Basin evolution in oceanic volcanic plateaux: seismic reflection evidence from the Kerguelen Plateau, South Indian Ocean

Abstract

Multi-channel seismic reflection data from the Kerguelen Plateau, South Indian Ocean, are used to describe the evolution of sedimentary basins on this large feature. A number of sedimentary basins are present, the largest of which (the Raggatt Basin) is over 150 km wide. All the sedimentary basins are underlain by basement which shows internal reflection indicative of volcanic flows. These reflections define basement wedges and synforms, overlain by a marked erosional unconformity, which developed early in the history of the plateau. Intra-basement synforms acquired their initial shape during the emplacement of the plateau before the erosional episode. The lateral continuity of the reflectors across most of the basement synforms suggests that the volcanic sources of the plateau lie outside of them. The basement synforms may represent low areas between elevated volcanoes. Subsidence of large volcanoes may have caused the subsidence of these basins as flexural moats. If so, superposition of the subsidence of several volcanoes on the plateau has resulted in the variable shape of the basins; it also induced subsidence of basins relative to some adjacent volcanoes. This relative subsidence seems to have been active throughout the lifetime of this Early Cretaceous plateau, as indicated by onlaps within the sediments and the small bathymetric deeps associated with the basins. The observation that the sources of the volcanic flows lie outside the basement synforms is not consistent with existing models which explain the origin of dipping basement reflectors along passive margins.