A geological transect across the Northern Apennine and insight into its post-collisional evolution

A regional geological cross section across the northern Apennine is presented, with an accompanying structural-geological map. New observations in the Alpi Apuane, Cerreto- Ligonchio, Abetone-M. Cimone and upper Val di Lima areas allow to reinterpret some of the major tectonic lineaments and the stratigraphic-tectonic setting of the northern Apennine and to set some constrains for the tectonic evolution of this sector of the chain. In the Alpi Apuane area detailed investigations in the central part of the metamorphic units allow to reconstruct a complex uplift history with superposition of different generation of normal and stike-slip faults. Most of these faults accomodate only minor displacements but have strong geomorphological evidence and play a key role in development of microstructures in marble rocks. The normal faults that now border the Alpi Apuane metamorphic complex are only responsible for the recent (still active) uplift of the region, but did not led to unroofing of metamorphic rocks and juxtaposition of non-metamorphic (Tuscan Nappe) above metamorphic rocks. The main extensional event in the area is related with an older top-NE main regional low-angle normal fault that developed a thick cataclasite (“Calcare cavernoso” Auctt.) and led to unroofing and uplift of the metamorphic rocks. This low-angle normal fault is later crosscut by the high-angle normal faults that now border the metamorphic complex. This main low-angle normal faulting event it is also responsible for development of cataclastic rocks at the base of the Tuscan nappe in the Lerici - San Terenzo - Punta Bianca area and for development of cataclasites in the Cerreto area, with clasts and slivers of medium grade metamorphic rocks embedded in Triassic dolomites and evaporites. This major low-angle normal fault represents therefore the basis of the Tuscan Nappe in the Alpi Apuane - La Spezia area and is the roof contact in the complex tectonic structure of the Cerreto area. This normal fault crosscuts tectonic contacts in the Sestola-Vidiciatico Unit, out-of- sequence thrusts in the M. Cusna area and represent therefore a recent tectonic contact, related to the post-collisonal evolution of the Northern Apennine, and linked with uplift and exhumation.