俯冲初始时板块分界面形状对俯冲过程的影响

Effects of plate interface geometry on the evolution of subduction

自板块理论建立以来,俯冲一直是学者们关心的热点问题.前人结合地质、地球物理、实验室物理实验和数值模拟等多种手段对这一问题进行了大量的研究.以往的研究更为关注俯冲过程中板块的作用、地幔流动的规律和物质的迁移与相变等问题,却常忽视了俯冲是如何开始的这一基本问题.同时,由于相关数据资料较为有限,更限制了俯冲启动的相关研究.因此,本文选取俯冲启动问题中板块分界面形状对俯冲过程的影响这一问题,使用有限元的方法进行了数值模拟.我们选择针对倾斜型、垂直型和弯曲型三种不同形状的板块分界面建立对比模型,比较它们演化至10Ma的过程我们发现:分界面几何形状的不同的确会对俯冲板块演化和海沟的深度产生影响.倾斜型模型的俯冲角度最大,海沟深度最深,俯冲深度最深;垂直型模型的俯冲角度和海沟深度仅次于倾斜型模型,俯冲深度最浅;弯曲型模型的俯冲角度最小,海沟深度最小,俯冲的深度介于倾斜型和垂直型之间.结合以上结论不难看出,俯冲角和海沟深度变化具有一定的相关性,俯冲角度越大,相应的海沟深度越大.

Subduction is one of focused issues since the establishment of the plate tectonics theory.In combination of geology,geophysics,laboratory physics experiments and numerical simulations,a great deal of studies on this topic have been conducted.Most of previous work focus on the aspects of plates,mantle flow,motion and phase transition of materials during subduction,while one basic question how subduction begins remains unsolved.Meanwhile,due to the lack of data,the study of this problem,if any,is limited.In this paper,we choose three kinds of interface geometry,using finite element numerical models to simulate subduction.What we want to see here is whether and how the interface geometry of a plate affects subduction evolution.We build three kinds of models with different initial geometries,“dipping”,“vertical”and“bending”.The results show that the plate interface geometry has an effect both on the subducting plate and the trench depth.In the“dipping”model,subduction angle is the biggest,and both the subducting and trench depths are also the largest.The subducting angle and the trench depth in the“vertical”model are smaller only than those in the“dipping”model and the subducting depth is the smallest.The“bending”model has the smallest subducting angle and trench depth,but has a intermediate subducting depth in the three cases.It seems that there is a relationship between subducting angle and trench depth,that is,when subducting angle gets larger,the trench becomes deeper correspondingly.