Paleomagnetic constraints on the Plio-Pleistocene geodynamic evolution of the external central-northern Apennines (Italy)

We report on new paleomagnetic results obtained from 27 sites sampled in th e Plio-Pleistocene sequences at the external front of the central-northern Apennines. Previous analyses of Miocene (Messinian) sediments indicated tha t the present shape of the northern Apenninic are is due to the oroclinal b ending of an originally straight belt oriented around N320 degrees and that vertical axis rotations accompanied the migration of the thrust fronts tow ard the Adriatic foreland [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153-3166]. We tried to provide new paleomagnetic constraints for the timin g and rates of the oroclinal bending process during the Pliocene and the Pl eistocene. The results suggest that CCW rotations observed in the northern part of the studied area are possibly younger than 3 Ma. No regional rotati on is recorded in the Pliocene and Pleistocene sediments from the southern part of the study area, analogously to the Messinian sediments of the 'Acqu asanta' domain of Speranza et al. [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153-3166]. A local significant CCW rotation (23 degrees +/- 10 degr ees) is identified in the Early Pleistocene sediments that crop out along t he Adriatic coast between Ascoli and Pescara, indicating differential motio n of the thrust sheets. This rotation must be younger than 1.43 Ma. (C) 200 0 Elsevier Science B.V. All rights reserved.