上地幔俯冲板块的动力学过程:数值模拟

Dynamics of subducting plate in the upper mantle:numerical modeling

大洋板块俯冲到地幔转换带,进而可形成不同的形态:板块可以停滞在660km不连续面,抑或穿过地幔转换带进入下地幔.这些不同的俯冲模式可进一步影响到海沟的运动.为更好地理解上地幔中俯冲板片的变形行为以及俯冲过程与海沟运动之间的关系,本文通过建立一系列高精度二维热-力学自由俯冲的数值模型,揭示了俯冲板块在上地幔中的变形方式及其与地幔转换带之间的相互作用过程.模拟结果显示,在俯冲板块与地幔转换带的相互作用过程中,其动力学过程可以分为以海沟后撤主导、海沟前进主导以及稳定型海沟等三种主要动力学类型.对于年龄较老,厚度较大的俯冲板块容易形成海沟后撤型俯冲,俯冲板块停滞在660km不连续面.相反,年龄较小,塑性强度较小的板块容易形成海沟前进型俯冲,俯冲板块穿越660km不连续面.

Oceanic plate subducts into the mantle transition zone and may result in different subduction modes: subducting slab stagnates at 660 km discontinuity or penetrates through the mantle transition zone. The different subduction modes also influence the trench motion. To better understand the subduction and trench migration processes,a series of high resolution 2D thermomechanical free subduction models are constructed to investigate the deformation style of the subducting slab in the upper mantle and its interaction with the mantle transition zone. The numerical results reveal three styles of subduction-induced trench migration: trench retreat,trench advance and stable trench. For the older and thicker subducting plate,it would be easier to achieve trench retreat mode,in which the subducting slab stagnates at 660 km discontinuity. In contrast,the younger and thinner subducting plate favors the formation of the trench advance mode,with the subducting slab penetrating through the 660 km discontinuity.