This record presents new SHRIMP U-Pb geochronological results from the Pine Creek Orogen, Tanami Region, Arunta Region and Amadeus Basin that were obtained through the NTGS-GA geochronology project in the period July–December 2004.
Eight samples were analysed from the Pine Creek Orogen. Granite sampled from drillcore from the Nabarlek uranium deposit yielded a crystallisation age of 1818 ± 8 Ma. A sample of Nourlangie Schist yielded a conservative maximum deposition age of 2024 ± 7 Ma, similar to that of the Wildman Siltstone. A drillcore sample of Welltree Metamorphics in the western Pine Creek Orogen yielded a conservative maximum deposition age of 1865 ± 4 Ma. A sample of Berinka Volcanics (Finniss River Group) in FERGUSSON RIVER1 yielded an age of 1861 ± 3 Ma. Another sample of Berinka Volcanics, from PORT KEATS, gave a small yield of zircons that appear to be consistent with those from the FERGUSSON RIVER sample, although insufficient age information could be obtained. A sample of Koolendong Granite from PORT KEATS yielded a median age of 1860 +3/-5 Ma. A possible high-level intrusion within the Chilling Sandstone contains an inherited zircon spectrum, with the youngest grains providing a maximum age of 1830 ± 7 Ma, suggesting that the Chilling Sandstone may be equivalent in age to the El Sherana or Edith River groups. An altered felsic gneiss sampled from the Ranger uranium mine contained zircons that were highly metamict and yielded no useful age information.
In the eastern Amadeus Basin, a thin tuffaceous unit was sampled from presumed Areyonga Formation (Neoproterozoic) in drillhole Ringwood-2A. This sample yielded a depositional age of 224 ± 3 Ma, with a Proterozoic inherited spectrum, suggesting that the tuff is Triassic in age and may form part of the Pedirka or Eromanga basins.
A sample of Helena Creek beds from BIRRINDUDU (Tanami Region) yielded a conservative maximum deposition age of 1841 ± 5 Ma.
From the Arunta Province, a sample of Koonoonyeri Granite from MOUNT PEAKE yielded a population of 1793 ± 3 Ma age, which is likely to be the crystallisation age, consistent with other granites in the area. Three samples from west of Emu Bore in LAKE MACKAY were analysed to provide age constraints on the poorly outcropping western Aileron Province. A sample of Lander Rock Formation yielded a maximum deposition age of 1842 ± 7 Ma, although metamorphic rims on broken grains have an age of 1773 Ma, which may be interpreted as the age of metamorphism or an alternative maximum deposition age. Five kilometres to the north, a ridge of Mount Thomas Quartzite is overlain by calc-silicate rock, and this calc-silicate rock is intruded by an unnamed granite. A sample of Mount Thomas Quartzite gave a maximum deposition age of 1800 ± 6 Ma, whereas the granite yielded a crystallisation age of 1773 ± 2 Ma. Despite some ambiguities in the interpretation of these ages, it may be interpreted that the Mount Thomas Quartzite was deposited around 1780–1775 Ma. Two samples were analysed from the western Warumpi Province in MOUNT RENNIE. A sample of Walungurru Volcanics yielded a maximum extrusion age of 1699 ± 14 Ma, whereas deposition of the protolith of a migmatitic metapelite of the Leisler Metamorphics is constrained by a maximum deposition age of 1704 ± 3 Ma.
Bibliographic Reference: Worden KE, Claoué-Long JC and Scrimgeour IR, 2006. Summary of results. Joint NTGS-GA geochronology project: Pine Creek Orogen, Tanami Region, Arunta Region and Amadeus Basin, July–December 2004. Northern Territory Geological Survey, Record 2006-006.
