Evolution of pull-apart basins with overlapping NE-trending strike-slip fault systems in the northern South China Sea margin: Insight from numerical modeling

Abstract

A pull-apart basin is a significant type of oil-bearing basin. Its formation mechanism is a hot and challenging issue in geodynamic research that involves the interaction of three-dimensional faults and stress states. In particular, the systematic and quantitative interpretation of the three-dimensional mechanism is not clear. Therefore, we use ASPECT simulation software to analyze how the main dynamic parameters affect the evolution of the basins. The following features were recognised: (1) The greater the degree of overlapping between parallel strike-slip faults, the longer the time of rapid subsidence at the initial stage, but the larger the range of subsidence and the shallower the depth of subsidence at the final stage. (2) All models generate two small basins at the beginning, but they connected together at different stages. The antithetic end-member models of different spacing faults subsided rapidly at the initial stage. However, the two independently developed small basins were connected with time. (3) Based on the comprehensive comparison of numerical modeling results with the evolution of strike-slip faulting in the Pearl River Mouth Basin (PRMB) in the northern South China Sea margin, this paper proposes that the 120° overlapping releasing stepover pattern is likely dominant at the early stage. Furthermore, this study finds a linear relationship between the strike-slip displacements and the depths of basin depocenter. Based on this relationship, the displacements of master strike-slip faults on both sides of the Baiyun Sag of the PRMB are less than 3.5 km. It can further help to understand the formation mechanism of the PRMB.