Geophysical Characterization and Modelling of Metamorphic and Sedimentary Units in East Timor : Insight into Tectonic, Basin Evolution, and Implications to Hydrocarbon and Ore Minerals

Abstract

Timor has a complex tectonic history, and it is reflected in the structure of the geological units in the area. This study performs a qualitative interpretation of the recently acquired aeromagnetic, radiometric, and aerogravity data to explore the distribution and structure of metamorphic and sedimentary units in East Timor. The qualitative interpretation reveals that the Bebe-Susu Metamorphic Complex is an association of the Banda and Gondwana blocks that were emplaced onto the Australian Continental Margin resulting from the arc-continent collision. Similarly, the Aileu Metamorphic Complex is an association of the Banda and Gondwana blocks, including metasediments of the underthrust Gondwana Megasequence that propagated into forearc in the north before backthrusted onto Australian Continental Margin. The Bebe-Susu Metamorphic Complex and the Aileu Metamorphic Complex can be geophysically distinguished from the underlying Gondwana sedimentary rocks and the Passive Margin sedimentary rocks. Analysis of the lineament pattern indicates a combined non-Andersonian and Andersonian conjugate faulting, where the faults intersect at high- and low-angles, respectively, relative to the maximum compressional stress. The interpreted geological units and structures favor the overthrust model, where the Australian Passive Margin Megasequence imbricates in front of the Banda forearc, while the Gondwana Megasequence underthrusts and develops duplex structure. Meanwhile, the underlying Australian basement stacked in front of the forearc continental sliver and developed basement-involved thrust, involving the overlying sedimentary sequence. At the Moho, the Mantle lithosphere detached from the overlying Australian crust and continuously subducted, and later experienced rollback due to the Banda forearc subsidence. These tectonic events had led to uplifting and exhumation in Timor ~5 km before it was eroded. The qualitative interpretation implies anticlinal structures of duplex structures and basement-involved thrusts which may be favorable for hydrocarbon traps within the sedimentary sequences of both upper and lower plates. The interpretation also identifies areas that may be prospective for mineralization; hydrothermal gold deposits within the Sula spur and Argo blocks, gold placer deposits within the Synorogenic Megasequence derived from the Bebe-Susu Metamorphic Complex, possible gold deposits along the Laclo and Caidara-lata faults, and chromite deposits within the ultramafic rocks, including possible ore deposits associated with the felsic and mafic dykes.