Geochemistry of water and gas discharges from the Mt. Amiata silicic complex and surrounding areas (central Italy)

Minissale, A.; Magro, G.; Vaselli, Orlando; Verrucchi, C.; Perticone, I

doi:10.1016/s0377-0273(97)00028-0

Cited by 83 publications

(72 citation statements)

References 56 publications

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“…The presence of CO 2 -rich gas discharges, characterized by d 13 C-CO 2 values slightly lower than À1‰ V-PDB (Table 7), certainly suggests the presence of a deep-seated source feeding these gas vents. Such values are indeed similar to those found in the fumarolic gas discharges from the Island of Volcano (e.g., Paonita et al, 2002) and Solfatara, Somma-Vesuvius and related submarine emissions (e.g., Chiodini et al, 2001;Caliro et al, 2007;Vaselli et al, 2011;Passaro et al, 2016) and many gas vents distributed along the peri-Tyrrhenian strip (e.g., Minissale et al, 1997) of the Italian peninsula. The origin of the periTyrrhenian vents is mainly related to thermometamorphic processes of marine limestone, although small contributions from a magmatic source cannot be excluded.…”

Section: Isotopic Composition Of Carbonates and Origin Of Mineralizinsupporting

confidence: 83%

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Franchi

Rovere

Gamberi

et al. 2017

Marine and Petroleum Geology

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a b s t r a c tPaola Ridge, along the NW Calabrian margin (southern Tyrrhenian Sea), is one of the few reported deep sea sites of precipitation of authigenic carbonates in the Tyrrhenian Sea. Here, the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite, siderite and other carbonate phases. The occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate-methane transition zone (SMTZ).Concretions of authigenic minerals formed in the near sub-bottom sediments of the Paola Ridge were investigated for their geochemical and isotopic composition. These concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs. The mud diapirs are dotted by pockmarks and dissected by normal faults, and are known for having been a site of fluid seepage for at least the past 40 kyrs. Present-day venting activity occurs alongside the two alleged mud volcanoes and is dominated by CO 2 -rich discharging fluids. This discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area.In this study, we used stable isotopes (carbon and oxygen) of carbonates coupled with rare earth element (REE) composition of different carbonate and non-carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates. The analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea-water.Authigenic calcite/aragonite concretions, from surficial sediments on diapiric structures, have depleted values. The siderite REE pattern shows consistent LREE (light REE) fractionation, MREE (medium REE) enrichment and positive Gd and La anomalies. As shown by the REE distribution, the 13 C-depleted composition and their association with chemosymbiotic fauna, calcite/aragonite precipitated at time of moderate to high methane flux close to the seafloor, under the influence of bottom seawater. Authigenic siderite, on the other hand, formed in the subseafloor, during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with 13 C-rich dissolved inorganic carbon (DIC) and 18 O-rich water, likely related to methanogenesis and intermittent venting of deep-sourced CO 2 .

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Section: Isotopic Composition Of Carbonates and Origin Of Mineralizinsupporting

confidence: 83%

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Franchi

Rovere

Gamberi

et al. 2017

Marine and Petroleum Geology

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“…Duchi et al (1992) have interpreted the composition of gases discharged with waters as typical of low enthalpy geothermal systems; H2 and H2S are generally below the detection limit, CO2 represents the most abundant gas (up to 99%) and the N2 and 02 contents vary depending on the mixing with recharge waters. He isotopic data of gas samples along the Arbia Line reveal a signifi cant mantle signal (3He/4He = 0.15-2 Ra) and 13C data are close to those for mantle-derived mag mas (-4 to -6%o; Minissale et al, 1997).…”

Section: Geological Settingsupporting

confidence: 60%

Effects of gas-water partitioning, stripping and channelling processes on radon and helium gas distribution in fault areas.

Guerra

Etiope

1999

Geochem. J.

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Gas samples for analysis of CO2, Rn and He were collected simultaneously in different types of natural occurrence, i.e., soil-air, groundwater, gas vent and soil-atmosphere exhalation flux, in the Siena-Rapolano geothermal area (central Italy). The results showed differential enrichment and depletion of Rn and He within small areas as an effect of gas-water partitioning and gas channelling in C02-rich faulted subsoil. In the same site low concentrations of Rn or He in water co-exist with high concentrations in the ground; low Rn in soil-air occurs in correspondence with Rn-rich gas vents; soil-gas Rn may be higher than the level induced by U decay in the ground or outcropping rocks. These results suggest that the analysis of a single "sub-system" of the geological environment (e.g., groundwater analysis only) may not provide data representative of gas occurrence and abundance at the investigated site. This must be taken into account in natural resource exploration, earthquake precursor studies and radiation protection zoning based on gas geochemistry.

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“…When applied to well-known geothermal areas, such as the Mt. Amiata area in Tuscany (Italy), only fluids discharging from deep geothermal wells align along the full equilibrium line, but mixing line(s) from deep wells and shallow springs in the so called mixing area, are commonly recognised (Minissale et al, 1997). Fig.…”

Section: Thermal Interpretation Of Manifestations and Geothermometrymentioning

confidence: 99%

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Minissale

Corti

Tassi

et al. 2017

Journal of Volcanology and Geothermal Research

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In this study, the occurrence, chemical composition, origin and geothermal significance of thermal springs and fumaroles naturally discharging in the area located north of the Lake Abaya (western margin of the Main Ethiopian Rift, East Africa) are reviewed in relation with recent tectonics. All thermal springs showed a dominantly Na-HCO 3 composition, consistent with observations dating from at least 1972, and most of them displayed a narrow range of δD and δ 18 O isotopic compositions for water similar to regional meteoric origins. These observations suggest that water-rock interaction processes occur in all aquifers and dominate the contributions of water that actively circulate within thermal fluids, and also suggest a similar elevation of groundwater recharge throughout the study area. Most of the thermal springs are dominated by a CO 2 -rich gas phase and discharge along the active faults bordering the western edge of the Main Ethiopian Rift valley. The δ 13 C values of CO 2 and the 3 He/ 4 He isotopic ratios are consistent with the presence of mantle-derived fluids similar to what is observed in many other areas along the kinematically active African Rift, especially within Ethiopia. The application of geothermometric techniques in the liquid and the gas phases suggests the presence of a deep reservoir in which the fluids equilibrated at a maximum temperature of approximately 180°C. Additionally, the presence of fumaroles at boiling temperatures and water/mud boiling pools in several places suggests that the geothermal reservoir is positioned at a relatively shallow depth and likely located in the western side of the study area. The analysis of data collected throughout time reveals that the waters of Lake Abaya have experienced an increase in salinity of 20% paralleled contemporaneously with a decrease in pH and δ 18 O and δD of water in the last 40 years; these changes do not appear to be related to climate changeinduced increases in temperature or evaporation at the global scale.

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Geochemistry of water and gas discharges from the Mt. Amiata silicic complex and surrounding areas (central Italy)

Cited by 83 publications

References 56 publications

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Effects of gas-water partitioning, stripping and channelling processes on radon and helium gas distribution in fault areas.

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

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