榴辉岩下地壳拆沉的数值模拟

发布时间：2018-03-21 17:41

本文选题：榴辉岩　切入点：拆沉　出处：《中国科学:地球科学》2017年01期 　论文类型：期刊论文

【摘要】：镁铁质的下地壳在一定的条件下可相变为榴辉岩并拆沉进入地幔,榴辉岩下地壳的拆沉可造成大陆地壳向长英质演化.地球化学研究显示,秦岭大别山地区在碰撞后期大约145-130Ma时还存在着加厚的榴辉岩下地壳;而到了130Ma时,加厚下地壳消失并产生了铁镁质和花岗质岩浆侵入.碰撞造山阶段,加厚的冷的地幔岩石圈的重力不稳定可造成岩石圈的拆沉,并携带下地壳一起进入地幔.但对碰撞造山构造运动后期的造山带或克拉通区域,地幔岩石圈基本处于稳定状态,下地壳榴辉岩化将对下地壳的拆沉起重要作用.本文采用二维有限元数值模拟的方法研究了岩石圈地幔重力稳定状态下,下地壳榴辉岩的拆沉过程以及拆沉时间.模型的主要参数包括下地壳榴辉岩的黏性(η_2)、密度(B_2)、总体规模(s)和岩石圈地幔的黏性(η_1).数值计算结果显示,由于下地壳榴辉岩的重力不稳定性,它能与其下的稳定岩石圈一起发生拆沉,拆沉过程的持续时间(t)与模型参数密切相关,大量计算分析显示t=7.3005×10~(-7)exp(0.6593η_2/η_1)η_1~(1.066)B_2~(-0.688)s~(0.1451η_2/η_1-0.9831).结果表明,岩石圈地幔的黏性对拆沉时间具有更重要影响,岩石圈地幔黏性的减小可促进下地壳榴辉岩的拆沉.若假定下地壳榴辉岩的密度为3.48×10~3kg/m~3(即B_2=1),黏性为5×10~(21)pa s,当岩石圈地幔的黏性减小到2×10~(21)pa s时,60km×30km范围的下地壳榴辉岩的拆沉时间可小于18Myr.
[Abstract]:Under certain conditions, the lower crust of magnesia-iron can be transformed into eclogite and delaminated into the mantle, and the delamination of the lower crust of eclogite can result in the evolution of continental crust to feldspar. In the Dabie Mountains of Qinling Mountains, there were thickened eclogite lower crust at about 145-130 Ma after the collision, while at 130 Ma, the thickened lower crust disappeared and resulted in iron-magnesian and granitic magma intrusion. The gravity instability of the thickened cold mantle lithosphere may cause the lithosphere to desink and carry the lower crust into the mantle together. However, for the orogenic belt or cratonic region of the late collisional orogenic movement, the mantle lithosphere is basically in a stable state. Eclogite in the lower crust will play an important role in the desubsidence of the lower crust. In this paper, a two-dimensional finite element numerical simulation method is used to study the gravitational stability of the lithospheric mantle. The main parameters of the model include the viscosity of eclogite in the lower crust (畏 _ 2, density B _ 2, total scale) and the viscosity of the lithospheric mantle (畏 _ 1). Due to the gravity instability of eclogite in the lower crust, it can desink along with the stable lithosphere under it, and the duration of the desinking process is closely related to the model parameters. A large number of calculation and analysis show that t _ (7.3005) 脳 10~(-7)exp(0.6593 / 畏 _ 1) 畏 _ 1 / T _ (1) / T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (1) T _ (. The viscosity of the lithospheric mantle has a more important effect on the desubsidence time. If the density of eclogite in lower crust is assumed to be 3.48 脳 10 ~ (3) kg / m ~ (-3) (i.e. B _ 2J ~ (-1)) and viscosity is 5 脳 10~(21)pa ~ s, when the viscosity of lithospheric mantle decreases to 2 脳 10~(21)pa _ s, the density of eclogite in lower crust is 60 km 脳 30km. The sinking time can be less than 18Myr.
【作者单位】：中国科学技术大学地球和空间科学学院地震与地球内部物理实验室;安徽蒙城地球物理国家野外科学观测研究站;
【基金】：国家自然科学基金项目(批准号:41474082,91014005)资助
【分类号】：P542.5

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