Fluid geochemistry of the Methana Peninsula and Loutraki geothermal area, Greece.

A geochemical survey on the thermal fluids released by the volcanic/geothermal system of Methana Peninsula and Loutraki area was undertaken. The Loutraki area is found in the southern part of Athens and the Methana volcano in the north-eastern part of Peloponnesus, which is characterized by high salinity waters. Chemical and isotopic contents were used for the investigation of the origin of thermal water, for the estimation of the mixing process between meteoric, magmatic and sea water involved in the deep geothermal systems and for the evaluation of the deep aquifer temperature. The chemical and isotopic data of the thermal Cl-rich water springs of Methana suggest that they are fed by thermal water mixed with local groundwater and seawater respectively. The parent hydrothermal liquid is a mixture of local groundwater (~43%), seawater (~34%) and arc-type magmatic water (~23%). The chemical and isotopic data of the thermal HCO3-rich water springs of Loutraki samples indicate a purely meteoric origin. Assessments from chemical and isotopic geothermometer applied on the thermal waters springs suggest the probable existence of a deep geothermal reservoir of middle enthalpy (150 °C) a Methana and low enthalpy (80 °C) in Loutraki area. However, the contribution of marine solutions to the geothermal fluids of Methana and Loutraki area is one of the main cases for the disturbance of the chemical and isotopic geothermometers rendering these calculated temperatures questionable.