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Temperature and Pressure Conditions of Archean Amphibolite-Granulite

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Temperature and Pressure Conditions of Archean Amphibolite-Granulite Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 2013 Temperature and pressure conditions of Archean amphibolite-granulite facies metamorphic xenoliths from the eastern Beartooth Mountains, Montana and Wyoming, USA Celina N. Will Louisiana State University and Agricultural and Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses Part of the Earth Sciences Commons Recommended Citation Will, Celina N., "Temperature and pressure conditions of Archean amphibolite-granulite facies metamorphic xenoliths from the eastern Beartooth Mountains, Montana and Wyoming, USA" (2013). LSU Master's Theses. 3997. https://digitalcommons.lsu.edu/gradschool_theses/3997 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]. TEMPERATURE AND PRESSURE CONDITIONS OF ARCHEAN AMPHIBOLITE-GRANULITE FACIES METAMORPHIC XENOLITHS FROM THE EASTERN BEARTOOTH MOUNTAINS, MONTANA AND WYOMING, USA 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 Celina N. Will A.B., Mount Holyoke College, 2009 May 2013 ACKNOWLEDGMENTS I thank my committee, Drs. Darrell Henry, Barb Dutrow and Jeff Hanor, for their valuable feedback and support over the past four years. Rick Young deserves special recognition for assistance with sample preparation and maintenance of instrumentation. Dana Thomas served ably as a field assistant during sample collection and as a magnificent DJ during our road trip. Dave Mogk and Gwendy Stuart are recognized for their kind hospitality while in Bozeman. Doug Tinkham helped tremendously with Theriak-Domino. The graduate school editors are not thanked. Lastly, but most importantly, my family is thanked for letting me play with rocks and hammers as a child. They rock. This project was funded by the Southeastern Geophysical Society, the Louisiana State University Department of Geology and Geophysics and the National Science Foundation (EAR #0609948). ii TABLE OF CONTENTS ACKNOWLEDGMENTS……………………………………………………………..…….……ii LIST OF TABLES……………………………………………………………...……..……...…...v LIST OF FIGURES………………………………………………………..…………..…………vi ABSTRACT……………………………………………………………………………...….…...ix CHAPTER I. INTRODUCTION……………………………………………………….…………1 1. Introduction……………………………………………………………...………...……1 CHAPTER II. GEOLOGIC SETTING……………………………………………..…..…………3 2.1 Wyoming Province…………………….………………………………...……………3 2.2 Beartooth Mountains……………………………………………………..…..………..6 2.2.1 Metamorphic ages and age constraints of xenoliths……………...………... 9 2.2.2 Structure………………………………………………………..…………. 12 CHAPTER III. METHODS……………………………………………………...….…...………14 3.1 Field Methods……………………………………………………….…….………... 14 3.2 Petrographic and Microanalytical Methods. …………………………………….......14 3.2.1 Petrographic Analysis……………………………………….…….….…....14 3.2.2 Mineral Chemical Analysis………………………………….…….….…....15 3.3 Determination of Pressure-Temperature Conditions……………….……………......16 3.3.1 Thermobarometers…………………………………………..…………......17 3.3.2 Petrogenetic Grids…………………………………………...…………......19 3.3.3 Equilibrium Assemblage Diagrams (Pseudosections) …………...……......20 CHAPTER IV. RESULTS………………………………………………………...………….….28 4.1 Sample Locations…………………………………………...………………..……... 28 4.2 Mafic Rocks…………………………………………………………...…..………... 30 4.2.1 Bulk Compositions……………………………………..……….………... 30 4.2.2 Melting Conditions Determined by Mafic Melt Geothermobarometry……32 4.2.3 Field and Petrographic Observations…… …………….………..………... 32 4.2.4 Mineral Chemistry……………………………………..………..………... 36 4.2.4.i Amphibole……………………………………………………......36 4.2.4.ii Garnet………………………………………..………………......37 4.2.4.iii Plagioclase……………………………………………………....38 4.2.4.iv Alkali-Feldspar……...……………………………….….……... 40 4.2.4.v Biotite………………………………………...……….….……... 40 4.2.4.vi Pyroxene……………………………………..……….………... 40 4.2.4.vii Epidote…………………………………………...…..………... 42 4.2.5 Thermobarometry…………………………………………….…………... 42 4.2.6 Pseudosections……………………………………………….….………... 47 4.2.6.i Amphibolite 125/53…………………………………..…..……... 47 iii 4.2.6.ii QC-51………………….……………………………...………... 48 4.2.6.iii QC-53………………………..…………………….…………... 51 4.2.7 Comparison of pseudosection and thermobarometry for QC-53 .................52 4.3 Sillimanite-Biotite-Quartz Mylonitic Gneisses………………….…………...……... 52 4.3.1 Sample Descriptions and Petrography…………….…..…………...……... 52 4.3.2 Chemical Analyses………………………………….……………...……... 57 4.3.3 Ti-in-biotite Thermobarometry………………………….…..…..………... 60 4.3.4 Interpretations…………………………………………………..….……... 61 4.4 Anthophyllite-Biotite-Quartz-Cordierite-Orthopyroxene Gneiss……..