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PRIMARY PRISTINE and ALTERED IRON SULFIDES in CM and CR CARBONACEOUS CHONDRITES: INSIGHTS INTO NEBULAR and PARENT BODY PROCESSES Sheryl A

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PRIMARY PRISTINE and ALTERED IRON SULFIDES in CM and CR CARBONACEOUS CHONDRITES: INSIGHTS INTO NEBULAR and PARENT BODY PROCESSES Sheryl A University of New Mexico UNM Digital Repository Earth and Planetary Sciences ETDs Electronic Theses and Dissertations Spring 2-14-2018 PRIMARY PRISTINE AND ALTERED IRON SULFIDES IN CM AND CR CARBONACEOUS CHONDRITES: INSIGHTS INTO NEBULAR AND PARENT BODY PROCESSES Sheryl A. Singerling University of New Mexico Follow this and additional works at: https://digitalrepository.unm.edu/eps_etds Part of the Geology Commons Recommended Citation Singerling, Sheryl A.. "PRIMARY PRISTINE AND ALTERED IRON SULFIDES IN CM AND CR CARBONACEOUS CHONDRITES: INSIGHTS INTO NEBULAR AND PARENT BODY PROCESSES." (2018). https://digitalrepository.unm.edu/ eps_etds/230 This Dissertation is brought to you for free and open access by the Electronic Theses and Dissertations at UNM Digital Repository. It has been accepted for inclusion in Earth and Planetary Sciences ETDs by an authorized administrator of UNM Digital Repository. For more information, please contact [email protected]. Sheryl Ann Singerling Candidate Earth and Planetary Sciences Department This dissertation is approved, and it is acceptable in quality and form for publication: Approved by the Dissertation Committee: Dr. Adrian J. Brearley, Chairperson Dr. Rhian H. Jones Dr. Lindsay P. Keller Dr. Zachary D. Sharp Dr. Charles K. Shearer, Jr. i PRIMARY PRISTINE AND ALTERED IRON SULFIDES IN CM AND CR CARBONACEOUS CHONDRITES: INSIGHTS INTO NEBULAR AND PARENT BODY PROCESSES BY SHERYL ANN SINGERLING B.Sc., Geology, University of North Carolina at Chapel Hill, 2010 M.Sc., Geology, University of Tennessee, 2012 DISSERTATION Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Earth and Planetary Sciences The University of New Mexico Albuquerque, New Mexico May, 2018 ii Dedication To my role model and devoted mother, Jodi Goodman-Nelson. Your tireless efforts in pursuing your own education and encouragement in mine instilled in me a lifelong love of learning. iii Acknowledgments While I am able to claim authorship of this work, it would never have been possible to complete without the help and support of so many others for the past several years. I would like to give a sincere thanks to my adviser, Adrian, for giving me the foundations for all my fascinating projects, for providing guidance when I needed it but also giving me the room I needed to grow as a researcher, and for providing me the flexibility to work from afar when an excellent internship opportunity presented itself. I would also like to thank my committee members; Rhian Jones, Lindsay Keller, Zach Sharp, and Chip Shearer; as well as my co-authors for the peer-reviewed papers generated from this research; Steve Sutton, Tony Lanzirotti, Matt Newville, and Cari Corrigan; for their welcome suggestions and the resulting improvements to my dissertation. My research would have never been possible without the use of meteorite samples generously provided by the Institute of Meteoritics, the Antarctic Meteorite Working Group, and the National Museum of Natural History. Though I spent countless hours in the lab collecting and interpreting data from those samples, the lab work would have been far more difficult and time-consuming had not been for all the help I received in training and in troubleshooting from Elena Dobrica, Mike Spilde, Ying-Bing Jiang, Tim Rose, and Tim Gooding. I also struggled less in interpreting my data and observations courtesy of the many discussions I had over the years with my friends and colleagues Elena Dobrica, Jon Lewis, Alison Santos, Nicole Lunning, Devin Schrader, Tim McCoy, and Aaron Bell. I must also acknowledge the untiring efforts of Cindy Jaramillo and Faith iv Mutchnik, especially in dealing with my unusual situation living out-of-state the past 2 years of my Ph.D. