Kerguelen Plateau bathymetry, sediment distribution and crustal structure

Abstract

The Kerguelen Plateau is a large topographic high situated in the south-central Indian Ocean, adjacent to Antarctica. The plateau rises some 2000 fathoms (∼ 3700 m) above the adjacent deep seafloor and, along its NW-SE-trending axis, exceeds 2000 km in length. The rugged northern part of the Kerguelen Plateau is dominated by NW-SE-trending normal faults and associated sediment-filled troughs and is believed to be young relative to the rest of the plateau. The central and southern parts lie in deeper water and are topographically subdued; fault trends in the central region are N-S, in the southern they are NW-SE, identical to the northern region. Sediments of Cenomanian age were sampled by a piston core taken on the eastern flank of the central region; we judge that the core penetrated the acoustic basement. Seismic profiles and piston cores from the central and southern parts of the plateau reveal a prominent sub-bottom reflector of Eocene age. It appears that significant areas of the plateau were peneplaned during the Eocene; this event was followed by general subsidence and normal faulting. Beneath the acoustic basement in the central plateau, sonobuoy measurements reveal a layer up to 1 km thick with a refraction velocity of 3.7 km/sec, underlain by material with an average velocity of 4.9 km/sec, presumably a crystalline basement. The 4.9 km/sec material must be considerably older than Cenomanian. No significant structural connection between Antarctica and the Kerguelen Plateau was observed. A sediment isopach map of the plateau and the deep ocean area to the east has been compiled. A sediment ridge paralleling the eastern margin of the plateau in abyssal depths appears to be the result of deposition by a westward-flowing bottom current that has been deflected northward by the plateau. Gravity data indicate a crust about 20–23 km thick beneath the plateau. We interpret this intermediate crustal thickness, the short-wavelength large-amplitude magnetic anomalies observed over the plateau, and other evidence discussed in the text, as evidence that the plateau is probably oceanic in origin. Anomalous depths to the top of the oceanic crust adjacent to the northeastern edge of the plateau and the plateau elevation itself are interpreted to result from a mantle hot spot, now centered beneath the active volcanoes in the northern part of the plateau. We suggest that the composite Kerguelen Plateau is an uplifted remnant of the Cretaceous ocean basin that existed to the west of Australia following the separation of India from Western Australia-Antarctica. Furthermore, it is speculated that the time transgressive eastern margin of the plateau has been created by a modest northerly drift of the locus of volcanic activity relative to the Antarctic plate.