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.
Highlights
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
Summary
Small xenoliths of probable eclogite have been found in some of the carbonatite-Iamprophyres. ane of these is seen in thin-section to be a mediumto coarse-grained rock consisting of garnet, very paIe green pyroxene, brown hornblende and plagioclase. It is clear that there is a difference of about 900 in the remanent magnetic directions of the Gradar and TD dyke swarms. 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.
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