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Durham University

Department of Earth Sciences


Publication details for Prof Roger Clive Searle

Searle, R. C., Cannat, M., Fujioka, K., Mevel, C., Fujimoto, H., Bralee, A. & Parson, L. (2003). FUJI Dome: A large detachment fault near 64°E on the very slow-spreading southwest Indian Ridge. Geochemistry, Geophysics, Geosystems 4(8): 9105.

Author(s) from Durham


A continuous, domed detachment surface (FUJI Dome) has been imaged on the very slow spreading South West Indian Ridge using deep-towed sidescan sonar, and has been investigated by manned submersible and sea-surface geophysics. The Dome is morphologically similar to other oceanic detachments, core complexes or mega mullions. In addition to bathymetric mullions observed in ship-borne bathymetry, finer scale spreading-parallel striations were imaged with the sidescan. On the detachment surface, metabasalt crops out near the termination, probably as part of a thin fault sliver. Gabbro and troctolite probably crop out near the summit of the dome. The rest of the detachment surface is covered with sediment and rubble which is basaltic except for a single sample of serpentinite. Most of the detachment surface dips toward the ridge axis at 10° - 20°, but near the breakaway it is strongly rotated outwards, and dips away from the axis at up to 40°. Normal, undeformed volcanic seafloor crops out adjacent to the detachment. Modelling of sea surface magnetic data suggest the detachment was active from 1.95 Ma for about 1 Ma during a period of reduced and asymmetric magmatic accretion. Modelling of sea surface and seafloor gravity requires laterally fairly uniform but high density material under the Dome, and precludes steeply dipping contacts between bodies with large density contrasts at shallow levels under the Dome.