青藏高原通道流模型动力环境的数值模拟

Numerical simulation of the geodynamical condition about the channel flow model in Tibetan plateau

"中、下地壳流"模型作为一种可能的动力学演化机制,在解决诸如喜马拉雅造山带和青藏高原东缘、南缘等区域地壳中岩层的通道流或韧性剪切挤出等方面的解释给出了相应的模型和阐述.本文基于青藏高原壳、幔介质平均速度模型,采用二维黏弹性数值模型对高原下地壳物质流动的动力学边界条件进行探讨.研究结果表明:(1)青藏高原下地壳与上地幔盖层物质作为坚硬的固态物质相接,不具备可运动的边界条件,难以在Moho界面处任意地域发生相互运动.壳、幔介质中需存在可供物质高速运动的边界条件,即以上地壳底部的低速层为上滑移面,以上地幔软流圈顶部为下滑移面,才有可能在足够强的力系作用下促使"下地壳+岩石圈盖层"物质发生同步运移;(2)若不具备这样的初始与边界条件是难以产生深部物质运移的.因此,青藏高原深部壳、幔物质运动不可能是普遍存在的,只能是局部和在特异环境下才能实现.

Being a possible geodynamical mechanism, ＂crustal flow＂ comes up with corresponding models in resolving and predicting the tectonics, metamorphism and exhumation of high terranes in the Himalayan-Tibetan orogenic system. This paper adopts 2-D viscoelastic models to discuss the geodynamical boundary condition for the deep material flow in Tibetan plateau, based on the average geophysical model of the crust and upper mantle. The result shows： （1） As non- smoothly contact mode, the solid materials of the lower crust and upper-mantle lid beneath the Tibetan plateau do not have the boundary condition to move mutually, which means that ＂channel flow＂ model cannot independently occur freely nearby Moho interface. The simultaneous transfer of the deep medium of ＂lower crust and upper-mantle lid＂ can possibly happen by the enough force source, which takes the low-velocity layers as upper detachment interface at depths 20 30 km, and the top of asthenosphere as lower detachment interface at depths 100 - 110 km. （2） ＂Channel flow＂ is hard to move without the former sufficient and necessary conditions. So, the deep materials flow in Tibetan plateau is not universal, and only happens in local andparticular circumstance.