Middle Carboniferous intracontinental subduction in the Outer Zone of the Variscan Belt (Montagne Noire Axial Zone, French Massif Central). A multimethod geochronological approach of the polyphase metamorphism

Abstract : In the migmatitic dome of the Montagne Noire Axial Zone (Variscan French Massif Central), mafic eclogites yield zircon and rutile U-Pb SHRIMP and SIMS ages around 315-308 Ma. These "young" dates, obtained in two different laboratories, do not comply with the geological constraints available for the study area that suggest an older age of the high pressure-low temperature (M1) metamorphism. Nevertheless, the Sm/Nd age of the same rock at ca 358 Ma appears in better agreement with the geological constraints, and thus might reflect the age of the HP event. Similar 357-352 Ma monazite U-Th-Pbtot ages are obtained from relict grains in the Axial Zone kinzigites that represent restites enclosed in migmatites. Fur thermore, monazite grains from biotite-garnet-staurolite micaschists from the outer dome envelope, and Axial Zone kinzigites, yield U-Th-Pbtot ages ranging between 340 and 320 Ma. These dates are in good agreement with previously documented zircon and monazite ages from the migmatite and anatectic granites that represent a high temperature-low pressure (M2) event. The significance of the zircon and rutile ages in the eclogites is discussed in terms of hydrothermal circulations. A crustal scale model involving a North-directed intracontinental subduction, responsible for the high pressure34 low temperature (M1) metamorphism, and coeval with km-scale S-vergent recumbent folds in the Palaeozoic non-metamorphic cover, is followed by the high temperature-low pressure (M2) event, which is coeval with the development of the Axial Zone migmatitic dome, and upright folding in the Palaeozoic non-metamorphic series.
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Submitted on : Wednesday, August 28, 2013 - 8:41:54 AM
Last modification on : Wednesday, August 14, 2019 - 8:32:01 PM

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Michel Faure, Alain Cocherie, Julien Gaché, Chloé Esnault, Catherine Guerrot, et al.. Middle Carboniferous intracontinental subduction in the Outer Zone of the Variscan Belt (Montagne Noire Axial Zone, French Massif Central). A multimethod geochronological approach of the polyphase metamorphism. Geological Society Special Publication, Lyell Collection, pp.289-311, 2014, ⟨10.1144/SP405.2⟩. ⟨insu-00854742⟩

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