UNIVERSITY OF CALIFORNIA, SAN DIEGO Petrogenesis of Intraplate Lavas from Isolated Volcanoes in the Pacific: Implications for the Origin of the Enriched Mantle Source of OIB A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Earth Sciences by Liyan Tian Committee in charge: Professor Paterno Castillo, Chair Professor David Hilton Professor James Hawkins Professor Mark Thiemens Professor Peter Lonsdale 2011 Copyright Liyan Tian, 2011 All rights reserved. The Dissertation of Liyan Tian is approved, and it is acceptable in quality and form for publication on microfilm and electronically: Chair University of California, San Diego 2011 iii This dissertation is dedicated to my parents, You Tian and Xiufen Jiang, who taught me to value education. iv TABLE OF CONTENTS SIGNATURE PAGE………………………………………………………………….iii DEDICATION………………………………………………………………………...iv TABLE OF CONTENTS……………………………………………………………...v LIST OF FIGURES………………………………………………………………….vii LIST OF TABLES…………………………………………………………………..viii ACKNOWLEDGEMENTS…………………………………………………………..ix VITA AND PUBLICATIONS………………………………………………………..xii ABSTRACT………………………………………………………………………….xv CHAPTER 1: Introduction…………………………………………………………….1 1.1. Scientific background and objectives of this dissertation………………………...1 1.2. Contents of the dissertation……………………………………………………….4 1.2.1. Chapter 2………………………………………………………………………..4 1.2.2. Chapter 3 and 4…………………………………………………………………6 1.2.3. Chapter 5………………………………………………………………………..7 1.3. Conclusions……………………………………………………………………….8 References……………………………………………………………………………12 CHAPTER 2: Major and trace element and Sr-Nd isotope signatures of the northern Lau Basin lavas: implications for the composition and dynamics of the back-arc basin mantle………………………………………………………………………………...15 Abstract………………………………………………………………………………15 2.1. Introduction……………………………………………………………………...16 2.2. Geological setting and sample analyzed………………………………………...18 2.3. Analytical methods……………………………………………………………....20 2.4. Results…………………………………………………………………………...21 2.5. Discussion……………………………………………………………………….23 2.5.1. Geochemical variations of the NLB lavas…………………………………….23 2.5.2. Nature of the NLB mantle…………………………………………………….27 2.5.2.1. The nature of composition of subduction components……………………...28 2.5.2.2. Water and extent of melting…………………………………………………33 2.5.2.3. Influence of OIB mantle components……………………………………….36 2.5.3. Tectonic implications………………………………………………………….39 2.6. Conclusions……………………………………………………………………...42 Acknowledgements…………………………………………………………………..43 Appendix……………………………………………………………………………..66 References……………………………………………………………………………78 CHAPTER 3: Petrology and Sr-Nd-Pb-He isotope geochemistry of post-spreading lavas on fossil spreading axes off Baja California Sur, Mexico……………………...88 Abstract………………………………………………………………………………88 3.1. Introduction……………………………………………………………………...89 v 3.2. Geological setting and sample description………………………………………91 3.3. Analytical methods………………………………………………………………95 3.4. Results…………………………………………………………………………...98 3.5. Discussion……………………………………………………………………...102 3.5.1. Geochemical variations of post-spreading lavas on fossil spreading axes off Baja California Sur………………………………………………………………….102 3.5.2. Comparison with post-spreading lavas on other fossil spreading axes in the eastern Pacific………………………………………………………………………104 3.5.3. Petrogenesis of post-spreading lavas on fossil spreading axes………………107 3.5.4. Nature of the mantle source………………………………………………….109 3.6. Summary and conclusions……………………………………………………...113 Acknowledgements…………………………………………………………………114 References…………………………………………………………………………..140 CHPATER 4: Geochemistry of post-spreading lavas from fossil Mathematician and Galapagos spreading axes, revisited………………………………………………..149 Abstract……………………………………………………………………………..149 4.1. Introduction…………………………………………………………………… 150 4.2. Geological setting and previous work………………………………………… 152 4.3. Samples and analytical methods……………………………………………….154 4.4. Results………………………………………………………………………….155 4.4.1. Mathematician Ridge area…………………………………………………...155 4.4.2. Galapagos Rise area………………………………………………………….157 4.5. Discussion……………………………………………………………………...159 4.5.1. Formation of magmas at the fossil spreading axes…………………………..159 4.5.2. Nature of the mantle source………………………………………………….161 4.6. Conclusions…………………………………………………………………….165 References…………………………………………………………………………..194 CHAPTER 5: A geochemical comparison of alkalic lavas in the Trans-Mexican volcanic belt, Baja California and intraplate volcanoes in the eastern Pacific……..200 Abstract……………………………………………………………………………..200 5.1. Introduction…………………………………………………………………….201 5.2. Geological setting and samples investigated…………………………………...203 5.3. Chemical and Sr and Nd isotopic compositions of alkalic lavas from TMVB...204 5.4. Discussion……………………………………………………………………...207 5.4.1. Hypotheses to explain the alkaline magmatism in the TMVB………………207 5.4.2. Are the alkalic lavas from TMVB the same lavas as those in peninsular Baja California and eastern Pacific?...................................................................................210 5.5. Conclusions…………………………………………………………………….212 References…………………………………………………………………………..221 vi LIST OF FIGURES Figure 1.1. Primitive mantle-normalized trace element concentration diagrams…....10 Figure 1.2. 