This record presents new SHRIMP U-Pb zircon geochronology results from the Tanami and northern Arunta Regions, obtained through the NTGS-GA1 geochronology project in the period 2000–2003. The samples were collected as part of geological mapping of these regions by NTGS in 1999–2002.
Eight samples of granite and granodiorite from the Tanami Region in TANAMI2 and THE GRANITES give SHRIMP UP-b zircon ages that range from 1815 ± 4 Ma in the southern Coomarie Dome to 1791 ± 4 Ma for The Granites Granite. These ages fall within the same range as previously dated granites from the region. In MOUNT SOLITAIRE, five granites have been dated from either side of the Tanami–Arunta regional boundary and have ages in a similar range, from 1813 +7/-5 Ma to 1792 ± 7 Ma. A granite from Waldrons Hill, near the northern margin of the Arunta Region in LANDER RIVER, intrudes mafic intrusions at that locality. This granite has an age of 1814 ± 4 Ma, placing a minimum age on the mafic intrusions. Foliated granites from further south in MOUNT THEO and MOUNT PEAKE have slightly younger ages of 1785 ± 4 Ma and 1789 ± 6 Ma, respectively.
A number of samples provide evidence for magmatic and thermal activity during the 1730–1700 Ma Strangways Orogeny. Undeformed granite near Mount Windajong in MOUNT PEAKE intruded at 1731 ± 4 Ma. Near Fiddlers Lake, in the southeastern Tanami Region, amphibolite facies metamorphic rocks are spatially associated with S-type granites. A metapsammite from this locality has a maximum deposition age of 1819 ± 10 Ma, with a provenance spectrum characteristic of the Lander Rock beds and Killi Killi Formation. A nearby S-type granite has a similar population of zircons, interpreted to be inherited from partial melting of the metasedimentary rocks, but with evidence of isotopic disturbance at, or later than 1740 ± 5 Ma. Another S-type granite, 20 km to the southwest, has a zircon population interpreted to be entirely inherited from the metasedimentary rocks, with a youngest population at 1731 ± 4 Ma.
Detrital zircons were analysed for three widely spaced metasedimentary rocks, and all gave maximum deposition ages within error of each other, ranging from 1828 ± 18 Ma to 1819 ± 10 Ma. These are slightly younger than most maximum deposition ages for the Killi Killi Formation and Lander Rock beds, although the detrital zircon populations are more typical of these units, with a major peak at about 1865 Ma.
A sample of coarse-grained undeformed granite interpreted to belong to the Southwark Suite in eastern LAKE MACKAY has an age of 1533 ± 5 Ma, which is around 35 my younger than a dated sample of the Southwark Suite in MOUNT DOREEN.
A number of samples show evidence for thermal events postdating crystallisation. A granite from near Fiddlers Lake has high-U rims that provided two concordant analyses of about 700 Ma. A granite from the Coomarie Dome has a grain with extremely high U that gave a near-concordant age of 324 ± 7 Ma (σ), possibly recording an event during the Alice Springs Orogeny.
Bibliographic Reference: Cross A, Claoué-Long JC, Scrimgeour IR, Crispe A and Donnellan N, 2005. Summary of results. Joint NTGS-GA geochronology project: northern Arunta and Tanami regions, 2000–2003. Northern Territory Geological Survey, Record 2005-003.
