A crustal balanced-cross section across the central Apennines and the relationship between thick- and thin-skinned tectonics

The Apennines form part of the Africa-Eurasia convergent plate boundary and are cored by two diachronous back-arc basins formed in response to slab retreat, separated by the Sardinia-Corsica continental ribbon. Subduction of oceanic lithosphere in the central Apennines lasted until the Oligocene - early Miocene, coevally with the opening of the Liguro-Provencal back-arc basin and led to the development of a thin-skinned thrust pile. The subsequent transition from subduction to collision occurred when the distal portion of the Adria passive margin became involved in the orogenic system. The arrival of a progressively thicker continental crust of the Adria rifted margin imposed a deceleration of trench retreat, arresting the opening of the first back-arc basin. This stage is evidenced by the almost stable position of the thrust front and of the peripheral bulge until the late Miocene. During Tortonian, the forelandward migration of the thrust front and of the peripheral bulge re-accelerated, coevally with the opening of the Tyrrhenian back-arc basin. In our view, this occurred as a consequence of the relocalization of the subduction interface in the basement.

In this contribution, via cross-section balancing, we focus on the crustal structure of the central Apennines to investigate the relationship between shortening in the basement and in the sedimentary cover. We employ well-constrained surface geological data from available public maps, as well as tomography and seismological data, supplemented by thermochronological, biostratigraphic, and radiometric dating. Furthermore, the data are integrated into a coherent geodynamic framework supported by a geometrically balanced kinematic model, giving insight on the coupled forward migration of compressional and extensional domains due to the slab pull/trench retreat system.