Middle Proterozoic ultramafic lamprophyre dykes in the Archaean of the Atâ area, central West Greenland

Abstract

During the mapping of gneisses and supracrustal rocks around Eqe in the eastern part of the Atâ area in 1988 a series of ultramafic dykes of lamprophyric affinity were discovered by the authors. The dykes are conspicuous in the field because of their lithology, with often high contents of carbonate, and the occurrence of brownish phlogopite phenocrysts. Their ductile type of deformation and aggressive aiteration of the wall-rock are distinctive. The purpose of this paper is to give a preliminary account of the mode of occurrence and lithology of the dykes based on the mapping results and a provisional inspection of a dozen thin sections. Their possibie age is discussed on the basis of their spatial relation to a large NNW-SSE trending dolerite dyke dated at 1645 ± 35 Ma by Kalsbeek & Taylor (1986).