The described anorthosites are confined to the Greenland equivalent of the Kenoran structural province between 61°N and 65°N lat. in southern West Greenland. They occur in gneisses as stratigraphic units up to 2 km wide and can be traced for about 400 km in West Greenland. The anorthosite is found in both the deep levels (granulite and retrogressed amphibolite facies) and higher levels (migmatitic amphibolite facies in linear belts) of the basement complex. In the deep-level Fiske- ncesset region, 125 km of chromite-layered anorthosites are associated with layers of hypersthene amphibolite, spinel-layered brorizitite, peridotite, chromite-layered bronzitite, magnetite-layered anorthosite, sapphirine- and corundum-bearing ultramafic rocks, and garnetite. The anorthosite and associated rocks are unmigmatized and contain inch-scale and phase layering and grading; the plagioclase has the composition of An80-90. In the higher level areas is homogeneous hornblende-bearing gabbro anorthosite (mostly with labradorite to bytownite) which is migmatized.
The chromite layering indicates that these anorthosites formed by gravitational accumulation of a basic magma. Thus they contrast with the volatile-rich ilmenite- and magnetite-layered anorthosites emplaced during the middle Precambrian in the Canadian shield. It is suggested that there is an anorthosite series beginning with early Precambrian, early magmatic bottom accumulates of anorthosite and ending with middle Precambrian, late magmatic plutons. Because about threÃ¨ fourths of the West Greenland anorthosite in the higher level areas is not chromite layered, a “metasedimentary” origin should be ascribed with caution to stratigraphic anorthosites.
Figures & Tables
North Atlantic—Geology and Continental Drift
The Gander Conference, an International Conference on Stratigraphy and Structure Bearing on the Origin of the North Atlantic Ocean, was held in Gander, Newfoundland, August 1967. The conference gave geologists familiar with the areas bordering the North Atlantic Ocean with an opportunity to present their knowledge and ideas to colleagues dealing with similar rocks and structures. This publication contains most of the papers that were presented at that conference and a few others that were prepared for the sessions.