南海成因及其演化模式探讨

尽管南海已进行深入的调查与研究，提出多种成因模型，包括挤出模型、弧后扩张模型、古南海俯冲拖曳模型等，但因其所处构造位置特殊，周边构造环境经历了复杂的改造，所有成因模式均未能得到广泛的认可。本文从三大板块相互作用入手，结合南海实测数据，提出南海形成的弧后扩张—左旋剪切模型。认为南海是古南海往北俯冲的弧后盆地，菲律宾海板块往北漂移形成的大规模左旋走滑是南海扩张的触发因素。印度—欧亚碰撞产生中南半岛挤出主要影响西南海盆扩张方向，使得扩张轴从近东西向转为北东向。南海及邻区晚中生代以来的演化可以分为以下阶段：1）早白垩世开始澳大利亚板块往北漂移，新特提斯洋往北俯冲消亡，导致弧后扩张，形成古南海；2）晚白垩世末—始新世，古南海往北俯冲，导致弧后拉张形成陆缘裂谷；3）早渐新世，受菲律宾海板块西缘大型左旋走滑影响，在原有裂谷的基础上从东往西海底扩张，形成南海；4）渐新世末，受俯冲后撤的影响，扩张中心往南跃迁，同时受西缘断裂左旋活动的影响，扩张轴从近东西西逐步转为北东向；5）早中新世晚期，南沙地块—北巴拉望地块与卡加延脊碰撞，南海扩张停止。

The formation and evolution of the South China Sea

Lots of investigation and research have been carried out in the South China Sea (SCS), and many genetic models, such as extrusion model of Indochina Peninsular, back-arc extension model and subduction and dragging model of Proto-South China Sea (PSCS), have been proposed. However, none of these models is widely accepted because they don''t fit with some geological phenomena. Due to its special tectonic location, the surrounding tectonic environment has undergone complex reorganization. Starting with the interaction of the three plates and in combination with the real data of SCS, the authors put forward a back-arc extension-sinistral shear model in this paper. It is considered that the SCS is a back-arc basin of PSCS northward subduction, and was triggered by the large-scale left-lateral strike-slip formed by the northward drift of the Philippine Sea Plate. The left-lateral strike-slip on the western margin of SCS caused by Indo-Eurasian collision changed the direction of spreading axis of the southwest sub-basin from nearly east-west to north-east direction. The evolution of the SCS and its adjacent area since the late Mesozoic can be summarized as the follows: 1) the Australian plate began to drift northward, and the Neotethys subducted northward in the early Cretaceous, leading to back-arc extension and the formation of PSCS; 2) From the end of Cretaceous to Eocene, the PSCS subducted northward, resulting in formation of continental margin rift; 3) In Early Oligocene, the large scale sinistral strike-slip on the western margin of the Philippine Sea plate triggered back-arc extension of SCS from east to west; 4) At the end of Oligocene, the rollback by subduction of PSCS resulted in the spreading axis jumping to the south; accordingly, it shifted from nearly E-W to NW direction by the influence of sinistral strike-slip on the west margin of SCS; 5) In late Early Miocene, SCS spreading was stopped by collision of Nansha-northern Palawan block with Cagayan Ridge.