Geological investigations of the Igaliko dyke swarm, South Greenland

Field work in 1984 in the Motzfeldt area included an investigation of the Gardar dyke swarm in this area. The dyke swarm was examined at the folIowing places in or near the Igaliko Complex: north of Motzfeldt Sø, north af Gieseckes Dal, Igaliko, Flinks Dal, Mellemlandet, in 0stfjordsdal (north-west side), and west of Narssarssuaq river. Except at Østfjordsdal, the dykes resemble assemblages found elsewhere in the TugtutoqIlimaussaq-Igaliko swarm. Porphyritic and non-porphyritic trachytes and phonolites (the latter less common), basalts and dolerites, lamprophyres, big feldspar dolerites and carbo- natites are all present. The latter are much more abundant than previously recognised, and are occasionally of considerable length. The relative proportions vary; basaltic and doleritic dykes are particularly abundant towards the centre of the swarm, Le. west of Narssarssuaq river where dilation due to dykes is greatest, at about 10 per cent; elsewhere values of 3-4 per cent were obtained.