| Based on geological structural interpretation of High-precision3D and2D seismic profiles, combined with Previous studies, geometry and kinematics characteristic of faults system in Baiyun Sag which is located on the continental slope have been studied by using theoretical analysis of geologic analysis such as basin nalysis, in dynamic analysis, plate tectonictheory, and analytic structural geology et al. while, balanced cross sections were used to renew the evolution of faults system in Baiyun Sag. Combined with the results of previous studies and the regional geological setting, the developmental mechanisms and the controlling factors of Baiyun Sag faults system have been analyzed. At the same time, this paper discussed the evolution model of fault systems on the slope of deep water.Baiyun Sag mainly developed transtensional normal faults, reverse faults is less. The faults system that are small-scale and little throw mainly distributed in the peripheral slope of Baiyun Sag. There are NWW-trend faults, NEE-rend faults and nearly EW-rend faults, while the NWW-rend faults were the dominant faults system. The trend of faults is clockwise rotation over time in the Cenozoic. In vertical sections a single fault may be of platy or listric shape, while multiple faults form ladder, parallel, flower, or fastigiated shape combinations. On plane view these faults form parallel, fastigiated, or en echelon combinations. According to the distribution faults can be divided into northeast slope, north slope and southwest slope. There are parallel, flower, and fastigiated shape combinations in northeast slope, parallel and ladder in north slope, while ladder in southwest slope.With multi-phase characteristic of the activities in cenozoic, faults sustained activity during post-rifting stage, while some faults devoleped to pleistocene strata. Activities of faults during rifting stage were strongly. There are two activities of32-21Ma and18.5-16.5Ma, and the activities after12.5Ma increased with little strength. Activities of faults were strong west to east during post-rifting phase in the northern slope of Baiyun Sag, while the east activity time is longer than the west during the second phase of the activities that is between18.5Ma to16.5Ma. Nearly EW-rend faults have reduced after23.8Ma, and NEE-trend faults reduced after15.5Ma.The thinning and stretching of lower crust controlled the morphological characteristic of the continental shelf break zone in Baiyun Sag, at the same time, the flowing of lower crust may be the main controlling factor of the continental shelf break zone occured north transition at23.8Ma. With thinning and stretching of crust and high heat flow in the region, the center of main sag stretching plastically and don’t developed faults. With the heat flow is reduced, faults developed in the the peripheral slope of Baiyun Sag that is a transition zone of plastic and brittle. The gravitational potential that formed by the main sag continuing subsided strongly was the main factor that controlled faults development and tectonic activities. Cenozoic stress field of Baiyun Sag by nearly NW-SE to SN clockwise rotation. The evolution of cenozoic stress field influenced by NW-trending subduction of Pacific plate, NNE-trending extrusion of Indian plate and the rifting of the South China Sea formed weakly compressive stress on northern margin.With crust stretching and rupture, asthenosphere upwelled in the rifting stage. Baiyun Sag developed Half-grabens, while the center of main sag deformed plastically. Faults that controlling sedimentation stretched strongly. With the rapid subsidence of mian sag, faults appear sustained activities and control sedimentation weakly. Both activities faults and quiet faults being in the stage of fault block uplift and subsidence. To some extent, Dong Sha movement activated faults in the study area, while Baiyun Sag deposited deepwater sediment. |
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