Transfer of melt between microscopic pores and macroscopic veins in migmatites

A new model is proposed to numerically simulate transfer of melt between mi croscopic 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 (1985) but add calculation s concerning the flow and local compaction processes around veins with diff erent inclinations to the maximum (compressive) deviatoric stress. inclusio ns perpendicular to sigma (1) tend to close while those parallel to sigma ( 1) tend to grow. Surrounding regions either compact or dilate and inclined veins propagate parallel to sigma (1). The incremental porosity decreases e xponentially with distance from the vein walls by, a factor equal to the co mpaction length. Local redistribution of melt from microscopic pores to mac roscopic veins strongly enhances melt segregation into the vein networks wh ich can lead to bodies sufficiently massive to become buoyant. (C) 2001 Els evier Science Ltd. All rights reserved.