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

Michele Marroni (1), (5), Giovanna Moratti (2), Armando Costantini (3), Sandro Conticelli (4), (2), Marco G. Benvenuti (4), (2), Luca Pandolfi (1), (5), Marco Bonini (2), Gianluca Cornamusini (3) & Marinella A. Laurenzi (5)
(1) Dipartimento di Scienze della Terra, Università degli Studi di Pisa, Via Santa Maria, 23 - I-56126, Pisa, Italy. E-mail: marroni@ dst.unipi.it
(2) Istituto di Geoscienze e Georisorse - UOS Firenze, Consiglio Nazionale delle Ricerche, Via Giorgio La Pira, 4 - I-50121, Firenze, Italy.
(3) Dipartimento di Scienze Fisiche, della Terra e dell'Ambiente, Università degli Studi di Siena, Strada Laterina, 8 - I-53100, Siena, Italy.
(4) Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via Giorgio La Pira, 4 - I-50121, Firenze, Italy.
(5) Istituto di Geoscienze e Georisorse, Consiglio Nazionale delle Ricerche, Via Moruzzi, 4 - I-56124, Firenze, 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 Pleistocene 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 Tectonic 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 extensional tectonics. The Neogene sedimentary deposits unconformably 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 contractional 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.

Geological map of Monte Amiata region, Tuscan, Sub-Ligurian and Ligurian Tectonic Units, Neogene basins, Monte Amiata-Radicofani volcanoes, petrography and geochemistry.