Layering in the Ilimaussaq alkaline intrusion, south Greenland.

Abstract

The Ilimaussaq alkaline intrusion in S Greenland provides examples of various types of igneous layering. Inch-scale layering occurs in the least differentiated rocks augite syenite and pulaskite and is probably caused by a nucleation-diffusion mechanism. Pegmatitic layering is found in the roof series of the agpaitic rocks (foyaite and naujaite) and is considered to have formed by upward concentration of volatiles under the downward crystallising roof. Isomodal layering is found in naujaite and especially in the latest rocks, the lujavrites. Mineral graded layering is found in the floor series of kakortokite and in some lujavrites. The mineralogy of the kakortokite series is described, and theories of formation of the layering reviewed.-from Authors