Geochemical constraints for the origin of thermal waters from western Turkey

Applied Geochemistry 17 (2002) 163 183 www.elsevier.com/locate/apgeochem Geochemical constraints for the origin of thermal waters from western Turkey Avner Vengosh a, *, Cahit Helvacı b,ismail H. Karamanderesi c a Department of Geological and Environmental Sciences, Ben Gurion University of the Negev, PO Box 653, Beer Sheva 84105, Israel b Dokuz Eylu l U niversitesi, Mu hendislik Faku ltesi, Jeoloji Mu hendisligˇ Bo lu mu, 35100 Bornova-I. zmir, Turkey c MTA Ege Bo lge Mu du rlu gˇ, 35042 Bornova-I. zmir, Turkey Received 14 February 2000; accepted 14 February 2001 Editorial handling by R.L. Bassett Abstract The combined chemical composition, B and Sr isotopes, and the basic geologic setting of geothermal systems from the Menderes Massif in western Turkey have been investigated to evaluate the origin of the dissolved constituents and mechanisms of water rock interaction. Four types of thermal water are present: (1) a Na Cl of marine origin; (2) a Na HCO 3 type with high CO 2 content that is associated with metamorphic rocks of the Menderes Massif; (3) a Na SO 4 type that is also associated with metamorphic rocks of the Menderes Massif with H 2 S addition; and (4) a Ca Mg HCO 3 SO 4 type that results from interactions with carbonate rocks at shallow depths. The Na Cl waters are further subdivided based on Br/Cl ratios. Water from the Cumalı Seferihisar and Bodrum Karaada systems are deep circulated seawater (Br/Cl=sea water) whereas water from C anakkale Tuzla (Br/Cl<sea water) are from dissolution of Messinian evaporites. Good correlations between different dissolved salts and temperature indicate that the chemical composition of the thermal waters from non-marine geothermal systems is controlled by: (1) temperature dependent water rock interactions; (2) intensification of reactions due to high dissolved CO 2 and possibly HCl gasses; and (3) mixing with overlying cold groundwater. All of the thermal water is enriched in B. The B isotopic composition (d 11 B=2.3% to 18.7%; n=6) can indicate either leaching of B from the rocks, or B(OH) 3 degassing flux from deep sources. The large ranges in B concentrations in different rock types as well as in thermal waters from different systems suggest the waterrock mechanism. 87 Sr/ 86 Sr ratios of the thermal water are used to differentiate between solutes that have interacted with metamorphic rocks ( 87 Sr/ 86 Sr ratio as high as 0.719479) and carbonate rocks (low 87 Sr/ 86 Sr ratio of 0.707864). # 2002 Elsevier Science Ltd. All rights reserved. 1. Introduction The chemistry of thermal waters has attracted the attention of numerous studies, in particular investigations of the influence of water rock interactions and the large diversity of the ionic composition of fluids that are found in geothermal systems (e.g. Mahon, 1970; Tonani, 1970; White, 1970; Fournier and Truesdell 1973; Ellis and Mahon, 1977; Fournier, 1979; Giggenbach et al., 1983; Giggenbach, 1988). The chemical and environmental isotope compositions were used to determine the * Corresponding author. E-mail address: avnerv@bgumail.bgu.ac.il (A. Vengosh). origin of geothermal waters, in particular to distinguish between meteoric and sea water (e.g. Davisson et al., 1994). The geothermal fields of western Turkey provide a unique setting of extremely high enthalpy combined with a large variation in chemical composition. The distribution of the thermal systems follows the tectonic patterns of Turkey. The presence of active structural systems that characterizes western Anatolia is associated with young acidic volcanic activity, block faulting (grabens), hydrothermal alteration, fumaroles, and more than 600 hot springs with temperatures up to 100 C (C aǧlar, 1961; Ercan et al., 1985; 1997). The major high-enthalpy geothermal fields of Turkey are Kızıldere (200 240 C), 0883-2927/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0883-2927(01)00062-2

164 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 O merbeyli Germencik (232 C), C anakkale Tuzla (174 C), Simav Ku tahya (165 C), and İzmir Seferihisar (232 C) (S ims ek and Gu leç, 1994; Go kgo z, 1998; Fig. 1). The geothermal energy potential of western Turkey is used for electricity production. During 1998, Turkey produced enough geothermal heat for 50,000 houses and greenhouses of 200,000 m 2 with350mwt,aswellas190 hot springs with 285 Mwt (Go kgo z, 1998). However, the high concentrations of dissolved constituents, in particular high dissolved B in geothermal effluent, presents a serious environmental problem. For example, effluents from the power plant in Denizli Kızıldere that have B concentrations of more than 20 mg/l are released into adjacent creeks and endanger natural biota that are sensitive to B. In addition, natural underground discharge of geothermal waters into overlying aquifers results in B contamination in the associated aquifers in western Anatolia (Filiz and Tarcan, 1995). Previous studies have investigated different aspects of the chemical and isotopic composition of geothermal waters in western Turkey (Filiz, 1984; Gülec, 1988; Tarcan and Filiz, 1990; Ercan, 1993; Conrad et al., 1995; Mützenberg, 1997; Balderer, 1997; Gökgo z, 1998; O zgu r et al., 1998). This study presents the chemical and B ( 11 B/ 10 B) and Sr ( 87 Sr/ 86 Sr) isotopic compositions of major geothermal fluids from western Turkey. The aim is to provide an overall assessment on the origin of the thermal fluids, in particular the origin of the elevated B dissolved in the geothermal waters. 2. General geology of western Turkey and Menderes Massif Turkey is located within the Alpine Himalayan orogenic belt. The distribution of seismicity and active regimes are concentrated along high strain zones, many of which are major strike-slip faults, such as the North Anatolian fault (Ketin, 1956, 1968), East Anatolian transform fault (Dewey and S engo r, 1979) and graben zones (e.g. Bu yu k Menderes graben, Ku c u k Menderes graben, Gediz graben, Simav, Manyas, Kızılcahamam) (Angelier et al., 1981; S engo r, et al., 1985). The broad tectonic framework of the Aegean region and the eastern Mediterranean region is dominated by the rapid westward motion of the Anatolian plate relative to the Black Sea (Eurasia) plate, and west to south-westward motion relative to the African plate (McKenzie, 1972, Dewey and S engo r, 1979). The Anatolian plate is considered a floating continental plate being pushed westward from the intercontinental Bitlis suture zone (the southern edge of the Arabian Eurasian convergent strain zone), where its motion relative to Africa, is characterized by subduction at the Hellenic Trench (Dewey and S engo r, 1979). The Anatolian region consists of a mosaic of fragments of continental crust originally scattered over Tethys. These fragments have been assembled as intervening oceanic crust has been eliminated by a series of subduction episodes during the past 200 ma (Crampin and Evans, 1986). The differential plate motions are responsible for the young, east and west Anatolian volcanic activities. Block faulting and North Anatolian transform movements apparently began in the mid-miocene. The movement on the North Anatolian fault is right lateral strike-slip on an E W fault, or normal to the movement between the major plates. The explanation of this remarkable observation is that the North Anatolian fault does not form a plate boundary between Eurasia and Africa, but the northern boundary of a small plate. The small plate is situated on central and western Turkey, and is rapidly moving westward, at about 40 mm/a (McKenzie and Yılmaz, 1991; Yılmaz, 1997). The motion in western Turkey yields a velocity of 70 mm/a in the front of the arc and an uplift of 2.4 cm/a between the Aegean and the Eurasian plates. The western Anatolian region is undergoing extension at some of the highest rates ever documented. Eyidogˇ an (1988) reported extension rates of 13.5 mm/a over the last 40 years. The Menderes Massif (Fig. 1) is one of the largest metamorphic massifs in Turkey, with a lengths of about 200 km N S between the Simav and Go kova grabens, and about 150 km E W between Denizli and Turgutlu in western Anatolia (Ketin, 1983). Philippson (1910) described the Menderes Massif as a dome-like structure, broken by faulting during the Alpine orogeny whereas Dixon and Pereira (1974) regard the Menderes Massif as one of a number of zwischengebirge, essentially microcontinental blocks, made up of pre-mesozoic basement rocks having some of the characteristics of the cratons but displaying evidence of Alpine tectonic and magmatic involvement (Blumental, 1951; Bas arir, 1970; İzdar, 1971; Du rr et al., 1978; O ztu rk and Koc yigit, 1983). The crystalline Menderes Massif is divided into two major units: the core and the cover series. The core series consists of Precambrian to Cambrian high-grade schist, metavolcanic gneisses, augen gneiss, metagranites, migmatites and metagabbros. The cover series is composed of Ordovician to Paleocene micaschists, phyllites, metaquartzites, meta leucogranites, chloritoid kyanite schists, metacarbonates and a metaolistostrom. In many places, metabauxites, probably upper Jurassic to Cretaceous in age occur in the upper levels of the metacarbonate sequence (Dora et al., 1987, 1995; Candan et al. (1992) observed that high-grade metamorphic rocks are located along tectonic contacts within the schist, phyllite and marble series, which is enveloping the core. This is supported by the field data and drilling data from the Germencik O merbeyli geothermal system (S imsek et al., 1983; Karamanderesi and O zgu ler, 1988; Karamanderesi et al., 1988). On a large scale, the post-metamorphic compressional phase conjugated with the paleotectonic evolution of

