A zircon age from gabbro-anorthosite inclusions in the gneisses of the Angmagssalik area, South-East Greenland

Abstract

Age determinations were made on 3 zircon fractions extracted from gabbroanorthosite inclusions which occur as tectonically dislocated pods in quartzofeldspathic gneisses on the eastern end of Kitak island, South-Bast Greeniand (fig. 5). The anorthosites were selected for study because they are derived from a lithologically distinctive suite of rocks found over a large part of the Archaean craton of the North AtIantic area (Bridgwater et al., 1973b). While there is no evidence that all the anorthosites of this type are contemporaneous their formation appears to require special conditions in the ernst and they are thus likely to be a useful stratigraphic tool. Furthermore the coarse-grained refractory nature of these rocks means that they retain their lithological identity during later tectonic, anatactic and metasomatic events to a far greater degree than the quartzofeldspathic, semipelitic and amphibolitic units making up the major part of the gneiss complex in which the anorthosites occur.