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Boron concentrations of the CO 2 -rich thermal waters in western Anatolia have a wide range of 1-63 mg/l. Cl/B molal ratios of high temperature waters (>150°C) have low values ranging from 1 to 10. In low-temperature thermal waters (<150°C), with the exception of samples that have some seawater, Cl/B ratios range from 2 to 88. The positive correlation between HCO 3 and B values for thermal waters means that B concentrations in thermal waters are also associated with the dissolution of carbonates. In addition to the water-rock interaction, boron in thermal waters is probably controlled by the contribution of B by degassing of magma intrusives. Sericite, illite and tourmaline minerals, which are abundant in Menderes Massif rocks, are considered to be the main reason for the high boron contents. High B concentrations of thermal waters causes environmental problems in groundwaters and surface waters in some agricultural areas of western Anatolia. Re-injection of thermal waters to the reservoir is the best way to dispose of the geothermal wastewater and prevent contamination problems.

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The Seferihisar-Balç ova Geothermal system (SBG) is characterized by complex temperature and hydrochemical anomalies. Previous geophysical and hydrochemical investigations suggest that hydrothermal convection in the faulted areas of the SBG and recharge flow from the Horst may be responsible for the observed patterns. A numerical model of coupled fluid flow and heat transport processes has been built in order to study the possible fluid dynamics of deep geothermal groundwater flow in the SBG. The results support the hypothesis derived from interpreted data. The simulated scenarios provide a better understanding of the geophysical conditions under which the different fluid dynamics develop. When recharge processes are weak, the convective patterns in the faults can expand to surrounding reservoir units or below the seafloor. These fault-induced drag forces can cause natural seawater intrusion. In the Melange of the Seferihisar Horst, the regional flow is modified by buoyant-driven flow focused in the series of vertical faults. As a result, the main groundwater divide can shift. Sealing caprocks prevent fault-induced cells from being overwhelmed by vigorous regional flow. In this case, over-pressured, blind geothermal reservoirs form below the caprocks. Transient results showed that the front of rising hot waters in faults is unstable: the tip of the hydrothermal plumes can split and lead to periodical temperature oscillations. This phenomenon known as Taylor-Saffman fingering has been described in mid-ocean ridge hydrothermal systems. Our findings suggest that this type of thermal pulsing can also develop in active, faulted geothermal systems. To some extent, the role of an impervious fault core on the flow patterns has been investigated. Although it is not possible to reproduce basin-scale transport processes, this first attempt to model deep groundwater geothermal flow in the SBG qualitatively supported the interpreted data and described the different fluid dynamics of the basin.

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