Structural evolution of a foreland fold-and-thrust belt: the Umbria-Marche Apennines, Italy

Outcrop-scale structures that record a progressive sequence of deformation can be used to clarify the kinematic evolution of an entire fold-and-thrust belt. The temporal progression of the compressional deformation as reconstructed by means of a mesoscopic structural analysis provides a key for unraveling the kinematic history of the Umbria-Marche Apennines (central Italy). Overprinting relationships at outcrop-scale allow for the recognition of three distinct structural stages which are, in sequence: A, layer-parallel shortening; B, folding; C, thrusting. Individual stages are explained in the framework of a progressive deformation model, where shortening of the sedimentary cover was continuous and occurred during a single contractional episode as a consequence of tip-line folding processes. A comparison of this history with those reported from other fold-and-thrust belts shows that layer-parallel shortening, folding and thrusting are sequentially dominant processes in areas which have experienced compressional deformation.