From Submarine to Subaerial Out-of-Sequence Thrusting and Gravity-Driven Extensional Faulting: Gran Sasso Massif, Central Apennines, Italy

Thrust wedge evolution is typically characterized by out-of-sequence thrusting, which can occur in both submarine and subaerial conditions to maintain the balance between gravitational and tectonic forces. The Gran Sasso Massif, in Central Italy, is a high topography region where the kinematics and environmental conditions of deformation of some fault zones are still controversial, and this bears important implications for the Central Apennines orogenic wedge evolution. To obtain further constraints on fault activity in the Gran Sasso Massif, we studied the Monte Camicia and Vado di Ferruccio thrusts using structural, petrographical, and geochemical analyses. Such dataset allowed us to constrain the structural-diagenetic evolution of the studied faults, which has first-order implications in the characterization of their paleo-hydraulic properties. Our results indicate that in the Vado di Ferruccio out-of-sequence thrust, pressure solution-mediated mass transfer promoted low-permeability conditions in the fault core that led to a semiclosed fluid circulation, pore fluid overpressuring, and dolomite crystallization in submarine conditions. In contrast, the Monte Camicia out-of-sequence thrust was characterized by dominant cataclasis in subaerial conditions, which facilitated meteoric fluid infiltration. By considering both fault zones as belonging to the same thrust system at crustal scale, we interpret these differences as indicating the occurrence of multiple pulses of thrusting during the exhumation of this sector of the Central Apennines, up to Quaternary times, when extensional faulting eventually dissected the thrust stack. This caused extensional reactivation of the Monte Camicia Thrust and related alteration in vadose zone conditions, leading to porosity enhancement, dolomite dissolution, and calcitization.