2026/07/10 by Cecilia Loyola, Juraj Farkaš, Alan S. Collins +5
Environmental Science · Earth and Planetary Sciences · Health Professions · #Methane Hydrates and Related Phenomena #Geological and Geochemical Analysis #Radioactivity and Radon Measurements
paper · doi:10.1016/j.chemgeo.2026.123603
The crystalline basement beneath the Amadeus Basin (central Australia) hosts one of the world's highest recorded helium (He) concentrations (up to 9%) together with significant hydrogen (~11%). The radiogenic 4 He accumulated in the Neoproterozoic sedimentary succession of the Amadeus Basin was generated by alpha decay of U and Th in minerals of the underlying Proterozoic granitic basement. Initially retained within mineral lattices, He was later released through microfracturing. Constraining the timing of basement formation and subsequent fracturing is therefore critical to quantify long-term 4 He production and migration. We applied in-situ Rb Sr dating using LA-ICP-MS/MS to primary K-rich igneous minerals (orthoclase, muscovite) and to secondary fine-grained micas and sericite hosted in microfractures from granitic basement beneath the Amadeus Basin, recovered from >2 km depth via the Jacko Bore 1 drillhole. Primary minerals yielded an age of 1100 ± 30 Ma, consistent with the timing of cooling following the Musgrave Orogeny. Secondary micas and sericite produced younger ages (642 ± 31 Ma to 517 ± 22 Ma), corresponding to deformation during the Ediacaran–Cambrian Petermann Orogeny. The concentrations of U and Th in basement rocks were determined by LA-ICP-MS and combined with Nuclear Emulsion Gel imaging to identify alpha-emitting and 4 He producing domains. Integration of geochronology and trace element data enabled modelling of radiogenic 4 He production from the Proterozoic to present. Modelled He isotope compositions agree with published 3 He/ 4 He ratios (0.031 Ra) from Jacko Bore 1 gas samples, demonstrating the utility of in-situ Rb Sr geochronology for evaluating radiogenic helium system.