AN ABSTRACT OF THE THESIS OF Manggon Abot for the degree of Master of Science in Geology presented on July_9, 2009. Title: Development of Continental Magmatic Systems: Insights from Amphi- bole Chemistry of the Altiplano Puna Volcanic Complex, Central Andes. Abstract approved: ____________________________________________________________ Anita L. Grunder The pressure history of a continental magmatic system can be deci- phered by analyzing the composition of amphiboles in the eruptive products where the pressure of equilibration correlates with the depth of the magmatic system. This can reveal vertical evolution of the magma as amphibole com- position varies significantly with temperature and pressure. The Altiplano Puna Volcanic Complex (APVC) is a long-lived and large continental mag- matic system that has produced episodic ignimbrite eruptions during the last 10 m.y. The amphiboles from ignimbrites of the various stages during the 10 Ma history have been analyzed, classified and the pressure and temperature calculated using thermodynamic calculation. The APVC amphiboles are cal- cic amphiboles and are magnesiohornblende, tschermakite, magnesiohast- ingsite, and edenite based on the Leake et al. (1997) classification and based on the Deer et al. (1992) scheme. The amphiboles are also calcic, namely, hornblende, tschermakite, pargasite, and edenite. They are broadly similar to amphiboles from other calc-alkaline dacitic systems through space and time. The calculated P-T conditions range from 0.2 to 2.5 kbar and 765oC to 871oC. The P-T conditions are generally similar throughout the 10 Ma time frame of the APVC, although higher minimum and maximum pressures are recorded in the most voluminous 4 Ma pulse. The APVC magmas are repre- sentative of calc-alkaline dacitic magmas associated with subduction and therefore it is a useful model for how large calc-alkaline dacitic systems might evolve. The lack of an obvious trend in P and T with time during the 10 million years history of the APVC, suggests that evolution of dacitic magmas prior to eruption is limited to a narrow depth range in the crust, which is probably pri- marily controlled by the density of the magmas. ©Copyright by Manggon Abot July 9, 2009 All Rights Reserved Development of Continental Magmatic Systems: Insights from Amphibole Chemistry of the Altiplano Puna Volcanic Complex, Central Andes. by Manggon Abot A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented July 9, 2009 Commencement June 2010 Master of Science thesis of Manggon Abot presented on July 9, 2009. APPROVED: ____________________________________________________________________ Major Professor, representing Geology ____________________________________________________________________ Chair of the Department of Geosciences ____________________________________________________________________ Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. __________________________________________________________________________________ Manggon Abot, Author ACKNOWLEDGEMENTS I would like to extend my gratitude to my main advisors, Shan de Silva and Anita L. Grunder, for providing me the opportunity to undertake this re- search project, and also, for their continued guidance, and patience with me, as I endeavor learning igneous petrology. Committee members Frank Tepley III and Roger L. Nielsen offered direction in my approach to understanding aspects of Volcanology and amphiboles chemistry, and various aspects of this research. A special thank you to William H. Warnes for his willingness and excitement to act as the GCR on my thesis committee. I would like to thank the following additional people, who through their technical support and discussion help me to refine various aspects of this thesis: Mike Iademarco, Erin Lieuallen, Allison Weinsteiger and BJ Walker. I would also like to acknowledge the VIPER (Volcanology, Igneous Petrology and Economic Research) Group for conducting series of talks and discussion on amphibole. Lastly, I would like to thank my family for their understanding and continued support that helped me moving forward to get through my masters work. TABLE OF CONTENTS Page 1. Introduction……………………….……………………………………..….....…1 1.1 Purpose and Scope……………………………………….…….……1 2. Geologic Setting…….………………………….…………………………….….3 2.1 Background……………………….………………………………..….3 2.2 Andes………………………………….………………………….……5 2.3 Central Andes………………………….……………………….……..7 2.4 Evolution of the Altiplano Puna Volcanic Complex…….……..…10 2.5 Rock chemistry……………………………………………………....13 2.6 Spatiotemporal eruption………………………………….………...16 3. Methodology………………………………………………………...….………20 3.1 Selection of samples…………………………………...