Age of gneissic rocks in the Caledonian nappes of the Alta district, northern Norway

Abstract

Result of a Rb-Sr geochronological investigation are presented which confirm the Precambrian age of gneisses forming parts of the Skillefjord and Nalganas Nappes of the West Finnmark Caledonian allochthon. In the case of the Skillefjord Nappe, granodiorite dikes which cut tonalitic gneisses have yielded an isochron age of ca. 3.000 Ma B.P. thus indicating the presence of Archaean elements tectonically incorporated in the nappe pile during the Finnmarkian orogenesis.