青藏高原壳幔形变数值模拟研究

Numerical modelling of the crust/mantle deformation in the Tibetan plateau

现有数值模拟研究已在很大程度上较合理地给出青藏高原演化运动学和动力学过程的图像。利用连续介质快速拉格朗日分析方法,笔者进行了青藏高原壳幔形变数值模拟研究。据此得到的青藏高原三维壳幔形变特征反映纬向上主碰撞带远、近程效应的差异和经向上地壳物质“逃逸”的存在,印证了青藏高原形成过程中南北双向挤压、而且南部作用大于北部作用的可能应力场特征。青藏高原壳幔形变不仅强烈依赖于随深度变化的岩石力学性质及其距离挤压作用前锋带的远近,而且存在强烈的横向不均一性。同时,强应变(剪切)带的存在对高原岩石圈形变具有重要影响,高原形变过程中地壳尺度的耦合流及壳-幔解耦共存。但是,常规数值模拟研究尚存在很大局限性:(1)物理-力学模型单一;(2)几何模型简单;(3)边界形态与条件理想化;(4)模型内部块体划分粗糙;(5)不连续体介质处理困难。借助具有可处理大形变能力的4-D数值模拟方法,将观测资料与数值模拟相互补充是深入研究青藏高原壳幔形变的关键。

Modern numerical modelling can reasonably provide images of the evolution kinetics and geodynamical processes of the Tibetan plateau. We have simulated the crust/mamle deformation in the Tibetan plateau since initial India-Eurasia convergence at about 50 Ma. Modelling of the process of deformation in the Tibetan plateau implies that： （a） the stress field was characterized by N-S compression, and the southern effect of collision was larger than that to the north; （b） lithospheric deformation in the spatial domain depends on rheological transitions with depth, and far-field and short-range effects related to latitudinal distance from the convergence zone; （c） lithospheric deformation in time depends on the rates of accumulation of tectonic stress and dissipation of strain energy; and （d） there may exist at least two kinds of optional deformation flow： intracrustal coupling flow and strong decoupling flow between the crust and the mantle. Combining observational data with numerical modelling, in four dimensions of temporal-spatial scales, is the key to understanding the crust/mantle deformation of the Tibetan plateau.