Geochemical constraints for the origin of thermal waters from western Turkey

Geochemical constraints for the origin of thermal watersfrom western Turkey

Avner Vengosha,*, Cahit Helvacıb, I.smail H. Karamanderesic

aDepartment of Geological and Environmental Sciences, Ben Gurion University of the Negev, PO Box 653, Beer Sheva 84105, IsraelbDokuz Eylul Universitesi, Muhendislik Fakultesi, Jeoloji Muhendislig Bolumu, 35100 Bornova-I

.zmir, Turkey

cMTA Ege Bolge Mudurlug, 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 fromthe 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) aNa–HCO3 type with high CO2 content that is associated with metamorphic rocks of the Menderes Massif; (3) a Na–SO4 type that is also associated with metamorphic rocks of the Menderes Massif with H2S addition; and (4) a Ca–Mg–

HCO3–SO4 type that results from interactions with carbonate rocks at shallow depths. The Na–Cl waters are furthersubdivided based on Br/Cl ratios. Water from the Cumalı Seferihisar and Bodrum Karaada systems are deep circulatedseawater (Br/Cl=sea water) whereas water from Canakkale–Tuzla (Br/Cl<sea water) are from dissolution of Messi-nian evaporites. Good correlations between different dissolved salts and temperature indicate that the chemical com-

position 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 CO2 and possibly HCl gasses; and (3) mixingwith overlying cold groundwater. All of the thermal water is enriched in B. The B isotopic composition (d11B=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 largeranges in B concentrations in different rock types as well as in thermal waters from different systems suggest the water-rock mechanism. 87Sr/86Sr ratios of the thermal water are used to differentiate between solutes that have interacted

with metamorphic rocks (87Sr/86Sr ratio as high as 0.719479) and carbonate rocks (low 87Sr/86Sr ratio of 0.707864).# 2002 Elsevier Science Ltd. All rights reserved.

1. Introduction

The chemistry of thermal waters has attracted theattention of numerous studies, in particular investiga-

tions of the influence of water–rock interactions and thelarge diversity of the ionic composition of fluids that arefound in geothermal systems (e.g. Mahon, 1970; Tonani,

1970; White, 1970; Fournier and Truesdell 1973; Ellisand Mahon, 1977; Fournier, 1979; Giggenbach et al.,1983; Giggenbach, 1988). The chemical and environ-mental isotope compositions were used to determine the

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 witha large variation in chemical composition. The distributionof the thermal systems follows the tectonic patterns of

Turkey. The presence of active structural systems thatcharacterizes western Anatolia is associated with youngacidic volcanic activity, block faulting (grabens), hydro-thermal alteration, fumaroles, and more than 600 hot

springs with temperatures up to 100�C (Caglar, 1961;Ercan et al., 1985; 1997). The major high-enthalpy geo-thermal fields of Turkey are Kızıldere (200–240�C),

0883-2927/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.

PI I : S0883-2927(01 )00062-2

Applied Geochemistry 17 (2002) 163–183

www.elsevier.com/locate/apgeochem

* Corresponding author.

E-mail address: [email protected] (A. Vengosh).

Omerbeyli–Germencik (232�C), Canakkale–Tuzla(174�C), Simav–Kutahya (165�C), and I

.zmir–Seferihisar

(232�C) (Simsek and Gulec, 1994; Gokgoz, 1998; Fig. 1).The geothermal energy potential of western Turkey is

used for electricity production. During 1998, Turkey pro-duced enough geothermal heat for 50,000 houses andgreenhouses of 200,000 m2 with 350 Mwt, as well as 190

hot springs with 285 Mwt (Gokgoz, 1998). However, thehigh concentrations of dissolved constituents, in particularhigh dissolved B in geothermal effluent, presents a serious

environmental problem. For example, effluents from thepower plant in Denizli–Kızıldere that have B concentra-tions 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 geother-mal waters into overlying aquifers results in B con-tamination 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; Gulec, 1988; Tarcanand Filiz, 1990; Ercan, 1993; Conrad et al., 1995; Mut-zenberg, 1997; Balderer, 1997; Gokgoz, 1998; Ozgur et al.,

1998). This study presents the chemical and B (11B/10B)and Sr (87Sr/86Sr) isotopic compositions of major geo-thermal fluids fromwestern 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 thegeothermal waters.

2. General geology of western Turkey and Menderes

Massif

Turkey is located within the Alpine–Himalayan oro-genic belt. The distribution of seismicity and active

regimes are concentrated along high strain zones, manyof which are major strike-slip faults, such as the NorthAnatolian fault (Ketin, 1956, 1968), East Anatoliantransform fault (Dewey and Sengor, 1979) and graben

zones (e.g. Buyuk Menderes graben, Kucuk Menderesgraben, Gediz graben, Simav, Manyas, Kızılcahamam)(Angelier et al., 1981; Sengor, et al., 1985). The broad

tectonic framework of the Aegean region and the easternMediterranean region is dominated by the rapid west-ward motion of the Anatolian plate relative to the Black

Sea (Eurasia) plate, and west to south-westward motionrelative to the African plate (McKenzie, 1972, Deweyand Sengor, 1979).

The Anatolian plate is considered a ‘‘floating’’ con-tinental plate being pushed westward from the inter-continental Bitlis suture zone (the southern edge of theArabian — Eurasian convergent strain zone), where its

motion relative to Africa, is characterized by subductionat the Hellenic Trench (Dewey and Sengor, 1979). TheAnatolian region consists of a mosaic of fragments of

continental crust originally scattered over Tethys. Thesefragments have been assembled as intervening oceaniccrust has been eliminated by a series of subduction epi-sodes during the past 200 ma (Crampin and Evans,

1986). The differential plate motions are responsible forthe young, east and west Anatolian volcanic activities.Block faulting and North Anatolian transform move-

ments apparently began in the mid-Miocene. Themovement on the North Anatolian fault is right lateralstrike-slip on an E–W fault, or normal to the movement

between the major plates. The explanation of thisremarkable observation is that the North Anatolianfault 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 Tur-key, 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 thefront of the arc and an uplift of 2.4 cm/a between theAegean and the Eurasian plates. The western Anatolian

region is undergoing extension at some of the highestrates ever documented. Eyidogan (1988) reported extensionrates of 13.5 mm/a over the last 40 years.

