Journal of Tropical Oceanography ›› 2023, Vol. 42 ›› Issue (3): 96-115.doi: 10.11978/2022133CSTR: 32234.14.2022133

• Marine Geology • Previous Articles     Next Articles

Heterogeneous extension and pulsed tectonic subsidence in the northern South China Sea margin*

ZHAO Zhongxian1,2,3(), SUN Zhen1,3(), MAO Yunhua4, ZHANG Huodai2   

  1. 1. CAS Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou 511458, China
    2. Key Laboratory of Marine Mineral Resources, Ministry of Natural Resources, Guangzhou Marine Geological Survey, Guangzhou 510760, China
    3. Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
    4. Kunming Engineering Corporation Limited, Kunming 650051, China
  • Received:2022-06-10 Revised:2022-08-15 Online:2023-05-10 Published:2022-09-07
  • Supported by:
    Youth Innovation Promotion Association CAS; Key Laboratory of Marine Mineral Resources, Ministry of Natural Resources(KLMMR-2018-B-06); Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou)(GML2019ZD0205); National Key Research and Development Program of China(2021YFC3100604); National Natural Science Foundation of China(42076077)

Abstract:

Under the influence of regional plate tectonics and deep mantle flow, the northern continental margin of the South China Sea has developed the complicated tectonic, magmatic and basement subsidence processes. In this study, the modified technique of back-stripping and four long seismic profiles are applied to conduct an in-depth investigation into the Cenozoic extensional deformation of the northern South China Sea margin and the syn- to post-rift tectonic subsidence history. Results show a significant difference in the crustal thinning in the northern South China Sea margin. From east to west, the strong and weak extensional zones occur alternatively. The Qiongdongnan Basin, the middle segment of the Pearl River Mouth Basin, and the Taixinan Basin experienced strong extension, and part of the crust is extremely thinned to less than 10 km; while the west and east segments of the Pearl River Mouth underwent minor extension, and the crustal thickness mostly remains above 20 km. The total strain between the strong and weak extensional margins are largely different, however, the strain rates both show a two-stage characteristics: slow in the early syn-rift period and fast in the post-rift period. In the strong extensional margin, the largest strain rate ranges between 4×10-15 and 7×10-15·s-1, and the maximum extensional factor is 4~10; while in the weak extensional margin, the largest strain rate is less than 1×10-15·s-1, and the maximum extension factor is less than 1.9. Moreover, the northern continental margin of the South China Sea is characterized by pulsed and alternative fast and slow tectonic subsidence. The tectonic subsidence was rapid during the syn-rift period. The post-rift period is characterized by four episodes of slow-fast-slow-slow tectonic subsidence, which happened early in the east then late in the west. The pulsed tectonic subsidence in the Qiongdongnan Basin is mainly related to deep mantle upwelling. The pulsed tectonic subsidence in the Pearl River Mouth and the Taixinan Basins may be affected by the diachronous opening of the South China Sea and the collision between the Luzon Island Arc and the South China Sea margin.

Key words: tectonic subsidence, strain rate, Qiongdongnan Basin, Pearl River Mouth Basin, South China Sea