A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 165 Fig. 1. General map of western Turkey and location of investigated geothermal systems.

166 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 western Anatolia is in a N S direction; and as a result it is pushed in a northward direction. This compressional force has given rise an extreme cataclastic structure. The post metamorphic granite plutons in Early Miocene have been strongly subjected to this compressional tectonics, and the allochtonous units are cut across by the graben systems of the neo-tectonic phase started in the Tortonian. It seems that the effective compressional tectonism in the Menderes Massif was during the Early Middle Miocene period. Neogene sediments overlie the allochthonous and autochthonous groups of rocks with angular unconformity in the south of the study area. The neotectonic period of the Menderes Massif and surrounding areas has been the subject of regional research for many years (Ketin, 1966; McKenzie, 1972; Dumont et al., 1979; Angelier et al., 1981; Satir and Friedrichsen, 1986). 3. Background on the investigated geothermal fields Extensive tectonic activity and formation of E W grabens have formed the shape of western Anatolia (Fig. 1). Of these, the Bu yu k Menderes and Gediz grabens host the main and most important geothermal fields of Turkey. The distribution of geothermal fields in Turkey closely follows the tectonic patterns. All of the hot springs with temperatures above 50 100 C in eastern and western Anatolia are clearly related to young volcanic activity and block faulting. The post-collosional volcanic activities, lasting from the upper Miocene to modern time have been responsible for heating up the geothermal fields (Demirel and S entu rk, 1996). The high thermal activities is reflected in the forms of widespread acidic volcanic activity with much hydrothermal alteration, fumaroles, and more than 600 hot springs with temperatures up to 100 C(C aǧlar, 1961). Table 1 summarizes the basic geological, temperature, water types, total dissolved salts, and lithological data of the investigated geothermal systems. Below the geological background of the investigated geothermal fields are described (Fig. 1 and Table 1). The Seferihisar geothermal field (samples HVK-1, HVK-2) is located on the Aegean coast of Turkey, 40 km SW of İzmir close to the Aegean Sea within the C ubukludagˇ graben. The stratigraphic series of the Seferihisar area consist of Paleozoic metamorphic rocks of the Menderes Massif, Upper Cretaceous İzmir flysch, which are all metamorphosed to greenschist facies and include schists, phyllites, spilites, and metasandstone, and Neogene units of alternations of conglomerate, sandstone, and claystone. Six research wells were drilled to a maximum depth of 1417 m and indicated that the fluid-bearing formation, composed of sandstone and conglomerate, has a thickness of 200 400 m (Demirel and S entu rk, 1996). Sample HVK-1 was collected from well CM-1 that was drilled down to a depth of 1417 m with temperature up to 146.5 C. Sample HVK-2 was collected from Dog anbey hot springs which have high temperature (71 77 C) and moderate salinity. The springs are located on the contact of the İzmir flysch within the overlying Yeniko y formation, along the southern boundary of the Karakoç Dog anbey horst in the SW of the Seferihisar geothermal area (Es der and S ims ek, 1975). The Germencik O merbeyli geothermal field (HVK-3, HVK-4), one of the geothermal areas with high enthalpy, is located in the western part of Menderes graben (Fig. 1). The geological strata are composed of Paleozoic metamorphic rocks of sedimentary origin and Miocene to Quaternary detrital and alluvial deposits. The metamorphism has produced marble, calcschist, graphitic schist and some quartzite. The Miocene sediments also include lignite or coal-bearing horizons, interbedded mainly with conglomerate, sandstone, silts and claystone. The thermal water is derived from two major sources: a sedimentary shallow and a deep basement reservoir (Karamanderesi et al. 1985; Gu ner et al. 1986). Samples HVK-3 and HVK-4 were sampled from deep wells (O B-9 and O B-3, respectively) from depth intervals of 896.9 1465 and 657 1196 m, respectively. The Aydın Ilıcabas ıimamko y field (HVK-5, HVK-6) is composed of Paleozoic mica-schist, gneiss blocks, locally quartzite and marble, and Pliocene sediments. The later consist of cobblestone, sandstone, siltstone and claystone, and alluvial sediments on top of these units. Samples HVK-5 and HVK-6 were collected from wells AY-1 and AY-2, respectively at depth intervals of 220 471 and 250 350 m. It should be noted that the water samples were collected from Pliocene sediments. The Aydın Salavatlı geothermal field (HVK-7) is located in the middle part of the Bu yu k Menderes graben, and is characterized by a normal fault structure. The stratigraphic sequence is composed of metamorphic rocks of the Menderes Massif and sedimentary rocks deposited during the Menderes Miocene rifting period. Field data suggests that there is a connection between tectonic development and periods of hydrothermal alteration. Several deep wells were drilled (AS-1, 1510 m and AS-2, 962m) revealing low resistivity zones (Karamanderesi, 1997). Kızıldere geothermal field (HVK-8, HVK-9) is located on the eastern part of Bu yu k Menderes graben, which extends for about 150 km in length with an E W trend. The field was the first to produce electrical energy in Turkey. Metamorphic basement rocks which compose the stratigraphy, cover 4 sedimentary formations. The basement rocks are composed of Paleozoic Menderes metamorphic units that are characterized by alterations of marble, calcschist, quartzite, schist, and gneiss (the İgˇ decik formation; S ims ek, 1985). Pliocene sediments overlie the basement and are divided into 4 lithological units (S ims ek, 1985). (1) Lower Pliocene

