Structure of the Sibumasu–Indochina collision, central Thailand: A section through the Khao Khwang Fold and thrust belt

Abstract

Mainland SE Asia is composed of a number of continental fragments and volcanic arcs, separated by oceanic suture zones, which were accreted to the growing Asian continent during the Triassic Indosinian orogeny. The evolution of this orogeny has always been quite controversial. Indeed, the effects of this orogeny in Thailand have often been interpreted without considering the detailed tectonic evolution of the portion of the Indochina Block’s margin formed by Khao Khwang Platform area of the Saraburi Group, in central Thailand. This area is unusual because: (1) an extensive area representing a thin-skinned fold and thrust belt is well-exposed due to quarrying; and, (2) the fold and thrust belt displays a series of E–W and WNW–ESE striking thrusts and associated folds that are not easily explained in the context of the traditional interpretation where the terranes have been accreted broadly along N–S striking collisional zones. Detailed structural observations in numerous quarries around Highway 21 in a 13km long dip-direction traverse have revealed that overall the thrust belt is composed of several large thrusts with an approximately northwards transport direction. In the southern part of the area, south-verging structures are present. Although the dominant structural trend is northwards-verging, interference structures, and late strike-slip faults indicate there is more than one phase of structural development present.