A Discussion on natural strain and geological structure - The kinetics of rock deformation by pressure solution
A simple model for rock deformation by pressure solution, assuming grain boundary diffusive mass transfer to be deformation rate controlling, is presented. The model leads to a constitutive flow law which is of the same form as that for Coble creep. It is argued that the presence of a fluid film in stressed grain boundaries leads to enhanced diffusivity of solute particles in the grain boundary. Some simple experiments are described, which demonstrate rapid diffusion in solutions in pores, much slower diffusion in stressed interfaces and deformation by pressure solution. By using the theoretical model, and by assuming that the pressure of the interfacial solution is equal to the applied normal stress, so that available experimental data on the effect of pressure on mineral solubility could be used, rates of deformation by pressure solution have been calculated. These are compared with rates of deformation by crystal plastic and high temperature diffusive flow processes, by using deformation mechanism maps. Predicted transition conditions between various deformation mechanisms are found to be consistent with those inferred from the study of textures of naturally deformed rocks.