Tugtilik

The dense Tertiary dyke swarm that parallels the East Greenland coast south of Kangerdlugssuaq consists principally of tholeiitic dolerites, but a suite sampled at Tugtilik includes alkaline types (Rucklidge et al., 1980); they are chilled against associated dolerites. The mineralogy is variable with clinopyroxene of different generations the most abundant mineral, often as phenocrysts and xenocrysts generally of diopside with aegirine overgrowths; there are occasional olivine phenocrysts, groundmass and xenocrystal titanian pargasite, accessory biotite and rare feldspar in a base which is difficult to resolve but shown by microprobe to consist of nepheline and sodalite or analcime, Ti-garnet and perovskite. Chemical analyses confirm these rocks as being nephelinites, and analyses of a number of mineral phases are given by Rucklidge et al. (1980). Inclusions of clinopyroxenite, wehrlite and amphibole wehrlite have been found in one dyke. Whether nephelinites are also to be found within the Tertiary dyke swarm along the coast to the northeast is not known, although Rucklidge et al. (1980, p. 4) point out that some of the dykes from Tasilaq, 40 km to the northeast, described in a report by Williams (1974), would appear to be similar.