Geochemical study of fluids on Lesbos island, Greece

Sixty-five water samples and seven associated gas samples have been collected on Lesbos island. The lithology and structural setting have resulted in two main types of hydrological circulation: a shallow circulation hosting low-salinity cold waters and a deeper one, hosting high-salinity hot waters...

Full description

Saved in:
Bibliographic Details
Published in:Geothermics 2004-10, Vol.33 (5), p.637-654
Main Authors: Bencini, Alberto, Duchi, Vittorio, Casatello, Antonio, Kolios, Nikolaos, Fytikas, Michalis, Sbaragli, Luca
Format: Article
Language:English
Subjects:
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Fluid geochemistry
Geothermics
Geothermometry
Greece
Lesbos
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Sixty-five water samples and seven associated gas samples have been collected on Lesbos island. The lithology and structural setting have resulted in two main types of hydrological circulation: a shallow circulation hosting low-salinity cold waters and a deeper one, hosting high-salinity hot waters that often emerge in thermal springs near the coast. The cold waters are characterized by Ca(Mg)-HCO 3(SO 4) composition, while the thermal waters generally have an Na-Cl composition. The chemical features of the former can be explained by their circulation in the ophiolite-bearing phyllitic basement and volcanic rocks. Waters circulating in the ultramafic layers of the basement are richer in Mg than the waters whose circulation is mainly within marble levels or volcanic rocks. The Na-Cl thermal waters are characterized by salinities ranging from 1910 to 35,700 mg/kg. As indicated by previous hydrogeochemical and isotopic studies, the Na-Cl composition of the thermal waters on Lesbos is the result of mixing between shallow meteoric waters and marine waters. While interacting with the minerals of the geothermal reservoir, the saline waters retain the Na/Cl sea water ratio but become enriched in Ca 2+ and depleted in Mg 2+ with respect to sea water. Processes of hydrothermal alteration at depth are activated by a gas phase enriched in CO 2, which reaches the geothermal reservoir by rising along the deep fractures of the basement. Thermodynamic calculations based on hydrothermal alteration processes occurring at the estimated temperatures of the geothermal reservoir (about 120 °C) indicate that the thermal waters of Lesbos are in equilibrium with talc and dolomite.
ISSN:0375-6505
1879-3576
DOI:10.1016/j.geothermics.2003.11.003