Residual topography, lithospheric structure and sunken slabs in the central Mediterranean

The central Mediterranean comprises subduction, collision, and backarc extension, all in a relatively small area. In this paper, we analyze the topography of this region, examining the influence of subducting slabs on overriding plates. We take the observed surface elevation, remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low, unusually high, or normal. Then, we calculate lithospheric thickness where local isostasy applies. The results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics. In particular, we found a difference between the south Tyrrhenian subduction zone and the Apennines, consistent with the processes of slab rollback and slab break-off, respectively. In the south Tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate (the Calabrian Peninsula) is uplifted. This opposite trend indicates weak plate coupling – that is, the subducting slab, which is rapidly rolling back, hangs almost entirely on the oceanic plate and the overriding plate is free. In contrast, in the Apennines high residual topography and uplifting are detected on both sides of the mountain belt, consistent with complete break-off of the subducted lithosphere.