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Contrasting magma types and timing of intrusion in the Permian layered mafic complex of Mont Collon (Western Alps, Valais, Switzerland): evidence from U/Pb zircon and 40Ar/39Ar amphibole dating

Monjoie, Philippe ; Bussy, François ; Schaltegger, Urs ; Mulch, Andreas ; Lapierre, Henriette ; Pfeifer, Hans-Ruedi

In: Swiss Journal of Geosciences, 2007, vol. 100, no. 1, p. 125-135

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    Titre
    • Contrasting magma types and timing of intrusion in the Permian layered mafic complex of Mont Collon (Western Alps, Valais, Switzerland): evidence from U/Pb zircon and 40Ar/39Ar amphibole dating
    Auteur
    • Monjoie, Philippe. Institute of Mineralogy and Geochemistry, IMG-ANTHROPOLE, University of Lausanne, CH-1015, Lausanne, Switzerland
    • Bussy, François. Institute of Mineralogy and Geochemistry, IMG-ANTHROPOLE, University of Lausanne, CH-1015, Lausanne, Switzerland
    • Schaltegger, Urs. Department of Mineralogy, University of Geneva, 13, rue des Maraîchers, CH-1205, Geneva, Switzerland
    • Mulch, Andreas. Institute of Mineralogy and Geochemistry, IMG-ANTHROPOLE, University of Lausanne, CH-1015, Lausanne, Switzerland
    • Lapierre, Henriette. Laboratoire de Géodynamique des Chaînes Alpines LGCA, University of Grenoble, 1381 rue de la Piscine, FR-38041, Grenoble Cedex, France
    • Pfeifer, Hans-Ruedi. Institute of Mineralogy and Geochemistry, IMG-ANTHROPOLE, University of Lausanne, CH-1015, Lausanne, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Swiss Journal of Geosciences, 2007, vol. 100, no. 1, p. 125-135. Birkhäuser-Verlag; www.birkhäuser.ch
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:317265
    Summary
    Abstract.: We have selected and dated three contrasting rock-types representative of the magmatic activity within the Permian layered mafic complex of Mont Collon, Austroalpine Dent Blanche nappe, Western Alps. A pegmatitic gabbro associated to the main cumulus sequence yields a concordant U/Pb zircon age of 284.2 ±0.6Ma, whereas a pegmatitic granite dike crosscutting the latter yields a concordant age of 282.9 ±0.6Ma. A Fe-Ti-rich ultrabasic lamprophyre, crosscutting all other lithologies of the complex, yields an 40Ar/39Ar plateau age of 260.2 ±0.7Ma on a kaersutite concentrate. All ages are interpreted as magmatic. Sub-contemporaneous felsic dikes within the Mont Collon complex are ascribed to anatectic back-veining from the country-rock, related to the emplacement of the main gabbroic body in the continental crust, which is in accordance with new isotopic data. The lamprophyres have isotopic compositions typical of a depleted mantle, in contrast to those of the cumulate gabbros, close to values of the Bulk Silicate Earth. This indicates either contrasting sources for the two magma pulses - the subcontinental lithospheric mantle for the gabbros and the underlying asthenosphere for the lamprophyres - or a single depleted lithospheric source with variable degrees of crustal contamination of the gabbroic melts during their emplacement in the continental crust. The Mont Collon complex belongs to a series of Early Permian mafic massifs, which emplaced in a short time span about 285-280Ma ago, in a limited sector of the post-Variscan continental crust now corresponding to the Austroalpine/Southern Alpine domains and Corsica. This magmatic activity was controlled in space and time by crustal-scale transtensional shear zones