Conceptual model of the Gülbahçe geothermal system, Western Anatolia, Turkey

19 Pages·2017·10.36 MB·English

by  Taygun Uzelli

Geothermics68(2017)67–85

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Geothermics
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Conceptual model of the Gülbahc¸e geothermal system, Western

Anatolia, Turkey: Based on structural and hydrogeochemical data

TaygunUzellia,AlperBabab,∗,GamzeGülMunganb,R.KadirDirika,HasanSözbilirc

aHacettepeUniversity,DepartmentofGeologicalEngineering,06800,Ankara,Turkey
bI˙zmirInsti tuteofTech nology,Geot he rmalEnerg yResearchan dAppl icationC enter,35430,I˙zmir,Turkey
cDokuz EylülUn iv ersity,Earth quakeResea rchand Applicati onC enter,35100 ,I˙zmir, Turkey

a r t i c l e i n f o a b s t r a c t

Articlehistory: TheGülbahc¸eGeothermalFieldislocatedontheeasternmarginoftheKaraburunPeninsula,about45km
Receiv ed20March2016 from thecity ofI˙zmir,we stern An atolia, Tur key .Thest ratigrap hy of thestudya reaisrepre sente db ya
AReccceepivteedd i1n6 rMevaisrechd 2fo0r1m7 10 March 2017 Mioc ene volc ano-sedim entary s uccession , includ ing s everal sedim en tary and vo lcan ic units. These u nit s
overliethebasementrocksoftheKaraburunPlatformandBornovaFlyschZonewhichconsistofsand-
Availableonline22March2017
stones,shalesandcarbonateblocks.TheserockunitsarecutanddeformedbyaseriesofNW-SE-to

NE-SW-trendingfaults,extendingfromSıg˘acıkBaytoGülbahc¸eBay.Structuralstudiessuggestthatwhile
Keywords:
mostofthegeothermalsystemsinwesternAnatoliaarecontrolledbynormalfaults,thegeothermalsys-
Geothermal fluid tema tG ülb ahc¸eiscontr olledby as trike-slip dominat eds hearzone, pr eviously name dth eI˙zmir-Balık esir
Gülbahc¸efaultzone
INseogtoaptieve fl owe r structure oTrfahnysdferor tZhoenrem. Aallloynmg othdeifi faeudlts ezaonwea, taesrs,oacniadtitohnuss otfh aectrievseu fltaiunlgt sneeggmateivnetsfl aocwcoemrmstroudcattuer edeiespt hceircpurilmataiorny

Highsalinity controlmechanismforthegeothermalsystem.
Hydro geochemica lpr ope rtiesofthefi eldshowthatsurfacetemperatureoffluidrangesfrom30to34◦C.

GeothermalfluidsinGülbahc¸ehavehighsalinity(EC>34mS/cm)andlowenthalpy.PiperandSchoeller

diagramsindicatethatgeothermalfluidisintheNaClfacies.Chemicalgeothermometerssuggestthat
thereserv oirtemp erat ureisaroun d53– 13 6◦ C.T heiso topic data(oxyg en-18,deuterium andtrit ium)

suggestthatgeothermalfluidsareformedbylocalrechargeanddeepcirculationofseawater.

©2017ElsevierLtd.Allrightsreserved.

1. Introduction ofMacedonia,Bulgaria,AlbaniaandWestAnatoliaarelocatedinthe

AegeanExtensionalProvince(AEP),whichisoneofthemostrapidly

Geological framework has been an important focus for inter- extendinganddeformingareasonthecontinenttoday(Robertsand

preting and finding suitable locations for geothermal systems Jackson,1991;Bozkurt,2001;BozkurtandMitwede,2001).

without any surface manifestation. Stratigraphic sequence, cap DeformationduetotectonismcausesN–Sextensionandforms

rock, reservoir rock, permeability and porosity, fluid dynamics, normal faulting with the development of many E–W oriented

fault-fracturerelationstoregionaland/orlocalstressregime,and continental basins in the AEP (S¸engör et al., 1985; Yilmaz et al.,

heatflowinlithospherearerequisiteparameterstodevelopafavor- 2000).Thegrabensystemsandmajorfaultsaccompaniedbyyoung

ablegeothermalsystem. volcanismformabundantgeothermalareasintectonically-active

Fromtheglobalviewpoint,platetectonicscontrolthethermal westernAnatolia(Bozkurt,2001).Geothermalspringsinwestern

