Geology of the Monte Amiata region, Southern Tuscany, Central Italy

This paper and the associated 1:50,000 geological map are devoted to describe the geological features of the Monte Amiata region. The tectono-stratigraphic setting of Monte Amiata region includes, from bottom to top, 1) the pre-Neogene stack of tectonic units, made up of Tuscan, Sub-Ligurian and Ligurian Tectonic Units, 2) the Neogene sedimentary deposits and 3) the Plei-stocene Radicofani and Monte Amiata volcanoes. The pre-Neogene stack of tectonic units includes, from bottom to top, the Tuscan Nappe, belonging to the Tuscan Domain, and Canetolo Tectonic Unit, belonging to the Sub-Ligurian Domain. These tectonic units, regarded as representative of the thinned continental margin of the Adria plate, are topped by the Santa Fiora and Ophiolitic Tec-tonic Units, interpreted as remnants of the Ligure-Piemontese oceanic basin and its transition to the Adria continental margin. All the tectonic units of the pre-Neogene stack have been affected by folds and thrusts originated during the convergence related to the Europe-Africa motion during the Middle Eocene-Early Miocene. Subsequently, these tectonic units were affected by a widespread reduction of thickness of their successions due to low-angle normal faulting related to the Middle Miocene exten-sional tectonics. The Neogene sedimentary deposits uncon-formably overlie the pre-Neogene stack of tectonic units. They consist of Upper Miocene to Pliocene continental and marine sediments, filling the Cinigiano-Baccinello, Velona, and Siena-Radicofani basins, adopting an informal hierarchy of different stratigraphic units where the first order units are synthems. The Pleistocene Radicofani and Monte Amiata volcanoes are made up by high-K basaltic andesitic to shoshonitic volcanic rocks and by trachydacitic to trachytic and olivine-latitic volcanic rocks, respectively. The geological mapping has provided evidences of a complex tectonic setting resulting from a long-lived history shifting from Cretaceous to Early Miocene compressive events to Middle Miocene extensional tectonics and Late Miocene-Pleistocene con-tractional and extensional events during which the Pleistocene magmatic activity occurred. In this regard, the Monte Amiata region can be regarded as a key area where the final result of a 200 Ma long geological history of the Northern Apennines is exposed. KEY WORDS: Geological map of Monte Amiata region, Tuscan, Sub-Ligurian and Ligurian Tectonic Units, Neogene basins, Monte Amiata-Radicofani volcanoes, petrography and geochemistry.