Geology of the Folldal area, southern Trondheim Region Caledonides, Norway.

Abstract

The lowest stratigraphic unit in the Folldal area is the Gula Group, comprising turbidites and minor greenstones in the lower part (the Singsås Formation) and graphitic pelites with subordinate marble and conglomerate in the upper part (the Åsli Formation). The overlying Fundsjø Group is bimodal with basalts and rhyodacites, comagmaic gabbros and a large subvolcanoc trondhjemitic intrusion. The bimodality, high content of volcaniclastics, intercalations of continental sediments, geochemistry and lead isotopes of massive sulphides reveal that the Fundsjø Group represents and island arc accumulation formed close to a continent. The contact between the Fundsjø and Gula Groups is interpreted to be primary, as shown by a gradual lithological transition and no break in metamorphism and structural elements across the contact. The Folldal Trondhjemite in the Fundsjø Group has yielded a U-Pb zircon age of 488 +- 2 Ma. Relationships between published ages from the Gula Group and rocks in the Seve Nappes suggest a possible tectonics and metamorphic link between the Seve and the lower part of the Gula Group. Either a primary unconformity or a thrust marks the contact between the Åsli and Singsås Formations in the Gula Group.