A transverse, thin-skinned, thrust-fault belt in the Paleozoic North Greenland Fold Belt

Abstract

The southern part of the North Greenland Fold Belt in Peary Land has been affected by two widely different orogenic events: an Early to Middle Devonian, westward-directed, thrust-fault deformation and a Late Devonian to an early Carboniferous folding on east-west axes that folded the earlier thrust faults. The deformation in this part of the North Greenland Fold Belt affected an ∼5-km-thick pile of lower Paleozoic shales, turbidites, and conglomerates deposited in the Franklinian–North Greenland, clastic trough. The thrust-fault belt is separated from the northern part of the North Greenland Fold Belt by the east-west–trending transcurrent Harder Fjord fault zone, north of which no westward-directed thrust faults have been recognized. The thrust fault region covers an area of 3,000 km 2 , and the main transport direction was toward the west with a refraction toward southwest along the sideland to the south. The thrust fault region is rimmed by a frontal thrust fault and fold zone. Behind the frontal zone, the uppermost stratigraphical unit, the Silurian flysch, forms an allochthonous mega-cover, draping imbricate thrust structures in the Ordovician units below. The central part of the thrust-fault belt consists of a western, north-south–striking, imbricate, thrust-fault fan and an eastern and southern area characterized by flat-lying, coherent thrust sheets. The imbricate fan is formed by 20 steeply east-dipping thrust sheets with an individual thickness of 500 m. The flat-lying thrust sheets are 100–300 m thick, and the relative displacement along individual thrust faults is in the order of 1–10 km. The subhinterland or proximal thrust zone is situated in the eastern part of the thrust-fault region and is dominated by the Cambrian Frigg Fjord Mudstones. This zone is regarded as a peel-off area from which the Ordovician and Silurian sediments were removed and displaced toward the west. The Frigg Fjord Mudstones compose the lowermost unit exposed in the region and contain the main decollement zone for the thrust faulting. The cumulative effect of the thrusting is a total transport of ∼100 km from east to west. The thrust fault deformation is herein named the “Volvedal orogeny” and is interpreted as a foreland deformation related to the Caledonian Mobile Belt, which involved gravity gliding in the hinterland of the thrust-fault belt.