A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatites

Autor: Giada Iacono-Marziano, Malcolm Massuyeau, Emmanuel Le Trong, Ida Di Carlo, Johann Tuduri, Fabrice Gaillard, Laurent Bailly, Jérémie Melleton, Grégory Rogerie, Zineb Nabyl
Přispěvatelé: Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Magma - UMR7327, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), University of Johannesburg [South Africa] (UJ), Institut für Mineralogie, Westfälische Wilhelms-Universität Münster = University of Münster (WWU), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), ANR-10-LABX-0100,VOLTAIRE,Geofluids and Volatil elements – Earth, Atmosphere, Interfaces – Resources and Environment(2010), European Project: 279790,EC:FP7:ERC,ERC-2011-StG_20101014,ELECTROLITH(2011), University of Johannesburg (UJ), Westfälische Wilhelms-Universität Münster (WWU)
Rok vydání: 2020
Předmět:
Zdroj: Geochimica et Cosmochimica Acta
Geochimica et Cosmochimica Acta, 2020, 282, pp.297-323. ⟨10.1016/j.gca.2020.04.008⟩
Geochimica et Cosmochimica Acta, Elsevier, 2020, 282, pp.297-323. ⟨10.1016/j.gca.2020.04.008⟩
ISSN: 0016-7037
DOI: 10.1016/j.gca.2020.04.008
Popis: International audience; Rare earth element (REE) enrichments in carbonatites are often described as resulting from late magmatic-hydrothermal or supergene processes. However, magmatic pre-enrichment linked to the igneous processes at the origin of carbonatites are likely to contribute to the REE fertilisation. Experimental constraints reveals that immiscibility processes between carbonate and silicate melts can lead to both REE enrichments and depletions in carbonatites making the magmatic processes controlling REE enrichments unclear.We link REE contents of carbonatites to the magmatic stage at which carbonatites are separated from silicate magma in their course of differentiation. We present results of experiments made at pressure and temperature conditions of alkaline magmas and associated carbonatites differentiation (0.2 to 1.5 GPa; 725 to 975 °C; FMQ to FMQ +2.5), simultaneously addressing crystal fractionation of alkaline magmas and immiscibility between carbonate (calcio-carbonate type) and silicate melts (nephelinite to phonolite type). The experimental data shows that the degree of differentiation, controlling the chemical composition of alkaline melts, is a key factor ruling the REE concentration of the coexisting immiscible carbonate melts. In order to predict carbonate melt REE enrichments during alkaline magma differentiation, we performed a parameterisation of experimental data on immiscible silicate and carbonate melts, based exclusively on the silica content, the alumina saturation index and the alkali/alkaline-earth elements ratio of silicate melts. This parameterisation is applied to more than 1600 geochemical data of silicate magmas from various alkaline provinces (East African Rift, Canary and Cape Verde Islands) and show that REE concentrations of their potential coeval carbonatite melts can reach concentration ranges similar to those of highly REE enriched carbonatites (∑REE > 30 000 ppm) by immiscibility with phonolitic/phono-trachytic melt compositions, while more primitive alkaline magmas can only be immiscible with carbonatites that are not significantly enriched in REE.
Databáze: OpenAIRE
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