2.1) (Fig. 2.5). In some locations, soft-sediment deformation of Lt1, in the form of squeeze-up pipes, is observed. Lt2 outcrops in the SE and N sections of CM and, by comparison, are thinly bedded, well-sorted (Fig. 2.4B). Beds of ultra-fine ash are up to 5 cm thick and dip shallowly in the downslope direction. In some outcrops, microfractures offset laminated beds, and truncated and shallow cross-beds are also observed. Lt2 is commonly observed as 1-2 m layers within thicker, massive Lt1 exposures (Fig. 2.2B; 2.4B) and displays fining upward grain sizes. 14 Table 2.1. Codes, descriptions, approximate edifice volume, and interpretations of Cracked Mountain volcanic lithofacies. Facies Code Vol. % Description Interpretation Figs. Volcaniclastic Lt1 25 Lapilli Tuff: Yellow to grey; massive to crudely bedded, monolithic, moderately to well sorted, and matrix-supported; clasts comprise 10-30% of the unit, with ~10-25% lapilli and >5% blocks; ~20-50% of clasts are glassy, highly vesiculated juveniles, with all other clasts being dense lava lithics; dense clasts are olivine and plagioclase porphyritic, Pl (5-10%) Ol (5%) with < 50% showing chilled margins.; matrix material is yellow orange ash and fine lapilli, comprised of ultra-fine (~5%), blocky (~60%), and cuspate (~30-35%) vitric juveniles; matrix contains intact to fragmented crystals, Pl (5-10% 0.5-2 mm) and Ol (5-10% 0.1-1 mm); lapilli tuff is stratigraphically lowest throughout the edifice. Subaqueous pyroclastic density currents derived from Surtseyan tephra cone buildup from the onset of the eruption. 2.2, 2.4, 2.5, 2.7 Lt2 3 Lapilli Tuff: Yellow to grey; thinly bedded, monolithic, moderately to well sorted, and matrix-supported; clasts comprise >10% of the deposit, with 100% being fine lapilli; ~50% of clasts are highly vesiculated vitric juveniles, and ~50% dense basalt lithics; dense lithics are olivine and plagioclase porphyritic to microlitic, Pl (5-10%) Ol (5%); matrix material is yellow ash, comprised of ultra-fine (~10-15%), blocky (~70%), and cuspate (15-20%) vitric juveniles; matrix contains intact to fragmented crystals, Pl (5-10% 0.5-2 mm) and Ol (5-10% 0.1-1 mm). Subaqueous low density (surge) deposits during phreatomagmatic buildup of the edifice. 2.2, 2.4 Lt3 1 Lapilli Tuff: Grey; massive, monolithic, poorly sorted, and matrix-supported; clasts comprise ~20-40% of the deposit, with ~10-15% lapilli and ~20% block; ~50% of clasts are highly vesiculated, fluidal to blocky, spatter juveniles, and ~50% dense basalt lithics; clasts are olivine and plagioclase porphyritic, Pl (5-10%) Ol (5%); the matrix grey, well-sorted, fine lapilli and ash, comprised of ultra-fine (~5%), blocky (~50), and cuspate (~45%) vitric juveniles; matrix contains intact to fragmented crystals, Pl (5-10% 0.5-2 mm) and Ol (5-10% 0.1-1 mm). Shallow subaqueous to subaerial lava fountaining during phreatomagmatic buildup of the edifice. 2.2, 2.4 15 Facies Code Vol. % Description Interpretation Figs. Volcaniclastic Pi 3 Peperite: Yellow to grey; massive, monolithic, moderately sorted, matrix to clast supported; clast shapes range from globular to blocky, clasts comprise <50% of the deposit, with ~40% lapilli and ~10% blocks; clasts ubiquitously show chilled margins and display jig-saw fracture patterns; clasts are vitric and highly vesicular, up to 50-60%, and are olivine and plagioclase porphyritic, (Pl 5-10%, Ol 5%); matrix material is yellow-orange ash, comprised of ultra-fine (~5-10%), blocky (~60%), cuspate (~30%) vitric juveniles; Pi is stratigraphically adjoining Lpi throughout the edifice. Quenched volcaniclastic material formed along bodies of (Lpi) by fuel coolant reactions within water saturated, unconsolidated lapilli tuffs (Lt1). 2.2, 2.6 Tb 16 Tuff Breccia: Yellow to grey; massive, monolithic, moderately to poorly sorted, and clast supported; clasts are subrounded to angular, ranging from 65-70% coarse lapilli and ~5-10% blocks; 10-30% of components are subrounded pillow lithics (Lpi, Lp), ~60-70% are dense to highly vesiculated blocky lava (Ls), and ~1-2% are lapilli to block sized rounded lapilli tuff lithic (Lt1); all coherent clasts are olivine and plagioclase porphyritic, Pl (5-10%) Ol (5%); matrix material is yellow-orange ash and lapilli, comprised of ultra-fine (~5%), dense (~60%), and cuspate (~35%) vitric juveniles; breccia blankets and fills in topography throughout the edifice. Near and proximal vent syn- and post-depositional debris flow avalanches in subaqueous and subaerial settings. 2.2, 2.7 Coherent Lp 20 Pillowed lava: Dark grey to black; intact to fragmented, rounded to oblong lobes, with individual diameters ranging from 0.2 to 0.5 m; vitric rims up to 1 cm are common; pillows are moderately to highly vesicular (50-65%) and commonly display concentric vesicle layers in cross-section; pillows are hypocrystalline, and olivine and plagioclase porphyritic, Pl (10-15%, 0.5-3 mm), Ol (5-10%, 0.1-1 mm); rare augite phenocrysts are observed in thin-section, Cpx (1-2%, 0.1-1 mm) pillows contain yellow-orange interstitial quench fragmented ash and lapilli between adjacent lobes. Subaqueous extrusion of lava at moderate to low eruption rates within ice-confined glacial lake. 2.2, 2.8 16 Facies Code Vol. % Description Interpretation Figs. Coherent Lpi 20 Pillowed lava: Dark grey to black; domains of intact to dispersed, subrounded to oblong pillowed lobes, with individual diameters ranging from 0.2 to 0.5 m; vitric rims up to 1 cm are common; lobes are moderately to highly vesicular (50-65%) and commonly display concentric vesicle layers in cross-section; lobes are hypocrystalline, and olivine and plagioclase porphyritic, Pl (10-15%, 0.5-3 mm), Ol (5-10%, 0.1-1 mm); lobes are mingled within moderately to highly palagonitized lapilli tuffs. Corrugated vitric rinds cover lobes and tubes in some exposures. Subaqueous intrusion of lava into unconsolidated, water saturated volcaniclastic sediments (Lt1). 2.2, 2.5 Ls 2 Jointed lava: Dark grey to black; columnar to blocky jointed, columns range from 0.2 to 0.5 m in diameter; lavas are dense, with moderate vesicularity (~20-30%); lavas are holocrystalline, and are olivine and plagioclase porphyritic, Pl (10-15%, 0.5-3 mm), Ol (5-10%, 0.1-1 mm); rare augite phenocrysts are observed in thin-section, Cpx (1-2%, 0.1-1 mm), little to no interstitial sediments are present between jointed lavas. Outcrops are poorly preserved and show signs of glacial scouring. Subaerial extrusion of lava at moderate to low eruption rates, at elevations above englacial lake level. 2.2, 2.8 Ld1 5 Dykes: Dark grey to black; subvertical to curved, thickness ranges from 0.5 to 1.5 m; dyke margins are poorly defined to pillowed margins; dykes are moderately vesicular (~20-40%); dykes are holocrystalline, and are olivine, plagioclase (glomero) porphyritic, Pl (10-15%, 0.5-3 mm) Ol (5-10%, 0.1-1mm) Early stage intrusions into unlithified Lt1 coinciding with emplacement of coherent lavas (Lpi, Lp). 2.2, 2.5 Ld2 5 Dykes: Medium to dark grey; subvertical and jointed, thickness ranges from 0.5 to 3 m; dyke margins are well defined with laterally pointing small columnar joints; dykes are moderately vesicular (~20-40%); dykes are holocrystalline, and are olivine, plagioclase, and augite (glomero) porphyritic, Pl (10-15%, 0.5-3 mm) Ol (10%, 0.1-1mm) Cpx (1-2%, 0.1-1 mm); dykes contain minor crustal xenoliths. Late-stage intrusions postdating lithification of Lt1 and growth of edifice. 2.2 17 Figure 2.3: Physiographic setting of Cracked Mountain volcano. A) NE-SW oriented Google Earth imagery of Cracked Mountain showing the location of volcanic deposits overlying basement rocks (white-arrows). Visible cracks parallel the steep drainages. B) South-West facing DEM hillshade map showing CM volcanics (red shaded outline) situated above present-day Meager Creek and Elaho Valleys. 18 Lt3 are locally stratified as defined by accumulations of lapilli and bomb-sized, fluidal to blocky, vesiculated (<60%) spatter clasts (Fig. 2.4C). The clasts are supported by a well-sorted, vitric ash matrix. Two small outcrops of Lt3 are located at upper elevations (i.e. high in stratigraphy) in the central and NE sections of the CM. Peperite (Pi) deposits, as defined by White et al., (2000) and Skilling et al., (2002), are volcaniclastic deposits resulting from the mingling of magma with wet, unconsolidated sediments. At CM, peperites occur as fragmented, globular to blocky components of vitric basalt supported by ash and lapilli tuff matrix (Figs. 2.2B; 2.6). Peperite deposits are distributed along the margins of the peperitic intrusive bodies (Lpi). We distinguish lithofacies Pi from Lpi (Table 2.1) as volcaniclastic and coherent, respectively. The thickness of peperites varies from a few cm to 2-3 m away from the margins of Lpi. Peperites rarely outcrop at the present-day CM surface but are commonly exposed in cracks at all locations of the volcano. Tuff breccias (Tb) blanket much of the topography in the central and north regions are the dominant map unit (Fig. 2.2), and obscure stratigraphically older volcanic lithofacies. At higher elevations, tuff breccias form thin 1-2 m-thick deposits that progressively thicken (<10 m) downslope (Fig. 2.7). The tuff breccias are massive and clast-supported, featuring monolithic lapilli-to block-sized lithic components. These lithics are olivine-and-plagioclase porphyritic lava fragments of Lpi, Ls, and Lp, where ~30-40% show rounded chilled margins. Minor yellow ash-sized interstitial sediment is present between breccia clasts. Rarely, block and lapilli-sized, rounded Lt1 lithics are present (Fig. 2.7B). 19 20 Figure 2.4: Field photos displaying bedform structures of CM lapilli tuffs: A) Field photo showing ~2 m thick exposure of massive, moderately sorted ash and lapilli tuff underlying poorly sorted tuff breccia (Tb). Half metre hammer (arrow in white) for scale. B) Field photo displaying a ~0.5m thick exposure of thinly bedded, well-sorted, ash, and a lapilli tuff (Lt2) interbedded within massive lapilli tuff (Lt1). One metre hammer for scale. C) Field photo showing ~10 m wide and ~4 m thick exposure of moderately to poorly sorted, locally spatter dominated, lapilli tuff (Lt3). One metre hammer for scale. The white box shows the location of the inset displaying fluidal clast surrounded by a vitric ash matrix. 2.4.2 Coherent The peperitic pillowed lava unit (Lpi) (Table 2.1) comprises coherent, mingled lavas that intrude volcaniclastic deposits (Lt) across all elevations and locations of the edifice (Fig. 2.2). Lpi is a mappable unit and is distinguished from coherent pillow lavas (Lp; Table 2.1) where Lpi intruded saturated sediments and Lp formed through subaqueous effusion. Lpi is commonly exposed in cracks as massive globular bodies up to 15-20 m across and 10-15 m high, comprised of chilled, subrounded lobes (Fig. 2.5A and B). Additionally, Lpi is often associated with ‘blooming’ dykes (Ld1) (Fig. 2.5C). Since Lpi intrudes and pillows into lapilli tuff (Lt) (i.e. host sediments) we interpret these lithofacies to be ‘peperitic’ intrusions. Here we use the adjective “peperitic” after White and Houghton (2006) which has a genetic connotation describing deposits resulting from intrusion and mingling of magma and unconsolidated. Pillow lava deposits (Lp) (Table 2.1) comprise individually stacked radial and quenched lobes, makeup ~20% of the edifice, and are the dominant lithofacies exposed at the edges of CM (Fig. 2.2). Pillow lava outcrop at the present-day, high elevations of CM (Figs. 2.2A) as 1-3 m thick piles and increases to ~ 10-40 m thick along the cliffs at the outer edges of the volcano (Figs. 2.2B; 2.8A and B). 21 Figure 2.5: Field photos illustrating the association of pillowed lava (Lpi), peperitic dykes (Ld1), and enclosing lapilli tuff (Lt1): A) Photomosaic of ~30 m wide by~ 4 m thick exposure of pillowed lava (Lpi) mingled with massive lapilli tuff (Lt1). Inset (white box) shows pillowed lobes with a lens of Lt1. Hammer (1 m) for scale. B) Annotated version of 2.5A. Note preserved 22 lenses of Lt1 within extensive Lpi deposits. C) Field photo showing ~5m wide and ~4m deep exposure of “blooming” pillowed lava (Lpi) within massive lapilli tuff (Lt1). Note a feeder dyke (Ld1) is visible through the coherent Lpi body. Inset (white box) shows pillowed lava in contact with a lens of Lt1. D) Annotated version of 2.5C. Individual pillows are bulbous, with diameters up to 50 cm (Fig. 2.8C). Interstitial quench-fragmented vitric sediment fills void spaces between intact pillows in some outcrops (Fig. 2.9A). Large radial columnar jointed pods up to 3 m in diameter make up a lesser amount of the lithofacies. Stratigraphically, Lp is overlain by tuff breccia (Tb), is cut by dykes (Ld2), and is observed to overlie outcroppings of lapilli tuff (Lt1) at the base of the edifice (Fig. 2.2B). Blocky and columnar jointed remnants of sheet lava (Ls) (Table 2.1) are preserved at the highest elevations of CM near the central and eastern regions (Fig. 2.2A). Sheet lava outcrops are small, ranging from ~10-30 m across, and 1-2.5 m thick. The sheet lavas have coarse columnar joints up to 0.4 m in diameter and occur at the present-day surface of CM. The tops of the sheet lavas are commonly glaciated as indicated by SW trending glacial striae and erratics (Fig. 2.8D). Over 50 dykes (Ld1-2) intrude the CM volcano (Fig. 2.2A). The dykes are predominantly subvertical and have widths ranging from 0.5 to 3 m in width and up to 100 m in length. The dominant trends of the dykes strike E-NE and W-NW. Dykes were divided into two groups based on their margins: 1) Ld1 (Table 2.1) have poorly defined, glassy, pillowed, or peperitic margins where they contact bodies of Lpi (Fig. 2.5C), and 2) Ld2 (Table 2.1) have sharp, chilled, and columnar jointed margins where they intrude all other lithofacies. Ld1 is prevalent in the central and high elevations of the edifice and is best exposed through extensional cracks. Ld2 sporadically outcrop in the central high elevations of CM and are high in density along the eastern margins where they intrude subvertically through the stacked walls of Lp. 23 Figure 2.6: Field photos illustrating the association of pillowed lava (Lpi) with peperites (Pi) and peperitic textures present at Cracked Mountain: A) Photomosaic of ~10 m wide and ~4 m thick exposure volcaniclastic peperite (Pi) formed along the margins of coherent bodies of pillowed lava (Lpi). Human for scale. Inset (white box) shows quench-fragmented peperite bounding Lpi. Marker for scale. B) Annotated version of 2.6A. C) Example of globular (fluidal) peperite (Pi) texture. Pen for scale. D) Example of blocky peperite (Pi) texture. Pen for scale. 24 Figure 2.7: Field photos illustrating the structure and variable clast types found in Cracked Mountain tuff breccias (Tb). A) Massive, ~1.5 m thick, tuff breccia (Tb) dominated by subrounded to blocky lava, overlying massive lapilli tuff (Lt1). Hammer (1 m) for scale. B) Massive, tuff breccia (Tb) dominated by subrounded to blocky lava, with minor, block-sized lapilli tuff lithics (Lt1) (white arrows). C) Rare lithic of pahoehoe (Ls) entrained within tuff breccia (Tb). Hammer (1 m) for scale. 2.5 Lithofacies associations The transitional eruptive history of CM involving explosive, effusive, and intrusive activity produced non-uniform deposition of all volcanic lithofacies. The deposits are not 25 stratigraphically ordered in a planar fashion (i.e. a layer-cake model). Instead, the buildup of the volcano was both lateral, where eruptive deposits spread out from higher elevations down to the margins of the edifice, and endogenous, through peperitic intrusions and dykes. The detailed stratigraphic relations are observed through the excellent crack exposures and allow us to determine four dominant lithofacies associations (A-D) (Table 2.2). 2.5.1 Lithofacies Association A Lithofacies association A comprises Lt1, Lpi, and Ld1 (Table 2.2). Lt1 is intruded by Lpi and Ld1 at all elevations of the edifice, including exposures at the base of CM (Figs. 2.2B; 2.5). Ld1 is observed to be in genetic relation to Lpi (Fig. 2.5C). Lt1 outcrops at all elevations of CM, and the deposits are pervasively palagonitized and lithified (Stroncik and Schmincke, 2002). The mingling of Lpi within Lt1 and examples of soft-sediment deformation indicate that Lt1 was saturated and unconsolidated at the time of intrusion. Additionally, the margins of Ld1 are often poorly defined and pillowed, further suggesting a saturated slurry-like host rather than a cooled and lithified host at the time of intrusion. Lastly, Ld1 is often seen tangential to ‘blooming’ Lpi, suggesting that these two intrusive bodies are temporally related. Further petrographic similarities (i.e. olivine and plagioclase phenocrysts) substantiate a co-genetic relationship between Lpi and Ld1. This lithofacies association reveals that unconsolidated ash and lapilli were intruded by peperitic bodies, processes that require a water-saturated eruptive environment. These stratigraphic relations imply an age succession of Lt1 > Lpi ≥ Ld1. 26 Table 2.2. Summary of distribution, descriptions, and interpretations of lithofacies associations at Cracked Mountain Association Lithofacies present Stratigraphic relationships Distribution Interpretation Figs.(A) Lt1, Lpi, Ld1 Lt1 is intruded by Ld1 and mingled with Lpi; Lpi blooms away from pillowed margins of Ld1 Ubiquitous in crack exposures throughout mid and upper elevations of the edifice; small localized outcrops at the base of edifice near basement contactLt1 was deposited in a water-rich environment and was intruded by Ld1 while it was still unconsolidated; as the Ld1 entered the saturated unconsolidated Lt1, the injecting magma pillowed due to water-rich environments and disaggregated due to reduced pressure 2.5(B) Lpi, Pi Pi is interbedded and adjacent to coherent Lpi, at times forming gradational contactsPi is exposed at the surface in small outcroppings in the central and high elevations of the edifice but is commonly observed within cracks exposures across the whole mountainPi formed along the margins of larger pods of Lpi where the highly saturated host sediment caused quenching and disaggegation of magma from the margins of the host intrusion. 2.6(C) Ls, Tb, Lp, Lpi, Lt1-3 Ls and Tb overly Lp, Lpi, and Lt1-3; Lithics of Ls, Lp, Lpi, and Lt1 are entrained within TbLs outcrops sporadically as small remnant outcrops near the present-day summit of the edifice, Tb blankets and fills topography, extending from the central summit toward the outer margins of the edificeLs formed subaerially as the englacial lake level dropped below the elevation of erupting magma; Tb formed as lava piles and slopes collapsed from over steepening and/ or oversaturation, spreading out as mass flow breccias across the highest levels of volcanic stratigraphy; near the summit and central vent, explosive bursts ejected ballistics of subrounded Lt1 which are entrained in Tb2.7, 2.8(D) Ld1 Ld2, Ls, Tb, Lp, Lpi, Pi, Lt1-3Ld2 cuts through all other lithofacies.Ld2 is present in the central vent area and high elevations of the edifice as well as seen cutting along the stacked lava at the edges of the mountainLd2 represent the latest stage of the Cracked Mountain eruptions; the other lithofacies were already cooled and lithified prior these late-stage intrusions 27 2.5.2 Lithofacies Association B Lithofacies association B comprises Lpi and Pi (Table 2); peperite deposits (Pi) are always spatially associated with masses of intrusive pillow lava (i.e. Lpi; Fig. 2.6). We interpret these occurrences as fuel-coolant interactions (FCI) where the sudden contact of hot magma (e.g. fuel) with cold, saturated sediment (e.g. coolant) generates a vapour film around the intruding body (i.e. Lpi) (Doyle, 2000; Hooten and Ort, 2002; Martin and Németh, 2007). Within the vapour films, instabilities may arise, causing local phreatomagmatic fragmentation along the borders of the intrusion. Regions that experienced more stable vapour films result in globular peperite texture (Fig. 2.6C) while areas with less film stability produce blocky peperite textures (Figs. 2.6D) (Martin and Németh, 2007). Most peperite deposits form along the margins of syn-volcanic intrusions and we take their widespread occurrence at or near the present-day surface of CM as an indicator of substantial post-eruptive erosion (e.g., Rosa et al., 2016). The field relations for Lpi and Pi show a contemporaneous origin, with both lithofacies forming as a result of intrusion into wet, unconsolidated lapilli tuffs. 28 Figure 2.8: Field photos illustrating pillow and subaerial lavas from Cracked Mountain. A) Stacked sequence of pillow lavas (Lp) (view looking NW at SE base of CM), ~150 m wide and ~40 m thick. White arrows mark approximate edifice basement contact at 1500 m a.s.l. B) Wall of pillow lava (Lp), ~10 m high, exposed on the S margin of the volcano. C) Coherent bulbous pillow lobes (Lp) up to ~0.5 m in diameter. Hammer (1 m) for scale. D) Remnant flow-top of 29 jointed sheet lava (Ls) near the summit of the volcano (~1,600 m a.s.l). Black arrows show granitic erratics and scour marks covering the surface of the lava. Hammer (1 m) for scale. 2.5.3 Lithofacies Association C This association comprises Tb, Ls, Lp, Lpi, and Lt (Table 2.2). The tuff breccia (Tb) blankets the upper surface of CM and contains a large proportion (<50%) of sheet lava (Ls) lithics, as well as moderate (30-40%) subrounded lithics of pillowed lava (Lp and Lpi), and minor (>5%) subrounded blocks of Lt (Fig. 2.7). The Tb matrix is comprised of moderately palagonitized, explosively derived fine ash, quench fragmented ash and lapilli, and coherent lapilli lithics. These findings suggest that Tb are syn-eruptive debris flows comprised of previously erupted volcanic lithics. The degree of palagonitization alteration throughout the unit indicates subaqueous deposition and may also have played a role in destabilizing the edifice slopes (Schiffman et al., 2006). The high volume of Ls lithics entrained within the widespread tuff breccias is our best line of evidence that sheet lavas made up a larger degree of edifice volume than what is preserved at the highly eroded present-day surface. Evidence of post-eruptive erosion (i.e. glacier erratics and scour marks; Fig. 2.8D) may explain why presently, Ls are only found as small remnant outcroppings. Given that the tuff breccias are comprised of earlier eruptive lithics (and not juveniles) this association suggests a temporal succession of Lt>Lpi≥Lp>Ls>Tb. 2.5.4 Lithofacies Association D Ld2 is associated with all other CM lithofacies (Table 2.2). At CM, Ld2 intrudes through all other lithofacies with sharp, columnar jointed margins, including cross-cutting Ld1 in select 30 locations. These contact relations indicate that Ld2 is the latest preserved lithofacies from the CM eruption. This last association suggests a temporal succession of Lt>Lpi=Pi≥Ld1≥Lp>Ls≥Tb>Ld2. 2.6 Chemistry and Petrography 2.6.1 Petrography Detailed mineral abundances and componentry based on standard polarizing light and scanning electron microscopy (Philips XL30) for all CM volcanic lithofacies are listed in Table 2.1. All coherent CM samples are olivine and plagioclase porphyritic, with glomeroporphyritic clots visible in hand samples. A smaller population of samples also contains phenocrystic augite. Petrographically, the pillowed dykes (Ld1) have similar mineralogy as found in pillowed (Lpi) and most sheet lavas (Ls). Jointed-dykes (Ld2) commonly contain phenocrystic augite as do a small proportion of pillow lava samples (Lp). Olivine phenocrysts are subhedral and unzoned. Plagioclase phenocrysts are tabular and moderately zoned, with a very minor percentage (>5%) showing sieve textures. When present, augite crystals are subhedral to anhedral. Volcaniclastic samples are distinguished by sorting, grain size, structures, and componentry. Lapilli tuffs (Lt1-3) are comprised of monolithic vitric juvenile fine ash and coarse lapilli (Figs. 2.9B-H) and microlitic tachylyte juvenile pyroclasts (5-30%). Intact to fragmented crystals of olivine and plagioclase are observed within the matrix of Lt1-3. Juvenile shapes range from blocky to highly vesicular (~60-70%) (Figs. 2.9B-H). Interstitial sediments are observed between coherent Lp clasts but are notably different (i.e. coarse, jig-saw fit clasts compared with Lt1-3 (e.g. Fig. 2.9A). 