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Siderophile Elements and Molybdenum, Tungsten, And ABSTRACT Title of Dissertation: SIDEROPHILE ELEMENTS AND MOLYBDENUM, TUNGSTEN, AND OSMIUM ISOTOPES AS TRACERS OF PLANETARY GENETICS AND DIFFERENTIATION: IMPLICATIONS FOR THE IAB IRON METEORITE COMPLEX Emily Anne Worsham, Doctor of Philosophy, 2016 Dissertation directed by: Professor Richard Walker, Department of Geology Isotopic and trace element abundance data for iron meteorites and chondrites are presented in order to investigate the nature of genetic relations between and among meteorite groups. Nebular and planetary diversity and processes, such as differentiation, can be better understood through study of IAB complex iron meteorites. This is a large group of chemically and texturally similar meteorites that likely represent metals with a thermal history unlike most other iron meteorite groups, which sample the cores of differentiated planetesimals. The IAB complex contains a number of chemical subgroups. Trace element determination and modeling, Re/Os isotopic systematics, nucleosynthetic Mo isotopic data, and 182Hf-182W geochronology are used to determine the crystallization history, genetics, and relative metal-silicate segregation ages of the IAB iron meteorite complex. Highly siderophile element abundances in IAB complex meteorites demonstrate that diverse crystallization mechanisms are represented in the IAB complex. Relative abundances of volatile siderophile elements also suggest late condensation of some IAB precursor materials. Improvements in the procedures for the separation, purification, and high- precision analysis of Mo have led to a ~2 fold increase in the precision of 97Mo/96Mo isotope ratio measurements, compared to previously published methods. Cosmic ray exposure-corrected Mo isotopic compositions of IAB complex irons indicate that at least three parent bodies are represented in the complex. The Hf-W metal-silicate segregation model ages of IAB complex subgroups suggests that at least four metal segregation events occurred among the various IAB parent bodies. The IAB complex samples reservoirs that were isotopically identical, but chemically distinct, and reservoirs that were chemically similar in some respects, yet isotopically different. Some IAB subgroups are genetically distinct from all other iron meteorite groups, and are the closest genetic relations to the Earth. The chemical differences between magmatic iron meteorite groups and some IAB subgroups likely originated as a result of their formation on undifferentiated parent bodies where impacting and mixing processes were important. This, in addition to the genetic difference between some IAB irons and magmatic groups, implies that these IAB parent bodies and magmatic parent bodies formed in a different location and/or time in the protoplanetary disk. SIDEROPHILE ELEMENTS AND MOLYBDENUM, TUNGSTEN, AND OSMIUM ISOTOPES AS TRACERS OF PLANETARY GENETICS AND DIFFERENTIATION: IMPLICATIONS FOR THE IAB IRON METEORITE COMPLEX by Emily Anne Worsham Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2016 Advisory Committee: Professor Richard Walker, Chair Dr. Conel Alexander Professor James Farquhar Professor William McDonough Professor Jessica Sunshine © Copyright by Emily Anne Worsham 2016 Preface Much of the research presented in this dissertation is submitted or previously published in peer-reviewed journals as standalone articles. I made significant contributions to co-authored works. Following is a summary of the contributions from each author. Chapter 2 Worsham E. A., Bermingham K. R., and Walker R. J. (2016) Siderophile element systematics of IAB complex iron meteorites: New insights into the formation of an enigmatic group. Geochimica et Cosmochimica Acta 188, 261-283. I collected ~60% of the highly siderophile element data and Os isotope data. I conducted all of the numerical trace element modeling of various crystallization processes. Katherine Bermingham and I collected ~ 40% of the data together, and she contributed to the discussion. Rich Walker helped interpret the results. I wrote the first draft of the manuscript, and co-authors provided edits. Chapter 4 Worsham E. A., Walker R. J., and Bermingham K. R. (2016) High-precision molybdenum isotope analysis by negative thermal ionization mass spectrometry. International Journal of Mass Spectrometry 407, 51-61. I improved the chemical separation procedures of Mo, and developed the loading and analytical routine, with input and suggestions from both co-authors. I made the spike- standard mixtures with help from Katherine Bermingham. I collected all data reported here, and I wrote the first draft of the manuscript, which was later reviewed by the co- authors. Chapter 5 Worsham E. A., Bermingham K. R., and Walker R. J., Molybdenum