A klippe of Nagssugtoqidian supracrustal rocks at Sarfartûp nunâ, central West Greenland

Abstract

Supracrustal rocks comprising subaqueous volcanics, basic and ultrabasic sills and clastic carbonate sediments are unconformable upon quartzo-feldspathic gneisses and together form a small klippe of imbricate thrust slices. The sills were intruded after the other rocks had been folded and metamorphosed at low amphibolite fades. The whole allochthon suffered penetrative strain in hydrous conditions as it translated southwards as two discordant sets of imbricate thrust nappes. All the thrusts are folded about axial planes which were originally recumbent. As the higher slices arrived, the deeper slices refolded about axial planes dipping about 60° NNW. All these early folds are close to co-axial with a strong mineral orientation in a syn-translation foliation. It is suggested that the sills are shallow correlatives of the Kangåmiut dykes and that the allochthon was transported 60 km from a Nag. 2 zone of strong ductile overthrusting near Ikertoq. The tectonic relationships of these Proterozoic supracrustals are intermediate between those in Phanerozoic ophiolites and Archaean greenstone belts.