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Contribution de la géochronologie U-Th-Pb sur monazite à la compréhension de la fusion crustale dans la chaîne varisque française et implication géodynamique.

Abstract : The French Variscan Belt results from collision between sourthern Gondwana and northern Laurussia continents. The French Massif Central is one of the meridional sections of the Variscan Belt where structural investigations point out to a polycyclic evolution. The Belt is mainly composed of micaschist of the Para-autochtonous Unit, the Lower Gneiss Unit of para and ortho-derived rocks, the Upper Gneiss Unit and the Thiviers-Payzac Unit composed of metagraywackes, rhyolites and quartzites. In addition, the numerous migmatitic complexes and granitoids bodies that crop out within the Belt were dated using electron micro probe dating of monazite to assess time scale of crustal melting according to the dynamic evolution. The high spatial (spot of ~2 µm in diametre) resolution of the method leads to investigate polyphase events recorded by a single crystal and to avoid the mixture of domains different in age like with other classical dating methods. Three melting events have been highlighted: a first anatexis ranges around 385-375 Ma, a second phase of melting was activated at 330-325 Ma, and a third one at 310-290 Ma. They result both from nappes stacking and “unstacking” and also from asthenospheric injections.
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Submitted on : Wednesday, February 8, 2006 - 10:42:36 AM
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  • HAL Id : tel-00011558, version 1

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Eugène Be Mezeme. Contribution de la géochronologie U-Th-Pb sur monazite à la compréhension de la fusion crustale dans la chaîne varisque française et implication géodynamique.. Géologie appliquée. Université d'Orléans, 2005. Français. ⟨tel-00011558⟩

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