31 Tuff breccia (Tb) componentry is highly variable. Tb is dominated by clasts of basalt (Lpi, Ls, Lp) and contains minor blocks of Lt1 within a matrix of vitric ash and lapilli. Tb matrix is overall coarser than Lt1-3 although still contains abundant blocky and highly vesiculated juveniles. Figure 2.9: Photomicrographs showing textures of CM volcaniclastic lithofacies. A-D, E, and G are plane-polarized images at 4x magnification with a white 2 mm scale. D and F are from Scanning Electron microscopy (SEM), shown with a 300 μm scale bar. A) Photomicrograph of 32 interstitial pillow lava sediment (Lp) comprised of coarse, jig-saw fractured, weakly vesiculated glass. B) Photomicrograph of massive, ash, and lapilli tuff (Lt1) showing fine-grain juvenile clasts including microlitic (Mlt), blocky (Bl), and highly vesiculated (Vsc) vitric clasts. The matrix contains a small proportion of intact to fragmented olivine (Ol) and plagioclase crystals. C) Photomicrograph of massive lapilli tuff (Lt1) showing size range of juvenile vitric clasts and shapes (i.e. blocky and cuspate). D) SEM photomicrograph of 9C showing both blocky and highly cuspate vesiculated shapes of fine ash fraction (~ 100 μm). E) Photomicrograph of massive lapilli tuff (Lt1) showing coarse to fine juvenile clasts and fragmental crystals olivine and plagioclase. Highly vesiculated vitric clasts are abundant. F) SEM photomicrograph of 9E showing a highly vesiculated (50-60%) coarse vitric juvenile clast. G) Photomicrograph of thinly bedded lapilli tuff (Lt2) showing layers of ultra-fine ash separating layers of coarser, blocky (Bl), and vesiculated (Vsc) vitric clasts. H) Photomicrograph of matrix material supporting spatter dominated lapilli tuff (Lt3) showing a highly vesiculated, vitric juvenile lapilli clast within an ash and fine lapilli-sized vitric matrix. 2.6.2 Geochemistry Whole-rock major and trace element geochemical compositions were measured for 26 samples by X-ray fluorescence (XRF) analyses of fused discs and by inductively coupled plasma-mass spectroscopy (ICP-MS), respectively. Representative compositions of whole rocks and glasses are reported in Table 2.3; analytical uncertainties are based on replicate analyses done by Acme Analytical Labs Ltd., Vancouver, BC, Canada. A subset of samples was analysed for FeO volumetrically by ALS Canada Ltd., North Vancouver, BC, Canada. Appendix A contains additional data and analytical uncertainties for whole-rock geochemistry conducted at the Peter Hooper Lab, Washington State University, USA. Figure 2.10A illustrates the chemical diversity of CM samples after Le Bas et. al, 1986 classification of volcanic rocks. All CM samples are subalkaline (Irvine and Baragar, 1971) but display moderate spread in SiO2 (~47-51 wt.%) and Na2O-K2O (~3-4 wt. %). Fig. 2.10B shows Mg#s (molar MgO/ (MgO +FeO*)∗100) of CM samples with relation to SiO2 wt.%. Within the Cascade arc, volcanic rocks having Mg# > 60 are considered “primitive” indicating limited 33 crustal influence (Green and Harry, 1999; Mullen and Weis, 2013). Our results show CM samples range from Mg# ~55-67 with the majority of samples (~80%) between 60-66. Cracked Mountain rare earth elements (REE) are normalized to a Chondrite (Sun and McDonough, 1989) and shown in Fig. 2.10C. All CM samples show similar anomalies (i.e. positive Eu2+). Little variations in trace element concentrations are observed between samples, suggesting a similar mantle source for all CM eruptive deposits. 34 Figure 2.10: Major (XRF) and trace elemental (ICP-MS) compositions for whole-rock samples (white) and glasses (black) from Cracked Mountain (Tables 2.3, 3.2-3, A1). A) Total alkali (Na2O + K2O) vs Silica (SiO2) wt. % (TAS) with the classification of Le Bas et. al. (1986) and Irvine and Baragar (1971). B) Mg# (molar MgO/ (MgO +FeO*)∗100) vs Silica (SiO2) wt. % for Cracked Mountain volcanics. CM samples not measured with ferric titration use the mean value of Fe 2+/ Ʃ Fe =0.7228 (N=7) for CM basalts that were determined. C) Rare Earth Trace Element (REE) compositions of Cracked Mountain volcanics, normalized to Chondrite after Sun and McDonough (1989). 35 Sample MH-19-024 MH-19-031 MH-19-055 MH-20-001 MH-20-008 MH-20-009 MH-20-014 MH-20-016 MH-20-020 MH-20-032 MH-20-039 MH-20-043 MH-20-045UTM East 460484 460964 461014 460535 460462 460462 460539 460551 460554 460505 460653 460972 460972UTM North 5599888 5599860 5599824 5599657 5599597 5599597 5599598 5599924 5599602 5599864 5599610 5599769 5599769Facies Code Ls Ld2 Lp Ld2 Ld1 Lpi Lt1 (glass) Ld1 Lt1 (glass) Lpi Ls Ld2 LpPhenocrysts Pl>Ol>Cpx Pl>Ol>Cpx Pl > Ol<Cpx Pl > Ol<Cpx Pl>Ol Pl>Ol Pl~Ol Pl>Ol Pl~Ol Pl>Ol Pl>Ol Pl>Ol>Cpx Pl>Ol>CpxSiO2 (0.28) 49.13 50.16 49.97 49.76 49.66 48.80 48.41 48.62 48.17 49.68 49.10 50.37 49.91TiO2 (0.02) 1.49 1.33 1.46 1.51 1.49 1.56 1.54 1.41 1.50 1.55 1.43 1.57 1.38Al2O3 (0.14) 15.19 15.23 15.34 15.33 15.40 15.06 15.05 15.54 15.25 15.24 14.93 15.63 15.83Fe2O31 - 2.01 2.25 2.13 2.82 - - 2.81 - - 2.41 - -FeO2 (0.02) 12.04 9.01 9.00 9.41 9.03 13.27 13.34 9.14 13.36 12.93 9.12 11.74 11.88MnO (0.02) 0.15 0.15 0.16 0.16 0.16 0.17 0.19 0.15 0.18 0.16 0.16 0.14 0.15MgO (0.56) 8.31 9.11 8.72 8.78 8.77 8.91 9.21 9.23 9.40 8.41 9.42 7.91 8.31CaO (0.08) 8.77 8.56 8.62 8.59 8.74 8.82 8.12 8.77 7.79 8.77 8.50 8.96 8.69Na2O (0.02) 2.98 3.18 3.05 3.22 3.14 3.11 2.96 3.27 2.85 3.20 3.11 3.23 3.10K2O (0.02) 0.71 0.64 0.80 0.67 0.60 0.64 0.57 0.31 0.41 0.62 0.50 0.50 0.73Cr2O3 (0.02) 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04P2O5 (0.02) 0.24 0.24 0.24 0.25 0.24 0.29 0.28 0.25 0.24 0.26 0.24 0.25 0.23Ba 0.01 0.02 0.02 0.02 0.01 0.01 0.02 0.00 0.00 0.01 0.00 0.01 0.00SO3 0.03 0.01 0.04 0.06 0.00 0.08 0.06 0.00 0.10 0.10 0.03 0.00 0.07Sr 0.04 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05Totals 99.13 100.74 100.76 101.03 101.17 100.81 99.84 100.61 99.33 101.02 100.05 100.40 100.37LOI -0.14 -0.31 -0.37 -0.49 -0.37 -0.41 0.82 -0.52 0.77 -0.32 -0.36 0.12 -0.25Mg#3 62.99 64.32 63.33 62.45 63.39 62.35 63.00 64.29 63.44 61.47 64.80 62.43 63.30FeO(T)*(0.44) 12.04 12.02 12.25 12.59 12.86 13.27 13.34 12.97 13.36 12.93 12.55 11.74 11.88La (0.8) 10.6 9.4 9.4 8.7 9.8 9.8 10.6 10.0 9.7 9.1 10.2 8.8 -Ce (1.2) 21.3 20.8 19.8 20.5 20.1 21.3 21.4 19.1 21.4 19.5 20.0 18.7 -Pr (0.08) 3.09 2.88 2.9 2.84 2.82 3.08 3.04 2.87 3.06 2.88 2.83 2.75 -Nd (0.6) 14.1 12.8 13.5 12.9 13.8 13.9 14.5 13.4 14.5 13.2 13.9 13.1 -Sm (0.16) 3.76 3.76 3.54 3.49 3.48 3.74 3.74 3.45 3.54 3.48 3.4 3.61 -Zr (5) 92 91 88 96 87 95 107 89 102 94 88 95 -Hf (0.24) 2.20 2.50 2.20 2.40 2.40 2.50 2.70 2.30 2.50 2.50 2.30 2.40 -Eu (0.10) 1.39 1.37 1.29 1.30 1.27 1.32 1.35 1.27 1.28 1.34 1.27 1.35 -Gd (0.08) 4.09 3.89 3.92 4.05 3.96 3.95 3.97 3.92 4.04 3.94 3.76 3.87 -Tb (0.02) 0.67 0.63 0.63 0.61 0.59 0.61 0.61 0.58 0.59 0.59 0.60 0.60 -Dy (0.12) 3.62 3.53 3.42 3.45 3.35 3.46 3.60 3.33 3.47 3.43 3.34 3.32 -Y (0.9) 18.2 17.5 16.8 16.9 17.5 17.1 18.1 17.2 16.6 16.4 17.8 17.0 -Ho (0.04) 0.73 0.67 0.69 0.66 0.69 0.66 0.70 0.62 0.65 0.65 0.69 0.61 -Er (0.06) 2.00 1.78 1.81 1.75 1.82 1.83 1.79 1.76 1.74 1.71 1.71 1.77 -Tm (0.02) 0.28 0.25 0.25 0.24 0.24 0.23 0.24 0.23 0.22 0.23 0.23 0.22 -Yb (0.08) 1.62 1.47 1.48 1.53 1.38 1.50 1.51 1.46 1.49 1.41 1.33 1.37 -Lu (0.02) 0.24 0.22 0.23 0.20 0.21 0.21 0.21 0.20 0.20 0.21 0.20 0.20 -*FeO(T) is total iron oxide wt % reported from XRF analyses for all samples 1Fe2O3 calculated for samples with known FeO, where Fe2O3 = (FeO(T) - FeO)/0.8998)2FeO determined separately through ferric titration for select samples 3Mg# computed as MgO/(MgO+FeO (mol. %). CM samples not measured with ferric titration use the mean value of Fe 2+/ Ʃ Fe =0.7228 (N=7) for CM basaltsTable 2.3. Representative whole rock major (wt. %) and rare earth (ppm) element compositions of Cracked Mountain volcanic rocks analysed by X-ray fluorescence and ICP-MS, respectively. Analytical precision (2s) on major and trace elements based on replicates is reported in brackets. 36 2.7 Geochronometry 2.7.1 Radiogenic 40Ar /39Ar Results Two CM samples (MH-19-055, 031) were selected for 40Ar /39Ar radiometric dating at the WiscAr Geochronology Labs, University of Wisconsin-Madison, USA. The holocrystalline dyke sample (MH-19-031) proved to be non-measurable because of excess argon trapped in the plagioclase minerals. This is a common issue with basaltic dykes (of young ages) (Brian Jicha, pers. comm. 2021) and with subglacially erupted deposits of all compositions (Clay et al., 2015). The second CM sample (MH-19-055) was collected from the radially jointed interior of a pillow lava outcrop. This sample contained low radiogenic argon but the analysis was still possible through twenty-four heating steps with moderate uncertainty. The results yielded a plateau age of 401.6 ± 38.1 ka for crystallization of the groundmass (Fig. B1). Errors are quoted at a 2σ (95% confidence) level and are propagated from all sources except for mass spectrometer sensitivity and the age of the flux monitor. Appendix B contains analytical procedures used and table B1 contains complete measured data for heating steps. 2.7.2 Paleomagnetic Methods and Results A total of nine sites were selected for sampling at CM, with the objectives of gaining representative data from approximately the oldest to youngest CM lithofacies. One sample site (Site 2) was replicated to test for field and lab reproducibility. All samples were drilled into volcanic lithofacies that cooled quickly, thus locking in the geomagnetic field orientation at the time of emplacement (e.g., Johnson et al., 2008). Efforts were made to sample in situ outcrops and avoid areas of obvious post-emplacement rotation. Standard 2.5-cm-diameter paleomagnetic 37 cores were drilled in the field. Approximately eight cores were taken from most sites and a minimum of three cores from each outcrop. Each sample was oriented using a magnetic compass, and where possible a sun compass was used in conjunction with magnetic orientations. Cracked Mountain samples were analyzed at the paleomagnetic laboratory at the University of Lethbridge, Alberta. Magnetic susceptibility was determined with a Sapphire Instruments (SI-2B) susceptibility meter. The magnetization of each sample was measured with an AGICO JR-6A spinner magnetometer before demagnetization and again after each level of stepwise demagnetization. Cracked Mountain samples were held in magnetic shields following field collection and between laboratory measurements. All samples were subjected to alternating field (AF) demagnetization, performed using an ASC Scientific D-2000 demagnetizer with a three-axis manual tumbler, and carried out at 10 milli-tesla (mT) steps (up to 200 mT). Thermal demagnetization was carried out at 100, 200, 300, 400, 500, 525, 550, and 580 °C, using an ASC Model TD48 dual-chamber thermal demagnetizer to confirm that alternating field demagnetization was sufficient to resolve the primary remanence. Directions of characteristic magnetization were determined for each sample by principal component analysis (Kirschvink, 1980) using Remasoft version 3.0 (Chadima and Hrouda, 2006). Mean directions of characteristic magnetization were calculated for each site and an overall mean was also calculated (Appendix C; Table C1). All samples were subject to stepwise AF demagnetization and principal component analysis and mean directions were calculated from the AF data only. 38 Figure 2.11. Stereographic plots of magnetic remanence directions for Cracked Mountain volcano and examples of typical, well-behaved demagnetization data. A) Stereographic plot of mean data from CM Sites 2-9 and their α95 (p = 0.05) confidence circles (see Table C1). The mean of sites 2-9 are shown in red. Site 1 is excluded as is an outlier (see details in Appendix C) that appears to represent rotation associated with extensional collapse. B) Stereographic plots (left) show magnetization directions after stepwise AF and thermal demagnetization of the Lt1 sample from Site 2 (CMV060A/B), where the filled circles lie on the lower hemisphere. Orthogonal plots (right) show horizontal projections as filled circles and vertical projections as open circles. Natural remanent magnetization is shown with a circle and cross. Units are in amperes per metre. Note that AF demagnetization for sample CMV060B produces more coherent results than does thermal demagnetization. C) Well-behaved stepwise demagnetization data for a dyke (Ld1) sample collected at Site 6 (CMV029A/B), layout, symbols, and units as 39 2.11B. Note, this sample shows identical results for AF and thermal demagnetizations. Based on the results of detailed AF and thermal demagnetization of pilot specimens from each site, AF demagnetization is the preferred treatment. All paleomagnetic samples are normally magnetized (Fig. 2.11A; Table C1). The site mean directions are consistent for eight of nine sites, where all eight sites plot within the uncertainty circle (α95) about the overall mean (N=8) with a declination of 346.54 ̊ and inclination of 76.54 ̊, and Fisher precision factor of k = 351, α95 = 2.99° (Fig. 12A). Typical, well-behaved demagnetization characteristics are shown for samples from Lt1 and Ld1 respectively in Figs 2.11B and C. All paleomagnetic samples produced stable directions of magnetization following stepwise demagnetization. Alternating field demagnetization, applied to all specimens, exhibited linear decay to the origin on orthogonal projections (Fig. 2.11A and B). The median destructive fields range from 20–80 mT and final directions are often stable up to 200 mT alternating field demagnetization (see CMV060A, Fig. 2.11B) indicative of single-domain magnetite. Thermal demagnetization showed complete demagnetization at 550 to 580 °C, typical of fine-grained (single domain) magnetite as the magnetic carrier (see CMV029, Fig. 2.11C). Note that single-domain magnetite is the optimal magnetic mineral and grain size for producing reliable paleomagnetic directions. The magnetic susceptibility values of CM volcanics range from 0.4-1.0 x 10-3 SI (median value of 0.5 x 10-3 SI) for the flows composed of pyroclastic density currents and 2.4-16.4 x 10-3 SI (median value of 4.5 x10-3 SI) for dykes. Mean natural remanent magnetization for CM volcanics is 9.4 A/m (range 0.4–22.0 A/m). These findings indicate that the bulk of the sampled lithofacies at CM have the same emplacement age (i.e. monogenetic). 40 One site (Site 1; Table C1) provided seven samples that were outliers compared to the results obtained from the eight other sites (2-9). The sampling location for Site 1 was from basal lava (Lp) exposed below the SE cliff margin of the edifice. Of the seven cores analyzed from Site 1, we accept three as likely due to edifice rotation not evident in the field at the time of sampling. These three samples gave coherent results with a mean declination and inclination of 34.37 ̊ and 72.88 ̊ respectively. From our observed crack orientations (e.g. Fig. C1) we believe the edifice is collapsing in the downslope directions. This suggests that Site 1 may have experienced east (southeast) trending rotation. Based on a comparison of the stereographic orientation of Site 1 mean data (from three coherent samples) with the whole CM mean data, we find that a rotation of ~12 ̊ E is observed (Fig. C1), which is consistent with our interpretation of extensional collapse. Additionally, we calculated the approximate crack width from the ~12 ̊ of interpreted rotation and thickness of block (e.g. deposit thickness above basement) to be ~20 m. Again, this calculated crack width is consistent with observed crack widths seen along the outer margins of CM, and further supports our interpretation of Site 1 paleomagnetic data. The remaining four samples collected from Site 1 returned highly dispersed results that were inconsistent with both the mean CM magnetic data of Sites 2-9 and the three Site 1 samples that plot within our plausible edifice collapse direction. We interpret the remaining four samples to be a result of the reorientation of blocks (i.e. not in situ to edifice lava wall) not obvious at the outcrop at the time of sampling. 41 2.8 Discussion 2.8.1 A glaciovolcanic eruption within an englacial lake Our mapping and analysis suggest CM is a monogenetic edifice with no evidence of time lapses during the eruption. The results of paleomagnetic analyses concur with our field observations that the varying lithofacies were emplaced in one paleomagnetic moment (< 1,000 years; Turner, 1987; Barletta et al., 2010; Lisé-Pronovost et al., 2013) at 401 ±38 ka based on our best 40Ar /39Ar age determination. Cracked Mountain lithofacies (i.e. pillow lavas, palagonitized tuffs, and peperites) indicate a subaqueous eruptive paleoenvironment, however, the edifice is situated in an alpine setting with extremely steep-sided valleys on all sides (Fig. 2.3). There are no reasonable physical barriers (i.e. mountains or ridges) to provide a paleo-closed catchment to form an alpine lake, thus, we ascribe a glaciovolcanic origin. CM lacks the lithofacies succession in a “Classic” mafic tuya model (e.g., pillow effusion, hyaloclastites, lava-fed deltas, and capping lava) (Smellie, 2007; Jakobsson and Gudmundsson, 2008; Edwards et al., 2015). The Russell et al., (2014) descriptive classification would describe CM as a transitional, tephra-dominated, tuya. The CM volcanic succession is ~250 m thick and subaqueous lithofacies outcrop at elevations as high as ~1,650 m a.s.l where they have relief of ~800 m above the major drainages. At the highest elevations of CM (~1,600-1650m a.s.l), we find small remnant subaerial sheet lavas (Ls) but no evidence of preserved ‘passage zones’ (i.e. surfaces that mark transitions between subaqueous and subaerial depositional environments during volcanic eruptions) (Jones, 1970; Smellie, 2006; Russell et al., 2013; Edwards et al., 2015). This provides strong evidence that the englacial meltwater lake was sustained throughout the majority of the eruption and the lake surface elevation continued to rise with the growth of the edifice. The absence of lava-fed 42 delta sequences containing pillow breccias at Cracked Mountain (i.e. aggradation of volcaniclastic material from lava flowing into the water; Edwards et al., 2015) suggests Ls formed as overlapping effusions of subaerial lava (e.g., Skilling, 2009; Russell et al., 2013) where the englacial lake had partially drained at a later time in the edifice buildup. The present-day Ls outcrops are small; however, we find substantial Ls lithics entrained in the thick, massive Tb that cover much of the CM surface. These findings suggest a significant volume of subaerial lava erupted during the late-stage edifice formation. Two scenarios would give rise to the subaerial capping lavas: 1) The edifice grew above the paleolake level, becoming emergent, where a passage zone would denote the maximum lake level, or 2) the water level dropped (via drainage) giving rise to dry, subaerial eruptive environment. In the latter case, the subaerial lavas would mark the minimum height that lake level reached (i.e., overlap) (Russell et al., 2013). We favour the second scenario of overlap lavas because we find no definitive passage zones that would suggest subaerial lavas aggraded into water (i.e. lava-fed-deltas) and our models of meltwater produced versus paleolake capacity suggest a moderately ‘leaky’ lake system must have been present in the later stages of the eruption (see section 8.4). Thus, the elevation of Ls (~1,650 m) marks the minimum level for the paleo-englacial lake. 2.8.2 Explosive Onset to Glaciovolcanic Eruption The lapilli tuff deposits (e.g. Figs. 2.9B-H) are comprised of coarse to fine ash (>100 μm) particles that are commonly highly vesiculated (<60%). The abundance of fine ash in CM Lt deposits suggests explosive magmatic and/or phreatomagmatic fragmentation (Zimanowski et al., 1991; White and Valentine, 2016; Latutrie and Ross, 2020). CM Lt deposits comprise both blocky ash (e.g. Fig. 2.9B) and micro-vesiculated cuspate ash (e.g. Figs. 2.9D and F) suggesting 43 that both phreatomagmatic (external water) and magmatic (internal volatiles) drove the explosive fragmentation processes. We note that blocky juveniles are dominant in Lt1-3 suggesting that phreatomagmatic reactions involving glacial meltwater played the largest role in the explosive eruptive style. Based on the overall bedform and textures found in Lt deposits, we assert that the depositional environment was wet and probably (shallow) subaqueous. The massive, moderate to poor sorting of Lt1 suggest an influx of fragmental material erupted through a sustained column (e.g., White, 1996, 2000) and the lack of welding between matrix and juvenile material suggests a water-rich intergranular phase (rather than gas) was present through these eruption-fed aqueous density currents (White, 2000; Brand and Clarke, 2009). The thinly bedded, moderate to well sorted, and weakly normally graded Lt2 is indicative of deposition from dilute pyroclastic density currents (i.e. pyroclastic surge; Fisher and Waters, 1970; Brand and Clarke, 2009). These deposits reflect phreatomagmatic explosive pulses that dispersed highly fragmented ash laterally and elutriated through the water column. The shallow dipping cross-bedding preserved in some Lt2 outcrops (Fig. 2.4B) is consistent with subaqueous pyroclastic deposits (Moorhouse and White, 2016). The overall lack of well-sorted beds of fine ash, characteristic of thick water column elutriation, makes a shallow subaqueous setting most plausible. Lt3 is composed of non-welded spatter within moderately to well-sorted ash and lapilli matrix (Fig. 2.4C). We propose that the Lt3 deposits record periods of increased magma flux, volatility, and/or a decreased water supply (at the vent), where a strombolian style burst ejected largely vesiculated and fluidal clasts (Latutrie and Ross, 2020). We find that the overall characteristics of the Lt3 deposits indicate a shallow aqueous to emergent depositional 44 environment. This assertion is based on a lack of bomb sags within these deposits and chilled but not quenched (or pillowed) spatter clasts. The two outcrops of Lt3 are located at upper elevations of CM, and not observed within lower to middle stratigraphy. Our interpretation is Lt3 represents localized magmatic generated fallout mixed with phreatomagmatically generated pyroclastic density currents in shallow aqueous to locally drained regions of CM. Explosively derived Lt deposits are present at all elevations of CM (Fig. 2.2) and we estimate that it comprises ~30% of the edifice by volume (Table 2.1). Our findings indicate that not only was the onset of the CM eruptions explosive but that explosivity was sustained through the middle to late stages of the eruption. This explosive-styled eruption makes CM unique within the GVB, being only one of five other identified tephra-dominated glaciovolcanic landforms (Wilson and Russell, 2018). We hypothesise that these explosive styled eruptions may not be uncommon in any glaciovolcanic setting but rather tephra-dominated landforms are less likely to be preserved, compared to lava-dominated tuyas, if multiple cycles of glaciation occur after edifice formation. We suggest CM’s transitional eruptive history, which produced intrusive and effusive coherent lavas, helped create a stronger structure more resistant to glacial erosion. 2.8.3 Model for CM eruption The glaciovolcanic deposits record a complex sequence of events indicative of a primarily subaqueous setting. We find that the interior of the edifice is dominated by tephra and peperitic intrusions, while the margins are comprised of coherent lavas and lava-dominated breccias. These variable lithofacies speak to transitions in eruptive style from explosive to effusive. Lastly, the shape and present-day partial collapse of CM (in the form of cracks) provide 45 a post-eruptive context for the paleoenvironmental setting of the eruption. Our model for the CM sequence of events (Fig. 2.12) is described below. 