3D structural controls of a high-enthalpy geothermal field in an extensional setting: the Kizildere geothermal field (Western Türkiye)

Abstract The Kızıldere Geothermal Field (KGF), situated at the eastern margin of the Büyük Menderes Graben, is the most productive high-enthalpy geothermal system in Türkiye, with reservoir temperatures exceeding 240 °C and an installed capacity of over 360 MW. Its heat is derived from crustal thinning, shallow Curie depths, and lithospheric extension related to the post‑Oligocene evolution of the Menderes Metamorphic Core Complex. This extensional tectonic setting produces high regional heat flow (up to 120 mW/m 2 ) and steep geothermal gradients that favour deep fluid circulation. To resolve the structural and hydrogeological controls on this system, we combined detailed field mapping, paleostress and kinematic analyses, 76 boreholes (530–3882 m), and 3D geological and thermal modelling. The results reveal that fault architecture is the principal control on fluid flow and geothermal productivity. E–W‑striking high‑angle normal faults act as major recharge pathways for meteoric waters, whereas NE‑trending sub‑vertical transfer faults, particularly the Gebeler Fault, form vertical conduits that enable the rapid ascent of thermal fluids. Intersections of these faults create favourable zones, where fractured marbles, quartzites, and carbonate‑rich basin‑fill units function as reservoirs, sealed by gneisses, schists, and clay‑rich Miocene deposits. This study demonstrates that the interplay between fault geometry and lithology governs the exceptional productivity of the KGF. The insights gained provide a predictive framework for targeting high‑permeability zones, extensional geothermal systems in Western Anatolia, and similar tectonic settings worldwide.