The contribution of 3D restoration for the reconstruction of pre-thrusting basin geometry

In the Umbria-Marche fold-and-thrust belt, excellent examples of positive inversion tectonics are documented. They are explained as the effect of the structural heritage of the opening of the Mesozoic Tethis Ocean, on the geo- metry of the Neogene compressional structures, related to the Alpine Orogeny. A portion of the southernmost belt, between the Nera river and the Rieti Basin, is used as natural example to test the kinematic consistency of linked fold-and-thrust systems, and infer the pre-thrusting geometry of the origi- nal extensional basin. The dominant thrust systems and related folds affec- ted a Triassic-Neogene marine sequence during the Late Miocene-Early Pliocene time. The overprinting structural relationships, both at the mesoscopic and macroscopic scales, provided keys for remove the effects of progressi- vely older deformation; in doing so, the sequential cross- section restoration technique was applied in conjunction with 3D monitoring of the resulting geometry, by using specific computer software (2DMove and Gocad). This approach allows for the definition of the thrust segment nucleation and linkage, and for infer the geometrical pat- tern of the pre-existing normal faults, hence the 3D archi- tecture of the pre-thrusting extensional basin. The close coincidence between extensional structures and the Neogene thrust ramps support the interpretation that the geometry of the latter was controlled by the map distribution of the former.