Insights from the Apennines metamorphic complexes and their bearing on the kinematics evolution of the orogen

The Apennine belt represents a typical orogenic segment of the western Mediterranean, characterized by the tectonic convergence between European and Africa plates after oceanic subduction. Both oceanic- and continent-derived metamorphic complexes, considered as the remnants of the subduction-exhumation cycle, crop out in the inner sectors of the Apennine belt, where extensional deformation has dominated since the Early Oligocene. We review the available structural, metamorphic and geochronological data coming from these metamorphic complexes in order to provide a kinematics reconstruction accounting for the tectono-metamorphic evolution of the Apennines, from oceanic subduction to final extensional reworking. During the Eocene, oceanic rocks were progressively subducted down to eclogite-facies conditions following a subductiontype metamorphic gradient. The transition from oceanic- to continental-subduction was coeval with a transition from subduction-type to Barrovian-type metamorphic gradient. Continental collision, at the Eocene–Oligocene boundary, post-dated the syn-orogenic exhumation of HP-rocks and was synchronous with the onset of post-orogenic extension in the hinterland domains. Extensional deformation migrated to the east, following the forelandward migration of the thrust system at the trench. The concomitance of extension and compression is here related to fast rollback of the subducting plate and delamination of the lithospheric mantle below the subducted continental crust. Implications on how the subduction tectonics, syn-orogenic exhumation and post-orogenic extension could have controlled the circulation of HP-rocks in the developing Apennines are also discussed.