| Summary: | Wide-angle seismic data collected during the Kerguelen ocean bottom seismometer experiment provide the first images of the deep structure of the southern Kerguelen Plateau and support a new interpretation of the origin of the plateau. Velocity models based on travel time inversions and reflectivity synthetic seismograms show a 22-km-thick crust composed of average 1.6 km of sedimentary cover, average 5.3 km of upper crust, average 11.0 km of lower crust, and a 4- to 6-km-thick reflective zone immediately above Moho. Velocities in the upper crust (from 3.8-4.5 km/s at top to 6.0-6.5 km/s at bottom) are consistent with the basaltic nature of this layer, the top of which was sampled during the Ocean Drilling Program. Velocities in the lower crust increase continuously from 6.60 km/s at the top to 6.90 km/s at 19.5 km depth. The reflective zone at the base of the crust identified by wide-angle reflections is observed only along the NNW-SSE direction. It consists of alternating high- and low-velocity layers with an average velocity of 6.70 km/s in the NNW-SSE direction and ?6.90 km/s in the perpendicular direction. Strong azimuthal anisotropy is also observed in the upper mantle with velocities of 8.60 and 8.00 km/s, in the NNW-SSE and E-W directions, respectively. The absence of high velocities at the base of the crust that characterizes many large-volume mafic provinces, the reflective lower crust, and anisotropy in upper mantle suggest that the southern Kerguelen Plateau represents a stretched continental fragment overlain by basaltic flows isolated from the Antarctic margin during the early opening of the Indian Ocean
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