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Tectonic Framework and Multiple Episode Tectonic Evolution in Deepwater Area of Qiongdongnan Basin,Northern Continental Margin of South China Sea

LEI Chao1,2,REN Jian-ye1,2,PEI Jian-xiang3,LIN Hai-tao1,YIN Xin-yi1,TONG Dian-jun1 1.Faculty of Earth Resources,China University of Geosciences,Wuhan 430074,China 2.Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education,China University of Geosciences,Wuhan 430074,China 3.China National Offshore Oil Corporation Limited,Zhanjiang 524057,China  
Based on geological structural interpretation of a number of available high-resolution geological-geophysical and drilling data etc.,a tectonic framework with zonal array in N-S direction and block division in W-E direction was established in deepwater area of Qiongdongnan basin (QDNB). A key tectonic revolutionary boundary,T70,was identified in QDNB by integrated analysis of tectono-stratigraphy,subsidence history and subsided depocentre migration. A series of small distributed NE-trending faulted basins developed widely below this boundary,while basin depocentre of QDNB above T70 boundary is located in center depression area trending NE-WE-NWW,forming a great fault-sag type basin,which is superimposed clearly over underlying faulted basin group above. Analyses of genetic type and geometry of basin-boundary fault indicate that NW-SE extensional tectonic stress field strongly controlled development of small distributed NE-trending faulted basin group underlying T70 boundary,and nearly SN extensional tectonic stress field resulted in formation of fault-sag basin over this boundary. The T70 boundary can be found and traced in northern continental margin basins of South China Sea. The evidence of regional and biostratigraphical correlation shows that the age of this boundary is 32 Ma,which is consistent with the time of initial spreading of South China Sea. Thus T70 boundary is a regional tectonic revolutionary boundary. The development of this boundary leads to complexity of tectonic framework and structure evolution. According to the T70 boundary,combining with other important boundaries identified in previous literatures in the basin filling sequence and subsidence analysis,four tectonic evolution episodes of QDNB,which are syn-rifted episode,fault-sag episode,post-rifted thermal subsidence episode and post-rifted accelerating subsiding episode,are proposed in this paper. Finally,Cenozoic lithospheric dynamic,kinematical reorganization of plates circum-South China Sea controlling on these tectonic episodes are discussed in depth.
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