1. An explosive, Surtseyan phase dominated the initial CM eruption, producing a subaqueous tephra cone comprised of Lt1 (Fig. 2.12A). This initial phase is evidenced by the predominant bedform structure and componentry of Lt1 (i.e. massive, moderately sorted vitric ash and lapilli) which we interpret to be derived from a sustained phreatomagmatic column and proximal high-density pyroclastic flows. Our temporal assessment for this phase is based on stratigraphic relations (i.e. Association A; Fig. 2.5) between Lt1 and Lpi. This association is seen from the base of the edifice (e.g. Fig. 2.2B) through to the summit and is supported by the fact that we find no exposure where CM volcanics post-date Lt1, making it the oldest mapped unit. 46 47 Figure 2.12: Schematic model (2x V.E) of volcanic evolution of CM. Stage 1: Explosive phreatomagmatic eruptions, building a subaqueous tephra cone. Stage 2: The sustained intrusion of lava into unconsolidated sediments, and endogenous growth of the edifice. Dykes that breached the margins of the volcanic pile produced pillowed lavas within the englacial lake. Stage 3: Involves the buildup of CM to the level of the englacial lake (or above) and subaerial eruption of lava as well as syn-eruptive debris flows forming deposits of massive tuff breccia. Stage 4: Post-eruptive, glacial retreat, where the top of the edifice is scoured off. Additionally, the removal of glacially confined margins causes extensional, gravity-driven stress on of the overs steeped volcanic successions, causing cracks to form and partial edifice collapse. 2. The second CM eruptive phase is characterized by the transition from explosive to effusive (and intrusive) activity (Fig. 2.12B). Peperitic dykes (Ld1) and bodies (Lpi) inflate the edifice from within, and dykes that reach the margins of the tephra pile form pillow lavas (Lp) that pile up on the margins of the volcano. The presence of peperites (Pi) along the margins of Lpi (Fig. 2.6) indicates that these large lava bodies were intrusive rather than extrusive. This relationship shows that phase 2 occurred rapidly after phase 1, where the previously erupted tephra was still unlithified. 3. The third CM eruptive phase involved continued intrusions and effusions through the earlier erupted lithofacies, forming effusive lavas (Ls), breccias (Tb), and dykes (Ld2) (Fig. 2.12C). The columnar jointing of the remnant Ls outcrops suggests the lake level was draining periodically at this point, likely through well-established drainage channels that prevented lake volumes from reaching amounts capable of floating the encapsulating glacier (see section 8.4 below). The massive tuff breccias contain lithics from all other volcanic lithofacies, including rounded, block-sized Lt1. This relationship suggests explosivity persisted throughout the later stages of the CM eruption, where underlying Lt1 was ripped up, subrounded, entrained, and deposited in Tb. The later stage explosivity is further substantiated by our findings of high stratigraphy fire-fountaining deposits (Lt3) that show 48 signs of ‘dryer’ deposition in locally drained regions of the edifice. The culmination of the CM eruption is marked by late-stage dyke activity (Ld2) that cut through all other lithofacies. Despite changes in eruptive styles (i.e. explosive and effusive) and environments (i.e. wet and dry), the paleomagnetic signatures of all CM deposits overlap within one paleomagnetic moment. Thus, the CM eruption taking place from stages 1-3 can be thought of as more or less continuous. 4. The final stage in the CM formation was non-eruptive and characterized by glacial erosion and edifice collapse (Fig. 2.12D). The timing of glacial retreat after the CM eruption is unclear, but we do find evidence of glaciation (i.e. erratics and scour marks) on the present-day surface. These findings show that at some point post-eruption, CM was once again enveloped in an ice sheet. We propose that this post-eruptive glaciation removed portions of the upper CM eruptive stratigraphy and carved the over-steepened edifice margins that we presently see today. The final process we model at CM is the formation of the cracks after the glacial unconfinement. We attribute this partial edifice collapse to the removal of confining pressure after the ice sheet retreated. The lack of glacial deposits within the cracks indicates that they formed after the localized last glacial maximum and are probably continuing to collapse to the present day. 49 50 Figure 2.13: Paleoclimate glacial reconstruction at the time of Cracked Mountain eruption, ~401 ka. A) Hillshade DEM for CM map area overlain showing the dispersal of glacial ice. We use the approximate summit of CM (~1650 m a.s.l) as the minimum height at which glacial ice is reached. All regions below 1650 m are shown in light blue (i.e. ice) and all regions above 1650 m are shown in brown. CM edifice is shown in green within a schematic englacial lake. B) Undivided N-S (A-A’) and E-W (B’-B) cross-sections for CM, shown at no VE. Volcanic rocks (green) overlie basement (pink) above steep valleys to the N (Meager Creek) and W (Elaho Valley). Schematic glacier ice is shown confining CM with an englacial lake forming around the volcano. The minimum thickness of the englacial lake is ~250 m estimated from the total thickness of the edifice. C) Schematic 3D DEM is shown for the CM map area. The same colours and symbols were used in 2.13A. Glacial ice is shown reaching minimum elevations of 1650 m a.s.l. with a minimum thickness of ~850 m based on the elevation of Meager Creek. Schematic drainage channels are shown based on the physiographic setting of the edifice. 2.8.4 Paleoenvironmental reconstruction We find englacial erupted CM lithofacies at elevations up to 1,650 m a.s.l, with the volcanic succession built ~250 m atop the basement rocks. These findings require that the englacial lake which CM erupted into would have been ~250 m deep along the edifice margins (Fig. 2.13B). We use these findings to investigate the minimum ice thickness at the time of the CM eruption. In glacial lakes, when the water level exceeds ~90% of ice thickness, the hydrostatic pressures exceed glaciostatic pressures, causing the ice to float (e.g., Tweed and Russell, 1999; Smellie, 2006; Edwards et al., 2015). In the case of CM, we find that to sustain a lake level of 250 m without resulting in hydrostatic drainage, the ice must have been at least ~280 m above the basement rocks. We find no field-based evidence of rapid subaerial edifice growth that would indicate a deluge of meltwater occurred (i.e. jökulhlaups; Tweed and Russell, 1999; Gudmundsson et al., 2004; Russell et al., 2013). Therefore, the minimum ice cover must have reached 1,680 m a.s.l. Given that CM is not located beneath peaks that could have sourced an alpine glacier, the encompassing ice must have been a continental ice sheet (CIS). We use the models of CIS growth and decay (e.g., Clague, 2009; Wilson et al., 2020) to show that the 51 surrounding Meager Creek and Elaho Valley’s would have been filled with ice, and only the upper elevation peaks of the Mount Meager massif would be emergent (Fig. 2.13A). We use the constraints of the surrounding topography to calculate the minimum thickness of the CIS. The lowest point in the northward Meager Creek valley is ~800 m a.s.l, thus the CIS was > 880 m thick (given the elevation of ice above CM at 1,680 m a.s.l) (Fig. 2.13C). We use the shape and size of CM and the surrounding topography to approximate the maximum dimensions and volume of a paleo-englacial lake. Based on the gradient of underlying basement rocks (Fig. 2.3), we estimate that the englacial lake is unlikely to have extended more than 50 m past the north and west CM borders, ~100 m from the south edge, and up to 300 m at the east edifice corner (Fig. 2.13A). We estimate that the lake had an asymmetric shape, 1800 m long and 1300 m wide, and a maximum depth of 250 m (Fig. 2.13B). From our estimated dimensions, and assumed uniform lake depth, we calculate maximum lake volume at ~0.36 km3. We estimate the volume of erupted material to be ~0.18 km3 based on present-day edifice dimensions and thickness. Throughout the eruption, water volume (within the lake) would have been displaced by erupting material, and by stage three (i.e. edifice maximum volume), only ~0.18 km3 (i.e. max lake volume – edifice volume) of water could have been stored in the lake. The heat capacity of a basaltic eruption the size of CM is capable of melting more than 2 km3 of water from surrounding ice (e.g., Gudmundsson et al., 2004; Kelman, 2005; Tuffen, 2007). This volume of meltwater exceeds the capacity of our proposed maximum paleolake and negates the possibility of a fully sealed lake catchment system. Instead, we propose a leaky lake system, with established drainage channels (Fig. 2.13). The CM age of 401 ± 38 ka fits within the waning of marine δ18O isotope stage (MIS) 12 glacial period (~470-425 ka) into the warming period of MIS 11 (~420-375 ka) (Lisiecki and 52 Raymo, 2005) (Fig. 2.14). The shift in global δ18O during MIS 12 to 11 is the most drastic of the Pleistocene cycles (e.g. Fig. 2.14), signifying rapid global warming. Thus, we believe a CIS thickness of ~850 m at 400 ka (i.e. middle of MIS 11) was unlikely. Instead, we favour a slightly older age of ~425 ka for the Cracked Mountain eruption. This slightly older age fits within the analytical uncertainty of the 40Ar /39Ar results and places the eruption more within the waning of the global ice period (MIS 12) (Lisiecki and Raymo, 2005; Batchelor et al., 2019). We also speculate that at this time, there may have been a large-scale decompression effect on the Earth’s crust driven by rapid deglaciation at the end of MIS 12. The link between volcanism and crustal unloading during periods of deglaciation has been modeled throughout the GVB (e.g., Wilson and Russell, 2020) and explored in Icelandic and Andean glaciovolcanic fields (e.g., Carrivick et al., 2009; Guillot and Ponce, 2021). We, therefore, find it entirely feasible that the CIS retreat in SW British Columbia would have triggered magmatic ascent through the unloaded crust, leading to the CM eruption. Lastly, since records of older glaciation cycles tend to be obscured by younger waxing and waning of ice sheets, our findings at CM provide useful temporal and physical constraints for the CIS extent in SW British Columbia during the mid-Pleistocene. 53 Figure 2.14: Mid to late Pleistocene Marine δ18O (o/oo) isotope record (MIS), modified from Lisiecki and Raymo (2005) showing fluctuations (and numbered stages) in global ice from, where higher δ18O represents periods of more global ice and lower δ18O represents periods of lower global ice. The vertical axis is a record of time (ka) with magnetic pole orientations shown through the Pleistocene. Dark bars are times of normal polarity and white bars are times of pole reversal. The dashed box indicates the blow-up portion of the MIS from 250-600 ka. The Cracked Mountain plateau age of 401.6 ± 38.1 ka is plotted (grey shaded) on the blow-up MIS portion, representing times from the waning of MIS 12 through MIS 11. 54 2.9 Summary The Garibaldi Volcanic Belt contains many Quaternary glaciovolcanic centres. The study of these volcanoes provides paleoclimatic evidence at the time of the eruptions and contributes to the understanding of magma, ice, and water interactions more generally. Here, we present the first physical volcanological study of Cracked Mountain, a transitional, tephra-dominated tuya. Our findings indicate an initially explosive eruption that later transitioned into a mixture of intrusive and extrusive styles. We characterize the explosivity as dominantly phreatomagmatic, manifested as Surtseyan style eruption in a shallow englacial lake. Peperitic intrusions and pillow lava effusions are the largest coherent units by volume, indicating that subaqueous conditions persisted through the middle and later stages of the eruption. Small remnants of subaerially erupted lavas are preserved at the highest elevations, suggesting that the lake drained periodically in the later stages of the eruption. This claim is supported by our modeling of paleolake dimensions and volumetric capacities. Lastly, our temporal investigation of the eruption concludes that CM was monogenetic, erupting ~425 ka between MIS 11 and 12. We model the localized, mid-Pleistocene CIS as having a minimum thickness of ~850 m, reaching elevations of 1,680 m a.s.l or higher. 55 Chapter 3: The Magmatic Origins of Cracked Mountain: Evidence for Cryptic Tapping of Two Magma Chambers During a Monogenetic Eruption 3.1 Introduction The Garibaldi Volcanic Belt (GVB) is the northern segment of the Cascade Volcanic Arc (Roddick and Souther, 1987; Green et al., 1988; Hildreth, 2007). Garibaldi belt volcanic deposits range from Pleistocene to Holocene in age and result from subduction of the Juan de Fuca plate beneath the North American Plate (Roddick and Souther, 1987; Green et al., 1988; Hildreth, 2007). Approximately 75% of GVB eruptive material is felsic (dacite and rhyodacite) (Hildreth, 2007), however, mafic vents (predominantly monogenetic) and flows are present on the peripheral margins for all five major GVB centres (e.g. Mount Baker, Glacier Peak, Mount Garibaldi, Mount Cayley, and Mount Meager) (Lawrence et al., 1984; Stasiuk and Russell JK, 1989; Green and Sinha, 2004; Hildreth, 2007). One such mafic occurrence is Cracked Mountain (CM), a ~0.18 km3 basaltic, glaciovolcanic landform situated on the southern flank of the MMVC (Fig. 3.1) (Wilson and Russell, 2018; Harris and Russell, 2021). The volcano was originally identified by Read (1979) as part of the Mosaic Assemblage, and revisited by Wilson and Russell (2018) who named it Cracked Mountain due to the abundant extensional cracks that dissect the entirety of the edifice. Here, we present new petrographic and geochemical data for individual lithostratigraphic units as defined by Harris et. al., (under review). Collectively, these data inform on the petrochemical differences observed at CM. While Harris et al., (under review) established that CM erupted continuously (i.e. monogenetic) within a shallow englacial lake enclosed by a continental ice-sheet, our new findings indicate CM 56 volcanic deposits contain two unique mineral assemblages. The first assemblage contains olivine-plagioclase phenocrysts, and the second has olivine-plagioclase-augite phenocrysts. Despite this distinct petrographic difference, CM rocks contain only minor variations in major, trace, and mineral geochemistry. Guided by our observations of the true mineralogy for the CM samples, we implement chemical and thermodynamic models to deduce the pre-eruptive pressure-temperature-H2O conditions of magma crystallization. Our findings show that CM magmas must have crystallized at two distinct pressure ranges (i.e. crustal depth) before a singular eruption, thereby contributing to the global study of monogenetic systems as well as informing on volcanic arc crustal magma chambers. 57 Figure 3.1: Location, geologic setting, and the sampling distribution of Cracked Mountain volcano. A) Map of the Cascade volcanic arc in the USA and Canada (i.e. Garibaldi volcanic belt (GVB)) (modified from Mullen and Weis, 2013; Wilson and Russell, 2017). B) Undivided geological map of MMVC distribution of Mt. Meager volcanic deposits (MV), basement (Bu) throughout the region (Woodsworth, 1977; Read, 1979; Harris and Russell, 2021). The youngest MMVC eruption, 2350 B.P. Pebble Creek Formation (PcF) (Hickson et al., 1999; Stewart et al., 2008) is differentiated from other MMVC volcanic deposits. Cracked Mountain (CM) is situated south of the main MMVC (Wilson and Russell, 2018; Harris and Russell, 2021). C) A N-S oriented Google Earth imagery with CM physiography overlain. The dark grey colour denotes the volcanic edifice and the solid black line marks the basement contacts. Sample sites are indicated with a black diamond (olivine-plagioclase porphyritic) or white circle (olivine-plagioclase-augite porphyritic). 3.2 Geological Background The Mount Meager volcanic complex is situated 160 km north of Vancouver in SW British Columbia (Fig. 3.1) and is one of eight major centres and volcanic fields comprising the GVB (Fig. 3.1A). Recent GVB geochemical and petrological studies show increases in melt alkalinity and a decrease in slab-derived signatures moving northward in the GVB (Green and Sinha, 2004; Mullen and Weis, 2013). In particular, the MMVC, Salal Glacier volcanic complex, and Bridge River volcanic field show a heightened primitive signature compared to the 58 southward GVB and the High Cascade volcanoes. These findings suggest that the Nootka Fault, located Northwest of the Bridge River cones (Fig. 3.1A), may mark the terminus of the Juan de Fuca subduction where a window between the Juan de Fuca and Northward Explorer plate allows upwelling of asthenospheric melts under the northernmost GVB centres (Mullen and Weis, 2013, 2015). The MMVC (Fig. 3.1B) contains Pleistocene to Holocene basalt to rhyolite overlying basement igneous and metamorphic rocks of the Coastal Plutonic complex (Fig 3.1B) (Woodsworth, 1977; Read, 1979; Green et al., 1988). The MMVC is also host to the youngest GVB eruptive deposits, namely the 2350 B.P. Pebble Creek formation (Hickson et al., 1999; Stewart et al., 2008). Intermediate to felsic lavas are dominant within the Mount Meager Massif, however, localized mafic centres are present in the north (Lillooet Ridge and River), west (Mosaic Ridge), and southwest (Cracked Mountain and Elaho Valley) regions of the volcanic complex (Fig. 3.1B) (Read, 1979, 1990; Harris and Russell, 2021). The ages of the Mosaic Ridge basalts and Elaho Valley basaltic andesites are ~90 and 140 ka respectively (Woodsworth, 1977; Green et al., 1988). 3.3 Cracked Mountain Volcano 3.3.1 Morphology The Cracked Mountain volcano unconformably overlies basement granodiorite and schist of the Gambier and Cadwallader Groups respectively (Read, 1979). The volcanic deposits form a slightly asymmetric, NE-SW trending ~250 m thick ridge that is ~1,300 m long and ~1,000 m wide. The eruptive volume of the edifice is conservatively 0.18 km3 based on present-day dimensions. The summit of CM rises to 1,650 m above sea level (a.s.l.) and the margins reach 59 elevations as low as 1,250 m. CM is surrounded by steep valleys of the Meager Creek and Elaho River tributaries to the north and west respectively (~850 m a.s.l). Extensional cracks dissect the entirety of CM, ranging from 0.5 to > 20 m in width and up to 30 m in depth. The fractures form parallel clusters that commonly trend perpendicular to the downslope direction. The extensional cracks intersect and displace all CM lithofacies. No glacial deposits (i.e. till, erratics) are found within the cracks, suggesting they have a post-eruptive and post-glacial origin (Harris et. al., under review). The shape and surface features of CM show evidence of glacial enveloping and scouring. The present-day surface is littered with cobble to boulder-sized granitic erratics and some locations have been smoothed and striated in an SW direction. These findings show that post-eruption Cordilleran Ice Sheets have reached elevations greater than the summit of CM. 3.3.2 Geology The absolute age of Cracked Mountain is 401 ± 38 ka (Harris et. al., under review). The volcanic edifice is comprised of massive to poorly stratified, moderately to pervasively palagonitized lapilli tuffs, coherent to disaggregated lobes of peperitic intrusions, stacked pillow lavas, sheet lavas, debris flow tuff breccias, and subvertical dykes (Harris and Russell, 2021; Harris et al., under review). Stratigraphically, the lapilli tuffs are the oldest, followed by peperitic intrusions, pillow lavas, sheet lavas, tuff breccias, and dykes. Subaqueous lithofacies (palagonitzed tephra, peperites, and pillows) are volumetrically dominant, and only minor (>5%) portions of the upper edifice contain remnant subaerial sheet lavas. A glaciovolcanic origin (e.g., Kelman et al., 2002; Smellie, 2007; Edwards et al., 2009) is established based on the absence of physical barriers (i.e. ridges or peaks) that could have sustained a closed catchment capable of 60 supporting a paleolake. Instead, a continental ice sheet (CIS) must have enclosed the entire edifice at the time of eruption (Wilson and Russell, 2018; Harris et. al., under review). 61 Figure 3.2: Photomicrographs showing textures of coherent CM samples (A-E) and one crystalline lapilli pyroclasts from a volcaniclastic deposit (F). All images are at 4x magnification with a back 2 mm scale. A, C, and E, display examples of the olivine-plagioclase-augite porphyritic sample suite (i.e. OPA) while B, D, and F display examples of the olivine-plagioclase sample suite (i.e. OP). 3.4. Petrological Results 3.4.1 Petrography Detailed mineral abundances and componentry based on standard polarizing light and scanning electron microscopy (Philips XL30) for all CM volcanic lithofacies are summarized in Table 3.1. The petrographic study established two distinct groups of CM volcanic deposits: 1) an olivine and plagioclase-phyric population (OP) (i.e. Fig. 3.2B, D, and F) and 2) olivine, plagioclase, and augite-phyric population (OPA) (i.e. Fig 3.2A, C, and E). The prevalence or lack of phenocrystic augite (< 3% volume) is the basis for our segregation. The OP phenocrystic suite includes pyroclasts separated from volcaniclastic deposits, pillow lavas, sheet lavas, and peperitic and non-peperitic intrusions. The OPA phenocryst suite is restricted to pillow lavas and late-stage dykes. Olivine phenocrysts are subhedral and unzoned. Plagioclase phenocrysts are tabular and moderately zoned; a minor percentage (<5%) are sieve textured. When present, augite crystals are subhedral to anhedral, and in some cases display rounded edges suggesting disequilibrium and partial resorption (Fig. 3.2E). 62 Table 3.1. Petrographic Summary of Cracked Mountain Volcanic Lithofacies Coherent DepositsPetrographic AssemblageAssociated LithofaciesTexture Phenocrysts GroundmassOPA Dykes, pillow lavas, and sheet lavasHolocrystalline to hypocrystalline, glomeroporphyritic; subophitic; sparsely vesicular (5-20%)Pl (10-15%, 0.5-3 mm); Ol (10%, 0.1-1 mm); Au (2-5 %)Pl (55%, microcrystalline); Cpx (25%), Ol (10%), Glass (5 %); Fe-Ti oxides (5%)OP Peperitic intrusions, dykes, pillow lavas, sheet lavasHolocrystalline to hypocrystalline, glomeroporphyritic; subophitic to intergranular; sparsely to moderately vesicular (5-30%)Pl (10-15%, 0.5-3 mm); Ol (5-10%, 0.1-1 mm)Pl (55%, microcrystalline); Cpx (25%), Ol (10%), Glass (5 %); Fe-Ti oxides (5%)Volcaniclastic DepositsComponentry Matrix OP Lapilli Tuff, Tuff Breccias, PeperitesMonolithic, ash to lapilli, moderately to highly vesicular, Pl (5-10%) Ol (5%) microlitic vitric juveniles (5-30%, 0.5-5mm); Intact to fragmented crystals, Pl (5-10% 0.5-2 mm) and Ol (5-10% 0.1-1 mm)Massive; moderately sorted, yellow-grey, ash to lapilli; ~ 25-40% cuspate and highly vesicular juveniles, ~60% dense and blocky juveniles 63 3.4.2 Major and Trace Element Geochemistry Whole-rock major and trace element geochemical compositions were measured for 26 samples by X-ray fluorescence (XRF) analyses of fused discs and by inductively coupled plasma-mass spectroscopy (ICP-MS), respectively. Representative compositions of whole rocks and glass major element (wt.%) chemistry are reported in Table 3.2, and trace element (ppm) in Table 3.3; analytical uncertainties are based on replicate analyses done by Acme Analytical Labs Ltd., Vancouver, BC, Canada. A subset of samples was analysed for FeO volumetrically by ALS Canada Ltd., North Vancouver, BC, Canada. Appendix A contains additional data and analytical uncertainties for whole-rock geochemistry conducted at the Peter Hooper Lab, Washington State University, USA. Figure 3.3A illustrates the chemical diversity of CM samples after Le Bas et. al, 1986 classification of volcanic rocks. All CM samples are subalkaline basalts (Irvine and Baragar, 1971) and display moderate spread in SiO2 (~47-51 wt.%) and Na2O-K2O (~3-4 wt. %). CM OP samples are predominantly lower in SiO2 wt.