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  • 1
    Electronic Resource
    Electronic Resource
    Elemental and isotopic geochemistry in the hydrothermal area of Chaves, Vila Pouca de Aguiar (northern Portugal) (1995)
    Springer
    Environmental geology 25 (1995), S. 232-238 
    Details
    ISSN: 1432-0495
    Keywords: Chaves ; Thermal waters ; Isotope geochemistry ; Recharge area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Chaves thermal waters (76°C) are the most important external manifestations of low-temperature geothermal systems occurring in Portuguese mainland. They are related to crystalline granitic rocks. This paper describes the use of the environmental isotopic composition (oxygen-18, deuterium, and tritium) of hot and cold waters of the Chaves area as an important hydrogeological tool to solve specific problems arising in the appraisal of the geothermal resources of the area (e.g., origin and “age” of waters, recharge area, and underground flow paths).18O and D analyses seem to confirm the meteoric origin of Chaves thermal waters. The local altitude dependence of meteoric waters was determined by18O and D analyses of superficial and shallow groundwaters of the Chaves plain and its bordering mountains. Chaves thermal waters seem to be related to meteoric waters, infiltrated on the highest topography areas (Bolideira granitic outcrop NE Chaves), that percolate at great depth and emerge in a discharge area at lower altitude (Chaves plain). Chaves thermal waters showing little oxygen-18 shift and low tritium concentrations could be considered external manifestations of an old geothermal system in which the isotopic water-rock interaction is adjusted to equilibrium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00766751
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  • 2
    Electronic Resource
    Electronic Resource
    Method for quasiclassical trajectory calculations on potential energy surfaces defined from gradients and Hessians, and model to constrain the energy in vibrational modes (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1908-1920 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for calculating quasiclassical trajectories on potential energy surfaces defined using a sequence of model quadratic surfaces (QCT/GH) is suggested, and tested for atom–diatom collisions against the traditional quasiclassical trajectory approach. A simple model is also suggested to constrain the classical energy of a bound vibrational mode to be greater than a specified amount, namely, its zero-point energy value. Essentially the model consists of assuming that the sum of the energies in the nonrelevant vibrational modes (typically unbound modes) of the supermolecular complex acts as a pool from which energy may be taken to compensate any leak of vibrational energy in the relevant bound modes, hence preventing the latter from falling below zero-point value. Extensive QCT/GH trajectory calculations carried out for the H+H2 exchange reaction, which occurs over an energy barrier, as well as exploratory trajectories for the reaction O+OH→O2+H, which occurs on a potential energy surface with a deep chemical well, have shown that the total energy and total angular momentum are conserved within a small numerical tolerance. Correcting for the leak of zero-point vibrational energy still leaves the total energy rigorously conserved but the total angular momentum is then only approximately kept constant. For H+H2(v=0, j=0)→H2(v', j')+H, the calculated state-to-state QCT/GH cross sections show reasonably good agreement with those of converged quantum results reported in the literature for the same H3 potential energy surface. This agreement does not deteriorate after correction of zero-point energy leak. For both H3 and HO2, accurate global analytical potential energy surfaces based on the double many-body expansion method have been utilized. Using these prototype systems, an assessment is made of the difficulties encountered on direct reaction dynamics using the novel QCT/GH method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466544
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  • 3
    Electronic Resource
    Electronic Resource
    A detailed state-to-state low-energy dynamics study of the reaction O(3P)+OH(2Π)→O2(X˜ 3Σg−)+H(2S) using a quasiclassical trajectory–internal-energy quantum-mechanical-threshold method (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4050-4065 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The quasiclassical trajectory (QCT) method has been used for a detailed study of the state-to-state dynamics of the reaction O(3P) + OH(2Π)→O2(Xˆ33Σ−g) + H(2S) over the range of translational energies 0.125 ≤ Etr/kcal mol−1≤2.0, corresponding to the temperature range 40≤T/K≤680. A novel variant of this method insuring that trajectory calculations properly account for the zero-point energy of the diatomic molecules, the so-called quasiclassical trajectory–internal-energy quantum-mechanical-threshold method, is also suggested and applied to the title reaction. The most recent and accurate double many-body expansion potential-energy surface for the ground doublet state of the hydroperoxyl radical has been employed in all calculations. The computed reactive cross sections for initial quantum rotational states of OH varying from J=0 to J=10 (the vibrational quantum number is kept fixed at v=0) are shown to have a marked decreasing dependence on translational energy, thus suggesting