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Convergent Margin Magmatism in the Central Andes and Its Near Antipodes in Western Indonesia: Spatiotemporal and Geochemical Considerations

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Convergent Margin Magmatism in the Central Andes and Its Near Antipodes in Western Indonesia: Spatiotemporal and Geochemical Considerations AN ABSTRACT OF THE DISSERTATION OF Morgan J. Salisbury for the degree of Doctor of Philosophy in Geology presented on June 3, 2011. Title: Convergent Margin Magmatism in the Central Andes and its Near Antipodes in Western Indonesia: Spatiotemporal and Geochemical Considerations Abstract approved: ________________________________________________________________________ Adam J.R. Kent This dissertation combines volcanological research of three convergent continental margins. Chapters 1 and 5 are general introductions and conclusions, respectively. Chapter 2 examines the spatiotemporal development of the Altiplano-Puna volcanic complex in the Lípez region of southwest Bolivia, a locus of a major Neogene ignimbrite flare- up, yet the least studied portion of the Altiplano-Puna volcanic complex of the Central Andes. New mapping and laser-fusion 40Ar/39Ar dating of sanidine and biotite from 56 locations, coupled with paleomagnetic data, refine the timing and volumes of ignimbrite emplacement in Bolivia and northern Chile to reveal that monotonous intermediate volcanism was prodigious and episodic throughout the complex. 40Ar/39Ar age determinations of 13 ignimbrites from northern Chile previously dated by the K-Ar method improve the overall temporal resolution of Altiplano-Puna volcanic complex development. Together with new and updated volume estimates, the new age determinations demonstrate a distinct onset of Altiplano-Puna volcanic complex ignimbrite volcanism with modest output rates beginning ~11 Ma, an episodic middle phase with the highest eruption rates between 8 and 3 Ma, followed by a general decline in volcanic output. The cyclic nature of individual caldera complexes and the spatiotemporal pattern of the volcanic field as a whole are consistent with both incremental construction of plutons as well as a composite Cordilleran batholith. Chapter 3 examines the spatiotemporal development of marine tephra deposits in deep sea sediment cores from the Sunda trench near Sumatra, which reveal evidence for seven large (minimum volume 0.6 – 6.3 km3), previously undocumented, explosive eruptions in this region over the last ~110,000 years, presumably sourced from mainland Sumatra. Sediment cores were collected within and adjacent to the Sunda trench from 3.3ºN to 4.6ºS at water depths between 1.8 and 5.5 km and distances of ~200 to 310 km from the active Sumatran volcanic arc. Glass shards within the tephra horizons were analyzed via the electron microprobe and laser ablation ICP-MS and define three compositional groups. Minimum volume estimates for the seven unique units are consistent with volcanic explosivity index (VEI; Newhall and Self, 1982) values of 4 - 5. The most frequent, widespread, and youngest deposits were found in the central region of the study area suggesting the central Sumatran arc as at the highest risk for large explosive eruptions. The first detailed chronological and geochemical data are presented for Tunupa volcano and nearby Huayrana lavas in chapter 4. New 40Ar/39Ar age determinations reveal edifice construction at ~1.5 Ma, a duration of ~90-240 k.y., and extrusion rates of 0.43 to 0.93 km3/k.y. Mineralogical compositional and textural data are consistent with shallow crustal storage (~7-18 km) and magma mixing. Volcano morphology, extrusion rates, mineralogy and textures are all similar to the Pleistocene to recent composite cones of the arc front, although new and available age data from the literature indicate that Western Cordilleran volcanism was concomitant with extrusion of both Huayrana (~11 Ma) and Tunupa (~1.5 Ma) lavas in the behind arc region. Arc-related volcanism was either widespread during these eruptive periods, or an additional melting mechanism was involved. Geochemical data, such as lower Ba/Nb ratios and enriched high field strength elemental concentrations, compared to volcanoes of the modern arc front suggest that Huayrana and Tunupa lavas were derived from a different source than the modern arc front. Geophysical and geochemical research in the central Andes indicate local variations in crustal and lithospheric thicknesses and compositions consistent with a dynamic continental lithosphere that has foundered in piecemeal fashion into the underlying asthenosphere throughout the mid to late Cenozoic. The data presented in this chapter for Tunupa and Huayrana indicate a complex petrogenetic origin and more research is necessary to determine the relative roles of arc and non-arc volcanism beneath the central Altiplano. ©Copyright by Morgan J. Salisbury June 3, 2011 All Rights