Digital outcrop model and structural analysis of Ban Pong Quarry, Chiang Mai province

Abstract

Ban Pong quarry in Hang Dong sub-district, Ban Pong district, Chiang Mai province is a surface quarry for soil and gravel products. Lithology composes of semi-consolidated sediments interbedded with coal seams that deposited during Cenozoic age and presents a series of structures related to Cenozoic Tectonic activities in Northern Thailand. This study aims to describe the geological evolution of Ban Pong quarry from Digital Outcrop Model and field investigation that was recorded on the twenty first of January, 2018. The structure in Ban Pong quarry is a family of NS trending normal fault related with the extension in east-west direction. This study divides normal faults in the quarry exposure into two groups, west-dipping normal faults and east-dipping normal faults that is major faults and antithetic normal faults respectively. The antithetic faults on the hanging wall of the major fault is focused in structural analysis process to study the evolution and estimate the deformation rate. According to structural analysis, the stretching of the outcrop exposure is non-uniform in outcrop scale. The upper part of outcrop has higher stretching factor represented by geometry of antithetic faults which is low-angle normal faults. This non-uniform extension is a result from drag along the major fault that caused the hanging wall rotation approximately 35 degrees in clockwise direction. A crustal wideness after extension and an initial crustal wideness were compared to evaluate the length of extension. Therefore, the extension rate of the Cenozoic basin in Northern Thailand based on the hanging wall deformation of the major fault ranges between 0.005-0.007 mm/year.