Structures of the northeasternmost South China Sea continental margin and ocean basin: geophysical constraints and tectonic implications |
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Authors: | Chun-Feng Li Zuyi Zhou Jiabiao Li Hujun Hao Jianhua Geng |
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Institution: | (1) School of Ocean and Earth Sciences, Tongji University, Shanghai, 200092, China;(2) 2nd Institute of Oceanography, State Oceanic Administration, Hangzhou, 310012, Zhejiang, China;(3) Nanhai East Institute of CNOOC Research Center, Guangzhou, 510240, Guangdong, China |
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Abstract: | The northeastern part of the South China Sea is a special region in many aspects of its tectonics. Both recent drilling into
the Mesozoic and new reflection seismic surveys in the area provide a huge amount of data, fostering new understanding of
the continental margin basins and regional tectonic evolution. At least four half-grabens are developed within the Northern
Depression of the Tainan Basin, and all are bounded on their southern edges by northwestward-dipping faults. One of the largest
half-grabens is located immediately to the north of the Central Uplift and shows episodic uplift from the late Oligocene to
late Miocene. Also during that period, the Central Uplift served in part as a material source to the Southern Depression of
the Tainan Basin. The Southern Depression of the Tainan Basin is a trough structure with deep basement (up to 9 km below sealevel
or 6 km beneath the sea bottom) and thick Cenozoic sedimentation (>6 km thick). Beneath the Southern Depression we identified
a strong landward dipping reflector within the crustal layer that represents a significant crustal fault. This reflector coincides
with a sharp boundary in crustal thicknesses and Moho depths. We show that the northeasternmost South China Sea basin, which
may have undergone unique evolution since the late Mesozoic, is markedly different from the central South China Sea basin
and the Huatung Basin, both geologically and geophysically. The Cenozoic evolution of the region was largely influenced by
pre-existing weaknesses due to tectonic inheritance and transition. The South China Sea experienced multiple stages of Cenozoic
extension. |
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Keywords: | Crustal structure Deep crustal reflector Episodic rifting Gravity modeling Seismic stratigraphy South China Sea Tainan basin |
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