On the role of surface tension in the migration of melts and fluids

It is shown that surface tension can cause redistribution of melt in a partially molten medium, in accordance with a non‐linear diffusion equation for the melt fraction. The associated diffusivity D depends on the surface energy and is positive (stable) for dihedral angle <60° and negative (unstable) for dihedral angle >60°. In the more likely stable case, D ∼ 10 −7 cm² .s −1 is typical for mantle melts, but a value as high as 10 −1 cm² .s −1 is conceivable for volatile‐rich fluids. Surface tension may play an important role in creating pathways for meta‐somatizing fluids in the Earth, but does not appear likely to affect substantially the existing estimates of large scale melt migration (e.g., beneath mid‐ocean ridges).