The Menderes Massif (Fig. 1) is one of the largestmetamorphic massifs in Turkey, with a lengths of about200 km N–S between the Simav and Gokova grabens,

and about 150 km E–W between Denizli and Turgutlu inwestern 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 asone of a number of ‘‘zwischengebirge’’, essentially micro-continental blocks, made up of pre-Mesozoic basement

rocks having some of the characteristics of the cratonsbut displaying evidence of Alpine tectonic and magmaticinvolvement (Blumental, 1951; Basarir, 1970; I

.zdar,

1971; Durr et al., 1978; Ozturk and Kocyigit, 1983).The crystalline Menderes Massif is divided into two

major units: the core and the cover series. The core seriesconsists of Precambrian to Cambrian high-grade schist,

metavolcanic–gneisses, augen gneiss, metagranites, mig-matites and metagabbros. The cover series is composedof Ordovician to Paleocene micaschists, phyllites, meta-

quartzites, 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 thathigh-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 fielddata and drilling data from the Germencik–Omerbeyligeothermal system (Simsek et al., 1983; Karamanderesi

and Ozguler, 1988; Karamanderesi et al., 1988).On a large scale, the post-metamorphic compressional

phase conjugated with the paleotectonic evolution of

164 A. Vengosh et al. / Applied Geochemistry 17 (2002) 163–183

Fig. 1. General map of western Turkey and location of investigated geothermal systems.

A. Vengosh et al. / Applied Geochemistry 17 (2002) 163–183 165

western Anatolia is in a N–S direction; and as a result itis pushed in a northward direction. This compressionalforce has given rise an extreme cataclastic structure. Thepost metamorphic granite plutons in Early Miocene

have been strongly subjected to this compressional tec-tonics, and the allochtonous units are cut across by thegraben systems of the neo-tectonic phase started in the

Tortonian. It seems that the effective compressionaltectonism in the Menderes Massif was during the Early–Middle Miocene period. Neogene sediments overlie the

allochthonous and autochthonous groups of rocks withangular unconformity in the south of the study area. Theneotectonic period of the Menderes Massif and surround-

ing areas has been the subject of regional research for manyyears (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–Wgrabens have formed the shape of western Anatolia(Fig. 1). Of these, the Buyuk Menderes and Gediz gra-

bens host the main and most important geothermalfields of Turkey. The distribution of geothermal fields inTurkey closely follows the tectonic patterns. All of the

hot springs with temperatures above 50–100�C in east-ern and western Anatolia are clearly related to youngvolcanic activity and block faulting. The post-collo-sional volcanic activities, lasting from the upper Mio-

cene to modern time have been responsible for heatingup the geothermal fields (Demirel and Senturk, 1996).The high thermal activities is reflected in the forms of

widespread acidic volcanic activity with much hydro-thermal alteration, fumaroles, and more than 600 hotsprings with temperatures up to 100�C (Caglar, 1961).

Table 1 summarizes the basic geological, temperature,water types, total dissolved salts, and lithological dataof the investigated geothermal systems. Below the geo-logical 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 I.zmir close to the Aegean Sea within the

Cubukludag graben. The stratigraphic series of theSeferihisar area consist of Paleozoic metamorphic rocks

of the Menderes Massif, Upper Cretaceous ‘‘I.zmir

flysch’’, which are all metamorphosed to greenschistfacies and include schists, phyllites, spilites, and meta-

sandstone, and Neogene units of alternations of con-glomerate, sandstone, and claystone. Six research wellswere drilled to a maximum depth of 1417 m and indi-cated that the fluid-bearing formation, composed of

sandstone and conglomerate, has a thickness of 200–400m (Demirel and Senturk, 1996). Sample HVK-1 wascollected from well CM-1 that was drilled down to a

depth of 1417 m with temperature up to 146.5�C. Sam-ple HVK-2 was collected from Doganbey hot springswhich have high temperature (71–77�C) and moderatesalinity. The springs are located on the contact of the

I.zmir flysch within the overlying Yenikoy formation,along the southern boundary of the Karakoc–Doganbeyhorst in the SW of the Seferihisar geothermal area

(Esder and Simsek, 1975).The Germencik–Omerbeyli geothermal field (HVK-3,

HVK-4), one of the geothermal areas with high

enthalpy, is located in the western part of Menderesgraben (Fig. 1). The geological strata are composed ofPaleozoic 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 sedi-ments also include lignite or coal-bearing horizons,

interbedded mainly with conglomerate, sandstone, siltsand claystone. The thermal water is derived from twomajor sources: a sedimentary shallow and a deep base-

ment reservoir (Karamanderesi et al. 1985; Guner et al.1986). Samples HVK-3 and HVK-4 were sampled fromdeep wells (OB-9 and OB-3, respectively) from depth

intervals of 896.9–1465 and 657–1196 m, respectively.The Aydın Ilıcabası I

.mamkoy 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, siltstoneand claystone, and alluvial sediments on top of theseunits. Samples HVK-5 and HVK-6 were collected from

wells AY-1 and AY-2, respectively at depth intervals of220–471 and 250–350 m. It should be noted that thewater samples were collected from Pliocene sediments.

The Aydın–Salavatlı geothermal field (HVK-7) islocated in the middle part of the Buyuk Menderes gra-ben, and is characterized by a normal fault structure.

The stratigraphic sequence is composed of metamorphicrocks of the Menderes Massif and sedimentary rocksdeposited during the Menderes Miocene rifting period.Field data suggests that there is a connection between

tectonic development and periods of hydrothermalalteration. Several deep wells were drilled (AS-1, 1510 mand AS-2, 962m) revealing low resistivity zones (Kar-

amanderesi, 1997).Kızıldere geothermal field (HVK-8, HVK-9) is loca-

ted on the eastern part of Buyuk Menderes graben,

which extends for about 150 km in length with an E–Wtrend. The field was the first to produce electrical energyin Turkey. Metamorphic basement rocks which com-

pose the stratigraphy, cover 4 sedimentary formations.The basement rocks are composed of Paleozoic Men-deres metamorphic units that are characterized byalterations of marble, calcschist, quartzite, schist, and

gneiss (the I.gdecik formation; Simsek, 1985). Pliocene

sediments overlie the basement and are divided into 4lithological units (Simsek, 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 I.zmir flysch and

Tertiary sediments.

Rhyolite 12.5 ma

Well 1417.45 m 140�C 19800 Schists, phyllites, spillites

and metasandstones

MTA, 1996

Esder and Simsek, 1975

Williamson, 1982

HVK-2 Seferihisar–Doganbey I.zmir flysch and

Tertiary sediments.

