Quaternary tectonic evolution of the central sector of Picentini Mountains (Southern Apennines) revealed by paleomagnetic and magnetic fabric analyses.

We present new paleomagnetic, Anisotropy of Magnetic Susceptibility (AMS), and structural data from the Acerno and Tizzano Quaternary intermontane basins, in the central sector of the Picentini Mts (Southern Apennines, Italy). The stratigraphic succession of these basins is related to fluvial-lacustrine depositional environments. The two basin outcrop at 750m and 900m a.s.l. respectively, and are well exposed because of the deep gorges excavated for hundred meters by the Tusciano river. The Acerno basin sedimentary sequence has been attributed to the Middle Pleistocene on the basis of radiometric ages obtained from volcanoclastic deposits. Conversely, the age of the Tizzano basin is essentially unknown, even if the basin has been considered older than the Acerno basin, on the basis of geomorphological evidences. We sampled 20 sites for paleomagnetic and AMS studies, in order to better constrain the age and the tectonic evolution of such basins. All the sites from the Acerno basin show a normal polarity, which confirm a Middle Pleistocene age for this sequence, according with radiometric age data. Conversely, paleomagnetic results from the Tizzano basin show an inverse polarity in the lower part of the stratigraphic section, and a normal polarity in the upper part. We interpret this reversal as the Brunhes-Matuyama boundary. AMS data show a well defined magnetic foliation parallel to the bedding planes, and a well defined magnetic lineation, with a shape of ellipsoids typically of weakly deformed sediments. The magnetic lineations obtained from the Tizzano basin cluster around a NNE-SSW trend, which is almost orthogonal to the NW-SE oriented normal faults which have been recognized in the field. The overall data set evidences that extensional tectonics in the Picentini Mts. was already active during the lower Pleistocene, along NW-SE normal faults.