Table 1 General data on the investigated geothermal systems from western Turkey Sample number Location name Production zone rocks Thermal source (springs or well) Well deep temp. or springs temp. TDS Lithology References HVK-1 Seferihisar-Cumalı field İzmir flysch and Tertiary sediments. Rhyolite 12.5 m a HVK-2 Seferihisar Doǧanbey İzmir flysch and Tertiary sediments. Rhyolite 12.5 m a HVK-3 Germencik Ömerbeyli Menderes massif metamorphics, marble Dacite, 13.1 m a HVK-4 Germencik Ömerbeyli Menderes massif metamorphics, marble Well 1417.45 m 140 C 19800 Schists, phyllites, spillites and metasandstones Well 350.00 m spring Well number 9 1466 m Well number 3 1196.75m HVK-5 Aydın Illıcabaşi Tertiary sediments Well Ayter-1 471.25 m HVK-6 Aydın Illıcabaşı Tertiary sediments Well Ayter-2 335 m HVK-7 Aydın Salavatlı Menderes massif Well AS-1 metamorphics, marble 1510 m HVK-8 Denzili Kızıldere Menderes massif metamorphics HVK-9 Denizli Kızıldere Menderes massif metamorphics HVK-10 Manisa Urganlı Mesozoic serpantinite and limestone HVK-11 Manisa Salihli Sart. Menderes massif metamorphics HVK-12 Manisa Salihli Menderes massif Kurşunlu metamorphics and Tertiary sediments HVK-13 HVK-14 Manisa Salihli Kurşunlu mineral water Manisa Salihli MTA well Menderes massif metamorphics and Tertiary sediments 78 C 62.5 C 22200 Schists, phyllites, spillites and metasandstones 224 C 5200 Menderes massif metamorphics and Tertiary sediments 232 C 3700 Menderes massif metamorphics and Tertiary sediments 84.5 C 7000 Tertiary and Quaternary sediments 101.5 C 4600 Tertiary and Quaternary sediments 167 C 4600 Menderes massif metamorphics and Tertiary sediments 201 C 4200 Menderes massif metamorphcs, marble 212 C 4600 Menderes massif metamorphics, marble Well KD-13 760 m Well KD-16 666.50 m Spring 82 C 2100 Mesozoic serpantinite, limestone Spring 50 C 1200 Menderes massif metamorphics, marble Spring 94 C 1650 Menderes massif metamorphics, marble Spring 39.5 C 1200 Menderes massif metamorphics, marble Tertiary sediments Well MTA-1 94 C Menderes massif metamorphics, marble Es der and S ims ek, 1975 Williamson, 1982 Es der and S ims ek, 1975 Williamson, 1982 Demange et al., 1989 Williamson, 1982 a Demange et al., 1989 Karamanderesi et al., 1990 Karamanderesi et al., 1990 Karamanderesi et al., 1988 S ims ek, 1985 S ims ek, 1985 Erentu z and Ternek, 1968 Karamanderesi, 1972 Erentu z and Ternek, 1968 Yenal et al., 1976 Erentu z and Ternek, 1968 (continued on next page) A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 167

Table 1 (continued) Sample number Location name Production zone rocks Thermal source (springs or well) Well deep temp. or springs temp TDS Lithology References HVK-15 Manisa Alas ehir Tertiary sediments Well 33 m 17 C Tertiary sediments Karamanderesi, 1998 Fish farm HVK-16 Manisa Alas ehir Tertiary sediments Well 92 m 24 C 1800 Tertiary sediments Karamenderesi, 1998 Fish farm HVK-17 Manisa Alas ehir hot spring Menderes massif Spring 31 C 700 Menderes massif Karamenderesi, 1998 metamorphics, Tertiary sediments metamorphics HVK-18 Manisa Alas ehir Sarıkız Menderes massif Spring 18 C 2300 Erentu z and Ternek, 1968 mineral water metamorphics HVK-19 Denizli Karahayit Mesozoic limestone Spring 55 C 1500 Mesozoic limestones HVK-20 Denizli Pamukkale Mesozoic limestone Spring 34.5 C 1300 Mesozoic limestone HVK-21 C anakkale Tuzla Magmatic and volcanic rocks. Granodiorite 280.8. Ignimbrite 17.1 a Spring 102 C 59000 Trachyandesite, trachyte. Ignimbrite Karamanderesi, 1986 Borsi et al. 1972 Fytikas et al., 1976 a HVK-22 C anakkale Tuzla Magmatic and volcanic Well T-1 rocks. Granodiorite 280.8 a 814 m HVK-23 Edremit Gu re Karakaya formation, Tertiary sediments. Granodiorite 23.5 m a HVK-24 Edremit Havran Karakaya formation, granite, Tertiary sediments. Granodiorite 23.5 m a HVK-25 Dikili kaynarca Volcanic rocks and Tertiary sediments. Yunt dağ volcanics, 14.1 m a Well Gu re-1 197 m 174 C 65000 Trachyandesite, trachyte, Ignimbrite Karamanderesi, 1986 Mu tzenberg, 1997 Borsi et al., 1972 a Fytikas et al., 1976 a 55 C 1000 Tertiary sediments Bürku t, 1996 a Well 33 m 70 C 800 Tertiary sediments Bürku t, 1966 a Well 29 m 100 C 1000 Quaternary alluvium Spring 33 C 35000 Laminated cherty JICA, 1987 a HVK-26 İzmir Balc ova İzmir flysch and Tertiary Well BD-1 140 C 1400 İzmir flysch sediments. Dacite, 19.2 m a 564 m Borsi et al., 1972 a HVK-27 İzmir Balc ova İzmir flysch and Tertiary Spring 62. C 850 I zmir flysch and Tertiary sediments. Dacite, 19.2 m a sediments Borsi et al., 1972 a HVK-28 Bodrum Karaada Limestone. Monzodiorite, Bas kan and Canik, 1983 11.2 m a limestone Pis kin et al., 1983 a 168 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 a 19.2 m a and Borsi et al. a (production zone rocks and related magmatic and volcanic rocks and age datermined by).

