A NEW MODEL FOR THE ORIGIN AND EVOLUTION OF THE RIFT BASIN FAULT-SYSTEMS IN THE EAST AND SOUTH CHINA –A CASE STUDY FROM BEIBUWAN BASIN

Rift basins are rich in oil and gas resources (Tian, 1996; Wu, 1997). Especially in China, about two-thirds of total oil reserves and production came from the rift basins in the east and south China (Jin et al., 1998). There are dozens of Cenozoic rift basins, such as Bohai Bay basin, Southern Yellow Sea basin, East Sea Continental Shelf basin, Beibuwan basin, Qiongdongnan basin and so on, along the coast of south-east Asian continent (onshore and/or offshore). The existing models of fault-system origin and tectonic evolution, which mainly based on Anderson’s faulting model and usually leaded to complicated tectonic evolution history, can not explain the phenomena of complicated fault system very well and were controversy with each other. On the basis of 3D seismic data interpretation, balanced evolution section reconstruction and sandbox modeling on Beibuwan basin, meanwhile, considering the basement pre-existing fabrics and applying the Activation Criterion of pre-existing fabric (Tong et al, 2010), a new model of two phases extension superposition (SE-NW direction extension before 40Ma and N-S direction extension after 40Ma) is proposed for the fault-system origin and evolution in Beibuwan basin in the paper. The model shows that the pre-existing fabrics, the superposition of two phases extension and progressive extension leaded to the complicated fault system in Beibuwan basin. Using this model, the complicated fault system in Beibuwan basin can be reasonably understood and interpreted. It played an important role in oil exploration afterwards. The model can also be used to reasonably explain the origin and evolution of basin fault-system in the east and south China. This model may provide a new insight into the tectonic evolution history in the east Asia.