Decoupling between lower and upper plate deformation along the Tindari-Alfeo Fault System, Calabrian Arc (Central Mediterranean Sea)

Abstract

The subduction of the Ionian oceanic crust under the Calabrian Arc is one of the major structural elements in the evolution of the central Mediterranean basin. The Calabrian subduction zone is characterized by a narrow slab that, in its south-western part, terminates on the Tindari-Alfeo Fault System (TAFS). This fault system represents a major NNW-SSE trending subduction-transform edge propagator (STEP) that plays an important role in the recent evolution of the Calabrian Arc. Thanks to a dense set of multichannel seismic reflection profiles with high penetration (up to 12 s), that allowed for a 3D reconstruction of the geological structures in the area, the TAFS results to presently be one of the best documented STEP systems in the world. We were able to characterize the geometrical arrangement, the timing of the deformation and the interplay between the Ionian lower plate and the upper-plate accretionary prism during the Plio-Quaternary. Our study highlights the presence of a mechanical decoupling between the lower plate and the upper plate. The Ionian oceanic (and/or transitional) crust in the lower plate hosts the master faults of the TAFS which do not propagate across the thick accretionary prism in the upper plate. This latter is affected by secondary deformation (bending-moment faulting, localized subsidence, stepovers, and restraining/releasing bends) associated to the activity of the TAFS at depth. The analysis of the secondary deformation in the upper plate, and in particular of the syn-tectonic Plio-Holocene basins, associated to the activity of the TAFS at depth, allow us to constrain the age of inception of the TAFS in the study area and to calculate the vertical component and the propagation rate of the deformation. Our findings highlight the mechanical behaviour that can be expected along major lithospheric boundaries that interact with previously formed structures and provide key elements to understand the significance of shallow geological structures with respect to the master faults at depth.