Rhyolite 12.5 ma

Well 350.00 m

spring

78�C

62.5�C

22200 Schists, phyllites, spillites

and metasandstones

MTA, 1996

Esder and Simsek, 1975

Williamson, 1982

HVK-3 Germencik–Omerbeyli Menderes massif

metamorphics, marble

Dacite, 13.1 ma

Well number 9

1466 m

224�C 5200 Menderes massif

metamorphics and Tertiary

sediments

Demange et al., 1989

MTA, 1996

Williamson, 1982a

HVK-4 Germencik–Omerbeyli Menderes massif


Well number 3

1196.75m



sediments

Demange et al., 1989

MTA, 1996

HVK-5 Aydın–Illıcabasi Tertiary sediments Well Ayter-1

471.25 m

84.5�C 7000 Tertiary and Quaternary

sediments

Karamanderesi et al., 1990

MTA, 1996

HVK-6 Aydın–Illıcabası Tertiary sediments Well Ayter-2

335 m

101.5�C 4600 Tertiary and Quaternary

sediments


MTA, 1996

HVK-7 Aydın–Salavatlı Menderes massif


Well AS-1

1510 m



sediments


MTA, 1996

HVK-8 Denzili–Kızıldere Menderes massif

metamorphics

Well KD-13

760 m


metamorphcs, marble

Simsek, 1985

MTA, 1996

HVK-9 Denizli– Kızıldere Menderes massif

metamorphics

Well KD-16

666.50 m



Simsek, 1985

MTA, 1996

HVK-10 Manisa–Urganlı Mesozoic serpantinite

and limestone

Spring 82�C 2100 Mesozoic serpantinite,

limestone

Erentuz and Ternek, 1968

Karamanderesi, 1972

MTA, 1996

HVK-11 Manisa–Salihli–Sart. Menderes massif

metamorphics

Spring 50�C 1200 Menderes massif


MTA, 1996

HVK-12 Manisa–Salihli–

Kursunlu

Menderes massif

metamorphics and

Tertiary sediments




MTA, 1996

HVK-13 Manisa–Salihli–

Kursunlu–mineral water

Menderes massif

metamorphics and

Tertiary sediments

Spring 39.5�C 1200 Menderes massif


Yenal et al., 1976

MTA, 1996

HVK-14 Manisa–Salihli–MTA

well

Tertiary sediments Well MTA-1 94�C – Menderes massif



MTA, 1996

(continued on next page)

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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–Alasehir

Fish farm

Tertiary sediments Well 33 m 17�C – Tertiary sediments Karamanderesi, 1998

HVK-16 Manisa–Alasehir

Fish farm

Tertiary sediments Well 92 m 24�C 1800 Tertiary sediments Karamenderesi, 1998

HVK-17 Manisa–Alasehir hot spring Menderes massif

metamorphics,

Tertiary sediments


metamorphics

Karamenderesi, 1998

HVK-18 Manisa– Alasehir Sarıkız

mineral water

Menderes massif

metamorphics

Spring 18�C 2300 Erentuz and Ternek, 1968

HVK-19 Denizli–Karahayit Mesozoic limestone Spring 55�C 1500 Mesozoic limestones MTA, 1996

HVK-20 Denizli–Pamukkale Mesozoic limestone Spring 34.5�C 1300 Mesozoic limestone MTA, 1996

HVK-21 Canakkale–Tuzla Magmatic and volcanic

rocks. Granodiorite

28�0.8. Ignimbrite 17.1a

Spring 102�C 59000 Trachyandesite, trachyte.

Ignimbrite

Karamanderesi, 1986

Borsi et al. 1972

Fytikas et al., 1976a

HVK-22 Canakkale–Tuzla Magmatic and volcanic

rocks. Granodiorite 28�0.8aWell T-1

814 m

174�C 65000 Trachyandesite, trachyte,

Ignimbrite

Karamanderesi, 1986

Mutzenberg, 1997

Borsi et al., 1972a

Fytikas et al., 1976a

HVK-23 Edremit–Gure Karakaya formation,

Tertiary sediments.

Granodiorite 23.5 ma

Well Gure-1

197 m

55�C 1000 Tertiary sediments MTA, 1996

Burkut, 1996a

HVK-24 Edremit–Havran Karakaya formation,

granite, Tertiary sediments.

Granodiorite 23.5 ma

Well 33 m 70�C 800 Tertiary sediments MTA, 1996

Burkut, 1966a

HVK-25 Dikili kaynarca Volcanic rocks and

Tertiary sediments. Yunt dag

volcanics, 14.1 ma

Well 29 m 100�C 1000 Quaternary alluvium MTA, 1996

JICA, 1987a

HVK-26 I.zmir–Balcova I

.zmir flysch and Tertiary

sediments. Dacite, 19.2 maWell BD-1

564 m

140�C 1400 I.zmir flysch MTA, 1996

Borsi et al., 1972a

HVK-27 I.zmir–Balcova I


sediments. Dacite, 19.2 maSpring 62�C 850 I


sediments

MTA, 1996

Borsi et al., 1972a

HVK-28 Bodrum–Karaada Limestone. Monzodiorite,

11.2 maSpring 33�C 35000 Laminated cherty

limestone

Baskan and Canik, 1983

Piskin et al., 1983a

a 19.2 ma and Borsi et al. a (production zone rocks and related magmatic and volcanic rocks and age datermined by).

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Kızılburun formation-alternating red and brown con-glomerates, sandstone, claystone, and lignite seams, up to200 m; (2) Lower Pliocene Sazak formation-intercalatedgrey limestone, marls and siltstone, 100 to 250 m; (3)

Lower Pliocene Kolonkaya formation- alternating layersof sandstone, claystone and clayey limestone, 500 m; and(4) The Plio-Quaternary Tosunlar formation- poorly con-

solidated conglomerates, sandstone, and mudstone withfossiliferous claystone, up to 500 m. The thermal waterin 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 Men-deres metamorphic reservoir (Igdecik formation) with a

temperature of 212�C.The Tekkehamam–Pamukkale–Karahayıt geothermal

fields (HVK-19, HVK-20) are located in the topo-graphic lows east of Kızıldere in the Tekkehamam area.

Several fumerols are found on the mountain slopes ofthe area and hot springs with temperatures rangingbetween 30 and 100�C. The hot springs issue at the

point where faults cut the valley. These springs deposittravertine and alteration minerals along the fault linesand in the vicinity of the springs. The hot springs of

Pamukkale are located at the intersection of the BuyukMenderes and Gediz grabens. In this area the thicknessof travertine reaches 85 m. The Pamukkale springs

deposit snow-white travertine, whereas the Kızıllegensprings deposit red travertine due to high Fe concentra-tions in the fluid. Pamukkale and Karahayıt are touristattractions, visited by 1.5 million tourists every year.

