Diffusion-creep modelling of fibrous pressure shadows II: Influence of inclusion size and interface roughness

This paper extends previous work by us to gain a fuller appreciation of the physical factors that affect polycrystal diffusion-creep simulations of fibrous pressure-shadow growth around a pyrite inclusion. The earlier work dealt with the effect of diffusion ratio or diffusional conductance of the inclusion/matrix interface. The new work also examines the effects of inclusion geometry: a smaller inclusion of similar smoothness to the original, a regularly serrated inclusion the same size as the original and a coarse irregular inclusion of the same size. The results show: (1) significant enhancement of fibrous pressure-shadow growth and change of matrix strain pattern with decreased inclusion size, similar to an increase in diffusion ratio; (2) approach towards a maximum fibrous pressure-shadow growth at high diffusion ratios in the small-pyrite model; (3) little influence of the model serrations; (4) significant sliding on the interface at low diffusion ratios in all of the models; and (5) enhanced sliding in the irregular-pyrite model at low diffusion ratios. The results are qualitatively consistent with diffusion creep of a single grain interacting with a deforming medium. They demonstrate factors that may influence development of the natural structures under similar conditions in rocks.