and tungsten isotope evidence for diverse genetics and chronology among IAB iron meteorite complex subgroups. Earth and Planetary Science Letters. In review. I conducted the chemistry and collected the Mo and W isotope analyses. I collected ~ 70% of the Osmium isotope data, and Katherine Bermingham and I collected the other 30%. I wrote the first draft of the manuscript and incorporated edits from the co-authors. ii Acknowledgements First of all, thank you to Rich Walker for all the advice, direction, humor, and patience. I want to thank my committee, Conel Alexander, James Farquhar, Bill McDonough, and Jessica Sunshine for your constructive comments and support. I was financially supported by a research and teaching assistantships, the ESSIC travel grant and the Goldhaber travel award, which I am also grateful for. Thanks to Tim McCoy and Linda Welzenbach for several tours of the Smithsonian meteorite collection and for trusting me to dissolve valuable meteorites to obtain valuable data. Thanks also to Katherine Bermingham, who has been my collaborator and confidant throughout my studies. I want to thank Greg Archer for many laughs and enlightening discussions. Other people who have supported me throughout this process, both in the lab and out, include Igor Puchtel, Richard Ash, Jingao Liu, James Day, Miriam and Nick Sharp, and Andi Mundl. I also want to acknowledge my supportive office mates past and present, Jeremy Bellucci, Kristy Long, Ming Tang, Kang Chen, Mitch Haller, and Connor Hilton. For guiding me in my early professional development, I thank Hap McSween, Larry Taylor, Paul Niles, and Linda Kah. I’ve had a lot of fun at Maryland and made a lot of great friends, and for that I thank all of the UMD Geology faculty, staff, and gradtuate students. I truly appreciate getting to know so many great people. I was lucky to have my some of my best friends, Ena Djordjevic and Austin Duck, independently choose to come to the University of Maryland as well. You’ve been invaluable emotional support and I know we will reminisce together about that time we all lived in Mount Rainier often. Thanks to my farther flung friends, Bonnie Buckles, Stephanie Riggs, Kurt McIntosh, iii Tammy Chamberlin, and Amber Hall for your support. Finally, thank you and I love you to my extended family; my mom and dad, Lesa and Paul Worsham; my sister, Rebecca Worsham; and my brother in law, Hans Hansen. You all inspired me to work hard in school and to be curious, you encouraged debate, and you indulged my love of science and space and rocks. I wouldn’t be who or where I am without you all. Thank you. iv Table of Contents Preface.......................................................................................................................... ii Acknowledgements..................................................................................................... iii Table of Contents..........................................................................................................v List of Tables..............................................................................................................viii List of Figures................................................................................................................x List of Abbreviations...................................................................................................xii Chapter 1: Introduction.................................................................................................1 1.1 Motivating questions.........................................................................................1 1.2 Overview of early solar system history recorded in meteorites........................1 1.3 IAB complex of iron meteorites........................................................................4 1.4 Isotope heterogeneity in the early solar nebula.................................................5 1.5 Introduction to Mo cosmochemistry.................................................................8 1.6 Genetics and chronology of IAB meteorites....................................................10 Chapter 2: Siderophile element systematics of IAB complex iron meteorites: New insights into the formation of an enigmatic group.....................................12 2.1 Abstract............................................................................................................12 2.2 Introduction......................................................................................................13 2.3 Samples............................................................................................................16 2.4 Analytical methods..........................................................................................18
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