Turkey)

The extensional stress regime is very effective in western Turkey since the Latest Oligocene-Early Miocene. Geothermal fields are positioned on the high-angle normal faults along the northern and southern margins of the Buyuk Menderes and Gediz grabens, respectively. The Ortakci geothermal field is located on the tectonically active northern margin of Buyuk Menderes graben. The discharge rate and temperature of the Ortakg hot spring is 2.41/s and 50.5 degrees C, respectively. Hot water discharges in the relay ramp representing the overlapping regions of two E-W normal faults related to N-S-oriented extension. The high-angle normal faults provide pathways for the fluid flow by increasing dilations. The field observations prove that all hot water outflows are related to the high-angle normal faults on the hanging wall of the detachment faults. Detailed structural analyses were performed on the Ortakci geothermal field, particularly on one of the active hot springs at the intersection of the E-W and N-S-oriented faults, to evaluate the tectonic activity in the area and the flow pathways for geothermal fluids. The heat source is the shallow mantle of a thinned lithosphere due to large extension rates, resulting in increased heat flow. The tectonic effects are on the heat transport mechanism, and the heat transport is controlled by faults in a convection dominated systems. The result is a high geothermal gradient because water can circulate deep and transports the heat upwards to the surface. (C) 2015 Elsevier Ltd. All rights reserved