青藏高原下地壳流动方式的数值模拟研究

Numerical Modeling of Lower Crustal Flow beneath the Tibetan Plateau

青藏高原存在柔性下地壳流动被越来越多的学者接受,但是关于下地壳流动方式及速度存在争议。地表运动有GPS等直接测量,上地幔运动有S波分裂间接反映,下地壳运动目前没有直接观测手段,使得开展数值分析非常重要。本文利用三维球壳黏弹性有限元模型研究了青藏高原下地壳柔性流动方式和流动速度。本文通过对地表GPS观测资料的拟合与不同数值模型的对比分析,认为青藏高原柔性下地壳东向流动遇到四川盆地的抵阻,下地壳物质可能仅在高原东南方向存在物质外溢通道,而在高原东北方向不存在类似的物质通道;下地壳的流动速度比地表运动速率每年快几毫米至十几毫米,对应的黏滞系数为1018～1019 Pa·s。

The idea of ductile flow beneath the Tibetan Plateau is widely accepted.However,there is a dispute on the way and speed of the lower crustal flow.Surface motion has direct measurements such as GPS,and mantle movement has indirect methods such as Swave splitting.As to the lower crustal movement,there is no direct observation,so that numerical analysis is very important.In this paper,we constructed a 3-D spherical viscoelastic finite element model of the Tibetan Plateau to simulate the crustal flow pattern.By fitting GPS data and comparing different models,we considered that the eastward flow of the ductile lower crust in the Tibetan Plateau has been resisted by the Sichuan Basin,a channel exists in the south-eastern corner of the plateau,and similar channels of substances do not exist on the northeast corner of the plateau.The lower crust moves several milimeter faster than the upper crust,the corresponding viscosity of the lower crust was between 1018～1019 Pa· s.