Summary of results. Joint NTGS-GA geochronology project: Pine Creek Orogen and Arunta Region January-June 2004

This record presents new SHRIMP U-Pb geochronological results from the Pine Creek Orogen and Arunta Region that were obtained through the NTGS-GA geochronology project in the period January–June 2004. A number of samples from across the Pine Creek Orogen were analysed to determine emplacement ages of igneous intrusions, in addition to extrusion ages for felsic volcanic rocks and maximum depositional ages for sedimentary protoliths. A sample that had been interpreted as Nimbuwah Complex in western Arnhem Land appears to have an Archaean precursor, with an age population of 2634 ± 4 Ma and probable metamorphic overgrowths at 2473 ± 12 Ma. In the central Pine Creek Orogen, a sample of Warrs Volcanic Member from near Daly River yielded a stratigraphic age of 1862 ± 3 Ma. A metapelitic unit within the Hermit Creek Metamorphics was analysed and yielded a conservative maximum age constraint of 1860 ± 3 Ma for the deposition of the sedimentary protolith. In the Arunta Region, a number of metasedimentary rocks from MOUNT THEO1 were analysed. Two of these yielded maximum deposition ages of 1785 +3/-5 Ma and 1746 ± 25 Ma, respectively, while the third yielded a bimodal age distribution, which was unmixed into two components of 1794 ± 4 Ma and 1813 ± 3 Ma. This implies the existence of widespread metasedimentary rocks that are younger than the 1850–1830 Ma Lander Rock beds. An unnamed granite from the Aileron Province in northeastern MOUNT RENNIE has an emplacement age of 1767 ± 4 Ma. Three samples were analysed from the low-grade Kintore Domain in the Warumpi Province in western MOUNT RENNIE. The Ininti Granite yielded a crystallisation age of 1688 ± 5 Ma, and a maximum deposition age of 1681 ± 8 Ma was calculated for the Sandy Blight Quartzite. The dacitic Walungurru Volcanics yielded an inherited age spectrum, with the youngest zircons providing a maximum extrusion constraint of ca 1846 Ma. Bibliographic Reference:Worden KE, Claoué-Long JC, Scrimgeour IR and Doyle N, 2006. Summary of results. Joint NTGS-GA geochronology project: Pine Creek Orogen and Arunta Region, January–June 2004. Northern Territory Geological Survey, Record 2006-005.