EAST TIMOR: THE LAND THAT PLATE TECTONICS (ALMOST) FORGOT

Geological research in East Timor since 2003 has yielded remarkable results that have significantly changed our understanding of the geology and tectonic evolution of this half-island, which forms part of the Outer Banda Arc. Working northwards from the northern Australian margin, we have focussed on examining the exposures of the deformed Australian passive margin (structural, tectonic, biostratigraphic), their links and relations to interleaved slices of Banda Arc origin, and the controls of deformation on the petroleum prospectivity, both onshore and offshore in East Timor. Some of our main results include that the type section of the Jurassic is Triassic in age, the type section of the Miocene is a thrust stack of Australian-derived Triassic to Cretaceous material (with no Miocene identified), and that a previously mapped, extensive package of schists actually contains MORB basalts and cumulates, and is likely to be a sliver of oceanic crust. Thrust contacts at both the base and top of the emplaced oceanic material have produced both extensive brittle and ductile shear zones. In addition, units of ocean-island basalts occur interleaved within thrust stacks of Gondwana material, in close stratigraphic association with a succession of Aptian to late Middle Miocene-aged pelagites that occur across the island. The pelagite/OIB association is known from oceanic plateaux on the northern Australian margin, and may indicate the preserved remnants of collided plateaux in Timor. A crush breccia of extensively reworked carbonates marks a local suture between Gondwanan and exotic Banda Terrane materials. Widely distributed, recently emplaced melange clays, probably re-worked Triassic muds, occur across the island, obscuring geological contacts in places and also raising exotic materials, for example fresh pillow basalts, to the surface, embedded in a mud matrix. The extensive mud diapirs attest to significant overpressure across the island, which is visible both onshore and in offshore seismic data, and causes high heat flows in places (Timor has hot springs). Finally, detailed logging of syn-orogenic sections indicates uplift and emergence of Timor Island approximately 3.3 Ma. We will present these results, as well as our current understanding of the tectonic evolution of this remarkable early-stage orogeny.