The NW trending Mae Ping shear zone exposes high-grade metamorphic rocks, the so called Lansang gneiss in the Tak region, western Thailand. The lithologies within the strike-slip zone mainly consist of orthogneisses and paragneisses. Using Fry's method for 2-dimensional strain analysis we find that the averaged finite strain ratio (R s ) of the XY-plane is R s = 1.35-1.69. Based on the kinematic vorticity analysis of the mylonitic gneisses in the shear zone, the kinematic vorticity number is W k = 0.8-1.0 with an average of W k = 0.95. The results imply that the homogeneously deforming rocks within the Mae Ping shear zone have a strong simple shear component with a minor pure shear contribution of about 15 %. The kinematic indictors from both outcrop and micro scopic scales indicate a sinistral strike-slip shear sense. We conclude that the Mae Ping shear zone accommodated crustal scale sinistral transpression.
The NW–trending Three Pagodas shear zone exposes a high–grade metamorphic complex named Thabsila gneiss in the Kanchanaburi region, western Thailand. The quartz mylonites within this strike–slip zone were selected for strain analysis. 2–dimensional strain analysis indicates that the averaged strain ratio (Rs) for the lower greenschist facies increment of XZ– plane is Rs = 1.60–1.97 by using the Fry’s method. Kinematic vorticity analysis of the quartz mylonites in the shear zone showed that the mean kinematic vorticity number of this increment is Wk = 0.75–0.99 with an average at 0.90 ±0.07. The results implied that the quartz mylonites within the Three Pagodas shear zone have a dominant simple shear component of about 72% with a small pure shear component. A sinistral shear sense is indicated by kinematic indicators from macro– to micro–scale. We conclude that the Three Pagodas shear zone deformed in the process of sinstral shear–dominated transpression, which is similar to the Mae Ping shear zone in the north.
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