Along strike variation of inversion-related folds in foreland thrust belts: implications for tectonic style and petroleum prospectivity

The along-strike variation of different fault-related folds in a curved thrust system is documented in the Central Apennines of Italy. Fold profiles and kinematic mechanisms are reconstructed by integrating geological and structural data with restoration of key balanced cross-sections and description of panoramic natural transects. The lateral variation from fault-bend to fault-propagation folding is promoted by selective reverse reactivation of precursor normal faults along the oblique and frontal ramps. Fault-bend reactivation and fault-propagation shortcut folding produce a characteristic fold interference pattern at the salient apex of the curved thrust system. The transition style depends on the pattern of the inherited normal fault template and on the amount of shortening achieved in the salient zone. The modest amount of shortening achieved by the inversion fault-related folds is consistent with a thick-skinned thrusting style. Inversion fold development modes and their diagnostic features are also important for petroleum prospectivity investigations.