Publication Date:
2021-12-01
Description:
Here we discussed the results of the first geochemical investigation of the fluids (groundwater and the associated
gases) emerging in the southwest of Yazd Province. We carried out two surveys, one in July 2019 and the second
in September 2019s, in the region of the Gariz aquifer (central Iran).Wefocused our attention to 1) the chemistry
of thewater (major and minor constituents coupled to the stable isotopes of oxygen and hydrogen), 2) the chemical
composition of dissolved gases in water together with 3) the isotopic composition of Helium (3He/4He)
and 4) the dissolved carbon in water (δ13CTDIC). Hydrogen and oxygen isotope values of groundwater display a
fairly narrow range and indicate that the waters are of meteoric origin. On the base of the major ions chemistry,
the bulk of the water samples are classified as Ca-HCO3, Ca\\Cl and Na\\Cl types. The groundwater chemistry is
mainly influenced by the interaction with CO2-rich fluids, leakage of chlorinated saline water into the alluvial
aquifer, and silicate dissolution. High dissolved carbon contents, mainly as bicarbonate ion, reflect the noticeable
interaction of the groundwater with CO2-rich fluids. CO2 is the dominant gaseous component in most samples
and its amount is always greater with respect to a water in equilibrium with the atmosphere (Air Saturated
Water, ASW). Such excess of CO2 contents (more than 730 cc/l STP) dissolved in groundwater also supports
the presence of a deep source of CO2-rich gas. The computed δ13C(CO2) in equilibriumwith the groundwater highlight
a mixing in different proportion between an inorganic deep sourced CO2 (13C-enriched) and organic CO2
(13C-depleted). We also used the helium isotopes as a tools to figure out the origin of helium in the aquifer
(air vs. mantle, and crust). The collected samples show a contribution of mantle-derived He in the Gariz aquifer
up to (~45%) and the crust suggesting that at regional scale the tectonic discontinuities had a connectionwith the
mantle or magmatic intrusions migrated through the crust transporting mantle volatiles to shallowcrustal layers.
However, we cannot infer the timing of this possible magmatism at depth in the complex tectonic evolution of
the area.
Description:
Ministry of Science, Research and Technology of Iran
Description:
Published
Description:
107324
Description:
1TR. Georisorse
Description:
JCR Journal
Keywords:
Zagros groundwater
;
Dissolved gases
;
δ13C of TDIC
;
Mantle-derived He
;
Collision zone
;
03.02. Hydrology
;
03. Hydrosphere
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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