An occurrence of the Gula Nappe in the Western Gneiss Region, central Scandinavian Caledonides

At Fosslia (100 km NNE of Trondheim, Western Gneiss Region), a cover sequence of metasedimentary and metavolcanic rocks overlies migmatitic gneisses and subordinate mafic rocks of the Precambrian crystalline basement. The cover comprises micaceous gneisses, quartz veined gneisses, quartz-feldspar gneisses, quartzites, felsites, amphibolites, graphitic schists, mica schists, and rusty weathering sulphide rich mica schist. These lithologies are similar to those in the Gula Nappe in the Trondheim Nappe complex. The proposed correlation is strengthened by U /Pb dating of zircons from a granodioritic dyke intruding the cover. The dyke is restricted to the cover sequence. The U-Pb zircon upper intercept age is 430 ± 12 Ma. This age is interpreted as the time of dyke crystallization. The age is close to those obtained on trondhjemitic dykes in the Gula Nappe in the Trondheim Complex. The Fosslia occurrence provides additional evidence of the existence of isolated allochthonous Caldeonian cover units in the northern part of the Western Gneiss Region, and that such units can be identified despite intense deformation and amphibolite facies metamorphism.