Late Miocene-Early Pliocene Out-of-Sequence Thrusting in the Southern Apennines (Italy)

We present a structural study on late Miocene-early Pliocene out-of-sequence thrusts affecting the southern Apennine orogenic belt. The analyzed structures are exposed in the Campania region (southern Italy). Here, thrusts bound the N-NE side of the carbonate ridges that form the regional mountain backbone. In several outcrops, the Mesozoic carbonates are superposed onto the unconformable wedge-top basin deposits of the upper Miocene Castelvetere Group, providing constraints to the age of the activity of this thrusting event. Moreover, a 4-km-long N-S oriented electrical resistivity tomography profile, carried out along the Caserta mountains, sheds light on the structure of this thrust system in an area where it is not exposed. Further information was carried out from a tunnel excavation that allowed us to study some secondary fault splays. The kinematic analysis of out-of-sequence major and minor structures hosted both in the hanging wall (Apennine Platform carbonates) and footwall (Castelvetere Group deposits and Lagonegro-Molise Basin units) indicates the occurrence of two superposed shortening directions, about E-W and N-S, respectively. We associated these compressive structures to an out-of-sequence thrusting event defined by frontal thrusts verging to the east and lateral ramp thrusts verging to the north and south. We related the out-of-sequence thrusting episode to the positive inversion of inherited normal faults located in the Paleozoic basement. These envelopments thrust upward to crosscut the allochthonous wedge, including, in the western zone of the chain, the upper Miocene wedge-top basin deposits.