Transfer of melt between microscopic pores and macroscopic veins in migmatites

Abstract

A new model is proposed to numerically simulate transfer of melt between microscopic pores and macroscopic veins in a deforming porous matrix. Matrix rheology is assumed to be visco-elastic. Darcy flow of porous melt through the matrix is calculated in accord with the theory of poroelasticity. Veins of melt are described separately. The model is realized using a code for a 2-D rectangle that is deformed at a constant strain rate. We reproduce in 2-D the main analytical results derived by Sleep (1988) but add calculations concerning the flow and local compaction processes around veins with different inclinations to the maximum (compressive) deviatoric stress. Inclusions perpendicular to σ₁ tend to close while those parallel to σ₁ tend to grow. Surrounding regions either compact or dilate and inclined veins propagate parallel to σ₁. The incremental porosity decreases exponentially with distance from the vein walls by a factor equal to the compaction length. Local redistribution of melt from microscopic pores to macroscopic veins strongly enhances melt segregation into the vein networks which can lead to bodies sufficiently massive to become buoyant.