Dating of marine authigenic minerals via in situ Rb Sr, U Pb, and Lu–Hf: A case study from the Georgina Basin, Australia

The in situ laser ablation–inductively coupled plasma tandem mass spectrometry (LA-ICP-MS/MS) technique enables rapid, high-resolution isotopic analysis with minimal contamination, ideal for dating authigenic minerals. This study employs LA-ICP-MS/MS triple dating (Rb Sr, U Pb, Lu Hf) on key authigenic minerals from the mid-Cambrian (∼505 ± 3 Ma) marine sequence of Australia's Georgina Basin. Glauconite, micrite, dolomite, and apatite were analyzed to constrain depositional ages and diagenetic overprints. Glauconite exhibits high porosity, extensive illitization, and secondary minerals, reflecting post-depositional alteration. In situ Rb Sr dating of glauconite yielded systematically younger ages (452 ± 13 Ma to 351 ± 8 Ma) coeval with two episodes of the Alice Springs Orogeny. Well-preserved micrite and fine dolomite yielded U Pb ages of 500 ± 17 Ma and 513 ± 19 Ma, consistent with the depositional age, whereas a coarser dolomite yielded a younger age of 478 ± 23 Ma with lower initial Pb. In situ Lu Hf dating of apatite from three dolostone samples yielded ages of 497 ± 69 Ma, 495 ± 79 Ma, and 493 ± 74 Ma, overlapping with the depositional window despite notable uncertainties. A phosphorite sample yielded a Lu Hf age of 425 ± 49 Ma, coeval with the Rodingan event. In situ U Pb apatite ages yielded dispersed and unrealistic ages demonstrating that the Lu Hf system provides more robust ages than U Pb for authigenic apatite, whereas Rb Sr ages reflect diagenetic resetting during orogeny. The integration of three radiometric systems provides a refined framework for reconstructing the basin's depositional and diagenetic history. • Rejuvenated glauconite Rb Sr ages correspond to episodes of the Alice Springs Orogeny. • Micrite and fine-crystalline dolomite yield U Pb ages consistent with depositional timing. • Coarse-crystalline dolomite exhibits evidence of a partially open U Pb system. • The Lu Hf system in authigenic apatite provides more robust ages than U Pb.