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Calcium Isotopes in Natural and Experimental Carbonated Silicate Melts

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Calcium Isotopes in Natural and Experimental Carbonated Silicate Melts Western University Scholarship@Western Electronic Thesis and Dissertation Repository 2-27-2018 2:30 PM Calcium Isotopes in Natural and Experimental Carbonated Silicate Melts Matthew Maloney The University of Western Ontario Supervisor Bouvier, Audrey The University of Western Ontario Co-Supervisor Withers, Tony The University of Western Ontario Graduate Program in Geology A thesis submitted in partial fulfillment of the equirr ements for the degree in Master of Science © Matthew Maloney 2018 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Geochemistry Commons Recommended Citation Maloney, Matthew, "Calcium Isotopes in Natural and Experimental Carbonated Silicate Melts" (2018). Electronic Thesis and Dissertation Repository. 5256. https://ir.lib.uwo.ca/etd/5256 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. Abstract The calcium stable isotopic compositions of mantle-sourced rocks and minerals were investigated to better understand the carbon cycle in the Earth’s mantle. Bulk carbonatites and kimberlites were analyzed to identify a geochemical signature of carbonatite magmatism, while inter-mineral fractionation was measured in co-existing Ca-bearing carbonate and silicate minerals. Bulk samples show a range of composition deviating from the bulk silicate Earth δ44/40Ca composition indicating signatures of magmatic processes or marine carbonate addition 44/40 to source materials. Δ Cacarbonate-silicate values range from -0.55‰ to +1.82‰ and positively correlate with Ca/Mg ratios in pyroxenes. A series of experiments designed to equilibrate clinopyroxene with carbonated melts of varying compositions were conducted to constrain the systematics of Ca isotopic fractionation in these systems. Results show significant fractionation between phases, with δ44/40Ca in Cpx ranging from +0.37 to +2.75‰ heavier than quenched melts. However, the influence of thermal diffusion on these results is not fully understood. Keywords Calcium Isotopes, Stable Isotopic Fractionation, Experiment, Carbonatites, Kimberlites, Peridotites, Carbonatite Magmatism, Mantle Geochemistry, i Acknowledgements First and foremost, I must thank my co-supervisors Dr. Audrey Bouvier and Dr. Tony Withers for giving me the opportunity to study here at Western and for providing me with continued guidance and support throughout this project. In addition to being model examples of what it takes to be a successful scientist, you have taught me the skills that are required to be an independent, critical thinker. You have challenged me to be a better researcher and a better person. I want to thank Dr. R. Bastian Georg for providing me with many hours of patient support and assistance while teaching me how to use the Neptune at the Trent Water Quality Centre and for conducting my strontium and iron isotopic analyses. You made the many trips to Trent University more enjoyable and infinitely more successful, and I always looked forward to the dinner at St. Veronus that became a tradition. Thank you to the staff and fellow students with whom I have shared the GEOMETRIC clean lab during my time here, whether it was assistance with a specific task, or simply some company during a long day (and/or night) running columns. A special thanks to Blair Gibson for his assistance operating the ICPMS and conducting the major, minor, and trace element analyses for many of my samples. Finally, I would like to thank my family for always being there for me throughout the many long years of academic endeavours; I would not be here without you. Thank you to all the great friends I have been lucky to make while here at Western, you made this experience better than I could have hoped. And a very special thank you to my partner, Heather. You gave me the encouragement to pursue my goals and the support to achieve them. ii Table of Contents Abstract ............................................................................................................................................ i Acknowledgements ......................................................................................................................... ii Table of Contents ........................................................................................................................... iii List of Tables ................................................................................................................................ vii List of Figures ................................................................................................................................. x Chapter 1 ......................................................................................................................................... 1 1. Introduction ................................................................................................................................. 1 1.1 Earth’s Carbon Cycle ............................................................................................................ 1 1.2 Carbonate Melts and Carbon-Rich Rocks............................................................................. 2 1.2. Carbonatites ......................................................................................................................... 4 1.3 High-Pressure and High-Temperature Experimental Work ................................................. 7 1.3.1 Experiments on the Origin of Carbonatites and Carbon-Bearing Melts ........................ 8 1.3.2 Experiments Using Geochemical Tracers .................................................................... 14 1.3.3 Experimental Determination of Stable Isotope Fractionation ..................................... 15 1.3.4 Thermal Diffusion ........................................................................................................ 18 1.4 Isotope Geochemistry ......................................................................................................... 20 1.4.1 Calcium Isotopes .......................................................................................................... 20 1.5 Thesis Objectives ................................................................................................................ 28 Chapter 2 ....................................................................................................................................... 29 2. Methods & Analytical Techniques ........................................................................................... 29 2.1 Sample Selection ................................................................................................................. 29 2.2 Natural Sample Preparation ................................................................................................ 29 2.3 Experimental Sample Design and Preparation ................................................................... 30 iii 2.4 Electron Probe Microanalyses ............................................................................................ 34 2.5 Silicate Mineral Acid Leaching Procedure ......................................................................... 34 2.6 Sample Dissolution Procedure ............................................................................................ 35 2.7 Calcium Purification ........................................................................................................... 36 2.8 Iron Purification .................................................................................................................. 40 2.9 Quadrupole Inductively Couple Plasma Mass Spectrometry (ICP-MS) ............................ 41 2.10 Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS)........... 42 Chapter 3 ....................................................................................................................................... 46 3. Sample Descriptions ................................................................................................................. 46 3.1 Carbonatites ........................................................................................................................ 46 3.1.1 Oka Carbonatites .......................................................................................................... 46 3.1.2 Phalaborwa Carbonatites ............................................................................................. 47 3.1.3 Lueshe Carbonatite ...................................................................................................... 48 3.1.4 Nemegos Carbonatite ................................................................................................... 48 3.1.5 Cape Verde Archipelago Carbonatites......................................................................... 49 3.1.6 Tamazert Massif (Morocco) Carbonatites ................................................................... 50 3.2 Kimberlites and Related Rocks ........................................................................................... 50 3.2.1 Kimberley Area Kimberlite ......................................................................................... 51 3.2.2 Kaapvaal Craton Peridotites ........................................................................................ 51 3.3 External Standards
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