The Manisa–Urganlı geothermal field (HVK-10) islocated in the western part of the Gediz graben, and ischaracterized by normal fault structures. The stratigraphic

sequence of the Urganlı geothermal field are composed ofPaleozoic schist and marble that form the basement of theto Menderes Massif. Mesozoic limestone serpentinite and

ophiolitic melange overlie the basement units. Thesequence continues with Pliocene conglomerate, sand-stone, siltstone and limestone. Travertine and alluviumare the youngest sediments in the area. The general fault

trends are W–E, NE–SW and also NW–SE. Also, athrust zone is observed between the Mesozoic ophioliticmelange and limestone in the NW of the area. The

potential reservoir rocks are Paleozoic marbles, occa-sionally schist and Mesozoic limestone cut by faultzones in the region (MTA, 1996).

The Manisa Salihli geothermal field (HVK-11, HVK-12, HVK-13, and HVK-14) is located along the south-ern boundary fault of the Gediz graben. Salihli is known

for its Hg mineralization of hydrothermal origin. Thefield is currently under reconsideration as a prospect forepithermal 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 themetamorphic units. The major faults in the field trenddominantly E–W and NW–SW while N–S and NE–SWtrending faults also exist on a smaller scale. In the Salihli

geothermal field hot springs are concentrated in the Kur-sunlu and Sart areas. A total of 6 wells were drilled in thefield. The highest temperature (150�C) was measured in

the deep drill well, SC-1. The flow rate of this well reaches2 l/s (Karamanderesi et al., 1995; MTA, 1996).The Alasehir and Kavaklıdere geothermal field

(HVK-15, HVK-16, HVK-17, HVK-18) is located in theGediz graben. Drilling to a depth of 750 m revealedtemperatures of up to 116�C and production of natural

gas with 15% CH4 and 85% CO2 and thermal water(Karamanderesi et al. 1998). Alasehir fish farm is a localshallow well with a depth of 92 m and temperature of24oC into alluvium deposits. Alasehir mineral water has

a temperature of 31oC (Erentuz and Ternek, 1968).The Canakkale–Tuzla geothermal field (HVK-21,

HVK-22) is located 80 km SW of Canakkale, 5 km from

the Aegean coast. The Tuzla field is a volcanic area. Thestratigraphy of the field is composed of Permian meta-morphic basement rocks, granodiorite intrusive rocks,

Miocene volcanic rocks, including rhyodacitic, ignimbrite,trachyte and trachyandesite lavas, monzonite, and Qua-ternary and recent alluvium sediments (Karamanderesi,

1986; Simsek, 1997). Thermal water is derived from ashallow volcanic reservoir at a depth of 330–350 m and adeep granite reservoir at a depth of 1020 m. The thermalwater of Tuzla is unique due to the extremely high dis-

solved salt content, up to 63 g/l. Samples were collectedfrom hot spring and well T-1 at a depth of 814 m (HVK-21 and HVK-22, respectively).

The Edremit–Gure and Havran geothermal fields(HVK-23, HVK-24) are located at the Edremit bay in thesouthern part of the Kazdag massif. The geological

sequence includes the Paleozoic Kazdag formation (com-posed of gneiss, amphibolite, and marble and crystallizedlimestone), Triassic conglomerate, arkose, siltstone, Per-mian and Carboniferous limestone and marble blocks,

and Upper Miocene Bayramic formation that consistsof conglomerate, sandstone, claystone, shale and marl.Dikili-Bergama Kaynarca geothermal field (HVK-25)

is located in Western Anatolia, 90 km north of I.zmir

and includes more than 20 hot springs. Compressionalfields that formed during late Miocene to early Pliocene

control the geological structure. As a result, the areabecame a site of N–S oriented tensional stress fields. In anarea between Dikili and Bergama, there are many hot

springs whose distribution is controlled by fracture pat-terns. The geology of the Dikili–Bergama area comprisesvarious rocks such as sedimentary andmetamorphic rocks(Paleozoic to recent), Kozak granodiorite (Eocene to Oli-

gocene), Yuntdag Volcanics (Late Miocene to Pliocene),and Dededag Basalt (Pleistocene). A deep well that wasdrilled by MTA (K-1) yielded temperatures of up to


130�C. Since the volcanic activity and tectonic move-ments in the Dikili–Bergama area are very intense, it isassumed that the heat source of geothermal activityderives from both tectonism and volcanism (MTA and

JICA, 1987)The I

.zmir–Balcova geothermal field (HVK-26, HVK-

27) is located approximately 10 km SW of I.zmir. The

geological section includes Upper Cretaceous I.zmir flysch

composed of metasandstone, phyllite, limestone, serpenti-nite and diabase, the Miocene Yenikoy formation com-

posed of conglomerates, sandstone and siltstone, andPliocene Cumaovası volcanics, which includes andesite,agglomerate, tuff, and rhyolites. The geothermal systems

are fed by the main NE–SW, NW–SE and E–W trend-ing fault (Yılmazer et al., 1989).The Bodrum geothermal field (HVK-28) is located

south west of I.zmir on the Agean coast. Hydrothermal

mineral deposits and some mineral water exposuressuggest a large geothermal potential of that field (Kar-amanderesi, 1998). The prospect covers the contact zone of

the Menderes Massif and Taurus Belt (Ercan et al., 1984;Robert, 1995; Ozcicek and Ozcicek, 1977; Piskin, 1980).

4. Analytical procedures

During the fall of 1995, 26 representative hydro-thermal samples were collected from major thermal sys-tems in western Turkey. Analyses of major ions wereperformed at the Analytical Laboratory of the Hydro-

logical Service in Jerusalem. Lithium concentrationswere measured by ICP–MS (Element, Finnigan) at theUniversity of California Santa Cruz. Lithium intensities

were normalized to the internal standard of Be. Spike-freesamples were scanned before the analyses and no detect-able levels of Be were found in the original samples. Bro-

mine was determined by flow injection ion analyzer(QuickChem 8000) at the Hydrological Service laboratoryin 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 adirect loading procedure, in which B-free sea water and

natural solutions were loaded directly onto Re filamentsand measured in a reverse polarity NBS-style 12 solid-source mass spectrometer at the University of California

Santa Cruz. A standard deviation of less than 1.5% wasdetermined by repeat analysis of NIST SRM-951 stan-dard (11B/10B=4.013�0.005). Isotope ratios are repor-

ted as � p11B values, where

d11B ¼ 11B=10B� �

sample= 11B=10B� ��1

NBS 951

h i� 1000

Strontium was separated by cation-exchange chro-matography using standard techniques at the Depart-ment of Geology, Hebrew University of Jerusalem.

