Petrology and geology of the Precambrian Gardar Dykes on Qaersuarssuk, South Greenland

Abstract

The Precambrian Gardar dykes on Qaersuarssuk consist of olivine dolerites, a group of undersaturated to saturated microsyenites including one nepheline-bearing dyke, trachydolerites and lamprophyres. The dykes are the fringe to the dense swarm of alkaline dykes on Tugtutôq to the east. As most of the dykes are sub-parallel, division is made based on their relations to movements along wrench faults. Composite dykes, with microsyenitic marginal components, and trachydoleritic centres often containing large aggregates of feldspar crystals and giant single crystals of feldspar, are comparatively common.