Map view retrodeformation of an arcuate fold-and-thrust belt: The Jura case

The mechanism of arcuate mountain range formation is a matter of debate. Here we perform a map view restoration of a detailed three‐dimensional model of the Jura arc, a typical arcuate mountain range in the foothills of the Swiss and French Alps. This retrodeformation is performed using the UNFOLD surface‐balanced program, based on a “block mosaic” method. It results in a displacement field divergent toward the deformation front. This displacement field suggests counterclockwise rigid rotations in the horizontal plane up to 30° in the southern Internal Jura and a corresponding vertical axis rotation or shear strain of the Savoie molasse basin hinterlandward. We also predict a 10° clockwise, vertical axis rotation of the molasse basin in Switzerland. All these rotations agree with those documented by paleomagnetic data. The former are taken to result from a substantial decrease in shortening at the southern Jura end, while the divergence of displacements is interpreted to result from variations in the detachment level distribution.