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation - Earth Sciences (EAR - 1634415) and Department of Energy- GeoSciences (DE-FG02-94ER14466). This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Other portions of this work were supported by NASA Cosmochemistry grants NNX11AK51G, NNX12AH61G, and NNX15AD28G to AJ Brearley (PI). Emotional support was as important as any form of academic support in ensuring the successful completion of my degree. There were times when I certainly wanted to give up, but I weathered through the tough times thanks to my family and friends. I thank my mother, Jodi Goodman-Nelson; my father, Roger Singerling, Jr.; my siblings, Shannon Singerling, Shea Singerling, and Shaun Singerling; and my friend and significant other, Alan Strom, for encouraging me, patiently listening to my endless complaints, and being incredibly understanding when I was deep in editing trances. v PRIMARY AND ALTERED IRON SULFIDES IN CM AND CR CARBONACEOUS CHONDRITES: INSIGHTS INTO NEBULAR AND PARENT BODY PROCESSES by Sheryl Ann Singerling B.Sc., Geology, University of North Carolina at Chapel Hill, 2010 M.Sc., Geology, University of Tennessee, 2012 Ph.D., Earth and Planetary Sciences, University of New Mexico, 2018 Abstract This work presents our detailed investigation of textures and major, minor, and trace element compositions of iron sulfides in CM and CR carbonaceous chondrites using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM) from focused ion beam-prepared (FIB) sections, and synchrotron X-ray fluorescence (SXRF) microanalysis. This study represents the first attempt to link micro- to nano-scale textural and chemical characteristics of CM and CR chondrite primary iron sulfides and their alteration products. The objectives of our studies included determining: 1) if primary sulfides are present in the least-altered CM and CR chondrites, and if so, 2) whether they formed by sulfidization and/or crystallization; 3) whether they are unstable under certain parent vi body conditions breaking down into alteration products in the moderately- to highly- altered CM and CR chondrites; 4) whether the textural and compositional characteristics of primary and altered primary sulfide grains allow us to determine their formation conditions (e.g., pH, fO2, , fS2 T, fluid composition, etc.) and thermal histories (e.g., cooling rates). Although iron sulfides are a minor phase in carbonaceous chondrites, we determined that primary sulfide grains are actually a major proportion of the sulfide grains in the weakly-altered CM2 and CR2 chondrites. We argue that pyrrhotite- pentlandite intergrowth (PPI) grains formed from crystallization of monosulfide solid solution melts, whereas sulfide rimmed metal (SRM) grains formed from sulfidization of Fe,Ni metal. Cooling rate calculations of PPI grains yield rates of <28 to 40 K/hr for CM2 chondrites and 42 to 82 K/hr for CR2 chondrites which pertain to a temperature range not frequently discussed for chondrule cooling (i.e., <600°C, significantly below the silicate solidus). Calculations of sulfur fugacity from SRM grains yield values that range from -18 to -10 (log units), largely in agreement with the predicted solar nebula. Coordinated FIB-TEM-SXRF microprobe analyses for trace element concentrations of primary pyrrhotite, pentlandite, and associated metal grains from chondrules in CM2 and CR2 chondrites allowed us to measure Co, Cu, Ge, Zn, and Se, in addition to Fe and Ni, at a spatial resolution of 2 µm. The similarity between the CM and CR PPI sulfide trace element patterns provides evidence for similar formation mechanisms and conditions. The similarity between the sulfide and metal trace element patterns provides evidence for a genetic relationship between the two, such as formation by sulfidization. Depletions in Ge and Zn imply that the former experienced vii volatilization, or else was never incorporated into the metal or sulfide precursor materials, while the latter is partially lithophile during chondrule formation. Trace element concentrations further support a crystallization model of formation for the PPI grains and a sulfidization model of formation for the SRM grains. In the more aqueously altered CM2 and CR2 chondrites, we observed that primary sulfides were unstable under some parent body conditions and began to break down into different products. The alteration styles consist of primary pyrrhotite altering to secondary pentlandite, magnetite, or phyllosilicates in grains that initially formed by crystallization (PPI grains) and primary metal altering to magnetite, iron carbides, or tochilinite in grains that initially formed by sulfidization (SRM grains). The range of alteration textures and products is the result of differences in conditions of alteration due to the role of microchemical environments and/or brecciation. The breakdown of primary sulfides is even more apparent in the heavily-altered CM1 chondrites where iron sulfides are largely present as relict primary pentlandite with the associated alteration products of primary pyrrhotite, including secondary pentlandite, magnetite, and serpentine. We argue that several different textural groups of the altered primary sulfides were initially PPI grains. The fact that such different alteration products could result from the same precursor sulfides even within the same meteorite sample further underscores
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