Evolution of the Eastern Indian Ocean since the Late Cretaceous Contraints from Geosat Altimetry (Paleoceanographic Mapping Project Progress Report No. 41-0888)
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We propose a new model for the tectonic evolution of the Eastern Indian Ocean from the Late Cretaceous to the present. Two types of data are used to improve previously-published reconstructions. First, reinterpreted seafloor magnetic anomalies, between Australia and Antarctica and in the Wharton basin, provide new constraints on spreading rates and the timing of major reorganizations. Second, vertical deflection profiles (i.e. horizontal gravity anomaly), derived from 22 repeat cycles of GEOSAT altimeter data, reveal the tectonic fabric associated with fracture zones. These new GEOSAT data provide tight constraints on paleo-spreading directions. For example, three prominent fracture zones can be traced from south of Tasmania to the George V Basin, Antarctica providing an important constraint on the relative motions of Australia and Antarctica through the Late Eocene. In addition, the GEOSAT profiles are used to locate the conjugate continental margins and continent-ocean boundaries of Australia and Antarctica, as well as the conjugate rifted margins of Kerguelen Plateau and Broken Ridge. Based on a compilation of magnetic anomaly data from the Crozet Basin, the Central Indian Basin, the Wharton Basin and the Australian-Antarctic Basin, ten plate tectonic reconstructions are proposed. Reconstructions at chrons 5 (11 Ma), 6 (21 Ma), 13 (36 Ma) and 18 (43 Ma) confirm that the Southeast Indian Ridge behaved as a single plate boundary since chron 18. The constraints from the GEOSAT data provide an improvement in the fit of the Kerguelen Plateau and the Broken Ridge at chron 20 (46 Ma). The opening of the Australian-Antarctic Basin from break-up to chron 24 requires a decoupling between the northern and southern provinces of the Kerguelen Plateau. Finally, the model for the relative motions of India, Australia and Antarctica is consistent with the emplacement of the Ninetyeast Ridge and the Kerguelen Plateau over a fixed hotspot.