Enrico Pandeli

Geological model of a young volcano-plutonic system: The geothermal region of Monte Amiata (Tuscany, Italy)

Abstract Geological, geophysical and petrologic data point to the presence of a granitic body below the geothermal region of Mt Amiata (central Italy). A broad area of about 900–1300 km 2 centered on Amiata volcano shows a regional uplift of the Pliocene beds to 950 m a.s.l. The uplift began during the lower Pliocene, with a regression of the Pliocene sea from an uplifted area centered in the volcano zone. The temperature distribution below the Piancastagnaio field shows an updoming of the isotherms, forming a thermal high, probably present since the earliest stages of interaction between geothermal fluids and country rocks. A re-evaluation of the petrologic data from the xenoliths included in the lava flows allows an estimate of the P-T conditions of the magma body; a minimum temperature of 575°C and pressures of 1550–2200 bars can be estimated for the confining rocks around the magma body. Magmatologic data show a temperature of 800–900°C and a P load - 1000 bar. Therefore the roof of the magma body should be present at about 6 km depth. Seismic reflection data reveal the continuous and widespread occurrence of a reflecting horizon ( K ) of all over the geothermal region. This horizon is present at a depth of 5–6 km. By analogy with Larderello, it is interpreted as a fracture interval filled with hot fluids, contact metamorphic minerals and hydrothermal minerals generated in the uppermost part of the granite and the basal levels of the wall rocks. By integrating geophysical and geological data, a two-dimensional gravimetric model of the volcano-plutonic system of Mt Amiata is proposed, with the following features: roof depth = 5–6 km, T = 820°C, d (magma) = 2.15 g cm −3 , d (wall rock) = 2.8 g cm −3 , shape of the intrusion is lens shaped or mushroom-like with possible thickening and roots just below Piancastagnaio. This model fits well with gravimetric data, which show a negative anomaly in correspondence with the uplifted area.

The East Variscan Shear Zone: new insights into its role in the Late Carboniferous collision in southern Europe

A comparison of the petro-tectonic features recorded in the Variscan Massifs scattered throughout the Alps, the Corsica-Sardinia-Maures-Tanneron Massif, the Calabria-Peloritani Arc, and the Northern Apennines, has allowed us to propose that they belonged to the same geodynamic realm until Late Carboniferous time. In the interval 330–300 Ma, the development of a regional dextral strike–slip shear zone, the East Variscan Shear Zone (EVSZ), affected all the massifs, leading to their spatial separation. The EVSZ developed, together with numerous regional shear zones, under a transpressional tectonic regime deriving from the Late Carboniferous collision between Gondwana, peri-Gondwana microcontinents (Armorica and Avalonia), and Laurussia plates. The EVSZ evidently played a key role in the evolution of the subsequent Alpine and Apenninic cycles, acting as a pre-existing tectonic barrier. Our proposed geodynamic reconstruction does not reflect the acquisition of new data, but is based on the analysis and review of the recent geological literature.

Metallogeny, exploitation and environmental impact of the Mt. Amiata mercury ore district (Southern Tuscany, Italy)

The Mt. Amiata mining district (Southern Tuscany, Italy) is a world class Hg district, with a cumulate production of more than 100,000 tonnes of Hg, mostly occurring between 1870 and 1980. The Hg mineralization at Mt. Amiata is younger than 0.3 Ma, and is directly related to shallow hydrothermal systems similar to presentday geothermal fields of the region. There is likely a continuum of Hg deposition to present day, because Hg emission from geothermal power plants is on-going. In this sense, the Mt. Amiata deposits present some analogies with hot-spring type deposits of western USA, although an ore deposit model for the district has not been established. Specifically, the source of Hg remains highly speculative. The mineralizing hydrothermal fluids are of low temperature, and of essentially meteoric origin. Recent results by our research group indicate that, 30 years after mine closure, the environmental effects of Hg contamination related to mining are still recorded by the ecosystem, namely on waterways of the Paglia and Tiber River basins. In particular, the close spatial connection between the town of Abbadia San Salvatore, the Hg mine within its immediate neighborhood, and the drainage catchment of the Paglia River has an influence also on Hg speciation, transported mainly in the particulate form by the river system. The extent of Hg contamination has been identified at least 100 km from Abbadia San Salvatore along the Paglia-Tiber River system. Estimated annual Hg mass loads transported by the Paglia River to the Tiber River were about 11 kg yr-1. However, there is evidence that flood events may enhance Hg mobilization in the Paglia River basin, increasing Hg concentrations in stream sediment. The high methyl-Hg/Hg ratio in water in this area is an additional factor of great concern due to the potential harmful effects on human and wildlife health. Results of our studies indicate that the Mt. Amiata region is at present a source of Hg of remarkable environmental concern at the local, regional (Tiber River), and Mediterranean scales. Ongoing studies are aimed to a more detailed quantification of the Hg mass load input to the Mediterranean Sea, and to unravel the processes concerning Hg transport and fluid dynamics.

