GEOELECTROMAGNETIC AND GEOTHERMIC INVESTIGATIONS IN THE IHLARA VALLEYGEOTHERMAL-FIELD

The Ihlara Valley is situated within a volcanic are that is formed by the collision of the eastern Mediterranean plate system with the Anato lian plate. In this study we will present data from a reservoir monito ring project over the Ihlara-Ziga geothermal field, located 22 km east of Aksaray, in central Anatolia. Although identified geothermal resou rces in the Ihlara Valley are modest, substantial undiscovered fields have been inferred primarily from the volcanic and tectonic setting bu t also from the high regional heat flow (150-200 mW m(-2)) on the Kirs ehir Massif. In 1988 and 1990, geoelectromagnetic surveys were underta ken by MTA-Ankara to confirm the presence of a relatively shallow (app roximate to 0.5-1 km), hydrothermally caused conductive layer or zone. CSAMT and Schlumberger resistivity data show good correspondence with each other, and 2-D geoelectric models are also in harmony with geolo gic data and gravity anomalies. The depth of the resistive basement, w hich is interpreted as Paleozoic limestone, is 200-250 m in the wester n part and increases eastward (approximate to 600-750 m). This may imp ly N-S-oriented normal faulting within the survey area. The parameters of the top layer are a resistivity of 25 to 95 ohm m and a thickness of between 100 and 250 m. The thickness of the conductive tuffs betwee n the top layer and the basement, whose resistivity is about 4-5 ohm m , also increases eastward (from 100 to 450 m). The apparent resistivit y maps for the frequencies between 32 and 2 Hz reveal a localized low resistivity anomaly to the east of Belisirma. (C) 1997 Elsevier Scienc e B.V.