…….….….20 3.2 Petrography……………………………………………...…….........20 3.3 Electron Microprobe………………………………………....…..….21 3.4 Calculation of pressure and temperature………………....……...23 3.5 Al-in-hornblende geobarometry…………………………….……...23 4. Result……………………………………………………………………….…...31 4.1 Amphibole classification………………………………………...….31 4.1.1 Leake et al. Classification Scheme…………………………..…..32 4.1.2 Deer et al. Classification Scheme…………………………..…....36 4.3 Classification of APVC amphiboles as a single suite………..…..37 TABLE OF CONTENTS (Continued) Page 4.3.1 Lower Rio San Pedro Ignimbrite (LRSPI); 10 Ma……………………………………………………………..……41 4.3.2 Sifon; 8.3 Ma…………………………………………….……..…..41 4.3.3 Toconce; 6.4 Ma …………………………………..………….......43 4.3.4 Linzor; 5.3 Ma……………………………………………...……....44 4.3.5 Puripicar; 4.18 Ma…………………………………………..…......44 4.3.6 Purico; 1.1 Ma……………………………………………….……..46 4.3.7 Tatio; 0.75 Ma………………………………………………...…....47 . 5. Discussion and Interpretation………………………………………………...49 5.1 APVC Unit comparison………………………………………….….49 5.2 P and T trend with time………………………………………….….50 5.3 Comparison of APVC to Other Silicic system…………...……….56 6. Conclusion…………………………………………………………………....…61 Bibliography……………………………………………………………..…..…….63 Appendices………………………………………………………………….……..69 Appendix A Representative samples……………………..…………….69 Appendix B Microprobe results……...…………………………………..76 LIST OF FIGURES Figure Page 1. The evolution of AVC consists of four pulses ………………………………..4 2. Map of western South America showing the plate tectonic framework………………………………………………………...6 3. Isotopic composition. Schematic illustration of Sr- and Nd-isotopic compositions relative to MORB…………………………....10 4. Distribution of major ignimbrite sources of APVC…………………………..11 5. APVC ignimbrites can be classified as high-K dacites to rhyolites. …………………………………………………………………...13 6. Summary of the Sr- and Nd-isotopic characterization of APVC Ignimbrites………………………………………………………….15 7. Age-volume data for known major ignimbrite in APVC………….….……...17 8. Summary of empirical and experimental calibrations of the Al-in-Hornblende Barometer………………………………...……23 9. Classification of the calcic amphiboles…………………………………..…..32 10. Deer et al. Classification scheme…………………………………………...35 11. The APVC amphiboles………………………………………….……..……..37 12. The APVC amphiboles with alkali concentration >0.5…………………....37 13. The classification based on Deer et al.(1992)…………….…………..…...38 14. Fractured magnesiohornblende from the Sifon ignimbrite with inclusion of plagioclase feldspar………………………………….……..40 15. Inclusion of plagioclase feldspar and thin rim reaction (<10 um) of magnesiohornblende from the Puripicar ignimbrite…….…………….……..……………………………………….43 16. BSE image of amphibole from the Purico Ignimbrite showing inclusions and perfect cleavages……………………………..44 LIST OF FIGURES (Continued) Figure Page 17. Plot showing the magmatic pressure of each units against age……………………………………………………………………..…...50 18. Plot showing the depth of each unit against age…...…..…….……….….50 19. Plot showing the temperature of each unit against age……............…….51 20. Plot showing the pressure versus temperature of each unit based on Holland and Blundy (1994). ………………………….....52 LIST OF TABLES Table Page 1. Samples used for microprobe analysis……………………………………….2 2. Major ignimbrites and sources calderas of the Altiplano Puna Volcanic Complex of the Central Andes………...………………16 3. Reproducibility and accuracy of hornblende standard……………………..22 4. Reproducibility and accuracy of plagioclase standard…...…….……...…..22 5. Summary of APVC amphiboles petrography and classification………..…39 6. Summary of pressure and temperature of APVC ignimbrite……..…….….39 7. Temperature range obtained from two geothermometers……..……….....52 8. Summary of other silicic volcanic field in comparison with APVC………...54 1. Introduction 1.1 Purpose and Scope This study was undertaken to gain an understanding of the vertical de- velopment and evolution of the Altiplano Puna Volcanic Complex (APVC) continental magmatic system by using amphibole chemistry to test the hy- pothesis that the APVC magmatic system is getting shallower with time. This study focused on the texture, composition and mineralogy of the amphibole phenocrysts and microphenocrysts that are susceptible to changes in pres- sure and temperature. Amphibole is a common phenocryst in all samples evaluated and the pattern of compositional profiles in amphibole portrays the temporal evolution of pressure and temperature in the magma system in gen- eral (Spear, 1981; Hammarstrom and Zen, 1986; Vyhnal et al., 1991). The changes of compositional profiles recorded in amphibole could also be inter- preted