Physics of Melt Extraction: Theory, Implications and Applications

This paper presents a general overview of ow in deformable porous media with emphasis on melt extraction processes beneath mid-ocean ridges. Using a series of simple model problems, we show that the equations governing magma migration have two fundamentally different modes of behaviour. Compressible two-phase ow governs the separation of melt from the solid and forms a non-linear wave equation that allows melt to propagate in solitary waves. Incompressible two-phase ow governs small scale mantle convection driven by lateral variations in melt content. The behaviour of both compressible and in-compressible ow is demonstrated in the context of mid-ocean ridges to show that both mechanisms may explain the observation of the narrowness of ridge volcanism. These results also suggest that melt extraction is an inherently time dependent process that may account for the timing, volume and chemistry of volcanism.