| Title | Geological and Hydrogeological Properties of the Girelli Geothermal Field (AlaÅŸehir Graben, Western Turkey) |
|---|---|
| Authors | Alper BABA, Murat KARAŞ, Hüseyin UYTUN, Hasan SÖZBİLİR |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Geothermal fluid, active tectonics, detachment fault, Gediz Graben, Turkey |
| Abstract | The Girelli Geothermal Area is located on the southern margin of the Alasehir (Gediz) graben in the west of Turkey where N-S trending extensional tectonics have been developed since Miocene time. The Gediz graben has a WNW–ESE trending structure bounded by a crustal-scale Gediz detachment fault that controlled supradetachment basin-fill deposits. The footwall of the Gediz detachment comprises gneiss, marble, and schist of the Menderes metamorphic core complex as well as Miocene synextensional granite. The hanging wall of the detachment fault comprises Miocene to Quaternary sedimentary units reaching up to 3000 m thick towards the basin center and pinched out northward end thus formed an asymmetric geometry. Many geothermal resources occur along the southern margin of Gediz Graben. One of them is the Girelli Area covers a depression having developed on the horst of one of the branches of the Gediz Detachment Fault. The measured reservoir temperature has been found to be as high as 287 °C in the northwest of the Girelli area. Geothermal fluid is one of the most significant indications in this area where intense silicic and argillic alteration is observed. Cation and anion concentrations in thermal waters are related to the level of chemical equilibrium the waters have achieved with the surrounding rock. Cold water resources are rich in Ca-Mg-HCO3 and Na-Ca-Mg-HCO3 ions and the fact that the anion and cation are parallel with each other at the water points shows that these waters have the recharge and reservoir of the same origin in the area. The geothermal fluid of region is rich in Na-HCO3 ions and the fact that the anion and cation values are parallel with each other just like in the case of cold waters shows that these waters have the recharge and reservoir of the same origin. Geothermometers based on cation and silica concentrations have been used to estimate reservoir temperature. They are based on the interaction between the water and surrounding rock chemistry. The geothermal fluid is likely equilibrating with chalcedony or quartz. Silica geothermometers suggest reservoir temperatures could be between 160°C and 180°C. A total of 30 MT survey points were conducted across the Girelli region. MT result provides potential geophysical evidence that helps to understand the occurrence of the partially hot point in the west part of Girelli village. |