The control of the mesozoic paleomargin architecture on the pliocene orogenic system of the central Apennines

The Central Apennines of Italy are a well- exposed foreland fold-and-thrust belt, characterized by good outcrop continuity and high vertical relief. Salient geometries of the thrust fronts represent a peculiar feature of the outer zones of this orogenic chain. These reflect the distribution of Mesozoic carbonate platforms and pelagic basins, differentiated during Triassic-Jurassic Tethyan rifting. The stratigraphic section, and the relationships between tectonics and sedimentation, are well- documented in the numerous foredeep and thrust- top basins, developed in response to the eastward migration of the Neogene thrust fronts. The proposed field trip focuses on the main geological and structural characteristics of the outer zones of the Central Apennines. A 3-day traverse across the Gran Sasso, Montagna dei Fiori, and Sibillini Mts, will provide an opportunity to illustrate normal faults inherited from Mesozoic rifting and Miocene foreland flexuring events, and to evaluate the influence that these structures played during the subsequent construction of the Apennine fold-and- thrust belt in Late Miocene-Pliocene times. (see: Guide Geologiche Regionali Vols 7 and 10). Geological and structural studies, carried out in recent decades, across several orogenic belts have shown that pre-existing normal faults, inherited from continental rifting stages, were important in controlling the architecture of younger, superimposed fold-and-thrust systems (positive inversion tectonics). Pre-existing normal faults were reactivated as reverse faults, or were modified, truncated, deformed and passively transported in the hanging-wall blocks of the upward-propagating thrusts. Other studies have outlined that, in the mature orogenic stages, several thrust faults were reactivated as low-angle normal faults, or truncated by high-angle normal faults, as a result of late-, or post-orogenic extension (negative inversion tectonics). A comprehensive description of the geometry and kinematics of inherited structures, and an illustration of how these structures behaved during two main inversion episodes, both positive and negative, are the main focus of the proposed field trip across the Central Apennines. An analysis of the superpositional relationships of contractional and extensional structures, will provide an opportunity to evaluate the role of inversion tectonics in the construction of the outer parts of the belt. These relationships indicate that the architecture of the Mesozoic passive margin, consisting of alternating pelagic basins and carbonate platforms, was important in controlling the location, geometry and physiography of the subsequent foredeep basins.