Southeast Indian Ridge Between the Rodriguez Triple Junction and the Amsterdam and Saint-Paul Islands: Detailed Kinematics for the Past 20 m.y.

The Southeast Indian Ridge has the fastest spreading rates of the three mid-oceanic ridge systems of the Indian Ocean and has recorded the movements of Antarctica relative to Australia and India since the Late Cretaceous. New bathymetric and magnetic data have been collected by the R/V Marion Dufresne (1983) and the R/V Jean Charcot (1984), on the western part of this ridge, between the Rodriguez Triple Junction (25.5°S, 70.0°E) and the Amsterdam and Saint-Paul islands (38°S, 78°E). These data bring additional information on the seafloor magnetic pattern produced by the Southeast Indian Ridge during the past 20 m.y. A new tectonic chart is proposed for the area around the Amsterdam and Saint-Paul islands. We have mapped 17 isochrons ranging from anomalies 6 to 1 (20.5-0.7 Ma) based on the compilation of all the data available in this area (25 cruises). Their distribution clearly shows asymmetric features. Reconstructions at short time intervals show that stage poles of rotation describe oscillatory movements along a direction parallel to the Southeast Indian Ridge axis. Observed changes in spreading rates and the stability of the spreading directions since the Miocene support this result.