Lower-crustal unzipping drives active orogenic deformation

Abstract

The Apennines-Tyrrhenian Sea system allows us to investigate seismotectonics in coupled thrust belt and back-arc realms driven by subduction retreat, continental collision, and crustal delamination. Since the late Miocene, active extension has progressively migrated forelandward, in tandem with contraction, away from the Tyrrhenian back-arc basin, inactive since ~2 Ma, to become localized tens of kilometers from the active thrust front. Integrating geodetic, seismic, and geological data, here we show that lower-crustal delamination is presently the primary geodynamic driver of Apennine tectonics and seismicity. This delamination propagates via a continuous hinge; an elastic flexural framework anchors crustal extension, contraction, and short-term vertical movements around the migrating hinge. Our results provide a template for other mature retreating subduction systems, where the onset of delamination and later waning of back-arc opening do not arrest deformation, but instead transfer its locus to a migrating zone of intra-lithospheric decoupling that sustains active deformation and seismicity. Lower-crustal delamination acts as the primary driver of present-day seismicity and upper-crustal deformation of the Apennines, according to an integration of geodetic, seismic, and geological data within an elastic flexural model to investigate active Apennine-Tyrrhenian dynamics.