Isotope ratios were determined using third generationFaraday detectors in static mode on a VG-54WARPmass spectrometer at the University of California SantaCruz. Zone refined Re filaments were used. All mea-

sured 87Sr/86Sr results were corrected to a 87Sr/86Sr ratioof 0.1194 using an exponential correction law. Correc-tion for 87Rb was negligible for all samples. Using this

procedure, NBS-987 87Sr/86Sr yielded a ratio of 0.71025(� 0.00001; n=5) during the period in which theunknowns were run.

5. Results and discussion

The locations (Fig. 1), geological structure, source,temperature, salinity, water types, and lithology of theinvestigated thermal systems are presented in Table 1.

Chemical and isotopic results are presented in Tables 2and 3, respectively. The chemical composition (Fig. 2)suggests several water types with different distribution

of the major ion composition. The different proportionsof Cl, HCO3 and SO4 ions (i.e. their ratios to total dis-solved constituents in meq/l, or the Cl–SO4–HCO3 dia-

gram; Giggenbach, 1991) are used to determine 4 basicwater types (Table 1; Fig. 2): (1) Na–Cl– (in thermalwaters of Cumalı Seferihisar, Bodrum Karaada island

and Tuzla–Canakkale); (2) Na–HCO3 (Aydın Ilıcabası,Salavatlı, Denizli-Kızıldere, Urganlı, Salihli); (3) Na–SO4 (Dikili–Kaynarca–Bergama, Edremit–Gure, Edre-mit–Havran); and (4) Ca–Mg–HCO3–SO4 (Karahayıt,

Pamukkale). Some systems have mixed compositionslike Na–Cl–HCO3 (Germencik Omerbeyli, I

.zmir–Bal-

cova). The variation of dissolved ions as normalized to

Cl and evaporation-dilution of modern sea water areillustrated in Fig. 3. Most ions show enrichment relativeto sea water with similar salinity. The temperature–ion

concentration relationships are presented in Fig. 4. The�11B values and 87Sr/86Sr ratios of the thermal watervary from �2.3 to 18.7% (n=6) and 0.707864 to0.719479 (n=5), respectively.

5.1. Marine vs. non-marine sources

In the following discussion the authors distinguishbetween soluble ions (e.g. Cl, Br, B) and rock-formingelements (e.g. Na, Ca, HCO3) in order to evaluate the

origin of the geothermal water. Fig. 3 shows two dis-tinctive correlation lines between Cl and other ions,particularly for the Cl–Na coordination. It is argued

that high salinity, Na–Cl water composition, and thelow (Na/Cl<1) of thermal fluids from Cumalı Sefer-ihisar and Tuzla–Canakkale suggest that most dissolvedsalts, in particular Cl and Na, are derived from a marine

origin. On the other hand, all other thermal waters withsignificantly 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 K Sr Li Cl HCO3 SO4 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 0.00482 Cumalı Seferihisar Doganbey Kaplıcası hot spring 5/10/95 100 60 1840 166 3180 640 200 7.5 9.8 5.0 6000 0.9 1.0 0.01013 Germencik Omerbeyli 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 0.11314 Germencik Omerbeyli 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 0.11355 Aydın Ilıcabası 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 0.67776 Aydın Ilıcabası 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 0.66657 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 0.67568 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 – 0.66569 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 0.732510 Urganli Hot spring 6/10/95 15 14 520 50 70 1440 8 2.5 9.1 4.5 2120 11.5 1.6 0.430211 Salihli Sart hot spring 6/10/95 25 17 190 30 40 930 30 0.1 16.4 1.0 1250 8.1 – 1.476312 Salihi Kursunlu hot spring 6/10/95 10 12 350 60 0.6 70 1110 90 33.0 2.2 1650 8.4 – 1.666113 Salihli Kursunlu mineral water 6/10/95 90 50 210 6 20 820 180 1.3 1200 15.5 – 0.195216 Alasehir fish farm Well 6/10/95 51 150 380 20 180 990 640 2.2 0.2 1770 3.3 0.041117 Alasehir fish farm Well 6/10/95 26 30 110 10 30 510 80 1.2 0.3 720 6.5 0.142118 Alasehir hot spring Alasehir hot spring 6/10/95 8 150 360 20 0.2 80 1700 140 29.4 0.5 2340 7.2 1.250119 Karahayıt hot spring Karahayıt hot spring 6/10/95 143 110 120 30 30 1040 830 0.9 2.3 1470 6.5 0.105420 Parmukkale Pamukkale hot spring 6/10/95 186 80 50 6 4.5 13 940 600 1.1 1.0 1280 5.6 0.269921 Canakkale–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 0.002622 Canakkale–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 0.002423 Edremit–Gure Well near Gure 7/10/95 25 – 270 7 65 60 430 0.4 3.0 6.1 430 6.3 0.152924 Edremit Havran Well Havran Kaplıcaları 7/10/95 41 – 260 6 60 30 460 1.9 4.7 410 6.2 0.097425 Dikili–Kaynarca–Bergama Well–1 7/10/95 17 6 450 30 60 480 530 3.0 4.8 1050 12.0 0.169126 I

.zmir–Balcova Balcova deep well 7/10/95 25 7 350 30 0.5 160 540 140 10.9 6.0 1130 3.3 0.2170

27 I.zmir–Balcova Balcova 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

etal./

Applied

Geochem

istry17(2002)163–183

171

constituents are derived from water-rock interactions.The Br/Cl ratios of the thermal waters can also be usedto distinguish marine from non marine sources, as all ofthe Cl-enriched marine water has typically Br/Cl ratio4sea water (Fig. 3).The different potential marine sources are deep circu-

lation of modern seawater, fossil seawater, and dissolu-

tion of marine evaporites. Assuming that deepcirculation of seawater was the source of the dissolvedsalts, one would expect to have seawater composition,

particularly for conservative elements such as Cl and Brthat are less affected by water-rock interactions. Kar-amanderesi and Helvacı (1994) measured the Br con-

centrations in different rock types in the Menderesmassif and found negligible Br levels (<1 ppm). Thus,modern Mediterranean seawater would have a chloridecontent of <22,000 mg/l (i.e. lower concentrations canbe derived from dilution with meteoric water) and a Br/Cl ratio of 1.5�10�3. The only water sources that havesimilar chemical characteristics are the saline water from

