Publications

Multibeam bathymetry data, combined with 2D seismic data and studies on land, provide new insights into the major structures in the northern and eastern Banda Arc. In the west, north of Buru, is the deep Buru basin where there is evidence of extension with probable Neogene oceanic crust. To the east, the thrust front of the Seram fold and thrust belt (FTB) can be traced along the Seram trough which turns from E-W to N-S to pass through the Kai Islands into the Tanimbar trough. The thrust front is not east of the Kai Islands as often drawn. Between the Kai and Aru Islands is the Aru trough bounded by NNE-SSW-trending normal faults which converge to the SW and can be traced southwards into the Tanimbar trough. An important WNW-ESE-trending, probably inactive, fault bounds the northern end of the Aru trough south of the Bird’s Head that we name the Kumawa fault. It is partly buried below disturbed sediments that have slumped from the shelf south of the Lengguru FTB. This is a major tectonic feature. To the north there is a late Neogene history of contraction that formed the Misool–Onin–Kumawa Ridge and Lengguru FTB. To the south, east of the thrust front, extensional structures dominate. We propose that the Kumawa fault links to the Kawa shear zone of Seram which together form a lithosphere-scale sinistral shear zone active during the Miocene and Pliocene which exhumed deep crust and mantle on Seram. The Kumawa fault offsets the Seram thrust front close to the Kumawa peninsula. To the east is the E-W-trending Tarera–Aiduna fault zone that can be traced offshore only a short distance from the Bird’s Head. This is a very young structure with little displacement which does not reach the Seram Trough. However, present-day seismicity indicates active E-W extension of the Aru trough and strike-slip movement on the Tarera–Aiduna fault zone. The Seram trough began to form in the Late Pliocene due to loading by the Seram FTB. The Tanimbar trough originated in the Late Miocene as an elongate extensional structure within the Australian continental margin. Neither troughs are subduction zones. Almost all active deformation in the Seram FTB is on Seram, and offshore south of the trough and north of the Kumawa fault. There is almost no seismicity at the trough itself, unlike modern subduction zones. South of the Kumawa fault is a wide FTB, trending roughly N-S towards the Kai Islands and Tanimbar, with young mud volcanism but little seismicity. Immediately west of the FTB is the Weber deep, the Earth’s deepest forearc basin, which is a young extensional basin bounded by a major low angle detachment on its eastern side. It is the most recent manifestation of eastward Banda subduction rollback, and may still be active.