% and Na2O-K2O wt.% than OPA samples. CM glass was collected from coarse crushed volcaniclastic samples and has the lowest SiO2 and Na2O-K2O wt.% found at CM. Ratios of major elements that are typically incompatible in basaltic magmas (K/P and Ti/P) are nearly all within 2 for all CM samples (e.g. OP, OPA, and glass) (Fig 3.4). When plotted against Mg# (molar MgO/ (MgO +FeO*)∗100) no distinct groupings are seen between different phenocryst assemblages. OPA samples tend to have a smaller spread (57-64) compared with OP samples (55-68) but the majority of all samples analysed (~80%) overlap between 60-66. (Fig 3.4). 64 CM rare earth elements (REE) are normalized to a Chondrite (Sun and McDonough, 1989) and shown in Fig. 3.3B. All CM samples (e.g. OP, OPA, glass) show similar anomalies (i.e. positive Eu2+). Little variations in trace element concentrations are observed between samples, suggesting a similar mantle source for all CM eruptive deposits. 65 Figure 3.3: Major (XRF) and trace elemental (ICP-MS) compositions for whole-rock samples from Cracked Mountain (Tables 3.2-3.3, A1). OPA samples are shown in green, OP samples in blue, and glass in black. Reference MMVC mafic data is shown in yellow (Table A2). A) Total alkali (Na2O + K2O) vs Silica (SiO2) wt. % (TAS) with the classification of Le Bas et. al. (1986) and Irvine and Baragar (1971). B) Rare Earth Trace Element (REE) compositions of Cracked Mountain volcanic deposits, normalized to a Chondrite after Sun and McDonough (1989). Figure 3.4: Incompatible element ratios (A) Ti/P, and (B) K/P versus Mg# (molar MgO/ (MgO +FeO*)∗100) for Cracked Mountain volcanic deposits. CM samples not measured with ferric titration use the mean value of Fe 2+/ Ʃ Fe =0.7228 (N=7) for CM basalts that were determined. Mean ratios are shown as a white box with 2σ bars. 66 Table 3.2. Whole rock major (wt.%) element compositions of Cracked Mountain volcanic rocks analysed by X-ray fluorescence. Analytical precision (2s) on major and trace elements based on replicates is reported in brackets. Whole-rock analyses conducted by Acme Labs Ltd., Vancouver BC. Ferric titration measured by ALS Canada Ltd., North Vancouver, BC. Normative Mineralogy (wt%) reported from Lowerstern, USGS (2000). Sample MH-19-024 MH-19-031 MH-19-032 MH-19-047 MH-19-055 MH-20-001 MH-20-008 MH-20-009 MH-20-010 MH-20-014 UTM East 460484 460964 460964 460450 461014 460535 460462 460462 460462 460539 UTM North 5599888 5599860 5599860 5599594 5599824 5599657 5599597 5599597 5599597 5599598 Phenocrysts Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol Pl > Ol<Cpx Pl > Ol<Cpx Pl>Ol Pl>Ol Pl>Ol Pl~Ol SiO2 (0.28) 49.13 50.16 50.04 49.24 49.97 49.76 49.66 48.80 50.26 48.41 TiO2 (0.02) 1.49 1.33 1.54 1.59 1.46 1.51 1.49 1.56 1.57 1.54 Al2O3 (0.14) 15.19 15.23 15.47 15.44 15.34 15.33 15.40 15.06 15.44 15.05 Fe2O31 - 2.01 - - 2.25 2.13 2.82 - - - FeO2 (0.02) 12.04 9.01 11.89 13.17 9.00 9.41 9.03 13.27 12.40 13.34 MnO (0.02) 0.15 0.15 0.15 0.16 0.16 0.16 0.16 0.17 0.15 0.19 MgO (0.56) 8.31 9.11 7.69 8.39 8.72 8.78 8.77 8.91 7.91 9.21 CaO (0.08) 8.77 8.56 8.85 9.10 8.62 8.59 8.74 8.82 8.95 8.12 Na2O (0.02) 2.98 3.18 3.13 3.30 3.05 3.22 3.14 3.11 3.19 2.96 K2O (0.02) 0.71 0.64 0.78 0.36 0.80 0.67 0.60 0.64 0.61 0.57 Cr2O3 (0.02) 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 P2O5 (0.02) 0.24 0.24 0.25 0.28 0.24 0.25 0.24 0.29 0.25 0.28 Ba 0.01 0.02 0.02 0.01 0.02 0.02 0.01 0.01 0.01 0.02 SO3 0.03 0.01 0.12 0.00 0.04 0.06 0.00 0.08 0.01 0.06 Sr 0.04 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Totals 99.13 100.74 100.02 101.13 100.76 101.03 101.17 100.81 100.84 99.84 LOI -0.14 -0.31 -0.19 -0.37 -0.37 -0.49 -0.37 -0.41 -0.08 0.82 Mg#3 62.99 64.32 61.47 61.11 63.33 62.45 63.39 62.35 61.14 63.00 FeO(T)* (0.44) 12.04 12.02 11.89 13.17 12.25 12.59 12.86 13.27 12.40 13.34 67 Sample MH-19-024 MH-19-031 MH-19-032 MH-19-047 MH-19-055 MH-20-001 MH-20-008 MH-20-009 MH-20-010 MH-20-014 UTM East 460484 460964 460964 460450 461014 460535 460462 460462 460462 460539 UTM North 5599888 5599860 5599860 5599594 5599824 5599657 5599597 5599597 5599597 5599598 Phenocrysts Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol Pl > Ol<Cpx Pl > Ol<Cpx Pl>Ol Pl>Ol Pl>Ol Pl~Ol Normative Mineralogy (wt%) Orthoclase 4.20 3.78 4.61 2.13 4.73 3.96 3.55 3.78 3.60 3.37 Albite 25.22 26.91 26.49 27.92 25.81 27.25 26.57 26.32 26.99 25.05 Anorthite 25.97 25.39 25.86 26.25 25.80 25.40 26.15 25.24 26.01 26.09 Nepeheline - - - - - - - - - - Diopside 13.21 12.62 13.60 14.15 12.53 12.71 12.71 13.76 13.90 10.23 Hypersthene 7.40 12.73 8.26 2.17 13.47 10.54 12.59 1.13 8.19 6.79 Olivine 19.64 12.21 17.48 24.75 10.70 13.44 11.01 26.78 18.49 24.59 Magnetite - 2.91 - - 3.26 3.09 4.10 - - - Ilmenite 2.83 2.53 2.93 3.02 2.77 2.87 2.83 2.96 2.98 2.93 Apatite 0.56 0.56 0.58 0.65 0.56 0.58 0.56 0.67 0.58 0.65 Sample MH-20-015 MH-20-016 MH-20-020 MH-20-032 MH-20-039 MH-20-041A MH-20-042 MH-20-043 MH-20-045 MH-20-046B UTM East 460385 460551 460554 460505 460653 460829 460929 460972 460972 460474 UTM North 5599035 5599924 5599602 5599864 5599610 5599578 5599760 5599769 5599769 5599682 Phenocrysts Pl>Ol Pl>Ol Pl~Ol Pl>Ol Pl>Ol Pl>Ol Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol SiO2 (0.28) 50.57 48.62 48.17 49.68 49.10 49.09 51.06 50.37 49.91 47.50 TiO2 (0.02) 1.77 1.41 1.50 1.55 1.43 1.59 1.69 1.57 1.38 1.54 Al2O3 (0.14) 15.21 15.54 15.25 15.24 14.93 15.24 15.88 15.63 15.83 14.87 Fe2O31 - 2.81 - - 2.41 - - - - - FeO2 (0.02) 13.07 9.14 13.36 12.93 9.12 13.86 12.26 11.74 11.88 12.65 MnO (0.02) 0.17 0.15 0.18 0.16 0.16 0.20 0.16 0.14 0.15 0.23 MgO (0.56) 6.65 9.23 9.40 8.41 9.42 7.93 6.61 7.91 8.31 8.75 CaO (0.08) 9.31 8.77 7.79 8.77 8.50 8.68 9.20 8.96 8.69 10.09 Na2O (0.02) 3.51 3.27 2.85 3.20 3.11 3.24 3.40 3.23 3.10 3.06 K2O (0.02) 0.48 0.31 0.41 0.62 0.50 0.41 0.70 0.50 0.73 0.46 Cr2O3 (0.02) 0.04 0.04 0.04 0.04 0.04 0.04 0.27 0.04 0.04 0.43 68 Sample MH-20-015 MH-20-016 MH-20-020 MH-20-032 MH-20-039 MH-20-041A MH-20-042 MH-20-043 MH-20-045 MH-20-046B UTM East 460385 460551 460554 460505 460653 460829 460929 460972 460972 460474 UTM North 5599035 5599924 5599602 5599864 5599610 5599578 5599760 5599769 5599769 5599682 Phenocrysts Pl>Ol Pl>Ol Pl~Ol Pl>Ol Pl>Ol Pl>Ol Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol P2O5 (0.02) 0.28 0.25 0.24 0.26 0.24 0.27 0.04 0.25 0.23 0.04 Ba 0.01 0.00 0.00 0.01 0.00 0.01 0.02 0.01 0.00 0.00 SO3 0.00 0.00 0.10 0.10 0.03 0.09 0.01 0.00 0.07 0.08 Sr 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Totals 101.12 100.61 99.33 101.02 100.05 100.70 101.35 100.40 100.37 99.71 LOI -0.33 -0.52 0.77 -0.32 -0.36 0.07 -0.22 0.12 -0.25 0.93 Mg#3 55.65 64.29 63.44 61.47 64.80 58.53 57.08 62.43 63.30 63.04 FeO(T)* (0.44) 13.07 12.97 13.36 12.93 12.55 13.86 12.26 11.74 11.88 12.65 Normative Mineralogy (wt%) Orthoclase 2.84 1.83 2.42 3.66 2.95 2.42 4.14 2.95 4.31 2.72 Albite 29.70 27.67 24.12 27.08 26.32 27.42 28.77 27.33 26.23 20.94 Anorthite 24.33 26.81 27.61 25.39 25.30 25.83 26.00 26.67 27.12 25.48 Nepheline - - - - - - - - - 2.69 Diopside 16.73 12.24 7.83 13.61 12.43 12.88 16.15 13.36 11.98 20.12 Hypersthene 5.76 8.19 11.07 4.74 12.04 5.04 6.19 10.02 7.46 - Olivine 17.67 15.44 22.71 22.80 13.13 23.29 16.46 16.42 19.97 24.26 Magnetite - 4.08 - - - - - - - - Ilmenite 3.36 2.68 2.85 2.94 2.72 3.02 3.21 2.98 2.62 2.93 Apatite 0.65 0.58 0.56 0.60 0.56 0.63 0.09 0.58 0.53 0.09 *FeO(T) is total iron oxide wt % reported from XRF analyses for all samples 1Fe2O3 calculated for samples with known FeO, where Fe2O3 = (FeO(T) - FeO)/0.8998) 2FeO determined separately through ferric titration for select samples 3Mg# computed as MgO/(MgO+FeO (mol. %). CM samples not measured with ferric titration use the mean value of Fe 2+/ Ʃ Fe =0.7228 (N=7) for CM basalts 69 Sample MH-19-024 MH-19-031 MH-19-032 MH-19-047 MH-19-055 MH-20-001 MH-20-008 MH-20-009 MH-20-010 MH-20-014UTM East 460484 460964 460964 460450 461014 460535 460462 460462 460462 460539UTM North 5599888 5599860 5599860 5599594 5599824 5599657 5599597 5599597 5599597 5599598Phenocrysts Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol Pl > Ol<Cpx Pl > Ol<Cpx Pl>Ol Pl>Ol Pl>Ol Pl~OlLa (0.8) 10.6 9.4 9.6 10.2 9.4 8.7 9.8 9.8 10.3 10.6Ce (1.2) 21.3 20.8 21.1 23.8 19.8 20.5 20.1 21.3 19.8 21.4Pr (0.08) 3.09 2.88 3.0 3.22 2.9 2.84 2.82 3.08 2.79 3.04Nd (0.6) 14.1 12.8 13.9 14.5 13.5 12.9 13.8 13.9 13.1 14.5Sm (0.16) 3.76 3.76 3.76 3.86 3.54 3.49 3.48 3.74 3.46 3.74Eu (0.10) 1.39 1.37 1.42 1.34 1.29 1.30 1.27 1.32 1.30 1.35Gd (0.08) 4.09 3.89 4.28 4.11 3.92 4.05 3.96 3.95 3.79 3.97Tb (0.02) 0.67 0.63 0.66 0.63 0.63 0.61 0.59 0.61 0.58 0.61Dy (0.12) 3.62 3.53 3.65 3.67 3.42 3.45 3.35 3.46 3.35 3.60Y (0.9) 18.2 17.5 17.5 17.7 16.8 16.9 17.5 17.1 16.7 18.1Ho (0.04) 0.73 0.67 0.73 0.71 0.69 0.66 0.69 0.66 0.65 0.7Er (0.06) 2.0 1.78 1.92 1.84 1.81 1.75 1.82 1.83 1.72 1.79Tm (0.02) 0.28 0.25 0.27 0.27 0.25 0.24 0.24 0.23 0.22 0.24Yb (0.08) 1.62 1.47 1.65 1.58 1.48 1.53 1.38 1.50 1.4 1.51Lu (0.02) 0.24 0.22 0.23 0.22 0.23 0.2 0.21 0.21 0.21 0.21Cs (0.2) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1Rb (0.4) 8.4 6.6 6.9 2.8 3.4 5.9 5.8 4.9 4.1 5.4Ba (7) 159 140 163 147 176 197 140 156 147 187Sr (34) 478 483 500 449 370 438 423 436 423 438Zr (5) 92 91 96 105 106 96 87 95 92 107Hf (0.2) 2.2 2.5 2.5 2.7 2.7 2.4 2.4 2.5 2.5 2.7Nb (0.2) 8.3 7.8 8.7 8.9 10.0 7.7 7.6 8.5 7.3 8.5Ta (0.2) 0.5 0.5 0.4 0.5 0.7 0.4 0.4 0.4 0.4 0.5Th (0.2) 0.8 0.6 0.8 0.9 0.8 0.7 0.6 0.7 0.6 0.8U (0.8) 0.3 0.3 0.3 0.2 0.3 0.4 0.2 0.3 0.3 0.2Ni (53.0) 173.3 183.1 131.0 159.7 174.1 166.9 167.7 188.5 137.8 182.1Cu (7.0) 55.0 48.1 46.6 43.4 65.5 42.7 44.8 40.9 42.2 35.8Zn (8) 89 87 73 76 125 92 80 83 75 80V (13) 162 134 160 195 131 180 167 180 176 167Pb (0.2) 0.9 0.9 1.2 1.4 2.3 5.7 1.1 4.9 1.3 1.2Table 3.3. Whole-rock trace element (ppm) compositions of Cracked Mountain volcanic rocks analysed ICP-MS. Analytical precision (2s) based on replicates is reported in brackets. Whole-rock analyses conducted by Acme Labs Ltd., Vancouver BC. 70 Sample MH-20-015 MH-20-016 MH-20-020 MH-20-032 MH-20-039 MH-20-041A MH-20-042 MH-20-043 MH-20-046BUTM East 460385 460551 460554 460505 460653 460829 460929 460972 460474UTM North 5599035 5599924 5599602 5599864 5599610 5599578 5599760 5599769 5599682Phenocrysts Pl>Ol Pl>Ol Pl~Ol Pl>Ol Pl>Ol Pl>Ol Pl>Ol>Cpx Pl>Ol>Cpx Pl>OlLa (0.8) 9.9 10.0 9.7 9.1 10.2 12.0 10.4 8.8 9.9Ce (1.2) 22.0 19.1 21.4 19.5 20.0 24.1 22.9 18.7 21.5Pr (0.08) 3.18 2.87 3.06 2.88 2.83 3.33 3.12 2.75 3.1Nd (0.6) 15.5 13.4 14.5 13.2 13.9 15.3 14.5 13.1 13.9Sm (0.16) 4.11 3.45 3.54 3.48 3.4 4.05 4.01 3.61 3.61Eu (0.10) 1.42 1.27 1.28 1.34 1.27 1.45 1.41 1.35 1.34Gd (0.08) 4.38 3.92 4.04 3.94 3.76 4.33 4.19 3.87 4.17Tb (0.02) 0.68 0.58 0.59 0.59 0.6 0.7 0.65 0.6 0.62Dy (0.12) 3.95 3.33 3.47 3.43 3.34 4.07 3.74 3.32 3.7Y (0.9) 18.6 17.2 16.6 16.4 17.8 18.6 18.6 17.0 17.6Ho (0.04) 0.78 0.62 0.65 0.65 0.69 0.77 0.72 0.61 0.68Er (0.06) 1.98 1.76 1.74 1.71 1.71 1.84 1.88 1.77 1.82Tm (0.02) 0.26 0.23 0.22 0.23 0.23 0.25 0.25 0.22 0.25Yb (0.08) 1.65 1.46 1.49 1.41 1.33 1.56 1.55 1.37 1.47Lu (0.02) 0.23 0.2 0.2 0.21 0.2 0.24 0.22 0.2 0.22Cs (0.20) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10Rb (0.4) 4.9 1.7 4.6 4.6 5.3 4.6 6.9 5.2 3.5Ba (7) 161 133 144 147 139 160 152 139 142Sr (34) 423 451 429 421 457 468 459 429 439Zr (5) 115 89 102 94 88 99 100 95 95Hf (0.2) 3.0 2.3 2.5 2.5 2.3 2.6 2.5 2.4 2.5Nb (0.2) 8.7 8.0 8.8 7.7 7.9 9.2 8.2 7.8 8.6Ta (0.2) 0.6 0.4 0.5 0.5 0.4 0.4 0.5 0.4 0.5Th (0.2) 0.7 0.6 0.7 0.7 0.7 0.7 0.6 0.7 0.8U (0.8) 0.3 0.2 0.2 0.2 0.2 0.2 0.3 0.2 0.5Ni (53.0) 90.9 189.0 208.4 157.8 209.3 150.9 80.0 139.6 161.0Cu (7.0) 43.1 42.7 43.3 39.2 40.9 30.3 32.5 39.2 36.4Zn (8) 84 78 98 71 72 69 74 80 66V (13) 193 158 139 167 191 190 176 162 170Pb (0.2) 1.3 1.2 1.2 0.9 0.5 0.9 1.5 1.4 1.1 71 3.4.3 EMP Mineral Compositions Major element concentrations of phenocryst and groundmass phases were determined with a Cameca Sx50 scanning electron microprobe (EMP) at the University of British Columbia, Vancouver British Columbia. EMP conditions include an acceleration voltage of 15keV, a beam current of 20 nA, and a beam diameter of 30 µm. A full compilation of EMP mineral data is presented in Appendix D. Forsterite contents (Fo%) of olivine phenocryst cores and rims, and groundmass olivine are plotted vs. nickel oxide (NiO) in Figure 3.5A. OP phenocrysts have higher forsterite (Fo79-83) and NiO (0.1-0.32%) than OPA phenocrysts (Fo77-80 and 0.1-0.26% respectively). Olivine groundmass phases for OP samples range from Fo73-79 while OPA has a tighter spread of Fo77-78. Both OP and OPA groundmass olivine have lower NiO% than the phenocryst phases (0.1-0.2%). Anorthite contents (An%) of plagioclase phenocryst cores, rims, and groundmass plagioclase are displayed in Figure 3.5B. OP phenocrysts are higher in anorthite (An60-65) than OPA (An56-65). Similarly, OP groundmass phases are higher in anorthite (An49-63) than OPA (An47-62). Clinopyroxene phenocryst and groundmass phase compositions (after Morimoto et al., 1988) are displayed in Fig 3.5C. All CM clinopyroxenes, phenocryst, and those present in the groundmass are Ca-rich. The OPA phenocrysts are chromian augite (i.e. Cr3+ > 0.01 cation) while both groundmass phases from OP and OPA samples are aluminian augite (i.e. Al3+ > 0.1 cation) (Morimoto, 1988). 72 73 Figure 3.5: Electron microprobe analyses of CM mineral compositions. OPA phenocryst phases are shown in green (circles) and groundmass phases in yellow (triangles). OP phenocryst phases are shown in blue (circles) and groundmass phases in teal (triangles). A) Olivine forsterite compositions (Fo%) versus NiO wt.% for OPA and OP phenocryst and groundmass phases. B) Plagioclase Anorthite (An%) compositions for OPA and OP samples. The frequency of An% is shown on the vertical axis of the bar charts. C) Clinopyroxene classifications (after Morimoto et al., 1988) for OPA phenocrysts and OPA and OP groundmass phases. OPA phenocrysts are all high-Ca augite, and both OPA and OP groundmass phases plot along the augite-diopside boundary. 3.5 Paleomagnetic Results Cracked Mountain samples are normally magnetized (Table 3.4). The means of eight sites are the same within error and have a mean declination of 347.33 ̊ and inclination of 75.14 ̊. The individual measurements are all within the uncertainty circle (α95 = 2.96°) with a Fisher precision factor of k = 351, (Fig 3.6). All paleomagnetic samples produced stable directions of magnetization following stepwise demagnetization. Alternating field demagnetization, applied to all specimens, exhibited linear decay to the origin on orthogonal projections. The median destructive fields range from 20–80 mT and final directions are often stable up to 200 mT alternating field demagnetization indicative of single-domain magnetite. Thermal demagnetization showed complete 74 demagnetization at 550 to 580 °C, typical of fine-grained (single domain) magnetite as the magnetic carrier. Note that single-domain magnetite is the optimal magnetic mineral and grain size for producing reliable paleomagnetic directions. The magnetic susceptibility values of CM volcanics range from 0.4-1.0 x 10-3 SI (median value of 0.5 x 10-3 SI) for the flows composed of pyroclastic density currents and 2.4-16.4 x 10-3 SI (median value of 4.5 x10-3 SI) for dykes. Mean natural remanent magnetization for CM volcanic deposits is 9.4 A/m (range 0.4–22.0 A/m). The paleomagnetic work was used to investigate the duration of volcanic activity at Cracked Mountain. Our findings indicate that the diverse lithofacies, including explosive, intrusive, and effusive activity all occurred within the uncertainty of the same magnetic moment (i.e. >1000 ka) (Harris et al., under review). 75 Table 3.4. Paleomagnetic AnalysesSample Site Nt Lithology1 Mineralogy Nc Ns UTM E UTM N Decl. Inc. k α951 CMV008-012, 014-015, 059-Lt1 OP 16 13 460554 5599602 340.3 75.14 109.01 3.992 CMV016-019 Ld2 OPA 3 4 460519 5599610 346.1 77.02 431.25 4.433 CMV020-022 Ld1 OP 3 3 460519 5599610 14.69 76.36 113.56 11.624 CMV023-025 Ld2 OPA 4 3 460519 5599610 333.8 72.76 134.74 10.665 CMV026-33 Ld1 OP 8 8 460477 5599585 343 73.03 291.75 3.256 CMV034-041 Ld2 OPA 8 8 460477 5599585 344.7 76.16 348.79 2.977 CMV042-049 Ld1 OP 8 8 460477 5599585 340.6 78.41 1874.69 1.398 CMV050-054, 056-057Ld2 OPA 8 7 460477 5599585 8.51 81.36 191.38 4.37Mean 8 347.3 76.63 351.00 2.96 Note: Nt, sample numbers for each site: Nc, total number of samples collected at each site: Ns, total number of samples used in calculation of mean direction for each site: Decl., declination: Incl., inclination: k, precision parameter: α95, radius of 95% confidence level1 Lithologies after Harris et al., under review map units 76 Figure 3.6. A stereographic plot of mean data from eight Cracked Mountain sites and their α95 (p = 0.05) confidence circles (see Table 3.4). The mean of sites 1-8 are shown in red. 3.6. Discussion 3.6.1 Isobaric Crystallization Models of CM Magmas Phenocryst assemblages in volcanic rocks provide critical quantitative information on pre-eruptive temperatures, H2O contents, and pressures (i.e. depth) of the corresponding magmas. Different minerals (i.e. olivine, plagioclase, and pyroxene) are stable at different P-T conditions (Gualda and Ghiorso, 2015). Thermodynamic models, in conjunction with the knowledge of true phenocryst proportions and estimates of magma composition, can uniquely constrain the conditions in the magma before the eruption. 77 We used the thermodynamic model Rhyolite-MELTS _v1.0 (Gualda et al., 2012; Gualda and Ghiorso, 2015) to constrain the pre-eruptive storage depths of crystallization for CM magmas. For samples without known FeO (i.e. not undergone ferric titration) total Fe was input into MELTS and computed redox function was used to calculate FeO and Fe2O3 respectively. All sample oxide contents were normalized anhydrously and values were stored in a separate file and used for each replicate simulation. Oxygen fugacity was determined for samples with known FeO contents based on the models from Ghiorso and Sack (1995) and these values for fO2 buffers were used consistently for each sample simulation. Samples without known FeO were modeled with assumed fO2 0 (QFM). Sixty-three isobaric crystallization simulations were conducted for each sample. Each isobaric simulation ran from liquidus conditions (< 1300˚C) to a temperature where the system was ~95% crystallized (~950˚C). The pressure range explored was from surface pressures (0.1kbar) to 4 kbar (~15 km depth) over increments of 0.5 kbar. Volatile content was also varied by changing the H2O wt. % (0-1.5) in steps of 0.25%. Possible phases were manually restricted to what was petrographically observed in real CM samples (i.e. olivine, plagioclase, and clinopyroxene). The resulting outputs were used to create mineral stability-field phase diagrams (Fig 3.7) that model the effect of 10% crystallization at equilibrium. The value of 10% crystallinity was chosen based on petrographic inspection of the CM holocrystalline samples. Glomeroporphyritic clots are observed to be 10% or less in all CM samples. These clots are assumed to originate during static magma crystallization (e.g. within the magma chamber) while other isolated phenocrysts cannot be constrained to crystallization during magma storage and could have derived from cooling during pre-eruptive ascent, syn, or post-eruptive cooling. 78 In the case of the OP samples (Fig 3.7A and B), the stable phases for only olivine and plagioclase crystallization range from <2 to 0 kbar (~5.5 to 0 km depth), and 0 to 1.5% H20 wt%. For OPA samples, (Fig 3.7C and D), the stability fields where olivine, plagioclase, and clinopyroxenes are all present are restricted to pressures between 2.5 to 1 kbar (~10 to 4 km depth), and 0 to 1% H2O wt%. 79 Figure 3.7: Phase portraits for CM volcanic samples, generated with magma crystallization simulations using Rhyolite-MELTS (Gualda and Ghiorso, 2015) display mineral stability fields with relation to pressure (i.e. depth) and varying water contents. Models were run at isobaric conditions ranging from 4 kbar to 0 kbar. At each pressure interval, simulations were modeled with varying H2O wt%, ranging from 0.1 to 1.5%. Oxygen fugacity (fo2) was manually adjusted to values determined through methods from Ghiorso and Sack (1995) for samples with known ferrous (Fe2+) iron via titration. All mineral phases not observed within CM samples were suppressed for each simulation. Plots A and B display phase portraits for two OP samples (20-008 and 20-016) while plots C and D display phase portraits for two OPA samples (15-168 and 19-031). Conditions at which water became an exsolved phase are indicated in each plot. 3.6.2 Origin of Chemical Variations in CM Samples CM whole-rock analyses show moderate variation in SiO2 wt. % (~4%), and the two phenocrystic assemblages (i.e. OP and OPA) show slight differences in their olivine and plagioclase mineral compositions. Here we investigate the nature of magmatic differentiation as indicated by the whole rock chemistry. Pearce element ratios (PERs), first devised by Pearce (1968) are a useful method to conduct such analyses. The basis for PERs uses whole-rock oxide weight percentages, converted to stoichiometric ratios containing cations of crystallizing minerals normalized to a conserved element in a magmatic system (Pearce, 1968; Russell and Nicholls, 1988; Nicholls and Russell, 2016). The advantage of PERs is that you can produce geochemical plots that model mineral accumulation and loss (i.e. fractionation), and test petrologic hypotheses such as multiple magma sources, or magma contamination, without distortion from closure in a magmatic system (Russell and Nicholls, 1988). To effectively implement PERs, you must choose appropriate conserved elements for the denominator. In our case, we have used a combination of titanium (Ti) and zirconium (Zr). Titanium was chosen since it has been shown to have smaller analytical uncertainty than 80 phosphorus (i.e. another commonly conserved major element) and is effectively conserved in basaltic systems (Nicholls and Russell, 1991). We avoid using potassium (K) because preliminary results with this element displayed trends associated with a non-conserved element. Additionally, Zr is a useful conserved element with low analytical uncertainty and was used in the denominator in several conserved element diagrams (Nicholls and Russell, 2016). Fig 3.8 shows a conserved element diagram for major elements (i.e. titanium and phosphorus) in CM samples. Both phenocryst assemblages (i.e. OP and OPA) overlap within 1σ of the mean of each respective data set (dashed and solid bars). Similar trends are observed in incompatible trace elements niobium (Nb) and yttrium (Y) (Fig. 3.8). These results indicate that all samples from CM likely originated from a single magmatic source. 81 Figure 3.8: Chemical variations for Cracked Mountain samples modeled through Pearce Element Ratios (PERs). Samples containing Olivine + Plagioclase (OP) phenocrysts are shown with an open-black circle. Samples containing Olivine + Plagioclase + Augite (OPA) phenocrysts are shown with a filled-black circle. 2σ error ellipses are shown around each data point. 