Thin- or thick-skinned models provide contradictory interpretations of orogenic belts. Each model is associated with different amounts of shortening, patterns of rotation around vertical axes, and origins of their curved shapes. Integrating paleomagnetic, geologic, and structural data, with particular attention to inversion tectonics, provides an important contribution to this discussion. This methodological approach has been applied to explain the structural style and origin of the outer Northern Apennines’ curved-shape fold-and-thrust belt, within the larger context of the Apennine-Maghrebide belt. The Northern Apennines Arc can be investigated independently of the rest of the chain because of its numerous differences from the Southern Apennines-Calabrian Arc, including paleogeographic domains, stratigraphic successions, structural setting, tectonic rotations, and geodynamic evolution.

Paleomagnetic and structural data indicate that the foreland Northern Apennines is a progressive arc whose development was influenced by inversion tectonics, involving the reactivation of pre-thrusting normal faults, which trended ca. N-S as oblique thrust fronts (the Ancona-Anzio line reactivated as part of the Olevano-Antrodoco-Sibillini thrust; Fig. 9). The architecture of the Mesozoic Adria paleomargin strongly influenced the curved shape of the Northern Apennines, as documented by the relationship between structural units and paleodomains (the OAS thrust separates the carbonate platform from the pelagic domains). The Northern Apennines’ curvature was accentuated during orogenesis by CCW and CW tectonic rotations in its northern and southern limbs, respectively. Based on the results of this study, we propose that primary or progressive curve-shaped foreland fold-and-thrust belts are likely to have evolved in an inversion tectonics context. Thrust location was influenced by pre-orogenic normal faults with a thick-skinned deformation style.

Figure 9. Schematic geologic map and 3D model.

Schematic geologic map and 3D model.

Schematic geologic map and 3D model showing the crustal inversion tectonic model proposed for the development of the progressive outer arc of the Northern Apennines (Olevano-Antrodoco-Sibillini thrust).