Origin and geochemical evolution of groundwaters at the northeastern extend of the active Fethiye-Burdur fault zone within the ophiolitic Teke nappes, SW Turkey

Abstract

Thermal and nonthermal, mineral and non-mineral spring waters in different physical and chemical characters occur along the active Fethiye-Burdur fault zone (FBFZ) in the southwestern Turkey and discharge mainly within the supra-subduction-type ophiolitic units of the Teke nappes. This research aims to determine the physical and hydrogeochemical characteristics, origin, and geochemical evolution of the groundwaters discharging from the same lithology and tectonic zone within the northeastern extend of the active Fethiye-Burdur fault zone. A total of representative nine groundwater samples were collected from the study area. Of which, one of the samples is thermal, and others are nonthermal groundwaters. One of the nonthermal groundwaters is mineral water type, and the other one is hyperalkaline (pH > 10). Based on the analytical results, the waters in the study area are divided into six different groundwater facies: (i) Mg-Ca-HCO3-SO4, (ii) Mg-HCO3-CO3, (iii) Ca-HCO3, (iv) Ca-Mg-HCO3, (v) Mg-HCO3, and (vi) Ca-Na-Cl-CO3 facies. The chemical characteristics of the groundwaters are mainly related to mineralogic and hence chemical composition of sub-surface rocks, residence time of the groundwater, and water-rock intereactions, whether or not the conditions closed to CO2. Neutral to moderate alkaline (pH 10) Ca-Na-Cl-CO3-type waters within deeper ultramafic rock aquifers under the conditions closed to CO2. Mainly altered mafic-ultramafic silicates and carbonate rocks are the major sources of mineralization in the study area. On the other hand, H2S (most probably magmatic origin) reacted with carbonate rocks underlying the ophiolitic melange units produced CO2(g). Dissolution of CO2 within groundwaters is thought to cause arising of acidic conditions, higher degree dissolution of mafic-ultramafic silicates, and mineral water formation.