The Tuscan Nappe structures in the Monte Amiata geothermal area (central Italy): a review

Abstract

The present knowledge on the structures affecting the Tuscan Nappe in the Monte Amiata area is here presented, highlighting that the tectonic evolution of the area is incorporated in the inner Northern Apennines framework. In fact, field and subsurface data indicate that the Tuscan Nappe is internally characterized by tectonic doublings, occurred during the collisional stage. Subsequently, as well as in the whole southern Tuscany, Miocene extension determined the lateral segmentation of the Tuscan Nappe; in the Mt. Amiata area, it resulted in three isolated geological bodies, partly cropping out. During Pliocene, the Tuscan Nappe was cross-cut by normal to oblique faults which contributed to channel the hydrothermal fluids that gave rise to the Pleistocene Hg-Sb ore deposits and Present geothermal resources. As it regards the deformation ages, since the late Oligocene-Aquitanian Macigno Fm is involved in the thrusts, the internal stacking of the Tuscan Nappe is related to the post-Aquitanian and pre-Langhian time period, on the basis of the Langhian sediments deposited in an extensional setting and presently recognised underneath the sediments of the nearby Pliocene Radicofani extensional Basin. It is therefore concluded that the switch from compression to extension occurred in a time span encompassed between early Burdigalian and early Langhian.A. BROGI ET ALII Fig. 1 -(A) Tectono-stratigraphic columns illustrating the main features of the paleogeographic domains of inner Northern Apeninnes. The Ligurian units consist of remnants of Jurassic oceanic crust, its Jurassic-Cretaceous mainly clayey cover. The Sub-Ligurian unit is made up of Cretaceous-Oligocene turbidites, believed to belong to a transitional crust paleogeographic domain. These units were thrust eastward over the Tuscan Nappe and the Metamorphic Tuscan units derived from the Internal and External Tuscan Domains, respectively, during late Oligocene-early Miocene time-period. The Tuscan Nappe is made up of rocks ranging from late Triassic evaporite to a Jurassic carbonate platform, Cretaceous-Oligocene pelagic sediments and late Oligocene-early Miocene turbidite. The greenschist metamorphic rocks from the External Tuscan Domain include late Triassic Jurassic metacarbonate, Cretaceous-Oligocene calcschists and Oligocene-early Miocene metasandstone. The crystalline basement of inner and outer Tuscan Domains is characterized by middle-late Triassic rocks, mainly represented by quartzite (Verrucano Group, Auct.) and Paleozoic phyllite; (B) Evolutionary tectonic sketch model of inner Northern Apennines, illustrating the coexistence between extension and magmatism, during thinning of the lithosphere (after CARMIGNANI et alii, 1994, modified).

Natural CO2 degassing in the Mount Amiata volcanic–geothermal area

“…The thermal springs of Bagni San Filippo (Fig. 1) are related to this transform fault system where massive deposition of travertines associated with CO 2 discharge occurs even today (Brogi et al, 2015).…”

Reconsidering the Variscan Basement of Southern Tuscany (Inner Northern Apennines)

“…Figure 2. Tectono-stratigraphic columns illustrating the main features of the paleogeographic domains of the inner Northern Apennines (redrawn from [27,31]).…”

Tectonics, hydrothermalism, and paleoclimate recorded by Quaternary travertines and their spatio-temporal distribution in the Albegna basin, central Italy: Insights on Tyrrhenian margin neotectonics

“…The Tuscan magmatic province hosts fossil and active hydrothermal systems. Endogenic fluid circulation within hydrothermal systems has been dominantly channelized by possibly active extensional faults (e.g., Barberi et al, 1994;Buonasorte et al, 1988;Chiarabba et al, 1995;Gianelli et al, 1997;Batini et al, 2003;Bellani et al, 2004;Annunziatellis et al, 2008;Brogi, 2008;Brogi et al, 2010bBrogi et al, , 2015Liotta et al, 2010;Rossetti et al, 2008Rossetti et al, , 2011.…”