Conclusions
We have proposed some new ideas on the tectonic evolution of the northern –central Apennines, based on high-resolution tomographic images of the lithosphere/asthenosphere system and seismicity. The remarkable difference in the deep structure and seismicity in the Apennines can be harmonized in a general process of delamination and foundering of the Adria continental edge lithosphere after the Africa-Europe plate collision. The complexity of this process, frozen in the deep lithosphere structure, is conditioned by lateral variations of the Adria continental margin following the subduction of the Ionian oceanic plate during the past 30 Ma. Thus, delamination can be a gravitational response of a continental margin developing in the far field of an oceanic subduction (the Ionian slab, in our case) and sustained by a mantle that was pervasively weakened by previous geodynamic processes.
This gravitation re-adjustment generates the paired compression and extension, and the collapse of the accreted wedge; re-mobilizing faults that, during times, experienced iterated tectonic inversions. This, along with the decoupling of deformation between the upper nappe, sometimes rootless, and the deeper basement, makes the individuation of active faults responsible for M>6 earthquakes in the Apennines difficult. Fluids released and mobilized during the delamination process favour the activation of pre-existing, not-optimally oriented faults, and tectonic inversion.