……..……... 63 4.4.1 Sample Description and Petrography…………………..……..…………... 63 4.4.2 Mineral Chemistry…………………………………………..………..…... 71 4.4.3 Pressure and Temperature Determinations……...………….……...……... 74 4.4.3.i Ti-in-biotite Thermometry…………………………..…………... 74 4.4.3.ii Pseudosections……………………………….…..……………... 75 4.4.4. Interpretations..…………………………………………..……..………... 76 CHAPTER V. DISCUSSION………………………………………………........………………81 CHAPTER VI. CONCLUSION..……………………………………………......………………85 REFERENCES………………………………………………………………..…..…………..…87 APPENDIX A: SUMMARY OF SAMPLE MINERAL ASSEMBLAGES..…….……………..92 APPENDIX B: BIOTITE EPMA DATA………………………………………..………………93 APPENDIX C: GARNET EPMA DATA……...…….………………….………………………97 APPENDIX D: EPIDOTE EPMA DATA………………………………………………….……99 APPENDIX E: CORDIERITE EPMA DATA………….…………………..….………………100 APPENDIX F: PYROXENE EPMA DATA…………..………………………...……..………101 APPENDIX G: PLAGIOCLASE EPMA DATA……...…………………...……..……………106 APPENDIX H: AMPHIBOLE EPMA DATA………...……………………….…....…………111 . VITA…………………………………………………………………………….……………...121 iv LIST OF TABLES 1. Mineral Abbreviations………………………………………………………………...…15 2. Mineral Standards for Electron Microprobe Analyses………………………………..…16 3. Sample Locations………………………………………………………………………...28 4. Mafic Sample Bulk Rock Compositions……………………..………………………..…30 5. Mafic Magma Thermobarometry Results………………………………………………..32 6. Mafic Sample Hornblende-Plagioclase Results …………………………………………43 7. Hornblende-Plagioclase Temperatures for Sample QC-53………………………………45 8. GBPQ Pressures for Sample QC-53………………………………………………..……46 9. GAPQ Pressures for Sample QC-53………………………………………………..……46 10. Sillimanite-Biotite Gneiss Ti-in-biotite Temperatures…………………………………..61 11. Orthopyroxene-Cordierite Gneiss Ti-in-biotite Temperatures…………………….…….74 v LIST OF FIGURES 1. Map of western North America showing the location of Precambrian provinces and the setting of the cratonic Wyoming Province …………..……………………………………4 2. Map showing the subprovinces of the Wyoming Province…………….…………………5 3. Map showing the subdomains of the Beartooth Mountains………………….……………7 4. KFMASH Petrogenetic grid for peraluminous migmatites from Hellroaring Creek…....11 5. Reproduction of Figure 2a from Diener et al. (2008) pseudosection of cordierite- orthoamphibole gneiss in FMASH………………………………………………………24 6. Reproduction of Figure 4a from Diener et al. (2008) pseudosection of cordierite- orthoamphibole gneiss in NCKFMASH……………………………………………. …..25 7. Reproduction of Figure 2a from Nagel et al. (2012) pseudosection of N-MORB...……26 8. Reproduction of Figure 2b from Nagel et al. (2012) pseuodosection of a tholeiite……..27 9. Location map for samples collected during summer 2010………………………...…….29 10. Outcrop photograph of a xenolithic amphibolite/granulite ……………………...………33 11. Photomicrographs of amphibolite/granulite…………………………………....………..33 12. Photomicrographs of large clinopyroxene in an amphibolite/granulite………….………34 13. Photomicrographs showing patchy development of amphibole and pyroxene with vermicular epidote……………………………………………………………………….34 14. Photomicrographs of a garnet-biotite gneiss…………………………………..…………35 15. Amphibole classification diagram for mafic rocks……………………….. …………….37 16. Compositional profile for a garnet traverse……………………………..………...……..38 17. Backscatter electron image showing analyzed points in a garnet traverse.………….…..39 18. Biotite compositions from all mafic samples plotted according to Ti (apfu) and XMg…..41 19. Biotite compositions from all mafic samples plotted according to Al (apfu) and XMg….41 20. Hornblende-plagioclase temperatures for mafic samples ……………………………….44 vi 21. Ti-in-biotite temperatures for mafic rocks ……………………………………………....46 22. Pseudosection for sample 125/53 with H2O calculated from analysis…………….…….49 23. Pseudosection for sample 125/53 with excess H2O ……………………………..………50 24. Pseudosection for sample QC-51 with H2O calculated from analysis ……………..……53 25. Pseudosection for sample QC-51 with half H2O calculated from analysis …….……….54 26. Pseudosection for sample QC-51 with excess H2O ……………………………………..55 27. Pseudosection for sample QC-53 with H2O calculated from analysis………………...…56 28. Photomicrographs of a sillimanite-biotite gneiss showing typical field of view ….…….57 29. Photomicrographs of a sillimanite-biotite gneiss showing acicular sillimanite...……….58 30. Photomicrographs of a sillimanite-biotite gneiss showing local folding….…………….58 31. Photomicrographs of a sillimanite-biotite gneiss showing fibrolite mat….…………….59 32. Photomicrographs of a sillimanite-biotite gneiss showing acicular sillimanite nucleating on biotite and graphite……………………………...……………………………...…….59
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