Bulletin of the Geological Society of Malaysia, Volume 33, Nov. 1993, pp. 105 – 118
Geological Research in Southeast Asia, Department of Geology
Royal Holloway and Bedford New College, Egham, Surrey, TW20 O~X, England
Present Address: Shellinternationale Petroleum MaatschapplJ B.V.
Postbus 162, 2501, AN Den Haag, Oostduinlaan 75, Nederland
Abstract: Timor and adjacent islands in Eastern Indonesia are the site of a currently active collision between the Australian continental shelf and the volcanic islands of the Banda Arc. Previously published sedimentological and micro-paleontological data from the islands and the subduction trench date the start of this collision at 2.5 to 3 Ma. Previously published work on seismicity in the Banda Arc shows the geometry of the subduction zone to be fairly simple and continuous down to below 650 km depth. In this paper, the geometry of both the top and bottom surfaces of the subducting slab is mapped to a higher degree of accuracy than before. The edge of Australia, which was previously a rifted passive margin, is shown to be markedly thickened in the collision zone itself and has been subducted to a depth of about 200 km. In addition, it appears that the subduction zone has major lateral and vertical discontinuities at depth. It is proposed that these discontinuities reflect slab separation during a previous microcontinental collisional event some 10 to 7 million years ago and that this collision was related to the transfer of continental lithosphere from the Indo-Australian plate to the South East Asian plate.