New Measurements Constrain Models of Mantle Upwelling Along a Midocean Ridge

It has long been known that as tectonic plates pull apart along the mid‐ocean ridge system, the mantle wells up to fill the gap. Partial melting of the mantle produces magma that percolates upward to the surface and solidifies into new crust within a few kilometers of the ridge. But the details of this process have been a mystery: Over what volume is the mantle melted to form this magma? What is the concentration of the melt? How connected are the pockets of molten material? To answer such questions, an international collaboration designed the Mantle Electromagnetic and Tomography (MELT) experiment, placing seismometers, electrometers and magnetometers on the ocean floor to span the midocean ridge known as the East Pacific Rise (see figure below). After several years of gathering and analyzing data, members of the collaboration presented their results at the Boston meeting of the American Geophysical Union at the end of May.

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