A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 169 Kızılburun formation-alternating red and brown conglomerates, sandstone, claystone, and lignite seams, up to 200 m; (2) Lower Pliocene Sazak formation-intercalated grey limestone, marls and siltstone, 100 to 250 m; (3) Lower Pliocene Kolonkaya formation- alternating layers of sandstone, claystone and clayey limestone, 500 m; and (4) The Plio-Quaternary Tosunlar formation- poorly consolidated conglomerates, sandstone, and mudstone with fossiliferous claystone, up to 500 m. The thermal water in the Kızıldere field is derived from two major sources: a shallow Pliocene sedimentary (Sazak Formation) reservoir with a temperature of 198 C and a deep Menderes metamorphic reservoir (Iğdecik formation) with a temperature of 212 C. The Tekkehamam Pamukkale Karahayıt geothermal fields (HVK-19, HVK-20) are located in the topographic lows east of Kızıldere in the Tekkehamam area. Several fumerols are found on the mountain slopes of the area and hot springs with temperatures ranging between 30 and 100 C. The hot springs issue at the point where faults cut the valley. These springs deposit travertine and alteration minerals along the fault lines and in the vicinity of the springs. The hot springs of Pamukkale are located at the intersection of the Bu yu k Menderes and Gediz grabens. In this area the thickness of travertine reaches 85 m. The Pamukkale springs deposit snow-white travertine, whereas the Kızılleg en springs deposit red travertine due to high Fe concentrations in the fluid. Pamukkale and Karahayıt are tourist attractions, visited by 1.5 million tourists every year. The Manisa Urganlı geothermal field (HVK-10) is located in the western part of the Gediz graben, and is characterized by normal fault structures. The stratigraphic sequence of the Urganlı geothermal field are composed of Paleozoic schist and marble that form the basement of the to Menderes Massif. Mesozoic limestone serpentinite and ophiolitic mêlange overlie the basement units. The sequence continues with Pliocene conglomerate, sandstone, siltstone and limestone. Travertine and alluvium are the youngest sediments in the area. The general fault trends are W E, NE SW and also NW SE. Also, a thrust zone is observed between the Mesozoic ophiolitic meˆ lange and limestone in the NW of the area. The potential reservoir rocks are Paleozoic marbles, occasionally schist and Mesozoic limestone cut by fault zones in the region (). The Manisa Salihli geothermal field (HVK-11, HVK- 12, HVK-13, and HVK-14) is located along the southern boundary fault of the Gediz graben. Salihli is known for its Hg mineralization of hydrothermal origin. The field is currently under reconsideration as a prospect for epithermal Au Sb mineralization (Larson and Erler, 1993). The stratigraphic succession in the field includes the Paleozoic metamorphic of the Menderes Massif, Miocene and Pliocene conglomerate, sandstone, siltstone, limestone, clay, tuff and lignite layers, and Quaternary travertine and alluvium unconformably overlay the metamorphic units. The major faults in the field trend dominantly E W and NW SW while N S and NE SW trending faults also exist on a smaller scale. In the Salihli geothermal field hot springs are concentrated in the Kurs unlu and Sart areas. A total of 6 wells were drilled in the field. The highest temperature (150 C) was measured in the deep drill well, SC-1. The flow rate of this well reaches 2 l/s (Karamanderesi et al., 1995; ). The Alas ehir and Kavaklıdere geothermal field (HVK-15, HVK-16, HVK-17, HVK-18) is located in the Gediz graben. Drilling to a depth of 750 m revealed temperatures of up to 116 C and production of natural gas with 15% CH 4 and 85% CO 2 and thermal water (Karamanderesi et al. 1998). Alas ehir fish farm is a local shallow well with a depth of 92 m and temperature of 24 o C into alluvium deposits. Alas ehir mineral water has a temperature of 31 o C (Erentu z and Ternek, 1968). The C anakkale Tuzla geothermal field (HVK-21, HVK-22) is located 80 km SW of C anakkale, 5 km from the Aegean coast. The Tuzla field is a volcanic area. The stratigraphy of the field is composed of Permian metamorphic basement rocks, granodiorite intrusive rocks, Miocene volcanic rocks, including rhyodacitic, ignimbrite, trachyte and trachyandesite lavas, monzonite, and Quaternary and recent alluvium sediments (Karamanderesi, 1986; S ims ek, 1997). Thermal water is derived from a shallow volcanic reservoir at a depth of 330 350 m and a deep granite reservoir at a depth of 1020 m. The thermal water of Tuzla is unique due to the extremely high dissolved salt content, up to 63 g/l. Samples were collected from hot spring and well T-1 at a depth of 814 m (HVK- 21 and HVK-22, respectively). The Edremit Gu re and Havran geothermal fields (HVK-23, HVK-24) are located at the Edremit bay in the southern part of the Kazdăg massif. The geological sequence includes the Paleozoic Kazdaǧ formation (composed of gneiss, amphibolite, and marble and crystallized limestone), Triassic conglomerate, arkose, siltstone, Permian and Carboniferous limestone and marble blocks, and Upper Miocene Bayramic formation that consists of conglomerate, sandstone, claystone, shale and marl. Dikili-Bergama Kaynarca geothermal field (HVK-25) is located in Western Anatolia, 90 km north of İzmir and includes more than 20 hot springs. Compressional fields that formed during late Miocene to early Pliocene control the geological structure. As a result, the area became a site of N S oriented tensional stress fields. In an area between Dikili and Bergama, there are many hot springs whose distribution is controlled by fracture patterns. The geology of the Dikili Bergama area comprises various rocks such as sedimentary and metamorphic rocks (Paleozoic to recent), Kozak granodiorite (Eocene to Oligocene), Yuntdagˇ Volcanics (Late Miocene to Pliocene), and Dededağ Basalt (Pleistocene). A deep well that was drilled by MTA (K-1) yielded temperatures of up to

