Styles of inversion structures and their mechanisms of the Cenozoic Xihu Sag,East China Sea Shelf Basin
Liu Weihong1,2, Lin Changsong1, Guo Zeqing2, Liu Jingyan1, Bo Dongmei3, Song Xiaoyong1
1. School of Energy Resources, China University of Geosciences, Beijing 100083;
2. Ganfang Branch, Research Institute of Petroleum Exploration and Development of China, Langfang Hebei 065007;
3. College of Earth Resources and Information, China University of Petroieum, Dongying, Shandong 257061
The detailed interpretation and analysis of seismic section revealed that evolution of the Xihu Sag, a suborder unit of the East China Sea Shelf Basin,experienced two phases during the Cenozoic,namely,extension from Paleocene to Eocene and fluctuated contraction from ear1y Oligocene to the present.The structural inversion occurred when basin-controlling faults reversed and became compressional ones.There occurred six single inversion structural styles and seven combinational modes.There were two styles of single inversion structures for a fault:both of the upper and lower parts being normal fault,the lower part normal and the upper part reversed fault.Also,there were two styles of single inversion structures for a fold:both of the upper and lower parts being convex,the lower concave and the upper convex.The combinational inversion structures included y-shaped inversion structure,λ-shaped inversion structure, flower-shaped inversion structure,brush structure,etc.The mechanisms of each inversion style were analyzed by calculating the growth index of fault and study of balanced sections.The Xihu Sag, with the thickness of Cenozoic sediments over 10 000 m,experienced multi-phase tectonic inversion,which was closely related to the tectonic evolution of the East Asian continental margin,and influenced by velocity changing between the Pacific plate to the Eurasia.The inversion ratio indicated that the inversion degree might be varied in each belt of the Xihu Sag, the inversion seemed stronger in the Central Uplift Belt, and the West Marginal and the East Marginal Belts being relatively gentle.The study on inversion structures in the Xihu had an important meaning for oil-gas exploration in the shelf of East China Sea.