Deformation and exhumation in Timor: Distinct stages of a young orogeny

Timor Island, in the Outer Banda Arc, bordering the Timor Sea, preserves the orogenic product of an arc–continent collision between the Australian Plate and the Banda Arc that commenced after 10.9–9.8 Ma GTS2004 but emerged above sea level only 3.1 Ma ago. The orogenic pile includes large tracts of material from the Australian margin, including the Permian to Middle Jurassic Gondwana Megasequence and the Late Jurassic to early Late Miocene Australian-Margin Megasequence, which occur in thrust slices. In addition, material from the Banda Arc side of the plate margin, referred to as the Banda Terrane, occurs throughout the island and includes both seafloor metamorphosed igneous material and cover sediments, also in thrust sheets. However the distribution of thrust slices is unclear in many areas, perhaps because only the uppermost nappes of the thrust pile are currently emergent and also because the thrust piles have been disrupted by later high-angle faulting.Evidence from East Timor suggests that the major break between deformed pre-collisional strata and the relatively undeformed overlying deposits was during the Late Miocene (9.8–5.5 Ma). We present evidence for the timing of three distinct phases of orogenic development, as determined from East Timor, including initial collision and emplacement of the early nappes creating loading and diapirism (within the 9.8–5.5 Ma interval), a tectonic quiet interval (5.5 Ma–4.5 Ma) that extended for about a million years during the middle of the collision and may represent the time of locking of the subduction system, and a post 4.5 Ma phase of uplift, unroofing and further diapirism in response to isostatic rebound. Our conclusions offer an alternative model for the evolution of this part of the Banda Arc.