Acadian basement thrusting, crustal delamination, and structural styles in and around the Humber Arm allochthon, western Newfoundland

Abstract

The leading edge of the Humber Arm allochthon in western Newfoundland coincides with the western limit of both the Taconian (Ordovician) and Acadian (Devonian) deformed zones. Taconian deformation is west-directed and confined to rocks of the allochthon. Acadian deformation extends to deeper crustal levels and affects underlying shelf carbonates and Grenville basement. Acadian structural style changes from westward-directed thrusts and folds forming an emergent thrust front along the northern and southern margins of the allochthon to eastward-directed thrusts and folds forming a buried front along the intervening central eastern margin. In this central region, cover and basement are delaminated by westward basement wedging and concomitant eastward backthrusting at a higher structural level.