Cenozoic characteristics and transformation mechanism of fault system in Zhu-1 depression, South China
Hu Yang1, Wu Zhiping1, Zhong Zhihong2, Zhang Jiangtao3, Yu Weigao1, Wang Guangzeng1, Liu Yiming1, Xie Fei1
1. School of Earth Sciences and Technology, China University of Petroleum(East China), Qingdao, Shandong 266580;
2. Shenzhen Branch of CNOOC, Guangzhou 510240;
3. Tianjin Branch of CNOOC, Tianjin 300450
Based on static characterization and dynamic analysis of the Cenozoic fault system characteristics in Zhu-1 depression, this paper analyzed spatio-temporal difference of fault system by using abundant 3D seismic data, and then discussed its transformation mechanism. The results showed that the difference and transformation of fault system were controlled by different regional dynamic backgrounds and lithospheric difference extension mechanisms. During rift stage(E2w-E2e), the strikes of basin-controlling faults changed from NNE and NE-NEE-trending to EW and NWW-trending. And lithospheric extension changed from wide rift system to narrow rift system and migrated from land(north)to ocean(south)as well, which resulted in the northward migration of faulting and faults in the south was less active than that in the north. It might attribute to the rotating extrusion of Indochina block and subduction of proto-South China Sea, which led to the clockwise rotation of regional tensional stress from NW-trending to NS-trending and the episodic evolution of the faults. While during depression stage(E3z—N1z-N1h), the activity of fault was weak, it might because the extensional center of lithosphere had migrated southward to spreading center of the South China Sea and the northern margin of the South China Sea was in the stage of post-rift subsidence. Then in tectonic activation stage(N1y-N2w—Q), NWW and subparallel EW pre-existing faults reactivated and the strike slip faults formed, which might be due to the NEE-trending dextral strike slipping resulted from arc-continent collision. Therefore, the characteristics of current fault system reflects the superimposed effect of multistage tectonism, and the identification of temporal and spatial differences of faults could be used as an important guideline for the oil and gas exploration in Zhu-1 depression.