Geometry and kinematics of Triassic-to-Recent structures in the Northern-Central Apennines: a review and an original working hypothesis

The geological evolution of the Northern-Central Apennines has been strongly controlled by structural features inherited from pre-thrusting stages. The Apennines consist of a fold-and-thrust belt developed during Neogene time, involving sedimentary successions that were deposited within different paleogeographic domains. The paleogeographic evolution was controlled by the effects of syn-sedimentary tectonics that were active in the Triassic-Neogene time interval, and that are, from Trias to Neogene, related to different geodynamic settings. The Jurassic extensional phase favoured the dissecting of the Triassic carbonate platform and led to the development of different paleogeographic domains. Main oblique and trasversal faults, with transtensive kinematics, characterized the boundaries between different domains. After the Jurassic phase, from Cretaceous to Neogene, the Northern-Central Apennines were characterized by the development of ridges and depressions. These structures were affected by the development of normal fault systems, bending processes within the ridges, with uplift of the crestal sectors and tilting in the peripheripheral ones. The geometries and the structural setting of the foreland domains, of the foredeep and piggy back basins and of the Neogene Apenninic thrust belt are controlled by evolution of the former tectonic elements evolution. The development of extensional faults, the uplift and bending observed in the Apenninic sedimentary sequences during the convergence phase and during a part of the continental collision phase could represent distal effect of the dominant compressional regime. In this geodynamic domain the first tectonic inversion processes in a positive sense occurred along the pre-existing Jurassic listric faults systems. The reactivation first affected the flat sectors of the fault planes and then progressively more superficial ones. In the upper sedimentary cover these processes favoured buckling, flexuring and faulting. Furthermore, during the subsequent involvement of the foreland domains in the foredeep and chain systems, the propagating thrust surface still reused former discontinuities both as a frontal and lateral ramp, completely inverting their movement. During the compressional stage the west-dipping listric normal faults were reactivated in positive sense. The former east-dipping normal faults have been eastward rotated or offset by thrust faults.