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Nakhlite Meteorites to Assess Carbonate Formation On STUDYING ANTARCTIC ORDINARY CHONDRITE (OC) AND MILLER RANGE (MIL) NAKHLITE METEORITES TO ASSESS CARBONATE FORMATION ON EARTH AND MARS A Dissertation by MICHAEL ELLIS EVANS Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chair of Committee, Piers Chapman Co-Chair of Committee, Paul Niles Committee Members, Niall Slowey Kathryn Shamberger Ethan Grossman Head of Department, Shari Yvon-Lewis May 2017 Major Subject: Oceanography Copyright 2017 Michael Ellis Evans ABSTRACT Carbonates are found in meteorites collected from Antarctica. The stable isotope composition of these carbonates records their formation environment on either Earth or Mars. The first research objective of this dissertation is to characterize the δ18O and δ13C values of terrestrial carbonates formed on Ordinary Chondrites (OCs) collected in regions near known martian meteorites. The second objective is to characterize the δ18O and δ13C values of martian carbonates from Nakhlites collected from the Miller Range (MIL). The third objective is to assess environmental changes on Mars since the Noachian period. The OCs selected had no pre-terrestrial carbonates so any carbonates detected are presumed terrestrial in origin. The study methodology is stepped extraction of CO2 created from phosphoric acid reaction with meteorite carbonate. Stable isotope results show that two distinct terrestrial carbonate species (Ca-rich and Fe/Mg-rich) formed in Antarctica on OCs from a thin-film of meltwater containing dissolved CO2. Carbon isotope data suggests the terrestrial carbonates formed in 13 18 equilibrium with atmospheric CO2 δ C = -7.5‰ at >15°C. The wide variation in δ O suggests the carbonates did not form in equilibrium with meteoric water alone, but possibly formed from an exchange of oxygen isotopes in both water and dissolved CO2. Antarctica provides a model for carbonate formation in a low water/rock ratio, near 0°C environment like modern Mars. Nakhlite parent basalt formed on Mars 1.3 billion years ago and the meteorites were ejected by a single impact approximately 11 ii million years ago. They traveled thru space before eventually falling to the Earth surface 10,000-40,000 years ago. Nakhlite samples for this research were all collected from the Miller Range (MIL) in Antarctica. The Nakhlite stable isotope results show two carbonate species (Ca-rich and Fe/Mg-rich) with a range of δ18O values that are similar to the terrestrial OC carbonates. The Nakhlite carbonates have distinctly different, heavier δ13C values from a presumed martian carbon reservoir. These carbonates cannot form in equilibrium at 15°C with the modern Mars atmospheric CO2 (measured by the Curiosity rover) δ13C = 46‰, but may reflect kinetic carbonate formation from a high pH fluid. Alternatively, the Nakhlite carbonates may have formed with a lighter, early Amazonian atmosphere of δ13C ≈ 30‰. Assuming the martian carbonates formed in a thin-film environment like the OC terrestrial carbonates, an oxygen mixing model predicts early Amazonian martian meteoric water δ18O = -30‰. iii DEDICATION I dedicate this work to my parents, who instilled in me a thirst for knowledge and a zest for life. They shaped my character to be confident, independent, and meticulous in all pursuits. My father modeled integrity with his work ethic that balanced professional and personal life. My love for family time stems from him. My mother has always been my greatest encouragement. She continues to model adult development with intelligence, humor, travel, outreach, and altruism. I also dedicate this work to my children with the hope that they grow, and evolve, and expand with every breath. I hope they treat life as a long education experience, and make wise decisions without fear of wondering “What if …” iv ACKNOWLEDGEMENTS I acknowledge my Texas A&M University (TAMU) committee chair, Dr. Piers Chapman, for accepting me as his wayward graduate student and guiding my evolution in the Oceanography Department. I have greatly enjoyed his gentle coaching as a teacher, a researcher, and a colleague. I encourage all grads to seek his wisdom over “Beers with Piers”. I also acknowledge my NASA committee co-chair, Dr. Paul Niles, who crafted a scientist from an engineer. His focus redirected my outlook from “How” to “Why” with the assurance that “Science is SLOW”. His assistance in coordinating NASA and TAMU logistics facilitated this successful research collaboration. I credit Rick Socki, Darren Locke, and Dr. Tao Sun for teaching me the skills to accomplish this research in NASA’s Light Element Analysis Laboratory (LEAL). I admire their patience, knowledge, and creativity in working to build, test, and maintain the finicky instruments and temperamental