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Muto, Francesco
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Muto, Francesco
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- PublicationRestrictedA multidisciplinary geochemical approach to geothermal resource exploration: The Spezzano Albanese thermal system, southern Italy(2023-07-07)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ; ; ; ; ; This work aims to define the geothermal conceptual model of the Spezzano Albanese thermal system located in the northern sector of the Calabria Region, along the western edge of the Sibari Plain. The study confirms that the deep thermal reservoir of Spezzano Albanese is mainly hosted within the permeable levels of the evaporite deposits of the Messinian succession including siltstones with manganese mineralisation, halite, and gypsumarenites. The thermal waters show discharging temperature between 20.2 and 26.6 ◦C and a high compositional variability, from Na–Cl to Na–Ca–HCO3. The compositional evolution (from Na–Cl to Na–HCO3) is accompanied by a decrease in both salinity and the concentrations of most dissolved constituents, including Cl, Br, B, Li, Na, K, Mg, Ca, and Ba. These variations are due to mixing between the thermal endmember, rich in Cl and related components, and low-salinity, cold shallow waters (temperature between 17.5 and 22.7 ◦C). The study points out that the thermal endmember derives by halite dissolution and more complex water-rock interaction processes involving (1) the dissolution of other solid phases of the Messinian deposits, as also confirmed by δ34S values of dissolved sulphate and sulphide, and (2) the precipitation of secondary solid phases (e.g., barite). The geothermometric modelling suggests that the thermal groundwaters in the deep reservoir are probably in equilibrium with either (i) quartz, calcite, disordered dolomite, low-albite, and K-feldspar, as well as with pyrophyllite and poorly crystalline kaolinite (as proxies of clay minerals) at temperatures of 65.5 ± 4.5 ◦C or (ii) quartz, calcite, disordered dolomite, low-albite, disordered adularia, laumontite and saponites at temperatures of 56.1 ± 4.3 ◦C, based on the first and second geothermometric model, respectively. The δ18O and δ2H values of water confirm a meteoric origin for the thermal waters with average recharge altitudes between 745 and 857 m a.s.l. These elevations are compatible with the recharge from the western side of the Esaro valley where evaporite successions are found close to the surface. The isotopic value of the dissolved CO2 associated to the Spezzano Terme water highlights its likely microbial origin, as recognised for other thermal circuits hosted in sedimentary rocks of the southern Apennines. Furthermore, the thermal endmember shows a noteworthy enrichment in CH4 with respect to air due to the interaction of groundwater with sediments rich in organic matter. Although methane could have a biogenic origin, the presence of a minor component of thermogenic methane in the gas phase dissolved in the Spezzano Terme waters cannot be completely excluded. The data obtained in this study allow to assume that the recharge meteoric waters descend to a maximum depth of about 1.1–1.4 km below the main emergence area and then the regional NE-SW fault systems probably act as a preferential pathway for the ascent of the thermal waters towards the surface. These waters discharge at Spezzano Albanese, where the crystalline-metamorphic units cropping out immediately upstream of the emergence area act as cap-rock favouring the final ascent towards the surface of the thermal waters.156 18 - PublicationRestrictedActive transpressive surface faulting in north-eastern calabria, southern Italy: early results of geomorphological, stratigraphic and paleoseismological analyses(2016)
; ; ; ; ; ; ; ; ; We here first described field evidence of Holocene transpressive faulting in north-eastern Calabria, about 15 km east of Rossano, in the area of Mirto. There, we analysed a stratigraphic sequence exposed along a WNW-ESE trending, 4-km-long scarp, anomalous in the local geomorphic context. The sequence was made of marine deltaic sediments with embedded colluvial deposits, daylighted by an excavation for a building. The excavation occurred on top of a fluvial terrace at ~15 m a.s.l., that was embedded in a MIS 5a marine terrace. Micropaleothological analysis and 14C radiometric dating defined an Early(-Middle) Pleistocene age for the marine sequence and a Holocene age for the overlain colluvial deposits. The whole sequence was back-tilted, warped and offset along shear planes showing an evident reverse sense of motion. The uphill sense of displacement, the local geomorphic setting and the available literature allowed to exclude