Nanoscale features revealed by a multiscale characterization of discordant monazite highlight mobility mechanisms of Th and Pb

• Published in: Contributions to Mineralogy and Petrology
• Main Authors: Turuani, Marion, J, Seydoux-Guillaume, Anne-Magali, Laurent, Antonin T, Reddy, Steve, Harley, Simon, Fougerouse, Denis, Saxey, David, Gouy, Sophie, de Parseval, P., Reynaud, S., Rickard, W.
• Other Authors: Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement (LGL-TPE), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Curtin University Perth, University of Edinburgh, Centre de microcaractérisation Raimond Castaing (Centre Castaing), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT), Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Laboratoire Hubert Curien (LHC), Institut d'Optique Graduate School (IOGS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), Université Jean Monnet - Saint-Étienne (UJM), INSU-CNRS
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: Monazite; Napier complex (Antarctica); Th and Pb mobility mechanisms; Pb-bearing nanophases; clusters; atom probe tomography and TEM; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy; Napier; Antarc*; Antarctica
• Online Access: https://hal.science/hal-04069718; https://hal.science/hal-04069718/document; https://hal.science/hal-04069718/file/Turuani_et_al_2023_CTMP_preproof_version.pdf; https://doi.org/10.1007/s00410-023-02015-x

International audience Understanding radionuclides mass transfer mechanisms in monazite (LREEPO4) and the resulting features, from the micro-to the nanoscale, is critical to its use as a robust U-Th-Pb geochronometer. A detailed multi-scale characterization of discordant monazite grains from a granulite which records a polymetamorphic history, explores the mechanisms of Th and Pb mobility in crystals. Some monazite grains display Th-rich linear features (0.1-1 µm thick) associated with a chemically varied suite of amorphous silicate (±Al, Mg, Fe) phases or sulphur (e.g. FeS). They are interpreted as precipitates within monazite crystals. They formed during replacement mechanism of monazite through fluid interactions. Two generations of Pb*bearing nanophases exist supported by previous geochronological data. The shielding effect of garnet and rutilated quartz (host minerals), limiting fluid access, induces plentiful Pb*-bearing nanophases precipitation (fluid saturation enhanced) and limits Pb*-loss at the grainscale. This multi-scale study provides new insights for interpretations of meaningless geochronological information thanks to nanoscale investigations.