Tectono-stratigraphy of Late Carboniferous to Triassic successions of the Khorat Plateau Basin, Indochina Block, northeastern Thailand: Initiation of the Indosinian Orogeny by collision of the Indochina and South China blocks

Abstract

The late Paleozoic and early Mesozoic Indosinian Orogeny in Southeast Asia was characterized by subduction in the Paleo-Tethys and collisions among continental blocks and fragments. The Khorat Plateau Basin in northeastern Thailand covers much of the Indochina Block and was subjected to complex tectonic activity during the late Paleozoic and Mesozoic. The Mesozoic sequence of the basin comprises thick, gently folded non-marine sediments that include red beds and is separated from the underlying upper Paleozoic sequence by the major angular unconformity of the Permo-Triassic boundary, which we refer to as the “Indosinian I event” in the Khorat Plateau Basin. Seismic and well data acquired for oil and gas exploration indicate that the upper Paleozoic sequence is heavily faulted and structurally complex. Our study showed that in some areas about 2000 m of the upper Paleozoic sequence has been eroded at the Indosinian I unconformity, although thicknesses of up to ∼6000 m of upper Paleozoic rocks remain in some areas. Previous interpretations of oil and gas exploration data attribute the erosional event to back-arc closure due to collision of the Indochina and Sibumasu blocks during subduction in the Paleo-Tethys Ocean. However, our detailed structural mapping indicated that the Indosinian I unconformity was a consequence of the collision of the Indochina and South China blocks during the late Permian to Middle Triassic. We propose that this collision initiated the Indosinian Orogeny in mainland Southeast Asia.