Zipper tectonics in the Tyrrhenian-Apennines system: linking rift inheritance with thrusting, back-arc extension and crustal delamination

Abstract

We review geological and geophysical data across the Tyrrhenian back-arc basin–central Apennines fold and thrust belt system and incorporate them into a crustal-scale balanced cross-section. The section allows us to derive a kinematic reconstruction of the subduction-to-collision system over the past 25 Myr and illustrates how its evolution was driven by the interplay between slab rollback and the inherited rifted margin architecture of the subducted plate. Oceanic subduction and slab rollback initially led to the formation of the Liguro-Provençal backarc basin and the thin-skinned Liguride accretionary wedge. Around 20 Ma, soft collision began as Adria rifted margin arrived at the subduction zone; the buoyant continental crust docked at the subduction zone, causing the deceleration of both slab rollback and thrust propagation. During the subsequent 8 Myr of soft collision, thrusting occurred in a thin-skinned framework. By 12–10 Ma, the shift to hard collision caused the subduction interface to move into the ductile middle crust, triggering a decoupling of contractional deformation into thin- and thick-skinned tectonics. This also renewed slab rollback, initiated lower crust delamination, and accelerated thrust propagation toward the foreland and back-arc extension in the belt’s axial zone. Since then, deformation and seismicity have been driven by the forelandward migration of a singularity point within the lower crust, where contractional and extensional structures converge. Lower crustal delamination caused foreland-dipping lowangle normal faulting, culminating in the opening of the Tyrrhenian back-arc basin. This evolution is captured in a zip-like tectonic model, of which the Apennines provide a world-class example.