IMAGING THE DEEP SEISMIC STRUCTURE BENEATH A MIDOCEAN RIDGE - THE MELT EXPERIMENT

The Mantle Electromagnetic and Tomography (MELT) Experiment was design ed to distinguish between competing models of magma generation beneath mid-ocean ridges. Seismological observations demonstrate that basalti c melt is present beneath the East Pacific Rise spreading center in a broad region several hundred kilometers across and extending to depths greater than 100 kilometers, not just in a narrow region of high melt concentration beneath the spreading center, as predicted by some mode ls. The structure of the ridge system is strongly asymmetric: mantle d ensities and seismic velocities are lower and seismic anisotropy is st ronger to the west of the rise axis.