Interpreted cross section from the Mantle Electromagnetic and Tomography (MELT ) experiment across the East Pacific Rise. The seismic imaging and anisotropic structure is interpreted to show an asymmetrical melting region extending to 100 km depth. Upper mantle material is being cycled through the melt zone, which is reflected in the composition of oceanic crust. (Image from MELT Seismic Team, 1998. Imaging the deep seismic structure beneath a mid-ocean ridge: The MELT Experiment, Science, 280(5367):1215–1218, doi:10.1126/science.280.5367.1215. Reprinted with permission from AAS.)