Petrology and Geochemistry of the Enriched Poikilitic Shergottite Northwest Africa 10169: Insight Into the Martian Interior
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UNLV Theses, Dissertations, Professional Papers, and Capstones May 2018 Petrology and Geochemistry of the Enriched Poikilitic Shergottite Northwest Africa 10169: Insight into the Martian Interior Logan Matthew Combs Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Geochemistry Commons, and the Geology Commons Repository Citation Combs, Logan Matthew, "Petrology and Geochemistry of the Enriched Poikilitic Shergottite Northwest Africa 10169: Insight into the Martian Interior" (2018). UNLV Theses, Dissertations, Professional Papers, and Capstones. 3235. http://dx.doi.org/10.34917/13568422 This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in UNLV Theses, Dissertations, Professional Papers, and Capstones by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. PETROLOGY AND GEOCHEMISTRY OF THE ENRICHED POIKILITIC SHERGOTTITE NORTHWEST AFRICA 10169: INSIGHT INTO THE MARTIAN INTERIOR By Logan M. Combs Bachelor of Science – Geology University of Tennessee Knoxville 2014 A thesis submitted in partial fulfillment of the requirements for the Master of Science – Geoscience Department of Geoscience College of Science The Graduate College University of Nevada, Las Vegas May 2018 Copyright 2018 by Logan M. Combs All Rights Reserved Thesis Approval The Graduate College The University of Nevada, Las Vegas April 10, 2018 This thesis prepared by Logan M. Combs entitled Petrology and Geochemistry Of The Enriched Poikilitic Shergottite Northwest Africa 10169: Insight Into The Martian Interior is approved in partial fulfillment of the requirements for the degree of Master of Science – Geoscience Department of Geoscience Arya Udry, Ph.D. Kathryn Hausbeck Korgan, Ph.D. Examination Committee Chair Graduate College Interim Dean Shichun Huang, Ph.D. Examination Committee Member Elisabeth Hausrath, Ph.D. Examination Committee Member Jason Steffen, Ph.D. Graduate College Faculty Representative ii ABSTRACT The martian meteorite Northwest Africa (NWA) 10169 is classified as a new member of the geochemically enriched poikilitic shergottites, based on mineral composition, Lu-Hf isotope systematics, and rare earth element (REE) composition. Akin to other poikilitic shergottites, it shows a similar bimodal texture to other enriched and intermediate poikilitic shergottites. In addition, olivine and pyroxene in the poikilitic zone have higher Mg#’s (Mg/Mg+Fe) than those in the interstitial areas, suggesting that the poikilitic texture represents early-stage crystallization, opposed to late-stage non-poikilitic crystallization. Calculated fO2 values are reduced (FMQ -2.3 ± 0.23) within the poikilitic texture, and more oxidized (FMQ -1.07 ± 0.14) within the interstitial areas likely representing auto-oxidation and degassing during magma crystallization. Melt inclusions within olivine crystals provide snapshots of magma composition throughout parent melt evolution. The calculated parental melt compositions share evolution trends with the enriched olivine-phyric shergottite Larkman Nunatuk (LAR) 06319, and suggest that two melts (K-poor and K-rich) were involved in the formation of NWA 10169, likely representing interaction with a metasomatized melt during the entrapment of the K-rich melt inclusions. The Lu-Hf crystallization age for NWA 10169 is 167 ± 31 Ma, consistent with the other enriched shergottites. Based on the isochron initial 176Hf/177Hf value, the modeled the source 176Lu/177Hf composition for NWA 10169 is 0.02748 ± 0.00037, identical within error to the source compositions of the enriched shergottites Shergotty, Zagami, LAR 06319, NWA 4468, and Roberts Massif (RBT) 04262, suggesting a shared, long-lived geochemical source, distinct from the source tapped by Los Angeles, NWA 856, and NWA 7320. This study reveals that at least two sources are responsible for the enriched shergottites, and a more heterogeneous martian mantle than previously thought. Additionally, the shared source with NWA 10169, coupled with consistent crystallization ages and magmatic iii histories indicates that a common magmatic system on Mars is likely responsible for the formation of this group of shergottites. iv ACKNOWLEDGEMENTS This work was funded in part by the National Aeronautics and Space Administration under Grant EPSCoR No. NNX15AIO2H, awarded to L. M. Combs. My committee, Dr. Arya Udry, Dr. Shichun Huang, Dr. Elisabeth Hausrath, and Dr. Jason Steffen are thanked