Reserved Convergent Margin Magmatism in the Central Andes and its Near Antipodes in Western Indonesia: Spatiotemporal and Geochemical Considerations by Morgan J. Salisbury A DISSERTATION Submitted to Oregon State University in partial fulfillment of the requirement for the degree of Doctor of Philosophy Presented June 3, 2011 Commencement June, 2012 Doctor of Philosophy dissertation of Morgan J. Salisbury presented on June 3, 2011. APPROVED: _____________________________________________________________________________________ Major Professor, representing Geology ______________________________________________________________________________________ Chair of the Department of Geosciences ______________________________________________________________________________________ Dean of the Graduate School I understand that my dissertation will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my dissertation to any reader upon request. ______________________________________________________________________________________ Morgan J. Salisbury, Author ACKNOWLEDGEMENTS There are many people who aided and abetted in the successful completion of this dissertation, but two deserve more recognition than I can express here. Above all I wish to thank my advisor, Adam Kent, for his genius as a geologist as well as a human being. Without his knowledge and expertise, this document would not be worthy of submittal to Oregon State University; without his encouragement, support, and confidence in my abilities, I would have never have made it this far in my studies. I am forever indebted. I also extend extraordinary gratitude to Ingeniero Néstor Jiménez of the Universidad Mayor de San Andrés in La Paz, Bolivia. Without his offer to study Volcán Tunupa under his guidance and expertise, I would not be writing these acknowledgments. I am forever indebted, mil gracias. I would also like to give thanks to Shan de Silva for his initial confidence in my potential as a graduate student and his continued trust in my ability to publish our work on the Bolivian Altiplano-Puna plateau. To Wendy Bohrson for her recommendation. To Brad Singer for overseeing our 40Ar/39Ar age determinations at the University of Wisconsin–Madison Rare Gas Geochronology Laboratory. To Brian Jicha for his high quality analytical work at UW and his considerable authorship and assistance in two of the chapters of this dissertation. To Michael Ort at Northern Arizona University for helping me wade through the trials of submitting a manuscript with so many authors. Anita Grunder and Andrew Meigs are appreciated for their efforts on my committee, their instruction in the classroom and field trips in the Pacific Northwest, and most of all, for their discussions of central Andean volcanism and lithospheric structure. John Dilles and Chris Goldfinger both spent short durations on my committee; I was sad to see them go. I thank Chris for his support and encouragement on the Sumatra project. My friend, peer, and colleague Jason Patton deserves particular appreciation for his hard work, sedimentological expertise, and good spirit. His effort on our Sumatra manuscript allegedly will not count towards his Ph.D., which, for the record, I think is unfair. He did a great job. I thank Barry Walker Jr. for his assistance in the field at Volcán Tunupa and for his assistance with petrological matters and their inherent connections with our daily lives that few understand or appreciate. Many thanks to my Bolivian friends and peers, Alvaro Moron and Paola Isabel Sanchez, who helped me collect rocks on the Altiplano as well as navigate the bars in La Paz. To Mauricio, Dan, Juan Pablo, and Waro for including me in Taparako, and to Rodrigo for introducing me his world on its other side. I received considerable high quality analytical support during my doctoral studies including assistance from Frank Tepley, Allison Weinsteiger, Dale Burns, Andy Ungerer, Dori Dick in Corvallis; Laureen Wagoner, Richard Conrey, and Charles Knack in Pullman, WA; and John (veinticuatro) Hora and Sarah Greene in Madison, WI. Many thanks. Federico Cernuschi is solely responsible for the formatting of this document. I am very grateful. I am very pleased that Fede and Silvi chose Corvallis as their temporary home and for adopting me as their trial child. I hope to make them proud. Within the VIPER research group at Oregon State University I was fortunate to have many excellent peers who enjoyed discussing the elements and were influential to my development as a scientist, particularly Ashley Hatfield and Abigail Stephens (my primary petrological study partners), Alison Koleszar, B.J., Fede, Mark Ford, Chris Harpel, Bob Peckyno, Ashley Bromley, Erin Lieuallen (who taught me that running through Wilkinson saves valuable time), Matt Loewen, Dale, and Stephanie Grocke. Other quality and influential peers include: office mates Jack Zunka (who could
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