FROM CINDER CONES TO SUBDUCTION ZONES: VOLATILE RECYCLING AND MAGMA FORMATION BENEATH THE SOUTHERN CASCADE ARC by KRISTINA JANINE WALOWSKI A DISSERTATION Presented to the Department of Geological Sciences and the Graduate School of the University of Oregon in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 2015 DISSERTATION APPROVAL PAGE Student: Kristina Janine Walowski Title: From Cinder Cones to Subduction Zones: Volatile Recycling and Magma Formation beneath the Southern Cascade Arc This dissertation has been accepted and approved in partial fulfillment of the requirements for the Doctor of Philosophy degree in the Department of Geological Sciences by: Dr. Paul Wallace Chairperson Dr. Ilya Bindeman Core Member Dr. Gene Humphreys Core Member Dr. Darren Johnson Institutional Representative and Scott L. Pratt Dean of the Graduate School Original approval signatures are on file with the University of Oregon Graduate School. Degree awarded June 2015 ii © 2015 Kristina Janine Walowski iii DISSERTATION ABSTRACT Kristina Janine Walowski Doctor of Philosophy Department of Geological Sciences June 2015 Title: From Cinder Cones to Subduction Zones: Volatile Recycling and Magma Formation beneath the Southern Cascade Arc Volatiles (H2O, CO2, S, Cl) play a key role in magmatic processes at subduction zones. In this study, the dissolved volatile contents of olivine-hosted melt inclusions from cinder cones in the Lassen segment of the Cascade arc are used to investigate dehydration of subducted oceanic lithosphere, magma formation in the sub-arc mantle wedge, and mafic magma storage and evolution in the crust. Relatively young, hot oceanic lithosphere subducts beneath the Cascade arc. The hydrogen-isotope and trace-element compositions of melt inclusions, when integrated with thermo-petrologic modeling, demonstrate that fluids in Cascade magmas are sourced from hydrated peridotite in the deep slab interior and that the oceanic crustal part of the slab extensively dehydrates beneath the forearc. In contrast to their slab-derived H, the melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), requiring little to no slab contribution of B, which is also consistent with extensive dehydration of the downgoing plate before it reaches sub-arc depths. Correlations of volatile and trace element ratios in the melt inclusions (H2O/Ce, Cl/Nb, Sr/Nd) demonstrate that geochemical variability in the magmas is the result of variable amounts of addition of a hydrous subduction component to the mantle wedge. Radiogenic iv isotope ratios require that the subduction component has less radiogenic Sr and Pb and more radiogenic Nd than the Lassen sub-arc mantle and is therefore likely to be a partial melt of subducted Gorda MORB. These results provide evidence that chlorite-derived fluids from the deep slab interior flux-melt the oceanic crust, producing hydrous slab melts that migrate into the overlying mantle, where they react with peridotite to induce further melting. The basaltic magmas that erupted at Cinder Cone near Mt. Lassen trapped melt inclusions during olivine crystallization at ~7-15 km depth. The melt inclusion compositions require that two different mantle-derived magmas were involved in the eruption, and temporal changes show that arrival of the two batches correlates with two explosive phases of activity. Both magmas experienced rapid crustal contamination before erupting, illustrating the complexities of cinder cone eruptions. This dissertation includes previously published and unpublished co-authored material. v CURRICULUM VITAE NAME OF AUTHOR: Kristina Janine Walowski GRADUATE AND UNDERGRADUATE SCHOOLS ATTENDED: University of Oregon, Eugene University of California, Los Angeles DEGREES AWARDED: Doctor of Philosophy, Geological Sciences, 2015, University of Oregon Bachelor of Science, Geology, 2015, University of California, Los Angeles AREAS OF SPECIAL INTEREST: Geochemistry, Petrology, Volcanology PROFESSIONAL EXPERIENCE: Graduate Teaching Fellow (2010-2015). University of Oregon, Department of Geological Sciences Research Assistant (2011-2015) University of Oregon, Department of Geological Sciences Advisor: Paul Wallace Undergraduate Research Assistant (2008-2010) University of California, Los Angeles, Department of Earth and Space Sciences Advisor: Jeremy Boyce GRANTS, AWARDS, AND HONORS: GeoPRISMS AGU Student Prize for Best Oral Presentation (2014). McMurray Award (2014). Department of Geological Science, University of Oregon. Goldschmidt Student Travel Grant (2013). Geochemical Society. Graduate Research Award (2013). Graduate School, University of Oregon. GeoPRISMS AGU Student Prize Honorable Mention (2012). Staples Scholarship (2012). Department of Geological Science, University