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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.
Under certain conditions, the mafic lower crust can transform into eclogites and detachment into the mantle, and the detachment of the crust beneath the eclogite can cause the evolution of the continental crust to the Chang-Ying. Geochemical studies show that the Dabie Mountains in Qinling In the later period of collision, about 145-130Ma, thickened eclogite crust also existed, while at 130Ma, the thickened lower crust disappeared and resulted in the intrusion of magnesian and granitic magma. In the collisional orogeny, thickened cold The gravitational instability of the mantle lithosphere can cause the delamination of the lithosphere and carry the lower crust into the mantle, but the mantle lithosphere is basically stable in the late orogenic or cratonic region of the collision tectonic movement, and the lithosphere of the lower crust The lithification will play an important role in the detachment of the lower crust.The paper studies the detachment process and detachment time of the lower crust eclogite under gravitational stability of the lithosphere mantle under the condition of lithospheric mantle under the lithosphere mantle, The parameters include the viscosity (η_2), density (B_2), total size (s) of the lower crust eclogites and the viscosity of the lithospheric mantle (η_1) .The numerical results show that due to the gravitational instability of the lower crust eclogites, Sexuality, (T) is closely related to the model parameters. A large number of calculation and analysis show that t = 7.3005 × 10 -7 exp (0.6593 η 2 / η_1) η_1 ~ (1.066) B_2 ~ (-0.688) s ~ (0.1451η_2 / η_1-0.9831) .The results show that the viscosity of the lithospheric mantle has a more important influence on the detachment time, and the reduction of the mantle viscosity can promote the deformation of the lower crust Eclogite delamination If the density of the lower crust eclogite is assumed to be 3.48 × 10 ~ 3 kg / m ~ 3 (ie B_2 = 1), the viscosity of the eclogite is 5 × 10 ~ (21) pa s, When the viscosity decreases to 2 × 10 ~ (21) Pa s, the detachment time of the lower crust eclogite in the range of 60km × 30km can be less than 18Myr.