170 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 130 C. Since the volcanic activity and tectonic movements in the Dikili Bergama area are very intense, it is assumed that the heat source of geothermal activity derives from both tectonism and volcanism (MTA and JICA, 1987) The İzmir Balc ova geothermal field (HVK-26, HVK- 27) is located approximately 10 km SW of İzmir. The geological section includes Upper Cretaceous İzmir flysch composed of metasandstone, phyllite, limestone, serpentinite and diabase, the Miocene Yeniko y formation composed of conglomerates, sandstone and siltstone, and Pliocene Cumaovası volcanics, which includes andesite, agglomerate, tuff, and rhyolites. The geothermal systems are fed by the main NE SW, NW SE and E W trending fault (Yılmazer et al., 1989). The Bodrum geothermal field (HVK-28) is located south west of İzmir on the Agean coast. Hydrothermal mineral deposits and some mineral water exposures suggest a large geothermal potential of that field (Karamanderesi, 1998). The prospect covers the contact zone of the Menderes Massif and Taurus Belt (Ercan et al., 1984; Robert, 1995; O zc içek and O zçic ek, 1977; Pis kin, 1980). 4. Analytical procedures During the fall of 1995, 26 representative hydrothermal samples were collected from major thermal systems in western Turkey. Analyses of major ions were performed at the Analytical Laboratory of the Hydrological Service in Jerusalem. Lithium concentrations were measured by ICP MS (Element, Finnigan) at the University of California Santa Cruz. Lithium intensities were normalized to the internal standard of Be. Spike-free samples were scanned before the analyses and no detectable levels of Be were found in the original samples. Bromine was determined by flow injection ion analyzer (QuickChem 8000) at the Hydrological Service laboratory in Jerusalem (Vengosh and Pankratov, 1998). Boron isotopes were measured by a negative thermal ionization mass spectrometry technique (NITIMS; Vengosh et al., 1989, 1994). Samples were analyzed by a direct loading procedure, in which B-free sea water and natural solutions were loaded directly onto Re filaments and measured in a reverse polarity NBS-style 12 solidsource mass spectrometer at the University of California Santa Cruz. A standard deviation of less than 1.5 % was determined by repeat analysis of NIST SRM-951 standard ( 11 B/ 10 B=4.0130.005). Isotope ratios are reported as p11 B values, where h d 11 B ¼ 11 B= 10 B sample = 11 B= 10 1 i B 1000 NBS 951 Strontium was separated by cation-exchange chromatography using standard techniques at the Department of Geology, Hebrew University of Jerusalem. Isotope ratios were determined using third generation Faraday detectors in static mode on a VG-54WARP mass spectrometer at the University of California Santa Cruz. Zone refined Re filaments were used. All measured 87 Sr/ 86 Sr results were corrected to a 87 Sr/ 86 Sr ratio of 0.1194 using an exponential correction law. Correction for 87 Rb was negligible for all samples. Using this procedure, NBS-987 87 Sr/ 86 Sr yielded a ratio of 0.71025 ( 0.00001; n=5) during the period in which the unknowns were run. 5. Results and discussion The locations (Fig. 1), geological structure, source, temperature, salinity, water types, and lithology of the investigated thermal systems are presented in Table 1. Chemical and isotopic results are presented in Tables 2 and 3, respectively. The chemical composition (Fig. 2) suggests several water types with different distribution of the major ion composition. The different proportions of Cl, HCO 3 and SO 4 ions (i.e. their ratios to total dissolved constituents in meq/l, or the Cl SO 4 HCO 3 diagram; Giggenbach, 1991) are used to determine 4 basic water types (Table 1; Fig. 2): (1) Na Cl (in thermal waters of Cumalı Seferihisar, Bodrum Karaada island and Tuzla C anakkale); (2) Na HCO 3 (Aydın Ilıcabas ı, Salavatlı, Denizli-Kızıldere, Urganlı, Salihli); (3) Na SO 4 (Dikili Kaynarca Bergama, Edremit Gu re, Edremit Havran); and (4) Ca Mg HCO 3 SO 4 (Karahayıt, Pamukkale). Some systems have mixed compositions like Na Cl HCO 3 (Germencik O merbeyli, İzmir Balc ova). The variation of dissolved ions as normalized to Cl and evaporation-dilution of modern sea water are illustrated in Fig. 3. Most ions show enrichment relative to sea water with similar salinity. The temperature ion concentration relationships are presented in Fig. 4. The 11 B values and 87 Sr/ 86 Sr ratios of the thermal water vary from 2.3 to 18.7% (n=6) and 0.707864 to 0.719479 (n=5), respectively. 5.1. Marine vs. non-marine sources In the following discussion the authors distinguish between soluble ions (e.g. Cl, Br, B) and rock-forming elements (e.g. Na, Ca, HCO 3 ) in order to evaluate the origin of the geothermal water. Fig. 3 shows two distinctive correlation lines between Cl and other ions, particularly for the Cl Na coordination. It is argued that high salinity, Na Cl water composition, and the low (Na/Cl<1) of thermal fluids from Cumalı Seferihisar and Tuzla C anakkale suggest that most dissolved salts, in particular Cl and Na, are derived from a marine origin. On the other hand, all other thermal waters with significantly lower Cl concentrations and typically Na/ Cl>1 are non-marine, and thus most of the dissolved

Table 2 Chemical data of geothermal waters from western Turkey Water type ID Name Source Date Ca Mg Na KSr Li Cl HCO 3 SO 4 Br B F TDS Na/Cl Br/Cl (10 3 ) B/Cl 1 Cumalı Seferihisar Well CM-1 5/10/95 560 40 6300 1025 13.5 8.7 10930 300 160 37.4 16.1 2.7 19200 0.9 1.5 0.0048 2 Cumalı Seferihisar Dogˇ anbey Kaplıcası hot spring 5/10/95 100 60 1840 166 3180 640 200 7.5 9.8 5.0 6000 0.9 1.0 0.0101 3 Germencik O merbeyli Well OB-9 5/10/95 20 15 1550 160 11.0 8.5 1570 1600 80 6.6 54.2 5.6 5000 1.5 1.9 0.1131 4 Germencik O merbeyli Well OB-3 5/10/95 20 1 1420 160 2.0 1470 1600 20 6.3 50.7 5.7 4720 1.5 1.9 0.1135 5 Aydın Ilıcabas ı Well AY-1 5/10/95 6 16 1840 180 1.7 240 4700 70 1.3 49.6 3.9 7040 11.8 2.4 0.6777 6 Aydın Ilıcabas ı Well AY-2 5/10/95 10 40 1130 160 1.5 4.2 220 3010 100 1.7 43.7 4.4 4610 8.1 3.4 0.6665 7 Aydın Salavantlı Well AS-1 5/10/95 6 1 1260 105 1.0 250 2900 150 2.2 51.1 15.5 4590 7.8 3.9 0.6756 8 Denizli Kızıldere Power plant well number 13 5/10/95 26 1360 170 0.4 100 2510 630 0.3 20.7 17.9 4200 20.5 0.6656 9 Denizli Kızıldere Power plant well number 16 5/10/95 1480 190 0.4 4.2 120 2730 670 0.3 25.9 23.1 4570 19.7 1.3 0.7325 10 Urganli Hot spring 6/10/95 15 14 520 50 70 1440 8 2.5 9.1 4.5 2120 11.5 1.6 0.4302 11 Salihli Sart hot spring 6/10/95 25 17 190 30 40 930 30 0.1 16.4 1.0 1250 8.1 1.4763 12 Salihi Kurs unlu hot spring 6/10/95 10 12 350 60 0.6 70 1110 90 33.0 2.2 1650 8.4 1.6661 13 Salihli Kurs unlu mineral water 6/10/95 90 50 210 6 20 820 180 1.3 1200 15.5 0.1952 16 Alas ehir fish farm Well 6/10/95 51 150 380 20 180 990 640 2.2 0.2 1770 3.3 0.0411 17 Alas ehir fish farm Well 6/10/95 26 30 110 10 30 510 80 1.2 0.3 720 6.5 0.1421 18 Alas ehir hot spring Alas ehir hot spring 6/10/95 8 150 360 20 0.2 80 1700 140 29.4 0.5 2340 7.2 1.2501 19 Karahayıt hot spring Karahayıt hot spring 6/10/95 143 110 120 30 30 1040 830 0.9 2.3 1470 6.5 0.1054 20 Parmukkale Pamukkale hot spring 6/10/95 186 80 50 6 4.5 13 940 600 1.1 1.0 1280 5.6 0.2699 21 C anakkale Tuzla Tuzla hot spring 7/10/95 2840 70 18700 1970 154 35320 70 150 51.6 27.6 3.6 59060 0.8 6.5 0.0026 22 C anakkale Tuzla Tuzla well T-3 7/10/95 3154 110 20600 2060 166 18.3 39500 130 190 66.3 29.0 3.9 65650 0.8 7.5 0.0024 23 Edremit Gu re Well near Gu re 7/10/95 25 270 7 65 60 430 0.4 3.0 6.1 430 6.3 0.1529 24 Edremit Havran Well Havran Kaplıcaları 7/10/95 41 260 6 60 30 460 1.9 4.7 410 6.2 0.0974 25 Dikili Kaynarca Bergama Well 1 7/10/95 17 6 450 30 60 480 530 3.0 4.8 1050 12.0 0.1691 26 İzmir Balc ova Balc ova deep well 7/10/95 25 7 350 30 0.5 160 540 140 10.9 6.0 1130 3.3 0.2170 27 İzmir Balc ova Balc ova hot spring 8/10/95 210 20 125 480 260 6.6 3.5 850 2.6 0.1719 28 Bodrum Karaada island Black island hot spring 9/10/95 12600 520 21100 510 2890 75.3 5.1 1.3 34800 0.9 1.6 0.0008 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 171