of Oregon. Valedictorian (2010), Department of Earth and Space Sciences, University of California, Los Angeles. vi PUBLICATIONS: Walowski, K. J., Wallace, P. J., Hauri, E. H., Wada, I., & Clynne, M. A. (2015). Slab melting beneath the Cascade Arc driven by dehydration of altered oceanic peridotite. Nature Geoscience, 8(5), 404-408. Walowski K, Wallace P, Clynne M. (2014). Slab Melting and Magma Formation beneath the southern Cascade Arc. AGU Fall Meeting Abstracts, V31G-03. Walowski K, Wallace P, Hauri E, Clynne M & Wada I (2014). Slab Dehydration beneath the Southern Cascade Arc Inferred from B and H Isotopes. Goldschmidt Abstracts, 2014, 2613. Walowski, K. J., Wallace, P. J., Hauri, E. H., Clynne, M. A., Rea, J., & Rasmussen, D. J. (2013). Magma formation in hot-slab subduction zones: Insights from hydrogen isotopes in Cascade Arc melt inclusions. In AGU Fall Meeting Abstracts (Vol. 1, p. 01). Walowski K, Wallace P, Clynne M, Wada I & Rasmussen D (2013). Magma Formation in Hot-Slab Subduction Zones: Insights from Volatile Contents of Melt Inclusions from the Southern Cascade Arc. Mineralogical Magazine, 77(5), 2441. Walowski K, Wallace P, Clynne M, Wada I & Rasmussen D (2012). Understanding magma formation and mantle conditions in the Lassen segment of the Cascade Arc: Insights from volatile contents of olivine-hosted melt inclusions. AGU Fall Meeting Abstracts, V14B-01. Walowski, K. J., Wallace, P. J., Cashman, K. V., & Clynne, M. A. (2011). Inferring the magmatic plumbing system and melt evolution from olivine-hosted melt inclusions at Cinder Cone, Lassen Volcanic National Park, California. In AGU Fall Meeting Abstracts (Vol. 1, p. 02). Walowski, K. J., and Boyce, J.W. (2009). Volatile History of the Bishop Tuff from Apatite Phenocrysts and Inclusions. AGU Fall Meeting Abstracts,V23C-2093. vii ACKNOWLEDGMENTS This dissertation has benefited from the contributions of many people. First, I would like to thank my advisor, Paul Wallace, for his guidance and support throughout my Ph.D. I can’t imagine a better Ph.D. advisor, and I am privileged to have gotten the opportunity to work with him. I’d also like to thank the faculty at the University of Oregon, and specifically, my dissertation committee members, Ilya Bindeman for teaching me about isotopes, Gene Humphreys for helping me see the bigger picture, and Darren Johnson. My dissertation benefited from a number of collaborations, and includes the contributions of many co-authors, apart from Paul and myself. Thanks to Erik Hauri, Ikuko Wada, Dominique Weis, Dan Rasmussen, Kathy Cashman, Katie Marks, and Philipp Ruprecht for their individual contributions, and John Donavan, Adam Kent, and Brian Monteleone for their assistance with various analytical instruments. In particular, I would like to thank Mike Clynne, whose Ph.D. thesis and continued work in the Lassen area laid the foundation my dissertation research, and for his important contributions to all three chapters. This work was largely funded by the National Science Foundation through research grants awards to Paul Wallace and Kathy Cashman (EAR-1019848 and EAR-1119224). I’d also like to thank the incredible graduate community that I was so lucky be a part of. To the few who were there from start to finish – Kristin Sweeney, Corina Cerovski-Darriau, and Scott Maguffin – we’ve had a great run, and I hope it doesn’t end here! Special thanks to Angie Seligman, who the first floor would not have been the same without, Randy Krogstad, who will always be one of my best friends, Amberlee Darold and Gillean Arnoux, who made Cascade 124 a better place, and, of course, Captain viii Malcom Reynolds. I’d also like to specially thank my first academic ‘dad’, Jeremy Boyce. He inspired me to follow this path and prepared me so well for the journey that has been my Ph.D. Five years later, he is still there for me whenever I need advice and guidance, which is something I truly value. To my Mom and Dad, I could never thank you enough for your unconditional love and support. You have both taught me so much, and given me everything I could have ever needed. It is difficult to put into words how much you both mean to me, and I love you both very much. To my brother, Chris, thank you for showing me the coolness of science. I truly value our friendship and look forward to joining you in the higher-ed scientist club. Finally, I’d like to thank my partner Alexander Handwerger, without whom none of this would have been possible. Thank you for being there for me every single step of the way, and bringing me so much happiness. Our time in Oregon has been incredible, and I can’t wait to start our next adventure together in Scotland! ix To My Family x TABLE OF CONTENTS Chapter Page I. INTRODUCTION