We review the methods based on the measurement of CO2 emissions for the computation of geothermal heat flow, both at a local (hydrothermal sites, a few km2) and regional scale (hundreds km2). At the ...local scale, we present and discuss the cases of the Latera caldera and Torre Alfina (Italy) geothermal systems. At Torre Alfina and Latera, the convection process sustains a CO2 emission of ~1 kg s−1 and ~4 kg s−1, and heat flows of 46 MW and 130 MW, respectively. At the regional scale, we discuss the case of the central Apennine (Italy), where CO2 mass and enthalpy balances of regional aquifers highlights a wide and strong thermal anomaly in an area of low conductive heat flow. Notably, the CO2/heat ratios computed for the central Apennines are very similar to those of the nearby geothermal systems of Latium and Tuscany, suggesting a common source of CO2-rich fluids ascribed to the Tyrrhenian mantle.
To determine the CO2 consumption due to chemical weathering in the Alps, water samples from the 32 main Alpine rivers were collected and analysed in two periods, spring 2011 and winter 2011/2012. ...Most of the river waters are characterized by a bicarbonate earth-alkaline composition with some samples showing a clear enrichment in sulphates and other samples showing a slight enrichment in alkaline metals. The amount of total dissolved solids (TDS) ranges between 96 and 551mg/L. Considering the major ion composition and the Sr isotopic composition of water samples, coherently with the geological setting of the study area, three major reservoirs of dissolved load have been recognized: carbonates, evaporites and silicates. Based on a chemical mass balance, the flux of dissolved solids, and the flux of carbon dioxide consumed by chemical weathering have been computed for each basin and for the entire study area. Results show that the flux of dissolved solids, ranges from 8×103 to 411×103kgkm−2y−1, with an average value of 127×103kgkm−2y−1, while the flux of carbon dioxide consumed by chemical weathering in the short-term (<1Ma) is 5.03×105molkm−2y−1 on average. Since part of the CO2 is returned to the atmosphere through carbonate precipitation and reverse weathering once river water reaches the ocean, the CO2 removed from the atmosphere/soil system in the long-term (>1Ma) is much smaller than the CO2 consumed in the short-term and according to our calculations amounts to 2.01×104molkm−2y−1 on average. This value is almost certainly a minimum estimate of the total amount of CO2 fixed by weathering on the long-term because in our calculations we assumed that all the alkaline metals deriving from rock weathering in the continents are rapidly involved in the process of reverse weathering in the oceans, while there are still large uncertainties on the magnitude and significance of this process. The values of CO2 flux consumed by weathering are strongly correlated with runoff while other potential controlling factors show only weak correlations or no correlation. Our estimation of the CO2 consumed by weathering in the Alpine basins is in the same order of magnitude, but higher than the world average and is consistent with previous estimations made in river basins with similar climatic conditions and similar latitudes.
•We determined the CO2 consumption by chemical weathering of the Alps.•We base the computation on the chemical mass balance of the main alpine rivers.•We recognized three sources of dissolved load: carbonates, evaporites and silicates.•Runoff is the main controlling factor of CO2 consumption flux.
The quaternary volcanic complex of Mount Amiata is located in southern Tuscany (Italy) and represents the most recent manifestation of the Tuscan Magmatic Province. The region is characterised by a ...large thermal anomaly and by the presence of numerous CO
2-rich gas emissions and geothermal features, mainly located at the periphery of the volcanic complex. Two geothermal systems are located, at increasing depths, in the carbonate and metamorphic formations beneath the volcanic complex. The shallow volcanic aquifer is separated from the deep geothermal systems by a low permeability unit (Ligurian Unit). A measured CO
2 discharge through soils of 1.8
×
10
9
mol
a
−1 shows that large amounts of CO
2 move from the deep reservoir to the surface. A large range in
δ
13C
TDIC (−21.07 to +3.65) characterises the waters circulating in the aquifers of the region and the mass and isotopic balance of TDIC allows distinguishing a discharge of 0.3
×
10
9
mol
a
−1 of deeply sourced CO
2 in spring waters. The total natural CO
2 discharge (2.1
×
10
9
mol
a
−1) is slightly less than minimum CO
2 output estimated by an indirect method (2.8
×
10
9
mol
a
−1), but present-day release of 5.8
×
10
9
mol
a
−1 CO
2 from deep geothermal wells may have reduced natural CO
2 discharge. The heat transported by groundwater, computed considering the increase in temperature from the infiltration area to the discharge from springs, is of the same order of magnitude, or higher, than the regional conductive heat flow (>200
mW
m
−2) and reaches extremely high values (up to 2700
mW
m
−2) in the north-eastern part of the study area. Heat transfer occurs mainly by conductive heating in the volcanic aquifer and by uprising gas and vapor along fault zones and in those areas where low permeability cover is lacking. The comparison of CO
2 flux, heat flow and geological setting shows that near surface geology and hydrogeological setting play a central role in determining CO
2 degassing and heat transfer patterns.
