Journal of Marine Sciences ›› 2019, Vol. 37 ›› Issue (2): 44-56.DOI: 10.3969/j.issn.1001-909X.2019.02.005

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Crustal structure features and origins of high-velocity lower crust in the northeastern South China Sea

LI Hai-long1,2, WU Zhao-cai*1,2, XU ming-ju1,2   

  1. 1. Second Institute of Oceanography, MNR, Hangzhou 310012, China;
    2. Key Laboratory of Submarine Geosciences, SOA,Hangzhou 310012, China
  • Received:2018-09-14 Revised:2019-01-22 Online:2019-06-15 Published:2022-11-15

Abstract: Abundant information about tectonic evolution in the northeastern South China Sea margin is essentially important for understanding the evolution of the South China Sea. The deep reflection seismic profiles and wide-angle reflection seismic profiles across the northeastern South China Sea were collected, and the crustal thickness and high-velocity lower crustal thickness were extracted respectively. Combining with geological and geophysical information such as bathymetry, gravity and magnetic anomalies, and lithospheric rheology, the crustal thinning of the northeastern South China Sea, nature of the Luzon-Ryukyu Transform Plate Boundary and distribution of the high-velocity lower crust and its origins were discussed. The northeastern crust is unevenly thin in lateral and vertical, dominated with lower crust thinning, like in the Taixinan Basin. There are similar extremely thinned crusts in the Baiyun Sag, Xisha Trough and Zhongjiannan Basin. They are always conjugated with or adjacent to rigid blocks. We agree that lower crust flow and mantle upwell caused by the existence of rigid blocks during initiated breakup are responsible for locally extreme thinning of the crust. Both sides of the Luzon-Ryukyu Transform Plate Boundary are different in the bathymetry, Cenozoic reflections, gravity and magnetic anomalies. The LRTPB intersected high magnetic anomaly zone caused by Mesozoic with a large-angle, indicating the Luzon-Ryukyu Transform Plate Boundary may be a boundary fault converted from the Mesozoic Paleo-Tethys tectonic domain to the Pacific tectonic domain. The distribution range of the extensive HVLC in the northeastern margin consistent with post-rift igneous. Combining with distribution interval of ratios Vp/Vs of the high-velocity lower crust, It is suggested that the high-velocity lower crust primarily consists of mafic rock caused by multiple-epoch underplating.

Key words: the northeastern South China Sea, crustal thickness, extremely thinning, Luzon-Ryukyu Transform Plate Boundary, high-velocity lower crust

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