87Sr/86Sr versus 143Nd/144Nd diagram........................................................11 Figure 2.1. Schematic tectonic map of the Lau Basin……………………………….44 Figure 2.2. Silica versus total alkalis diagram.............................................................45 Figure 2.3. MgO versus major elements oxides diagrams…………………………...46 Figure 2.4. Normal-MORB normalized trace element concentration diagrams.….....47 Figure 2.5. 87Sr/86Sr versus 143Nd/144Nd plot ………………………………..…........48 Figure 2.6. (La/Sm)N versus (a) Ba/Nb and (b) Nb/Yb ratios……………………….49 Figure 2.7. (a) Nb/Yb versus Ba/Yb, (b) Ba/Th versus Th/Nb, (c) Ba/Th versus 87Sr/86Sr, and (d) Th/Nb versus 143Nd/144Nd ratios…………………………………..50 Figure 2.8. Plots of 87Sr/86Sr versus 143Nd/144Nd ratios showing the influence of subduction and OIB components to the NLB mantle……………………………......52 0 Figure 2.9. C H2O versus F…………………………………………………………....54 Figure 2.10. (a) Ti8 and (b) Na8 versus Fe8, and (c) Ti8 and (d) Na8 versus H8, and (e) Fe8 versus H8…………………………………………………………………………55 Figure 2.11. Plots of 3He/4He versus (a) 87Sr/86Sr and (b) 143Nd/144Nd ratios……….57 Figure 3.1. Simplified map showing the study area………………………………...115 Figure 3.2. Silica versus total alkalis diagram……………………………………...117 Figure 3.3. MgO versus major elements oxides diagrams………………………….118 Figure 3.4. Primitive mantle-normalized trace element concentration diagrams…..119 Figure 3.5. Sr-Nd-Pb isotopic compositions………………………………………..120 Figure 3.6. 3He/4He ratios and 4He abundances…………………………………….122 Figure 3.7. MgO versus trace elements diagrams…………………………………..123 Figure 3.8. Plots of Zr versus Ba, La versus Sm, Zr versus Nb and Ta.....................124 Figure 3.9. Plots of (a) Rb/Sr versus 87Sr/86Sr and (b) La/Sm versus 143Nd/144Nd....125 Figure 4.1. Simplified map showing the study area..................................................167 Figure 4.2. Silica versus total alkalis diagram……………………………………...168 Figure 4.3. MgO versus major elements oxides diagrams………………………….169 Figure 4.4. Primitive mantle-normalized trace element concentration diagrams......172 Figure 4.5. Sr-Nd-Pb isotopic compositions………………………………………..174 Figure 4.6. Plots of (a) Nb versus Zr and (b) La versus Sm………………………...176 Figure 4.7. Plots of Nb/Zr and Sr-Nd-Pb isotopic ratios versus La/Sm………….....178 Figure 4.8. Plots of (a) Rb/Sr versus 87Sr/86Sr and (b) La/Sm versus 143Nd/144Nd…180 Figure 5.1. Simplified map of the Trans-Mexican Volcanic Belt (TMVB)………...213 Figure 5.2. Silica versus total alkalis diagram……………………………………...215 Figure 5.3. Primitive mantle-normalized trace element concentration diagrams…..216 Figure 5.4. 87Sr/86Sr versus 143Nd/144Nd plot.............................................................218 Figure 5.5. Plots of (a) La versus Sm and (b) Zr versus Nb………………………..219 vii LIST OF TABLES Table 2.1. Dredge locations………………………………………………………….58 Table 2.2. Trace element and Sr-Nd isotope compositions………………………….59 Table 2.3. End-member compositions for the mixing calculations………………….65 Table 2.A1. Major element compositions…………………………………………....67 Table 3.1. Dredge locations………………………………………………………...127 Table 3.2. Major and trace element compositions………………………………….128 Table 3.3. Sr-Nd-Pb compositions………………………………………………….137 Table 3.4. Helium isotope compositions……………………………………………139 Table 4.1. Dredge locations…………………………………………………………182 Table 4.2. Major and trace element compositions…………………………………..183 Table 4.3. Sr-Nd-Pb isotope compositions………………………………………….192 viii ACKNOWLEDGEMENTS Writing a Ph.D. dissertation has taken a lot of hard work on my part, but could not have been accomplished without substantial help and input from a number of people. First and foremost, I would like to express my deepest gratitude to my research advisor, Professor Paterno Castillo, for his never-ending support, both financially and emotionally, ingenious guidance and cordial encouragement throughout my Ph.D. education at Scripps. Professor Castillo has guided me through the steps of research - from sample analysis to writing up the results as scientific publications; in addition, he is full of ideas, and lots of these ideas are incorporated into the chapters of this dissertation. Never can I thank enough