Continuous mantle melt supply beneath an overlapping spreading center on the East Pacific Rise

Tomographic images of upper mantle velocity structure beneath an overlappin g spreading center (OSC) on the East Pacific Rise indicate that this ridge axis discontinuity is underlain by a continuous region of Low P-wave veloci ties. The anomalous structure can be explained by an approximately 16-kilom eter-wide region of high temperatures and melt fractions of a few percent b y volume. Our results show that OSCs are not necessarily associated with a discontinuity in melt supply and that both OSC Limbs are supplied with melt from a mantle source Located beneath the OSC. We conclude that tectonic se gmentation of the ridge by OSCs is not the direct result of magmatic segmen tation at mantle depths.