Possible crystalline gastroliths of large marine Vertebrata from Oligocene pelitic sediments of the Northern Apennines, Italy

Randomly dispersed erratic clasts are found within the pelagic marly-shaly sequences of the Oligocene Scisti Varicolori Formation (Cervarola-Falterona unit of the Tuscan domain). These clasts are centimeters to decimeters in size and subrounded to well rounded; their shape suggests an origin in a fluvial and partly littoral environment. The clasts are composed of low- to medium-grade metamorphic rocks, andesitic volcanic rocks, and Late Jurassic–Early Cretaceous pelagic limestones. The source area of the crystalline material is interpreted to be the central-western sector of the Alpine chain or the Corsica-Sardinia area. In addition, the peculiar surfaces of these clasts, as well as their isolated occurrence in the pelagic shales of the Scisti Varicolori, suggest an uncommon depositional mechanism, such as redeposited gastroliths of large marine Vertebrata.

Structural Setting of the Paleozoic Crystalline Basement of the Northern Apennines (Italy)

The upper part of the crystalline basement of the Northern Apennines is made up of a complex pile of tectonic wedges derived from Alpine low-grade metamorphic units (T= temperature = 300°–450°C; P= pressure = 3–4 Kbar), Paleozoic (?Late Cambrian-Permian) to Tertiary in age. The Paleozoic rocks also show evidence of pre-Alpine deformation (e.g. Hercynian schistosity relics and folding).

Updated picture of the Ligurian and Sub-Ligurian units in the Mt. Amiata area (Tuscany, Italy): elements for their correlation in the framework of the Northern Apennines

The Mt. Amiata region (Southern Tuscany, Italy) represents the southernmost area of the Northern Apennines in which different lithologies belonging to the Ligurian and Sub-Ligurian units crop out widely. This paper provides an update on the stratigraphic, paleontological and structural features of the Ligurian and Sub-Ligurian units in the Mt. Amiata area by integrating new data from the Regional Geological Mapping project with those available from the existing literature. In the study area, the Sub-Ligurian units are represented by the Canetolo unit, which comprises the middle Eocene (Zone NP15) Argille e Calcari and Vico Fms showing heteropic relationships. The Ligurian units are represented by the Ophiolitic and Santa Fiora units. The Ophiolitic unit consists mainly of Early Cretaceous Palombini Shale associated with scattered Middle-Late Jurassic ophiolites. The age of the Palombini Shale spans from late Hauterivian-Barremian Zone CC5 to Aptian Zone CC7 of [Sissingh (1977)][1]. The Ophiolitic unit overlies the Santa Fiora unit consisting of the Pietraforte Fm and Varicoloured Shales topped by the Santa Fiora Fm. The Pietraforte Fm shows heteropic relationships with the Varicoloured Shale, and both formations can be referred to the ?Aptian to middle Coniacian. The age of the Santa Fiora Fm seems to span from the late Coniacian-early Santonian (Zone CC14) to middle-late Campanian (Zones CC21-CC22). Structural analyses indicate that all the Ligurian and Sub-Ligurian units experienced complex polyphase deformation through several folding phases during the closure of the Ligurian-Piemontese oceanic basin and the subsequent continental collision, which began in the middle Eocene. The Ligurian and Sub-Ligurian units now come into contact through low-angle shear zones developed during the last deformation phase identified in these units, i.e. middle Miocene extensional tectonics. This tectonic phase produced strong delamination through low-angle faults with staircase geometry, so that not only several stratigraphic levels but also entire tectonic units were omitted. Despite the extensional tectonics, the collected stratigraphic and structural data suggest a correlation between the Ligurian and Sub-Ligurian units of the Mt. Amiata area and the units cropping out in Southern Tuscany and the Ligurian-Emilian Apennines. [1]: #ref-77

The Elba Island: an intriguing geological puzzle in the Northern Tyrrhenian Sea

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Relationships between the Sakarya Zone and the Ankara–Erzincan suture (central-northern Turkey): geological and petrographic data from the Ankara–Çankiri, Çorum and Amasya areas

