The crustal role of the Agulhas Plateau, southwest Indian Ocean: evidence from seismic profiling

• Published in: Geophysical Journal International
• Main Authors: Gohl, Karsten, Uenzelmann-Neben, Gabriele
• Format: Text
• Language: English
• Published: Oxford University Press 2001
• Subjects: Research Papers; Kerguelen; Indian; Bouvet; Antarc*; Antarctica
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/144/3/632; https://doi.org/10.1046/j.1365-246x.2001.01368.x

Its key geographical position near the reconstructed centre of the Gondwana break-up between Antarctica, South America and Africa has brought attention to the Agulhas Plateau, an oceanic plateau in the southwest Indian Ocean, with regard to its crustal nature and origin. The majority of previous studies have suggested a dominantly continental origin. As part of the project SETARAP (Sedimentation and Tectonics of the Agulhas Ridge and Agulhas Plateau), we conducted an extensive seismic survey over the plateau with the aim of solving the questions about its crustal structure, origin and role in a plate tectonic reconstruction context. In addition to 1550 km of high-resolution seismic reflection profiles, we recorded deep-crustal large-offset and wide-angle reflection/refraction data from an ocean-bottom hydrophone (OBH) profile across the southern plateau. The reflection data show clear indications of numerous volcanic extrusion centres with a random distribution. We are able to date this phase of voluminous volcanism to Late Cretaceous time, a period when numerous other large igneous provinces formed. Traveltime inversion of the deep-crustal OBH records reveals an up to 25 km thick crust with velocities between 7.0 and 7.6 km s−1 for the lower 50–70 per cent of its crustal column. We do not find indications for continental affinity but rather a predominantly oceanic origin of the Agulhas Plateau, similar to that inferred for the Northern Kerguelen and Ontong–Java plateaus. In Late Cretaceous time, its main crustal growth was controlled by the proximity of spreading centres and by passage over the Bouvet hotspot at 80–100 Ma.