Thermal Structure of Mid-Crustal Shear Zones

Analysis of quartz c-axis fabrics and microstructures from ductily deformed rocks allows for the examination of the kinematics associated with crustal deformation. This thesis expands on the current knowledge of the kinematic evolution of the Himalayas and Scottish Caledonides, by examining samples from the Main Central Thrust (MCT) (Himalayas) and the Sgurr Beag Thrust (SBT) (Scottish Caledonides). Metamorphic temperatures (Tm) associated above the MCT are inverted; chapter one attempts to test if deformation temperatures (Td) correlate to Tm, indicating that ductile shearing occurred during peak Tm. In the Scottish Caledonides, Td and Tm increase from foreland to hinterland, potentially indicating a right way up thermal structure; chapter two presents Td and Tm associated with the region around the SBT. Above the MCT, quartz c-axis fabrics yield Td ranging between 500-650 °C, corresponding to the temperatures of dynamic recrystallization for subgrain rotation (SGR) and grain boundary migration (GBM). Up to 1000m above the MCT, Td and Tm are within error of each other, suggesting that shearing occurred during peak Tm; while further away from the MCT Tm is significantly hotter than Td, suggesting that shearing continued past Tm. Deformation associated with the upper part of the Moine thrust sheet and the SBT yields quartz c-axis fabrics with Td ranging between 395-583 °C, corresponding to the regional dynamic recrystallization. Tm calculations original to this study yield pressure-temperature constraints of 4.8-5.8 kbar and 586-625 °C. Tm is within error of Td, suggesting that deformation and metamorphism were synchronous. Acknowledgments First and foremost my parents, Ralph and Kate Mazza, deserve much credit and thanks for all they have done for me. They raised me to peruse my dreams and allowed me to develop into the woman I am today. They encouraged constant discovery through multiple life enhancing experiences. Without their constant support I would not be where I am today. Anne Mazza, my little sister who always has (and always will) inspired me to be the best person I can be. Drew Coleman and Allen Glazner, my undergraduate professors and mentors who sparked my curiosity for geological sciences. Rick Law, my Masters advisor, who provided the ideal amount wisdom and support. He has allowed me to develop this thesis around ideas and concepts I found interesting, all the while encouraging me to further grow as a geologist. I have valued the time we have worked together, both in the lab and in the field, and look forward to future years as colleagues and friends. And to his wife, Clare, who provided good laughs and times both in Ullapool and at the pub in town. Mark Caddick and Jim Spotila, mentors and committee members who provided discussion that enhanced my learning and geologic discovery. Don Stahr, Matt Francsis, Kyle Ashley, and Nick Heaverlo, who kept ideas flowing in the office, and served as much needed sounding boards. Lastly, my amazing boyfriend, James Dale, who has always shown support of my academic development. I have learned so much about life with him, and have cherished all of our adventures.