Structural, lithological, and geodynamic controls on geothermal activity in the Menderes geothermal Province (Western Anatolia, Turkey)

Abstract

Western Turkey belongs to the regions with the highest geothermal potential in the world, resulting in significant electricity production from geothermal resources located predominantly in the Menderes Massif. Although geothermal exploitation is increasingly ongoing, geological, and physical processes leading to the emplacement of geothermal reservoirs are hitherto poorly understood. Several studies on the Menderes Massif led to different interpretations of structural controls on the location of hot springs and of the heat source origin. This paper describes geological evidence showing how heat is transmitted from the abnormally hot mantle to the geothermal reservoirs. On the basis of field studies, we suggest that crustal-scale low-angle normal faults convey hot fluids to the surface and represent the first-order control on geothermal systems. At the basin scale, connected on low-angle normal faults, kilometric high-angle transfer faults are characterized by dilational jogs, where fluids may be strongly focused. In addition, favourable lithologies in the basement (e.g., karstic marble) could play a critical role in the localization of geothermal reservoirs. Finally, a compilation of geochemical data at the scale of the Menderes Massif suggests an important role of the large mantle thermal anomaly, which is related to the Hellenic subduction. Heat from shallow asthenospheric mantle is suggested to be conveyed toward the surface by fluid circulation through the low-angle faults. Hence, geothermal activity in the Menderes Massif is not of magmatic origin but rather associated with active extensional tectonics related to the Aegean slab dynamics (i.e., slab retreat and tearing).