Three-stage extension in the Cenozoic Pearl River Mouth Basin triggering onset of the South China Sea spreading

Abstract

In the Cenozoic, the East Asian Continental Margin developed intense rifting, producing massive rift basins and marginal seas. Among these, the South China Sea (SCS) and adjacent continental margin have attracted attention due to the obscure opening mechanism and strong lithospheric thinning. Based on the seismic sections and fault architecture data in this paper, we perform a delicate study of fault geometry, kinematics, and dynamics in the Pearl River Mouth Basin (PRMB). Three-stage Cenozoic extension is identified in the PRMB. The earliest NNW-SSE-directed extension occurred as early as the Paleocene, resulting in the NE- and ENE-trending faulting with dextral oblique extension to continue until the Middle Eocene. The second extension in the N-S direction resulted in NE-trending dextral transtension in the Late Eocene to Early Oligocene. Subsequently, the latest extension with the NNW-SSE direction occurred during the Late Oligocene, resulting in the sinistral strike-slip of a large number of WNW-trending faults. This second-third extension produced a NE-striking transtensional fault system with dextral right-stepping characteristics. In the Oligocene, this fault system resulted in the N-S directed scissor-type opening of the SCS with a progressively westward younging oceanic crust. During the Early Miocene, the dextral transtensional fault system disappeared due to the Pacific Plate subduction eastward retreat and the cease of the RRF sinistral strike-slipping. At this time, the SCS ridge spreading was controlled only by the NW-SE-oriented slab-pull linked to the proto-SCS.