Mechanical and thermodynamic constraints on fluid distribution in partial melts

Abstract

In this paper we examine the mechanical and thermodynamic criteria which are necessary for equilibrium to exist in partial melts that are subject to hydrostatic stress. Existing theory satisfactorily demonstrates (1) that crystal‐liquid interfaces will have no sharp edges and will approach constant curvature and (2) that the liquid will form a continuously interconnected network by distributing itself in channels along intergranular edge intersections provided that the liquid wetting angle is less than 60°. However, the full textural implications of the thermodynamics have apparently not been realized previously. Currently accepted theoretical developments have been extended to show how equilibrium melt distribution varies with wetting angle. We find that contrary to a widely accepted view a homogeneous fluid phase cannot completely wet intergranular faces, regardless of the exact wetting angle. As a result the intercrystalline faces will remain in mechanical contact throughout the assemblage even when it is characterized by a 0° dihedral angle.