A model of displacement and strain for arc-shaped mountain belts applied to the Jura arc

A plan view geometric model for simple, parallel, differential displacements is presented. As an analogue for models of arcuate mountain belt formation we use the model to predict strain patterns produced by parallel displacement in front of a rigid versus deformable indenter. A rigid indenter is simulated by an irregular quadrilateral displaced a constant amount along its hinterland boundary. A deformable indenter is simulated by an irregular quadrilateral displaced along a hinterland boundary that is allowed to rotate. Some simple test cases show that the deformable indenter model leads to a pattern of strain very similar to that encountered in arcuate mountain belts. Short axes orientations are most deviated from the transport direction along the lateral edges of the model with minimum displacement and shortening and vary across the central domain, mirroring strain features with variable orientations from mountain belts such as fold trends and minor deformation features such as horizontal stylolite peaks. The rigid indenter model also generates short axes deviated from the transport direction but showing far less variation. Displacement–strain relationships from the Jura mountains (Switzerland and France) are quantified based upon a simplified version of the finite displacement field for the Jura fold–thrust belt of Philippe, Y. (1995) ["Rampes latérales et zones de transfer dans le chaines plissées". (Unpublished PhD thesis, Université de Savoie)]. We find that the model short axis orientation pattern is very similar over at least the eastern and central Jura to the stylolite patterns from the region whilst the long axes closely match the fold axes trends. The model suggests that the Jura mountains could have formed as a result of a progressive deformation with uniform transport in a general northwest direction.