Cumalı Seferihisar (with Cl content of 10,926 mg/l) andBodrum 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 SO4/Cl ratios,d11B value of 2.3%), however, are different from thoseof seawater and suggest that the original seawater wasmodified by intensive water-rock interactions. The

depletion of Mg and enrichment of Ca, B, Li, and F, aswell as the depletion of �11B are typical of oceanichydrothermal water (Spivack et al., 1987; You et al.,

1994). This conclusion is consistent with the chemicaland �18O data reported by Conrad et al. (1995) whoshowed 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

0.7�10�3, which are higher and lower than those ofseawater, respectively. In addition, the Tuzla brines arecharacterized by a d11B value of 18.7%, 87Sr/86Sr ratioof 0.709633 (Table 3), and d34S of 12% (Mutzenberg,

1997). Balderer (1997) and Mutzenberg (1997) suggestedthat the Tuzla brines were derived from lateral migra-tion of fossil Miocene brines that were trapped in the

Miocene sediments. The fossil brines could have origi-nated from relics of evaporated sea water trapped in thesediments (e.g. Vengosh and Starinsky, 1993; Vengoshet al., 1994, 1998) or, alternatively, from dissolution of

Messinian evaporites.Several lines of evidence suggest that the Tuzla ther-

mal water could not be derived from evaporated sea

water. First, relics of evaporated sea water or diag-enetically modified sea water (e.g. Dead Sea) would havehigh d11B values (d11B >39%) as demonstrated recentlyby the composition of pore water from the Mediterra-nean with d11B values of up to 66% (Vengosh et al.,2000). In contrast, salts derived from evaporite dissolu-

tion would have lower d11B values (<39% Vengosh etal., 1992; 1998). In high-temperature environments,however, a large fraction of the dissolved B is alsoderived from leaching of the rocks. Thus, the original

isotopic composition could be modified. This is clearlydemonstrated in the case of thermal water from CumalıSeferihisar where marine Na/Cl and Br/Cl ratios are

associated with non-marine low �11B values (2.3%) andhigh B/Cl ratios. The d11B values of the hypersalineTuzla thermal water is 18.7% which is significantly

higher than the values expected for leached B from localigneous rocks (granodiorite, trachyandesite, trachyte,rhyodacite, ignimbrite) with d11B �0%. The relativelyhigh d11B can be interpreted as a reflection of modifiedhigh d11B evaporated sea water that was modifiedtowards lower d11B values due to water–rock interac-tion. Alternatively, the relative lower d11B value mayindicate dissolution of late-stage evaporites withd11B<39%.Second, the Na/Cl and Br/Cl ratios of the Tuzla water

are not consistent with the ratios expected for evapora-tion of sea water. During >10-fold evaporation beyondthe halite saturation stage, the residual evaporated sea

water has Na/Cl<0.86 and Br/Cl>1.5�10�3 (McCaf-frey et al., 1987). Fig. 5 illustrates the evolution of eva-porated seawater compared to the composition ofthermal water from the Tuzla and Seferihisar thermal

waters. The data points are not consistent with the eva-poration line (i.e. low Br/Cl ratios below the seawaterratio) and thus rule out the relic sea water model.

Table 3

Isotopic data of geothermal waters from western Turkey

ID Name Source Date 87Sr/86Sr d11B

1 Cumalı–Seferihisar Well CM-1 5/10/95 2.31

3 Germencik–Omerbeyli Well OB-9 5/10/95 0.710867 �0.17

5 Aydın–Ilıcabasi 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 Canakkale–Tuzla Tuzla well T-3 7/10/95 0.709633 18.70


Fig. 2. Pie diagrams of the chemical composition (in meq l�1) of selected geothermal fields from western Turkey.


Third, the 87Sr/86Sr ratio of 0.709633 and d34S valueof 12% are respectively higher and lower relative to theexpected Miocene fossil evaporated sea water (87Sr/86Sr

�0.7081; d34S �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 reflectthe mineralogical composition of these deposits with apossible mineral assemblage of gypsum and Ca- and

Na-borates. This mineral composition is typical formany Neogene salt-deposits in western Turkey (Helvacı,1994, 1995; Palmer and Helvacı, 1977).

5.2. The impact of water–rock interactions and origin ofboron

Following the Ellis and Mahon (1977) classification,HCO3

� waters are considered to occur in volcanic geo-thermal areas where steam containing CO2 condenses

into the liquid phase. Bicarbonate water can also reflectinteraction of CO2 charged fluids at lower temperaturesand migration path as well as mixing with local groundwater (Giggenbach, 1991). Sodium–HCO3 waters are

common in geothermal systems associated with meta-morphic rocks which is consistent with the generallithology of the Menderes Massif (Table 1) and the high

Fig. 3. Log chloride vs. log dissolved salts concentrations in geothermal waters from western Turkey.


CO2 content that is typical of the thermal water of wes-

tern Turkey (Filiz, 1984; Ercan et al., 1994). The originof the high dissolved CO2 according to d13C and Heisotopic data is magmatic (Filiz, 1984; Ercan et al.,

1994). The Na–HCO3 chemical composition is therefore

a combination of high CO2 flux and extensive water-rock interactions with metamorphic rocks. Similarly, theNa–SO4 water type can be derived from H2S condensing

Fig. 4. Source temperatures (as measured in the investigated thermal systems) vs. different dissolved ions (mg/l) in geothermal waters

from western Turkey.


into the liquid phase as well as from interaction withsulfate minerals (e.g. Ellis and Mahon, 1977).

The dependence of the ion composition on tempera-ture is demonstrated by the correlations between differ-ent ion concentrations and temperatures measured in

the thermal sources (Fig. 4), particularly for Na, K, Mg(reverse correlation), B and F. These positive correla-tions clearly indicate that much of the dissolved salts ofthe non-marine thermal waters are derived from water–

rock interactions. The chloride–temperature relation-ship may also reflect an absorption of HCl gas into theliquid phase as well as extraction of Cl from the rocks.

