Carbonatite-lamprophyre dykes of Mesozoic age

Abstract

Associated with the TD dolerites on Igaussaq island and the adjacent mainland south of Frederikshåb there occurs a parallel (NW-SE) swarm of carbonatite-lamprophyre dykes. These range in thickness from veins of a few millimetres to dykes of 1.5 m. The carbonatites are most abundant in the extreme west of the area, as are the TD dolerites, and die out towards the east. They cut all generations of dykes earlier than TD, and in one case can be seen to be intruded into a TD parallel to its margin. This field evidence suggests that they are probably contemporaneous with the TD dolerites. An isotopic age date for one of these carbonatites is given in the article by Ole Larsen at the end of this volume.