1. Inquadramento geologico regionale dell’ area del Monte Amiata. In: C. Principe, G. Lavorini & L.M. Vezzoli C Eds. – Il vulcano di Monte Amiata.

This work aims to show a geological introduction of the Monte Amiata area and takes into account the latest researches concerning stratigraphy and tectonics of the Ligurian, sub-Ligurian and Tuscan Units, but also its sedimentary and tectonic evolution during Neogenic-Quaternary times. In particular, three main units have been distinguished within the Ligurids l.s. (from the geometric bottom to top): (a) the Canetolo Unit (or Sub-Ligurian Unit, Paleocene-Eocene), represented by dark grey to green shales with grey calcilutite and calcarenite beds, locally with K-feldspar-free, more or less calcareous sandstone intercalations; (b) the Santa Fiora Unit, consisting of a complex pile of tectonic elements made up of Cretaceous successions and, in particular, a dominant marly-calcareous flysch with local Pietraforte-like intercalations (Santa Fiora Formation) and of the siliciclastic turbiditic Pietraforte Formation. with its basal shaly-silty lithofacies (Manganesiferous Varicoloured Shales Formation); (c) Ophiolitic Unit, mostly represented by often chaotic shales with siliceous limestone intercalations and quartz-arenites of Lower Cretaceous age (Palombini Shales Formation), which locally include ophiolitic olistoliths (mostly serpentinites locally associated with ophicalcites and ophiolitic breccias), Lower Cretaceous Murlo-like marls and Albian-Turonian olivine-basalt dykes, sills and pillow-lavas. The tectonic setting of the Ligurian, Sub-Ligurian and Tuscan units in the Monte Amiata area is similar to that in southern Tuscany. In particular, the studies indicate a complex tectonic evolution which mostly occurred in the Lower Miocene to Pliocene time interval and including the following events: (1) syn-collisional and «serrage» folding and stacking of the units (Early Miocene-Middle Miocene); (2) tectonic lamination of the Tuscan Nappe (the so-called «Reduced Tuscan Sequence») and of the overlying Ligurian l.s. stack in the Serravallian-Lower Tortonian; (3) development of the intramontane continental to marine basins (Upper Miocene-Pliocene) and of high-angle faulting. In particular, during the Early-Middle Miocene, doublings of the Tuscan Nappe in the the Monte Amiata region (e.g. that of Poggio Zoccolino) and in other parts of Tuscany (e.g.in the Larderello-Travale geothermal field) also occurred as well as the building up of the regional Tuscan Nappe Front (Monte Orsaro-Lima Valley-Monti del Chianti- Monte Cetona structural alignment). This event also produced doublings and refoldings in the underlying crystalline Triassic-Paleozoic successions of the Monte Amiata subsurface, which probably belong to the Umbrian Domain. During the Middle Miocene shortening and immediately later, syn- and post-tectonic, low-angle faulting produced the «Reduced Tuscan Sequence». Since Upper Miocene- Pliocene, this complex tectonic pile was dismembered by high angle normal fault systems (which mainly strike NW-SE, NE-SW and N-S) and produced the growth of the Siena-Radicofani and the Cinigiano-Baccinello morphological-structural depressions and of the Montalcino - Monte Amiata - Monte Razzano ridge. The uplift of the Montalcino - Monte Amiata area continued in more recent times (e.g. the outcrops of Lower Pliocene sediments at about 500 m between Montalcino and Castelnuovo dell’Abate, and at about 1000 m in the Monte Labbro area) and is probably connected to the magmatic processes of the Quaternary Monte Amiata volcano.