利用矿物流变性质对面理岩石流变性质的有限元方法计算

Calculations of rheological properties of multi-mineral foliated rocks using finite element method based on the rheological properties of minerals

高温高压下岩石表现出流变性质.流变参数是数值模拟地球动力过程必需的重要参数.获得流变参数需要借助于室内的高温高压蠕变实验以及野外的地球物理资料观测的反演.对单矿物的高温高压实验比较多,多矿物组成的岩石的实验则较难较少.本文探讨在单矿物流变参数已知的条件下,能否运用有限元法,计算多矿物岩石整体的流变参数.研究表明,计算结果与高温高压实验获得的参数可以对应.即使矿物力学性质可以近似为各向同性时,如果矿物排列有优势方向(例如存在面理的花岗质糜棱岩),计算表明岩石整体会显示各向异性.当加载外力与矿物面理方向垂直或平行时,岩石的等效黏滞系数较大;当所成角度为30°左右时,等效黏滞系数最小.

Rocks show rheological properties under high temperature and high pressure.Rheological parameter is an important parameter for numerical simulation of the dynamic process of the earth. The rheological parameters can be obtained by means of the high temperature and high pressure creep experiments in the laboratory and by the inversion of the field geophysical data. There have been some high temperature and high pressure experiments on single minerals. However,it is difficult to carry out multi-mineral experiments. In this study,we discuss the possibility of using thefinite element method to calculate the rheological parameters of multi-mineral rocks under the condition that the rheological parameters of minerals are known. The results show that the calculated results match the parameters obtained in the high temperature and high pressure experiments. The results show that the rock as a whole will show anisotropy if the mineral arrangement has the advantage of direction（ such as the existence of the granitic mylonite foliation）,even though mineral mechanical properties are approximatly isotropic. When loading force is perpendicular or parallel to mineral foliation,equivalent viscous coefficient of rock is larger; and when the angle is 30 degrees,equivalent viscous coefficient is minimized.