172 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 Table 3 Isotopic data of geothermal waters from western Turkey ID Name Source Date 87 Sr/ 86 Sr d 11 B 1 Cumalı Seferihisar Well CM-1 5/10/95 2.31 3 Germencik Ömerbeyli Well ÖB-9 5/10/95 0.710867 0.17 5 Aydın Ilıcabaşi Well AY-1 5/10/95 0.714490 2.34 9 Denizli Kızıldere Power plant well number 16 5/10/95 0.719479 1.79 20 Pamukkale Pamukkale hot spring 6/10/95 0.707864 2.51 22 C anakkale Tuzla Tuzla well T-3 7/10/95 0.709633 18.70 constituents are derived from water-rock interactions. The Br/Cl ratios of the thermal waters can also be used to distinguish marine from non marine sources, as all of the Cl-enriched marine water has typically Br/Cl ratio4 sea water (Fig. 3). The different potential marine sources are deep circulation of modern seawater, fossil seawater, and dissolution of marine evaporites. Assuming that deep circulation of seawater was the source of the dissolved salts, one would expect to have seawater composition, particularly for conservative elements such as Cl and Br that are less affected by water-rock interactions. Karamanderesi and Helvacı (1994) measured the Br concentrations in different rock types in the Menderes massif and found negligible Br levels (<1 ppm). Thus, modern Mediterranean seawater would have a chloride content of <22,000 mg/l (i.e. lower concentrations can be derived from dilution with meteoric water) and a Br/ Cl ratio of 1.510 3. The only water sources that have similar chemical characteristics are the saline water from Cumalı Seferihisar (with Cl content of 10,926 mg/l) and Bodrum Karaada island (21,097 mg/l) with marine Na/ Cl and Br/Cl ratios. The other geochemical features (i.e. the B/Cl, Li/Cl, F/Cl, Ca/Cl, Mg/Cl, and SO 4 /Cl ratios, d 11 B value of 2.3%), however, are different from those of seawater and suggest that the original seawater was modified by intensive water-rock interactions. The depletion of Mg and enrichment of Ca, B, Li, and F, as well as the depletion of 11 B are typical of oceanic hydrothermal water (Spivack et al., 1987; You et al., 1994). This conclusion is consistent with the chemical and 18 O data reported by Conrad et al. (1995) who showed that Seferihisar thermal water originated from a mixture of sea water and local ground water. In contrast, the thermal water of the Tuzla system has a Cl concentration of 39,500 mg/l and a Br/Cl ratio of 0.710 3, which are higher and lower than those of seawater, respectively. In addition, the Tuzla brines are characterized by a d 11 B value of 18.7%, 87 Sr/ 86 Sr ratio of 0.709633 (Table 3), and d 34 Sof12% (Mu tzenberg, 1997). Balderer (1997) and Mu tzenberg (1997) suggested that the Tuzla brines were derived from lateral migration of fossil Miocene brines that were trapped in the Miocene sediments. The fossil brines could have originated from relics of evaporated sea water trapped in the sediments (e.g. Vengosh and Starinsky, 1993; Vengosh et al., 1994, 1998) or, alternatively, from dissolution of Messinian evaporites. Several lines of evidence suggest that the Tuzla thermal water could not be derived from evaporated sea water. First, relics of evaporated sea water or diagenetically modified sea water (e.g. Dead Sea) would have high d 11 B values (d 11 B >39%) as demonstrated recently by the composition of pore water from the Mediterranean with d 11 B values of up to 66% (Vengosh et al., 2000). In contrast, salts derived from evaporite dissolution would have lower d 11 B values (<39% Vengosh et al., 1992; 1998). In high-temperature environments, however, a large fraction of the dissolved B is also derived from leaching of the rocks. Thus, the original isotopic composition could be modified. This is clearly demonstrated in the case of thermal water from Cumalı Seferihisar where marine Na/Cl and Br/Cl ratios are associated with non-marine low 11 B values (2.3%) and high B/Cl ratios. The d 11 B values of the hypersaline Tuzla thermal water is 18.7% which is significantly higher than the values expected for leached B from local igneous rocks (granodiorite, trachyandesite, trachyte, rhyodacite, ignimbrite) with d 11 B 0%. The relatively high d 11 B can be interpreted as a reflection of modified high d 11 B evaporated sea water that was modified towards lower d 11 B values due to water rock interaction. Alternatively, the relative lower d 11 B value may indicate dissolution of late-stage evaporites with d 11 B<39%. Second, the Na/Cl and Br/Cl ratios of the Tuzla water are not consistent with the ratios expected for evaporation of sea water. During >10-fold evaporation beyond the halite saturation stage, the residual evaporated sea water has Na/Cl<0.86 and Br/Cl>1.510 3 (McCaffrey et al., 1987). Fig. 5 illustrates the evolution of evaporated seawater compared to the composition of thermal water from the Tuzla and Seferihisar thermal waters. The data points are not consistent with the evaporation line (i.e. low Br/Cl ratios below the seawater ratio) and thus rule out the relic sea water model.

A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 173 Fig. 2. Pie diagrams of the chemical composition (in meq l 1 ) of selected geothermal fields from western Turkey.

174 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 Fig. 3. Log chloride vs. log dissolved salts concentrations in geothermal waters from western Turkey. Third, the 87 Sr/ 86 Sr ratio of 0.709633 and d 34 S value of 12% are respectively higher and lower relative to the expected Miocene fossil evaporated sea water ( 87 Sr/ 86 Sr 0.7081; d 34 S 20%). Consequently, it is suggested that the hypersaline thermal water of Tuzla is derived from dissolution of salt deposits. The high Na (20,000 mg/l), Ca (3000 mg/ l), K(2000 mg/l), and B (29 mg/l) concentrations reflect the mineralogical composition of these deposits with a possible mineral assemblage of gypsum and Ca- and Na-borates. This mineral composition is typical for many Neogene salt-deposits in western Turkey (Helvacı, 1994, 1995; Palmer and Helvacı, 1977). 5.2. The impact of water rock interactions and origin of boron Following the Ellis and Mahon (1977) classification, HCO 3 waters are considered to occur in volcanic geothermal areas where steam containing CO 2 condenses into the liquid phase. Bicarbonate water can also reflect interaction of CO 2 charged fluids at lower temperatures and migration path as well as mixing with local ground water (Giggenbach, 1991). Sodium HCO 3 waters are common in geothermal systems associated with metamorphic rocks which is consistent with the general lithology of the Menderes Massif (Table 1) and the high

A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 175 Fig. 4. Source temperatures (as measured in the investigated thermal systems) vs. different dissolved ions (mg/l) in geothermal waters from western Turkey. CO 2 content that is typical of the thermal water of western Turkey (Filiz, 1984; Ercan et al., 1994). The origin of the high dissolved CO 2 according to d 13 C and He isotopic data is magmatic (Filiz, 1984; Ercan et al., 1994). The Na HCO 3 chemical composition is therefore a combination of high CO 2 flux and extensive waterrock interactions with metamorphic rocks. Similarly, the Na SO 4 water type can be derived from H 2 S condensing

