NE-trending transtensional faulting in the Pearl River Mouth basin of the Northern South China Sea margin

Abstract

The joint tectonic interaction to the Pearl River Mouth Basin (PRMB) between the collision of the Indo-Australia and Eurasian plates and the subduction of the Pacific Plate (the Philippine Sea Plate) made the present-day complex structures. The basement of the northern South China Sea (SCS) margin has an affinity to the South China Block basement, which has experienced multi-stage tectonic events. The divisions of tectonic units and events, and dynamics of the PRMB are always controversial. Based on the structural analysis to seismic interpretation, and taking the Xijiang, Baiyun and Liwan sags as examples, we conclude that the PRMB sub-basins are transtensional basins. The PRMB can be subdivided into three Cenozoic structural layers in profiles from bottom to top: Early Cenozoic graben, Mid-Cenozoic half-graben and Late Cenozoic depression. In the early Cenozoic (∼55–45 Ma), the Izanagi-Pacific Mid-ocean Ridge subducted beneath the East Asian Continental Margin, and the study area entered the NNW-SSE diffusive extension stage, forming the ENE-trending wide rift. In the middle Cenozoic (45–25 Ma), the Paleo-Pacific Plate subducted from NNW to WNW under the East Asian Continental Margin, and the Mesozoic structure was activated, showing NE-NNE-trending dextral faulting. In the late Cenozoic (since 25 Ma), the Philippines Sea Plate wedged WNW-ward, and the South China Sea began to subduct eastward under the Philippines Sea Plate. Combined with the extrusion of the Indochina Block, the regional stress field was dominated by the NNE-SSW-directed extension, and the NW-trending sinistral structures developed.