Contractional deformation and Neogene tectonic evolution of the Pergola-Melandro valley area (Southern Apennines)

The Pergola-Melandro valley, located in the axial zone of the Southern Apennines, is characterized by the presence of the Brienza-Paterno envelopment thrust which juxtaposes two main Southern Apennine domains: the carbonate Apennine Platform in the hangingwall (represented by the Maddalena Mts platform margin Unit) and the Lagonegro Basin in the footwall. The fieldwork and the structural analysis allowed to reconstruct the Neogene tectonic evolution and the structural setting of this area. The Meso-Cenozoic Lagonegro successions showed a pattern due to the presence of superposed folding and thrust sheets characterized by an “Apenninic” trend (NW-SE). The Mesozoic-Cenozoic Maddalena Mts Unit is affected by a lower deformation generating folds with both E-W and “Apennine” trending axes. Deposits of the Sicilide Unit were observed to be sandwiched between the Maddalena Mts and Lagonegro Units. In the articulated Neogene tectonic evolution, three contractional events have been recognized: - the first event, probably occurred between Serravallian and Tortonian time, affected the Maddalena Mts unit generating the fold system with a broadly E-W trending axis. - the second event (Late Tortonian-Messinian) generated the main NW-trending “Apenninic” structures, consisting of anticlines and thrusts. During the first part of this stage (between Late Tortonian and Early Messinian) the Sicilide Unit overthrust both the Maddalena Mts Unit and Lagonegro succession. Later on the Brienza-Paterno Thrust activated, leading to the overlap of the Apennine carbonate platform margin on the Lagonegro successions, with the interposition of the Sicilide nappe. This tectonic stage can be linked to the strong shortening that affected the Apennine accretionary prism after the opening of the Tyrrhenian basin in Late Tortonian time. - a later mild NNE-directed shortening event led to the refolding of some of the previously formed “Apenninic” structures. This phase could be linked to the contractional deformation affecting the buried Apulian Platform during the Pliocene. The tectonic history is further complicated by the presence of low-angle extensional faults affecting the Lagonegro succession, probably developed during Late Miocene-Pliocene.