University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2014-10-24 A Second North American Hot-spot: Pleistocene Volcanism in the Anahim Volcanic Belt, west-central British Columbia Kuehn, Christian Kuehn, C. (2014). A Second North American Hot-spot: Pleistocene Volcanism in the Anahim Volcanic Belt, west-central British Columbia (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/25002 http://hdl.handle.net/11023/1936 doctoral thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY A Second North American Hot-spot: Pleistocene Volcanism in the Anahim Volcanic Belt, west-central British Columbia by Christian Kuehn A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY GRADUATE PROGRAM IN GEOLOGY AND GEOPHYSICS CALGARY, ALBERTA OCTOBER, 2014 © Christian Kuehn 2014 Abstract Alkaline and peralkaline magmatism occurred along the Anahim Volcanic Belt (AVB), a 330 km long linear feature in west-central British Columbia. The belt includes three felsic shield volcanoes, the Rainbow, Ilgachuz and Itcha ranges as its most notable features, as well as regionally extensive cone fields, lava flows, dyke swarms and a pluton. Volcanic activity took place periodically from the Late Miocene to the Holocene. A systematic decrease in the ages of individual centres from the western part of the AVB to its eastern end is interpreted as the effect of a hot-spot underlying the Interior Plateau of British Columbia. Other hypotheses for the existence of the AVB include regional extension, a plate edge/slab window effect along the northern edge of the subducted Juan de Fuca/Explorer plates, and a fracture propagating west to east. In this study, I first summarise existing works to provide a context for AVB volcanism. Then I report new whole-rock geochemical data and 40Ar/39Ar age determinations for two previously little-studied cone fields around Satah Mountain and Baldface Mountain in the central part of the AVB. Individual volcanic centres in these fields are generally small in extent and volume and most have been heavily modified by glacial erosion. These centers are compositionally heterogeneous but overall the lavas erupted in either field are similar to those erupted from the larger Itcha Range shield volcano nearby. Rock types include minor alkali basalts and basanites (44−52 wt% SiO2), but more evolved trachyandesites, trachytes and phonolites (59−64 wt% SiO2) are the most abundant lithologies. Timing of volcanism in the Satah Mtn. field is constrained by 11 40Ar/39Ar ages which indicate volcanism between 2.21 and 1.43 Ma; in the Baldface Mtn. field, seven age data indicate volcanism from 2.52 to 0.91 Ma. The data further indicate that volcanic activity in these fields was, at least partially, coeval with the Itcha Range. These new data provide additional support for the mantle plume/hot-spot ii hypothesis, the only hypothesis that accounts for both the (per)alkaline character of AVB magmatism and the linear age-succession of volcanic centres. iii Acknowledgements Firstly, I would like to thank Bernard Guest for his willingness to take me on as a PhD student after my first supervisor had left and to find a project that would be of interest to the both of us. Thanks, Bernard, for your patience and constant encouragement and jumping into “the financial I’m looking at the Department and Graduate Studies in particular. What a poor performance by either entity. breach” when no one else would (i.e., in nine out of ten cases). To Kelly Russell, I extend similar thanks for his unwavering support, especially during and after my defense, and for seeing and believing in the worth of my work (since I rarely did). From my supervisory and examination committee, I thank Mike Wieser and especially Rajeev Nair for their constructive comments and interest in my thesis. Further thanks for their roles and Despite the latter being quite unprofessional in her role as an examiner, in addition to being underhanded and manipulative. Go home, Jen. advice go to Catherine Hickson and Jen Cuthbertson. On the technical and analytical side, I thank the staffs at the Trace Element Analytical Labora- tory (McGill University, Montréal), at the Peter Hooper GeoAnalytical Lab (Washington State University, Pullman, WA) and at the Mineralogisches Institut (Albert-Ludwigs-Universität, Freiburg i. Br.) as well as Lorraine Bloom for her help with the thinst section photography and If only the Department could and would finally invest in bringing its preparation facility into the 21 century… Mickey Horvath for helping with sample preparation. To Jeff “Apple” Benowitz at the University of Alaska-Fairbanks, I offer a triple “Hooray! Hooray! Hooray!” for his exemplary work on the Ar-Ar age determinations, unceasing encouragement and good humour throughout the past three years. Should we meet again, drinks will be on me! iv To Will Matthews I extend my thanks for his generous help in producing impeccable GIS maps and for always interesting/intriguing comments, some of which had unintended consequences! Without my field assistants, I would have gone insane (at best) or “gone dead” (at worst) during field work in 2010-12. So to Hazel Jenkins, Stephen Ainsworth and Lincoln Hanton my sincere thanks for not only being willing to help me and become, essentially, glorified porters of vol- canic rocks, but also for being such incredibly good sports in dealing with frugal food and accommodations, heat/rain/cold/difficult terrain, myriads of bugs and one moody German… I would also like to acknowledge the invaluable, generous and selfless help of Lori and Chris Schmid (and “Spud”) of Alexis Creek (B. C.), for providing local information and assistance du- ring field work on the Chilcotin Plateau. I will continue to pay it forward! Thanks also go to the BC Forest Service and the Tsi Del Del Tsilhqot’in First Nation for assistance during field work. The debts of gratitude that I owe my friends here in Calgary and back home in Germany are endless and it feels wrong having to limit myself to a few scant lines here, but alas! On the Canadian side, I say “Thank You” to Carmen most especially, to Vikki & Kenny (and family), to Adar & Oren, to Keith, and last, but certainly not least, to my good friend Scott. On the German side, I say “Danke schön!” to Buddi & Steffi, to Ulli, to Justus & Agi, to Benny, to both Matze M.s and to Brigitte and Dieter for their patience, comfort and infinite encouragement. And Johannes, Ingrid and Petra belong here, too. And the entire Kühn and Juli families. And my Chörli! The list is sooo long… Finally, to my Mama and Papa, I will say my thanks and so much more in person. v Dedication Dedicated to my indomitable stubbornness to see things through that I’ve started, with all the good, bad and ugly this usually entails. And to my parents for their never-ending patience, support and worries about their volcano-obsessed son! And in the place of honour, I dedicate this work to my Aunt Heidi (†) who unknowingly helped start my fascination with volcanoes 25 years ago but then very knowingly supported me without fail. How I wish that she could have been around to see this endeavour come to a good end… vi Table of Contents Abstract ........................................................................................................................................... ii Acknowledgements ........................................................................................................................ iv Dedication ...................................................................................................................................... vi Table of Contents .......................................................................................................................... vii List of Tables .................................................................................................................................. x List of Figures and Illustrations ..................................................................................................... xi List of Symbols, Abbreviations and Nomenclature ..................................................................... xiv Epigraph ........................................................................................................................................ xv CHAPTER ONE: INTRODUCTION ........................................................................................... 16 1.1 Thesis Overview ................................................................................................................. 16 1.2 Volcanic activity in western Canada .................................................................................. 18 1.3 Volcanotectonic association of volcanic fields and provinces in British Columbia ........... 23 CHAPTER TWO: PREVIOUS WORK ....................................................................................... 27 2.1 The western part of the Anahim Volcanic Belt .................................................................