The effect of active extensional tectonics on the structural controls and heat transport mechanism in the Menderes Massif geothermal province: Inferred from three-dimensional electrical resistivity structure of the Kurşunlu geothermal field (Gediz Graben, western Anatolia)

Abstract

The current study in the Menderes Massif geothermal province aims to assert a crustal-scale geoelectrical evidence showing the role of extensional tectonics on the flow of geothermal fluids through both high-angle and low-angle normal (detachment) faults and on the heat transport mechanism in the convection dominated-amagmatic geothermal play systems, on the basis of three-dimensional electrical resistivity structure of the Kurşunlu geothermal field, Gediz Graben, western Anatolia. The electrical resistivity structure was derived from the three-dimensional inversion of the magnetotelluric data acquired from 74 sites in the period range from 0.001 s to 1000s. The resistivity model brings out two different types of reservoirs, namely (i) a shallow low resistivity reservoir (secondary reservoir) corresponding to the Kurşunlu hot spring in the sedimentary layer of the Gediz Graben and (ii) a deep more resistive reservoir (primary reservoir) beneath a prominent highly conductive (≤ 10 ohm-m) hydrothermal clay alteration zone. The circulation of geothermal fluids in reservoirs is dominantly controlled by high-angle normal faults including the main graben-bounding fault and low-angle Gediz detachment fault. The possible heat source for the geothermal system has been attributed to high heat arising from upwelling asthenosphere through the mantle window in the northward subducting and retreating African slab, which has been accompanied by crustal extension resulting in a thin crust and shallow mantle, and the deeply penetrating main graben-bounding fault acting as a conduit through which heat is transported from the deeper parts of the crust to near surface probably controls heat transport in the area.