Ductile flow by grain fracture/granulation is called cataclasis and the rocks cataclasites. At deeper crustal levels, flow generally occurs by deformation within mineral grains by plastic flow, and movement of crystal defects, or diffusive mass transfer or diffusion of atoms or point defects through a crystal.
In consolidated rock, grains are locked in place by irregularity of shape, by cohesive grain boundaries, and by cement. During cataclastic flow, rock deforms without localizing fracture or strain at a hand sample scale, but the individual grains fracture and slide relative to one another to accommodate changes in shape.The grains behave as rigid particles, and the relative displacement of grains is by fracture or granulation. The overall or bulk deformation in such cases is a ductile flow which takes place primarily at low lithostatic pressures found at shallow crustal levels. The rocks get mylonitised and by rapid chilling into fault movement related glasses such as pseudotachylytes. The transition from cataclasis to mylonitization is a function of temperature and therefore of the depth.