In situ chemical dating of tectonothermal events in the French Variscan Belt

Abstract

In situ U–Th–Pb geochronology on monazite using Electron Probe Micro Analyser has been performed on migmatite in the southern French Variscan Massif Central in order to decipher its complex history. After the Early Visean (340 Ma) nappe stacking, the Cévennes area experienced a regional migmatization already dated 330–325 Ma in northern Cévennes. In these rocks two monazite populations are recognized on the basis of petrology texture and geochemistry. The oldest monazite generation that appears as inclusion in K‐feldspar is dated at 331 ± 4 Ma. This age complies with that of the crustal melting experienced by the Cévennes metamorphic series. The youngest monazite generation is interstitial and gives an age of 320 ± 5 Ma. A hydrothermal origin, coeval with the peraluminous magmatism that predates the formation of the Late Carboniferous Velay Dome is proposed as a working hypothesis to account for the formation of this second monazite generation.

New age constraints on emplacement of the Cévenol granitoids, South French Massif Central

“…This metamorphism developed in a late-orogenic extensional context is coeval with the thermal perturbation induced by the Early Velay anatexis dated at 335-324 Ma . A second stage of migmatization affected the Velay dome at about 310-295 Ma (Mougeot et al 1997;Be Mezeme et al 2005) and our data suggest that this late Velay anatexis is synchronous with the emplacement of the Mont Lozère and Aigoual-St Guiral-Liron granitoids (Fig. 12).…”

The thermal–mechanical evolution of crustal orogenic belts at convergent plate boundaries: A reappraisal of the orogenic cycle

“…In the Himalaya-Tibet, the age of the oldest leucogranites emplaced in the Higher-Himalayan Crystallines is Oligocene (Deniel et al, 1987;Edwards and Harrison, 1997;Harrison et al, 1999;Chung et al, 2005) that might provide a minimum age for the onset of partial melting beneath Tibet (Vanderhaeghe and Teyssier, 2001b). In the Variscan belt of western Europe exposed in the French Massif Central, leucogranites and migmatites span a 40 Myr age range (Duthou et al, 1984;Mougeot et al, 1997;Be Mezeme et al, 2005;Faure et al, 2009;Melleton et al, 2009). …”

Precambrian protoliths and Early Paleozoic magmatism in the French Massif Central: U–Pb data and the North Gondwana connection in the west European Variscan belt

“…Two HT metamorphic events dated as Middle Devonian and Middle Carboniferous (late Visean) are known in the FMC ([Lafon, 1986], [Duthou et al, 1994], , [Be Mezeme et al, 2005a], [Be Mezeme et al, 2005b] and [Faure et al, 2008]). The Middle Devonian event is related to the nappe stacking event ( [Ledru et al, 1989] and and enclosed references).…”