Deformation Styles of the Uthai Thani-Nakhon Sawan Ridge within the Chainat Duplex, Thailand

Uthai Thani-Nakhon Sawan structural ridge is the 35 km mountain length lying in N-S direction within the Chainat duplex at the Central Thailand. The ridge, which is clearly seen from satellite image in the flat areas of the Central Plain, is composed of Triassic mylonitic granite and Silurian-Devonian metamorphosed sedimentary rocks. Satellite image interpretation, geological mapping, field data and microstructure analysis have been integrated for the understanding of structural style of Uthai Thani-Nakhon Sawan ridge. The rocks within the ridge had been deformed under sinistral ductile shear which was shown by foliations, stretching lineations, S-C fabrics, sigmoid clasts, mineral fish and S-folded both in outcrops and under microscope. The major N-S, minor NNW-SSE striking ridges and foliation planes indicate the paleostress of σ₁ in the NW-SE direction. The major sinistral motion of this region probably ended at ~30 Ma. All structural elements and deformation style of Uthai Thani-Nakhon Sawan ridge relate to the Chainat duplex geometry and Mae Ping fault zone activity during Tertiary.