Rb-Sr geochronological evidence suggesting a reinterpretation of part of the north Norwegian Caledonides

Geochronological data are presented for a variety of rock-types from a large area of Nordland. An early to mid-Proterozoic age (1800-1650 m. y.) is confirmed for the granite-gneiss basement culminations. The Hornblendic Rock of the Meløy Group has a maximum age of 758 m.y. (Precambrian). This age is at variance with data from the Meløy Group kyanite-schists which show evidence of a mid - Proterozoic event (1360-1038 m. y.). Consequently the boundary between the two groups is interpreted as a major tectonic break within the Meløy Group. The calc-alkaline rocks of the Harefjell Gneissic Group were intruded into the Beiarn Nappe during Cambro-Silurian times (529-411 m. y. ). This and other evidence indicates that the Beiarn Nappe is older than previously supposed.