Geochemical evidence of seawater intrusion into a coastal geothermal field of central Greece: example of the Thermopylae system |
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| Authors: | A Duriez C Marlin E Dotsika M Massault A Noret J L Morel |
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| Institution: | (1) Laboratoire Interactions et Dynamique des Environnements de Surface, UMR IDES 8148, CNRS-Université Paris-Sud 11, Bat 504, Orsay, France;(2) Equipe Dynamique des systèmes faillés, Université Paris-Sud 11, UMR 7072 Tectonique, Université Pierre et Marie Curie, Paris, France;(3) Laboratory of Archeometrie, Institute of Material science, Demokritos, 15310 Aghia Paraskevi (Athens), Greece |
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| Abstract: | Thermal water of Thermopylae and from other geothermal fields located in the southern part of the Sperchios basin (central
Greece) are characterized by high salinity (total dissolved salts, or TDS, range from 1.2 to 30.3 g L−1) associated with a degassing of CO2. To determine the mineralization processes, geochemical and isotopic investigations (major elements, 18O, 2H and 13C) have been carried out upon 17 thermal waters from springs and boreholes. This study emphasizes that all the thermal waters
result from the mixing of a seawater end-member, several fresh water components depending on the field location, and a mantle-derived
CO2 rising upward through an E–W fault system. The seawater identified in the thermal mixture is likely to be evolved Aegean
seawater (ASW). Once intruded into the basin sediments, the trapped seawater has its chemical content modified by both water–rock
interactions and massive dissolution of the deep CO2 (pCO2 of 100.5 atm). The modelling performed with PHREEQC indicates that the anomalous major ion ratios measured in the so-called evolved
ASW are explained by the dissolution of calcite and dolomitization process associated to precipitation of gypsum within the
thermal aquifer. |
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| Keywords: | Geochemistry PHREEQC Sea-water intrusion Thermal water Greece |
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