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| Titel |
Model for origin and evolution of water at volcanoes in São Miguel, Azores (Portugal), based on geochemical and isotopic data set |
| VerfasserIn |
Julia Woitischek, Martin Dietzel, J. Virgílio Cruz, Salvatore Inguaggiato, Albrecht Leis, Michael E. Böttcher |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122672
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| Publikation (Nr.) |
 EGU/EGU2016-1766.pdf |
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| Zusammenfassung |
| A conceptual model is presented to better constrain the origin and evolution
of discharges at Sete Cidades, Fogo and Furnas Volcano, using geochemical
and isotopic analyses of rock and water as well as recalculated gas
composition. The evolution of thermal water clearly reveals that
Na-HCO$_{3}$ and Na-SO$_{4}$ type of springs have their origin in meteoric
water as isotope data are close to the local meteoric water line ($\delta
^{18}$O$_{H2O}$ =-3 $\pm $ 1 \permil\ V-SMOW; $\delta
$D$_{H2O}$= -13 $\pm $ 7 \permil\ V-SMOW) with exception of a
Na-Cl spring named Ferraria, Sete Cidades area ($\delta ^{18}$O$_{H2O}$ =
0.45 \permil\ V-SMOW ; $\delta $D$_{H2O}$= 4.18
\permil\ V-SMOW). Analysed solutions are chemical evolved by
evaporation, uptake of volcanic gas, leaching of local basaltic rocks,
precipitation of solids, partly admixture of sea water and/or biological
activity. Following the individual concentrations supports this model e.g.:
HCO$_{3}$ concentration and the recalculated isotopic composition of gaseous
CO$_{2}$ ($\delta ^{13}$C$_{CO$_2$}$ = -4 $\pm $ 2.5 \permil\
V-PDB) reflect evolved magmatic CO$_{2}$ uptake and the subsequent leaching
progress; High SO$_{4}^{2-}$ concentration of up to 16.5 mmol L$^{-1}$
with $\delta ^{34}$S$_{SO4}$ = 0.35 $\pm $ 0.3 \permil\
(V-CDT) reflects magmatic origin which mainly control water chemistry of
boiling pools of both Fogo and Furnas lake; $\delta ^{18}$O$_{SO4}$ = 10.5
\permil\ (V-SMOW) suggests organic origin and fits together with
the observation of stromatolitic structures in the related precipitates;
Molar Mg/Ca$^{ }$ratio ($\approx $ 0.77) of all thermal discharges reflects
leaching of analysed local basalt (Mg/Ca$^{ }\approx $ 0.78). Furthermore,
shallow and evolved outgassing effects can be distinguished. Equilibrium
temperatures for various minerals given in SI vs. T plots and further
geothermometers (e.g. Na-K, Na-K-Ca geothermometers) were discussed to
estimate temperatures of reservoirs. |
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