U–Pb zircon SIMS ages from the French Massif Central and implication for the pre-Variscan tectonic evolution in Western Europe

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 2.1 Ga), all analyses are concordant to sub-concordant and fall into three age groups: 617 ± 17, 526 ± 14, and 457 ± 23 Ma. 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.