地幔柱与岩石圈相互作用过程的数值模拟

Numerical simulation on process of the plume-lithosphere interaction

地幔柱的研究是地球科学研究的热点之一.本文主要集中研究地幔柱与岩石圈的相互作用过程.基于质量守恒方程、动量守恒方程和能量守恒方程,通过有限元数值方法可以计算得到地幔柱与岩石圈相互作用的温度场、速度场和有效黏度等的时空图.本文的流变本构模型主要基于非牛顿流体的有效黏度模型,通过数值模拟计算分析了地幔柱与岩石圈相互作用过程,着重讨论了地壳流变结构对此过程的影响.数值模拟结果显示,地幔柱与岩石圈的相互作用分为三个阶段:地幔柱上升期,时间持续到0.2 Ma,平均速度为2.75m·a-1,地幔柱顶部地形开始向上隆起;地幔柱与岩石圈纵向作用期,时间从0.2 Ma到0.26 Ma,地幔柱上升的平均速度为0.83m·a-1,地表地形隆升达到最大值;地幔柱与岩石圈横向作用期,0.26 Ma以后,岩石圈开始剪切变形,地幔柱水平运动速度为0.47m·a-1,当剪切变形达到一定程度,岩石圈底部开始出现拆沉作用.当下地壳流变强度比较小时,上地壳的流变结构控制着地幔柱顶部地表地形隆起程度,流变强度越大,隆升高度越小;而下地壳的流变结构控制着地幔柱两侧地表地形的下沉幅度,下地壳流变强度越小,下沉幅度越大.最后,讨论了数值模拟对峨眉山大火成岩省地幔柱发展演化的应用.

Being the most likely cause of Large Igneous Provinces（LIPs）,the study of plume has become a hot spot in earth sciences.In this paper,we perform numerical simulation of the process of plume-lithosphere interactions,and then analyze the effects of the crust′s rheological structure on this process.On the basis of mass,momentum and energy conservation equations,using finite element numerical method,we can obtain the temporal and spacial diagrams of the plume-lithosphere interactions.Based on non-Newtonian fluid approximation,making use of finite-element code＂Ellipsis3D＂,we firstly perform numerical simulation of the process of plumelithosphere interactions.Secondly,with different models the effects of the crust′s rheological structure on this process are analyzed emphatically.Finally,the process of plume-lithosphere interactions in Emeishan Large Igneous Province（ELIP）is discussed. From the results of the numerical simulations,there are three stages in the process of the plume-lithosphere interactions.At the first stage,the plume ascends with the velocity of 2.75m·a^-1 during the first 0.2 Ma,and the surface topography on the top of plume begins to uplift;at the second stage,the plume ascends with the velocity of 0.83m·a^-1 during 0.2Ma to 0.26 Ma,and the surface topography reaches the peak value;At last stage,after 0.26 Ma the plume begins to move horizontally with the velocity of 0.47 m·a^-1 and the bottom of lithosphere begins shear deformation,and when shear deformation reaches a certain degree,the bottom of lithosphere begins to perform delamination.The rheological strength of the crust deeply influences the process of plume-lithosphere interactions.When the rheological strength of the lower crust is weaker,the upper crust′s rheological structure controls the degree of the uplift of surface topography.Otherwise,the rheological strength of the lower crust controls the degree of the subsidence of the both sides of the plume.In addition,the simulated results of Emeishan Large Igneous Province（ELIP）are in accordance with the previous results.The simulation results in this paper reflect the process of plume-lithosphere interactions and the effects of the crust′s rheological structure on this process better and more clearly.Because of the faults are widely distributed in Emeishan Large Igneous Province（ELIP）,which are not considered in this paper,the further research looks forward to take the faults in to account.