A granular flow theory for the deformation of partially molten rock

A model is developed for deformation of partially molten rock in which the primary mechanism is the relative movement of grains and the strain rate is controlled by the rate at which the interferences to this movement are acc ommodated by local melting. It is concluded that, in multicomponent rocks w ith moderate melt fractions where this model is applicable, the strain rate is generally determined by the rate of diffusion of the grain components i n the melt, with linear dependence on deviatoric stress, quadratic dependen ce on melt fraction, and inverse quadratic dependence on grain size. Where melt is free to escape, the strain rate is somewhat higher than for a close d system but the melt escape rate is more strongly dependent on the pressur e differential between grains and melt (effective pressure) than on the app lied principal stress difference. Unless the stress difference is large com pared with the effective pressure, any substantial increase in rate of melt release due to deformation would have to come from other factors such as i ncrease in permeability due to microfracturing. (C) 2001 Elsevier Science B .V. All rights reserved.