Contrasting styles of fault reactivation in curved orogenic belts: Examples from the Central Apennines (Italy)

Abstract

The geometry of the Apennine fold-and-thrust belt has been strongly influenced by the original architecture of the Adria paleomargin. In the Central Apennines, pre-thrusting normal faults (pre-orogenic Permian(?)/Triassic–Jurassic and synorogenic Neogene) were reactivated with compressional kinematics during the Neogene–Quaternary orogenesis. We present a study of the control of preexisting extensional faults on thrust tectonics in the Central Apennines. We describe positive inversion geometries of some salient fold-and-thrust structures from the Central Apennines (Setteporte, the Sabini Mountains, the Sibillini Mountains, Montagna dei Fiori, the Gran Sasso range, Maiella Mountain, and Casoli-Bomba) by integrating surface geological data and seismic-line interpretation. In these structures, different styles of fault reactivation depend on their orientation with respect to the subsequent compressional NE-SW-trending stress field. The NW-SE– and WNW-ESE–trending pre-thrusting normal faults in the backlimbs of the anticlines were displaced and passively translated in the hanging-wall blocks of the thrust planes, thus exhibiting a classical shortcut geometry (shortcut anticlines). Differently, pre-orogenic normal faults in the N-S–trending anticlines were reactivated in a transpressive deformational context, as documented by the mainly dip-slip and strike-slip kinematics along the thrusts and back thrusts, respectively (reactivation anticlines). The cases studied document differences in geometry in fold-and-thrust structures related to the trend of preexisting extensional faults, showing that different reactivation geometries linked to the same inversion event can coexist at regional scale in curved fold-and-thrust belts. The proposed inversion tectonic model and the resulting geometry of the fold-and-thrust belt could possibly be applied to analogous orogenic belts.