A model for the evolution of the Indian Ocean and the breakup of Gondwanaland

Magnetic anomaly and fracture zone information is used to develop a self‐consistent tectonic history of the Indian and South Atlantic oceans. Working backward in time we have made three reasonably well constrained (39, 53, and 65 Ma) and two speculative (80 and 115 Ma) reconstructions of the positions of the Gondwana continents (Ma is m.y.B.P.). Our final fit, which is constrained by the recognition of Mesozoic anomalies off Antarctica and in the Mozambique Basin, places Dronning Maud Land against southern Mozambique and Madagascar in the northern position against Kenya. We suggest that after the initial rifting, Antarctica moved away from Africa in a southerly direction relative to present‐day Africa. This started the formation of the Southwest Indian Ridge. Most of the present length and geometry of the ridge result from migration of triple junctions so do not reflect predrift continental outlines. India and Madagascar moved with Antarctica until India separated from first Antarctica then Madagascar, when it started moving north toward Asia. In our reconstructions we find no necessity for significant relative motion between the Antarctic Peninsula and South America from the early Cretaceous to the Oligocene. From the breakup of Gondwanaland to the present we identify seven significant events. These are (1) first break in the late Triassic/early Jurassic between East and West Gondwanaland with initial motion along long transform faults parallel to the present African east coast, (2) early Cretaceous separation of Africa and South America and possibly simultaneous separation between India and Australia‐Antarctica, (3) cessation of motion between Africa and Madagascar, (4) break between India and Madagascar in the late Cretaceous, (5) Paleocene reorganization in the northwest Indian Ocean when the Seychelles left India, (6) Eocene separation between Australia and Antarctica with Australia joining the Indian plate, and (7) India's collision with Asia and subsequent commencement of spreading on the Central Indian Ridge, and later opening of Drake Passage.