  Partially molten rock is a densely packed, melt-saturated, granular medium,
but it has seldom been considered in these terms. In this manuscript, we extend
the continuum theory of partially molten rock to incorporate the physics of
granular media. Our formulation includes dilatancy in a viscous constitutive
law and introduces a non-local fluidity. We analyse the resulting
poro-viscous--granular theory in terms of two modes of liquid--solid
segregation that are observed in published torsion experiments: localisation of
liquid into high-porosity sheets and radially inward liquid flow. We show that
the newly incorporated granular physics brings the theory into agreement with
experiments. We discuss these results in the context of grain-scale physics
across the nominal jamming fraction at the high homologous temperatures
relevant in geological systems.
