Thermal fluids along the East Anatolian Fault Zone (EAFZ): Geochemical features and relationships with the tectonic setting

Abstract

A geochemical investigation has been carried out on the gas phase associated to thermal fluids discharged along three different segments of the East Anatolian Fault Zone (EAFZ, Turkey) running from Malatya to the Triple Junction area (Karlıova) where the East and North Anatolian Faults cross each other. CO 2 is always the major gaseous component in both bubbling and dissolved gases with variable amounts of nitrogen helium and CH 4. The isotopic ratios of helium range from 0.44 to 4.41Rac (values corrected for the atmospheric contamination) and cover a range spanning from crustal to magmatic-type values. The isotopic composition of carbon (CO 2) shows values in the range from −5.6 to −0.2‰ vs PDB for the bubbling gases in contrast with the positive values (from 0.3 to 3.4‰ vs PDB) detected for the Total Dissolved Inorganic Carbon (TDIC). Coupling the information from the isotopic and chemical compositions, it results that mantle-derived fluids are driven to the surface by lithospheric structures. Despite the absence of outcropping volcanic products, the tectonic setting of the different segments plays a major role in releasing mantle-type fluids. The mantle derived fluids interact at shallower levels with circulating waters and originate geothermal systems which equilibration temperatures are estimated to be up to 360°C. The collected thermal fluids show different geochemical features consistent with processes occurring at two different levels: a deep level where mantle-originated fluids are taken either from the upper mantle or from intruded magma batches, and a shallower level, in the upper crust, where Gas Water Interactions (GWI), secondary CO 2 production, and fractionation processes induced chemical and isotopic modifications of the pristine gas composition.

Geochemistry of dissolved gases from the Eastern Carpathians - Transylvanian Basin boundary

“…The chemical composition of the dissolved gases was calculated taking into account the solubility coefficients (Bunsen coefficients "") of each gas species, the volume of the gas extracted (in cm 3 ) and the volume of the extracted water sample (in cm 3 ) as described by Italiano et al (2009Italiano et al ( , 2013. The gas-chromatographic analyses (see (Mamyrin and Tolstikhin, 1984).…”

“…The dissolved gases were extracted after equilibrium was reached at constant temperature with a host-gas (high-purity argon) injected in the sample bottle (further details found in Italiano et al 2009Italiano et al , 2013. Chemical analyses were carried out by gaschromatography (Perkin Elmer Clarus 500, equipped with a double TCD-FID detector) using argon as the carrier gas.…”

Isotope and chemical compositions of thermal fluids at Tekman Geothermal Area (Eastern Turkey)

“…All of the gas samples were collected taking care to avoid even tiny bubbles to prevent atmospheric contamination (details in Italiano et al, 2009Italiano et al, , 2013. The dissolved gases were obtained from water samples stored into 240 ml glass bottles and sealed in the field by rubber septa using special pliers.…”

Travertine occurrences along major strike-slip fault zones: structural, depositional and geochemical constraints from the Eastern Anatolian Fault System (EAFS), Turkey

“…Gas and fluid discharge and accompanying travertine precipitation in some places along the EAFS were reported from a few localities (e.g. Bağın, Golan and Hacılar) in recent studies (Italiano, Sasmaz, Yuce, Okan, 2013;Italiano et al, 2013;Öztekin Okan & Çetindağ, 2005). Where travertine precipitation occurred at Hacılar, Elmalı and Baltaşı localities along the KBS and the BYS to the northeastern part of the EAFS, intensely fractured recrystallised limestones and marbles of the Bitlis Massif, that are resulted from left-lateral strike-slip movement, form ideal rock units for hydrothermal circulation (Figure 16).…”