U-Pb isotopic ages of zircons from Precambrian rocks of South Greenland

Results of age determinations on zircons from samples of gneiss, granite, syenite and diorite from the Ketilidian mobile belt of South Greenland are presented. The lead isotopes were determined by a direct ionisation method. As three of the four zircon concentrates gave more or less discordant results, their interpretation is difficult. However, the data agree with the view that late Ketilidian granite emplacement took place roughly 1800 m.y. ago and not around 1600 m.y. age as the previously available K/Ar dates on pre-Gardar rocks seemed to indicate.