压力负载对南海西南次海盆不对称共轭陆缘形成影响的数值模拟研究

The formation process and mechanism of the conjugated continental margin of the southwest sub-basin are the research frontiers and hotspots of tectonic evolution in the South China Sea. At present, the study on the asymmetry of conjugate continental margin focuses on the comparison of tectonic features, and its formation mechanism is mainly explained by the lithospheric rift mode. But in addition, the compression from the surrounding tectonic structure also plays an important role on the formation of the continental margin. Base on the constraints of geophysical exploration and the latest drilling results in the South China Sea, this application project intends to use numerical simulation method to simulate the lithosphere rifting and rupture processes of margins in the South China Sea which under different compression loads from the Indochina peninsula before or after the change of seafloor spreading direction (23 Ma). By comparing the present crustal structure, the rift modes of continental lithosphere in the South China Sea will be analyzed, and the formation mechanism of asymmetric extra-wide continental margin will be discussed. The implementation of this project will not only provide theoretical basis for further understanding of the tectonic evolution of the South China Sea, but also expand the understanding of the different extension mechanisms of global passive continental margin.

南海西南次海盆共轭陆缘的形成过程和机制是当今南海构造演化地球动力学研究的前沿和热点。目前针对该共轭陆缘不对称性的研究集中于构造特征的对比，对其形成机制主要通过岩石圈破裂模式来解释。但除此之外，周缘构造对陆缘的压力负载在张裂陆缘形成过程中同样起着至关重要的控制作用。本申请项目拟在地球物理探测及最新南海钻探成果的约束下，利用数值计算方法，模拟南海扩张方向跳转（23 Ma）前、后，印支半岛对海盆两侧陆缘压力负载不同情况下的岩石圈张、破裂过程；对比现今地壳结构形态，剖析南海大陆岩石圈破裂模式，探讨不对称超宽陆缘的形成机制。本项目的实施，不仅可以为进一步理解南海构造演化提供理论依据，也将拓展对全球被动大陆边缘伸展机制的认识。

南海西南次海盆共轭陆缘的形成过程和机制是当今南海构造演化地球动力学研究的前沿和热点。本申请项目在地球物理探测及最新南海钻探成果的约束下，利用构造沉降回剥的方法，重建了南海陆缘盆地沉降历史，厘定了张裂前地壳和岩石圈厚度以及裂后沉降量。通过对南海共轭陆缘构造特征的研究可以得出：南海西南海盆共轭陆缘的地壳厚度约15 km。海盆两侧减薄陆壳的范围非常宽广，超过了200 km。陆缘的莫霍面热流非常高，这表明陆缘处于相对热的状态。低壳幔热流比表明海底热流主要受深部热源控制。共轭陆缘热岩石圈厚度约60 km，减薄岩石圈的范围也非常的广。利用有限元数值模拟方法，模拟了南海大陆岩石圈破裂过程，岩石圈地幔受到热软流圈抬升的影响先发生破裂，随后陆壳再发生拉伸减薄。对比南海西南共轭陆缘的结构形态，分析了南海陆缘超宽减薄陆壳形成过程，进一步揭示了南海岩石圈的张破裂模式和陆缘形成机制。本项目的实施，不仅可以为进一步理解南海构造演化提供理论依据，也将拓展对全球被动大陆边缘伸展机制的认识。