Thermal Structure of Mid-Crustal Shear Zones

• Main Author: Mazza, Sarah Elizabeth
• Other Authors: Geosciences
• Format: Others
• Published: Virginia Tech 2013
• Subjects: quartz fabric; deformation temperature; dynamic recrystallization; P-T conditions; Main Central Thrust; Sgurr Beag Thrust
• Online Access: http://hdl.handle.net/10919/23284

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. === Master of Science