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Bimodal magmatism as a consequence of the post-collisional readjustment of the thickened Variscan continental lithosphere (Aiguilles Rouges-Mont Blanc Massifs, Western Alps)

Bussy, François ; Hernandez, Jean ; Von Raumer, Jürgen

In: Transactions of the Royal Society of Edinburgh: Earth Sciences, 2000, vol. 91, no. 1-2, p. 221-233

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    Titre
    • Bimodal magmatism as a consequence of the post-collisional readjustment of the thickened Variscan continental lithosphere (Aiguilles Rouges-Mont Blanc Massifs, Western Alps)
    Auteur
    • Bussy, François. François Bussy, Earth Sciences Department, Royal Ontario Museum, Toronto, Canada; and IMP-BFSH2, UNIL, CH-1015 Lausanne, Switzerland e-mail: francois.bussy@imp.unil.ch
    • Hernandez, Jean. Jean Hernandez, IMP-BFSH2, UNIL, CH-1015 Lausanne, Switzerland e-mail: jean.hernandez@imp.unil.ch
    • Von Raumer, Jürgen. Jürgen Von Raumer, Institut de Minéralogie, Pérolles Université, CH-1700 Fribourg, Switzerland e-mail: juergen.vonraumer@unifr.ch
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Transactions of the Royal Society of Edinburgh: Earth Sciences, 2000, vol. 91, no. 1-2, p. 221-233. Royal Society of Edinburgh Scotland Foundation
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:299875
    Summary
    ABSTRACT: High Precision U-Pb zircon and monazite dating in the Aiguilles Rouges-Mont Blanc area allowed discrimination of three short-lived bimodal magmatic pulses: the early 332 Ma Mg-K Pormenaz monzonite and associated 331 Ma peraluminous Montées Pélissier monzogranite; the 307 Ma cordierite-bearing peraluminous Vallorcine and Fully intrusions; and the 303 Fe-K Mont Blanc syenogranite. All intruded syntectonically along major-scale transcurrent faults at a time when the substratum was experiencing tectonic exhumation, active erosion recorded in detrital basins and isothermal decompression melting dated at 327-320 Ma. Mantle activity and magma mixing are evidenced in all plutons by coeval mafic enclaves, stocks and synplutonic dykes. Both crustal and mantle sources evolve through time, pointing to an increasingly warm continental crust and juvenile asthenospheric mantle sources. This overall tectono-magmatic evolution is interpreted in a scenario of post-collisional restoration to normal size of a thickened continental lithosphere. The latter re-equilibrates through delamination and/or erosion of its mantle root and tectonic exhumation/erosion in an overall extensional regime. Extension is related to either gravitational collapse or back-arc extension of a distant subduction zone