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Zhen Sun, South China Sea Institute of Oceanology (China)
Zhihong Zhong, Shenzhen branch of CNOOC (China)
Dongsheng Cai, Zhanjiang branch of CNOOC (China)
Xushen Li, Zhanjiang branch of CNOOC (China)
Di Zhou, South China Sea Institute of Oceanology (China)
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From the deformation style on the northern continental margin of the South China Sea and the analogue modeling experiments, we find that the rift zone located on the shelf is characterized by half grabens or strongly asymmetric grabens controlled mainly by long faults with large vertical offset. It's supposed to be formed with normal lithosphere extension. On slope, when the lithosphere is very hot, composite grabens composed of symmetric grabens developed. The boundary and inner faults are all short with small vertical offset, which can't cover the great extension of the slope basin. Between the very hot and normal lithosphere, symmetric grabens, or composite grabens composed of half grabens or asymmetric grabens formed, the boundary faults are long with large vertical offset, while the inner faults are relatively short. Along with the thickness decrease of the brittle part of the crust, the deformation becomes more sensitive to the shape of the pre-existing weakness zone and shows orientation variation along strike. We supposed that the rheological structure of the lithosphere should be modified from the very early stage of rifting affected by the thermal perturbation due to stretching and mantle uprising toward breakup point, which in turn leads to different rifting patterns from shelf to slope. When there is a short bend in the pre-existing weakness zone, and pulled clockwise from southeastward to south southeastward as the northern continental margin of the South China Sea, the strongest deformation always occurs along the middle segment and at the transition area from the middle to eastern segment, which contribute to a hotter lithosphere in the middle segment, where the deep Baiyun sag formed.
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