Thrust kinematics and internal deformation in basement‐involved fold and thrust belts: The eastern Orobic Alps case (Central Southern Alps, northern Italy)

Abstract

A new model, which integrates original detailed structural data and published geological data, is proposed for the Alpine (Cretaceous to present) convergent evolution of the northern portion of the Central Southern Alps. The Central Southern Alps are believed to have developed from the very beginning of their convergent evolution as a critical wedge, characterized by plastic deformation at depth. Clear evidence for the existence of a brittle‐plastic transition at depth within the Central Southern Alps wedge during pre‐Oligocene evolutionary stages comes from detailed structural data (original 1∶10000 form surface mapping). A regionally verified fabric sequence manifests the superposition of brittle to plastic to brittle structures developed during the path followed by the same volume of rocks within the wedge. On the other side no direct evidence exists in the rear part of the wedge for the occurrence of plastic deformation at depth during post‐Oligocene stages. However, considerations driven by the comparison of timing and amount of deformations in the Central Southern Alps and brittle wedge theory predictions strongly support this hypothesis. Different deformation mechanisms operating at different structural levels have been controlling a crustal scale strain partitioning between deep plastic and shallow brittle portions of the Central Southern Alps wedge. Plastic deformations have strongly controlled the overall mechanical behavior of the Central Southern Alps wedge, reducing sensitively the amount of internal deformation required in order to attain criticality of the wedge.