Influence of viscosity on growth of high pressure phases in computer experiments

Abstract

The general aim of the project is the examination of microstructures that develop under HP conditions in computer experiments. Starting point is an interest in the dynamics of HP phase transitions, as for instance the probably catastrophic phase-change event of olivine to spinel in the upper mantle. This is either explained by large overpressure or failure during the development of micro-structures during the growth of the spinel phase. Experimental results on this subject are rare, and do not lead by themselves to a deeper insight into the complicated stress/strain/volumechange/ micro-crack relationships of the transition. We developed a central force spring model, where particles can undergo a phase change using parameters of olivine and spinel. The algorithm is capable of simulating the local growth of the mentioned phases on the basis of direction-dependant rate laws. In the current context newtonian viscosity is added to the previously solely elastic system, since under HP/HT conditions the viscous flow within the material will have a large influence on the distribution of elastic energies, which in turn have an important influence on the driving force of the transition. Thus we are dealing with a visco-elastic system, which will be subjected to timedependant strain.