Late Archaean metamorphic Rb-Sr isochron ages from basic and ultrabasic rocks in the Bjørnesund – Ravns Storø region, southern West Greenland

Abstract

The Archaean complex of South-West Greenland (Bridgwater et al., 1976) consists largely of polyphase quartzo-feldspathic gneisses which intrude horizons of amphibolite and anorthosite with genetically and spatially associated ultramafic rocks and minor occurrences of meta-sedimentary material. In the Bjørnesund - Ravns Storø region (fig. 46) 150 km south of Godthåb the amphibolite units are structurally linked together and are considered to represent the same unit (Friend, 1975). The complex was variably metamorphosed to hornblende-granulite or amphibolite-facies conditions. This metamorphism accompanied three main phases of deformation within the region (Kalsbeek & Myers, 1973) and post-dated the formation of the precursors of the amphibolites.