Structural geology of Northern Koh Samet, Changwat Rayong

Abstract

Koh Samet is the biggest N-S island in Changwat Rayong. This study emphasized in the northern of Koh Samet. There are the metamorphic rocks in Koh Samet that are mainly schist. Based on evidences in mesoscopic structures and microstructures of study area, the ductile deformation dominates all rock types in study area. Dispersion of poles trend of stereonet can show a pattern of folding. S-folded, M-folded, W-folded, conjugate joint set and minor folds in the field supported ductile deformation. Elongated porphyloblasts are mainly evidences for both dextral and sinistral ductile shear in the field. On thin section, S-C and S-C’ fabrics, mineral orientations, mica fish, and porphyloblasts indicate shear sense both dextral and sinistral. The bulging (BLG), basal gilde, the local grain boundary migration (GBM), undolose extinction and the local subgrain together with the mineral assemblage in quartz indicate low grade metamorphism at the temperature between 300-400°C in greenschist facies. In conclusion, the mesoscopic structures, structural analysis and microstructures analysis were interpreted as folding with shear sense which fits to the flexural shear fold model.