KINEMATIC MODEL FOR THE CURVATURE OF THE NORTHERN SUB-ALPINE CHAIN, FRANCE

Analyses of cross-sectional shortening, mapped faults and calcite twin strain are used in conjunction with geometric-kinematic modeling to i nterpret the mechanism of curvature formation in the northern Subalpin e Chain of France. There is a 45-degrees change in strike around the C hain 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 curve d fold-thrust belt and can be used to predict the magnitude and orient ations 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-paralle l simple shear. Two principal criteria for distinguishing among the mo dels geometrically are the horizontal tangential strain (extension or contraction parallel to strike) and cross-sectional shortening. The tr ansport-parallel simple shear model predicts no tangential extension i n the central domain and greater radial shortening and significant tan gential extension in the northeastern and southern domains. This is th e pattern observed in the northern Subalpine Chain. Therefore, the cur vature of the northern Subalpine Chain is attributed to a transport-pa rallel simple shear mechanism.