Compressive neogene-quaternary tectonics in the hinterland area of the northern Apennines

The NW-SE trending Northern Apennine Mountains consist of a series of alloc hthonous units which were thrust generally to the NE during Neogene crustal shortening, in the direction of a foreland basin to the east and NE. On th e hinterland (internal) side of this fold-wild-thrust belt, a ser-ies of sm all-scale sedimentary basins developed from the late Miocene and were defor med at the same time. The late Tortonian-Pleistocene evolution of the North ern Apennines has previously been considered by most authors in terns of a classical model of a NE-migrating compressional front, which was followed i n time and space by a hinterland extensional regime related to the developm ent of the Tyrrhenian Basin. This paper presents new structural data from both the external parts of the Northern Apennines and the late Tortonian-Pleistocene basins located in th e internal sector. In the Northern Apennine thrust belt, reactivation and o ut-of-sequence geometries for the thrust faults have been recorded. In the hinterland basins, compressional deformation has been documented and is usu ally associated with thrust ramps and regional unconformities. The timing o f both thrust reactivation and of the major compressional phases affecting the hinterland basins is closely correlated with periods of magmatic quiesc ence, and with compressional phases detected in the external margin of the Northern Apennines (the Padan-Adriatic foredeep). Data presented in this paper indicate that compressional deformation has pl ayed a major role in the recent evolution of the Northern Apennines. The me chanism envisaged to explain this tectonic framework takes account of the p iggy-back emplacement of basement thrusts from internal to external sectors , which occurred in post-Serravallian time. Activity on basement thrusts ma y have caused reactivation of thrusts in the internal cover sequence, givin g rise to out-of-sequence geometries and controlling the development and/or deformation of the hinterland basins. This type of structural evolution ha s resulted in a complex geometry for the thrust sheets, and this must be ta ken into consideration during re-interpretation of the structure of the Nor thern Apennines. It may also have important implications for petroleum expl oration.