2σ error bars (dashed and solid bars respectively) are shown for each mineral assemblage data mean. A) Conserved element diagram showing no significant variation between major elements in the two phenocrystic assemblages (i.e. OP and OPA). B) Conserved element diagram showing no significant variation between trace elements in the two phenocrystic assemblages (i.e. OP and OPA). Assemblage test diagrams for crystal sorting of olivine alone are shown in Figs 3.9A and B. If olivine fractionation was responsible for the observed chemical variation seen in CM samples, then the data would fall along the model line with a slope of 1. This hypothesis is rejected as data from both OP and OPA samples plot above the model slope line. A two-phase assemblage test for crystal sorting of olivine and plagioclase is shown in Figs 3.9C and D. In this case, nearly all OP samples all fall within 2 of the model slope line (Fig 3.9C) while the OPA samples fall slightly above the model slope line (Fig. 3.9D). These models indicate that for the samples containing olivine and plagioclase only (i.e. OP), the observed chemical variations can be closely attributed to the crystal fractionation of the two-mineral system. However, the samples containing augite (i.e. OPA) reject the two-phase hypothesis as the data do not fall within the uncertainty of the model line. 82 Figure 3.9: Chemical variations for Cracked Mountain samples modeled through Pearce Element Ratios (PERs). The same symbology is used in Figure 3.8. In each assemblage test, a model line with a slope of 1 is projected through the data set’s most primitive point. A and B) Single-phase (olivine) assemblage test for OP and OPA samples respectively. Both phenocryst assemblages fall off the model line and therefore chemical variations cannot be explained by the crystal sorting of olivine alone. C) Two-phase (olivine-plagioclase) assemblage test for CM OP samples. Nearly all samples fall within 2σ uncertainty of the model line, indicating the chemical variation within OP samples can be attributed to the crystal sorting of olivine and plagioclase. D) Same assemblage test as shown in plot E, now with CM OPA samples. Here the OPA samples fall above the model line, indicating the chemical variation cannot be explained by crystal sorting of olivine and plagioclase alone. 83 Finally, a combined three-phase assemblage test for crystal sorting of olivine, plagioclase, and augite, is shown in Fig 3.10. In this diagram, two model lines are drawn through the most primitive sample of each respective phenocryst assemblage, and the results show that all CM data fall within the upper (OP) and lower (OPA) limits of self-mixing (e.g., Russell and Stanley, 1990). Figure 3.10: Chemical variations for Cracked Mountain samples modeled through Pearce Element Ratios (PERs). The same symbology is used in Figures 3.8-9. A model line with a slope of 1 is projected through each data set’s most primitive point. A combined three-phase assemblage (olivine-plagioclase-clinopyroxene) test for both OPA and OP samples. Here the most primitive samples of each assemblage suite (20-016, OP) (19-031, OPA) define upper and lower trend boundaries where all other CM samples fall between. This trend implies a degree of mixing (field shown in grey) between the two distinct petrographic suites. 84 Sample1 15-178 20-016 20-008 20-039 15-182 19-55 15-168 19-31 20-001 20-45Mineral Assemblage2 OP OP OP OP OP OPA OPA OPA OPA OPAOl lqd ( ̊ C) 1260 1238 1228 1254 1214 1242 1224 1256 1244 1228Cp lqd ( ̊ C) 1162 1158 1160 1158 1158 1170 1174 1170 1168 1166Pl lqd ( ̊ C) 1172 1172 1164 1166 1166 1164 1166 1170 1168 1168Upper P (kbar)4 1.5 2 2 1.5 1 2.5 2.5 2.5 2 2.5Lower P (kbar)5 0 0 0 0 0 2 1.5 2 2 2(OP) (OPA)Mean Upper P 1.6 2.4Mean Lower P 0 1.9Mean Ol lqd 1238.8 1238.8Mean Cp lqd 1159.2 1169.6Mean Pl lqd 1168 1167.2Table 3.5: Thermodynamic summary for Cracked Mountain Samples. The table displays the olivine (Ol), clinopyroxene (Cp), and plagioclase (Pl) liquidus temperatures and mineral stability pressure conditions recovered from simulations run with Rhyolite_MELTS1 Labels for samples are abreviated, where samples starting with 19 and 20 have a full prefix of 'MH-' and samples starting with 15 have a full prefix of 'AW-'2 Mineral assembalages are either olivine-plagioclase-augite (OPA) or olivine-plagioclase (OP). OPA samples modeled at isobaric conditions for 2kbar, OP samples modeled at isobaric conditions for 1.5 kbar3 Oxygen fugacity detrmined for samples with known FeO wt% through methods from Ghiorso and Sack (1995). Values are reported relative to a Nickel-Nickel-Oxide buffer (NNO)4 Highest value of pressure where stable minerals (OP or OPA) are present at ≥0.5 H2O (wt%) extracted from the MELTs 5 Lowest value of pressure where stable minerals (OP or OPA) are present at ≥0.5 H2O (wt%) extracted from the MELTs 85 3.6.3 Temperature and H2O Constraints for CM Magmas Through combined methods of PERs and MELTS simulations, we constrain the temperatures at which pre-eruptive crystallization would have occurred and bracket the maximum amount of water (H2O wt%) in the system at the time of crystallization. Figure 3.11 shows chemical plots with axes designed for PERs as seen in Fig 3.9 and 3.10. Major element oxide data was extracted from the outputs of MELTS simulations for the two most primitive samples in each petrographic suite (20-016 and 19-031) at varying water contents (0.1-1 H2O wt%) and transposed onto the PERs as dashed lines. In all diagrams, the chemical trends for both OP and OPA samples mimic that of a system modeled with ≤ 0.5 H2O wt%. Furthermore, temperature (˚C) markers are labeled for two respective primitive sample simulations containing 0.5 H2O wt%. These markers constrain the liquidus temperatures for each phenocryst suite, where all the data for OP samples fit within ~1240-1155 ˚C while OPA samples fit within 1250-1150 ˚C (Fig 3.11). A full summary of thermodynamic liquidus temperatures for CM MELTS models is shown in Table 3.5. Given these findings, both OP and OPA samples crystallized in a nearly “dry” system with less than >5% H2O wt.%. With this further refinement of water content in the crystallizing systems, we constrain the pressure conditions for stable OP and OPA systematics respectively (e.g. Fig. 3.7). The OP samples must have been stored at pressures ≤2 kbar, with a mean upper pressure of 1.6 kbar (N=5) (Fig. 3.7; Table 3.5). The OPA samples are restricted to pressures 1.5 ≥ 2.5 kbar, with the mean conditions falling within 1.9 ≥ 2.4 kbar (N=5) (Fig. 3.7; Table 3.5). 86 1 87 Figure 3.11: Chemical variations and Thermodynamic conditions for CM samples modeled through Pearce Element Ratios (PERs) and Rhyolite-MELTS. Same symbology as in Fig. 3.8-10. Sample 20-016 was chosen as a proxy for OP samples and MELT simulations were run at 1.5 kbar from 1 to 0.1% H2O. Sample 19-031 was chosen as a proxy for OPA samples, and MELT simulations were run at 2 kbar from 1 to 0.1% H2O. Diagrams are formatted as PERs, with axes designed to test for sorting processes involving olivine (Ol) (A and B), Ol and plagioclase (Pl) (C and D), and Ol and Pl and augite (Au) (D). Liquidus lines of ascent are shown for various H2O% conditions plotted at 20 ̊ C intervals. Models run at 0.5% H2O have temperature intervals labeled in the PER space. Simulations indicate that for both phenocryst assemblages (i.e. OP and OPA) less than 0.5% H2O is required to follow the cotectic (inflection-points) trends of fractional crystallization modeled by the PERs. 3.6.4 Storage, Transport, and Eruptive Model for CM Through our multifaceted petrochemical investigation, we propose the following model for the eruption and evolution of Cracked Mountain (e.g. Fig. 3.12):  A single primitive mantle melt (i.e. Mg#’s > 60) ascended from the lower crust, undergoing nearly complete dehydration, likely degassed (~dry melt). The single melt source is based on the indistinguishable conserved major and trace (REE) element signatures of all CM samples (e.g. Fig 3.3B; Fig 3.9A and B), while the ‘dehydrated conditions’ are supported through the chemical trends observed in Fig. 3.11.  As the melt reached the upper crust, it segregated, stalling at two discrete isobaric conditions capable of producing two unique phenocryst assemblages (i.e. OP and OPA). These textural differences are irrefutable under petrographic inspection (Fig. 3.2) and can only be explained through separate pressure (i.e. depth) crystallization conditions (Fig 3.7). Through repeated thermodynamic simulations we show that the OPA magmas were restricted to storage depths of ~7-9 km within the upper crust, while OP magmas crystallized at depths likely 6 km or less in the upper crust (Fig 3.7; Fig 3.12). 88  Mixing processes likely occurred during transport and eruption. We find evidence of these mixing signatures in the major element chemical models (PERs) that define a field that encompasses all CM samples and their fractionation trends (Fig. 3.10). Additionally, although shown to be stable at different crustal depths, the OP and OPA magmas were in all likelihood quite close to one another both vertically and laterally (given the small area at which intrusions reached the surface; Fig 3.1). Thus, we assert that it is improbable that throughout the single eruptive event, the two magma systems could rise through the upper crust without coming in contact with one another.  Lastly, the two magmas erupted concurrently in geologic time (monogenetic) producing a small basaltic edifice with two unique phenocryst assemblages (i.e. OP and OPA). The evidence of short-lived and coeval timing for the two magmas is supported by the field evidence which shows no break-in time in volcanic stratigraphy (Harris and Russell, 2021; Harris et. al., under review) and is bolstered by the paleomagnetic signatures of all deposits overlapping within one magnetic moment (Fig 3.6). 89 Figure 3.12: Schematic depiction of crustal storage conditions for the CM volcano. The volcanic profile above the dashed line is shown with no vertical exaggeration (VE). Regions below the dashed line are not shown to scale. Results of chemical and thermodynamic models indicate dry melts (>0.5 H2O%) ascended into the upper crust, where two batches segregated and crystalized different pressure conditions (i.e. depth). The OPA batch (white) crystalized at ~2 kbar while the OP batch (dark grey) was at <1.5 kbar. Mixing of the two magmas is depicted as the lower OPA erupted concurrently with OP during the monogenetic eruption of CM. 90 3.6.5 Implications for Monogenetic Volcanoes Monogenetic volcanoes are found globally within all major tectonic environments. These short-lived eruptive centres have garnered increasing interest, in part due to their threat as natural hazards (Smith and Németh, 2017). A variety of methods have been used in their study, including seismic tomography, geochemistry, petrography, and experimental and numerical modeling. These studies have elucidated greater complexity in their magmatic underpinning that belies their apparent single eruptive histories. The presence of polymagmatic crustal magma chambers beneath active monogenetic systems has been shown seismically for volcanoes in Kamchatka, Russia (Kugaenko and Volynets, 2019) and Jeju, Korea (Song et al., 2018). Additionally, geochemical variations in erupted materials in Jeju, Korea (Brenna et al., 2011), Mt. Gambier, Australia (Van Otterloo et al., 2014), and Bahariya, Egypt (Khalaf and Sano, 2020) have also brought forth speculation that polymagmatic systems have fed these small-volume monogenetic volcanoes. Cracked Mountain volcano is not active and the geochemical variations between erupted units are not overwhelmingly distinct (e.g. Fig 3.3). Seismic tomography or strictly geochemistry cannot provide the data needed to fully understand the pre-eruptive conditions for the paleo magmatic system. Instead, our best line of evidence for understanding the past CM volcanic plumbing comes from our petrographic observations in conjunction with geochemical measurements. Our findings of two unique petrographic suites (i.e. OP and OPA) guide our subsequent chemical and thermodynamic models that we use to constrain the pre-eruptive crystallization conditions. Our findings require two discrete pressure fields (i.e. crustal depths) to erupt materials containing two unique mineral assemblages, indicating tapping of a polymagmatic system during the eruption of the CM volcano. 91 Similar petrochemical methods have been conducted at other monogenetic volcanoes and have provided insight into magma chamber dynamics (Pollock et al., 2014; Liu et al., 2021). Particularly in non-active monogenetic volcanic systems, relying on chemical signatures alone may not yield enough information to model the shallow crustal magma chamber dynamics. As Annen et al., (2006) suggest, the chemical signature of magma is dictated by deep-crustal processes, while texture and mineralogy for magma are defined by the ascent and crystallization path within the shallow crust. As the study of monogenetic systems advances, so do the insights into their eruptive complexities. Monogenetic volcanoes tend to have two or more eruptive phases (Kereszturi and Németh, 2012), commonly driven by combinations of internal (e.g., volatiles) and external (e.g., groundwater or fluids) factors. Cracked Mountain most closely resembles a monogenetic classification of a Surtseyan tuff cone with spatter and lava flows (Kereszturi and Németh, 2012) however its true classification is that of a glaciovolcanic transitional, tephra-dominated, tuya (Russell et al., 2014; Harris et al., under review). The presence of an impounding ice-sheet at the time of the Cracked Mountain eruption represents an external factor that played a major role in its style of eruption, the lithofacies diversity, and the volcano's unique morphology (Harris et al., under review). However, it may have impacted magma-crustal dynamics as well. There have been recent studies that show linkages between magma ascent times with lithostatic compression and decompression during periods of glaciation and deglaciation respectively (e.g., Wilson and Russell, 2020; Guillot and Ponce, 2021; Russell et al., 2021). With ice caps shrinking globally across regions of well-documented volcanism (e.g., Antarctica, British Columbia, Iceland, and South America) (Peltier et al., 2015), there may be an increased opportunity and 92 need to further investigate the role in which glaciers may impact magma chamber dynamics in within the earth’s crust. 3. 7. Summary Cracked Mountain (CM) is shown to be a monogenetic basaltic landform in Southwest, British Columbia, Canada (i.e. Garibaldi Volcanic Belt). We identify two unique CM petrographic suites, an olivine-and-plagioclase phyric assemblage (OP) and an olivine-plagioclase-and-augite phyric assemblage (OPA). Major and minor conserved elements, as well as rare earth (REE) signatures, show no difference between the two petrographic suites, indicating a singular melt source. However, variations in major element compositions are modeled with Pearce Element Ratios (PER) and suggest that the two distinct petrographic assemblages (OP and OPA) can be explained by crystal fractionation in two different systems that underwent minor mixing. We further show through thermodynamic modeling that the differences in CM phenocryst assemblage require distinct storage conditions before the eruption. Our results show OP magmas must have been stored at depths less than 6 km depth (<2 kbar), at temperatures between 1240-1155 ̊ C. In contrast, the OPA magmas crystallized at depths between 7-9 km (~2-2.5 kbar) between 1250-1150 ̊ C. Both magmas are shown to be nearly “dry” with less than 0.5 H2O wt% in their respective systems. This study concludes that the magmatic plumbing system at Cracked Mountain mirrors the complexities seen elsewhere in global studies of monogenetic systems. We recommend that detailed petrographic analyses should always play a role in the methodology of monogenetic volcano studies as they can provide insights into the shallow crustal crystallization conditions. 93 Chapter 4: Conclusion This thesis examines Cracked Mountain, a tephra-dominated tuya, within the southwest Mount Meager Volcanic Complex, BC of the Garibaldi volcanic belt. Cracked Mountain was selected for investigation because it is built of subaqueous volcanic lithofacies but located within an alpine setting, thus implying a glaciovolcanic origin. The cracks that incise the volcano provide excellent lithostratigraphic exposure that allows for a detailed recovery of the volcanic eruptive succession. Since Cracked Mountain has not been studied in detail before this thesis, my work provides the first temporal constraints (i.e. eruptive age and duration) and has therefore contributed to the understanding of paleoclimates within British Columbia. Furthermore, this thesis finds that Cracked Mountain basaltic rocks contain two distinct phenocryst assemblages, that although only differ slightly in mineral contents, are ideal for investigations using Pearce element ratio chemical and thermodynamic models (MELTS) to recover the magma chamber P-T-H2O conditions. Thus, the overall complexity of Cracked Mountain volcanic lithofacies and mineralogy has bolstered this thesis's dual focus on the physical and chemical volcanic evolution. This thesis uses a combination of field mapping and stratigraphy, geochronology, petrography, geochemistry, and thermodynamic modeling. The chemical and thermodynamic model results provide insight into the pre- eruptive volcanic processes within the upper crust, and the geologic maps, stratigraphic logs, and paleomagnetic results provide information on syn-eruptive volcanic processes and their durations. The broader implications of this study include 1) establishment of the paleoenvironment of SWBC during the mid-Pleistocene, 2) documentation of an explosive onset to the Glaciovolcanic eruption, in contrast to conventional tuya eruptive models (e.g., Smellie, 2007; Edwards et al., 2015; Smellie and Edwards, 2016), and 3) new 94 insights into crustal storage conditions of monogenetic systems within the Garibaldi volcanic belt. 4.1 Physical Volcanology of Cracked Mountain The size, shape, stratigraphy, and morphology of glaciovolcanic landforms directly inform on the paleo-environment at the time of eruption (Smellie, 2007; Russell et al., 2014; Edwards et al., 2015; Smellie and Edwards, 2016). Through detailed physical volcanology, we recover evidence of eruptive style (i.e. explosive or effusive), environment (i.e. subaqueous or subaerial), and duration (i.e. monogenetic or polygenetic). Chapter 2 of this thesis addresses the physical volcanological evolution of Cracked Mountain. The data used in this chapter of the thesis comes from field mapping, lithostratigraphy, petrography, paleomagnetic, and geochronological analysis. Here we present detailed lithofacies that indicate the eruption of Cracked Mountain transitioned in style from an explosive onset to intrusive and effusive style in the middle to late eruptive stages. Subaqueous lithofacies such as palagonitized lapilli tuffs, peperites, and pillow lavas are ubiquitous throughout the edifice, indicating a sustained standing body of water at the time of the eruption. These findings, in conjunction with an absence of any physiographic closed catchment, invoke the presence of an enclosing paleo ice-sheet (i.e. glaciovolcanic). The edifice morphology constrains the paleo ice-sheet to a minimum of  850 m thick, capable of holding a ‘leaky’ paleolake with a maximum of ~0.36 km3 of water. The results of paleomagnetic analyses indicate the eruptive sequence took place over a single magnetic moment (at ~100-1000 ka) (Turner, 1987; Barletta et al., 2010; Lisé-Pronovost et al., 2013). The absolute 40Ar/39Ar age of ~401 ± 38 ka for Cracked Mountain represents an important record of the Cordilleran Ice sheet 95 (CIS) in southwestern BC during the mid-Pleistocene, making it the first detailed assessment of the presence and thickness of CIS within Southwest British Columbia at this time. Globally, the timing of the Cracked Mountain eruption fits within the waning of MIS 12 and onset of MIS 11(Lisiecki and Raymo, 2005; Batchelor et al., 2019), potentially tieing in with proposed causal linkages between deglaciation and increased volcanism (e.g., Wilson and Russell, 2020) 4.2 Petrological and Chemical Volcanology of Cracked Mountain The textures and phenocrysts preserved within volcanic rocks are directly related to shallow crustal magma chamber conditions (i.e. pressures, temperatures, and H2O contents) (e.g., Annen et al., 2006). Different minerals (i.e. olivine, plagioclase, and pyroxene) are stable at different P-T conditions (Gualda and Ghiorso, 2015), and therefore can be thermodynamically modeled to constrain the pre-eruptive conditions. Chapter 3 of this thesis addresses the petrochemical evolution of the Cracked Mountain magmatic system. The data used for this chapter stems from petrography, major and trace bulk chemistry, and mineral chemistry. Additionally, I use computational methods to generate phase equilibria models using both Pearce Element Ratio analysis and Rhyolite-MELTS. I present the findings of two unique Cracked Mountain petrographic suites, an olivine-and-plagioclase phyric assemblage (OP) and an olivine-plagioclase-and-augite phyric assemblage (OPA). The results of MELTS thermodynamic modeling show OP magmas must have been stored at depths less than 6 km (<2 kbar), at temperatures between 1240-1155 ̊ C. In contrast, the OPA magmas crystallized at depths between 7-9 km (~2-2.5 kbar) between 1250-1150 ̊ C. Additionally, both crustal-stored magmas are shown to be nearly “dry” and contained less than 0.5 H2O wt%. These findings, particularly, the “dry” magma chamber systematics are uncharacteristic of subduction zone 96 magma systems but have been similarly observed in other GVB mafic occurrences such as Wilson and Russell (2017) Lillooet Glacier basalts. Thus, the GVB volcanism, particularly northward, may mark deviations from the southerly Cascade volcanism which contain more evidence of subduction zone magma signatures (e.g., Mullen and Weis, 2013, 2015; Mullen et al., 2017). This chapter concludes that the incompatible element compositions of all Cracked Mountain samples point towards a singular melt source. However, slight variations in major element compositions are investigated with Pearce Element Ratios (PER) and suggest that the two distinct petrographic assemblages (OP and OPA) can be explained by crystal fractionation in two different systems that underwent minor mixing. The magmatic plumbing modeled at Cracked Mountain mirrors some of the complexities (i.e., polymagmatic) seen elsewhere in global studies of monogenetic systems, and indirectly informs on the connectivity of shallow crustal magma chambers in the Garibaldi volcanic belt. 4.3 Future Implications of Study Through the study of the Cracked Mountain volcano, I provide the complete physical and chemical evolution of a single eruptive event taking place ~400 ka within the Mount Meager Volcanic (MMVC) complex of SWBC. The merit of volcanological studies on single eruptions such as Cracked Mountain volcano (e.g. Harris et al., under review), Lillooet Glacier Basalts (e.g. Wilson and Russell, 2017), or Mount Meager (Plinth) eruption (Russell et al., 2021b) is that they can be hyper-focused, providing a detailed eruptive story. There are, however, also advantages to broader-scale studies of a region's volcanic history as this allows for a longer-lived story across extended geologic time. 97 For this thesis, I conducted widespread field mapping and sampling across the MMVC (e.g., Harris and Russell, 2021). Through this expanded work, I accumulated additional 40Ar/39Ar ages, major and trace element chemistry, and lead (Pb), neodymium (Nd), strontium (Sr), and hafnium (Hf) isotopic ratios for samples located in the North Lillooet Ridge and River (North MMVC), Lillooet Glacier (North MMVC), Mosaic Ridge (West MMVC), Devastator Creek (West MMVC), and Elaho Valley (SW MMVC). This collection of data was not included in Chapters 2 and 3 as they fall outside the scope of the Cracked Mountain volcanological story, but the data is presented as supplementary within Appendices A, B, and E. The results of my supplementary thesis data tell an expanded story of volcanism within the Mount Meager Volcanic complex and are worth consideration for future studies. The preliminary geochronological findings suggest mafic volcanism within the MMVC has persisted across the last 500 ka, with eruptive periods occurring at ~450-400 ka, ~200 ka, ~115 ka, and <17 ka (Appendix B; Wilson and Russell, 2018). Glaciovolcanic deposits within the MMVC are not limited to Cracked Mountain (e.g., Wilson and Russell, 2017, 2018; Harris and Russell, 2021; Russell et al., 2021), and thus the additional 40Ar/39Ar data provide the backbone for expanded paleoclimate reconstruction within the localized GVB over the last 500 ka (e.g. Fig. B2.4) Furthermore, the new isotope data contributes to the previous work of Mullen and Weis (2013, 2015) who investigated the regional melt source trends for the mafic GVB occurrences. The preliminary isotopic findings indicate that even within a localized volcanic MMVC, melt signatures of mafic volcanism are diverse, where some eruptions retain a primitive signature and others reflect a subducted slab input (e.g. Appendix E). Prior geochemical studies indicate a latitudinal trend in Cascade arc melt signature (e.g., Green and Sinha, 2005; Mullen and Weis, 98 2013, 2015; Mullen et al., 2017). However, the new and expanded isotope data for the localized MMVC, in combination with new absolute ages for eruptive events, suggests there may also be a chronological trend in volcanic arc melt-slab signature (Appendix E). In conclusion, the multi-faceted investigation of the Cracked Mountain volcano tells the unique story of a glaciovolcanic eruptive event in the mid-Pleistocene. 