176 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 Fig. 5. Na/Cl vs. Br/Cl ratios of evaporated sea water as compared to those from thermal water from Tuzla and Seferihisar. into the liquid phase as well as from interaction with sulfate minerals (e.g. Ellis and Mahon, 1977). The dependence of the ion composition on temperature is demonstrated by the correlations between different ion concentrations and temperatures measured in the thermal sources (Fig. 4), particularly for Na, K, Mg (reverse correlation), B and F. These positive correlations clearly indicate that much of the dissolved salts of the non-marine thermal waters are derived from water rock interactions. The chloride temperature relationship may also reflect an absorption of HCl gas into the liquid phase as well as extraction of Cl from the rocks. It seems that only in the Germencik O merbeyli system is Cl derived from such sources with significantly high Cl/ TDI ratio (0.3). It should be emphasized that mixing with local ground water also controls the chemical composition of the hydrothermal water. Thus, the linear correlations of most dissolved ions with chloride (Fig. 3) reflect both the original source of the thermal systems and mixing (i.e. dilution) with local cold ground water. Go kgo z (1998) showed that geothermometry temperatures calculated by applications of Na Kand Na K Ca geothermometers of geothermal water from Kızıldere area vary between 188 and 245 C which is consistent with actual temperatures measured at the bottom of research wells in that area. While the HCO 3 ion can be derived also from mixing with cold shallow groundwater, it seems that the HCO 3 / TDI ratio, which would be less affected by dilution, can be a useful tracer for delineating the sources of the salts. Positive correlation between the HCO 3 /TDI ratio and Na/Cl, K/Cl, and B/Cl ratios (Fig. 6) probably reflects the role of CO 2 in water rock interactions. Similarly, the correlation between Cl and other dissolved salts (Fig. 3) may also derive from the influence of HCl gas. The CO 2 and HCl gases can thus be considered as the triggers for the intensified water rock interactions and enhance leaching of dissolved ions in the thermal water. The Br/Cl ratio of most of the non-marine thermal water is higher than that of sea water (Fig. 3). The relative enrichment of Br can be explained by extraction of Br from organic matter in the Tertiary sediments, or, from preferential degassing of Br gases from deep sources. The high linear correlation between Cl and Br that characterizes the thermal water favors the second possibility. Thermal waters from western Turkey have typically high B content, which also causes environmental and operational problems. The association of high B and high CO 2 levels led Tarcan (1995) to suggest that B is also derived from a deep mantle source. Demirel and S entu rk (1996) also suggested that high B, NH 4, and CO 2 concentrations in thermal water from the Kızıldere geothermal field reflect ascent of magmatic emanations from depth although there is no evidence of recent volcanic activity in the area. Based on 3 He/ 4 He ratios, Gu leç (1988) argued that the involvement of mantlederived He, in the Kızıldere geothermal field does not exceed 30%. Two models should therefore be considered for the origin of B in the thermal water: (1) dissolved Cl, HCO 3, and B are derived from deep mantle flux of HCl, CO 2 and B(OH) 3 gasses; or (2), water-rock interactions leach B to the liquid phase. Next, these two conflicting models will be evaluated. Karamanderesi and Helvacı (1994) and Karamanderesi (1997) measured REE and other elements extracted from well cuttings and core rock samples from different geothermal fields (Fig. 7) and surface rock samples in the Menderes Massif. Their data showed that: 1. Different rock units from the Salavatlı geothermal field have high concentrations of B (range of 800 to 1600 ppm) relative to those (independent of lithology) of the O merbeyli field (O B-7, a range of 50 230 ppm). The difference in the B content of the rocks is also reflected in relatively higher B/Cl ratio in the associated thermal waters from these two systems (0.7 relative to 0.1), whereas the absolute B concentrations are similar. 2. Boron is unevenly distributed among different rock types. Boron is particularly enriched in (decreasing order) quartz vein, tourmaline gneiss, illite chlorite feldspar zone, and quartz chlorite schist zone. Boron is relatively depleted in marble and gabbro. 3. The vertical distribution of B (and Li) with depth is not uniform and is heavily dependent on the lithology. Boron is depleted in the marble zone in the O merbeyli field (50 ppm B at depth of 1400 m) relative to the albite-amphibolite schist zone (200 ppm, 1400 m).

A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 177 Fig. 6. HCO 3 /TDI ratio vs. Na/Cl, K/Cl, and B/Cl ratios of non-marine water from western Turkey. If indeed all of the B was derived from deep mantle flux as argued by Tarcan (1995) one would expect to have uniform B composition with similar B/Cl ratios in all of the thermal systems (i.e. the B/Cl ratio is used to eliminate the dilution factor). Moreover, one would not expect to have any relationships between B contents in local rocks and thermal waters, and yet the Salavatlı geothermal field is significantly enriched in B relatively to the O merbeyli field. Boron is easily leached from rocks and remains in its volatile form even at lower temperatures relative to the HCl that is converted to less volatile NaCl. The B/Cl ratio can thus be used to assess the maturity of the thermal system. Fluids from older systems are expected to be depleted in B relative to young systems (Go kgo z, 1998). The large difference between the Salavatlı and O merbeyli fields may be related to this factor. Consequently, it seems that B is mainly derived from local water-rock interactions and the source rocks strongly control the B, concentration in the water (e.g. quartz vein or tourmaline gneiss versus marble). Nevertheless, the overall B budget of a geothermal system can also be controlled by the original B concentrations in the rock or original parent magma fluids, as well as the degree of maturation in which water-rock interactions can contribute B to the thermal system. Since the lower mantle reservoir is enriched in primordial 3 He with respect to shallow MORB and radiogenic 4 He is generated by the decay of unstable isotopes of U and Th and radiogenic 3 H in the crust, the 3 He/ 4 He ratio can be a sensitive tracer to detect the presence of mantle helium in thermal water (Gu lec, 1988; Hoke et al., 2000). The 3 He/ 4 He ratio is normalized to atmospheric He (R/Ra=1) and consequently deep manlederived He would have high R/Ra values (>30) whereas crustal He production has a low ratio (R/Ra values of a typical continental crust are 0.005 to 0.02). While springs from the vicinity of Germencik O merbeyli yielded R/Ra values of 0.2 to 0.8 (n=3), which is typical of a crustal source, a spring from the Denizli

