Accretionary wedge collision in the Ionian Sea: Timing and movement of the Calabrian arc and the Mediterranean ridge in the central Mediterranean Sea

In convergent plate boundaries, the pre-collisional stages, when most of the oceanic crust has already been subducted, are hidden and reshaped inside the tectonic units forming orogenic wedges. The central-eastern Mediterranean Sea is an example of a debated remnant ocean basin ideal for reconstructing these pre-collisional/early collisional stages of the mountain chain, hosting two subduction systems that develop along the irregular Africa-Eurasia plate boundary: the Calabrian and Hellenic Arcs. They include two opposite-verging accretionary wedges—the Mediterranean Ridge and the Calabrian Arc—separated by the Ionian Abyssal Plain, recognized for having an array of deep, reverse/transpressive faults, derived from previous extensional structures aligned with the Kefalonia Transfer Zone. It progressively narrows towards the NE, where the two wedges are facing each other. We analyse a geophysical dataset including bathymetric and seismic reflection profiles to reconstruct the structural evolution of the collisional setting and attempt a kinematic reconstruction at the transition between the Mediterranean Ridge and the Calabrian Arc. Opposite-verging, large-wavelength folds with high deformation rates are present at the transitional area between the two wedges. This structural style is different from the very low, tapered outer accretionary wedge present in the areas where the abyssal plain is still present. Seismo-stratigraphic analyses and kinematic reconstruction suggest that throughout the Pliocene, the Mediterranean Ridge's outward growth was prevalent, while starting from the Middle Pleistocene, the Calabrian Arc structural vergence prevails, and this is possibly related to the Calabrian Arc's clockwise rotation and its SE-ward migration. However, in recent times, such NE-SW-oriented positive inverted faults affect the Calabrian Arc-Mediterranean Ridge contact zone. We propose a polyphasic interaction between the two wedges, requiring a multidisciplinary approach including onshore-offshore correlations to reconstruct its driving mechanisms. These results shed new light on the complexities of the pre-collisional setting of Ceno-Mesozoic and older collisional orogens.