New limits on the motion between India and Australia since chron 5 (11 Ma) and implications for lithospheric deformation in the equatorial Indian Ocean

• Published in: Geophysical Journal International
• Main Authors: Royer, Jean-Yves, Gordon, Richard G., DeMets, Charles, Vogt, Peter R.
• Format: Text
• Language: English
• Published: Oxford University Press 1997
• Subjects: Articles; Indian; Antarc*; Antarctica
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/129/1/41; https://doi.org/10.1111/j.1365-246X.1997.tb00937.x

We present new aeromagnetic data from a 1990 survey across the Central Indian and Carlsberg ridges between 18°S and 5°N. The 86 new crossings of anomaly 5 fill a gap of more than 2000 km in previously identified crossings. We furthermore present 15 crossings from Project Magnet aeromagnetic data and 79 crossings from shipboard data to add to 56 previously identified crossings used in prior plate reconstruction work. These combine to give a total of 236 crossings of anomaly 5 flanking the Carlsberg Ridge and Central Indian Ridge. Fracture-zone crossings are extracted from satellite-derived gravity profiles from the Seasat, Geosat/ERM, ERS1 and Topex spacecraft-based altimeters giving 177 useful new crossings near anomaly 5 on 22 conjugate palaeotransform fault pairs; these data replace the 23 crossings used in prior plate reconstruction work. These and many other new altimetry crossings along other portions of the fracture zones permit all the fracture zones flanking the Central Indian and Carlsberg ridges to be recognized and delineated. We use these new plate-motion data to improve the reconstruction of the relative positions of the African, Indian and Australian plates at chron 5 (11 Ma). The improved quality and increased number of magnetic anomaly and fracture-zone crossings allow a great shrinking relative to prior work of the uncertainties in the relative rotations since chron 5 of the African, Australian and Indian plates. The volume of the 95 per cent confidence region is 98 times smaller than found before for the Africa-India rotation, 76 times smaller than found before for the Africa-Australia rotation, and 188 times smaller than found before for the Australia-India rotation. Unlike prior work, in which the Africa-Australia rotation depended strongly on estimates of Australia-Antarctica and Africa-Antarctica rotations, the Africa-Australia rotation can now be estimated accurately from data only along the Central Indian Ridge. The new small-confidence regions exclude all prior best estimates of these ...