Turkish Journal of Earth Sciences

Hydrogeology of the Turgutlu Geothermal Field




The basement is formed from Menderes Massif rocks, which consist of schist, marbles, schist-marble-phyllite intercallations and dolomitic marbles from bottom to top. The ophiolitic rocks, which belong to the İzmir Anakara Zone, overlie the dolomitic marbles of Menderes Massif rocks wit a low angle thrust fault. The Neogene aged terrigenous sediments, which consist of conglomerate, sandstones, claystones, maris, and lacustrine limestone, cover all of the units discordantly. The Quaternary alluvium and travertine are the youngest units in the study area. The hot water in this area is of meteoric orijin and its circulation velocity in the ground is slow. Since the marbles are the resevoir rock of the hot water and the clay levels of the Neogene sediments are the cap rocks of the geothermal system, a heat convection trend occurs. the total spring yield varies between 50 I/s--100I/s and their temperatures vary from 30^0C to 80^0C. The resevoir temperature of these waters varies between 100^0C-150^0C according to the geothermometry applications. All of the waters are plotted on the kaolinite and montmonrillonite zones on the stability diagrams. In addition, the hydrochemical facies and geochemistry maps of groundwater in the study area were prepared showing the areal distribution of water types. Reference points in the study area were divided into seven groups on the basis of orijin, temperature and chemical composition. These are; cold mineral water, thermal mineral water, Gediz Stream water, Neogene sediments water, alluvial water,marble water and rain water. all of the thermal and mineral waters in the study area reflect the sodium bicarbonate water types. The increase in sodium and decrease in calsium can be explained by ion exchange and rapid calsium carbonate precipitation. The most likely possibility appears to be natural softening reaction of cation exchange for Na^+ on clays in schists or in the Neogene sediments and these will be discussed here.

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