MELT MIGRATION IN PLUME-RIDGE SYSTEMS

Abstract

We assess the potential for melt migration, separate from solid flow, to accommodate the transport of plume-signature material from off-axis mantle plumes to nearby mid-ocean ridges. We use a boundary-element method to estimate the solid pressures induced by buoyant plume flow, and find that the solid pressure gradients are small compared to melt buoyancy, suggesting that melt streamlines in mantle plumes are essentially vertical. We combine our plume pressure solutions with analytical pressure fields for ridge corner flow and find that the combined plume-ridge pressure field is not sufficient to drive porous flow in the upper mantle over the distances (hundreds of km) observed in many natural systems. We also examine melt transport via porous flow in a melt-rich layer at the base of the lithosphere for plume-ridge systems, and find that melts can traverse plume-ridge offsets of several hundred kilometers in a few hundred thousand years, or less. Our results suggest that plume signatures observed in ridge basalts can be explained by lateral migration of plume melts in a sub-lithospheric channel augmented by solid flow pressure gradients. We apply our models to the Galapagos plume-ridge system and find that melt migration, as opposed to solid flow, provides a means to explain many aspects of the observed chemical anomalies on the Galapagos Spreading Center, including the position of the maximum anomalies due north of the archipelago, the symmetric pattern, and the gradual along-axis gradient.