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Comptes Rendus Géoscience
Volume 339, n° 9
pages 613-621 (août 2007)
Doi : 10.1016/j.crte.2007.07.008
Received : 8 November 2006 ;  accepted : 9 July 2007
U-Pb zircon SIMS ages from the French Massif Central and implication for the pre-Variscan tectonic evolution in Western Europe
Âges U-Pb sur zircon (SIMS) dans le Massif central français et implications pour l'évolution pré-Varisque de l'Europe occidentale
 

Paul Alexandre
Department of Geological Sciences and Geological Engineering, Queenʼs University, Kingston ON, K7L 3N6, Canada 

Abstract

Zircons from a metagranite sample from the Lower Gneiss Unit in Limousin (French Massif Central) were dated by the U-Pb ion probe method. Apart from inherited Palaeoproterozoic ages (1.8 to 2.1Ga), all analyses are concordant to sub-concordant and fall into three age groups: 617±17, 526±14, and 457±23Ma. Distinct oscillating banding domains within the zircons analysed suggest that the ages correspond to at least two consecutive episodes of protolith reworking. The ages obtained are similar to other found in the French Massif Central, but the fact that here they are seen in a single zircon grain or in a single grain population points out to the cyclic evolution of the protolith in a succession of tectonic events also affecting the microplates between Laurussia and Gondwana.

The full text of this article is available in PDF format.
Résumé

Les zircons extraits d'un métagranite de l'unité inférieure des gneiss dans le Limousin (Massif central) ont été datés par la méthode U-Pb à la sonde ionique. Mis à part les âges paléoprotérozoïques (de 1,8 à 2,1Ga), toutes les analyses sont concordantes ou subconcordantes, et forment trois groupes d'âges : 617±17, 526±14, et 457±23Ma. Des zones de croissance oscillatoires observées dans les zircons datés suggèrent que ces âges correspondent à au moins deux épisodes consécutifs de recyclage du protolithe. Des âges similaires ont été obtenus ailleurs dans le Massif central, mais le fait qu'ils soient observés ici dans une seule population de grains révèle le caractère cyclique de l'évolution du protolithe, dans le cadre d'une suite d'événements tectoniques qui affectent les microplaques entre l'Eurasie et le Gondwana.

The full text of this article is available in PDF format.

Keywords : U-Pb geochronology, Ion microprobe, Variscan Orogeny, Pre-Variscan evolution, Massif Central, France

Mots clés : Géochronologie U-Pb, Sonde ionique, Orogénie varisque, Évolution pré-Varisque, Massif central, France


1  Nancy University, ENSG-INPL, BP 20, 54501 Vandœuvre-les-Nancy, France; cheille@crpg.cnrs-nancy.fr.
2  Nancy University, UMR G2R CREGU, BP 239, 54506 Vandœuvre-les-Nancy, France; michel.cuney@g2r.uhp-nancy.fr.
3  Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden.
4  Additional reference : E. Deloule, P. Alexandrov, A. Cheilletz, B. Laumonier, P. Barbey, In-situ U-Pb zircon ages for Early Ordovician magmatism in the eastern Pyrenees, France: the Canigou orthogneisses, Int. J. Earth Sci. (Geol. Rundsch.) 91 (2002) 398-405).


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