THE FORMING MECHANISM OF ZHUJIANGKOU BASIN

Zhoujiangkou basin was developed at the passive continental margin of South China.After the Middle and Late Eocene tectonic event, the basin underwent three evolution stages, i.e. fault down (rifting), warp down (subsidence) and depression. The basin has a tectonic pattern of south-north zonation(NEE trend) and east-west zonation (NE trend).The NE trending structure is formed under the tectonic regime of the early stage.While the NEE trending structure can be related to the north-south extention of South China Sea basin taking place about 32-17 million years ago. The intereaction of the two tectonic regimes created the inharmony between the NE trending structure on the land and the NEE trending structure of the sea area. The Zhujiangkou basin shows that the NEE newly formed structure superimposed on the NE trending inherited structure. The compression occurring in the lower part of the crust caused the extension of the upper part, and made the Zhoujiangkou a great basin. The Moho raised obviously, and a "converted image" is formed with convex at the bottom and hollow at the top. The characteristics of the local structures within the basin depended on the intensity of the movements and their time spans. Zhoujiangkou basin not only possesses some favourable conditions such as large area,thick sediments,and well developed local structure, but also has a rather high geothermal gradient and a rather low intensity in tectonic movement,favouring oil generation and accumulation. Therefore, Zhonjiangkou basin has a bright prospect in oil finding.