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Wilson, A.M., Russell, J.K., and Ward, B.C., 2020, Paleo-glacier reconstruction in southwestern British Columbia , Canada : A glaciovolcanic model: Quaternary Science Reviews, v. 218, p. 178–188, doi:10.1016/j.quascirev.2019.06.024. Woodsworth, G., 1977, Geology of Pemberton (92J) Map Area: Geological Survey of Canada, p. 1 sheet. 108 Zimanowski, B., Fröhlich, G., and Lorenz, V., 1991, Quantitative experiments on phreatomagmatic explosions: Journal of Volcanology and Geothermal Research, v. 48, p. 341–358, doi:10.1016/0377-0273(91)90050-A. 109 Appendix A: Additional Whole-Rock Geochemical Data A.1: Whole-Rock Major and Trace Geochemical Compositions for Cracked Mountain Samples [Table A1] Table A1 shows additional whole-rock, major, and trace elemental geochemical data from Cracked Mountain volcano not included in Tables 2.3, 3.2, or 3.3 but are incorporated into figures and analyses throughout Chapters 2 and 3. Table A1 contains data analysed at Peter Hooper Lab, Washington State University, USA. 110 Table A1. Whole rock major (wt. %) and rare earth (ppm) element compositions of Cracked Mountain volcanic rocks analysed by X-ray fluorescence and ICP-MS, respectively. Analytical precision (2s) on major and trace elements based on replicates is reported in brackets. Whole-rock analyses conducted by Peter Hooper Lab, Washington State University, Pullman, WA. Ferric titration measured by ALS Canada Ltd., North Vancouver, BC. Sample AW-15-168 AW-15-175a AW-15-175b AW-15-178 AW-15-181 AW-15-182 UTM East 460545 460857 460857 460807 460472 460461 UTM North 5599555 5599930 5599930 5599494 5599672 5599598 Phenocrysts Pl>Ol>Cpx Pl>Ol Pl>Ol Pl>Ol Pl>Ol Pl>Ol SiO2 (0.30) 50.22 49.59 49.87 48.91 48.90 49.98 TiO2 (0.04) 1.50 1.50 1.54 1.40 1.55 1.59 Al2O3 (0.12) 15.42 15.04 15.19 15.02 15.07 15.36 Fe2O32 2.16 - - 2.31 - - FeO¹ (0.02) 8.64 11.13 11.18 8.08 11.44 11.09 MnO (0.02) 0.15 0.16 0.16 0.15 0.17 0.15 MgO (0.14) 8.05 9.00 8.64 9.72 8.72 7.76 CaO (0.30) 8.94 8.51 8.75 8.56 8.88 9.03 Na2O (0.06) 3.19 3.17 3.11 3.05 3.14 3.24 K2O (0.04) 0.75 0.45 0.64 0.38 0.48 0.50 P2O5 (0.02) 0.23 0.24 0.24 0.23 0.31 0.25 Totals 99.04 98.78 99.33 98.72 98.66 98.95 LOI 0.36 0.33 0.31 0.77 0.69 0.65 Mg#3 62.42 66.35 65.58 68.20 65.29 63.33 *FeO(T) (0.60) 10.59 11.13 11.18 11.29 11.44 11.09 111 Sample AW-15-168 AW-15-175a AW-15-175b AW-15-178 AW-15-181 AW-15-182 UTM East 460545 460857 460857 460807 460472 460461 UTM North 5599555 5599930 5599930 5599494 5599672 5599598 Phenocrysts Pl>Ol>Cpx Pl>Ol Pl>Ol Pl>Ol Pl>Ol Pl>Ol La (2.28) 8.66 8.72 8.97 8.48 10.22 9.74 Ce (5.72) 19.52 20.09 20.80 19.29 23.2 21.33 Pr (0.72) 2.88 2.87 2.94 2.74 3.29 3.14 Nd (3.43) 13.36 13.51 13.69 12.71 14.99 14.65 Sm (0.46) 3.83 3.88 3.94 3.67 4.06 4.15 Eu (0.24) 1.43 1.43 1.47 1.41 1.52 1.52 Gd (0.90) 4.3 4.2 4.31 3.95 4.48 4.52 Tb (0.10) 0.67 0.67 0.67 0.62 0.7 0.72 Dy (0.58) 3.86 3.83 3.95 3.64 4.15 4.18 Y (4.02) 18.14 17.76 18.21 16.94 19.88 19.8 Ho (0.14) 0.72 0.73 0.76 0.69 0.79 0.79 Er (0.40) 1.84 1.79 1.84 1.72 2.01 1.98 Tm (0.06) 0.25 0.24 0.25 0.23 0.27 0.26 Yb (0.40) 1.4 1.39 1.44 1.35 1.57 1.55 Lu (0.04) 0.21 0.21 0.22 0.2 0.23 0.23 Cs (0.2) 0.1 0.1 0.1 0.0 0.1 0.1 Rb (0.2) 6.5 5.1 6.0 4.2 5.5 5.7 Ba (60) 148 144 142 133 152 144 Sr (84) 461 446 460 463 475 470 Y (4.0) 18.1 17.8 18.2 16.9 19.9 19.8 Zr (26) 87 89 90 84 97 94 Hf (0.6) 2.4 2.3 2.4 2.3 2.5 2.5 Nb (3.8) 7.5 7.8 8.1 7.6 9.1 8.3 Ta (0.2) 0.5 0.5 0.5 0.5 0.6 0.5 112 Sample AW-15-168 AW-15-175a AW-15-175b AW-15-178 AW-15-181 AW-15-182 UTM East 460545 460857 460857 460807 460472 460461 UTM North 5599555 5599930 5599930 5599494 5599672 5599598 Phenocrysts Pl>Ol>Cpx Pl>Ol Pl>Ol Pl>Ol Pl>Ol Pl>Ol Th (0.2) 0.7 0.7 0.7 0.6 0.7 0.7 U (0.2) 0.3 0.3 0.3 0.2 0.3 0.2 Ni (53.0) 151.9 191.1 173.7 239.0 191.3 156.1 Cu (7.0) 42.3 44.6 42.8 54.7 46.0 48.7 Zn (8.4) 107.3 112.3 111.5 110.7 110.4 109.6 V (51) 178 172 177 165 179 189 Pb (0.2) 1.3 1.3 1.3 1.2 1.3 1.3 1Fe2O3 calculated for samples with known FeO, where Fe2O3 = (FeO(T) - FeO)/0.8998) 2FeO determined separately through ferric titration for select samples 3Mg# computed as MgO/(MgO+FeO (mol. %). CM samples not measured with ferric titration use the mean value of Fe 2+/ Ʃ Fe =0.7228 (N=7) for CM basalts 113 A.2: Whole-Rock Major and Trace Geochemical Compositions for Ancillary Mount Meager Volcanic Complex Samples [Table A2] Table A2 contains reference whole-rock major and trace element data collected from other MMVC mafic samples. This data is presented in Figure 3.3A. 114 Table A2: Whole rock major (wt. %) and trace element (ppm) compositions of ancillary Mount Meager mafic occurrences, analysed by X-ray fluorescence and ICP-MS, respectively. Analytical precision (2s) on major and trace elements based on replicates is reported in brackets. Whole-rock analyses conducted by Acme Labs Ltd., Vancouver BC. Sample MH-19-004 MH-19-006 MH-19-008 MH-19-015 MH-19-017 MH-19-018A MH-19-113 Mafic Centre Lillooet River Lillooet River Lillooet River Elaho Valley Elaho Valley Elaho Valley Lillooet Ridge UTM East 464179 464179 464179 458120 458429 458429 463955 UTM North 5616808 5616808 5616808 5598544 5597720 5597720 5619051 Phenocrysts Ol>Pl Ol>Pl Ol>Pl Pl=Ol Pl=Ol Pl=Ol Pl>Ol>Cpx SiO2 (0.28) 48.82 47.39 48.82 52.53 53.71 52.48 51.11 TiO2 (0.02) 1.7 1.45 1.67 1.39 1.31 1.46 1.54 Al2O3 (0.14) 15.21 13.09 15.15 16.22 16.25 16.06 16.77 FeO(T)* (0.44) 12.27 13.29 12.52 10.47 10.38 10.84 10.22 MnO (0.02) 0.16 0.18 0.16 0.14 0.14 0.15 0.15 MgO (0.56) 7.82 13.47 7.99 6.55 6.29 6.86 5.86 CaO (0.08) 9.07 7.86 9.29 8.03 7.58 8.23 8.21 Na2O (0.02) 3.36 3.05 3.23 3.91 4.01 3.76 3.5 K2O (0.02) 0.77 0.68 0.78 0.91 1.05 0.87 1.02 Cr2O3 (0.02) 0.04 0.04 0.04 0.03 0.03 0.25 0.02 P2O5 (0.02) 0.32 0.29 0.33 0.25 0.24 0.03 0.35 Ba 0.12 0.13 0.02 0.04 0.03 0.03 0.04 SO3 0.21 0.10 0.08 0.00 0.00 0.00 0.02 Sr 0.06 0.05 0.06 0.05 0.06 0.06 0.08 Totals 99.93 101.07 100.14 100.52 101.08 101.08 98.89 LOI -0.24 -0.25 0.20 -0.58 -0.66 -0.64 0.51 La (0.8) 16.1 14.1 14.6 13.5 12.8 13.2 23.6 Ce (1.2) 33.1 29.5 30.6 28.8 25.7 26.5 46.7 Pr (0.08) 4.55 3.91 4.08 3.79 3.39 3.67 6.24 Nd (0.6) 19.7 16.4 17.7 15.9 14.3 15.8 25.9 Sm (0.16) 4.53 3.93 3.98 3.76 3.38 3.82 5.07 115 Sample MH-19-004 MH-19-006 MH-19-008 MH-19-015 MH-19-017 MH-19-018A MH-19-113 Mafic Centre Lillooet River Lillooet River Lillooet River Elaho Valley Elaho Valley Elaho Valley Lillooet Ridge UTM East 464179 464179 464179 458120 458429 458429 463955 UTM North 5616808 5616808 5616808 5598544 5597720 5597720 5619051 Phenocrysts Ol>Pl Ol>Pl Ol>Pl Pl=Ol Pl=Ol Pl=Ol Pl>Ol>Cpx Dy (0.12) 3.85 3.44 3.51 3.36 2.97 3.34 3.86 Y (0.9) 19.8 16.7 18.3 16.8 15.7 16.6 19.9 Ho (0.04) 0.79 0.63 0.68 0.65 0.59 0.66 0.78 Er (0.06) 2.05 1.71 1.82 1.83 1.55 1.87 2.14 Tm (0.02) 0.31 0.25 0.23 0.25 0.22 0.25 0.29 Yb (0.08) 1.66 1.47 1.49 1.56 1.29 1.60 1.78 Lu (0.02) 0.25 0.22 0.21 0.23 0.2 0.24 0.25 Cs (0.20) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 Rb (0.4) 9.2 6 9 9.6 13.3 9.9 13.1 Ba (7) 315 234 260 330 350 308 467 Sr (34) 582 506 540 589 516 563 914 Nb (0.2) 16.1 14.3 14.8 10 9 10.2 16 Ta (0.2) 0.9 0.9 0.8 0.6 0.5 0.5 1.0 Th (0.2) 1.3 1.2 1.3 1.5 1.6 1.5 2.4 U (0.8) 0.8 1.5 2.3 0.6 0.7 0.5 1.0 Ni (53.0) 107.6 368.1 146 68.7 56.1 68 61 Cu (7.0) 34.0 48.4 33.4 29.1 30.8 47.8 26.0 Zn (8) 55 91 63 46 37 53 48 V (13) 193 157 208 157 174 159 174 Pb (0.2) 1.3 1.8 1.9 0.7 2.5 1.2 1.7 116 Sample MH-19-114 MH-19-115 MH-19-116 MH-19-119 MH-19-120 MH-20-047A MH-20-048 Mafic Centre Lillooet Ridge Lillooet Ridge Lillooet Ridge Lillooet Ridge Lillooet Ridge Mosaic Ridge Mosaic Ridge UTM East 463920 463884 463843 463789 463346 457933 457830 UTM North 5618947 5618893 5618872 5619051 5618989 5611861 5611847 Phenocrysts Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx SiO2 (0.28) 51.42 50.38 50.28 51.46 51.15 50.87 49.37 TiO2 (0.02) 1.49 1.53 1.44 1.49 1.54 1.27 1.24 Al2O3 (0.14) 15.88 15.72 15.91 16.01 16.34 17.90 18.56 FeO(T)* (0.44) 10.74 11.12 11.03 10.77 10.71 9.98 9.68 MnO (0.02) 0.15 0.15 0.15 0.15 0.15 0.15 0.14 MgO (0.56) 6.99 7.35 7.6 6.96 6.45 6.29 5.79 CaO (0.08) 8.55 8.65 8.79 8.58 8.46 9.79 9.94 Na2O (0.02) 3.63 3.51 3.47 3.68 3.71 3.73 3.47 K2O (0.02) 0.98 0.88 0.83 0.93 1.02 0.79 0.67 Cr2O3 (0.02) 0.03 0.04 0.04 0.03 0.03 0.01 0.01 P2O5 (0.02) 0.29 0.29 0.27 0.3 0.34 0.35 0.29 Ba 0.05 0.04 0.04 0.05 0.05 0.03 0.03 SO3 0.02 0.07 0.01 0.02 0.05 0.00 0.00 Sr 0.07 0.06 0.06 0.07 0.08 0.12 0.12 Totals 100.29 99.80 99.92 100.50 100.08 101.28 99.32 LOI -0.34 -0.12 -0.47 -0.47 0.25 -0.41 0.03 La (0.8) 18.5 17.7 16.3 19.5 21.7 17.8 16.2 Ce (1.2) 38.2 37.6 35.7 40 44.6 39.2 36 Pr (0.08) 5.01 4.95 4.49 5.29 5.77 5.17 5.05 Nd (0.6) 22.1 20.7 18.4 22.1 23.6 22.8 21.9 Sm (0.16) 4.42 4.4 4.13 4.59 4.9 4.44 4.16 117 Sample MH-19-114 MH-19-115 MH-19-116 MH-19-119 MH-19-120 MH-20-047A MH-20-048 Mafic Centre Lillooet Ridge Lillooet Ridge Lillooet Ridge Lillooet Ridge Lillooet Ridge Mosaic Ridge Mosaic Ridge UTM East 463920 463884 463843 463789 463346 457933 457830 UTM North 5618947 5618893 5618872 5619051 5618989 5611861 5611847 Phenocrysts Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Pl>Ol>Cpx Dy (0.12) 3.64 3.69 3.47 3.76 3.86 3.26 3.25 Y (0.9) 18.2 19 16.8 18.4 18.8 16.2 16.8 Ho (0.04) 0.72 0.72 0.7 0.75 0.73 0.62 0.64 Er (0.06) 1.91 2.01 1.85 1.93 2.00 1.72 1.86 Tm (0.02) 0.27 0.27 0.24 0.25 0.26 0.25 0.25 Yb (0.08) 1.61 1.72 1.51 1.71 1.80 1.57 1.60 Lu (0.02) 0.24 0.24 0.22 0.25 0.26 0.24 0.23 Cs (0.20) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 Rb (0.4) 13.3 10.6 11.8 9.6 11.9 4.8 4.3 Ba (7) 370 359 330 389 411 341 334 Sr (34) 707 684 700 760 796 1016 1086 Nb (0.2) 13.4 13.9 12.1 13.5 15.2 6.6 6.6 Ta (0.2) 0.8 0.8 0.7 0.7 0.9 0.4 0.3 Th (0.2) 1.9 1.8 1.6 1.9 2.2 1.6 1.7 U (0.8) 0.7 0.5 0.6 0.7 0.7 0.5 0.5 Ni (53.0) 88.8 99.1 99.1 92.1 67.3 27.8 24.2 Cu (7.0) 48.6 29.0 36.6 47.1 25.6 24.7 16.6 Zn (8) 78 61 74 79 56 60 56 V (13) 175 181 178 181 187 189 197 Pb (0.2) 1.2 0.8 0.9 1.8 1.4 1.8 1.5 * Total iron (Fe2+ + Fe3+) determined through XRF analyses 118 Appendix B: Radiogenic 40Ar /39Ar Data Samples were chosen based on fresh, holocrystalline, and non-vesiculated groundmass. Once received by the WiscAr Labs, samples were sent to the research reactor at Oregon State University, USA, for irradiation. Once irradiated, samples were returned to WiscAr Labs, where 10-15 mg of sample groundmass was separated into a 5 mm diameter well, cut in a copper planchet. A 60 W CO2 laser beam of a Noblesse 5 Collector Mass Spectrometer was then defocused to a 4 mm diameter to evenly heat the entire sample during each heating step of the analyses. Instrument detectors simultaneously measured 40Ar /39Ar, 36Ar /39Ar, and 37Ar /39Ar ratios through cycles of beam switching. Ages were calculated relative to the 1.1864 Ma Alder Creek sanidine standard (Jicha et al., 2016). Argon decay constants and isotopic abundances are after Min et al., (2000). B1: 40Ar /39Ar results for Cracked Mountain Sample MH-19-055 [Table B1; Figure B1] A plateau age of 401.6 ± 38.1 ka was determined from the inverse-variance-weighted mean of selected steps (Fig. B1). The error on the plateau age is reported as 2σ calculated by multiplying the inverse-variance-weighted mean error (Taylor, 1982) by root MSWD where MSWD >1. The second age of 413.5 ± 88.8 ka was determined through a reverse isochron plot of 36Ar /40Ar vs 39Ar /40Ar for all twenty-four measured steps (Fig. B1). Table B1 presents the full heating steps involved in the absolute age determination for Cracked Mountain sample MH-19-055. 119 Table B1. Complete data from twenty-four step heating analyses of Cracked Mountain sample MH-19-055 with Noblesse 5 Collector Mass Spectrometer conducted by the WiscAr Lab, University of Wisconsin-Madison, USA. N Power Age ±1σ K/Ca ±1σ Cum. %39Ar %40Ar % (ka) (ka) (%) (%) 01A 1.6 -88 350 2.237 0.05 1.609 -0.152 01B 1.75 318 230 1.616 0.02 4.319 0.813 01C 1.85 404 186 1.273 0.02 8.358 1.286 01D 1.95 291 160 0.918 0.01 11.516 1.114 01E 2.05 408 136 0.739 0.009 19.859 1.712 01F 2.05 537 130 0.744 0.009 25.551 2.369 01G 2.15 567 123 0.597 0.007 30.687 2.686 01H 2.25 455 116 0.457 0.005 35.750 2.324 01I 2.35 454 128 0.410 0.004 39.880 2.125 01J 2.5 446 106 0.316 0.004 44.122 2.554 01K 2.65 354 100 0.246 0.003 48.630 2.178 01L 2.85 401 93 0.192 0.002 53.182 2.697 01M 3.1 324 85 0.145 0.002 57.998 2.393 01N 3.75 419 73 0.093 0.001 63.050 3.628 01O 4.2 368 71 0.079 0.0009 68.193 3.297 01P 4.7 423 70 0.069 0.0008 73.352 3.770 01Q 5.4 418 72 0.065 0.0007 78.302 3.744 01R 6.3 399 75 0.060 0.0007 82.599 3.516 01S 7.4 348 72 0.055 0.0006 86.907 3.190 01T 8.7 489 69 0.049 0.0006 90.479 4.752 01U 10.5 418 71 0.044 0.0005 93.323 4.556 01V 13 375 74 0.035 0.0004 95.828 4.342 01W 20 329 89 0.014 0.0002 98.524 3.156 01X 27 255 164 0.006 0.00007 100.000 1.562 120 N 40Ar*/39ArK ±1σ 39Ar/40Ar ±1σ 36Ar/40Ar ±1σ 40Ar1 (cps) 01A -0.092 0.364 0.017 0.00002 0.0034 0.00002 236298 01B 0.330 0.238 0.025 0.00003 0.0033 0.00002 266819 01C 0.419 0.193 0.031 0.00003 0.0033 0.00002 319673 01D 0.302 0.166 0.037 0.00004 0.0033 0.00002 207969 01E 0.423 0.142 0.040 0.00003 0.0033 0.00002 500638 01F 0.557 0.135 0.043 0.00004 0.0033 0.00002 324966 01G 0.589 0.128 0.046 0.00004 0.0033 0.00002 273183 01H 0.473 0.121 0.049 0.00004 0.0033 0.00002 249944 01I 0.471 0.133 0.045 0.00004 0.0033 0.00002 222098 01J 0.463 0.110 0.055 0.00005 0.0033 0.00002 186646 01K 0.367 0.104 0.059 0.00005 0.0033 0.00002 184475 01L 0.416 0.096 0.065 0.00006 0.0033 0.00002 170383 01M 0.336 0.088 0.071 0.00007 0.0033 0.00002 163987 01N 0.434 0.076 0.084 0.00008 0.0032 0.00002 146878 01O 0.382 0.073 0.086 0.00008 0.0032 0.00002 144492 01P 0.439 0.073 0.086 0.00008 0.0032 0.00002 145732 01Q 0.433 0.075 0.086 0.00008 0.0032 0.00002 139085 01R 0.414 0.078 0.085 0.00008 0.0032 0.00002 122894 01S 0.361 0.075 0.088 0.00009 0.0032 0.00002 118348 01T 0.508 0.072 0.094 0.00010 0.0032 0.00002 92668 01U 0.434 0.073 0.105 0.0001 0.0032 0.00003 65686 01V 0.389 0.077 0.112 0.0001 0.0032 0.00003 54532 01W 0.341 0.092 0.092 0.0001 0.0032 0.00003 70798 01X 0.264 0.170 0.059 0.0001 0.0033 0.00003 60602 121 N 38Ar ±1σ 37Ar ±1σ 36Ar ±1σ J (cps) (cps) (cps) 01A 210 6 126 3 793 5 0.000527 01B 272 7 293 4 887 5 0.000527 01C 350 8 552 7 1058 6 0.000527 01D 254 8 597 8 690 4 0.000527 01E 651 12 1956 23 1651 9 0.000527 01F 429 9 1323 15 1065 6 0.000527 01G 358 8 1485 17 893 5 0.000527 01H 344 11 1908 21 821 5 0.000527 01I 300 5 1734 19 731 4 0.000527 01J 273 8 2310 26 613 4 0.000527 01K 284 12 3138 36 610 4 0.000527 01L 261 9 4052 48 562 3 0.000527 01M 282 8 5674 68 545 3 0.000527 01N 275 9 9277 106 489 3 0.000527 01O 278 8 11121 123 486 3 0.000527 01P 285 10 12763 141 491 3 0.000527 01Q 259 7 13018 143 470 3 0.000527 01R 226 6 12211 134 417 3 0.000527 01S 233 5 13291 155 406 3 0.000527 01T 184 7 12252 143 316 2 0.000527 01U 149 7 10934 130 228 2 0.000527 01V 139 5 12191 145 195 2 0.000527 01W 172 5 32126 381 283 2 0.000527 01X 122 7 42702 479 271 2 0.000527 122 N ±1σ 39Ar Decay 37Ar Decay Lambda K Monitor Age Monitor Name Monitor Material 01A 0.0000002 1.000641 5.995592 5.464E-10 1.1864 ACS-2 sanidine 01B 0.0000002 1.000642 6.005838 5.464E-10 1.1864 ACS-2 sanidine 01C 0.0000002 1.000643 6.018577 5.464E-10 1.1864 ACS-2 sanidine 01D 0.0000002 1.000643 6.031338 5.464E-10 1.1864 ACS-2 sanidine 01E 0.0000002 1.000644 6.044126 5.464E-10 1.1864 ACS-2 sanidine 01F 0.0000002 1.000645 6.056109 5.464E-10 1.1864 ACS-2 sanidine 01G 0.0000002 1.000645 6.064874 5.464E-10 1.1864 ACS-2 sanidine 01H 0.0000002 1.000646 6.075242 5.464E-10 1.1864 ACS-2 sanidine 01I 0.0000002 1.000646 6.082362 5.464E-10 1.1864 ACS-2 sanidine 01J 0.0000002 1.000647 6.092750 5.464E-10 1.1864 ACS-2 sanidine 01K 0.0000002 1.000647 6.099051 5.464E-10 1.1864 ACS-2 sanidine 01L 0.0000002 1.000648 6.108632 5.464E-10 1.1864 ACS-2 sanidine 01M 0.0000002 1.000648 6.114110 5.464E-10 1.1864 ACS-2 sanidine 01N 0.0000002 1.000649 6.126699 5.464E-10 1.1864 ACS-2 sanidine 01O 0.0000002 1.000649 6.134647 5.464E-10 1.1864 ACS-2 sanidine 01P 0.0000002 1.000650 6.139312 5.464E-10 1.1864 ACS-2 sanidine 01Q 0.0000002 1.000650 6.147264 5.464E-10 1.1864 ACS-2 sanidine 01R 0.0000002 1.000650 6.151937 5.464E-10 1.1864 ACS-2 sanidine 01S 0.0000002 1.000651 6.159903 5.464E-10 1.1864 ACS-2 sanidine 01T 0.0000002 1.000651 6.163742 5.464E-10 1.1864 ACS-2 sanidine 01U 0.0000002 1.000651 6.170869 5.464E-10 1.1864 ACS-2 sanidine 01V 0.0000002 1.000652 6.174286 5.464E-10 1.1864 ACS-2 sanidine 01W 0.0000002 1.000652 6.177708 5.464E-10 1.1864 ACS-2 sanidine 01X 0.0000002 1.000652 6.184432 5.464E-10 1.1864 ACS-2 sanidine 123 N (40Ar/3939)K ±1σ (38Ar/3939)K ±1σ (37Ar/3939)K ±1σ (39Ar/3737)Ca 01A 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01B 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01C 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01D 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01E 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01F 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01G 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01H 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01I 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01J 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01K 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01L 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01M 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01N 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01O 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01P 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01Q 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01R 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01S 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01T 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01U 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01V 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01W 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 01X 0.000730 0.000090 0.012150 0.000030 0.000224 0.000016 0.000702 124 N ±1σ (38Ar/3737)Ca ±1σ (36Ar/3737)Ca ±1σ (36Ar/3838)Cl Ca/K 01A 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01B 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01C 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01D 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01E 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01F 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01G 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01H 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01I 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01J 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01K 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01L 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01M 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01N 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01O 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01P 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01Q 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01R 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01S 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01T 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01U 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01V 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01W 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 01X 0.000012 0.000020 0.000001 0.000270 0.000000 263.000000 2.320000 125 N Cl/K 01A 0.227000 Integrated K/Ca ±2σ 0.082114 0.00059401B 0.227000 Plateau Age ±2σ 401.581 38.112 n=24/24 MSWD=*0.49101C 0.227000 Total Integrated Age ±2σ 403.010 49.52301D 0.227000 Isochron Age ±2σ 413.508 88.793 MSWD=0.52401E 0.227000 (40Ar/36Ar)trapped ±2σ 298.29 2.0101F 0.22700001G 0.22700001H 0.22700001I 0.22700001J 0.22700001K 0.22700001L 0.22700001M 0.22700001N 0.22700001O 0.22700001P 0.22700001Q 0.22700001R 0.22700001S 0.22700001T 0.22700001U 0.22700001V 0.22700001W 0.22700001X 0.227000126 Notes: 1Corrected: Isotopic intensities corrected for blank, baseline, radioactivity decay and detector intercalibration, not for interfering reactions. X symbol preceding sample ID denotes analyses excluded from plateau age calculations. Errors quoted for individual analyses include analytical error only, without interfering reactions or J uncertainties. Integrated age calculated by summing isotopic measurements of all steps. Plateau age is inverse-variance-weighted mean of selected steps. Plateau age error is inverse-variance-weighted mean error (Taylor, 1982) times root MSWD where MSWD>1. Decay constants and isotopic abundances after Min et al. (2000) Ages calculated relative to 1.1864 Ma Alder Creek sanidine standard (Jicha et al., 2016) 127 Figure B1: 40Ar /39Ar geochronometry for samples from Cracked Mountain Volcano. A) Plateau diagram for sample MH-19-055, a largely holocrystalline, radially jointed interior of pillow lava with an apparent age of 401.6 ± 38.1 ka. The height of individual boxes (steps) is 2 σ error. B) Inverse isochron plot for MH-19-055 showing all heating steps, returning an age of 413.5 ± 88.8 ka. Ellipses show 2 σ errors. Note the large uncertainty is due to low levels of radiogenic argon and excess atmospheric argon in the analyzed sample. 128 B2: 40Ar /39Ar results for additional MMVC Samples [Table B2; Figures B2.1-4] B2.1: Rationale In addition to Cracked Mountain, mapping was done across the MMVC and nearly 200 geologic samples were collected. To build upon prior studies such as Woodsworth (1977), Read (1979, 1990), and Green et al., (1988), much of the mapping and sample collections were conducted throughout previously understudied areas of the volcanic complex (e.g., Harris et al., 2020; Harris and Russell, 2021). From this expanded work, we selected a small suite of samples from newly mapped and understudied geological deposits for age-dating (Fig B2.1). The further sample selection criterion was based on whether the geological samples were fresh, unaltered, holocrystalline, and contained non-vesiculated groundmasses. 129 Isochron PlateauSamples UTM Easting UTM Northing Material 40Ar/36Ari ± 2s Age (ka) ± 2s N39Ar % MSWD Age (ka) ± 2sDevastator CreekMH-19-052 457900 5603470 groundmass 297.3 ± 2.4 502.7 ± 6.6 14/17 92.8 1.13 499.7 ± 3.7Lillooet RiverMH-19-007 464179 5616808 groundmass 297.2 ± 2.2 450.9 ± 17.7 15/15 100.0 1.16 441.7 ± 9.8MH-19-006 464179 5616808 groundmass 299.0 ± 2.2 454.8 ± 10.0 15/17 99.8 1.06 456.5 ± 5.8Cracked MountainMH-19-055 461014 5599824 groundmass 298.3 ± 2.0 413.5 ± 88.8 24/24 100.0 0.49 401.6 ± 38.1Lillooet RidgeMH-19-116 463843 5618872 groundmass 300.0 ± 2.9 197.8 ± 16.1 18/18 100.0 0.59 205.1 ± 6.5MH-19-119 463789 5619051 groundmass 298.1 ± 1.5 206.8 ± 20.0 21/21 100.0 1.12 201.1 ± 11.8Mosaic RidgeMH-20-047A 457933 5611861 groundmass 296.9 ± 2.8 127.6 ± 22.6 13/13 100.0 0.26 115.2 ± 9.7Elaho ValleyMH-19-015 458120 5598544 groundmass 296.1 ± 3.8 126.5 ± 31.4 11/15 88.3 0.65 106.3 ± 11.0Table B2: 40Ar/39Ar data for Mount Meager volcanic complex samples. Samples prepared and analysed by WiscAr laboratories, University of Wisconsin-Madison, Madison WI, USAAges calculated relative to 1.1864 Ma Alder Creek sanidine standard using the decay constants of Min et al. (2000). Atmospheric 40Ar/36Ar = 298.56 ± 0.62 (Lee et al., 2006)N = number of plateau steps/number of total incremental heating steps130 Figure B2.1: Undivided Geological Map of MMVC shows the large-scale dispersion of intermediate volcanics (MVi) and peripheral mafic volcanics (MVm) overlaying basement lithologies (Bu). We used pre-existing large-scale maps of Read (1979) and Woodsworth (1977) as well as our field mapping to accurately depict unit locations and contacts. The youngest MMVC eruption, 2350 B.P Pebble Creek Formation (PcF) is distinguished from other volcanics (Hickson et al., 1999; Stewart et al., 2008). Locations for samples selected for 40Ar/39Ar dating are also shown. 