Role of grain boundaries in magma migration and storage

We employ a continuous theory of two-phase flow to investigate the influence of grain boundary tension on distribution and migration of melts through a viscous matrix. The ‘disaggregation melt fraction’, the volume fraction of partial melt at which grain boundaries are completely wetted, is crucial in determining the total interfacial force per unit volume. In partially molten aggregates with small dihedral angles and containing less melt than the disaggregation fraction, capillary action on grain boundaries tends to retain melt in tubules along triple grain junctions. As a consequence, pulses of buoyant magma decay during their ascent through the mantle. Strong interfacial tension on matrix grain boundaries also influences the thickness of a heavy partially molten layer. In aggregates with large dihedral angles, strong tension on grain–melt interfaces can give rise to self-separation of the melt from the matrix.