for their helpful edits and advice given throughout this project. I would like to thank Minghua Ren for his help and advice regarding EMP and SEM analyses at UNLV. I also thank Stephanie Suarez for providing assistance with column chemistry at UH, and Racheal Johnson for her invaluable help with heavy liquid separation at UNLV. My office mates Chris Defelice and Dalton McCaffrey provided comradery, and useful scientific discussions, while also preventing mental degradation during late night work sessions. Most of all, I would like to thank Susie Hertfelder for being a true legend through all of the adventures that we have been thrust into. On the non-human side of things, PBR and Taco Bell contributed greatly to my morale, and equipped me with the fuel needed to tackle any challenges encountered along the way. Finally, I express my sincerest gratitude to the Mojave Desert, whose astounding beauty, mysticism, and warm embrace healed me when I needed it most. v TABLE OF CONTENTS ABSTRACT…………………………………………………………………………………...…iii ACKNOWLEDGEMENTS...……………………………………………………………………..v TABLE OF CONTENTS…………………………………………………………………………vi LIST OF TABLES………………………………………………………………………………viii LIST OF FIGURES…………………………………………………………………………….....ix CHAPTER 1. INTRODUCTION…………………...……….…………...………………………..1 CHAPTER 2. ANALYTICAL METHODS………...………...……….…………………………..5 2.1 Electron microprobe analyses……………………………………….……………………..5 2.1.1 In situ major and minor element analyses…………………………………………...5 2.1.2 Melt inclusion analyses……………………………………………………………...5 2.2 Quantitative textural analyses……………………………………………………………..6 2.3 Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS)……..7 2.4 Inductively Coupled Plasma – Mass Spectrometry (ICP-MS)…………………………..…8 2.5 176Lu/177Hf isotopic analyses………………………………………………………………8 CHAPTER 3. RESULTS………………………...………………………………………………11 3.1 Petrography………………………………………………………………………………11 3.2 Major, minor and trace element mineral composition………………………….………...12 3.2.1 Pyroxene………………………………………………………………….………...12 3.2.2 Olivine……………………………………………………………………………...15 3.2.3 Maskelynite………………………………………………………………………...16 3.2.4 Fe-Cr-Ti oxides…………………………………………………………………….17 vi 3.2.5 Phosphates………………………………………………………………………….18 3.3 Crystal size distribution…………………………………………………………………..18 3.4 Olivine-hosted polymineralic melt inclusions……………………………………………19 3.5 Lu-Hf crystallization age and isotope systematics………………………………………..21 CHAPTER 4. DISCUSSION……………...……………………………………………………..23 4.1 Crystallyzation sequence of NWA 10169………………………………………………...23 4.2 Olivine growth in NWA 10169…………………………………………………………...25 4.3 Conditions of formation…………………………………………………………………..27 4.3.1 Emplacement of NWA 10169………………………………………………………27 4.3.2 Temperature, pressure, and oxygen fugacity……………………………………….29 4.3.3 Relationship of oxygen fugacity to geochemical sources…………………………..32 4.4 Geochemical classification and REE budget……………………………………………..33 4.5 Parental melt of NWA 10169…………………………………………………………….35 4.6 Shergottite crystallization ages and model Lu-Hf source composition…………………..41 4.7 Petrogenetic model for NWA 10169 and the enriched shergottites……………………...43 CHAPTER 5. SUMMARY………………………...….…………………………………………47 APPENDIX A: TABLES……………………......……………………………………………….50 APPENDIX B: FIGURES……..…………………………………………………………………56 REFERENCES…………………………………………………………………………………..78 CURRICULUM VITAE…………………………………………………………………………96 vii LIST OF TABLES Table 1……………………………………………………………………………………………50 Table 2……………………………………………………………………………………………51 Table 3……………………………………………………………………………………………52 Table 4……………………………………………………………………………………………53 Table 5……………………………………………………………………………………………54 Table 6……………………………………………………………………………………………55 viii LIST OF FIGURES Figure 1…………………………………………………………………………………………..56 Figure 2…………………………………………………………………………………………..57 Figure 3…………………………………………………………………………………………..58 Figure 4…………………………………………………………………………………………..60 Figure 5…………………………………………………………………………………………..62 Figure 6…………………………………………………………………………………………..63 Figure 7…………………………………………………………………………………………..64 Figure 8…………………………………………………………………………………………..65 Figure 9…………………………………………………………………………………………..67 Figure 10…………………………………………………………………………………………68 Figure 11…………………………………………………………………………………………69 Figure 12…………………………………………………………………………………………70 Figure 13………………………………………………………………………………………....71 Figure 14…………………………………………………………………………………………72 Figure 15…………………………………………………………………………………………73 Figure 16…………………………………………………………………………………………75 Figure 17…………………………………………………………………………………………76 ix 1. INTRODUCTION Shergottites are the most abundant of the three main groups of martian