Melt migration beneath mid-ocean ridges

Using a two-phase flow model, we investigate the formation of a high-percen tage melt layer beneath the oceanic lithosphere and focusing of the melt to wards the ridge axis, taking into account freezing and melt extraction. Mel t migration is modelled dynamically within a viscous permeable media that i ncludes the asthenosphere and viscous part of the lithosphere. Due to a muc h faster melt migration in the brittle part of the lithosphere, the melt mi gration is simulated by instantaneous melt extraction from an assigned melt extraction region beneath the ridge axis. It is shown that a high-percenta ge melt layer forms and successfully focuses melt to a narrow zone beneath the mid-ocean ridge. Performance of the melt focusing mechanism is not sign ificantly sensitive to the size of the melt extraction region, the melt ext raction threshold and the spreading rate. In all of our models, about half of the total melt production freezes beneath the base of the lithosphere an d the rest is focused towards the ridge and forms the crust.