Publication Date:
2020-11-26
Description:
The volcano–hydrothermal system of El Chichón volcano, Chiapas, Mexico, is characterized by numerous
thermal manifestations including an acid lake, steam vents and boiling springs in the crater and acid and
neutral hot springs and steaming ground on the flanks. Previous research on major element chemistry reveals
that thermal waters of El Chichón can be divided in two groups: (1) neutral waters discharging in the crater
and southern slopes of the volcano with chloride content ranging from 1500 to 2200 mg/l and (2) acid-toneutral
waters with Cl up to 12,000 mg/l discharging at the western slopes. Our work supports the concept
that each group of waters is derived from a separate aquifer (Aq. 1 and Aq. 2). In this study we apply Sr
isotopes, Ca/Sr ratios and REE abundances along with the major and trace element water chemistry in order to
discriminate and characterize these two aquifers. Waters derived from Aq. 1 are characterized by 87Sr/86Sr
ratios ranging from 0.70407 to 0.70419, while Sr concentrations range from 0.1 to 4 mg/l and Ca/Sr weight
ratios from 90 to 180, close to average values for the erupted rocks. Waters derived from Aq. 2 have 87Sr/86Sr
between 0.70531 and 0.70542, high Sr concentrations up to 80 mg/l, and Ca/Sr ratio of 17–28. Aquifer 1 is
most probably shallow, composed of volcanic rocks and situated beneath the crater, within the volcano
edifice. Aquifer 2 may be situated at greater depth in sedimentary rocks and by some way connected to the
regional oil-gas field brines. The relative water output (l/s) from both aquifers can be estimated as Aq. 1/Aq. 2–
30. Both aquifers are not distinguishable by their REE patterns. The total concentration of REE, however,
strongly depends on the acidity. All neutral waters including high-salinity waters from Aq. 2 have very low
total REE concentrations (b0.6 μg/l) and are characterized by a depletion in LREE relative to El Chichón
volcanic rock, while acid waters from the crater lake (Aq. 1) and acid AS springs (Aq. 2) have parallel profile
with total REE concentration from 9 to 98 μg/l. The highest REE concentration (207 μg/l) is observed in slightly
acid shallow cold Ca-SO4 ground waters draining fresh and old pyroclastic deposits rich in magmatic
anhydrite. It is suggested that the main mechanism controlling the concentration of REE in waters of El
Chichón is the acidity. As low pH results from the shallow oxidation of H2S contained in hydrothermal vapors,
REE distribution in thermal waters reflects the dissolution of volcanic rocks close to the surface or lake
sediments as is the case for the crater lake.
Description:
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Description:
Published
Description:
55-66
Description:
1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
Description:
JCR Journal
Description:
reserved
Keywords:
hydrogeochemistry
;
geothermal systems
;
Sr isotopes
;
REE
;
El Chichón Volcano
;
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::03.04.05. Gases
;
03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems
;
04. Solid Earth::04.08. Volcanology::04.08.01. Gases
;
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
;
04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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