南海东部俯冲系统分段性及相关盆地群成盆动力学机制
SEGMENTATION OF SUBDUCTION SYSTEM IN THE EASTERN SOUTH CHINA SEA AND DYNAMICS OF RELATED BASIN GROUPS
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摘要: 南海东部位于欧亚板块和太平洋板块(菲律宾海板块)的汇聚地带,该区域东侧为马尼拉俯冲带、吕宋岛弧和东吕宋-菲律宾俯冲带,构成对倾的沟-弧-盆体系,本文称为俯冲系统。该系统具有明显的分段性,表现为地貌、地震、火山、断裂、盆地和地球物理特征等方面都具有明显差异,以巴布延走滑断裂和锡布延走滑断裂为界,可划分为北、中、南三段。其北段受台湾造山带碰撞挤压的影响,台湾造山带西侧的北港隆起对菲律宾海板块NWW向的楔入产生阻碍作用,导致南海东北部陆块挤出,产生了台西南盆地、台西盆地、笔架南盆地等,是紧密相关的一系列碰撞-楔入-挤出构造。中段受南海死亡的洋中脊俯冲过程中形成的"板片窗"影响,使得该段的地震、岩浆活动、地貌特征和应力状态等存在南北方向上的差异,产生的一系列盆地受弧内走滑断裂调节。南段受菲律宾海板块向西俯冲作用的控制,紧邻该俯冲带地震和火山强烈;但西侧受南沙地块(巴拉望地块)的阻挡作用,在菲律宾群岛中部的菲律宾大断裂的调节作用下,导致马尼拉海沟平面上发生弯曲,该段西侧地震和火山活动性减弱。分布在该段的盆地是在不同性质的地块碎片碰撞的基础上,受后期走滑断裂的调节拉分作用,呈现现今的盆地分布格局。总之,南海东部俯冲系统的南、北分别受菲律宾海板块NWW向楔入和西向俯冲影响,而南海海盆沿马尼拉海沟向东的俯冲对该俯冲系统中段的构造演化起了主导作用。Abstract: The east part of the South China Sea is located at the convergence zone between the Eurasian Plate and the Pacific Plate (the Philippine Sea Plate). To the east of the South China Sea, there are the Manila Subduction Zone, the Luzon Arc and the East Luzon Philippine Subduction Zone, consisting of a opposite-dipping trench-arc-basin system which is called subduction system in this paper. The system can be subdivided into three segments from north to south by the Babuyan Strike-slipping Fault and the Sibuyan Strike-slipping Fault respectively, based on the differences in geomorphology, earthquakes, volcanism, faulting, basins and geophysical characteristics. The north segment is affected by the collision of the Taiwan Orogen, and the NWW-directed indentation of the Philippine Sea Plate and the stopping of the Beikang Uplift to the west of the Taiwan Orogen, resulted in the extrusion of the continental blocks of northeastern South China Sea, and the formation of the Taixinan Basin and the Taixi Basin,which are a series of collision-wedge-extrusion related basins. The middle segment is controlled by "Slab Window" during the subduction of fossil mid-oceanic ridge of the South China Sea, the earthquakes, magmatism, geomorphology and stress fields are different from north to south, and the formation of the basin group is controlled by arc strike-slip faults. The south segment is dominated by west-dipping subduction of the Philippine Sea Plate. The intensive earthquakes and volcanism are near the Philippine Trench. However, the stopping of the Sunda Block and the Palawan Block to the west of the Manila trench and the adjustment of the Great Philippine Fault in the central Philippine islands result in curvature of the Manila Trench in plane and decrease in earthquakes and volcanism in the west of the segment. The basin group is located in the segment developed on the basement resulting from collisions of different block fragments. The adjustment and pull-apart faulting of strike-slip faults caused the present-day basin pattern and distribution. The subduction system in the east of the South China Sea is affected by the NNW-directed indentation in the north segment and west-directed subduction in the south segment of the Philippine Plate, while the tectonic evolution of the middle segment of the subduction system is dominated by the east-directed subduction of the Manila Trench.