汤加地区地幔结构及俯冲演化的地球动力学研究  

Geodynamic study on mantle structure and subduction evolution in the Tonga area

作　　者：张丹[1] 赵永红[1] 

机构地区：[1]北京大学地球物理学系,北京100871

出　　处：《地球物理学报》2018年第1期127-137,共11页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(40874043)资助

摘　　要：汤加的俯冲板块结构复杂,板块形态的起因和形成机制不是很清晰.为了探索其演化,我们借助于板块运动学、海底年龄和关键的大地构造特征,用地球动力学模型模拟了本区域40 Ma之后的俯冲历史.通过研究我们发现,沿着海沟的分布位置,不同的黏度、流体的吸力与浮力比特征控制着板块的力学强度,从而影响着板块的俯冲角度和形态.我们的模型显示在俯冲板块形成前,研究区表面西侧的黏度剖面形成的弱化带为水平低黏度区,它对俯冲的发生有一定的引导作用,高黏度的上覆板块的存在和俯冲导致的地幔流体的吸力降低了俯冲板块的倾角,15°S附近的俯冲板块的分离发生在16—8 Ma之间.最后我们通过匹配实际的构造特征,包括贝尼奥夫带和波速结构剖面,用所得的相关性最佳的模型对本区的地幔结构随时间演化提供探索.In the Tonga area, the subduction structure is complex, and the genesis of the plate shape and the formation mechanism of the outboard slab remains enigmatic. In order to explore its evolution, we use the plate kinematics, ages of seafloor and key tectonic features to simulate the subduction history over 40 Ma in this area. It is found that the velocity, viscosity and buoyancy ratio of different tectonic plates control the mechanical strength of the plate along the trench, which influences the subduction angle and shape of the plate. Our model shows that the weakened zone on the west side of the study area is formed before the formation of the subducting plate. It is a low-level area with low viscosity, guiding the occurrence of subduction. The existence of high-viscosity overlying plate and the mantle-fluid suction reduces the inclination of the slab. The separation of the subducting plate near 15S occurred between 16-8 Ma. Finally, by matching the actual structural features, including the Benioff zone and the velocity profile, the mantle structure of this region is investigated by using the best correlation model to explore the temporal evolution of the mantle structure.

关 键 词：地幔结构 拆离断层 黏度 浮力比 俯冲角 

分 类 号：P313[天文地球—固体地球物理学]