178 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 Fig. 7. Variations of B concentrations in rocks with depths in OB-7 and AS-1 drill holes (data from Karamanderesi and Helvacı, 1994 and Karamanderesi, 1997). area had a significantly higher value of 2.5 (Gu leç, 1988). Consequently, the available 3 He/ 4 He data in springs from western Turkey does not exlusively indicate on the origin of He, which in turn cannot support any evidence for the origin of B. Moreover, in the Germencik area thermal water has a low 3 He/ 4 He ratio that indicates a crustal source, while the B content is the highest among the investigated thermal waters. Previously, special attention has been given to the B isotope composition of hydrothermal fluids from a marine setting. The B isotope composition of hydrothermal fluids such as those venting from mid-ocean ridge crests (d 11 B ¼26.7 to 36.8%) suggests a mixture between seawater B and MORB-derived B leached from the basalt without resolvable isotopic fractionation (Spivack and Edmond, 1987). Hydrothermal fluids from a sediment-starved back-arc spreading center (Mariana Trough; d 11 B ¼22.5 to 29.8%; Palmer 1991) and from a classic sediment-hosted basin (Guaymas Basin and Escanaba Trough; d 11 B=10.1 to 23.2%; Spivack et al., 1987; Palmer, 1991) are characterized by lower d 11 B values and higher B concentrations, reflecting interactions with the hosted rocks. Thermal fluids from continental geothermal fields are characterized by even lower d 11 B values (Salton Sea, California, d 11 B ¼ 2.6 to 1.1%; Yellowstone National Park, d 11 B ¼ 9.3 to 4.4%; Palmer and Sturchio, 1990), reflecting the isotopic compositions of the source rocks. The influence of seawater B in geothermal systems has been traced in central Japan (d 11 B ¼ 5.8 to 27.1%; Musashi et al., 1988) and Iceland (d 11 B ¼ 6.7 to 30.7%; Aggarwal et al.,1992). The B isotopic composition cannot be used to distinguish between mantle flux and rock leaching processes due to the overlap in the isotopic composition of these two sources. The d 11 B range of the Na-HCO 3 waters is 2.3 to 1.8% (Table 3; n=3) and can thus reflect both leaching of igneous rocks and flux of mantle B (e.g. Spivack and Edmond, 1987). The B-isotope fractionation is controlled by the B species as B with tetrahedral coordination is isotopically depleted (low d 11 B) relative to B with trigonal coordination. Selective formation and

A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 179 Fig. 8. Schematic illustration of different geothermal water types from western Turkey. removal of B(OH) 3 species may cause a relative depletion of d 11 B in the residual fluid. Nevertheless, it seems that the magnitude and thus the effect of this isotopic fractionation is negligible in high-temperature environments. 5.3. Distribution of the water types The thermal systems of western Turkey exhibit a wide range of chemical composition that reflect the complex nature and different sources of thermal waters (Table 1). As shown above, the authors distinguish between 4 major groups that reflect different origin and mechanism of water-rock interactions. The Na Cl type originated from deep circulation and water rock interactions of modern sea water in the case of Seferihisar and Bodrum systems and from deep fossil brines originated from dissolution of Miocene evaporites in the case of Tuzla geothermal waters. The Na HCO 3 type characterized thermal waters from the systems of Aydın Ilıcabas ı, Salavatlı, Urganlı, Alasehir, Denizli Kızıldere and Salihli. Thermal waters

180 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163 183 from Germencik O merbeyli and İzmir Balc ova have a mixed Na Cl HCO 3 water composition. d 18 O dd data (Filiz, 1984; Ercan et al., 1994) suggest that the origin of these waters is meteoric whereas the temperature ion concentrations relationships suggest that most of the dissolved constituents (Fig. 4) were derived from extensive water rock interactions. As shown above, the high CO 2 content that characterizes these waters, presumably derived from a mantle source (Filiz, 1984; Ercan et al., 1994), enhances water rock interaction. In most cases the local bedrocks of the geothermal systems are the metamorphic of the Menderes Massif (Germencik O merbeyli, Aydın Ilıcabas ı, Salavatlı, Urganlı and Salihli). Yet in other systems, where the local rocks are composed of other rock units (e.g. Manisa Urganlı serpantinite and limestone) the associated thermal waters also have a Na HCO 3 composition. The 87 Sr/ 86 Sr ratio of Na HCO 3 type thermal water (0.710867 in Germencik O merbeyli and 0.71449 in Aydın Ilıcabası) reflect leaching of Sr from a highradiogenic source, which suggests that the source rock has a high Rb/Sr ratio). The system of Denizli-Kızıldere is one of the highest enthalpy geothermal field and most producing field in Turkey. The d 18 O dd data indicates that the origin of the water is meteoric, modified by intensive water-rock interactions. In addition, Go kgo z (1998) showed that calculated temperatures based on chemical geothermometers are similar to measured temperatures of up to 245 C. The high 87 Sr/ 86 Sr ratio (0.719479) of the geothermal water from Kızıldere system suggests that the deep aquifer units (schist and quartzite) are the predominant rock sources of Sr while the shallow limestone unit has negligible effects on the dissolved Sr budget in the thermal waters. The Na SO 4 type characterizes thermal waters from Edremit Gu re and Havran and Dikili Kaynarca geothermal fields, which are located at the Edremit bay in the southern part of the Kazdag massif. Sulfate can be derived from hydrogen sulfide condensing into the liquid phase as well as dissolution of sulfate minerals (e.g. Ellis and Mahon, 1977). Since the local geology (see above) is not different from other thermal systems in the Menderes Massif with a Na HCO 3 composition, it seems that the second explanation can be ruled out. The Ca Mg SO 4 HCO 3 type characterizes geothermal systems from Karahayıt and Pamukkale. It seems that this composition reflect shallow sources and interaction with shallow carbonate rocks. The Pamukkale hot spring has a 87 Sr/ 86 Sr ratio of 0.707864 that is distinctively low relative to the other non-marine thermal systems. This low 87 Sr/ 86 Sr signature reflects interaction with carbonate rocks of the Pliocene Sazak formation that consists of intercalated limestone, marls and siltstone, or the Pliocene Kolonkaya formation composed of alternating layers of sandstone, claystone and clayey limestone. The low 87 Sr/ 86 Sr ratio rules out interaction with the underlying Paleozoic Menderes metamorphic, which is consistent with the chemical composition of this water type. 6. Conclusions The chemical data, combined with isotopic data for B and Sr of thermal waters from western Turkey reveal 4 types of water, which originate from marine and nonmarine sources. The marine source has a Na Cl composition and Na/Cl ratio<1 whereas the non-marine waters typically have Na/Cl>1 (Fig. 8). The Br/Cl ratio is used to distinguish between direct penetration of sea water or recycled marine salts in the form of evaporite dissolution. The non-marine water shows 3 types of chemical compositions, reflecting different source rocks and depth of circulation. Na HCO 3 and Na SO 4 compositions reflect deep circulation and interactions with metamorphic rocks and gneiss while Ca Mg SO 4 HCO 3 composition is associated with shallow circulation in carbonate rocks and mixing with cold ground water. The 87 Sr/ 86 Sr ratio further constrains the nature of the source rocks (i.e. igneous and metamorphic versus carbonate rocks). Systematic changes in Na, K, Ca, and Mg with temperature (Fig. 4) show that concentrations of these dissolved constituents are largely dependent on the temperature and depth of circulation. Water rock interaction results in high concentrations of dissolved constituents such as Na, K, and B. The data suggest that B is derived from water rock interaction rather then deep mantle flux of B(OH) 3 gas. The high B concentration in the thermal water is typical of many non-marine geothermal fields, worldwide, and thus can be used as a sensitive tracer to monitor advection and mixing of underlying geothermal fluids with shallow groundwater. Acknowledgements We thank Irena Pankratov (Hydrological Service, Jerusalem) for her dedicated laboratory work. We thank Jim Gill (University of California at Santa Cruz) for his generous hospitality and allowing A.V. to use his laboratory. We are especially grateful to MTA and the managers for their generosity during fieldwork in Turkey. We appreciate and thank Randy L. Bassett, George Swihart and an anonymous reviewer for their thorough review of the earlier version of the manuscript. References Aggarwal, J.K., Palmer, M.R. Ragnarsdottir, K.V., 1992. Boron isotope composition of Iceland hydrothermal system. In 7th Internat. Symp. Water-Rock Interaction WRI-7, Park City, Vol. 2, 893 895.

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