Publication Date:
2023-02-28
Description:
The carbon isotopic composition of dissolved C-bearing species is a powerful tool to discriminate the origin of carbon
in thermal waters from volcanic and hydrothermal systems. However, the δ13C values of dissolved CO2 and
TDIC (Total Dissolved Inorganic Carbon) are often different with respect to the isotopic signature that characterizes
the potential carbon primary sources, i.e. deep hydrothermal reservoirs, magmatic gases and organic activity.
The most commonly invoked explanation for such isotopic values is related to mixing processes between deep
and shallow end-members. Nevertheless, experimental and empirical investigations demonstrated that isotopic
fractionation due to secondary processes acting on the uprising fluids from the hydrothermal reservoirs is able to
reproduce the measured isotopic values. In this paper,we investigated the chemistry of thermalwaters, collected
at Campi Flegrei and Vulcano Island (southern Italy),whose origin is related to interaction processesamongmagmatic
gases, meteoric water, seawater and hosting rocks. A special focus was dedicated to the δ13C values of dissolved
CO2 (δ13CCO2(aq)) and total dissolved inorganic carbon (δ13CTDIC). The δ13CCO2(aq) and δ13CTDIC values in the
water samples fromboth these systems ranged from(i) those measured in fumarolic gases, likely directly related
to the deep hydrothermal-magmatic reservoir, and (ii) those typically characterizing biogenic CO2, i.e. produced
by microbially-driven degradation of organic matter. A simple mixingmodel of the two end-members, apparently
explaining these intermediate carbon isotopic values, contrastswith the chemical composition of the dissolved
gases. On the contrary, isotopic fractionation due to secondary processes, such as calcite precipitation, affecting
hydrothermal fluids during their underground circulation, seems to exhaustively justify both the chemical and
isotopic data. If not recognized, these processes, which frequently occur in volcanic and hydrothermal systems,
may lead to an erroneous interpretation of the carbon source, causing an underestimation of the contribution
of the hydrothermal/magmatic fluids to the dissolved carbon species. These results pose extreme caution in
the interpretation of intermediate δ13CCO2(aq) and δ13CTDIC values for the assessment of the carbon budget of hydrothermal-
volcanic systems.
Description:
Published
Description:
46–57
Description:
2V. Struttura e sistema di alimentazione dei vulcani
Description:
4V. Dinamica dei processi pre-eruttivi
Description:
JCR Journal
Keywords:
Thermal waters
;
Carbon isotopes
;
Dissolved CO2
;
TDIC
;
Volcanic-hydrothermal systems
;
Secondary fractionation processes
;
04.08. Volcanology
;
03.02. Hydrology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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