Field observations on the kakortokites of the Ilímaussaq intrusion, South Greenland

Abstract

Detailed mapping, sample collection and studies of zirconium and niobium distributions in the kakortokites of the Ilimaussaq intrusion have been carried out. Each of the 29 major rhythmic units has been mapped and a comprehensive sample collection made for further work. A horizon caused by slumping of the unconsolidated crystal mush has been recognised and it has been shown that a number of large inclusions are confined to a single horizon. The sIumped rocks indicate that the depth of unconsoIidated material was of the order of 20 m, (compared with only a few metres for other intrusions discussed in the literature) with a maximum angle of rest of some 20°. FauIts, fine-scale layering, trough banding, the border pegmatite and later intrusions are described. A programme of fieId and laboratory determinations of Zr and Nb has delimited their distribution within these rocks and allowed a first estimate of the total, easily-accessibIe quantities of these elements to be made.