that long-range forces play a major role on the dynamics of the O(3P) + OH(2Π) reaction. A comparison of the thermalized rate coefficients with the results of direct experimental measurements is shown to agree best with the data of Howard and Smith over the whole range of temperatures covered by experiment. It is also shown that nonstatistical recrossing effects are important for all translational energies and rotational states, while a nearly linear dependence is shown over the range of translational energies that have been studied. Finally, appropriate averaging over the initial conditions shows that the dependence on temperature of the calculated recrossing factor is in good agreement with the corresponding estimate from recent direct thermalized QCT calculations using the same potential-energy surface while fitting well by a recently proposed model for this recrossing factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463934
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  • 4
    Electronic Resource
    Electronic Resource
    Letters to the editor (1984)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 20 (1984), S. 1169-1174 
    Details
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/nme.1620200616
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  • 5
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    Methane in serpentinized ultramafic rocks in mainland Portugal (2015)
    Elsevier Science
    Details
    Publication Date: 2020-12-09
    Description: We report a new case of methane (CH4) of apparent abiotic origin in continental serpentinized ultramafic rocks. Multiple analytical techniques, on-site and in the laboratory, revealed methane and ethane degassing from hyperalkaline (pH 〉 11) Ca2þ eOH mineral waters in boreholes drilled in the Alter-do- Chão igneous intrusion, at Cabeço de Vide, in mainland Portugal. The C and H isotopic composition of CH4 (d13C w 20&; d2H: 283&) suggests a dominant abiotic origin, although minor thermogenic contributions cannot be excluded. Similarly, low methane-to-ethane ratios suggest a predominantly nonmicrobial source, consistent with previous microbiological data showing the lack of methanogenic archaea in these waters. Heavier hydrocarbons, CO2 and H2 are below detection limits. This case study confirms that CH4 from serpentinized ultramafic rocks can be transported by hyperalkaline fluids linked to deep circulation of meteoric waters. Maximum depth of Cabeço de Vide serpentinized rocks is less than 1 km, and present temperatures are likely lower than 50 C. Serpentinization and related gas formation may have occurred at any time during thermal evolution of the igneous intrusion, so gas formation temperature cannot be easily determined. This case is an opportunity to test thermometry provided by CH4 isotopologue analyses. The existence of methane in continental serpentinized igneous rocks is more widespread than previously thought and petroleum systems with similar serpentinized ultramafics in reservoir rocks may have traces of the observed 13C-enriched CH4
    Description: Published
    Description: 12-16
    Description: 7A. Geofisica di esplorazione
    Description: JCR Journal
    Description: restricted
    Keywords: Abiotic methane, serpentinization ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    The relative abundances of resolved l2 CH 2 D 2 and 13 CH 3 D and mechanisms controlling isotopic bond ordering in abiotic and biotic methane gases (2018)
    Details
    Publication Date: 2021-06-21
    Description: We report measurements of resolved 12CH2D2 and 13CH3D at natural abundances in a variety of methane gases produced naturally and in the laboratory. The ability to resolve 12CH2D2 from 13CH3D provides unprecedented insights into the origin and evolution of CH4. The results identify conditions under which either isotopic bond order disequilibrium or equilibrium are expected. Where equilibrium obtains, concordant D12CH2D2 and D13CH3D temperatures can be used reliably for thermometry. We find that concordant temperatures do not always match previous hypotheses based on indirect estimates of temperature of formation nor temperatures derived from CH4/H2 D/H exchange, underscoring the importance of reliable thermometry based on the CH4 molecules themselves. Where D12CH2D2 and D13CH3D values are inconsistent with thermodynamic equilibrium, temperatures of formation derived from these species are spurious. In such situations, while formation temperatures are unavailable, disequilibrium isotopologue ratios nonetheless provide novel information about the formation mechanism of the gas and the presence or absence of multiple sources or sinks. In particular, disequilibrium isotopologue ratios may provide the means for differentiating between methane produced by abiotic synthesis vs. biological processes. Deficits in 12CH2D2 compared with equilibrium values in CH4 gas made by surface-catalyzed abiotic reactions are so large as to point towards a quantum tunneling origin. Tunneling also accounts for the more moderate depletions in 13CH3D that accompany the low 12CH2D2 abundances produced by abiotic reactions. The tunneling signature may prove to be an important tracer of abiotic methane formation, especially where it is preserved by dissolution of gas in cool hydrothermal systems (e.g., Mars). Isotopologue signatures of abiotic methane production can be erased by infiltration of microbial communities, and D12CH2D2 values are a key tracer of microbial recycling.
