Use of chlorine-36 as tracer for the evolution of waters in geothermal and tectonically active areas in Western Turkey

Problems frequently arise in the determination of residence times for groundwaters of tectonically active regions. The commonly applied isotope techniques are often not appropriate because i) the high amount of water-rock interaction, ii) the underground production of nuclides in crystalline fissured rocks under geothermal conditions, iii) the occurrence of highly saline waters at boiling temperature affected by water-rock interaction processes, and iv) the high fluxes of CO2. Therefore the application of the chlorine-36 method looks very promising. By considering the sources of chlorine-36 and the water-rock interactions with respect to the chloride cycle for each area additional information on the ongoing processes of groundwater circulation and evolution as meet as the ranges of residence times of these waters were gained. Additional information, from independent hydrodynamic and coupled geothermal modeling and measurements of other environmental isotopes give additional support to our interpretation.