Geochemical cycle of boron and isotope fractionation in geothermal fluids ofWestern Anatolia

Development of NW-SE trending grabens at Neotectonic period is due to absolute NE movement and relative SW movement of Anatolia and surrounding area. This new tectonic model shows an adaptation with young magmatic and geothermal system of Western Anatolia as well. According to this new model, geothermal localities in the Aegean region and continuousness of geothermal systems which have been classified due to their heat sources can be explained. Boron including fluids derived from altered oceanic crust and thick oceanic sediments, ascend towards the surface and change their isotopic composition by fractionation in different geological process (partial melting, crystallizations in the different environments), so that the boron occurs in different environments in differing amounts. Geothermal systems which have deep circulation in Western Anatolia (Kızıldere, Germencik, Salihli) have rather high amount of boron. These geothermal fluids which are hotter and have deep circulation interact with metamorphic rocks of Menderes Massif including some pegmatitic minerals. Generally these rocks have relatively low ?11B values and these values fit the low ?11B values of geothermal waters in contact with these rocks. According by, water-rock interaction appears to be as the main source for boron. Boron contents of geothermal waters having shallower circulation, like Pamukkale and Karahayıt, are lower. On the other hand ?11B values of these waters are a little bit high due to their lithological differences. In geothermal systems having sea water contribution, higher ?11B values indicate that boron comes from sea water and also from water-rock interaction.