Gardiner intrusion, an ultramafic complex at Kangerdlugssuaq, East Greenland

Abstract

The Gardiner intrusion is an ultramafic complex in the inner region of Kangerdlugssuaq fjord, forming part of the East Greenland Tertiary Igneous Province. The rocks of the intrusion can be placed into three categories. (1) An older sequence is composed of dunites, pyroxenites, and a narrow marginal zone of alkali rich rocks. The rocks of the marginal zone consist of melteigite where the bordering country rock is plateau basalt, and of contaminated rocks where the country rock is the basement gneisses. The bordering gneisses have a narrow fenitized zone. (2) A strongly alkaline and undersaturated dyke sequence comprises amphibole pyroxenites, tawites, urtites, and sodalite, nepheline and alkali-feldspar syenites. (3) A younger sequence consists of uncompahgrites (intrusive melilite rich rocks) and calcite carbonatite dykes. Parts of the uncompahgrite show layered accumulations of magnetite, perovskite and apatite on the one hand, and melilite on the other. Massive aggregate concentrations of perovskite and magnetite are also recorded. The intrusion of uncompahgrite and carbonatite has resulted in intense alkali metasomatism of the rocks of the older and the dyke sequences.