The Apula plate's response to the interaction between Calabrian and Hellenic orogens: tectono-stratigraphic evolution and implications on intra-plate deformation (Northern Ionian Sea, Central Mediterranean)

The Apula plate in the Northern Ionian Sea, is a sliver of continental crust covered by around 8 km of Mesozoic carbonates. It acts as the foreland of two opposite verging chains: the SE-verging Southern Apennine to the southwest, which merges with the Calabrian Arc wedge at the Taranto Gulf and the SW-verging External Hellenides to the northeast. In this work we use deep seismic reflection profiles to illuminate the structures and stratigraphic relationships between the frontal part of the orogenic belts and adjacent foreland, as well as to determine the key tectonic processes that have governed the onset of the region's existing structural architecture. A detailed seismo-stratigraphic study allows us to recognize three major regional unconformities: i) the Jurassic/Cretaceous unconformity which is marked by Cretaceous reflectors that clearly onlap the Jurassic carbonate platform; ii) the Messinian unconformity, related to a regional erosive event linked to the Messinian desiccation of the Mediterranean Sea; and iii) the middle Pliocene unconformity, an erosive and angular unconformity that truncates the Lower Pliocene reflectors. Although the Apula plate is typically thought to be a stable foreland zone, our study shows that it underwent extensive deformation strongly influenced by its interaction with the neighboring Southern Apennine/Calabrian Arc and Hellenic wedges. An active NW-SE-striking extensional fault system is possible due to the Apula plate bending under the stress of the two opposing orogens. Compressive and transpressive structures (e.g., smooth and open folds at the plate contact zone as well as active NE-SW striking positive flower structures) accommodate shortening processes and oblique plate convergence. Transpressive tectonic structures resulted from inherited Mesozoic normal faults that have been reactivated since the middle Pliocene and such compressive/transpressive regime promoted the mobilization and squeezing of Upper Triassic evaporites into teardrop diapirs. These findings make the regional geological setting and the pre-collisional grain of the Apula plate critical aspects in defining the tectonic evolution of the Northern Ionian Sea as well as the position and geometry of tectonic structures located in this area.