Sulphate incorporation in monazite lattice and dating the cycle of sulphur in metamorphic belts

Abstract : Microgeochemical data and transmission electron microscope (TEM) imaging of S-rich monazite crystals demonstrate that S has been incorporated in the lattice of monazite as a clino-anhydrite component via the following exchange Ca2+ + S6+ = REE3+ + P5+, and that it is now partly exsolved in nanoclusters (5–10 nm) of CaSO4. The sample, an osumilite-bearing ultra-high-temperature granulite from Rogaland, Norway, is characterized by complexly patchy zoned monazite crystals. Three chemical domains are distinguished as (1) a sulphate-rich core (0.45–0.72 wt% SO2, Th incorporated as cheralite component), (2) secondary sulphate-bearing domains (SO2 >0.05 wt%, partly clouded with solid inclusions), and (3) late S-free, Y-rich domains (0.8–2.5 wt% Y2O3, Th accommodated as the huttonite component). These three domains yield distinct isotopic U–Pb ages of 1034 ± 6, 1005 ± 7, and 935 ± 7 Ma, respectively. Uranium–Th–Pb EPMA dating independently confirms these ages. This study illustrates that it is possible to discriminate different generations of monazite based on their S contents. From the petrological context, we propose that sulphate-rich monazite reflects high-temperature Fe–sulphide breakdown under oxidizing conditions, coeval with biotite dehydration melting. Monazite may therefore reveal the presence of S in anatectic melts from high-grade terrains at a specific point in time and date S mobilization from a reduced to an oxidized state. This property can be used to investigate the mineralization potential of a given geological event within a larger orogenic framework.
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Article dans une revue
Contributions to Mineralogy and Petrology, Springer Verlag, 2016, 171 (11), 〈10.1007/s00410-016-1301-5〉
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https://hal-clermont-univ.archives-ouvertes.fr/hal-01637392
Contributeur : Sylvaine Jouhannel <>
Soumis le : vendredi 17 novembre 2017 - 15:15:53
Dernière modification le : mercredi 19 septembre 2018 - 01:34:43

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Antonin Laurent, Anne-Magali Seydoux-Guillaume, Stéphanie Duchêne, Bernard Bingen, Valérie Bosse, et al.. Sulphate incorporation in monazite lattice and dating the cycle of sulphur in metamorphic belts. Contributions to Mineralogy and Petrology, Springer Verlag, 2016, 171 (11), 〈10.1007/s00410-016-1301-5〉. 〈hal-01637392〉

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