On the tectonic evolution of the Ligurian accretionary complex in southern Italy

Unraveling the deformation pattern characterizing the transition from the final oceanic subduction stages to the early stages of deformation of the foreland continental margin is crucial for a better understanding of geodynamic processes taking place at convergent plate boundaries. In particular, the combined role of internal wedge dynamics and continental margin architecture in controlling the tectonic evolution of an accretionary complex during its final emplacement onto the foreland continent is discussed in this study. To this purpose, integrated structural, stratigraphic and low-T thermochronometric analyses have been performed on the Ligurian accretionary complex units exposed in the Campania region (Italy) and on continental margin successions located in their footwall, as well as on related foredeep and wedge-top basin deposits. Our results point out a series of late Early Miocene (Burdigalian) shortening events, also involving buttressing of the accretionary wedge against the crustal ramp of the foreland continental margin. Emplacement of the overthickened accretionary complex onto the distal part of the continental margin was followed by horizontal extension and wedge thinning, aiding the development of wedge-top depocenters. Extension may be either related with reduced subduction rates during the Middle Miocene, or with a period of subduction erosion (known to have occurred in the northern Apennines in the same time frame). Early Miocene NW-SE shortening recorded by Ligurian accretionary complex units is completely unrelated with later (Late Miocene to Pleistocene) NE-directed thrusting in the Apennines, which was coeval with back-arc extension in the Tyrrhenian Sea. Therefore, our results emphasize the occurrence of a major discontinuity in the Neogene geodynamic evolution of the southern Apennines, whose tectonic history may be clearly subdivided, from a kinematic point of view, into pre- and syn-Tyrrhenian back-arc extension stages.