俯冲板片熔融柱的数值模拟:上覆板块破坏及动力地形效应

Numerical simulation of subduction-induced molten plume: destruction of overriding plate and its dynamic topographic responses

洋壳俯冲过程中温度、压力升高和密度差异,可导致俯冲板片熔融柱的快速上涌,并作用在上覆板块岩石圈地幔底部,从而导致岩石圈的破坏减薄以及地表形态的剧烈变化,该过程类似于地幔柱对岩石圈的破坏作用。目前,对于俯冲板片熔融柱的形成及其对岩石圈破坏程度的研究相对较少,特别是地表动力地形变化与深部岩石圈破坏作用之间的响应关系依然不清楚。为此,本文将利用I2VIS有限差分方法,基于质量守恒方程、动量守恒方程以及能量守恒方程,通过给定材料参数和一定边界条件,计算揭示俯冲洋壳在不同时间和不同深度下发生部分熔融并形成俯冲板片熔融柱的过程,从而模拟再现该熔融柱对上覆板块岩石圈的破坏过程,并进一步分析其导致的浅部地表地形变化响应。数值模拟结果显示,在大洋板片俯冲过程中,由俯冲的陆源沉积物以及洋壳形成的混合熔融柱垂向侵蚀岩石圈底部,造成岩石圈减薄。在熔融柱的横向侵蚀过程中,岩石圈地幔熔融范围增加,可达300km。在地形变化方面,板块俯冲造成大陆前缘受挤压变形,引起构造变形,构造变形范围可达300km。同时,与俯冲相关形成的熔融柱对岩石圈地幔底部的侵蚀作用逐渐增强,动力地形变化幅度增大,并持续抬升,最终可垂向抬升至4km。动力地形的变化范围局限在300km以内,这与岩石圈地幔的破坏范围保持一致。

In the process of oceanic crust subduction,with the increase in temperature and pressure and the difference in density,the subductioninduced molten plume will rise rapidly and act on the lithospheric mantle bottom of the overriding plate,which may lead to the decrease in the lithospheric damage and the drastic change of surface morphology.This process is similar to the destruction of the lithosphere caused by mantle plume.So far,there have been little studies on the formation of subduction-induced molten plumes and their damage to the lithosphere, especially on the responses of surface dynamic topographic changes to the deep destruction.Based on the conservation equations of matter, momentum and energy,the I2VIS finite difference method is adopted by the authors to calculate and reveal the partial melting of the subducted oceanic crust at different times and depths under given material parameters and boundary conditions.The process of forming a subductioninduced molten plume is obtained,and then the process of molten plume-lithosphere interactions is further simulated,and the response of shallow topographic changes are analyzed.The numerical simulation results show that in the process of oceanic plate subduction,the composite molten plumes formed by subducted terrigenous sediment and oceanic crust eroded the bottom of the lithosphere longitudinally,and resulted in lithospheric thinning.During the transverse erosion of the molten plumes,the melting range of the lithospheric mantle increases up to 300 km. In terms of geomorphic change,plate subduction results in compression deformation of the continental front,which may reach 300 km.At the same time,the erosion of the molten plumes associated with subduction to the bottom of the lithospheric mantle is gradually strengthened,and the dynamic topographic changes increased,while uplifting continued,and ultimately reached a figure of 4 km.The variation range of dynamic topography is limited to 300 km,which is consistent with the damage range of lithospheric mantle.