equipment. I thank my committee members, Dr. Niall Slowey, Dr. Katie Shamberger, and Dr. Ethan Grossman for their guidance and support throughout the course of my TAMU education and research. I appreciate the faculty within Oceanography Department for their dedication to teaching excellence during my coursework. I acknowledge Dr. Debbie Thomas for her enthusiastic support (and comradeship on AGU runs). My life at TAMU has been enhanced because of a close family of graduate students (especially Steph, Natalie, Chris, Cody and Kat) in the Oceanography v Department. From shared coursework to OCNG-252 TA meetings to exploring the Galapagos Islands to Friendsgivings to AGU with tailgates, football games, rallys, movie nights, “Mug Club” and pub crawls - I am thankful. I also developed dear friendships through church (especially Linda, Glenn, & Vinnie) and choir in College Station that enriched my soul. My heart resides in Aggieland. Thanks to the Oceanography Department staff (especially Amy, Wendy, Janet and Debra) for their assistance with the paperwork that provided funding, benefits, and reimbursements for my educational expenses. This dissertation would not have been possible without the support of everyone. vi CONTRIBUTORS AND FUNDING SOURCES Contributors This work was supervised by a dissertation committee with members of the TAMU College of Geosciences, including Dr. Piers Chapman (co-chair), Dr. Niall Slowey, and Dr. Katie Shamberger, of the Oceanography Department, and Dr. Ethan Grossman of the Geology and Geophysics Department. Dr. Paul Niles of NASA/JSC functioned as both co-chair of the dissertation committee and management supervisor of the student at NASA. All experimental work conducted for this dissertation was completed by the student independently in the NASA/JSC Light Element Analysis Laboratory (LEAL) located in Houston, Texas. Funding Sources Graduate study was supported by a stipend from Texas A&M University – Galveston as a Teaching Assistant (TA) for CHEM-117 Chemistry Lab for Engineers (Fall 2011 and Spring 2012), as a TA for OCNG-252 Oceanography Lab (Fall 2012, Spring 2013, and Fall 2013) and as a Graduate Assistant Lecturer (GAL) for OCNG-251 Oceanography (Fall 2014, Fall 2015, and Fall 2016). Graduate study was also made possible with a scholarship from the family of Louis and Elizabeth Scherck for the 2015-2016 and 2016-2017 school years. Travel grants from the TAMU Oceanography Graduate Council (OGC) provided funds to present research at the 2014 American Geophysical Union (AGU) conference and at the vii 2017 Lunar Planetary Science Conference (LPSC). NASA provided funds to present research at the 2015 and 2016 AGU conference, and the LPSC in 2016 and 2017. The remainder of my graduate funding was earned as salary while working as a summer scientist for Jacobs Engineering (Summer 2012) and as a NASA Pathways Graduate Student (Summer 2013, Jan-Aug 2014, Jan-Aug 2015, Jan-Aug 2016, Jan-May 2017). viii TABLE OF CONTENTS Page ABSTRACT .......................................................................................................................ii DEDICATION .................................................................................................................. iv ACKNOWLEDGEMENTS ............................................................................................... v CONTRIBUTORS AND FUNDING SOURCES ............................................................vii TABLE OF CONTENTS .................................................................................................. ix LIST OF FIGURES ........................................................................................................ xiii LIST OF TABLES .......................................................................................................... xvi CHAPTER I INTRODUCTION AND BACKGROUND ................................................ 1 Understanding Mars ........................................................................................................... 1 Why Study Mars? ....................................................................................................... 1 Mars Environmental Changes .................................................................................... 2 Meteorites ......................................................................................................................... 14 Meteorite Types ........................................................................................................ 16 Undifferentiated Meteorites ................................................................................. 16 Differentiated Meteorites ....................................................................................
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