Duffy, B1, Lew, B1, Boland, K1, Kohn, B1, Matchan, E1, Maas, R1, Dixon, D1, Pedro, L2, de Carvalho, P2, Sandiford, M1
1School of Earth Sciences, The University Of Melbourne, Melbourne, Australia, 2Instituto do Petroleo e Geologia, Dili, Timor-Leste
Timor occupies a critical position within Wallacea and within the Indonesian throughflow, but its tectonic history remains poorly constrained compared to other parts of the region. Tectonic models typically divide the island into 1) Australian affinity rocks, including a thick sequence of Paleozoic and Mesozoic rocks and metamorphosed equivalents, and 2) Asian affinity rocks, made up of predominantly Cretaceous and Paleogene rocks and their metamorphosed equivalents, known as the Lolotoi Metamorphic Complex (LMC). New field mapping shows that the type-area of the LMC is pre-Permian basement exposed in an erosional window. Much of the previously mapped LMC is actually overlying alkaline Permian basalt. LA-ICPMS U-Pb ages for zircons, apatites and titanites from the LMC type-area are Precambrian and consistent with those from Gondwanan continental slivers that now form the basement of eastern Java and West Sulawesi. Such basement ages are also identified in peaks from inherited zircons from the LMC elsewhere in Timor. Basement faults separating the LMC from Triassic and Jurassic sediments contain white micas yielding Ar-Ar ages of c.38 Ma, which are within the age range of white micas from the Asian affinity Mutis metamorphic complex of West Timor. Zircon and apatite (U-Th)/He thermochronometric data and low vitrinite reflectance values across much of the study area do not support previous models suggesting Cenozoic overthrusting. However, close to the basement fault the thermochronometric data indicate rapid Eocene-Oligocene cooling and like the white mica ages, this is consistent with the thermal history of the Mutis complex of West Timor. On the basis of these data, we revive Barber’s (1978) interpretation that almost all of the pre-Neogene exhumed rocks of eastern Timor, including the Gondwanan rocks, resided in Sundaland during the Cenozoic. This finding strongly supports hydrocarbon prospectivity onshore in Timor and has implications for the geodynamics of the Banda Arc, reconstructions of Wallacea, and the Neogene paleogeography of the Indonesian Throughflow.
Brendan Duffy is a research fellow in structural geology and tectonics at The University of Melbourne. His research focuses on the structural and geomorphic development of convergent boundaries of the Australian plate, at single earthquake to Cenozoic timescales.