Discovery of an alkaline orthogneiss in the eclogite-bearing Cellier Unit (Champtoceaux Complex, Armorican Massif): a new witness of the Ordovician rifting

An alkaline orthogneiss from the Lower Allochton of the Champtoceaux Complex has been identified by its mineralogy and its whole-rock chemistry, including trace elements and Sr and Nd isotopes. An U/Pb study of the zircons using the conventional method gives an upper intercept age of 481 +6/−5 Ma. The alkaline orthogneiss is thus a new witness of the Ordovician rifting in the Variscan Belt. To cite this article: M. Ballèvre et al., C. R. Geoscience 334 (2002) 303–311.