Tectonic history of aseismic ridges in the eastern Indian Ocean

Abstract

We have devised a model for the origin of the Ninetyeast Ridge, the Broken Ridge–Naturaliste Plateau, and the Kerguelen Plateau in the eastern Indian Ocean which demonstrates that they were created by fixed hot spots now beneath the Amsterdam–St. Paul and Kerguelen Islands. The model employs reconstructions constrained by relative motions between plates; the model was deduced from sea-floor data and by paleolatitudes from Australian paleomagnetic pole data. Paleolongitudes were constrained by holding the Ninetyeast Ridge over the Amsterdam–St. Paul spot. Predicted age gradients and trajectories result, and these agree very well with geologic observations on the aseismic ridges. The Ninetyeast Ridge was laid down mainly from the Amsterdam–St. Paul hot spot, but also from the spot now under Kerguelen. The ridge is predicted to be from about 90 to 20 m.y. old. Broken Ridge–Naturaliste Plateau and the Kerguelen Plateau were both formed from the Kerguelen Islands hot spot and were joined prior to the Australia-Antarctic rift about 55 m.y. B.P. Broken Ridge–Naturaliste Plateau is predicted to be from more than 100 to about 80 m.y. old. Kerguelen Plateau should be from more than 100 to 0 m.y. old, but several volcanic hiatuses are predicted.