The Origin of Complicated Fault System in Beibuwan Basin and the Application for the Evolution of South China Sea

Abstract

Beibuwan Basin, located in the north part of South China Sea, is rich in oil and gas resources. In the whole Beibuwan Basin, 3D high-precision seismic data are obtainable. The fault system in Beibuwan Basin is as complicated as that in other rift basins in the Southeast China. Interpretation of the whole 3D seismic data, results of sandbox modeling, and theoretical analysis with application of our new brittle faulting model with multiple pre-existing weaknesses are used to investigate the complicated fault systems of Beibuwan basin. Results show that Beibuwan basin are formed by the superposition of two-phase extension with different directions. In the first rifting stage during E1ch-E2l2 (65-38Ma), the regional extension direction is NW-SE (about N 40°W), and the boundary fault of the basin is Weixinan Fault (strike N 50°E). In the second-phase rifting (E3W, 38-23.3Ma) and post-rifting (N-Q, 23.3-0 Ma), the regional extension direction rotates to N-S direction. No.1 Fault becomes the north boundary fault of the basin, while the activation process of Weixinan fault stops. During the post-rifting, a large number of faults keep active. Extension of NS direction continues, but the extension intensity reduces. This tectonic model can reasonably explain all phenomena of the complicated fault systems in Beibuwan basin. This tectonic model has a significant influence on the evolution of South China Sea, which is a key region to understand the interactions among the plates of Eurasia, India - Australia, the Pacific and Philippine. However, the origin mechanism and spreading history of South China Sea are still controversial. According to the origin of the fault system in Beibuwan basin, the origin of South China Sea is the result of extension of NS direction, and the South-west Trough (NE trend), which is on the basis of a large pre-existing weakness. The analysis also shows that the strike-slip activation of Honghe Fault in the north part of South China Sea is passive. As such, the tectonic escape model of Tapponnier (1982) for the origin of South China Sea can be excluded.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016