Summary of results. Joint NTGS-GA geochronology project : August 2003-December 2003

This record presents new SHRIMP U-Pb zircon geochronology from the Arunta Region and Pine Creek Orogen that were obtained through the NTGS-GA geochronology project in the period August-December 2003. Four samples were analysed from the Pine Creek Orogen to place timing constraints on the deposition of the sedimentary succession. Two samples of volcaniclastic sediments from the Wildman Siltstone (Mount Partridge Group) give maximumdeposition ages of 2025 +8/-5 Ma and 2029 ± 12 Ma, that are likely to be close the timing of volcaniclastic sedimentation. In contrast, two samples of the Gerowie Tuff from the overlying South Alligator Group have homogeneous zircon populations with ages of 1864 ± 3 Ma and 1862 ± 3 Ma, which are interpreted to reflect the timing of volcaniclastic sedimentation. This is significantly younger than the previously published conventional U-Pb zircon age of 1885 Ma for the South Alligator Group. A sample of presumed metavolcanic rock from the Masson Formation in the South Alligator Valley produced nil zircon. Zircons from ten samples of igneous and metasedimentary rocks from the Arunta Region were separated and mounted, of which seven had zircons suitable for analysis. Three metasedimentary rocks from the northern Arunta were successfully analysed. A greywacke from the Lander Rock beds in the Walkeley Hills (MOUNT SOLITAIRE1) has a dominant youngest detrital zircon population that provides a well constrained maximum deposition age of 1869 ± 4 Ma. In the Wabudali Range, the Lander Rock beds have a more complex provenance with a spectrum of ages from 3200 to 1825 Ma, and a maximum deposition age of 1847 ± 26 Ma. These are overlain by the Mount Thomas Quartzite of the Reynolds Range Group, which has a maximum deposition age in the Wabudali Range of 1834 ± 38 Ma. Three granites from MOUNT SOLITAIRE were analysed and all gave ages in the range 1805–1800 Ma. A sample of the Redhackle Granite from southwestern MOUNT PEAKE has an age of 1772 ± 3 Ma, with indications of a metamorphic overprint at 1580 Ma. The Wabudali Granite yielded only metamict zircons. BIBLIOGRAPHIC REFERENCE: Worden KE, Claoué-Long JC, Scrimgeour IR and Lally JH, 2004. Summary of results. Joint NTGS-GA geochronology project: August 2003–December 2003. Northern Territory Geological Survey, Record 2004-004.