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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

Abstract : U–Pb geochronological data were collected on zircon by LA-MC-ICP-MS on orthogneiss and paragneiss from the Limousin area in the French Massif Central (FMC), in order to investigate the connection between the west European Variscan belt and the northern margin of Gondwana. Fifteen samples were collected in the four main tectonostratigraphic units of the FMC, namely: the Para-Autochthonous Unit, the Lower Gneiss Unit (LGU), the Upper Gneiss Unit (UGU) and the Thiviers–Payzac Unit. Orthogneiss yield intrusion age between 521 ± 7 and 446 ± 6 Ma. Considering all the results from both magmatic and metasedimentary samples, two peaks at 531 and 473 Ma are recognized. Rifting processes taking place along the North Gondwana margin during the Lower Paleozoic went on until the end of the Ordovician, as suggested by the magmatic event recorded around 450 Ma. Several maximum depositional ages were ascertained in the metasedimentary formations of the FMC, as determined by the youngest detected detrital zircon crystal, ranging from 604 ± 16 Ma for metasediments of the Para-Autochthonous unit, 573 ± 12 Ma for the LGU, 564 ± 9 Ma for the Thiviers–Payzac Unit, and 523 ± 4 Ma in the UGU. Minimum depositional ages are given by magmatic emplacement ages obtained in the crosscutting orthogneiss. There is some evidence for a decrease of this maximum age upwards in the tectonostratigraphy. Detrital zircon in metasedimentary formations and inherited zircon in orthogneiss display a wide spectrum of ages with significant peaks at around 590 Ma and 560 Ma. Archean, Paleoproterozoic and Neoproterozoic detrital zircons suggest a West African craton source of the sedimentation. The large amount of Neoproterozoic and Lower Paleozoic ages obtained in this study suggests that these periods played a significant role in the continental crustal growth history of Western Europe.
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Jérémie Melleton, Alain Cocherie, Michel Faure, Philippe Rossi. 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. Gondwana Research, Elsevier, 2010, 17, pp.13-25. ⟨10.1016/j.gr.2009.05.007⟩. ⟨insu-00442947⟩

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