Field evidence of very old Precambrian rocks in the Godthåb area, West Greenland

Abstract

The Godthåb area, situated in the old central gneiss complex of West Greenland, has yielded two of the oldest radiometric dates yet obtained from Greenland. They are both K/Ar biotite dates, one of 2710 ± 130 m.y. on granodiorite gneiss from Godthåb (Armstrong, 1963), and the other of 2610± 50 m.y. on gneiss collected 55 km to the north and on the opposite side of Godthåbsfjord (Larsen and Møller, this report). The latter gneiss shows evidence of having undergone retrograde metamorphism from granulite facies to amphibolite facies, and its date is presumed to be related to this retrogression (Windley, in press).