Publication Date:
2017-04-04
Description:
This study presents baseline data for future
geochemical monitoring of the active Tacaná volcano–
hydrothermal system (Mexico–Guatemala). Seven groups
of thermal springs, related to a NW/SE-oriented fault scarp
cutting the summit area (4,100m a.s.l.), discharge at the
northwest foot of the volcano (1,500–2,000m a.s.l.);
another one on the southern ends of Tacaná (La Calera).
The near-neutral (pH from 5.8 to 6.9) thermal (T from
25.7°C to 63.0°C) HCO3–SO4 waters are thought to have
formed by the absorption of a H2S/SO2–CO2-enriched
steam into a Cl-rich geothermal aquifer, afterwards mixed
by Na/HCO3-enriched meteoric waters originating from the
higher elevations of the volcano as stated by the isotopic
composition (δD and δ18O) of meteoric and spring waters.
Boiling temperature fumaroles (89°C at ~3,600m a.s.l. NW
of the summit), formed after the May 1986 phreatic
explosion, emit isotopically light vapour (δD and δ18O as
low as −128 and −19.9‰, respectively) resulting from
steam separation from the summit aquifer. Fumarolic as
well as bubbling gases at five springs are CO2-dominated.
The δ13CCO2 for all gases show typical magmatic values of
−3.6 ± 1.3‰ vs V-PDB. The large range in 3He/4He ratios
for bubbling, dissolved and fumarolic gases [from 1.3 to
6.9 atmospheric 3He/4He ratio (RA)] is ascribed to a
different degree of near-surface boiling processes inside a
heterogeneous aquifer at the contact between the volcanic
edifice and the crystalline basement (4He source). Tacaná
volcano offers a unique opportunity to give insight into
shallow hydrothermal and deep magmatic processes affecting
the CO2/3He ratio of gases: bubbling springs with lower
gas/water ratios show higher 3He/4He ratios and consequently
lower CO2/3He ratios (e.g. Zarco spring). Typical
Central American CO2/3He and 3He/4He ratios are found
for the fumarolic Agua Caliente and Zarco gases (3.1 ± 1.6
× 1010 and 6.0 ± 0.9 RA, respectively). The L/S (5.9 ± 0.5)
and (L + S)/M ratios (9.2 ± 0.7) for the same gases are
almost identical to the ones calculated for gases in El
Salvador, suggesting an enhanced slab contribution as far as
the northern extreme of the Central American Volcanic Arc,
Tacaná.
Description:
This study
was financially supported by DGAPA UNAM #IN101706 and INGVPalermo.
Description:
Published
Description:
319-335
Description:
1.3. TTC - Sorveglianza geodetica delle aree vulcaniche attive
Description:
JCR Journal
Description:
partially_open
Keywords:
Tacaná volcano
;
Fluid geochemistry
;
Volcano–hydrothermal system
;
Bubbling gases
;
Fumaroles
;
Isotopes
;
Volcanic surveillance
;
01. Atmosphere::01.01. Atmosphere::01.01.07. Volcanic effects
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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