南海东部次海盆的轴外构造与岩浆过程

Great progress has been achieved about the tectonics in the continental margin and fossil spreading ridge in the South China Sea, but researches on the deep sea-basin are still limited, which hinder our understanding of the Cenozoic tectonic evolution of the South China Sea. Based on geophysical and geological data, including multi-channel seismic, gravity, bathymetric, and drilling data, we want to study the off-ridge tectonic-magmatic process in the East Sub-basin, focusing on the deep structure, deformation features, magmatism, and the related sedimentary and topographic features. We will obtain the offshore ridge changes of oceanic crust thickness and mantle temperatures with studies on the residual mantle gravity anomalies (RMBA), with constraints from the Moho depth identified from seismic data. Neogene tectono-sedimentary features of the oceanic basement will also be studied with detailed geological interpretations on seismic and bathymetric data, including the effects of some locational geological activities on the off-ridge process. With all these works we want to figure out the controlling factors of the off-ridge tectonic-magmatic process and reconstruct the tectonic-sedimentary evolution of the deep sea basin during and after seafloor spreading.

相比较南海的陆缘及残留扩张脊，对于南海主体的深海盆地的系统性研究相对较为缺乏。本次研究以南海东部次海盆的扩张脊轴外构造与岩浆过程为目标，在多种地质（钻井数据）与地球物理数据（多道地震，多波束，重力，磁力）观测的基础上，对研究区的洋壳结构、构造变形、岩浆作用以及沉积-地貌响应进行研究，具体包括（1）通过重力反演获取海盆区离轴洋壳厚度及地幔温度的变化，并以多道地震数据识别的莫霍面进行约束，获取海盆区深部结构及离轴变化规律；（2）通过多道地震和多波束地貌数据探索海盆区洋壳构造变形-岩浆作用及地貌和沉积对其的响应，了解独特地质活动对轴外过程的影响。进而与周边板块构造事件结合，对东部次海盆离轴深部结构、构造变形和岩浆活动的变化规律及控制因素进行分析，以期从系统上认识南海海盆的轴外构造-岩浆过程。该研究有助于补充南海从陆缘裂解-海盆扩张-扩张停止过程的重要一环，从而完整的理解南海的构造动力学过程。

边缘海如何形成是地球科学的基本问题。申请者聚焦地壳深部结构和三维全变形机制，在南海陆缘张裂-海盆扩张的构造动力学研究中取得重要进展：（1）“大陆破裂非均一“”：拉张过程垂向上分层非均一，受拆离系统控制；裂离过程横向上高变化，中-东侧岩浆作用主导，西侧构造作用主导。（2）“海盆扩张非对称”：受周期性地幔活动主导，扩张表现为两次洋脊南向跃迁，方向也发生多次转变，导致南海扩张的不连续-非对称性。据此提出西太俯冲背景下周缘受限型海盆高变化-非均衡扩张模式的新认识，丰富大陆边缘动力理论。