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| Titel |
Water and gas geochemistry of the Calatrava Volcanic Province (CVP) hydrothermal system (Ciudad Real, central Spain) |
| VerfasserIn |
Orlando Vaselli, Barbara Nisi, Franco Tassi, Luciano Giannini, Fidel Grandia, Tom Darrah, Francesco Capecchiacci, Pèrez del Villar |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082106
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| Zusammenfassung |
| An extensive geochemical and isotopic investigation was carried out in the water and gas discharges of the Late Miocene-Quaternary Calatrava Volcanic Province (CVP) (Ciudad Real, Spain) with the aim reconstruct the fluid circulation in the area. CVP consists of a series of scattered (monogenetic) vents from where alkaline lava flows and pyroclastic deposits formed in two different periods. The first stage (8.7-6.4 Ma) mainly included ultra-potassic mafic extrusives, whilst the second stage (4.7-1.75 Ma) prevalently originated alkaline and ultra-alkaline volcanics. Both stages were followed by a volcanic activity that extended up to 1.3 and 0.7 Ma, respectively.
This area can likely be regarded as one of the most important emitting zones of CO2 in the whole Peninsular Spain along with that of Selva-Emporda in northeastern Spain (Cataluña) and it can be assumed as one of the best examples of natural analogues of CO2 leakages in Spain. This latter aspect is further evidenced by the relatively common water-gas blast events that characterize the CCVF. In the last few years the presence of a CO2-pressurized reservoir at a relatively shallow level as indeed caused several small-sized explosion particularly during the drilling of domestic wells.
The fluid discharging sites are apparently aligned along well-defined directions: NW-SE and NNW-SSE and subordinately, ENE-WSW, indicating a clear relationship between the thermal discharges and the volcanic centers that also distribute along these lineaments.
The CVP waters are mostly hypothermal (up to 33 °C) and are generally Mg(Ca)-HCO3 in composition and occasionally show relatively high concentrations of Fe and Mn, with pH and electrical conductivity down to 5.5 and up to 6.5 mS/cm, respectively. The oxygen and hydrogen isotopes suggest a meteoric origin for these waters.
The mantle source of these volcanic products is apparently preserved in the many CO2-rich (up to 990,000 mmol/mol) gas discharges that characterize CVP, whose carbon and helium isotopic signature is characterized by values between -6.8 and -3.2 ‰ (V-PDB) and up to 2.7 R/Ra, respectively. Nitrogen and argon are atmospheric in origin and their contents are up to 11,850 and 313 mmol/mol, respectively, while H2S and CH4, despite occurring in the great majority of the CVP samples, have concentrations that rarely achieve 71 and 81 mmol/mol, respectively. It is worthwhile to mention that the N2/Ar ratios are occasionally characterized by values higher that those of the atmospheric and air saturated water and the respective 40Ar/36Ar values are higher than the atmospheric ratio (295.5), suggesting a deep source for these inert gases. |
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