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Chlorine Enrichment of Hydrous Minerals In Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 2015 Chlorine Enrichment of Hydrous Minerals in Archean Granulite Facies Ironstone from the Beartooth Mountains, Montana, USA: Implications for High-Grade Metamorphic Fluids Nicholas Michael Daigle Louisiana State University and Agricultural and Mechanical College, [email protected] Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses Part of the Earth Sciences Commons Recommended Citation Daigle, Nicholas Michael, "Chlorine Enrichment of Hydrous Minerals in Archean Granulite Facies Ironstone from the Beartooth Mountains, Montana, USA: Implications for High-Grade Metamorphic Fluids" (2015). LSU Master's Theses. 1188. https://digitalcommons.lsu.edu/gradschool_theses/1188 This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. CHLORINE ENRICHMENT OF HYDROUS MINERALS IN ARCHEAN GRANULITE FACIES IRONSTONES FROM THE BEARTOOTH MOUNTAINS, MONTANA, USA: IMPLICATIONS FOR HIGH-GRADE METAMORPHIC FLUIDS A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The Department of Geology and Geophysics by Nicholas M. Daigle B.S., Louisiana State University, 2013 August 2015 ACKNOWLEDGMENTS First and foremost I would like to thank my advisor, Dr. Darrell Henry, for his constant guidance and support over the last two years, and also my committee members, Dr. Barbara Dutrow and Dr. Jianwei Wang, for their suggestions and valuable feedback. My fellow classmates are also greatly appreciated for discussions and constructive criticism. The saintly individuals who aided me in my attempt to keep the microprobe alive and running deserve special recognition: Celina Will, who instructed me on how to run the probe and was always willing to help in any way she could even after leaving LSU; Clayton Loehn, for spending hours of his time away from the SIF to help brainstorm and fix the endless issues with the probe; Rick Young and Wanda Leblanc, for assisting me with maintenance and upkeep for the machines in the probe lab as well as various other tasks I asked of them; and Joe Geller and Chuck Herrington, for being patient and not ignoring the constant barrage of emails I sent them when the probe started acting funny. Lastly I would like to graciously thank The Red River Desk and Derrick Club, New Orleans Geologic Society, Geologic Society of America, the AAPG LSU student chapter, and the LSU Department of Geology and Geophysics for various monetary support during my research efforts. ii TABLE OF CONTENTS ACKNOWLEDGMENTS ................................................................................................... ii LIST OF TABLES ............................................................................................................ v LIST OF FIGURES ......................................................................................................... vii ABSTRACT .................................................................................................................... xii CHAPTER I. INTRODUCTION ........................................................................................ 1 CHAPTER II. GEOLOGIC SETTING ............................................................................... 7 2.1 Wyoming Province .......................................................................................... 7 2.2 Beartooth Mountains .................................................................................... 10 CHAPTER III. METHODS ............................................................................................. 15 3.1 Sample Collection and Preparation .............................................................. 15 3.2 Petrographic and Microanalytical Methods ................................................... 15 3.2.1 Petrographic Analysis ..................................................................... 15 3.2.2 Mineral Chemical Analysis .............................................................. 19 3.3 Determination of Pressure-Temperature-Fluid Conditions ........................... 22 3.3.1 Thermobarometers ......................................................................... 22 3.3.2 Equilibrium Assemblage Diagrams (Pseudosections) ..................... 24 3.4 Halogen Fugacity Calculations………………………………………………….. 26 CHAPTER IV. RESULTS .............................................................................................. 27 4.1 Sample Locations ......................................................................................... 27 4.2 Sample Descriptions and Petrographic Observations .................................. 27 4.2.1 Non-banded Samples ..................................................................... 33 4.2.2 Banded Samples............................................................................. 34 4.2.3 Petrography .................................................................................... 36 4.3 Backscattered Electron Imaging (BEI) .......................................................... 44 4.4 Mineral Chemistry ......................................................................................... 47 4.4.1 Garnet ............................................................................................. 48 4.4.2 Pyroxene ......................................................................................... 52 4.4.3 Feldspar .......................................................................................... 59 4.4.4 Amphibole ....................................................................................... 59 4.4.4.1 Peak Metamorphic Amphibole .......................................... 61 4.4.4.2 Secondary Amphibole ....................................................... 67 4.4.5 Biotite .............................................................................................. 69 4.5 Bulk Rock Chemistry .................................................................................... 72 CHAPTER V. DISCUSSION ......................................................................................... 74 CHAPTER VI. CONCLUSION ....................................................................................... 85 iii REFERENCES .............................................................................................................. 86 APPENDIX A: GARNET EPMA DATA .......................................................................... 94 APPENDIX B: PYROXENE EPMA DATA ................................................................... 111 APPENDIX C: FELDSPAR EPMA DATA .................................................................... 129 APPENDIX D: AMPHIBOLE EPMA DATA .................................................................. 133 APPENDIX E: BIOTITE EPMA DATA ......................................................................... 151 VITA ............................................................................................................................ 158 iv LIST OF TABLES 1.1. Some recorded occurrences of Cl-rich amphibole and biotite in various high- grade metamorphic terranes ........................................................................................... 2 3.1. List of minerals and their abbreviations .................................................................. 17 3.2. Mineral standards used for electron microprobe analyses ..................................... 20 4.1. Iron-formation sample locations in the Beartooth Mountains .................................. 27 4.2. Visually Estimated Mineral Modes for Quad Creek Samples ................................. 29 4.3. Visually Estimated Mineral Modes for Rock Creek Samples .................................. 30 4.4. Visually Estimated Mineral Modes for Hellroaring Plateau Samples ...................... 30 4.5. Mineral Modes Determined by Point Counts (based on 1000 points) .............................. 31 4.6. Mineral Modes Determined with ImageJ ................................................................ 31 4.7. Representative Garnet Compositions in wt% ......................................................... 49 4.8. Representative Orthopyroxene Compositions in wt% ............................................ 53 4.9. Representative Clinopyroxene Compositions in wt% ............................................. 55 4.10. Representative Feldspar Compositions in wt% .................................................... 60 4.11. Structural Formulae for Primary Calcium Amphibole Endmembers ..................... 61 4.12. Representative Amphibole Compositions in wt% ................................................. 62 4.13. Species and Representative Formulae from Amphiboles in Table 4.12. .............. 65 4.14. Representative Biotite Compositions in wt% ........................................................ 70 4.15. Summary of Representative Biotite Compositions in Table 4.14 .......................... 70 4.16. Bulk Compositions in wt% oxides .................................................................... 73 5.1. Results of Garnet-amphibole-plagioclase-quartz Barometry .................................. 77 5.2. Results of Hornblende-plagioclase Thermometry..................................................
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