131 B2.2: Results Devastator Creek The Devastator Creek lava was first identified by Harris et al., (2020) and was included in Harris and Russell’s (2021) Geological Map of W MMVC. The newfound lava outcrops on the Southwest flank of the Mount Meager massif ~2 km NW of Devastator Creek at ~1,700 m a.s.l (Fig B1). The lava is a subaerial, columnar jointed dacite (Harris and Russell, 2021). One sample was sent to the WiscAr lab for age-dating (19-052) (Fig B2.1, Table B2). The sample returned a plateau age of 499.7 ± 3.7 ka and an isochron age of 502.7 ± 6.6 ka (Fig B2.2A, B2.3A). Lillooet River The Lillooet River volcanic deposits are located in the north MMVC, exposed above the present-day Lillooet River (Fig B2.1). Samples were collected at a waterfall formed by a cliff of basaltic hyaloclastites at ~1,100 m a.s.l (Harris et al., 2020; Harris and Russell, 2021). Multiple dykes intrude the cliffs of hyaloclastite and geochemical analyses of hyaloclastite material and dykes show they are sourced from the same magma. The morphology of the deposit and types of lithofacies present at the waterfall exposure indicate a glaciovolcanic origin. Two dyke samples were sent to WiscAr lab, 19-006 and 19-007 (Fig B2.1, Table B2). The two dykes returned plateau ages of 456.5 ± 5.8 ka and 441 ± 9.8 respectively (Fig B2.2B and C). Isochron ages are 454.8 ± 10.0 and 450.9 ± 17.7 ka respectively (Fig B2.3B and C). Cracked Mountain Cracked Mountain is a subglacial landform located in the Southwest corner of the MMVC (Fig B2.1)(Wilson and Russell, 2018; Harris et al., under review). The edifice is comprised of basaltic tephra and intrusive and effusive lava that reach a summit of ~1,650 m a.s.l (Harris and Russell, 2021; Harris et al., under review). Field-based analyses and paleomagnetic data indicate a monogenetic eruption. Two samples were sent to WiscAr lab, 19-031 (dyke) and 19-055 (pillow lava interior) (Fig B2.1, Table B2). Sample 19-031 was loaded with excess argon and undatable. Sample 19-055 had low radiogenic argon but returned a plateau age of 401 ± 38 ka and isochron age of 413 ± 88.8 (Fig B2.2D, B2.3D). 132 Lillooet Ridge The Lillooet Ridge basalts are located in the north MMVC, ~2 km above the present-day Lillooet River at elevations of ~2,000 m a.s.l (Fig B2.1). The deposits are radially jointed pods of basaltic pillow lava, hyaloclastites, and dykes. The location and type of lithofacies indicate a glaciovolcanic origin, and the petrochemical signatures indicate these basalts are different than the basalts exposed within the Lillooet River valley (Harris and Russell, 2021). Two samples were sent to WiscAr lab Samples, 19-116 and 19-119 (dykes) (Fig B2.1, Table B2). Their plateau ages are 205 ± 6.5 and 201.1 ± 11.8 ka respectively (Fig B2.2E and F). The isochron ages are 197.8 ± 16.1 and 206.8 ± 20.0 ka respectively (Fig B2.3E and F). 133 Figure B.2.2. 40Ar /39Ar geochronometry for samples from six previously un-dated volcanic deposits within the MMVC. Plateau diagrams show individual heating steps used to integrate the plateau age for each sample. The height of individual boxes (steps) is 2 σ error. 134 Figure B.2.3. 40Ar /39Ar geochronometry for samples from six previously un-dated deposits within the MMVC. Inverse isochron plots display all heating steps for each sample. Ellipses show 2σ errors for each step. 135 Mosaic Ridge The mosaic ridge lavas are located in the NW flank of Mount Meager Massif (Fig B2.1) (Read, 1979, 1990). The deposits are a series of subaerial basaltic lavas, tephras, and dykes that outcrop at ~1,700 m a.sl. One sample was sent to WiscAr lab, 20-047A (dyke) (Fig B2.1, Table B2). The sample returned a plateau age of 115.2 ± 9.7 ka and an isochron age of 127.6 ± 22.6 ka (Fig B2.2G, B2.3G). Elaho Valley The Elaho Valley lavas are located in the Southwest corner of the MMVC (Fig B2.1). The lavas likely source above a waterfall at the head of the Elaho valley at ~1,000 m a.sl, are subaerial, columnar jointed basaltic andesites, and extend ~20 km south (Woodsworth, 1977; Read, 1990; Harris and Russell, 2021). Two samples were sent to the WiscAr lab, 19-015 and 19-018A (Fig B2.1, Table B2). Sample 19-018A was loaded with atmospheric argon and undatable. Sample 19-015 returned a plateau age of 106.3 ± 11.0 ka and an isochron age of 126.5 ± 31.4 ka (Fig B2.2H, B2.3H). B2.3: Age Relationships and Implications Our new 40Ar/39Ar age dates record six discrete eruptive events within the MMVC over the past 500 ka. This data shows that mafic occurrences within the MMVC are older than previously shown by Green et al., (1988) and Read (1990). We identify three separate periods of mafic volcanism, from ~450-400 ka (Lillooet River and Cracked Mountain), ~200 ka (Lillooet Ridge), and ~115-100 ka (Mosaic Ridge and Elaho Valley). Additionally, our data has regional paleoenvironmental implications as the dates provide land-based records for the presence and absence of continental ice sheets (CIS) over the past 500 ka. The newly dated glaciovolcanic deposits at the Lillooet River, Cracked Mountain, and Lillooet Ridge require that a CIS reached elevations of 1650 m a.s.l., and 2,000 m a.s.l., at ~450 ka and ~200 ka respectively (Fig B2.4B and C). Conversely, the newly dated subaerial erupted lavas record an absence of CIS at elevations below 1,700 m a.sl at ~500 ka (Devastator Creek) and again at ~115 ka (Mosaic Ridge and Elaho Valley) (Fig B2.4A and D). The evidence of 136 Fraser Glaciation (~25 ka) (Fig B2.4E) within the MMVC has been documented through prior glaciovolcanic studies (e.g., Wilson and Russell, 2017; Russell et al., 2021) and our new age-dates expand the story of a localized waxing and waning of CIS across the MMVC throughout the late Pleistocene. 137 Figure B2.4. Paleoclimate glacial reconstruction for the MMVC over five periods of time within the last 500 ka. All maps are composed of Hillshade DEMs showing the dispersal of glacial ice (blue), and regions absent of glacial ice (brown). Upper elevation show snow caps (grey). Ice-elevation models are based on land-based records of precisely dated volcanic deposits (shown with an X). A) The land-based proxy of the subaerial Devastator Creek lava, requires that elevations up to 1,700 m must have been ice-free at ~500 ka. B) The land-based records of the Lillooet River and Cracked Mountain glaciovolcanic eruptions require a minimum height of 1,650 m for glacial ice at ~450 ka. C) The land-based record of the Lillooet Ridge glaciovolcanic deposits require that elevations up to ~2,000 m must have been under glacial ice at ~200 ka. D) The land-based records of the subaerial Mosaic Ridge and Elaho Valley lavas require that elevations from 1,700 m down into the valleys (~850 m) must have been ice-free at ~115 ka. E) The land-based record of the Plinth Block and Ash (Russell et al., 2021) and Lillooet Glacier Basalts (Wilson and Russell, 2017, 2018) glaciovolcanic deposits require that valley filling glaciers were present at elevations up to ~1000 m at ~25 ka. B4: Summary Here we present new 40Ar/39Ar age dates for six late-Pleistocene eruptions within the MMVC. Our findings provide the first age constraints for the newly mapped Devastator Creek lavas, Cracked Mountain volcano, Lillooet River, and Lillooet Ridge volcanic deposits. We also provide new dates for the Mosaic Ridge and Elaho Valley lavas with smaller uncertainties than reported in prior studies (Woodsworth, 1977; Green et al., 1988; Read, 1990). Overall, this new collection of data bolsters the understanding of volcanic activity within the MMVC over the past 500 ka. 138 Appendix C: Paleomagnetic Data for Cracked Mountain Volcano [Table C1; Fig C1] Figure C1: Stereographic plot and google earth imagery of Paleomagnetic Site 1. A) Mean paleomagnetic directional data from Site 1 is shown with mean data (redpoint) for Sites 2-9. The approximate distance and direction of tilt is ~12 ̊ E. B) Google earth imagery of Site 1 at the SE base of the edifice. Large cracks were seen above (outlined in dashed white) extend downslope approx. E-SE. The degree and direction of the rotated paleomagnetic data are plausible based on the observed cracking orientations (~perpendicular to downslope direction) observed in this area of the volcano. 139 Table C1. Paleomagnetic Analyses Sample Site Nt Lithology Nc Ns UTM Easting UTM Northing Decl. Inc. k α95 1 CMV001,003, 006 Lp 7 3 460385 5599035 34.37 72.88 476.41 5.65 2 CMV008-012, 014-015, 059-063, 065 Lt1 16 13 460554 5599602 340.31 75.14 109.01 3.99 3 CMV016-019 Ld2 3 4 460519 5599610 346.14 77.02 431.25 4.43 4 CMV020-022 Ld1 3 3 460519 5599610 14.69 76.36 113.56 11.62 5 CMV023-025 Ld2 4 3 460519 5599610 333.84 72.76 134.74 10.66 6 CMV026-33 Ld1 8 8 460477 5599585 343.03 73.03 291.75 3.25 7 CMV034-041 Ld2 8 8 460477 5599585 344.66 76.16 348.79 2.97 8 CMV042-049 Ld1 8 8 460477 5599585 340.6 78.41 1874.69 1.39 9 CMV050-054, 056-057 Ld2 8 7 460477 5599585 8.51 81.36 191.38 4.37 Mean (CM Site 1-9) 9 344.92 75.51 84.59 4.99 Mean (excl. Site 1) 8 347.33 76.63 351.00 2.96 Note: Nt, sample numbers for each site: Nc, total number of samples collected at each site: Ns, total number of samples used in calculation of mean direction for each site: Decl., declination: Incl., inclination: k, precision parameter: α95, radius of 95% confidence level 140 Appendix D: Electron-Microprobe Analyses for Cracked Mountain Samples D1: Olivine Analyses [Table D1] 141 Table D1: Electron Microprobe (EMP) major element analyses (wt. %) of CM olivine phenocryst Cores (PC), phenocryst rims (PR), and groundmass phases (GM). Analyses conducted at University of British Columbia, Vancouver, Canada. Olivine Analyses Total number of olivine analyses: 137 Label1 LOD2 SD3 M-045A-C4-1 M-045A-C4-2 M-045A-C4-3 M-045A-C4-4 M-045A-C4-5 M-045A-C4-8 M-045A-C4-9 M-045A-C4-12 M-045A-C4-13 M-045A-C4-14 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type PC PC PC PC PC PC PC PC PC PC SiO2 0.06 0.19 38.55 38.53 38.45 38.74 38.86 38.86 38.94 38.58 38.91 38.83 TiO2 0.05 0.01 0.00 0.00 0.01 0.05 0.05 0.07 0.02 0.04 0.01 0.05 Al2O3 0.05 0.01 0.05 0.05 0.04 0.05 0.00 0.00 0.00 0.06 0.02 0.01 FeO 0.09 0.38 20.25 19.92 19.94 19.24 19.75 20.22 20.38 20.55 20.12 20.17 MgO 0.06 0.27 40.75 41.27 40.17 41.16 41.16 40.49 40.97 40.38 40.45 40.33 MnO 0.09 0.05 0.25 0.27 0.28 0.24 0.31 0.31 0.24 0.25 0.24 0.27 NiO 0.11 0.06 0.15 0.14 0.15 0.25 0.17 0.18 0.20 0.18 0.13 0.08 CaO 0.04 0.02 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 Wt % Total 100.24 100.41 99.28 99.97 100.54 100.37 100.98 100.26 100.11 99.98 Cation Total 3.01 3.01 3.00 3.00 3.00 3.00 3.01 3.00 3.00 3.00 Fo% 78.20 78.69 78.22 79.23 78.79 78.12 78.18 77.80 78.18 78.09 142 Label1 LOD2 SD3 M-045A-C4-15 A-168-C5-1 A-168-C5-2 A-168-C5-3 A-168-C5-4 A-168-C5-5 A-168-C5-6 A-168-C5-7 A-168-C5-8 A-168-C5-9 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type PC PC PC PC PC PC PC PC PC PC SiO2 0.06 0.19 38.65 38.55 38.58 38.91 38.61 38.64 38.98 38.48 38.97 39.11 TiO2 0.05 0.01 0.02 0.01 0.00 0.03 0.00 0.02 0.02 0.03 0.03 0.03 Al2O3 0.05 0.01 0.05 0.02 0.04 0.03 0.02 0.01 0.06 0.01 0.00 0.01 FeO 0.09 0.38 20.28 19.94 20.23 21.07 21.62 20.33 20.30 20.46 20.36 20.09 MgO 0.06 0.27 40.43 40.24 40.32 39.93 39.88 40.56 40.39 39.71 40.48 40.48 MnO 0.09 0.05 0.35 0.29 0.26 0.28 0.33 0.27 0.30 0.29 0.28 0.31 NiO 0.11 0.06 0.10 0.13 0.16 0.17 0.13 0.17 0.16 0.14 0.21 0.18 CaO 0.04 0.02 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 Wt % Total 100.11 99.41 99.83 100.66 100.83 100.24 100.44 99.35 100.56 100.45 Cation Total 3.00 3.00 3.00 3.00 3.01 3.00 3.00 3.00 3.00 3.00 Fo% 78.04 78.25 78.04 77.16 76.68 78.06 78.01 77.57 77.99 78.22 Label1 LOD2 SD3 A-168-C5-10 A-168-C5-11 A-168-C6-1 A-168-C6-2 A-168-C6-6 A-168-C6-7 A-168-C6-8 A-168-C6-9 A-168-C6-10 M-045A-C4-6 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Pillow Lava Mineral Type PC PC PC PC PC PC PC PC PC PR SiO2 0.06 0.19 39.33 39.18 39.00 39.41 39.09 39.42 39.19 39.33 38.96 38.87 TiO2 0.05 0.01 0.01 0.02 0.00 0.03 0.00 0.00 0.02 0.00 0.01 0.01 Al2O3 0.05 0.01 0.02 0.07 0.05 0.09 0.01 0.06 0.03 0.00 0.02 0.01 FeO 0.09 0.38 20.43 20.15 20.64 19.22 19.03 18.59 19.52 19.74 19.91 20.41 MgO 0.06 0.27 40.52 40.24 40.74 41.60 41.69 42.42 41.44 41.17 40.79 40.38 MnO 0.09 0.05 0.21 0.29 0.29 0.30 0.25 0.23 0.27 0.28 0.34 0.17 NiO 0.11 0.06 0.16 0.12 0.11 0.24 0.27 0.21 0.20 0.20 0.11 0.09 CaO 0.04 0.02 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 Wt % Total 100.90 100.30 101.07 101.12 100.58 101.15 100.91 100.96 100.38 100.17 Cation Total 3.00 2.99 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 Fo% 77.96 78.07 77.87 79.42 79.61 80.27 79.10 78.80 78.50 77.91 143 Label1 LOD2 SD3 M-045A-C4-7 M-045A-C4-10 M-045A-C4-11 A-168-C6-3 A-168-C6-4 A-168-C6-5 A-168-C6-11 A-168-C6-12 A-168-C6-13 A-168-C6-14 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Pillow Lava Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type PR PR PR PR PR PR PR PR PR PR SiO2 0.06 0.19 38.50 38.52 38.76 39.06 39.08 38.93 39.06 39.21 39.04 39.22 TiO2 0.05 0.01 0.00 0.00 0.02 0.03 0.04 0.03 0.02 0.00 0.01 0.03 Al2O3 0.05 0.01 0.02 0.00 0.01 0.02 0.04 0.00 0.08 0.00 0.00 0.09 FeO 0.09 0.38 20.21 20.62 20.28 20.41 20.53 20.65 21.16 20.89 20.56 20.27 MgO 0.06 0.27 39.51 39.86 40.67 40.61 41.08 40.47 40.91 40.21 40.61 39.51 MnO 0.09 0.05 0.31 0.25 0.24 0.29 0.26 0.32 0.40 0.29 0.26 0.22 NiO 0.11 0.06 0.16 0.13 0.13 0.16 0.20 0.14 0.19 0.15 0.20 0.10 CaO 0.04 0.02 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 0.23 Wt % Total 98.94 99.61 100.36 100.81 101.45 100.78 102.06 100.99 100.92 99.68 Cation Total 3.00 3.00 3.00 3.00 3.01 3.00 3.01 3.00 3.00 2.99 Fo% 77.70 77.51 78.14 78.01 78.10 77.74 77.51 77.44 77.88 77.65 Label1 LOD2 SD3 A-168-C6-15 M-045A-D1-1 M-045A-D1-2 M-045A-D1-3 M-045A-D1-4 M-045A-D1-5 M-045A-D1-6 M-045A-D2-6 M-045A-D2-7 M-045A-D2-8 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Dyke Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type PR GM GM GM GM GM GM GM GM GM SiO2 0.06 0.19 38.96 38.77 38.45 38.31 38.21 38.92 38.40 38.19 38.02 38.36 TiO2 0.05 0.01 0.01 0.05 0.02 0.02 0.04 0.02 0.01 0.04 0.03 0.01 Al2O3 0.05 0.01 0.05 0.40 0.13 0.00 0.00 0.01 0.11 0.04 0.00 0.00 FeO 0.09 0.38 20.23 20.08 20.14 20.32 20.73 20.57 20.38 20.35 20.92 20.80 MgO 0.06 0.27 40.31 39.10 39.70 39.96 39.91 40.85 39.87 39.82 39.37 40.31 MnO 0.09 0.05 0.31 0.25 0.25 0.29 0.30 0.29 0.30 0.31 0.29 0.34 NiO 0.11 0.06 0.18 0.12 0.16 0.09 0.17 0.18 0.14 0.17 0.17 0.14 CaO 0.04 0.02 0.23 0.28 0.28 0.30 0.27 0.24 0.25 0.27 0.28 0.25 Wt % Total 100.28 99.06 99.13 99.29 99.62 101.08 99.46 99.20 99.09 100.21 Cation Total 3.00 2.99 3.00 3.00 3.01 3.01 3.00 3.00 3.01 3.01 Fo% 78.03 77.63 77.84 77.81 77.44 77.97 77.71 77.72 77.04 77.55 144 Label1 LOD2 SD3 M-045A-D2-9 M-045A-D2-10 M-045A-D2-11 M-045A-D2-12 M-045A-D2-13 M-045A-D3-6 M-045A-D3-7 M-045A-D3-8 M-045A-D3-9 M-045A-D3-10 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.06 0.19 38.16 38.08 38.62 38.61 38.66 38.51 38.44 38.74 38.42 38.19 TiO2 0.05 0.01 0.03 0.03 0.06 0.00 0.00 0.00 0.06 0.01 0.00 0.05 Al2O3 0.05 0.01 0.06 0.00 0.02 0.00 0.02 0.03 0.06 0.02 0.01 0.08 FeO 0.09 0.38 20.51 20.74 20.62 20.67 20.67 20.88 20.64 20.71 20.66 20.21 MgO 0.06 0.27 39.67 39.57 40.38 40.40 39.93 40.31 39.92 40.42 39.85 40.10 MnO 0.09 0.05 0.27 0.36 0.18 0.30 0.26 0.23 0.28 0.29 0.28 0.26 NiO 0.11 0.06 0.17 0.11 0.14 0.15 0.15 0.20 0.16 0.18 0.17 0.15 CaO 0.04 0.02 0.29 0.27 0.23 0.23 0.25 0.29 0.27 0.27 0.22 0.26 Wt % Total 99.16 99.15 100.25 100.36 99.94 100.45 99.82 100.64 99.61 99.30 Cation Total 3.00 3.01 3.00 3.01 3.00 3.01 3.00 3.00 3.00 3.01 Fo% 77.51 77.28 77.73 77.70 77.50 77.48 77.52 77.68 77.47 77.96 Label1 LOD2 SD3 M-045A-D3-11 A-168-D1-1 A-168-D1-2 A-168-D1-3 A-168-D3-1 A-168-D3-2 A-168-D3-3 A-168-D2-1 A-168-D2-2 A-168-D2-3 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.06 0.19 38.56 37.94 37.95 37.49 38.02 38.28 38.70 38.03 38.15 38.08 TiO2 0.05 0.01 0.04 0.04 0.00 0.01 0.02 0.02 0.02 0.02 0.00 0.02 Al2O3 0.05 0.01 0.02 0.03 0.03 0.05 0.00 0.01 0.02 0.00 0.04 0.05 FeO 0.09 0.38 20.43 21.02 21.22 20.72 20.95 20.89 20.78 20.69 20.55 20.28 MgO 0.06 0.27 40.30 39.79 39.71 39.37 39.95 40.05 40.30 40.15 40.34 40.04 MnO 0.09 0.05 0.29 0.32 0.30 0.28 0.30 0.23 0.32 0.31 0.27 0.32 NiO 0.11 0.06 0.17 0.15 0.09 0.15 0.15 0.19 0.11 0.11 0.12 0.11 CaO 0.04 0.02 0.28 0.23 0.23 0.24 0.27 0.27 0.25 0.22 0.22 0.22 Wt % Total 100.08 99.54 99.53 98.32 99.65 99.95 100.51 99.53 99.68 99.13 Cation Total 3.00 3.01 3.01 3.01 3.01 3.01 3.00 3.01 3.01 3.01 Fo% 77.86 77.14 76.94 77.20 77.27 77.37 77.56 77.57 77.77 77.87 145 Label1 LOD2 SD3 A-168-D2-4 A-168-D2-5 A-178-C1-1 A-178-C1-2 A-178-C1-3 A-178-C1-4 A-178-C1-5 A-178-C1-6 A-178-C1-7 A-178-C1-8 Phenocryst Assemblage OPA OPA OP OP OP OP OP OP OP OP Rock Type Dyke Dyke Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type GM GM PC PC PC PC PC PC PC PC SiO2 0.06 0.19 38.24 38.31 39.04 38.70 38.58 38.62 38.90 38.98 38.84 39.10 TiO2 0.05 0.01 0.02 0.02 0.00 0.03 0.03 0.03 0.00 0.02 0.00 0.00 Al2O3 0.05 0.01 0.00 0.02 0.00 0.02 0.02 0.01 0.04 0.01 0.03 0.02 FeO 0.09 0.38 20.97 20.78 19.44 19.90 19.78 19.84 19.83 19.93 19.84 19.96 MgO 0.06 0.27 39.90 39.94 40.80 41.34 41.07 41.22 40.94 41.06 41.19 40.98 MnO 0.09 0.05 0.24 0.27 0.27 0.32 0.26 0.25 0.25 0.30 0.25 0.26 NiO 0.11 0.06 0.15 0.12 0.17 0.14 0.18 0.15 0.18 0.18 0.15 0.18 CaO 0.04 0.02 0.28 0.26 0.26 0.25 0.21 0.24 0.26 0.27 0.27 0.23 Wt % Total 99.82 99.71 99.99 100.69 100.15 100.37 100.39 100.76 100.58 100.73 Cation Total 3.01 3.01 3.00 3.01 3.01 3.01 3.00 3.00 3.01 3.00 Fo% 77.23 77.41 78.91 78.74 78.73 78.74 78.63 78.60 78.72 78.54 Label1 LOD2 SD3 A-178-C1-9 A-178-C2-7 A-178-C2-8 A-178-C2-9 A-178-C2-10 A-182-C2-1 A-182-C2-2 A-182-C2-3 A-182-C2-4 A-182-C2-5 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Dyke Dyke Dyke Dyke Dyke Mineral Type PC PC PC PC PC PC PC PC PC PC SiO2 0.06 0.19 38.84 39.00 38.97 38.85 38.40 38.74 38.78 38.51 38.51 38.75 TiO2 0.05 0.01 0.02 0.02 0.00 0.01 0.00 0.02 0.00 0.00 0.02 0.02 Al2O3 0.05 0.01 0.00 0.03 0.01 0.01 0.02 0.02 0.01 0.04 0.04 0.00 FeO 0.09 0.38 19.37 18.44 18.47 20.01 19.74 19.87 19.69 19.68 19.92 19.83 MgO 0.06 0.27 41.22 42.13 41.87 40.96 40.95 40.80 40.91 41.04 41.04 41.08 MnO 0.09 0.05 0.25 0.26 0.25 0.30 0.25 0.25 0.28 0.28 0.30 0.28 NiO 0.11 0.06 0.12 0.26 0.24 0.11 0.19 0.18 0.22 0.16 0.17 0.13 CaO 0.04 0.02 0.25 0.21 0.19 0.27 0.25 0.26 0.23 0.26 0.25 0.28 Wt % Total 100.07 100.35 100.00 100.53 99.80 100.13 100.13 99.97 100.25 100.37 Cation Total 3.00 3.01 3.00 3.00 3.01 3.00 3.00 3.01 3.01 3.01 Fo% 79.14 80.29 80.16 78.49 78.72 78.54 78.74 78.80 78.60 78.69 146 Label1 LOD2 SD3 A-182-C2-6 A-182-C2-7 A-182-C2-8 A-182-C2-9 A-182-C4-4 A-182-C4-5 A-182-C4-6 A-182-C4-10 A-182-C4-11 A-178-C2-1 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Pillow Lava Mineral Type PC PC PC PC PC PC PC PC PC PR SiO2 0.06 0.19 38.51 38.44 38.52 38.50 40.06 39.35 39.58 39.29 39.45 39.43 TiO2 0.05 0.01 0.00 0.00 0.02 0.00 0.00 0.02 0.01 0.04 0.03 0.01 Al2O3 0.05 0.01 0.03 0.00 0.01 0.02 0.01 0.01 0.01 0.02 0.03 0.04 FeO 0.09 0.38 20.14 19.93 19.83 20.22 16.52 16.10 16.33 17.52 16.21 19.60 MgO 0.06 0.27 41.04 40.51 40.78 41.01 43.87 44.48 43.85 43.00 44.39 41.54 MnO 0.09 0.05 0.27 0.32 0.27 0.30 0.24 0.17 0.24 0.18 0.19 0.22 NiO 0.11 0.06 0.25 0.14 0.18 0.15 0.23 0.32 0.21 0.29 0.23 0.17 CaO 0.04 0.02 0.27 0.28 0.26 0.26 0.23 0.22 0.20 0.20 0.23 0.27 Wt % Total 100.52 99.62 99.86 100.47 101.16 100.68 100.44 100.55 100.73 101.30 Cation Total 3.01 3.01 3.01 3.01 3.00 3.01 3.00 3.00 3.01 3.00 Fo% 78.41 78.37 78.56 78.33 82.56 83.12 82.72 81.40 83.00 79.07 Label1 LOD2 SD3 A-178-C2-2 A-178-C2-3 A-178-C2-4 A-178-C2-5 A-178-C2-6 A-182-C4-1 A-182-C4-2 A-182-C4-3 A-182-C4-7 A-182-C4-8 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Dyke Dyke Dyke Dyke Dyke Mineral Type PR PR PR PR PR PR PR PR PR PR SiO2 0.06 0.19 39.34 38.81 39.26 39.07 38.61 39.04 39.24 39.40 38.65 38.53 TiO2 0.05 0.01 0.04 0.00 0.00 0.02 0.05 0.01 0.03 0.00 0.03 0.00 Al2O3 0.05 0.01 0.00 0.01 0.00 0.00 0.03 0.05 0.02 0.03 0.02 0.05 FeO 0.09 0.38 19.18 19.55 19.32 19.55 19.59 19.79 19.19 19.89 19.81 19.98 MgO 0.06 0.27 41.36 41.01 41.22 41.26 41.44 41.63 41.94 41.79 40.82 40.48 MnO 0.09 0.05 0.26 0.28 0.31 0.24 0.26 0.26 0.27 0.24 0.26 0.23 NiO 0.11 0.06 0.19 0.09 0.17 0.24 0.21 0.13 0.27 0.12 0.18 0.18 CaO 0.04 0.02 0.28 0.27 0.24 0.27 0.27 0.23 0.21 0.25 0.23 0.28 Wt % Total 100.66 100.02 100.53 100.66 100.46 101.14 101.17 101.72 100.00 99.73 Cation Total 3.00 3.00 3.00 3.00 3.01 3.01 3.00 3.00 3.00 3.00 Fo% 79.36 78.90 79.18 79.00 79.04 78.94 79.58 78.93 78.60 78.32 147 Label1 LOD2 SD3 A-182-D2-16 A-182-D2-17 A-178-D1-6 A-178-D1-7 A-178-D1-8 A-178-D2-1 A-178-D2-2 A-178-D2-3 A-178-D2-4 A-178-D3-1 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Dyke Dyke Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.06 0.19 39.29 38.91 37.67 37.77 38.36 39.00 38.58 38.40 38.53 38.54 TiO2 0.05 0.01 0.01 0.02 0.06 0.02 0.00 0.01 0.04 0.03 0.00 0.02 Al2O3 0.05 0.01 0.02 0.04 0.03 0.04 0.00 0.05 0.05 0.02 0.00 0.01 FeO 0.09 0.38 19.96 20.11 22.28 23.07 22.65 20.20 20.13 19.85 20.47 22.20 MgO 0.06 0.27 40.94 40.92 38.06 37.97 38.31 41.20 40.69 40.61 40.65 39.01 MnO 0.09 0.05 0.27 0.28 0.26 0.31 0.36 0.29 0.29 0.23 0.25 0.34 NiO 0.11 0.06 0.17 0.13 0.16 0.09 0.15 0.17 0.16 0.18 0.15 0.15 CaO 0.04 0.02 0.26 0.29 0.34 0.33 0.32 0.24 0.25 0.28 0.25 0.26 Wt % Total 100.91 100.71 98.86 99.60 100.15 101.16 100.20 99.60 100.30 100.52 Cation Total 3.00 3.00 3.00 3.01 3.00 3.01 3.01 3.01 3.01 3.00 Fo% 78.52 78.39 75.28 74.57 75.10 78.43 78.27 78.48 77.98 75.80 Label1 LOD2 SD3 A-178-D3-2 A-178-D3-3 A-178-D3-4 A-178-D3-5 A-178-D3-6 A-178-D3-7 A-178-D3-8 Phenocryst Assemblage OP OP OP OP OP OP OP Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type GM GM GM GM GM GM GM SiO2 0.06 0.19 37.92 37.46 38.37 38.55 38.24 38.34 37.92 TiO2 0.05 0.01 0.03 0.03 0.02 0.02 0.04 0.07 0.02 Al2O3 0.05 0.01 0.03 0.03 0.02 0.04 0.02 0.05 0.00 FeO 0.09 0.38 24.03 24.57 19.96 20.05 22.93 21.53 22.51 MgO 0.06 0.27 37.59 36.81 40.67 41.21 38.46 39.14 38.16 MnO 0.09 0.05 0.35 0.37 0.30 0.24 0.34 0.26 0.30 NiO 0.11 0.06 0.15 0.13 0.12 0.17 0.12 0.14 0.14 CaO 0.04 0.02 0.28 0.26 0.26 0.26 0.32 0.33 0.32 Wt % Total 100.37 99.66 99.72 100.54 100.46 99.85 99.38 Cation Total 3.01 3.01 3.01 3.01 3.00 3.00 3.00 Fo% 73.61 72.75 78.41 78.56 74.93 76.42 75.14 1 Samples starting with 'M' retain full prefix of MH-20, labels starting with 'A' retain full prefix of AW-15. Sample label format: "sample # - grain # - analysis #" 2 Limit of detection 3Analytical uncertainty given as 2σ 148 D2: Plagioclase Analyses [Table D2] 149 Table D2: Electron Microprobe (EMP) major element analyses (wt. %) of CM olivine phenocryst Cores (PC), phenocryst rims (PR), and groundmass phases (GM). Analyses conducted at Univer`sity of British Columbia, Vancouver, Canada. Plagioclase Analyses Total number of plagioclase analyses: 132 Label1 LOD2 SD3 M-045A-C2-1 M-045A-C2-2 M-045A-C2-5 M-045A-C2-6 M-045A-C2-7 M-045A-C2-8 M-045A-C2-9 M-045A-C2-10 M-045A-C3-4 M-045A-C3-5 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type PC PC PC PC PC PC PC PC PC PC SiO2 0.06 0.21 52.79 52.84 52.33 51.78 51.89 53.17 52.91 52.36 52.85 52.85 Al2O3 0.04 0.17 29.66 29.27 28.73 28.68 29.13 28.71 28.75 29.24 29.12 28.87 Fe2O3 0.09 0.06 0.63 0.66 0.67 0.57 0.59 0.56 0.59 0.65 0.62 0.60 MgO 0.06 0.03 0.15 0.19 0.08 0.14 0.14 0.12 0.16 0.11 0.17 0.12 CaO 0.04 0.13 12.92 12.58 12.18 12.25 12.67 11.89 12.45 12.59 12.46 12.44 Na2O 0.09 0.13 4.00 4.21 4.35 4.42 4.07 4.47 4.18 4.19 4.32 4.25 K2O 0.04 0.02 0.12 0.13 0.13 0.11 0.11 0.11 0.13 0.12 0.12 0.10 Wt % Total 100.28 99.87 98.45 97.95 98.59 99.02 99.17 99.26 99.65 99.23 Cation Total 4.99 4.99 