Neogene crustal shortening and basin evolution in Tuscany (Northern Apennines).

The structural studies carried out in the Northern Apennines during the last decade show that the Neogene tectonic evolution of this area is much more complex than the classical model which proposed a NE-directed shifting of the compressive front followed by lateral extension in the internal zone tied to the development of the Tyrrhenian basin. Recent structural data systematically collected both in the chain and in the sedimentary fill of the hinterland basins, allow us to propose an alternative model for the development of the basins and for the Neogene evolution of the whole Northern Apennines sector. In the central sector of the chain (Tuscan-Romagna Apennines), there is evidence of polyphase thrust reactivations and out-of-sequence thrusting. In the hinterland basins, compressive deformations usually occur in correspondence of thrust ramps and regional unconformities have been found. The timing of both thrust reactivations in the chain and of the major compressive phases affecting the hinterland basins (Radicondoli-Volterra, Baccinello, Velona and Siena-Radicofani basins) well correlates with the periods of magmatic quiescence and with the compressive phases detected in the external sector of the Northern Apennines (Padan-Adriatic foredeep). The presented data allow us to propose that compressive tectonics played a major role in the recent evolution of the Northern Apennines.