Longmen Shan fold-thrust belt and its relation to the western Sichuan Basin in central China: New insights from hydrocarbon exploration

Abstract

The Longmen Shan fold-thrust belt is one of the key regions of demonstrable Mesozoic–Cenozoic tectonic evolution in China, and the Sichuan Basin was the first natural-gas-producing area in China. In this article, the structural features of the Longmen Shan belt are presented, using both seismic profiles and field data. The complex structures of the northeast-trending Longmen Shan fold-thrust belt and its foreland in the western Sichuan Basin are formed by southeast-directed thrusting. Several eastward-verging, rootless thrust sheets and imbricates of Cambrian–Triassic rocks have been recognized in the northern Longmen Shan belt. Evidence suggests that the northern Longmen Shan belt experienced at least two major periods of deformation in the Late Triassic and Cenozoic. However, the southern Longmen Shan belt is represented by the basement-involved thrust structures and klippen, and its major periods of deformation were in the latest Cretaceous–early Cenozoic. Sedimentary features in the western Sichuan Basin reflect a two-phase flexural-loading history and illustrate that the Late Triassic foreland basin extends along the foredeep of the entire length of the Longmen Shan belt, but the uppermost Cretaceous–Paleogene rejuvenated foreland basin is restricted in the southern part of the western Sichuan Basin. Structural geometries suggest that prospective traps are mainly developed in the frontal zone of the Longmen Shan fold-thrust belt and in the southern part of the western Sichuan Basin. One of the major contributions of this article is finding preexisting Paleozoic rift basins under the Cenozoic thin-skinned thrust belts, which represent a new potential hydrocarbon play.