Quartz C-Axis Fabric Characterization of the Strike-Slip Ductile Deformation within the Three Pagodas Shear Zone, Western Thailand

The Three Pagodas shear zone is associated with mainland Southeast Asia deformations. The evolution of the shear zone is divided into deformation phases D 1a , D 1b , and D 2 . The first phase (D 1a ) involved ductile sinistral shearing and metamorphism. Foliations show NW–SE trending strike with variable dips from east to west. Stretching lineations are well developed in a NW–SE and flatly plunge to the south. Based on deformation patterns exhibited by outcrop and microscopic analysis, D 1a shows NW–SE trending ductile deformation with sinistral shearing. Additionally, the quantitative analysis of mylonitic quartzite exhibits an oblique angle of quartz graine shape fabric and quartz c-axis fabric asymmetry. Sinistral simple shear was confirmed by kinematic velocity (W k ). The spatial distribution of the kinematic velocity number (W k ) of D 1a shows a range between 0.93 and 0.99 at the central and western parts of the shear zone, which is higher than the 0.82–0.85 range for the eastern part of the shear zone. The strain variation within the Three Pagodas shear zone derived from the kinematic velocity number (W k ) shows that the central and the western parts have been deformed under simple shear more than the eastern part. D 1b is dominated by sinistral transpression, which is related to the exhumation of a lens-shaped high-grade metamorphic complex. The last stage (D 2 ) is represented by dextral strike-slip faults, which is the inversion of this strike-slip system.