Gravity tectonics driven by Quaternary uplift in the Northern Apennines: insights from the La Spezia-Reggio Emilia geo-transect.

The neotectonics of the Northern Apennines is illustrated using a crustal-scale geoseismic cross-section, based on seismic profiles and field mapping. The geological profile crosses a variety of tectonic settings, from the Val di Vara and Val Magra (VV–VM) grabens in the inner side of the Apennines, to the pede-Apennine thrust fronts (PTF), and finally to the external fronts of the Apennines. Both the VV–VM extensional system and the PTF show evidence of Early Pleistocene tectonic activity, whereas thrusting in the external Apennine ended by Late Pliocene. The sole decollement of the external thrusts cuts down westwards into the basement to a depth of about 15 km, whereas the PTF joins a shallower detachment surface that follows the top of the basement. This basal surface also represents the basal detachment of the VV–VM extensional system, with the VV–VM and PTF defining a large-scale gravitational spreading system. We hypothesise that the regional Quaternary uplift that affected the internal sector of the Apennines promoted a gravitational spreading in the upper part of the orogenic wedge, accounting for the coeval extension in the VV–VM and shortening at the PTF, and applicable to a 100km long sector of the Northern Apennines.