any other cause (e.g. deep-seated or shallow landsliding, salt diapirism) than tectonics for the observed deformations. By considering the current knowledge about the structural and active tectonic framework of the northern Calabrian Arc, the observed reverse fault planes can be the surface expression of either local active compressional deformations (i.e. restraining bend) along the Rossano-Cirò Marina strike slip shear zone, being part of the regional, left-later strike-slip Pollino Line, or an inland splay of the active transpressional tectonic structures offshore of the Sibari Plain and the Rossano area. Even if at an early stage, our observations can represent a new piece in the active tectonics puzzle of the boundary region between the Calabrian Arc and the southern Apennines. They also provide new hints for seismotectonic evaluations, taking into thorough consideration that the ob-served tectonic features occur in the epicentral area of the 1836 (Mw 6.2) earthquake, the causative fault of which is still debated. Ultimately, the present study raises new questions about reverse surface faulting hazard assessment for this region.115 7 - PublicationOpen AccessSeismotectonics of Southern Calabria Terrane (South Italy)Seismic data of earthquakes recorded during the last 40 years in southern Calabria have been compared with geological data in order to obtain a seismotectonic picture of the area. We sought for any possible correlation between the main regional tectonic st ructures, the distribution of earthquake hypocentres and the focal mechanism of earthquakes with magnitude (Ml)≥3. Studies of historical and recent seismicity and analysis of geological stru ctures allowed to define the main shear strips on a regional scale. More than 2600 earthquakes with 1.5 ≤ Ml ≤ 4.5 have been considered. The focal mechanisms of earthquakes with Ml≥3 have been compared with the kinematics of known faults and used to give insight on the current active stress field. From the analysis carried out it was possible to expand the cognitive framework regarding the activity of the main tectonic structures present in the area. This study also served to identify areas of high seismicity which do not correspond to any evidence of tectonic structures on the surface, and areas where recognized tectonic structures have not shown any seismicity during the la st decades. These cases could be the subject of future investigation in order to correctly assess the se ismic hazard in Calabria. This task is important in the context of seismic hazard evaluation and mitigation.
62 18 - PublicationRestrictedFluid geochemistry in a low-enthalpy geothermal field along a sector of southern Apennines chain (Italy)(2020)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The chemical and isotopic features of the fluids (water and gases) in the Lucane thermal area (southern Italy) have been investigated in order to verify their origin, water temperature in the geothermal reservoir, and to recognize the main natural processes concerning the water composition during ascent towards the surface. The Lucane geothermal system is placed in the southern sector of the Apennines chains, a seismically active area, close to the southern base of the Mt. Alpi carbonate massif. Along the study area, two main sets of high-angle faults form an almost orthogonal fault system that, as suggested by local structural geology, acts as a preferential pathway for uprising deep fluids. Here, we recognized two different types of waters: (i) cold shallow waters having a meteoritic origin and interacting with carbonate rocks (dolomite and calcite), whose dissolved gases show a dominant atmospheric contribution and (ii) hypothermal waters (average temperature of 21 °C), having a meteoritic origin and interacting with both carbonate rocks and inter-bedded evaporitic deposit. Geochemical data allow estimating a geothermal reservoir temperature between 30 °C and 60 °C, according to silica and Ca/ Mg geothermometers, respectively. A heat discharge related to hypothermal groundwater flow between 7.75E +06 and 2.00E+07 J/s was computed. δ18O and δ2Η data allowed recognizing a meteoric origin for hypothermal (hereafter TL) waters, with mean recharge (infiltration) elevations between 1300 and 1700 m a.s.l. These waters are gas-rich (e.g., CO2 and He), which amounts are higher than those in air-saturated water (ASW). Carbon and helium isotope signature in the TL waters indicate their mainly crustal origin and involve a tectonic control on fluid migration through the crust. Furthermore, we observe that the He isotopic signature in gases dissolved in TL waters is stable over time and its monitoring could be a powerful tool to assess the seismogenetic processes since their preparatory phases.118 8