Nanoscale features revealed by a multiscale characterization of discordant monazite highlight mobility mechanisms of Th and Pb
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 granu...
Published in: | Contributions to Mineralogy and Petrology |
---|---|
Main Authors: | , , , , , , , , , , |
Other Authors: | , , , , , , , , , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2023
|
Subjects: | |
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 |
Summary: | 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. |
---|