5.00 5.01 4.99 4.99 4.99 5.00 5.00 4.99 An% 63.65 61.85 60.29 60.12 62.86 59.15 61.71 61.98 61.02 61.46 150 Label1 LOD2 SD3 A-168-C3-1 M-045A-C3-1 A-168-C3-2 A-168-C3-4 A-168-C3-6 A-168-C3-7 A-168-C4-2 A-168-C4-3 A-168-C4-5 M-045A-C2-4 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Dyke Dyke Dyke Dyke Dyke Dyke Dyke Pillow Lava Mineral Type PC PC PC PC PC PC PC PC PC PR SiO2 0.06 0.21 51.75 54.66 52.66 51.28 52.01 51.34 50.77 52.41 52.34 53.33 Al2O3 0.04 0.17 28.77 28.82 28.76 28.89 28.61 28.79 28.94 29.33 29.03 28.82 Fe2O3 0.09 0.06 0.59 0.52 0.64 0.65 0.56 0.68 0.60 0.63 0.60 0.59 MgO 0.06 0.03 0.12 0.15 0.13 0.13 0.13 0.12 0.12 0.12 0.14 0.14 CaO 0.04 0.13 12.22 12.06 12.17 12.34 12.16 12.83 12.62 12.71 12.46 12.29 Na2O 0.09 0.13 4.43 4.49 4.25 4.18 4.33 4.07 4.20 4.14 4.14 4.37 K2O 0.04 0.02 0.11 0.14 0.12 0.12 0.15 0.10 0.12 0.11 0.12 0.11 Wt % Total 98.00 100.83 98.73 97.60 97.94 97.94 97.37 99.44 98.85 99.65 Cation Total 5.01 4.98 4.99 5.00 5.00 5.00 5.01 4.99 4.99 4.99 An% 59.98 59.27 60.87 61.53 60.31 63.15 61.99 62.53 61.98 60.45 Label1 LOD2 SD3 M-045A-C3-2 M-045A-C3-6 M-045A-C3-8 M-045A-C3-9 M-045A-C3-10 M-045A-C3-11 M-045A-C3-12 A-168-C3-3 A-168-C4-4 A-168-C4-6 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Dyke Dyke Dyke Mineral Type PR PR PR PR PR PR PR PR PR PR SiO2 0.06 0.21 53.84 53.73 54.42 53.52 53.03 53.81 53.22 52.51 53.27 51.69 Al2O3 0.04 0.17 28.96 28.28 28.56 28.70 28.90 29.09 28.99 28.94 29.03 29.53 Fe2O3 0.09 0.06 0.68 0.67 0.59 0.61 0.66 0.67 0.72 0.74 0.61 0.64 MgO 0.06 0.03 0.11 0.13 0.11 0.14 0.16 0.09 0.14 0.11 0.07 0.12 CaO 0.04 0.13 12.31 11.72 11.93 11.99 12.27 12.21 12.23 12.05 12.21 13.09 Na2O 0.09 0.13 4.37 4.56 4.47 4.62 4.34 4.46 4.48 4.46 4.53 3.85 K2O 0.04 0.02 0.12 0.13 0.13 0.11 0.13 0.12 0.15 0.12 0.14 0.09 Wt % Total 100.37 99.20 100.21 99.69 99.49 100.44 99.93 98.94 99.87 99.01 Cation Total 4.98 4.98 4.98 5.00 4.99 4.99 5.00 5.00 5.00 4.99 An% 60.45 58.25 59.15 58.53 60.48 59.79 59.61 59.44 59.34 64.93 151 Label1 LOD2 SD3 M-045A-D1-7 M-045A-D1-8 M-045A-D1-9 M-045A-D1-10 M-045A-D1-11 M-045A-D2-1 M-045A-D2-2 M-045A-D2-3 M-045A-D2-4 M-045A-D2-5 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.06 0.21 53.45 54.04 53.73 54.78 52.46 52.92 53.55 52.99 52.42 52.47 Al2O3 0.04 0.17 29.24 29.00 28.94 28.25 29.04 29.65 28.66 28.62 28.91 28.84 Fe2O3 0.09 0.06 0.82 0.83 0.84 0.87 0.75 0.78 0.82 0.80 0.75 0.78 MgO 0.06 0.03 0.15 0.14 0.17 0.15 0.11 0.12 0.15 0.14 0.10 0.12 CaO 0.04 0.13 12.43 12.41 12.17 11.60 12.50 12.74 12.26 12.31 12.25 12.37 Na2O 0.09 0.13 4.41 4.57 4.43 4.82 4.19 4.12 4.59 4.31 4.42 4.30 K2O 0.04 0.02 0.13 0.12 0.14 0.17 0.21 0.09 0.14 0.11 0.12 0.14 Wt % Total 100.63 101.10 100.41 100.64 99.24 100.42 100.16 99.27 98.98 99.04 Cation Total 5.00 5.00 4.99 4.99 5.00 4.99 5.00 4.99 5.00 5.00 An% 60.44 59.62 59.80 56.53 61.51 62.80 59.15 60.84 60.03 60.86 Label1 LOD2 SD3 M-045A-D3-1 M-045A-D3-2 M-045A-D3-3 M-045A-D3-4 M-045A-D3-5 A-168-D4-1 A-168-D4-3 A-168-D4-4 A-168-D4-5 A-168-D4-6 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Dyke Dyke Dyke Dyke Dyke Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.06 0.21 52.56 53.20 54.93 52.88 53.14 53.22 53.50 54.68 53.78 54.84 Al2O3 0.04 0.17 28.90 28.99 27.57 29.06 28.84 28.18 28.20 27.44 28.79 28.01 Fe2O3 0.09 0.06 0.84 0.80 1.12 0.90 0.80 0.78 0.75 0.79 0.91 0.94 MgO 0.06 0.03 0.15 0.12 0.20 0.13 0.10 0.15 0.11 0.11 0.11 0.11 CaO 0.04 0.13 12.11 12.32 10.69 12.48 12.37 11.75 11.89 11.13 11.89 11.15 Na2O 0.09 0.13 4.42 4.45 5.45 4.40 4.41 4.71 4.33 5.41 4.71 5.15 K2O 0.04 0.02 0.11 0.13 0.17 0.10 0.14 0.13 0.21 0.17 0.15 0.15 Wt % Total 99.09 100.00 100.12 99.94 99.80 98.92 99.00 99.73 100.35 100.36 Cation Total 5.00 5.00 5.01 5.00 5.00 5.00 4.98 5.01 5.00 5.00 An% 59.82 60.03 51.52 60.71 60.32 57.51 59.52 52.68 57.72 54.02 152 Label1 LOD2 SD3 A-168-D3-4 A-168-D3-5 A-168-D3-6 A-168-D3-7 A-168-D2-6 A-168-D2-7 A-168-D2-8 A-168-D2-9 A-168-D2-10 A-178-C3-2 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OP Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Pillow Lava Mineral Type GM GM GM GM GM GM GM GM GM PC SiO2 0.06 0.21 56.35 56.19 53.88 54.34 53.24 53.62 53.59 55.08 54.18 53.52 Al2O3 0.04 0.17 27.15 26.95 28.54 28.24 29.22 28.79 28.65 28.32 28.73 29.46 Fe2O3 0.09 0.06 1.02 1.42 0.85 0.98 0.92 0.72 0.77 0.90 0.82 0.64 MgO 0.06 0.03 0.12 0.08 0.14 0.13 0.16 0.15 0.10 0.14 0.16 0.10 CaO 0.04 0.13 10.22 9.94 11.97 11.62 12.46 12.35 11.80 11.57 11.96 12.73 Na2O 0.09 0.13 5.82 5.77 4.65 4.77 4.42 4.44 4.67 4.86 4.78 4.11 K2O 0.04 0.02 0.20 0.21 0.15 0.17 0.13 0.13 0.14 0.16 0.17 0.12 Wt % Total 100.87 100.56 100.17 100.24 100.55 100.18 99.72 101.03 100.80 100.69 Cation Total 5.00 5.00 5.00 4.99 5.00 4.99 4.99 4.99 5.00 4.98 An% 48.70 48.18 58.20 56.84 60.45 60.15 57.83 56.26 57.50 62.68 Label1 LOD2 SD3 A-178-C3-4 A-178-C3-5 A-178-C3-6 A-178-C3-7 A-178-C4-1 A-178-C4-2 A-178-C4-3 A-178-C4-4 A-178-C4-5 A-178-C4-6 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type PC PC PC PC PC PC PC PC PC PC SiO2 0.06 0.21 52.78 51.80 52.63 52.92 53.20 53.54 52.98 52.07 52.04 53.20 Al2O3 0.04 0.17 29.30 29.80 29.18 29.56 29.70 29.24 29.52 29.63 29.81 29.00 Fe2O3 0.09 0.06 0.58 0.63 0.53 0.62 0.62 0.63 0.62 0.60 0.59 0.68 MgO 0.06 0.03 0.12 0.07 0.15 0.14 0.17 0.13 0.16 0.16 0.13 0.16 CaO 0.04 0.13 12.73 13.02 12.77 12.74 12.88 12.42 12.76 13.18 12.93 12.43 Na2O 0.09 0.13 4.09 3.87 4.23 4.24 4.23 4.24 4.30 3.93 3.96 4.37 K2O 0.04 0.02 0.13 0.10 0.12 0.14 0.16 0.12 0.13 0.13 0.11 0.12 Wt % Total 99.73 99.30 99.61 100.36 100.95 100.33 100.46 99.69 99.56 99.96 Cation Total 4.99 4.99 5.00 5.00 5.00 4.98 5.00 5.00 4.99 5.00 An% 62.80 64.65 62.11 61.95 62.18 61.38 61.66 64.49 63.94 60.67 153 Label1 LOD2 SD3 A-178-C4-7 A-178-C4-8 A-178-C4-9 A-182-C1-1 A-182-C1-2 A-182-C1-4 A-182-C1-5 A-182-C1-6 A-182-C1-7 A-182-C1-10 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Pillow Lava Pillow Lava Pillow Lava Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type PC PC PC PC PC PC PC PC PC PC SiO2 0.06 0.21 52.51 52.02 53.32 52.79 53.33 51.64 52.42 52.42 52.91 53.22 Al2O3 0.04 0.17 29.43 29.62 29.28 29.81 29.37 29.59 28.36 29.26 29.54 29.23 Fe2O3 0.09 0.06 0.65 0.60 0.67 0.73 0.60 0.48 0.65 0.57 0.66 0.57 MgO 0.06 0.03 0.12 0.11 0.13 0.13 0.12 0.11 0.16 0.15 0.16 0.11 CaO 0.04 0.13 12.47 13.10 12.18 13.33 12.52 13.11 12.10 12.37 12.52 12.53 Na2O 0.09 0.13 4.26 3.90 4.40 3.94 4.42 3.92 4.53 4.27 4.34 4.36 K2O 0.04 0.02 0.12 0.10 0.12 0.10 0.15 0.12 0.13 0.13 0.11 0.11 Wt % Total 99.57 99.45 100.11 100.83 100.50 98.96 98.36 99.18 100.24 100.13 Cation Total 5.00 4.99 4.99 4.99 5.00 5.00 5.01 5.00 5.00 4.99 An% 61.34 64.59 64.76 60.53 64.45 59.14 61.10 61.07 60.95 60.65 Label1 LOD2 SD3 A-182-C3-7 A-182-C3-8 A-182-C3-9 A-178-C3-1 A-178-C3-3 A-178-C3-8 A-178-C3-9 A-178-C4-10 A-182-C1-3 A-182-C1-8 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Dyke Dyke Dyke Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Dyke Dyke Mineral Type PC PC PC PR PR PR PR PR PR PR SiO2 0.06 0.21 52.81 52.91 53.65 53.92 53.24 54.07 53.19 52.48 52.44 52.41 Al2O3 0.04 0.17 29.11 29.76 29.68 29.24 29.15 29.56 29.77 29.60 29.42 29.78 Fe2O3 0.09 0.06 0.66 0.64 0.59 0.65 0.65 0.56 0.62 0.61 0.67 0.66 MgO 0.06 0.03 0.18 0.11 0.11 0.13 0.14 0.12 0.15 0.11 0.14 0.11 CaO 0.04 0.13 12.44 12.84 13.00 12.43 12.34 12.89 13.23 12.78 13.04 12.81 Na2O 0.09 0.13 4.22 4.10 4.14 4.27 4.40 4.33 3.93 4.08 4.12 3.94 K2O 0.04 0.02 0.12 0.12 0.11 0.13 0.12 0.12 0.11 0.10 0.11 0.15 Wt % Total 99.55 100.48 101.26 100.78 100.03 101.64 101.00 99.77 99.96 99.86 Cation Total 4.99 4.99 4.99 4.98 4.99 4.99 4.98 4.99 5.00 4.99 An% 62.95 63.06 64.63 61.21 60.37 61.81 60.04 62.99 63.21 63.67 154 Label1 LOD2 SD3 A-182-C1-9 A-182-C3-1 A-182-C3-3 A-182-C3-4 A-182-C3-5 A-182-C3-6 A-182-C3-10 A-182-D2-1 A-182-D2-2 A-182-D2-3 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type PR PR PR PR PR PR PR GM GM GM SiO2 0.06 0.21 53.51 52.83 52.57 53.49 52.96 53.62 52.99 53.05 53.29 53.51 Al2O3 0.04 0.17 29.21 29.60 28.89 29.85 29.42 29.39 29.46 29.51 29.35 29.26 Fe2O3 0.09 0.06 0.62 0.60 0.58 0.55 0.64 0.82 0.66 0.67 0.63 0.68 MgO 0.06 0.03 0.14 0.10 0.11 0.11 0.15 0.13 0.14 0.14 0.15 0.15 CaO 0.04 0.13 12.43 12.83 12.45 13.04 12.65 12.45 12.65 12.83 12.85 12.70 Na2O 0.09 0.13 4.25 4.12 4.27 4.11 4.25 4.42 4.27 4.08 4.31 4.36 K2O 0.04 0.02 0.12 0.10 0.11 0.11 0.10 0.13 0.11 0.11 0.12 0.13 Wt % Total 100.28 100.19 98.98 101.27 100.17 100.95 100.27 100.39 100.69 100.79 Cation Total 4.98 4.99 4.99 4.99 4.99 4.99 5.00 4.99 5.00 5.00 An% 61.32 62.89 61.29 63.24 61.84 60.45 61.71 63.03 61.82 61.24 Label1 LOD2 SD3 A-182-D2-4 A-182-D2-5 A-182-D2-6 A-182-D2-7 A-182-D2-8 A-182-D3-1 A-182-D3-2 A-182-D3-3 A-182-D3-4 A-182-D3-5 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.06 0.21 52.84 54.10 53.31 53.42 54.23 53.46 52.44 53.85 52.70 52.53 Al2O3 0.04 0.17 29.70 29.23 29.33 29.52 29.24 27.99 28.10 27.89 28.95 28.92 Fe2O3 0.09 0.06 0.66 0.62 0.67 0.62 0.59 0.89 0.91 0.79 0.91 0.78 MgO 0.06 0.03 0.08 0.11 0.11 0.12 0.14 0.13 0.13 0.15 0.15 0.15 CaO 0.04 0.13 12.98 12.60 12.83 13.18 12.10 11.32 11.63 11.46 12.27 12.15 Na2O 0.09 0.13 4.15 4.27 4.17 4.07 4.45 4.94 4.58 4.90 4.45 4.51 K2O 0.04 0.02 0.12 0.12 0.13 0.14 0.13 0.16 0.14 0.16 0.12 0.14 Wt % Total 100.53 101.06 100.56 101.08 100.88 98.89 97.93 99.21 99.55 99.18 Cation Total 5.00 4.98 4.99 4.99 4.98 5.00 5.00 5.00 5.00 5.01 An% 62.91 61.53 62.49 63.64 59.58 55.34 57.89 55.86 59.95 59.35 155 Label1 LOD2 SD3 A-182-D3-6 A-182-D3-7 A-182-D3-8 A-182-D4-1 A-182-D4-2 A-182-D4-3 A-182-D4-4 A-182-D4-5 A-182-D4-6 A-178-D1-1 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Pillow Lava Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.06 0.21 54.14 53.44 53.46 52.36 52.55 52.44 53.08 53.87 54.27 53.47 Al2O3 0.04 0.17 28.31 28.73 28.02 29.41 29.17 28.74 28.26 28.79 28.25 29.33 Fe2O3 0.09 0.06 0.80 0.85 0.99 0.72 0.87 0.88 0.92 0.80 0.81 0.67 MgO 0.06 0.03 0.17 0.18 0.12 0.13 0.12 0.16 0.17 0.13 0.15 0.07 CaO 0.04 0.13 11.69 12.19 11.85 12.74 12.81 12.09 11.84 11.83 11.50 12.54 Na2O 0.09 0.13 4.82 4.47 4.73 4.22 4.13 4.50 4.68 4.76 5.12 4.53 K2O 0.04 0.02 0.13 0.11 0.13 0.11 0.11 0.15 0.17 0.15 0.16 0.13 Wt % Total 100.05 99.96 99.30 99.69 99.76 98.96 99.12 100.33 100.25 100.75 Cation Total 5.00 4.99 5.00 5.00 4.99 5.01 5.00 5.00 5.01 5.00 An% 56.86 59.72 57.63 62.14 62.78 59.21 57.71 57.36 54.91 60.02 Label1 LOD2 SD3 A-178-D1-2 A-178-D1-3 A-178-D1-4 A-178-D1-5 A-178-D2-5 A-178-D2-6 A-178-D2-7 A-178-D2-9 A-178-D3-9 A-178-D3-10 Phenocryst Assemblage OP OP OP OP OP OP OP OP OP OP Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.06 0.21 53.13 52.12 52.94 53.19 53.91 54.11 52.81 52.63 53.61 52.47 Al2O3 0.04 0.17 29.08 29.13 29.32 29.12 29.14 28.99 28.74 29.49 28.96 29.33 Fe2O3 0.09 0.06 0.66 0.69 0.73 0.73 0.71 0.92 0.90 0.70 0.83 0.74 MgO 0.06 0.03 0.13 0.12 0.11 0.14 0.13 0.13 0.21 0.09 0.11 0.10 CaO 0.04 0.13 12.52 12.74 12.72 12.42 12.36 12.21 12.36 12.88 12.40 12.64 Na2O 0.09 0.13 4.55 4.05 4.28 4.35 4.29 4.48 4.40 4.05 4.37 4.21 K2O 0.04 0.02 0.13 0.10 0.12 0.10 0.10 0.12 0.12 0.11 0.12 0.12 Wt % Total 100.21 98.94 100.22 100.05 100.65 100.96 99.54 99.96 100.40 99.60 Cation Total 5.01 4.99 5.00 4.99 4.98 4.99 5.00 4.99 4.99 5.00 An% 59.86 63.11 61.75 60.81 61.05 59.70 60.39 63.31 60.61 61.96 156 Label1 LOD2 SD3 A-178-D3-11 A-178-D3-12 Phenocryst Assemblage OP OP Rock Type Pillow Lava Pillow Lava Mineral Type GM GM SiO2 0.06 0.21 52.72 53.44 Al2O3 0.04 0.17 29.49 29.35 Fe2O3 0.09 0.06 0.64 0.63 MgO 0.06 0.03 0.15 0.13 CaO 0.04 0.13 13.05 12.83 Na2O 0.09 0.13 4.09 4.22 K2O 0.04 0.02 0.12 0.11 Wt % Total 100.27 100.71 Cation Total 5.00 4.99 An% 63.38 62.29 1 Samples starting with 'M' retain full prefix of MH-20, labels starting with 'A' retain full prefix of AW-15. Sample label format: "sample # - grain # - analysis #" 2 Limit of detection 3Analytical uncertainty given as 2σ 157 D3: Clinopyroxene Analyses [Table D3] 158 Table D3: Electron Microprobe (EMP) major element analyses (wt. %) of CM clinopyroxene phenocryst cores (PC), phenocryst rims (PR), and groundmass phases (GM). Analyses conducted at University of British Columbia, Vancouver, Canada. Clinopyroxene Analyses Total number of clinopyroxene analyses: 48 Label1 LOD2 SD3 M-045A-C1-1 M-045A-C1-2 M-045A-C1-3 M-045A-C1-4 M-045A-C1-6 M-045A-C1-8 M-045A-C1-9 M-045A-C1-10 A-168-C1-1 A-168-C1-2 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Pillow Lava Dyke Dyke Mineral Type PR PR PC PR PC PC PR PC PR PR SiO2 0.05 0.20 51.17 50.74 50.87 50.76 50.53 50.67 50.71 50.70 52.20 51.90 TiO2 0.05 0.04 0.78 0.86 0.92 0.85 1.07 0.91 1.00 1.06 0.57 0.60 Al2O3 0.05 0.06 3.45 3.65 3.52 3.53 3.63 3.65 3.49 3.68 2.62 2.93 Cr2O3 0.08 0.06 0.69 0.80 0.85 0.75 0.86 0.58 0.41 0.62 0.59 0.83 FeO 0.09 0.18 8.75 7.83 7.68 8.15 8.44 9.02 8.76 8.61 7.64 7.58 MgO 0.06 0.18 17.01 16.18 16.22 16.30 16.03 16.80 16.12 15.99 17.36 16.98 MnO 0.09 0.05 0.23 0.18 0.16 0.16 0.19 0.20 0.20 0.25 0.18 0.17 CaO 0.04 0.16 18.16 19.49 19.49 19.10 19.30 18.10 19.11 19.17 19.11 19.25 Na2O 0.11 0.07 0.38 0.40 0.47 0.34 0.39 0.40 0.35 0.40 0.34 0.40 Total 100.62 100.14 100.16 99.94 100.44 100.32 100.15 100.47 100.61 100.63 Cation Total 4.03 4.02 4.02 4.02 4.02 4.03 4.02 4.02 4.02 4.02 Mg # 77.61 78.64 79.01 78.08 77.19 76.86 76.63 76.79 80.19 79.98 159 Label1 LOD2 SD3 A-168-C1-3 A-168-C1-4 A-168-C1-5 A-168-C1-6 A-168-C1-7 A-168-C2-1 A-168-C2-2 A-168-C2-3 A-168-C2-4 A-168-C2-5 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type PC PC PC PC PR PR PC PC PR PC SiO2 0.05 0.20 51.04 50.79 50.65 50.75 52.34 52.10 52.66 50.71 50.78 50.80 TiO2 0.05 0.04 0.84 0.82 0.84 0.85 0.59 0.59 0.56 0.93 0.82 0.85 Al2O3 0.05 0.06 4.33 3.70 3.87 3.46 2.05 2.12 2.15 3.70 3.61 3.94 Cr2O3 0.08 0.06 0.32 0.72 0.86 0.89 0.56 0.57 0.57 0.96 0.77 0.68 FeO 0.09 0.18 8.28 7.85 8.16 7.63 7.96 7.78 8.08 7.64 8.40 8.27 MgO 0.06 0.18 16.19 16.30 16.29 16.06 17.86 17.76 17.60 16.03 16.84 16.73 MnO 0.09 0.05 0.14 0.21 0.22 0.13 0.19 0.15 0.20 0.12 0.22 0.19 CaO 0.04 0.16 18.72 19.31 19.05 19.99 18.41 18.98 18.83 20.09 18.67 18.96 Na2O 0.11 0.07 0.50 0.41 0.39 0.42 0.28 0.36 0.38 0.32 0.40 0.45 Total 100.37 100.10 100.34 100.17 100.23 100.42 101.04 100.51 100.50 100.86 Cation Total 4.02 4.02 4.02 4.03 4.02 4.03 4.02 4.02 4.03 4.03 Mg # 77.70 78.73 78.05 78.96 79.99 80.28 79.53 78.89 78.13 78.28 Label1 LOD2 SD3 A-168-C2-6 A-168-C2-7 A-168-D1-6 A-168-D1-9 A-168-D1-10 A-168-D1-11 A-168-D1-13 A-168-D4-8 A-168-D4-10 A-168-D4-11 Phenocryst Assemblage OPA OPA OPA OPA OPA OPA OPA OPA OPA OPA Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type PC PC GM GM GM GM GM GM GM GM SiO2 0.05 0.20 50.20 50.84 47.02 48.07 46.83 47.99 47.05 46.58 46.16 47.91 TiO2 0.05 0.04 0.79 0.78 2.15 1.86 2.40 2.37 2.57 2.53 2.61 1.57 Al2O3 0.05 0.06 3.68 3.39 4.11 2.59 3.97 3.96 4.42 4.50 4.12 3.43 Cr2O3 0.08 0.06 0.82 0.76 0.13 0.01 0.11 0.14 0.14 0.17 0.10 0.01 FeO 0.09 0.18 7.62 8.09 11.47 14.57 11.59 11.91 11.42 11.90 12.21 12.11 MgO 0.06 0.18 16.40 17.40 13.08 12.26 13.07 13.38 13.09 12.97 12.90 13.44 MnO 0.09 0.05 0.14 0.24 0.20 0.29 0.19 0.24 0.21 0.22 0.18 0.26 CaO 0.04 0.16 19.69 18.98 20.21 19.65 20.08 19.97 20.44 20.13 19.62 19.26 Na2O 0.11 0.07 0.39 0.40 0.39 0.40 0.32 0.43 0.45 0.39 0.33 0.34 Total 99.72 100.89 98.76 99.70 98.56 100.39 99.81 99.39 98.24 98.34 Cation Total 4.03 4.04 4.05 4.05 4.04 4.04 4.05 4.05 4.05 4.04 Mg # 79.33 79.32 67.03 60.01 66.78 66.69 67.14 66.03 65.32 66.42 160 Label1 LOD2 SD3 A-168-D4-13 A-168-D3-8 A-168-D3-10 A-168-D2-11 A-168-D2-12 A-182-D1-9 A-182-D1-10 A-182-D1-11 A-182-D2-9 A-182-D2-10 Phenocryst Assemblage OPA OPA OPA OPA OPA OP OP OP OP OP Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.05 0.20 47.70 48.80 47.55 47.85 47.81 46.90 47.15 47.72 46.85 47.44 TiO2 0.05 0.04 1.78 1.79 1.94 2.18 2.30 2.49 2.11 2.12 2.95 2.46 Al2O3 0.05 0.06 3.33 2.83 3.72 3.79 3.28 4.49 4.06 3.48 4.50 4.72 Cr2O3 0.08 0.06 0.03 0.01 0.08 0.01 0.00 0.16 0.17 0.04 0.19 0.07 FeO 0.09 0.18 11.89 13.44 11.74 12.44 14.14 11.04 10.82 12.92 11.76 11.42 MgO 0.06 0.18 13.44 13.27 12.99 12.98 12.15 12.80 13.41 12.93 12.54 12.60 MnO 0.09 0.05 0.20 0.27 0.24 0.22 0.33 0.18 0.17 0.35 0.19 0.26 CaO 0.04 0.16 19.57 19.46 20.47 20.05 19.67 20.93 20.59 19.51 20.28 20.66 Na2O 0.11 0.07 0.33 0.50 0.40 0.43 0.46 0.38 0.38 0.38 0.41 0.47 Total 98.27 100.39 99.13 99.96 100.14 99.36 98.85 99.45 99.68 100.08 Cation Total 4.04 4.05 4.05 4.05 4.05 4.05 4.05 4.04 4.04 4.04 Mg # 66.82 63.77 66.36 65.04 60.51 67.40 68.83 64.08 65.52 66.29 Label1 LOD2 SD3 A-168-D4-13 A-168-D3-8 A-168-D3-10 A-168-D2-11 A-168-D2-12 A-182-D1-9 A-182-D1-10 A-182-D1-11 A-182-D2-9 A-182-D2-10 Phenocryst Assemblage OPA OPA OPA OPA OPA OP OP OP OP OP Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type GM GM GM GM GM GM GM GM GM GM SiO2 0.05 0.20 47.70 48.80 47.55 47.85 47.81 46.90 47.15 47.72 46.85 47.44 TiO2 0.05 0.04 1.78 1.79 1.94 2.18 2.30 2.49 2.11 2.12 2.95 2.46 Al2O3 0.05 0.06 3.33 2.83 3.72 3.79 3.28 4.49 4.06 3.48 4.50 4.72 Cr2O3 0.08 0.06 0.03 0.01 0.08 0.01 0.00 0.16 0.17 0.04 0.19 0.07 FeO 0.09 0.18 11.89 13.44 11.74 12.44 14.14 11.04 10.82 12.92 11.76 11.42 MgO 0.06 0.18 13.44 13.27 12.99 12.98 12.15 12.80 13.41 12.93 12.54 12.60 MnO 0.09 0.05 0.20 0.27 0.24 0.22 0.33 0.18 0.17 0.35 0.19 0.26 CaO 0.04 0.16 19.57 19.46 20.47 20.05 19.67 20.93 20.59 19.51 20.28 20.66 Na2O 0.11 0.07 0.33 0.50 0.40 0.43 0.46 0.38 0.38 0.38 0.41 0.47 Total 98.27 100.39 99.13 99.96 100.14 99.36 98.85 99.45 99.68 100.08 Cation Total 4.04 4.05 4.05 4.05 4.05 4.05 4.05 4.04 4.04 4.04 Mg # 66.82 63.77 66.36 65.04 60.51 67.40 68.83 64.08 65.52 66.29 161 Label1 LOD2 SD3 A-182-D2-13 A-182-D3-10 A-182-D3-11 A-182-D3-12 A-182-D4-7 A-182-D4-8 A-182-D4-9 A-182-D4-10 Phenocryst Assemblage OP OP OP OP OP OP OP OP Rock Type Dyke Dyke Dyke Dyke Dyke Dyke Dyke Dyke Mineral Type GM GM GM GM GM GM GM GM SiO2 0.05 0.20 47.11 47.71 46.88 48.03 47.13 48.85 47.91 46.90 TiO2 0.05 0.04 2.66 2.16 2.41 2.33 2.14 2.17 2.26 2.72 Al2O3 0.05 0.06 4.22 3.91 4.64 4.66 4.15 3.81 3.96 4.11 Cr2O3 0.08 0.06 0.09 0.12 0.11 0.09 0.10 0.02 0.09 0.07 FeO 0.09 0.18 12.23 11.81 10.84 10.60 11.66 12.56 12.87 12.83 MgO 0.06 0.18 12.53 12.92 13.14 13.15 12.48 12.63 12.85 12.56 MnO 0.09 0.05 0.23 0.21 0.18 0.23 0.25 0.24 0.26 0.16 CaO 0.04 0.16 20.19 21.02 20.74 20.73 20.51 20.28 19.53 19.87 Na2O 0.11 0.07 0.48 0.34 0.41 0.41 0.35 0.38 0.46 0.38 Total 99.74 100.20 99.35 100.24 98.77 100.94 100.19 99.59 Cation Total 4.04 4.05 4.05 4.03 4.04 4.03 4.04 4.04 Mg # 64.63 66.11 68.36 68.86 65.60 64.19 64.01 63.58 1 Samples starting with 'M' retain full prefix of MH-20, labels starting with 'A' retain full prefix of AW-15. Sample label format: "sample # - grain # - analysis #" 2 Limit of detection 3Analytical uncertainty given as 2σ 162 Appendix E: Isotope Geochemistry E1: Methods Sr, Nd, Hf, and Pb isotope ratios were measured at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia. All chemical procedures were conducted in Class 100 and 10,000 clean laboratories. Sample powders (∼0.1 g) were digested in 15 mL screw-top Savillex beakers on a hotplate at 120–130 ̊ C for 2–3 days in a 10:1 mixture of concentrated sub-boiled HF and HNO3. Samples were then dried and fluxed within sub-boiled 6N HCl on a hotplate at 120–130 ̊C for at least 24 hours. Separate aliquots of sample powders were digested as outlined above after multi-step leaching in 6N HCl after Silva et al., (2010). Pb, Sr, Nd, and Hf were separated from dissolved sample solutions using sequential ion-exchange column chemistry. Separation procedures for Pb, Sr, and Nd are after Weis et al., (2006, 2007): Pb was separated first on columns of Biorad AG1-X8 resin with each sample undergoing two repeated passes through the resin. The second was Sr, separated from the REE and HFSE by cation exchange using Biorad AG50-X8 resin. The third was Nd, separated from the other REE using HDEHP-coated Teflon resin. Lastly, Hf separations were conducted using Todga resin after Connelly et al., (2006). Pb, Nd, and Hf isotope ratios were measured by MC-ICP-MS (Nu Instruments Ltd., Nu 021 or Nu II 214) and Sr isotope ratios on a Thermo Finnigan Triton TIMS after Weis et al., (2006, 2007). Duplicate and replicate analyses of samples are presented in Table E1. Reference materials were also analyzed to monitor the reproducibility of isotope measurements and values and displayed in the footnotes of Table E1. 163 E2: Results [Table E1; Cracked Mountain 143Nd/144Nd 2SE εNd 87Sr/86Sr 2SE 176Hf/177Hf 2SE εHf 208Pb/204Pb 2SE 207Pb/204Pb 2SE 206Pb/204Pb 2SEMH-19-031 460964 5599860 0.513008 0.000007 7.2 0.703165 0.000007 0.283022 0.000004 8.8 38.0390 0.0023 15.5677 0.0009 18.4777 0.0009MH-19-055 461014 5599824 0.513016 0.000006 7.4 0.703155 0.000007 0.283016 0.000005 8.6 38.0441 0.0020 15.5652 0.0008 18.4871 0.0008AW-15-168 460545 5599555 0.513013 0.000007 7.3 0.703153 0.000007 0.283036 0.000006 9.3 38.0683 0.0020 15.5491 0.0007 18.6973 0.0008AW-15-168D 460545 5599555 0.513019 0.000007 7.4 0.703159 0.000008 0.283029 0.000006 9.1 38.0717 0.0020 15.5504 0.0007 18.6983 0.0008AW-15-178 460807 5599494 0.513032 0.000005 7.7 0.703134 0.000008 0.283029 0.000006 9.1 38.0731 0.0018 15.5498 0.0007 18.7111 0.0008AW-15-178R 460807 5599494 0.513032 0.000006 7.7 38.0727 0.0020 15.5500 0.0008 18.7110 0.0010Lillooet RiverMH-19-004 464179 5616808 0.513033 0.000006 7.7 0.703163 0.000008 0.283057 0.000004 10.1 38.0730 0.0016 15.5571 0.0007 18.5525 0.0007MH-19-004R 464179 5616808 0.513039 0.000005MH-19-006 464179 5616808 0.513028 0.000006 7.6 0.703152 0.000007 0.283042 0.000005 9.6 38.0705 0.0020 15.5583 0.0008 18.5333 0.0009MH-19-007 464179 5616808 0.513025 0.000007 7.5 0.703135 0.000007 0.283055 0.000004 10.0 38.0793 0.0017 15.5439 0.0007 18.6652 0.0008Lillooet RidgeMH-19-116 463843 5618872 0.512987 0.000006 6.8 0.703309 0.000008 0.283041 0.000005 9.5 38.1919 0.0021 15.5644 0.0008 18.6868 0.0009MH-19-119 463789 5619051 0.512991 0.000006 6.9 0.703336 0.000007 0.283049 0.000005 9.8 38.2051 0.0021 15.5663 0.0008 18.6878 0.0009Lillooet GlacierAW-15-065 448836 5621401 0.513001 0.000006 7.1 0.703248 0.000008 0.283049 0.000004 9.8 38.1224 0.0018 15.5483 0.0007 18.6560 0.0007AW-15-065D 448836 5621401 0.513004 0.000005 0.703241 0.000009 0.283054 0.000005 38.1224 0.0017 15.5479 0.0007 18.6552 0.0008AW-15-069 448672 5621981 0.512996 0.000007 7.0 0.703188 0.000008 0.283030 0.000004 9.1 38.2189 0.0020 15.5618 0.0007 18.6251 0.0008AW-15-069R 448672 5621981 0.512983 0.000006 0.283029 0.000004Mosaic RidgeAW-15-184 457936 5611858 0.512999 0.000006 7.0 0.703328 0.000008 0.283114 0.000005 12.1 38.2144 0.0021 15.5565 0.0008 18.7057 0.0009AW-15-186 458010 5611877 0.513002 0.000006 7.1 0.703309 0.000009 0.283106 0.000005 11.8 38.2232 0.0022 15.5616 0.0008 18.6451 0.0008AW-15-186R 458010 5611877 38.2220 0.0027 15.5615 0.0009 18.6449 0.0011Elaho ValleyMH-19-015 458120 5598544 0.512984 0.000006 6.8 0.703303 0.000010 0.283064 0.000004 10.3 38.1551 0.0022 15.5633 0.0008 18.6131 0.0009MH-19-018A 458429 5597720 0.512981 0.000005 6.7 0.703277 0.000008 0.283058 0.000004 10.1 38.1328 0.0019 15.5652 0.0007 18.5555 0.0008Table E1: Nd. Sr. Hf. and Pb Isotope Ratios for Mount Meager volcanic complex, SW, BC. Samples prepared and analysed by PCIGR laboratories, University of British Columbia, Vancouver, BC, Canada.Easting NorthingR Replicates (repeat analysis of the same chemically prepared solution by MC-ICP-MS)D Duplicates (analysis of a separate solution prepared by the same chemical process by MC-ICP-MS)BCR-2 reference material (Weis et al., 2007) used for all isotopic analysesεNd calculated using a CHUR value of 143Nd/144Nd = 0.512638 [Jacobsen and Wasserburg, 1980] εHf calculated using a CHUR value of 176Hf/178Hf = 0.282772 [Blichert-Toft and Albarede, 1997]164 Figure E1: Isotope data for MMVC samples vs. Age (ka). All data are drawn larger than 2σx̅, dots represent new data (i.e. Table E1), diamonds represent reference data from prior studies of Mullen and Weis (2013, 2015). a: ΔPb (the difference in 208Pb/204Pb between samples and MORB at the same 206Pb/204Pb (ΔPb=208Pb/204Pbsample − [206Pb/204PbMORB∗0.8542 +22.05] b: εHf, c: εNd, d: 86Sr/87Sr.
Thesis/Dissertation
eng
Geological Sciences
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Russell, J. K. (J. Kelly)
Physical and chemical evolution of Cracked Mountain glaciovolcano, SW British Columbia
Text