Sulfuric acid caves are widespread worldwide. In Central Italy, the Fiume-Vento karstic complex represents the most important active hypogenic cave system hosting several interconnected lakes where ...groundwater moves towards sulfidic springs emerging along the Sentino Stream. Stratification and dilution phenomena between freshwater and sulfidic water occur in many underground lakes, even if they remain still open if these processes are driven by stream-aquifer interaction or dripping water. The speleological knowledge coupled with geochemical surveys can help study groundwater circulation in the karst system’s inner and outer portions. The geochemical analyses on water samples taken along the Sentino Stream, inside the caves (dripping and lakes water) and in sulfidic springs allow establishing the origin of the dilution water in the dripping water. However, stream-aquifer interactions cannot be excluded during flood events. Using the tracer masse balance method (chloride and sodium ions), the discharge of the sulfidic springs ranges between 65 and 11 L/s. The results presented in this study may help understand groundwater circulation and dilution phenomena in other karst systems characterised by sulfuric acid speleogenesis type.
Chemical weathering is the main natural mechanism limiting the atmospheric carbon dioxide levels on geologic time scales (>1 Ma) but its role on shorter time scales is still debated, highlighting the ...need for an increase of knowledge about the relationships between chemical weathering and atmospheric CO2 consumption. A reliable approach to study the weathering reactions is the quantification of the mass fluxes in and out of mono lithology watershed systems. In this work the chemical weathering and atmospheric carbon dioxide consumption of ultramafic rocks have been studied through a detailed geochemical mass balance of three watershed systems located in the metaophiolitic complex of the Voltri Massif (Italy). Results show that the rates of carbon dioxide consumption of the study area (weighted average = 3.02 ± 1.67 × 105 mol km−2 y−1) are higher than the world average CO2 consumption rate and are well correlated with runoff, probably the stronger weathering controlling factor. Computed values are very close to the global average of basic and ultrabasic magmatic rocks, suggesting that Voltri Massif is a good proxy for the study of the feedbacks between chemical weathering, CO2 consumption, and climate change at a global scale.
Early Pleistocene marine deposits in southwestern Umbria (Orvieto–Allerona area, Italy) recently revealed the presence of more than forty carbonate conduits distributed over 2 km along the Paglia ...riverbed. In order to investigate their origins, analyses of their mineralogy, δ18O and δ13C stable isotopes, and organic geochemistry were conducted. All the carbonate conduits are made of euhedral microcrystals of dolomite with subordinate quartz, plagioclases, and micas. The stable carbon and oxygen isotope values of the bulk concretionary carbonates range from −0.57 to +4.79‰ (δ13C) and from +1.58 to +4.07‰ (δ18O), respectively. The lack of organic geochemical biomarkers of anaerobic methane oxidation (AOM) and the very low values of extractable organic matter suggest a non-biological origin for the dolomite precipitation. The latter is probably related to the rise of volcanic carbon dioxide due to the incipient Vulsini magmatism recorded in Early Pleistocene marine deposits all around the study site. The spatial distribution of the structures indicates that the upward migration of the CO2 was controlled by the fault system, while the vertical development of the conduits suggests that carbon dioxide degassing occurred, with multiple events. Carbon dioxide was probably stored in pockets within the clayey sediments until the pressure exceeded the eruptive threshold. These structures represent the first documentation of a volcanic carbon dioxide marine seepage event in the Umbria region.
