Kinematic model for the curvature of the northern Subalpine Chain, France

Abstract

Analyses of cross-sectional shortening, mapped faults and calcite twin strain are used in conjunction with geometric-kinematic modeling to interpret the mechanism of curvature formation in the northern Subalpine Chain of France. There is a 45° change in strike around the Chain that is convex towards the foreland (northwest). Five models for fold-thrust belt curvature are applied to the northern Subalpine Chain. They can reproduce the geometry and the kinematic history of a curved fold-thrust belt and can be used to predict the magnitude and orientations of strains and the three-dimensional geometry of the curvature. The models are: pure bending; radial thrusting; curve-parallel simple shear; uniform displacement-uniform shortening; and transport-parallel simple shear. Two principal criteria for distinguishing among the models geometrically are the horizontal tangential strain (extension or contraction parallel to strike) and cross-sectional shortening. The transport-parallel simple shear model predicts no tangential extension in the central domain and greater radial shortening and significant tangential extension in the northeastern and southern domains. This is the pattern observed in the northern Subalpine Chain. Therefore, the curvature of the northern Subalpine Chain is attributed to a transport-parallel simple shear mechanism.