Two-stage regional rare-element pegmatite formation at Tysfjord, Norway: implications for the timing of late Svecofennian and late Caledonian high-temperature events

Abstract Pegmatite fields within granite plutons are commonly considered to have formed from residual melts of their host. This is not always true as demonstrated by the Tysfjord gneiss and its two groups pegmatites. The gneiss, exposed in a tectonic window Caledonides northern Norway, part transscandinavian igneous belt (TIB) that includes several phases granitic magmatism. In Hamarøy area (Drag-Finnøy), where most rare-element pegmatites occur, Paleoproterozoic metamorphosed Group 1 allanite–(Ce)–fluorite metapegmatites similar bulk rock chemical composition TIB rocks, indicating these melts. metapegmatites, which up 400 m size, among largest known intra-plutonic with Nb–Y–F (NYF) signature. formation unusually large granite-hosted NYF may been facilitated overall high F content gneisses. Undeformed 2 amazonite–tourmaline yield columbite zircon U–Pb ages range 400–379 Ma. These interpreted be anatectic partial melting gneiss. pegmatites, including those Træna Island Sjona (400 414 Ma), during late Caledonian ductile shearing incipient unroofing central Scandinavian record progressively younger this event SW NE.