[S-MP21] Oceanic and Continental Subduction Processes: petrologic and geochemical perspective

[SMP21-P05] Structural evolution in southern extension of the Klaeng fault zone, eastern Thailand

*Kittichai Chansom¹, Pitsanupong Kanjanapayont¹ (1.Basin Analysis and Structural Evolution Research Unit, Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand)

Keywords:Deformation, Structural geology, Klaeng fault zone, Klaeng tectonic line, Thailand

The rock within southern extension of the Klaeng fault zone plays an important role in understanding the deformation history in eastern Thailand as a part of Klaeng tectonic line between the Sibumasu block and Chanthaburi terrane. The geology of rock is mostly consisting of Middle-Upper Paleozoic clastic sedimentary rocks, Ordovician mylonitic and low-to-medium-grade metamorphic rocks, Triassic quartz-rich S-type (west) and I-type (east) granite rocks, and Mesozoic red bed sandstone. Field observation and structural analysis reveal that the rocks within this area experienced mainly four deformation events (D₁-D₄). The first deformation (D₁) found in Middle-Upper Paleozoic clastic sedimentary rock which exhibits NNE-SSW to NE-SW trending of fold with tight to isoclinal folding. It was strongly deformed by a compressional stress, predominantly in W-E to NW-SE compression during the Triassic Indosinian orogeny. The second deformation (D₂) found in red bed sandstone that displayed a gentle dipping angle and open folding structure by striking in NNW-SSE to NE-SW which resulted from the transpressional stress in mostly W-E direction. The third deformation (D₃) is observed in granite including with top-to-the-E (normal) ductile shear sense for S-type granite, and a well-developed in sinistral ductile shear sense (strike-slip) for I-type granite. The last deformation (D₄) is dominantly showed by an overprinting of brittle deformation of fracture sets over every deformation which may occurred in the late of D₃ or younger. The D₃ and D₄ were tectonically influenced from the movement of intra-continent strike-slip fault through out SE Asia from the early phase of India-Eurasia collision in Himalayan orogeny.