    Description: Published
    Description: 235-264
    Description: 6A. Geochimica per l'ambiente
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Abiotic methane seepage in the Ronda peridotite massif, southern Spain (2018)
    Details
    Publication Date: 2020-11-25
    Description: Abiotic methane in serpentinized peridotites (MSP) has implications for energy resource exploration, planetary geology, subsurface microbiology and astrobiology. Once considered a rare occurrence on Earth, reports of MSP are increasing for numerous localities worldwide in low temperature, land-based springs and seeps. We report the discovery of six methane-rich water springs and two ponds with active gas bubbling in the Ronda peridotite massif, in southern Spain. Water is hyperalkaline with typical hydrochemical features of active serpentinization (pH: 10.7 to 11.7, T: 17.1 to 21.5 C, CaeOH facies). Dissolved CH4 concentrations range from 0.1 to 3.2 mg/L. The methane stable C and H isotope ratios in the natural spring and bubbling sites (d13CCH4: 12.3 to 37‰ VPDB; d2HCH4: 280 to 333‰ VSMOW) indicate a predominant abiotic origin. In contrast, springs with manmade water systems, i.e., pipes or fountains, appear to have mixed biotic-abiotic origin (d13CCH4: 44 to 69‰; d2HCH4: 180 to 319‰). Radiocarbon (14C) analyses show that methane C in a natural spring is older than ca. 50,000 y BP, whereas dissolved inorganic carbon (DIC) analysed in all springs has an apparent 14C age ranging from modern to 2334 y BP. Therefore most, if not all, of the CH4 is allochthonous, i.e., not generated from the carbon in the hyperalkaline water. Methane is also released as bubbles in natural ponds and as diffuse seepages (~101e102 mg CH4 m 2d 1) from the ground up to several tens of metres from the seeps and springs, albeit with no overt visual evidence. These data suggest that the gas follows independent migration pathways, potentially along faults or fracture systems, physically isolated from the hyperalkaline springs. Methane does not seem to be genetically related to the hyperalkaline water, which may only act as a carrier of the gas. Gas-bearing springs, vents and invisible microseepage in land-based peridotites are more common than previously thought. In addition to other geological sources, MSP is potentially a natural source of methane for the troposphere and requires more worldwide flux measurements.
    Description: Published
    Description: 101-113
    Description: 6A. Geochimica per l'ambiente
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Mantle-derived carbon in Hercynian granites. Stable isotopes signatures and C/He associations in the thermomineral waters, N-Portugal (2010)
    Elsevier
    Details
    Publication Date: 2021-01-27
    Description: Na–HCO3–CO2-rich thermomineral waters issue in the N of Portugal, within the Galicia-Trás-os-Montes region, linked to a major NNE-trending fault, the so-called Penacova-Régua-Verin megalineament. Along this tectonic structure different occurrences of CO2-rich thermomineral waters are found: Chaves hot waters (67 °C) and also several cold (16.1 °C) CO2-rich waters. The δ2H and δ18O values of the thermomineral waters are similar to those of the local meteoric waters. The chemical composition of both hot and cold mineral waters suggests that water–rock reactions are mainly controlled by the amount of dissolved CO2 (g) rather than by the water temperature. Stable carbon isotope data indicate an external CO2 inorganic origin for the gas. δ13CCO2 values ranging between −7.2‰ and −5.1‰ are consistent with a two-component mixture between crustal and mantle-derived CO2. Such an assumption is supported by the 3He/4He ratios measured in the gas phase, are between 0.89 and 2.68 times the atmospheric ratio (Ra). These ratios which are higher than that those expected for a pure crustal origin (≈0.02 Ra), indicating that 10 to 30% of the He has originated from the upper mantle. Release of deep-seated fluids having a mantle-derived component in a region without recent volcanic activity indicates that extensive neo-tectonic structures originating during the Alpine Orogeny are still active (i.e., the Chaves Depression).
