Analog modelling of melt segregation and migration during deformation

Abstract

Abstract Analog experiments of melt segregation and migration in lower crustal rocks have been conducted using paraffin wax. The wax has a mechanical planar anisotropy which reproduces the pervasive foliation of high-grade metamorphic rocks. The shortening of a layer of partially molten wax (melt fraction between 15 and 20%) results in the movement of a part of the liquid from the microscopic porosity of the wax to the outside of the layer in large accumulation sites. Four stages can be identified: (1) from the beginning of the shortening, melt segregates into dilatant foliation-parallel veins; (2) the development of a fold occurs with an increasing accumulation of liquid in the limbs; (3) strain localization and vein connection allows the nucleation of shear bands; (4) melt migration is channelled by the shear band toward external pockets. The first two stages involve melt percolation from kinematically controlled high-stress areas around growing veins. The third stage is associated with local attainment of a segregated melt critical concentration estimated at 14–15%. The last point involves both horizontal and upward migration of the melt. Melt segregation and migration are highly scale- and strain-dependent mechanisms.