Early-Middle Pleistocene extensional faulting in the Amatrice Basin (central Apennines, Italy) at the hanging wall of the seismogenic structures

The Amatrice Basin is an intermountain morphostructural depression of the central Apennines (Italy) that hosted large amount of the epicentral distribution activated during the 2016-2017 seismic sequence. The basin rests on the hanging wall of the Gorzano-Laga Fault, a major NW-SE-striking extensional fault that is part of the complex seismogenic fault array. While structures and kinematics have been previously documented for the Gorzano-Laga Fault, no details on kinematics, styles of deformation, and time of activity have been yet provided for the fault systems resting within the Amatrice Basin. This work deals with the mechanisms of nucleation and development of the Amatrice Fault System (AFS), a ~10 km-long fault system located in the depocentre of the Amatrice Basin. Our multidisciplinary approach combines geological-structural investigations with geochronological (230Th/234U, Uranium-series disequilibrium) and geochemical (?13C and ?18O stable isotope) analyses on selected carbonate structures (calcite-filled veins and calcite fibres on fault surfaces). Our results are used to address the spatial-temporal evolution of the AFS in a complex mechanism of growth and link of isolated segments, likely assisted by fluid migration and calcite mineralisation. The stale isotope compositions and the geochronological dating attest for a meteoric water ingress through and along the AFS extensional faults in the Early-Middle Pleistocene. The AFS constrains the long-term history of the extensional tectonics regime in the Amatrice Basin, providing useful correlation with the activity of the basin-bounding Gorzano-Laga Fault.