Melt migration beneath mid-ocean ridges

Summary Using a two-phase flow model, we investigate the formation of a high-percentage melt layer beneath the oceanic lithosphere and focusing of the melt towards the ridge axis, taking into account freezing and melt extraction. Melt migration is modelled dynamically within a viscous permeable media that includes the asthenosphere and viscous part of the lithosphere. Due to a much faster melt migration in the brittle part of the lithosphere, the melt migration is simulated by instantaneous melt extraction from an assigned melt extraction region beneath the ridge axis. It is shown that a high-percentage melt layer forms and successfully focuses melt to a narrow zone beneath the mid-ocean ridge. Performance of the melt focusing mechanism is not significantly sensitive to the size of the melt extraction region, the melt extraction threshold and the spreading rate. In all of our models, about half of the total melt production freezes beneath the base of the lithosphere and the rest is focused towards the ridge and forms the crust.