Abstract

Recent information from magnetic surveys and from deep-sea drilling allows Sclater and Fisher's Late Cretaceous and Cenozoic reconstructions of the eastern Indian Ocean to be extended back almost to the beginning of the Cretaceous Period. After a short phase of spreading off northwestern Australia in Middle and Late Jurassic time, Greater India and Antarctica-Australia dispersed near the beginning of Cretaceous time (130 m.y. B.P.) with the opening between them of a landlocked sea; between 110 to 120 and 105 m.y. B.P., Greater India cleared Antarctica-Australia, and the sea floor generated between them became continuous with the rest of the Indian Ocean. In Santonian time (80 m.y. B.P.), a new pattern of rapid spreading (as much as 17.5 cm/yr) began and caused an oceanic part of the Indian plate to be transferred to the Antarctic-Australian plate. Rapid spreading continued nearly to the end of Paleocene time (53 m.y. B.P.). With the inception at this time of spreading between Antarctica and Australia, three plates (Indian, Antarctic, and Australian) spread at a slow rate until the end of early Oligocene time (32 m.y. B.P.). At 32 m.y. B.P., the separate Indian and Australian plates became united, as they are today, while Antarctica remained a separate plate.

Together with paleomagnetic and other determinations that show that Southeast Asia lay at or north of the Equator, the trail of sea floor generated during Greater India's northward flight implies that Southeast Asia rotated westward across this trail to its present position no earlier than middle to late Miocene time (10 m.y. B.P.).

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