The petrology and structure of the country around Julianehaab, South-West Greenland

Abstract

Field relations of several granite types, garboroio and dioritic plutons and ampnibolitic, doleritics and alkaline dykes A camptonitic sill is also described. From the study of the amphibolitic dykes, two granite generations are differentiated by their relationship to the dykes. These are termed the Ketilidian and Sanerutian Granites. On the basis of xenolths within the granites and petrological observations, it is suggested that the older granites formed in suit while the younger (Sanerutian) granite was intruded as a magma which resulted from the fusion of the Ketilidian Granites. Detailed photographic descriptions are given of all the major rock types. It is suggested that the gaboro-norite rocks are remnants of differentiated basic intrusion, now represented by amphibolites and that the dioritic amphibolties are probably metamorphosed igneous plutons. Modal data on the course-grained rocks using a technique devised during this study is shown to be reliable and results obtained on the granite are discussed. Chemical and X-ray analyses of ten representative microclines separated from the Ketilidian and Sanerutian Granites, are used to show that the method of analysis of alkali feldspar by X – ray techniques (Orville, 1957 and 1960) is as accurate as conventional chemical analysis.