Lake Trasimeno is a shallow, endorheic lake located in central Italy. It is the fourth Italian largest lake and is one of the largest endorheic basins in western Europe. Because of its shallow depth ...and the absence of natural outflows, the lake, in historical times, alternated from periods of floods to strong decreases of the water level during periods of prolonged drought. Lake water is characterised by a NaCl composition and relatively high salinity. The geochemical and isotopic monitoring of lake water from 2006 to 2018 shows the presence of well-defined seasonal trends, strictly correlated to precipitation regime and evaporation. These trends are clearly highlighted by the isotopic composition of lake water (δ18O and δD) and by the variations of dissolved mobile species. In the long term, a progressive warming of lake water and a strong increase of total dissolved inorganic solids have been observed, indicating Lake Trasimeno as a paradigmatic example of how climate change can cause large variations of water quality and quantity. Furthermore, the rate of variation of lake water temperature is very close to the rate of variation of land-surface air temperature, LSAT, suggesting that shallow endorheic lakes can be used as a proxy for global warming measurements.
Water-rock interaction processes and trace elements distribution were studied in the Triassic dolomite aquifers of Sassolungo and Sella group (Dolomite mountains, northern Italy). These systems ...consist of almost pure dolomite and constitute an extremely favourable situation to study water-rock interactions and trace elements mobility in aquifers hosted by dolomite rocks. The chemical and isotopic composition of 26 springs was analysed together with mineralogical and geochemical data of the host rocks from the Sciliar Dolomite Fm. (Sassolungo) and the Dolomia Principale Fm. (Sella Group). Rock samples were found to be formed by almost ordered and stoichiometric dolomite (dolomite wt.% > 93) and minor phases, such as calcite, Mg-calcite and, to a smaller extent, albite and gypsum. The sampled waters are characterised by a Ca-Mg bicarbonate composition and aqueous speciation calculations, coupled with the analyses of isotopic data, reveal that congruent dissolution of dolomite is the main process governing the composition of groundwater. For most of the samples, dolomite dissolution occurs in an open system with PCO2 between 10-2 and 10-3 bar. The study of trace elements distribution shows that during dolomite dissolution alkaline metals, alkaline earth elements larger than Ca and some transition metals are relatively enriched in the solutions while the solutions result to be depleted in Fe, Al, Y and REE.
In the present work we summarize the first achievements of the RockStar Group of the Department of Physics and Geology (at the University of Perugia, Italy), which is made of a strict collaboration ...between Physicists and Geologists on astrophysical and planetological studies. The RockStar Group acts on two research lines: (i) astrophysical modeling and (ii) mineralogical and geochemical studies of meteorites. In the first part of the article we review the recent results concerning the development of theoretical modeling of nucleosynthesis and mixing process in asymptotic giant branch. In the second part we report (1) the catalog of the Meteorite collection of University of Perugia and (2) major and trace elements mapping, performed through EPMA and LA-ICP-MS, of the Mineo pallasite, a unique sample hosted by the collection. The new data constrain the Mineo meteorite among the Main Group Pallasites and support the hypothesis of the “early giant impact” formation.
In central Italy Mesozoic carbonates represent the principal reservoir of freshwater of the region. The hydrogeological setting is linked to the geological evolution of the Apennine chain and is ...generally characterised by a lower aquifer and one or more shallower aquifers separated by thin aquicludes. In these systems, groundwater composition is the result of a complex array of regional and local geochemical processes. The main geochemical processes are the dissolution of calcite, the influx of deeply derived CO
2 related to a regional process of mantle degassing, dedolomitization and mixing with deep saline fluids. The occurrence of saline fluids, characterised by a Na–Cl(HCO
3) composition, is related to the presence of a deep regional aquifer at the base of Mesozoic carbonates. The extremely high
pCO
2 values computed for the saline waters suggest that the deep aquifer is also a structural trap for the mantle derived CO
2 during its ascent towards the surface. In central Italy, geological and geophysical data highlight the presence of two different crustal sectors: the eastern sector, where the geometry of the Apennine thrust belt is still preserved, and the western sector, where the compressive structures are dislocated by important extensional deformations. In the western sector, the normal faults disrupting the compressive structures allow the mixing of the deep Na–Cl(HCO
3) fluids with the shallow groundwater causing a salinity increase and the natural deterioration of groundwater quality.
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