Statistical tests of the data from the Southeast Indian Ridge alone are not sufficient to confirm it, but motion about the Rodriguez Triple Junction (RTJ) suggests some non-rigidity in the Antarctica-Australia-Somalia circuit. These new observations strongly support the hypothesis that the Capricorn plate exists. Several recent geophysical cruises to the Southeast Indian Ridge, including a cruise within the proposed boundary, provide many new data for investigating the validity of the Capricorn plate model. The proposed boundary is Ëœ2000 km wide where it intersects the Southeast Indian Ridge. An additional boundary, further dividing the Australian plate into Australian and Capricorn plates has been proposed to account for much of the remaining inconsistency and the pattern of intraplate earthquakes. An equatorial, diffuse boundary dividing the plate into separate Indian and Australian plates significantly improves the fit of kinematic plate models to the spreading rates, transform azimuths, and earthquake slip vectors on the spreading center boundaries. Plate motions in the Indian Ocean are inconsistent with a rigid Indo-Australian plate. Seafloor spreading on the Southeast Indian Ridge over the last one million years: a test of the Capricorn plate hypothesis Observed changes in spreading rates and the stability of the spreading directions since the Miocene support this result. Reconstructions at short time intervals show that stage poles of rotation describe oscillatory movements along a direction parallel to the Southeast Indian Ridge axis. Their distribution clearly shows asymmetric features. 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). A new tectonic chart is proposed for the area around the Amsterdam and Saint-Paul islands. These data bring additional information on the seafloor magnetic pattern produced by the Southeast Indian Ridge during the past 20 m.y. 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, 70.0Â☎) and the Amsterdam and Saint-Paul islands (38°S, 78Â☎). 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. Southeast Indian Ridge Between the Rodriguez Triple Junction and the Amsterdam and Saint-Paul Islands: Detailed Kinematics for the Past 20 m.y.
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