Continental Collision Structures and Post-Orogenic Geological History of the Kangerlussuaq Area in the Southern Part of the Nagssugtoqidian Orogen, Central West Greenland

摘要

Deep-seated continental collision sutures, formed at a depth of more than 20 km, are exposed near Kangerlussuaq, close to the Greenland ice cap, on the southern margin of the Nagssugtoqidian orogen in Central West Greenland, thus offering a rare opportunity to study the tectonic deformation style of such an orogen. This paper adds new information on the tectonic history of the southern flank of the Nagssugtoqidian orogen. It focuses on (1) the results of a detailed structural investigation of lineament zones revealed from remote sensing of geophysical and topographic data and aerial photo interpretation, (2) detailed geological mapping at key locations and (3) a tectonic structural model describing the geological development of the area. The area has undergone several episodes of deformation, which have been compiled into an event succession that recognizes eight tectonic events overprinting each other: Two stages of folding (F1 and F2) have been identified along with one major episode of intrusion of the Kangâmiut mafic dyke swarm (2.05 Ga) into the Archaean continent. These dyke intrusions are very important, since by examining the style of deformation for these intrusions it is possible to define the transition from the North Atlantic Craton in the south to the mobile belts in the Nagssugtoqidian orogen in the north. Five different types of pronounced lineaments and one less pronounced lineament post-dating the Kangâmiut dykes extending from ductile deformation shearing events to brittle deformation with extensive faulting. These lineaments cover both the collisional and post-collisional tectonic history of the area. The study focused on two types of lineaments: one semi-ductile type trending E–W with a dextral sense of shear and a second, a pronounced lineament outlining the Kangerlussuaq–Russell thrust fault. These two features are interpreted to be related to the Nagssugtoqidian orogeny, while the latter lineaments have a more brittle appearance and are regarded to be considerably younger and probably related to post-orogenic tectonic events.