Structural development of the Neogene Radicondoli-Volterra and adjoining hinterland basins in Western Tuscany (Northern Apennines, Italy)

This paper presents a geological-structural study of some Neogene hinterlan d basins of the Northern Apennines, located on the Tyrrhenian side of the c hain. These basins developed on the already delineated thrust-fold belt fro m middle-late Tortonian times. Their evolution has been commonly referred t o an extensional tectonic regime, related to the opening of the Tyrrhenian Sea. New data have allowed us to hypothesize a different tectonic evolution for the chain, where compressive tectonics plays a major role both in the external and in the hinterland area. In this frame, the hinterland area located west of a major outcropping crus tal thrust (Mid-Tuscany Metamorphic Ridge) has been the target of a geologi cal-structural investigation. The field mapping and structural analysis has been focused on the syntectonic sediments of the Radicondoli-Volterra basi n as well as on adjoining minor basins. These basins commonly display a syn clinal structure and are generally located in between basement culminations , probably corresponding to thrust anticlines. Sediments of the hinterland basins have been affected by compressive deformation and regional unconform ities separate stratigraphic units due to the activity of basement thrusts. In the study area, normal faulting either accommodates the thrusting proce sses or post-dates compressive deformation. A chronology of faulting and a six-stage evolution of this area are present ed, providing further insights for the Neogene tectonic evolution of the No rthern Apennines. (C) 1998 John Wiley & Sons, Ltd.