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 displacement s is presented. As an analogue for models of arcuate mountain belt formatio n we use the model to predict strain patterns produced by parallel displace ment in front of a rigid versus deformable indenter. A rigid indenter is si mulated by an irregular quadrilateral displaced a constant amount along its hinterland boundary. A deformable indenter is simulated by an irregular qu adrilateral 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 bel ts. Short axes orientations are most deviated from the transport direction along the lateral edges of the model with minimum displacement and shorteni ng and vary across the central domain, mirroring strain features with varia ble orientations from mountain belts such as fold trends and minor deformat ion features such as horizontal stylolite peaks. The rigid indenter model a lso generates short axes deviated from the transport direction but showing far less variation. Displacement-strain relationships from the Jura mountai ns (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 laterales et zones de transfer dans le chaines plissees ". (Unpublished PhD thesis, Universite de Savoie)]. We find that the model short axis orientation pattern is very similar over at least the eastern an d central Jura to the stylolite patterns from the region whilst the long ax es closely match the fold axes trends. The model suggests that the Jura mou ntains could have formed as a result of a progressive deformation with unif orm transport in a general northwest direction. (C) 2000 Elsevier Science L td. All rights reserved.