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Investigation of the High-Pressure Behavior of Amphiboles

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Investigation of the High-Pressure Behavior of Amphiboles INVESTIGATION OF THE HIGH-PRESSURE BEHAVIOR OF AMPHIBOLES A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERISTY OF HAWAI‘I AT MĀNOA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN EARTH AND PLANETARY SCIENCES MAY 2019 By TOMMY W. YONG Thesis Committee: Przemyslaw Dera, Chairperson Bin Chen Julia E. Hammer Keywords: Amphibole, phase transition, high pressure, single-crystal X-ray diffraction, crystallography, diamond anvil cell, synchrotron source Acknowledgements It has been my greatest privilege to have had the opportunity to conduct this research as a student of the University of Hawai‘i at Mānoa. I owe my deepest gratitude to my advisor, Dr. Przemyslaw Dera, without whom it would not have been possible to complete this work. He opened my eyes to the field of high-pressure crystallography, for which I am eternally grateful for. It has been an absolute pleasure working with him over the last two years. Additionally, I am extremely thankful for my committee members, Dr. Bin Chen and Dr. Julia E. Hammer, who provided valuable feedback throughout this project. I am tremendously grateful to have had the opportunity to take classes from the both of you and the knowledge that you both have imparted on me has been invaluable towards the completion of this thesis. I also owe a great debt of gratitude to Dr. Robert Downs and Dr. Hexiong Yang for inspiring me to continue my education in the geosciences and for their mentorship during my undergraduate studies. Many thanks go to my research group, Dr. Hannah Shelton, Dr. Dongzhou Zhang, Dr. Gregory Finkelstein, Dr. Yi Hu and May Chornkrathok for serving as role models, colleagues and friends throughout my time in Hawai‘i and Chicago. I would like to thank the support from the Fred M. Bullard Endowed Graduate Fellowship, National Science Foundation Grant EAR-1722969 and EAR-1541516, the Department of Earth Sciences at the University of Hawai‘i at Mānoa and Hawai‘i Institute of Geophysics and Planetology. Lastly, this thesis would not have been possible without the support of my parents and wife-to-be, Lauren Ward. You are my greatest supporters, my pillar of strength and my inspiration, without you none of this would have been possible. i Abstract Amphibole group minerals are important constituents in many metamorphic and igneous rocks. They have an unusually high chemical variety, which allows them to be used as petrogenetic indicators. Owing to their structural and chemical complexity, developments on quantitative descriptions of amphiboles have been hindered. High-pressure structural studies using a synchrotron X-ray source were conducted on two different amphibole mineral species, namely, grunerite (Fe7Si8O22(OH)2) and gedrite (Mg2(Mg3Al2)(Si6Al2)O22(OH)2). In both minerals, new pressure-induced displacive phase transitions are observed around 20 GPa that closely mirror the phase-transition sequences known in pyroxenes. The phase transitions are characterized by a greater degree of kinking in the double silicate chains of tetrahedra. The experimental findings of this study demonstrate the parallel pressure-induced phase transformation behavior between amphiboles and pyroxenes, suggesting that structures with comparable topology behave similarly in response to high-pressure. In the lithospheric mantle, amphiboles are the most abundant hydrous species, consequently they play an important role in numerous petrological and geophysical processes, such as partial melting and devolatilization. The geophysical implications of the experimental findings of this study are discussed in terms of subducting slabs along disequilibrium pathways that deviate from an average mantle geotherm. The metastable persistence of amphibole group minerals into higher-pressure regimes may have possible implications towards slab buoyancy or as a potential trigger for seismic events. ii Table of Contents Acknowledgements ...................................................................................................................... i Abstract ...................................................................................................................................... ii List of Tables ............................................................................................................................. iv List of Figures ............................................................................................................................. v Chapter 1. Introduction ..................................................................................................... 1 1.1 Thesis Overview ....................................................................................................... 1 1.2 Introduction to Amphiboles ...................................................................................... 2 1.3 Overview of Common Amphibole Crystal Structures .............................................. 3 Chapter 2. Single crystal X-ray Diffraction of Grunerite up to 25.6 GPa: A New High-Pressure Clinoamphibole Polymorph ................................................. 9 2.1 Introduction ............................................................................................................. 10 2.2 Experimental Procedures ........................................................................................ 11 2.3 Results and Discussion ........................................................................................... 16 2.4 Implications............................................................................................................. 22 2.5 Tables and Figures .................................................................................................. 25 Chapter 3. A New High-Pressure Phase Transition in Natural Gedrite ........ 33 3.1 Introduction ............................................................................................................. 34 3.2 Experimental Procedures ........................................................................................ 35 3.3 Results ..................................................................................................................... 40 3.4 Discussion ............................................................................................................... 44 3.5 Tables and Figures .................................................................................................. 50 Chapter 4. Conclusions and Future Work ................................................................ 60 References ............................................................................................................................. 63 iii List of Tables 2.1 Microprobe analyses of grunerite ....................................................................................... 25 2.2 Single-crystal structure refinement details .......................................................................... 26 2.3 Unit cell parameters of grunerite ........................................................................................ 26 2.4 Atomic positional coordinates of grunerite ......................................................................... 27 2.5 Bond lengths of grunerite.................................................................................................... 28 2.6 Equation of state data for grunerite ..................................................................................... 28 3.1 Microprobe analyses of gedrite ........................................................................................... 50 3.2 Microprobe analyses of standards ....................................................................................... 51 3.3 Hydrogen bond distances .................................................................................................... 51 3.4 Single-crystal structure refinement details .......................................................................... 51 3.5 Atomic positional coordinates of gedrite ............................................................................ 52 3.6 Anisotropic displacement parameters of gedrite ................................................................. 55 3.7 Unit cell parameters of gedrite ............................................................................................ 55 3.8 Polyhedra volumes and distortion parameters of gedrite .................................................... 56 iv List of Figures 1.1 C2/m amphibole structure ..................................................................................................... 5 1.2 Pnma amphibole structure .................................................................................................... 7 1.3 P21/m amphibole structure .................................................................................................... 8 2.1 Grunerite (α, β, γ) crystal structure ..................................................................................... 29 2.2 Normalized unit cell parameters of grunerite ..................................................................... 30 2.3 Chain displacement factor in grunerite ............................................................................... 30 2.4 Unit cell volume of grunerite .............................................................................................. 30 2.5 Kinking angle of grunerite .................................................................................................. 30 2.6
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