Along-strike variation of fault-related inversion folds within curved thrust systems: The case of the Central-Northern Apennines of Italy

The along-strike variation of fault-related inversion folds within curved thrust systems is documented by presenting cases from the Central-Northern Apennines of Italy. Fold structures are reconstructed by integrating geological field data and structural restoration of various key balanced cross-sections, which are also constrained by the detailed interpretation of panoramic views, geological field mapping, and structural analysis. The lateral variation from fault-bend to fault-propagation folding is promoted by selective reverse reactivation of precursor, mainly rift-related, normal faults preferentially located along the oblique and frontal ramps. Their space variability is identified within single curved thrust systems of three different size testifying a scale-invariant phenomenon. 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 resulting from fault-related inversion folding along regional curved thrust systems is consistent with a basement-involved thick-skinned thrusting style. Recognition of fault-related inversion fold styles and of their along-strike variations represents a useful predictive tool when unravelling the kinematic evolution of curved orogenic belts resulting from positive inversion. Inversion fold development modes and their diagnostic features are also important for investigations of subsurface Earth resources.