Isotopic evidence for the Precambrian provenance and Caledonian metamorphism of high grade paragneisses from the Seve Nappes, Scandinavian Caledonides

摘要: The Seve Nappes can be followed for more than 700 km along the Scandinavian Caledonides. paragneisses are in part migmatitic, metamorphosed to granulite facies and eclogite-bearing. This probably reflects an ancient continent-continent collision. Zircon data presented here from a migmatitic paragneiss leucosome give almost concordant Caledonian U-Pb ages, define together with strongly discordant zircons discordia line intercept ages 423±26 Ma 1512±36 Ma. Strongly zircon another paragneiss, composed of cores overgrown thick transparent mantles, also fits this chord. A stepwise dissolution experiment on these demonstrates existence component age crystals, 3 5 steps plot defined by conventional analyses same sample. reflect high grade metamorphism sediments Proterozoic protoliths. Sm-Nd model (TDM TCHUR) whole rock samples cluster around 1.9 1.55 Ga, respectively, demonstrating average crustal provenance detritus sediments. support correlation between Western Gneiss Region Norway.