It seems that only in the Germencik Omerbeyli system isCl 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 chemicalcomposition of the hydrothermal water. Thus, the linearcorrelations 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.Gokgoz (1998) showed that geothermometry tempera-tures calculated by applications of Na–K and Na–K–Ca

geothermometers of geothermal water from Kızılderearea vary between 188 and 245�C which is consistentwith actual temperatures measured at the bottom of

research wells in that area.While the HCO3 ion can be derived also from mixing

with cold shallow groundwater, it seems that the HCO3/

TDI ratio, which would be less affected by dilution, canbe a useful tracer for delineating the sources of the salts.Positive correlation between the HCO3/TDI ratio andNa/Cl, K/Cl, and B/Cl ratios (Fig. 6) probably reflects

the role of CO2 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 CO2 and HCl gases can thus be considered as thetriggers for the intensified water–rock interactions andenhance 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 relativeenrichment of Br can be explained by extraction of Brfrom organic matter in the Tertiary sediments, or, from

preferential degassing of Br gases from deep sources. Thehigh linear correlation between Cl and Br that char-acterizes the thermal water favors the second possibility.

Thermal waters from western Turkey have typicallyhigh B content, which also causes environmental andoperational problems. The association of high B and

high CO2 levels led Tarcan (1995) to suggest that B isalso derived from a deep mantle source. Demirel andSenturk (1996) also suggested that high B, NH4, andCO2 concentrations in thermal water from the Kızıldere

geothermal field reflect ascent of magmatic emanationsfrom depth although there is no evidence of recent vol-canic activity in the area. Based on 3He/4He ratios,

Gulec (1988) argued that the involvement of mantle-derived He, in the Kızıldere geothermal field does notexceed 30%.

Two models should therefore be considered for theorigin of B in the thermal water: (1) dissolved Cl, HCO3,and B are derived from deep mantle flux of HCl, CO2and B(OH)3 gasses; or (2), water-rock interactions leachB to the liquid phase. Next, these two conflicting modelswill be evaluated.Karamanderesi and Helvacı (1994) and Karamander-

esi (1997) measured REE and other elements extractedfrom well cuttings and core rock samples from differentgeothermal 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 800to 1600 ppm) relative to those (independent oflithology) of the Omerbeyli field (OB-7, a range of50–230 ppm). The difference in the B content of

the rocks is also reflected in relatively higher B/Clratio in the associated thermal waters from thesetwo systems (0.7 relative to 0.1), whereas the

absolute B concentrations are similar.2. Boron is unevenly distributed among differentrock types. Boron is particularly enriched in

(decreasing order) quartz vein, tourmaline gneiss,illite–chlorite–feldspar zone, and quartz–chloriteschist zone. Boron is relatively depleted in marble

and gabbro.3. The vertical distribution of B (and Li) with depthis not uniform and is heavily dependent on thelithology. Boron is depleted in the marble zone in

the Omerbeyli field (�50 ppm B at depth of 1400m) relative to the albite-amphibolite schist zone(�200 ppm, �1400 m).

Fig. 5. Na/Cl vs. Br/Cl ratios of evaporated sea water as com-

pared to those from thermal water from Tuzla and Seferihisar.


If indeed all of the B was derived from deep mantleflux as argued by Tarcan (1995) one would expect tohave uniform B composition with similar B/Cl ratios inall of the thermal systems (i.e. the B/Cl ratio is used to

eliminate the dilution factor). Moreover, one would notexpect to have any relationships between B contents inlocal rocks and thermal waters, and yet the Salavatlı

geothermal field is significantly enriched in B relativelyto the Omerbeyli field.Boron is easily leached from rocks and remains in its

volatile form even at lower temperatures relative to theHCl that is converted to less volatile NaCl. The B/Clratio can thus be used to assess the maturity of the

thermal system. Fluids from older systems are expectedto be depleted in B relative to young systems (Gokgoz,1998). The large difference between the Salavatlı andOmerbeyli fields may be related to this factor. Conse-

quently, it seems that B is mainly derived from localwater-rock interactions and the source rocks stronglycontrol 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 becontrolled by the original B concentrations in the rockor original parent magma fluids, as well as the degree of

maturation in which water-rock interactions can con-tribute B to the thermal system.Since the lower mantle reservoir is enriched in pri-

mordial 3He with respect to shallow MORB and radio-genic 4He is generated by the decay of unstable isotopesof U and Th and radiogenic 3H in the crust, the 3He/4He

ratio can be a sensitive tracer to detect the presence ofmantle helium in thermal water (Gulec, 1988; Hoke etal., 2000). The 3He/4He ratio is normalized to atmo-

spheric He (R/Ra=1) and consequently deep manle-derived He would have high R/Ra values (>30)whereas crustal He production has a low ratio (R/Ravalues of a typical continental crust are 0.005 to 0.02).

While springs from the vicinity of Germencik–Omer-beyli yielded R/Ra values of 0.2 to 0.8 (n=3), which istypical of a crustal source, a spring from the Denizli

Fig. 6. HCO3/TDI ratio vs. Na/Cl, K/Cl, and B/Cl ratios of non-marine water from western Turkey.


area had a significantly higher value of 2.5 (Gulec,

1988). Consequently, the available 3He/4He data insprings from western Turkey does not exlusively indi-cate on the origin of He, which in turn cannot supportany evidence for the origin of B. Moreover, in the Ger-

mencik area thermal water has a low 3He/4He ratio thatindicates a crustal source, while the B content is thehighest among the investigated thermal waters.

Previously, special attention has been given to the Bisotope composition of hydrothermal fluids from amarine setting. The B isotope composition of hydro-

thermal fluids such as those venting from mid-oceanridge crests (d11B ¼26.7 to 36.8%) suggests a mixturebetween seawater B and MORB-derived B leached from

the basalt without resolvable isotopic fractionation(Spivack and Edmond, 1987). Hydrothermal fluids froma sediment-starved back-arc spreading center (MarianaTrough; d11B ¼22.5 to 29.8%; Palmer 1991) and from aclassic sediment-hosted basin (Guaymas Basin andEscanaba Trough; d11B=10.1 to 23.2%; Spivack et al.,1987; Palmer, 1991) are characterized by lower d11B

values and higher B concentrations, reflecting interac-

tions with the hosted rocks. Thermal fluids from con-tinental geothermal fields are characterized by evenlower d11B values (Salton Sea, California, d11B ¼ �2.6to �1.1%; Yellowstone National Park, d11B ¼ �9.3 to

4.4%; Palmer and Sturchio, 1990), reflecting the iso-topic compositions of the source rocks. The influence ofseawater B in geothermal systems has been traced in

central Japan (d11B ¼ �5.8 to 27.1%; Musashi et al.,1988) and Iceland (d11B ¼ �6.7 to 30.7%; Aggarwal etal.,1992).

