Interaction of accretion mechanisms and deep fluids in continental orogenesis

Mountain-building often involves the subduction of continental margins during the convergence of tectonic
plates. Rheological heterogeneities and structural inheritance in the subducting lithosphere are
main factors controlling the evolution of the process and deformation partitioning in orogenic wedges.
Here, we present tomographic evidence of a main along-strike change in the structure of the
Apennines belt, where frontal accretion diminishes laterally, as well as plate bending, and the contribution
of underplating to crustal thickening becomes evident. We hypothesize that the diverse mechanisms
of mountain formation can be attributed to rheological heterogeneity in the crust and interactions with
fluids liberated during the subduction process. The development of shallow decollements versus underplating
is favored by differing amounts and styles of deep fluid liberation from the subducting crust.