Summary of results. Joint NTGS-GA geochronology project: Crystalline basement intersected by the Mount Kitty 1 and Magee 1 drillholes south of Alice Springs, March 2021

Abstract

This Record presents data collected in March 2021 as part of the ongoing Northern Territory Geological Survey–Geoscience Australia SHRIMP geochronology project under the National Collaborative Framework agreement and Geoscience Australia's Exploring for the Future Program. New U–Pb SHRIMP zircon eochronological results were derived from igneous and meta-igneous rock chip samples of crystalline basement collected from two petroleum exploration wells (Mount Kitty 1 and Magee 1) drilled in the Amadeus Basin south of Alice Springs in the Northern Territory.

Zircons from granitoid rock at the base of Mount Kitty 1 contain two chemically and morphologically distinct subpopulations. The volumetrically major and minor zircon subpopulations yielded weighted mean 207Pb/206Pb and 238U/206Pb ages of 1586 ± 5 Ma and 1167 ± 10 Ma respectively. Both ages are typical of the Musgrave Province immediately to the south of Mount Kitty 1. U-Pb ages of zircons from 'Musgravian gneisses' are commonly ca 1600-1400 Ma, and those from the widespread granites of the Pitjantjatjara Supersuite of the Musgrave Province are ca 1220-1120 Ma.

No zircons in either subpopulation preserves any visual evidence for polyphase growth (eg core-rim relationships) that would indicate interaction between the two age components. The chemically and morphologically discrete nature of the two isotopically distinct zircon subpopulations suggests that the sample (which comprises drill chips collected over a 35 metre interval) represents a mixture of two discrete rock types. We interpret the volumetrically dominant zircon subpopulation to represent a granitic rock that crystallised at 1586 ± 5 Ma, whereas the lesser subpopulation represents minor dykes, hosted by the granite, that crystallised at 1167 ± 10 Ma.

Zircons from granitic gneiss in Magee 1 form a single age population with a weighted mean age of 1607 ± 7 Ma. Although granitic gneiss of this age is identified in parts of the Warumpi Province to the west of Alice Springs, it is a common age component in the Musgrave Province.

Zircon U-Pb ages from both Mount Kitty 1 and Magee 1 suggest that ca 1600 Ma granitic gneiss may be a major component of crystalline basement beneath the Neoproterozoic-Palaeozoic strata of the Amadeus