Proterozoic evolution and provenance of the high-grade Jotun Nappe Complex, SW Norway: U-Pb geochronology

New U-Pb geochronological data are used to explore the Proterozoic history and provenance of the Jotun Nappe Complex in the Scandinavian Caledonides, SW Norway. Orthogneisses in the upper part of the complex, the high-grade Upper Jotun Nappe, yield protolith ages of 1.66, 1.63 and 1.26 Ga. During the Sveconorwegian orogeny, the rocks underwent penetrative deformation and metamorphism up to granulite facies conditions. Later shearing, hydration and retrogression under amphibolite-facies conditions is dated to 954 ± 3 Ma by local, syntectonic melting of granitic gneiss and 950 ± 1 Ma emplacement of syntectonic, syn-retrogression pegmatites, suggested to reflect decompression and partial exhumation of the lower crustal rocks. A second cycle of granulite-facies metamorphism is dated to 934 ± 1 Ma, coeval with 934 ± 3 Ma anatexis of granitic gneiss. We propose that the second cycle represents post-collisional elevated heat flow, correlated to granulite-facies metamorphism in the related Lindås Nappe, and to anorthosite and granite plutonism at higher crustal levels in the western Baltic Shield, possibly in response to late-orogenic underplating or delamination. The tectonometamorphic record of far-travelled, high-grade crystalline rocks in the Jotun Nappe Complex, the Lindås Nappe and the Dalsfjord Nappe confirms their origin in the Baltic Shield, and suggests that they provide a glimpse of a deeper segment of the Sveconorwegian orogen than presently exposed in the basement of SW Norway.