Lateral shifts of Apenninic foredeep depocentres reflecting detachment of subducted lithosphere

The hypothesis of lateral migration of slab detachment was formulated on the basis of seismic tomography results on the 3-D structure of subduction zones in the Mediterranean region [M.J.R. Wortel and W. Spakman, Structure and dynamics of subducted lithosphere in the Mediterranenan region, Proc. K. Ned. Akad. Wet. 95 (1992) 325–347]. The redistribution of slab pull forces associated with the tearing process is taken to affect foredeep development by adding a lateral component to internal–external depocentre migrations. In the case of the Apenninic Arc the direction of detachment and associated depocentre migration is expected to be southeast. This prediction has been confronted with the tectonostratigraphy of Oligocene to Recent Apenninic foredeeps. Results show there are two episodes marked by important lateral shifts of foredeep depocentres. During the early Late Miocene (Tortonian) the depocentre of the Northern Apennines foredeep shifted towards the southeast. This is evidenced by the relative positions of the depocenters of the Burdigalian–Serravallian Marnoso Arenacea and the Tortonian Umbrian–Marchean and Lazian “Minor Basins”. A further, stepwise southeastward migration can be inferred from the Plio-Pleistocene records of the Central and Southern Apennines. In a more general sense, our results indicate that slab detachment may play a significant role in the evolution of foredeeps along convergent plate boundaries.