What Constraints Do Detrital Zircon Ages and Nd Isotopes In Paleoproterozoic Eastern Australian Basins Provide for Models Linking Australia and Southwestern Laurentia?

Zircon U–Pb geochronology and Nd isotope data from sedimentary rocks may be used to provide constraints on palaeogeographic reconstructions. Detrital zircon ages can be used to pattern match to crystalline sources, but this method alone can be ambiguous, unless the source rock age is unique.

Paleo- to Mesoproterozoic metasedimentary rocks in the northern Australian Mt. Isa, Coen, and Georgetown Inliers and the southern Australian Curnamona Province, along the eastern margin of Australia, represent the truncated present-day eastern boundary of Proterozoic Australia. Provenance data from these basins may provide an important constraint in models that reconstruct pre-Rodinian plate configurations.

Western Laurentia is a candidate for the continental mass joined to the present-day east of Proterozoic Australia in a number of pre-Rodinian reconstruction models. Crystallisation events in each region are similar in age, so that detrital zircon ages overlap substantially. But the southern Laurentian margin was an area of accretion of dominantly juvenile material, from the ca 1840 Ma Penokean Orogeny through the ca 1640-1600 Mazatzal Orogeny, with initial ε_Nd values largely positive. Conversely, juvenile initial ε_Nd values for magmatic rocks in any Archean to Paleoproterozoic eastern Australian source are rare.

Nd isotope data from ca 1800 to 1650 Ma sedimentary packages along the eastern Australian margin record highly crustally evolved sources with initial ε_Nd values from -2 to -7. Only in the uppermost sedimentary packages in the Curnamona and Georgetown Inlier is there a suggestion of less crustally evolved material, as initial ε_Nd values range up to 0.1. The rifting that resulted in the early basin fill along Proterozoic Australia's eastern margin was probably intracratonic, with proximal Australian terrains able to account for the age and isotope signature of basin fill. Only in the uppermost sedimentary packages is there suggestion of sources not found in cratonic Australia.