地幔柱与岩石圈相互作用过程中熔融问题的数值模拟

Numerical simulation on the melting process of the mantle plume-lithosphere interaction

地幔柱是最可能形成大火成岩省的原因之一,同时地幔柱与岩石圈的相互作用也极大的影响着岩石圈的构造演化.本文主要集中研究地幔柱与岩石圈相互作用过程中熔融相关的问题.利用开源程序Ellipsis3D,基于质量守恒方程、动量守恒方程、能量守恒方程和岩石流变本构关系,以及不同的熔融损耗关系,通过有限元数值方法模拟得到地幔柱与岩石圈相互作用过程中熔融程度的动态变化.数值模拟结果显示,地幔柱与岩石圈相互作用的熔融相关过程分为三个阶段:地幔柱的初融阶段,地幔柱自身熔融占主导,减压熔融为主因;地幔柱与岩石圈的纵向作用阶段,岩石圈地幔开始熔融,地幔柱以减压熔融为主,岩石圈地幔以升温熔融为主;地幔柱的横向展平阶段,随着地幔柱的扩展岩石圈地幔熔融范围增加,以升温熔融为主,地幔柱自身熔融程度减小.最后基于数值模拟结果及现场资料对峨嵋山大火成岩省地幔柱的发展演化以及峨眉山大火成岩省的形成进行了讨论.

The mantle plume is the most likely cause for the formation of Large Igneous Provinces（LIPs）,and its interaction with the lithosphere can affect the tectonic evolution of the crust and upper mantle.This study focuses on the melting process of mantle plume-lithosphere interaction.On the basis of mass,momentum and energy conservation equations,and material′s rheological relation,as well as different melt depletions,using the open-source finite-element code＂Ellipsis3 D＂,we firstly perform numerical simulation in the melting process of plume-lithosphere interactions.The results show that there are three stages of this process.At the first stage,the mantle plume melts itself mainly through decompression melting.At the second stage,the mantle plume mostly interacts with the lithosphere in Zdirection.In this stage,mantle lithosphere begins tomelt because of temperature rising and mantle plume keeps on decompression melting.At the last stage,the mantle plume begins to move horizontally along X direction.As a result of temperature rising,the melting range of the mantle lithosphere increases gradually along with the plume spreading.At the same time,the melting degree of the plume itself decreases because of heat transfer.Then such simulation is made to the Emeishan Large Igneous Province（ELIP）,and the results are largely in accordance with previous work.Finally,this paper discusses the formation and evolution of the ELIP based on this numerical simulation and data from field investigations.