EARLY DEVELOPMENT OF THE SOUTHERN KERGUELEN PLATEAU (INDIAN-OCEAN) FROM SHALLOW WIDE-ANGLE OCEAN-BOTTOM SEISMOMETER AND MULTICHANNEL SEISMIC-REFLECTION DATA

We examine the early geological history of the southern Kerguelen Plat eau (Indian Ocean) using ocean bottom seismometer (OBS), multichannel seismic (MCS), and Ocean Drilling Program data. Velocity-depth models in the sedimentary Raggatt Basin are constrained by near-range OBS dat a (refractions and reflections, including multiples and converted shea r waves) and migrated MCS data. The models elucidate the significance of lower Cretaceous lava flows, Albian to Coniacian/Santonian terrestr ial and terrigenous sediment, and Maastrichtian and Paleocene seismic sequences. The Albian/Aptian basaltic basement complex consists of an upper and a lower series. The upper series is characterized by average V(p)s of 4.6-4.7 km/s, an upward increase of intercalated terrestrial sediment and altered flowtops, and a concomitant decrease in flow thi ckness; the lower series is marked by average V(p)s of 5.3-5.5 km/s, a nd contains thicker flows and less sediment. A volcanic center in the Raggatt Basin shows relatively low V(p)s (3.7-3.9 km/s for the upper s eries, 4.7-4.9 km/s for the lower series), and dipping reflections on the Raggatt Basin's flanks are also recorded as refractions. Terrestri al and terrigenous sediment of the Raggatt Basin, immediately overlyin g basement, is characterized by a seismic low-velocity layer with Vps ranging from 2.2-2.9 km/s and a thickness of >1100 m in the central ba sin. Nearby source regions (e.g., Banzare Bank and other elevated area s south of the basin) account for a terrestrial and terrigenous sedime nt volume of similar to 12,500 km(3), deposited over similar to 20 m.y . The depocenter of the Raggatt Basin began shifting in Santonian to e arly Maastrichtian time, and concluded by early late Paleocene time.