Plate Tectonics and the Boundary between Alps and Apennines

Andrea Argnani(*)
(*) ISMAR-CNR. Via Gobetti, 101 - 40129 Bologna. E-mail: andrea.argnani@bo.ismar.cnr.it.

A new proposal attempting to solve the long-debated issue of the polarity of subduction in the Corsica-Northern Apennine system is presented. Models adopting an original W-dipping subduction and models preferring a flip in the polariy of subduction, from E-dipping to W-dipping, encounter major difficulties at a regional scale. It is considered here that the main inconsistencies faced by both models are due to the two-dimensional approach of reconstructions. The Late Cretaceous to Present-Day kinematics of the Central Mediterranean has been reconstructed using the magnetic anomalies in the Atlantic Ocean and assuming a solid connection between Africa and Adria. Oligocene to Present calcalkaline volcanism and backarc extension in the Balearic and Tyrrhenian basins requires the presence of a wide oceanic embayment to the west of the Adriatic Promontory. It follows that the continental collision that gave rise to the Alps s.s. could not continue SW-ward of Adria. The flip of subduction polarity that can be currently observed, going from the Alps, where Africa is overriding Europe, to the Apennines, where the opposite occurs, was likely on original feature since the beginning of convergence. Kinematic reconstructions allow the point along the plate boundary where the flip of polarity occurs to be tracked back in time. Following the N-ward motion of the colliding Adriatic Promontory, the point of polarity flip moved along the plate boundary from Late Cretaceous to Eocene. As a result, areas that previously experienced continental collision were subsequently affected by oceanic subduction. This sequence of events led to the collapse of the Alpine belt of Corsica and to the opening of the Balearic backarc basin above a retreating oceanic subduction. A similar kinematic evolution is currently ongoing in Taiwan. Finally, the Northern Tyrrhenian basin opened when delamination affected the Adriatic continental margin, following the consumption of oceanic lithosphere at the end of Corsica-Sardinia rotation.

Alps-Apennines boundary, Alpine Corsica, Northern Apennines, Plate kinematics, subduction polarity.