New K/Ar age determinations from southern West Greenland

Abstract

The following four samples are from the pre-Ketilidian/pre-Nagssugtoqidian central gneiss complex of west Greenland (Pulvertaft, 1968), in which there are several amphibolite facies linear belts with conformable greenschist layers that contrast on a major scale with the complexly folded granulite facies complexes (Windley, in press). The following dates together with those published by Armstrong (1963) and Larsen and Møller (1968) suggest that the linear belts have an isotopic age in the range 2410-2710 m. y., whilst the granulite facies complex in the Fiskenæsset region has an age of at least 3210 m. y. There was also plutonic activity in the period 1940-1820 m. y. expressed by a weak metamorphism in late supracrustal rocks only preserved within the Godthåb-Isua linear belt and in the pegmatites around the Qôrqut granite (Larsen and Møller, op. cit.).