南海三维热岩石圈结构及地表构造响应

Three-dimensional thermal structure of the lithosphere and its relationship to surface structure in the South China Sea

为系统了解南海海底热流特征和岩石圈热结构与地表构造的关系,本文首先以最新海底热流为约束,采用三维数值模拟方法计算得到整个南海的“热”岩石圈底部边界(底界)的埋深,然后开展详细分析壳、幔热流贡献以及岩石圈热结构与地表不同构造单元之间的对应关系.结果显示南海岩石圈底部边界埋深为30~100 km,最浅埋深集中分布在南海海盆水深大于3000 m的区域(如南海西北次海盆、西南次海盆和东部次海盆西侧),以及南海北部陆缘中部、莺歌海盆地、中建南盆地和南薇西盆地,体现了南海深部结构对地表不同构造单元的控制作用;靠近海盆东侧的马尼拉海沟具有较低的海底热流,对应岩石圈底界埋藏也较深,可能与南海和古南海洋壳俯冲有关;吕宋岛弧(119°E—122°E和13°N—17°N)表现出较高的海底热流,同时具有较浅的热岩石圈底界埋深,可能与南海板块和菲律宾海板块双向俯冲有关.

This paper systematically studies the seafloor heat flow characteristics,the lithospheric thermal structure,and its relationship to the surface structures in the South China Sea.A three-dimensional numerical method is used to obtain the lithospheric depth of the entire South China Sea region under constraints of the newly compiled seafloor heat flow data.Then the contribution to the heat flow from the crust and mantle,respectively,and relationships between the surface tectonic units and the lithospheric thermal structure are analyzed.Results show that the depth of the lithosphere-asthenosphere boundary(LAB)in the South China Sea is 30~100 km.The shallowest LAB appears in the water depth of more than 3000 m in the South China Sea Basin,such as the northwestern sub-basin,the southwestern sub-basin,and the western side of the eastern sub-basin,as well as in the middle of the northern continental margin of the South China Sea,the Yinggehai Basin,Zhongjiannan Basin and Nanweixi Basin,reflecting the control of deep structure on different structural units on the surface.Along the Manila Trench in the east side of the South China Sea basin,the deep LAB and low heat flow are probably related to the subduction of the South China Sea and the Paleo-South China Sea.On the contrary,the Luzon Island Arc(area 119°E—122°E and 13°N—17°N),located in the intersection of the Manila trench and the extinct South China Sea spreading ridge,has a shallow LAB and high heat flow,which are probably related to the opposite subduction of the South China Sea Plate and the Philippine Sea Plate.