Earth Science Frontiers ›› 2022, Vol. 29 ›› Issue (4): 307-318.DOI: 10.13745/j.esf.sf.2022.3.29

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Multiphase rift and migration mechanism in the Pearl River Mouth Basin

ZHAN Cheng1(), LU Shaoping1, FANG Penggao2,*()   

  1. 1. School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China
    2. Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China
  • Received:2022-03-07 Revised:2022-03-27 Online:2022-07-25 Published:2022-07-28
  • Contact: FANG Penggao

Abstract:

The formation and evolution of the South China Sea is controlled by the mutual movements of the Indo-Australian, Eurasian and Pacific plates, which provides an important window for the study of plate collisions and their long-range effects in the context of plate convergence. To reveal the multi-episodic rifting process under this context, we select the entire Pearl River Mouth Basin rich in geologic information as the typical area of South China, and used three high-precision seismic sections to calculate the fault activity and tectonic subsidence rates and perform comprehensive analysis for each geological unit in the basin. According to our calculation, the average fault activity rates for the main sag-controlling faults of the eastern, central and western parts of the basin during the rifting period were 85, 203 and 93 m/Ma, respectively, and the average subsidence rates were 8.5, 34 and 12.7 m/Ma, respectively. Basinwide, rifting was strongest in the center and gradually weakened to the west and east, which, we believe, is related to the pre-existing faults and initial crustal thickness. The pre-existing NE-trending faults are known to be more active in the east than in the center. Therefore, under Cenozoic tensile stress, the east is more likely to experience the strongest rifting, followed by the center then the west. Whilst under the influence of pre-Cenozoic subduction, magmatic underplating caused the crust to thicken thus rifting intensity to drop sharply in the east, resulting in the difference in rifting intensity between west and east. In addition, the fault activity and subsidence rates in southern basin had surged during the rifting period, causing rifting to migrate to the south. We speculated that under the influence of depth-dependent extension, the southern sag witnessed increased crustal temperature and weakened crustal strength. As a result, rapid tensile thinning occurred under extensional stress, resulting in a southward migration of the rift center accompanied by mantle upwelling. At the same time, intrusive magmatic material caused the high-angle normal fault to convert into a low-angle normal fault, further promoting the southward migration of the rift center.

Key words: Pearl River Mouth Basin, multiphase rift, migration mechanism, fault activity rate, tectonic subsidence

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