Petrographic evidence for diachronous metamorphism of the Skaiti Supergroup, Köli Nappe Complex, Arctic Scandinavian Caledonides

Abstract

The Skaiti Supergroup is the uppermost major tectono-stratigraphic unit of the Koli Nappe Complex, which comprises Precambrian to Lower Palaeozoic rocks immediately north of the Arctic Circle in Scandinavia. This complex was derived from within the Iapetus Ocean and emplaced during the Scandian phase of the Caledonian Orogeny. Petrographic evidence along a hinterland to foreland traverse of the Skaiti Supergroup demonstrates that garnet, staurolite and kyanite porphyroblastesis was diachronous with respect to fabric development, becoming later towards the hinterland. The hinterland rocks experienced two discrete phases of heating, whereas the foreland rocks only experienced one. These observations are consistent with a recent tectonic model for diachronous burial and exhumation of the Koli Nappe Complex during emplacement.