On the structure and petrography of the Ipernat Dome, western Greenland

Abstract

A well exposed area with a Precambrian gneiss dome was investigated. Photogeological methods were used to a great extent; the aerial photographs are reproduced and a geological map, scale 1:75000, is presented. The folding appears to be rather gentle. For the greatest part the rocks crystallized under the conditions of hornblende-granulite subfacies. Subsequently, a large proportion of them metamorphosed retrogressively. Chemical analyses of three granodioritic and quartz dioritic rocks and one garnet are presented. Refraction indices and unit cell dimensions of three garnets, optical properties of some pyroxenes and triclinicity values of some potash feldspars are given. Twenty determinations of the sodium and potassium content of representative samples indicate that potassium is not concentrated in the gneiss core of the dome.