Salt tectonics and gliding in the Tyrrhenian Sea: a centripetal salt deformation system in a back-arc basin

The Tyrrhenian Sea salt is part of the Messinian Mediterranean salt giant. Its regional distribution was mapped during the early exploration of the Tyrrhenian back-arc basin. More recently, detailed studies have focused on the reconstruction of the salt setting in the Sardinian offshore. A regional overview of salt tectonics character in the Tyrrhenian Sea is thus missing. With this in mind, we present the first basin-scale interpretation of a combined data set of multibeam bathymetry and seismic lines. In the relatively flat, proximal areas of the Cornalia and the Campania Terraces, vertical rise of diapirs is the dominant style of salt movement. Whereas most of the diapirs are buried, some of them emerge at the seafloor and their circular form of salt stocks is apparent. Widespread extensional faulting of the overburden is indicative of reactive diapiric rise and control the location and evolution of local depocentres. However, large parts of the Tyrrhenian Sea consist of areas dipping seaward, towards the centre of the Tyrrhenian Sea. Here, salt gliding is the prevalent style of salt deformation. In the Sardinian margin a belt characterized by salt gliding spans a length of 230 km and is up to 130 km wide, reaching the Vavilov Basin in the centre of the back-arc system. In the Campanian margin  a more equant salt gliding area has a length of 106 km and a width of 80 km. Smaller areas with evidence of salt gliding are located at the foot of the base-of-slope escarpment in the northern Sicilian margin to the south of the Vavilov Basin. Salt gliding results in discrete lobes with complex pattern of deformation. Deformation in the overburden often originates polygonal networks of grabens, scalloped scarps, circular or elongate minibasins, growth anticlines and synclines. When the halokinetic structures are present at the seafloor, their relative importance in the different sectors of the main lobes is apparent. Discrete zones of deformation, and a highly 3-D style of salt gliding and overburden deformation are thus recognized. Belts dominated by strike-slip deformation separate the different sectors of the main lobes and are often associated with salt stocks or faults. They are indicative of the linkage between discrete salt gliding systems with different movement direction. A complex deformation style and movement is thus evident in the Tyrrhenian Sea and the deformation of the overburden indicate the recent or active character of salt flow. Our analysis illustrate the processes and elements that characterize salt tectonics in irregular continental slope, with divergent gliding, and where different system interact.   At the basin-scale, salt deformation style does not comply with the simple patterns often observed in passive margins, consisting, moving seaward, of three domains: extensional, translational and contractional. In the Tryrrhenian Sea a more complex pattern is evident and can be related to the complex trend of the peripheral zone of the gliding salt masses inherited from the rifting stage. The crustal evolution and magmatic history of the basin also influences the discrete, but kinematically linked, slat gliding domains.