Full length ArticleIsotopic (U-Pb, Nd) and geochemical constraints on the origins of the Aileu and Gondwana sequences of Timor

- Zircon age data suggests an east Pangaea origin for the Aileu and Gondwana sequences.
- Geochemical and Nd isotope data from these rocks differ substantially.
- Aileu and Gondwana sequences have different east Pangaea sources.
- Aileu and Gondwana sequences were deposited in widely separated basins.
- Miocene-Recent collision between Indo-Australia and Sundaland juxtaposed these strata.

Detrital zircon U-Pb age data collected from the argillitic sedimentary rocks of the Timorese Aileu Complex and Gondwana Sequence indicate that both units were derived from a common source containing 200-600 Ma, 900-1250 Ma and 1450-1900 Ma zircon. The modally most significant age population within this range of ages dates to c. 260 Ma. The observed spectrum of ages can be traced to the eastern active margin of Pangaea and its immediate foreland, which today is best exposed along the northeast coast of Australia. Compared to the relative homogeneity of the detrital zircon age data, geochemical and Nd isotopic data show that the mudstones of the Aileu Complex are on average more siliceous, have higher K2O/Na2O, Rb/Sr, Th/Sc and yield notably older Nd TDM model ages when compared to those from the Gondwana Sequence. These data are interpreted to suggest that, although both sequences share a common east Pangaea provenance, they were eroded from different sections of this active margin and deposited in spatially separated basins. The present proximity of these units is a result of their tectonic juxtaposition during the Pliocene to Recent collision between the northern edge of the Indo-Australia plate and the Banda Arc.

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