Intrusive events at Kvanefjeld in the Ilimaussaq igneous complex

Abstract

The geology of the Kvanefjeld region in the Ilimaussaq intrusive complex is reviewed with special empha­sis on intrusive mechanism and on the spatial distribution of rock units before the intrusion of the lujavrite. The lujavrite was emplaced by permissive intrusion, and subsidence of blocks of the older rocks derived from the roof of supracrustals, gabbro, and from the earlier syenites of llimaussaq, took place extensively. It is argued that the present level of erosion in the K vanefjeld area is about 300 m below the roof of the intrusion. The early augite syenite and alkali syenite in the southern and central part of K vanefjeld are believed to be close to their original position as a large raft in the naujaite. The northern limit of the augite syenite intrusion was probably close to the present limit of the augite syenite. The origin of the marginal deformation zones in the country rock xenoliths is discussed and it is proposed that the deformed zones represent early shear zones and joints which were heated and metaso­matically altered before the intrusion of the. lujavrite. The ultimate shearing and deformation occurred during the collapse of the roof when the bulk of the lujavrite was intruded.