A new crustal balanced cross-section through the Central Apennines (Italy)

The Apennines fold-and-thrust belt, forming part of the Africa-Eurasia plate boundary, developed due to the Neogene subduction of the Alpine Tethys underneath Europe and to the subsequent involvement of the Adria rifted margin into the collisional process. Since the Miocene, E-ward retreat of the slab caused extensional deformation to affect the thrust pile, which eventually led to the opening of the Tyrrhenian back-arc basin at the rear of the belt. Multiple schools of thought exist about the structural style of the Apennines, which propose irreconcilable models. The amount of shortening, the involvement of the crystalline basement, the architecture of the inherited rifted system and its degree of reactivation during convergence, and the role played by compressive inheritance during back-arc extension, are still highly debated.

In this contribution we focus on the Central Apennines. We integrate publicly available geological maps, interpretation of vintage seismic sections, borehole data, recent seismicity studies, previously published surficial geological cross-sections, and the latest thermochronological insights to build a balanced cross-section across the inner portion of the belt. Our aim is to critically evaluate previous models and to better define its deeper part. Our results suggest a dominantly thin-skinned style, in which inherited Mesozoic extensional faults developed during Adria rifting have been partly reactivated during thrusting. The major thrusts of the area are characterized by large displacements, ranging between 10 and >20 km, and sole into a basal décollement located at the base of the post-Variscan sedimentary sequence. Post-thrusting back-arc extension is accommodated by faults that either displace the compressional décollement levels or reactivate them with opposite kinematics.