南海的盆地群与盆地动力学

  • 摘要: 南海发育有众多的新生代盆地,按发育位置,总体可分为陆架盆地、陆坡盆地和深海海盆,陆架、陆坡盆地成因上与大陆边缘的裂解、转换密切相关,可分为走滑拉分-伸展盆地群、挤出-断陷盆地群、伸展-俯冲挠曲型盆地群,这些盆地进一步发展可形成不同阶段的洋盆群,西南次海盆发育程度低,中央次海盆发育程度高,因而南海盆地群的盆地动力学不是单一的动力学机制下形成的,机制非常复杂多变。这些盆地新生代以来经历了神狐、南海、东沙等多期构造运动,形成了复杂的角度不整合分布,且这些角度不整合时空上存在一定迁移规律。伴随着盆地构造迁移演化,断裂、岩浆、沉积沉降中心、成藏、灾害等都表现出显著的跃迁规律。南海成因的动力学背景复杂,受多种因素影响,其中板块动力因素既有东侧太平洋板块俯冲、菲律宾海板块楔入的影响,又有西侧印度洋板块斜向俯冲、洋中脊俯冲,还可能有北侧青藏高原隆升、大陆块体挤出的影响;同时,深部底侵、拆沉、地幔柱、地幔水化过程等地幔动力学背景也不可忽视。最终提出南海海盆的开启模式可能为走滑拉分模式,与太平洋构造域演化关系更为密切。

     

    Abstract: The South China Sea was formed in Cenozoic. Basins in the South China Sea could be divided into different types, such as continental shelf basins, continental slope basins and deep sea basins, which are closely related with the rifting and transition of the continental margins, and thus could be grouped into strike-slip-related pull-apart and extensional basins, extrusion-escape-related rifting basins, extension-and subduction-related buckling basins. They developed further into some ridge-spreading-related oceanic sub-basins in different stages. These basins were formed not under a single dynamics but under a very complex and changeable dynamics. These basins have suffered from a series of Cenozoic tectonic movements, such as the Shenhu, the South China Sea, the Dongsha, resulting in the formation and spatial-temperal migration of complex angular unconformities in these basins. Accompanying with the tectonic migrations and evolutions in these basins, faulting, magmatism, shifting of sedimentary subsidence centers and depocenters, oil accumulation and geohazards show a significant feature of jumping. The complex dynamic settings of the South China Sea have caused many controversies on their origin. The plate dynamic factors include the Pacific Plate subduction and the indentation of the Philippine Sea Plate along the Taiwan Orogen to the east side of the South China Sea, and the Indian Plate oblique subduction and mid-ocean ridge subduction to the west side. They may also be responsible for the uplifting of the Tibetan Plateau and the related extrusions of continental blocks to the north side. At the same time, the mantle dynamics of deep-seated magma underplating, delamination, mantle plume and mantle-hydrated process should not be ignored. At last, this paper proposes one strike-slipping pull-apart model to explain the onset of the South China Sea Basin which is closely related to the tectonic evolution of the Pacific Tectonic Domain.

     

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