The B isotopic composition cannot be used to distin-guish between mantle flux and rock leaching processesdue to the overlap in the isotopic composition of these

two sources. The d11B range of the Na-HCO3 waters is�2.3 to 1.8% (Table 3; n=3) and can thus reflect bothleaching of igneous rocks and flux of mantle B (e.g.Spivack and Edmond, 1987). The B-isotope fractiona-

tion is controlled by the B species as B with tetrahedralcoordination is isotopically depleted (low d11B) relativeto B with trigonal coordination. Selective formation and

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).


removal of B(OH)3 species may cause a relative deple-

tion of d11B in the residual fluid. Nevertheless, it seemsthat the magnitude and thus the effect of this isotopicfractionation is negligible in high-temperature environ-

ments.

5.3. Distribution of the water types

The thermal systems of western Turkey exhibit a widerange of chemical composition that reflect the complexnature and different sources of thermal waters (Table 1).

As shown above, the authors distinguish between 4

major groups that reflect different origin and mechanismof water-rock interactions.The Na–Cl type originated from deep circulation and

water–rock interactions of modern sea water in the caseof Seferihisar and Bodrum systems and from deep fossilbrines originated from dissolution of Miocene evapor-ites in the case of Tuzla geothermal waters.

The Na–HCO3 type characterized thermal watersfrom the systems of Aydın Ilıcabası, Salavatlı, Urganlı,Alasehir, Denizli–Kızıldere and Salihli. Thermal waters

Fig. 8. Schematic illustration of different geothermal water types from western Turkey.


from Germencik Omerbeyli and I.zmir–Balcova have a

mixed Na–Cl–HCO3 water composition. d18O–dD data

(Filiz, 1984; Ercan et al., 1994) suggest that the origin ofthese waters is meteoric whereas the temperature–ion

concentrations relationships suggest that most of thedissolved constituents (Fig. 4) were derived from exten-sive water–rock interactions. As shown above, the high

CO2 content that characterizes these waters, presumablyderived 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 themetamorphic of the Menderes Massif (GermencikOmerbeyli, Aydın Ilıcabası, Salavatlı, Urganlı and Sal-

ihli). Yet in other systems, where the local rocks arecomposed of other rock units (e.g. Manisa–Urganlı–serpantinite and limestone) the associated thermalwaters also have a Na–HCO3 composition. The87Sr/86Sr ratio of Na–HCO3 type thermal water(0.710867 in Germencik Omerbeyli and 0.71449 inAydın Ilıcabası) reflect leaching of Sr from a high-

radiogenic source, which suggests that the source rockhas a high Rb/Sr ratio). The system of Denizli-Kızıldereis one of the highest enthalpy geothermal field and most

producing field in Turkey. The d18O�dD data indicatesthat the origin of the water is meteoric, modified byintensive water-rock interactions. In addition, Gokgoz

(1998) showed that calculated temperatures based onchemical geothermometers are similar to measuredtemperatures of up to 245�C. The high 87Sr/86Sr ratio(0.719479) of the geothermal water from Kızıldere sys-

tem suggests that the deep aquifer units (schist andquartzite) are the predominant rock sources of Sr whilethe shallow limestone unit has negligible effects on the

dissolved Sr budget in the thermal waters.The Na–SO4 type characterizes thermal waters from

Edremit–Gure and Havran and Dikili–Kaynarca geo-

thermal fields, which are located at the Edremit bay inthe southern part of the Kazdag massif. Sulfate can bederived from hydrogen sulfide condensing into theliquid 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 systemsin the Menderes Massif with a Na–HCO3 composition,

it seems that the second explanation can be ruled out.The Ca–Mg–SO4–HCO3 type characterizes geother-

mal systems from Karahayıt and Pamukkale. It seems

that this composition reflect shallow sources and inter-action with shallow carbonate rocks. The Pamukkalehot spring has a 87Sr/86Sr ratio of 0.707864 that is dis-

tinctively low relative to the other non-marine thermalsystems. This low 87Sr/86Sr signature reflects interactionwith carbonate rocks of the Pliocene Sazak formationthat consists of intercalated limestone, marls and silt-

stone, or the Pliocene Kolonkaya formation composedof alternating layers of sandstone, claystone and clayeylimestone. The low 87Sr/86Sr ratio rules out interaction

with the underlying Paleozoic Menderes metamorphic,which is consistent with the chemical composition ofthis water type.

6. Conclusions

The chemical data, combined with isotopic data for Band Sr of thermal waters from western Turkey reveal 4types of water, which originate from marine and non-

marine sources. The marine source has a Na–Cl com-position and Na/Cl ratio<1 whereas the non-marinewaters typically have Na/Cl>1 (Fig. 8). The Br/Cl ratio

is used to distinguish between direct penetration of seawater or recycled marine salts in the form of evaporitedissolution. The non-marine water shows 3 types ofchemical compositions, reflecting different source rocks

and depth of circulation. Na–HCO3 and Na–SO4 com-positions reflect deep circulation and interactions withmetamorphic rocks and gneiss while Ca–Mg–SO4–

HCO3 composition is associated with shallow circula-tion in carbonate rocks and mixing with cold groundwater. The 87Sr/86Sr ratio further constrains the nature of

the source rocks (i.e. igneous and metamorphic versuscarbonate rocks). Systematic changes in Na, K, Ca, andMg with temperature (Fig. 4) show that concentrations of

these dissolved constituents are largely dependent on thetemperature and depth of circulation. Water–rock inter-action results in high concentrations of dissolved con-stituents such as Na, K, and B. The data suggest that B

is derived from water–rock interaction rather then deepmantle flux of B(OH)3 gas. The high B concentration inthe thermal water is typical of many non-marine geo-

thermal fields, worldwide, and thus can be used as asensitive tracer to monitor advection and mixing ofunderlying geothermal fluids with shallow groundwater.

Acknowledgements

We thank Irena Pankratov (Hydrological Service,Jerusalem) for her dedicated laboratory work. We thankJim Gill (University of California at Santa Cruz) for his

generous hospitality and allowing A.V. to use hislaboratory. We are especially grateful to MTA and themanagers for their generosity during fieldwork in Tur-

key. We appreciate and thank Randy L. Bassett, GeorgeSwihart and an anonymous reviewer for their thoroughreview of the earlier version of the manuscript.

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