KH-07-4, Leg 2

The mid-ocean ridge process depends on a balance between spreading rate and melt supply, and the melt supply should reflect the physical and chemical character of mantle beneath the ridge. We target on the Southwest Indian Ridge 34-40ºE, because the spreading rate (ultraslow, ~15mm/yr) is the same along this long portion of the ridge. On the other hand, the eastern part of the area appears to have anomalously large melt supply maybe due to the proximity to the Marion hotspot, but this effect does not seem to reach the western segments where each ridge axis has an offset along a series of fracture zones. We conducted surface geophysical survey, marine magnetotelluric transect for imaging upper mantle structure, seismic survey for imaging crust structure, and dredge for rock sampling in this area to understand the contribution of mantle geochemistry to the structure and spreading style of mid-ocean ridges.