Sveconorwegian Granulite Facies Metamorphism of Polyphase Migmatites and Basic Dikes, South Norway

Abstract

Migmatites in the Nelaug-Krossvatnet-Ubergsmoen area in the amphibolite facies part of the Bamble Sector were intruded by the Ubergsmoen Augen Gneiss (UAG) and by younger basic dikes. Both are critical time markers and show that the area underwent two phases of deformation and migmatization during the Gothian Orogeny (1600-1500 Ma) before emplacement of the augen gneiss, and four subsequent phases of deformation during the Sveconorwegian Event (1200-950 Ma), accompanied by amphibolite facies metamorphism and a minor third migmatization. Mineral assemblages in the basic dikes and in the migmatites indicate local granulite facies conditions resulting from lowered at nearly constant temperature of at 8.7 kb. It is suggested that this Sveconorwegian granulite facies overprinting was due to the introduction of fluids released during the crystallization of another charnockitic magma at a deeper level.