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Discovery of an albite gneiss from the Ile de Groix (Armorican Massif, France): geochemistry and LA-ICP-MS U-Pb geochronology of its Ordovician protolith

El Korh, Afifé ; Schmidt, Susanne ; Ballèvre, Michel ; Ulianov, Alexey ; Bruguier, Olivier

In: International Journal of Earth Sciences, 2012, vol. 101, no. 5, p. 1169-1190

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    Titre
    • Discovery of an albite gneiss from the Ile de Groix (Armorican Massif, France): geochemistry and LA-ICP-MS U-Pb geochronology of its Ordovician protolith
    Auteur
    • El Korh, Afifé. Department of Mineralogy, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland
    • Schmidt, Susanne. Department of Mineralogy, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland
    • Ballèvre, Michel. Geosciences Rennes (UMR CNRS 6118), University of Rennes 1, 35042, Rennes Cedex, France
    • Ulianov, Alexey. Institute of Mineralogy and Geochemistry, University of Lausanne, Anthropole, 1015, Lausanne, Switzerland
    • Bruguier, Olivier. Geosciences Montpellier (UMR CNRS 6250), University of Montpellier 2, 34095, Montpellier Cedex 05, France
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • International Journal of Earth Sciences, 2012, vol. 101, no. 5, p. 1169-1190. Springer-Verlag
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:311652
    Summary
    For the first time, an albite orthogneiss has been recognised and dated within the HP-LT blueschist facies metabasites and metapelites of the Ile de Groix. It is characterised by a peraluminous composition, high LILE, Th and U contents, MORB-like HREE abundances and moderate Nb and Y values. A U-Pb age of 480.8±4.8Ma was obtained by LA-ICP-MS dating of zircon and titanite. It is interpreted as the age of the magmatic emplacement during the Early Ordovician. Morphologically different zircon grains yield late Neoproterozoic ages of 546.6-647.4Ma. Zircon and titanite U-Pb ages indicate that the felsic magmatism from the Ile de Groix is contemporaneous with the acid, pre-orogenic magmatism widely recognised in the internal zones of the Variscan belt, related to the Cambro-Ordovician continental rifting. The magmatic protolith probably inherited a specific chemical composition from a combination of orogenic, back-arc and anorogenic signatures because of partial melting of the Cadomian basement during magma emplacement. Besides, the late Devonian U-Pb age of 366±33Ma obtained for titanite from a blueschist facies metapelite corresponds to the age of the HP-LT peak metamorphism