    Description: Published
    Description: 49-56
    Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi
    Description: JCR Journal
    Description: reserved
    Keywords: CO2-rich thermomineral waters ; mantle volatiles ; isotopes ; Chaves geothermal system ; N-Portugal ; 03. Hydrosphere::03.02. Hydrology::03.02.02. Hydrological processes: interaction, transport, dynamics ; 03. Hydrosphere::03.02. Hydrology::03.02.03. Groundwater processes ; 03. Hydrosphere::03.04. Chemical and biological::03.04.03. Chemistry of waters ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
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    Mantle-derived carbon in Hercynian granites. 1 Stable isotopes signatures 2 and C/He associations in the thermomineral waters, N-Portugal (2010)
    Elsevier
    Details
    Publication Date: 2017-04-04
    Description: Na–HCO3–CO2-rich thermomineral waters issue in the N of Portugal, within the Galicia-Trás-os-Montes region, linked to a major NNE-trending fault, the so-called Penacova-Régua-Verin megalineament. Along this tectonic structure different occurrences of CO2-rich thermomineral waters are found: Chaves hot waters (67 °C) and also several cold (16.1 °C) CO2-rich waters. The δ2H and δ18O values of the thermomineral waters are similar to those of the local meteoric waters. The chemical composition of both hot and cold mineral waters suggests that water–rock reactions are mainly controlled by the amount of dissolved CO2 (g) rather than by the water temperature. Stable carbon isotope data indicate an external CO2 inorganic origin for the gas. δ13CCO2 values ranging between −7.2‰ and −5.1‰ are consistent with a two-component mixture between crustal and mantle-derived CO2. Such an assumption is supported by the 3He/4He ratios measured in the gas phase, are between 0.89 and 2.68 times the atmospheric ratio (Ra). These ratios which are higher than that those expected for a pure crustal origin (≈0.02 Ra), indicating that 10 to 30% of the He has originated from the upper mantle. Release of deep-seated fluids having a mantle-derived component in a region without recent volcanic activity indicates that extensive neo-tectonic structures originating during the Alpine Orogeny are still active (i.e., the Chaves Depression).
    Description: In press
    Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi
    Description: JCR Journal
    Description: open
    Keywords: CO2-rich thermomineral waters ; mantle volatiles ; isotopes ; Chaves geothermal 9 system ; 03. Hydrosphere::03.02. Hydrology::03.02.02. Hydrological processes: interaction, transport, dynamics ; 03. Hydrosphere::03.02. Hydrology::03.02.03. Groundwater processes ; 03. Hydrosphere::03.04. Chemical and biological::03.04.03. Chemistry of waters ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
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    Nitrogen isotopes determination in natural gas: analytical method and first results on magmatic, hydrothermal and soil gas samples (2010)
    Taylor & Francis
    Details
    Publication Date: 2022-06-08
    Description: A continuous-flow GC/IRMS technique has been developed to analyse δ15N values for molecular nitrogen in gas samples. This method provides reliable results with accuracy better than 0.15‰and reproducibility (1σ) within ±0.1‰ for volumes of N2 between 1.35 (about 56 nmol) and 48.9μL (about 2μmol). The method was tested on magmatic and hydrothermal gases as well as on natural gas samples collected from various sites. Since the analysis of nitrogen isotope composition may be prone to atmospheric contamination mainly in samples with low N2 concentration, we set the instrument to determine also N2 and 36Ar contents in a single run. In fact, based on the simultaneously determined N2/36Ar ratios and assuming that 36Ar content in crustal and mantle-derived fluids is negligible with respect to 36Ar concentration in the atmosphere, for each sample, the degree of atmospheric contamination can be accurately evaluated. Therefore, the measured δ15N values can be properly corrected for air contamination.
    Description: Published
    Description: 141–155
    Description: 2.4. TTC - Laboratori di geochimica dei fluidi
    Description: JCR Journal
    Description: reserved
    Keywords: Argon-36 ; isotope measurement and technique ; nitrogen-15 ; volcanic and hydrothermal gas ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.06. Subduction related processes ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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