SHIPBOARD GEOPHYSICAL INDICATIONS OF ASYMMETRY AND MELT PRODUCTION BENEATH THE EAST PACIFIC RISE NEAR THE MELT EXPERIMENT

Near the Mantle Electromagnetic and Tomography (MELT) Experiment, seam ounts form and off-axis lava flows occur in a zone that extends farthe r to the west of the East Pacific Rise than to the east, indicating a broad, asymmetric region of melt production. More seamounts, slower su bsidence, and less dense mantle on the western flank suggest transport of hotter mantle toward the axis from the west. Variations in axial r idge shape, axial magma chamber continuity, off-axis volcanism, and ap parent mantle density indicate that upwelling is probably faster and m ore melt is produced beneath 17 degrees 15'S than beneath 15 degrees 5 5'S. Recent volcanism occurs above mantle with the lowest seismic velo cities.