The study was performed in central-northern Anatolia (from Ankara to Amasya) to investigate the relationships of the Sakarya Zone units and the Izmir–Ankara–Erzincan suture (IAES) melange. It reveals that all the Sakarya Zone units are metamorphic and three main tectonostratigraphic units have been distinguished for the first time: the BAA (metasiliciclastic rocks capped by metacarbonates and varicoloured phyllite), the BKC (poly-metamorphic garnet-bearing micaschist and metabasite with a well-preserved relict HP–LT amphibole in a low-amphibolitic to greenschistfacies framework) and the AMC (meta-arkose passing vertically to carbonate–phyllitic alternations and, then, to a thick succession of prevailing acidic to intermediate–basic metavolcanites and volcanicrich metasediments). The BAA and AMC, whose metamorphic frameworks are of Cimmerian age, underlie the Mesozoic carbonate cover sequences (e.g. t2-3, j3–k1) that often show tectonic detachments and slicing. The piling up of the BAA above the HP–LT BKC can be correlated to the tectonic superposition of two similar units (i.e. the Cimmerian Çangaldağ Complex and the Alpine Middle– Upper Cretaceous Domuzdağ Complex, respectively) defined by previous authors in other sectors of the Central Pontides front. The ophiolitic melange generally underlies the Sakarya Zone, but locally (e.g. SE of Amasya) tectonically rests above the latter, probably owing to back-thrusting that occurred during the Tertiary syn-collisional shortenings and the later strike-slip tectonics. We hypothesize that, also in these areas, the Sakarya Zone–IAES consists of a complex tectonic stack of different units, belonging to different palaeogeographic domains and orogenic events (Cimmerian versus Alpine orogenies), but originated within a single long-lived (since Late Triassic to Paleocene/Eocene times), prograding subduction–accretion system in front of the Laurasian continent.

The Scaglia Toscana Formation of the Monti del Chianti: new lithostratigraphic and biostratigraphic data

The Scaglia Toscana Formation (Scisti Policromi Auctt.) is one of the most investigated formation of the Tuscane Nappe. The Formation is widely exposed in the Chianti Mounts and despite the number of studies in this area, some aspects remain poorly known and debated. In this paper new litho- and bio-stratigraphic data from eight key-sections distributed over the entire area are provided and discussed in order to clarify the stratigraphic relationshpis among different lithostratigraphic members, as well as the depositional ages of each member. The Formation deposited in the Cretaceous-Oligocene time interval and it can be subdivided into five lithostratigraphic members: i) the Argilliti di Brolio (wine-red shales with sporadic siliceous calcilutites and rare interbedded cherts); ii) the Marne del Sugame (red and pink marls, calcareous marls and marly limestones with interbedded calcarenitic beds and ruditic lens-shaped bodies including calcareous-siliceous clasts); iii) the Argilliti di Cintoia (grey-green to black shales, locally with manganese-rich siliceous calcilutites and cherts); iv) the Calcareniti di Montegrossi (thin beds of calcilutites and calcarenites with varicoloured shaly-marly interbeds); and v) the Argilliti e Calcareniti di Dudda (alternating thin beds of calcilutites and calcarenites with varicoloured shaly-marly interbeds). These members deposited in a marine environment and have been interpreted as deposited in a turbiditic system, in which shaly and calcareous turbiditic members have been attributed to a basin plain below the CCD, whereas the marls and marly limestones of the Marne del Sugame Member can be settled in a slope/ramp environment above or close to the CCD. Furthermore, the combination of these new data with structural informations coming from literatures allowed to a better paleogeographic reconstruction of the paleobasin. In order to better explain these data, the paper is accompanied by two geological maps realized in the past but never distributed. The two geological maps, at the scale of 1:25,000, cover the whole area from the Cintoia (south of Florence) to the San Gusme (north of Siena) villages.

Le potenzialità geotermiche di alcune aree del Medio Campidano oggetto di ricerca di risorse a media entalpia

The middle part of the Campidano Valley has gained a renewed interest in the geothermal exploration due to the attention of private investors determined to define the presence of medium-enthalpy geothermal resources in the subsurface of this sector of Sardinia. The study area is a portion of the Plio-Pleistocene Campidano Graben that is bordered both to the north and to the south by structural highs (e.g. the Iglesiente-Sulcis horst) mostly made of Paleozoic metamorphic rocks, deformed and recrystallized during the Variscan Orogeny. Available data suggest that the geothermal reservoir can be positioned in the fractured Paleozoic metamorphic rocks below the Miocene-Quaternary sedimentary filling of the Campidano Graben. The thermal fluids locally reach the surface in correspondence of the border normal fault systems of the graben.Research activities include a first phase of surface investigations, such as geological, hydrogeological and geochemical surveys, and fa geophysical prospecting aimed to assess the quality and quantity of the geothermal resources.