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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