Timing of fluid alteration events by multiscale geochronology of uraninite and (Y,REE,U,Th)–(Nb,Ta,Ti) oxide minerals: An evaluation of the potential to detect hidden fluid events in Earth history
Final Report Abstract
Aqueous solutions play a significant role in the geochemical and geodynamic evolution of the Earth's crust. The timing of fluid events is currently determined primarily based on minerals precipitated directly from these fluids, which incorporate measurable amounts of radioactive elements that can be used for isotopic dating. However, fluid events can also be dated chemically and isotopically by analysing alteration domains of U- and Th-bearing minerals, as well as U-Th-bearing alteration products, using micro- and nano-analytical techniques. In this project, laser ablation with inductively coupled plasma mass spectrometry, the electron microprobe, and the atom probe were used to evaluate the potential and limitations of U-Pb dating of fluid-rock interactions through chemical and isotopic U-Th-Pb dating of alteration domains/products in titanite, uraninite, and especially in (Y,REE,U,Th)-(Nb,Ta,Ti) oxides. The dating attempts were accompanied by detailed mineralogical investigations. Field observations suggest that the pegmatites of the Proterozoic Evje-Iveland pegmatite field in southern Norway were overprinted by two distinct fluid events, namely a metasomatic and a later hydrothermal (350 to 150°C) event. The U-Th-Pb dating of titanite, euxenite, and uraninite, as well as their alteration products, from several pegmatites indicate that up to eight distinct fluid-rock interaction events influenced these pegmatites until today. This demonstrates that not all fluid events in geological history have been recognized to date, especially when they are not related to obvious magmatic or tectonic events. The combination of micro- to nanoanalytical techniques on samples from the Evje-Iveland pegmatite field has provided a more detailed atomistic understanding of the alteration reaction(s) between aqueous solutions and U/Th-bearing, often metamict minerals, and of the behaviour of U, Th, and radiogenic Pb. However, nano-scale observations from atom probe tomography also raised new questions concerning the behaviour of U, Th and Pb in (Y,REE,U,Th)-(Nb,Ta,Ti) oxides. The systematic dating of altered, U-Th-bearing minerals and accompanying alteration products potentially offers an extraordinary opportunity to detect hidden geological events in geological history.
Publications
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U-Pb dating of fluid interactions: Hidden tectonic events of the Telemark domain (southern Norway). GeoMin- Köln 2022
Öz, D., Tomaschek, F., Werner, R., Lagos, M. & Geisler, T.
