The spreading center is almost identical to a mid-ocean ridge., erupting MORB lavas with some influence of ocean island (OIB) components (Eissen et al., 1994). High-temperature hydrothermal activity occurs in a 2-km-wide axial graben atop the spreading ridge and has many similarities to high-temperature black smoker vents on the East Pacific Rise (Auzende and Urabe, 1994).