Palinspastic restoration of a post‐Taconian successor basin deformed within a transpressive regime, northern Appalachians

Abstract

Restoration of transpressional orogens requires a three‐dimensional analysis of the strain state in order to take into account both the pure shear and simple shear components of the deformation and assess their relative contribution throughout the deformation history. Restoration of the post‐Taconian successor basin, the Gaspé Belt located within the external part of the Acadian orogen in the Canadian Appalachians, was performed by using a step‐by‐step method based on the successive removal of strain increments. The pure shear component contributed 70% of the total strain during the first stages of the deformation whereas the simple shear component contributed 30% of the total strain during the last stages. Three retrodeformation steps are defined, starting with restoration of the last deformation stage and working back to the first deformation stage. The first step is to restore slip along Acadian strike‐slip faults. The second step is to restore shortening related to the horizontal extension during the Acadian regional simple shear event. Finally, the third step is to restore vertical extension related to the pure shear event by removing slip along the reverse faults, unfolding and removing internal strain associated with cleavage development. Retrodeformation of the simple shear component of the transpressive deformation during the first two steps is performed on a horizontal view of the Gaspé Belt basin which contains the horizontal extension direction and which is perpendicular to the Acadian NW–SE directed compression. Likewise, restoration of the pure shear component is performed in vertical sections which contain the vertical extension and which are perpendicular to the Acadian NW–SE directed compression. The palinspastic map presented here is a much more appropriate base map for the basin and allows for a more realistic paleogeographic interpretation of the Gaspé Belt.