FELDSPATHIC INCLUSIONS IN THE GARDAR IGNEOUS ROCKS OF SOUTH GREENLAND AND THEIR RELEVANCE TO THE FORMATION OF MAJOR ANORTHOSITES IN THE CANADIAN SHIELD
Anorthosite xenoliths and plagioclase megacrysts occur in Gardar igneous rocks over an area of approximately 50 000 sq km in South Greenland. The anorthosite inclusions represent a top accumulate of labradorite, which crystallized at a relatively early stage from the developing Gardar magmas at depth, while the megacrysts are regarded as feldspars that remained suspended in their parent magmas for a considerable period at a later stage when the Gardar magmas had developed their dominantly alkaline character. The formation of anorthosite was a continuous process, which probably started about 1300 m.y. ago (the age of the earliest Gardar intrusions) and continued to about 1200 m.y.The Gardar anorthosites formed in the period immediately preceding the development of the Grenville metamorphic belt of the Canadian Shield. They are particularly relevant to the problem of the anorthosites in the Canadian Shield, since they provide evidence for the formation of anorthosites in pre-Grenville, post-Elsonian non-oro...