conditionsinthecrustandgeothermalsystemsareshapedbylarge- AEProughlyparallelthetrendsofthegraben-boundingfaultsofthe

scalemovementsofplates.Likewise,geothermalsystemsinTurkey MenderesMetamorphicCoreComplex(MMCC),youngvolcanism

fallwithintheactiveAlpine-HimalayanFoldandThrustBeltwhere andgenerallyhydrothermallyalteredareas(S¸imsek,1997;Mutlu

the collision of African and Eurasian plates and also the closure andGülec¸,1998;S¸imseketal.,2002;BabaandÁrmannsson,2006;

oftheTethysOceanoccurstoday(Bozkurt,2001).Aspartofthe BabaandSözbilir,2012)(Fig.1(a)).

Alpine-HimalayanFoldandThrustBelt,theAegeanSea,Greece,FYR Fig.1showsthegeologicalmapofwesternAnatoliawiththe

maingraben-horststructureswhicharelimitedbyamajorstrike-

slipshearzoneatthewesternboundaryoftheregionwherethe
stud yarea isloc at ed.T hestrike -slipshear zo ne, namely theI˙zm ir-
∗ Correspondingauthor. Balıke sirT ra nsferZon e(I ˙BTZ),prev iously acted asade epcrustal
E-mailaddresse s:[email protected],[email protected](A.Baba).

http://dx.doi.org/10.1016/j.geothermics.2017.03.003
0375-6505/©2017ElsevierLtd.Allrightsreserved.
68 T.Uzellietal./Geothermics68(2017)67–85

Fig.1. (a)TectonicmapoftheeasternMediterraneanregionshowingmainneotectonicstructuresanddistributionofgeothermalareasofTurkey(compiledfrom;S¸imsek

etal.,2002;Yig˘itbas¸etal.,2004;BabaandArmannsson,2006;BabaandSözbilir,2012)(SBT,SouthernBlackSeaThrust;NAFZ,NorthAnatolianFaultZone;NEAFZ,Northeast

AnatolianFaultZone;EAFZ,EasternAnatolianFaultZone;WAGS,WesternAnatolianGrabenSystem;DSF,DeadSeaFaultZone;BZS,Bitlis-ZagrosSuture)(b)Simplified

tectonicmapofwesternAnatoliawithknowngeothermalfields(afterSözbiliretal.,2011)withthezoneofstrike-slipfaulting.

transformfaultzoneduringtheLateCretaceous,whileduringthe TheNE-SW-trendingI˙BTZincludesstrike-slipfaultsthatgen-

Neogene stress regimes in the region changed and it was con- erally have N-S, NE-SW and NW-SE orientations. Some of the

trolled by transtensional stresses (Okay and Siyako, 1993; Okay strike-slipfaultsformgeothermalsystemsintheregionbetween
etal.,1 99 6;Ringetal.,1 999;Söz biliret al., 2008;Sö zbilir etal., Balıkesir a nd I˙zm ir ci ties. The so uthern p ar t of the I˙B TZ, I˙zmir

2011;ÖzkaymakandSözbilir,2008;UzelandSözbilir,2008;Uzel anditssurroundings,containsimportantgeothermalfieldssuchas

etal.,2012,2013,2015;Özkaymaketal.,2011).Thetranstensional Balc¸ova,Seferihisar,Dikili,Bergama,Özbek-IlıksuandC¸es¸me,and

tectonic regime also controls the deformation of pre-Neogene alsotherearemanyhotwaterspringsonKaraburunPeninsula.The

basementrockunits,Miocenevolcano-sedimentaryunitsandQua- studyareaislocatedontheeasternmarginofKaraburunPeninsula

ternaryunits(Fig.1(b)).
T.Uzellietal./Geothermics68(2017)67–85 69

andisabout45kmfromthecityofI˙zmirinthesouth-westcoast Kocadag˘volcanicscompriselavas,pyroclasticblocksandashflow

ofGülbahc¸eBay(Fig.1(b)).TheGülbahc¸eregionhastwoimpor- deposits.Theandesiticlavasarecharacterizedbyplagioclaseand

tanthot-waterspringswithgeothermalorigin;Gülbahc¸eandIlıksu brown amphibole phenocrysts in a glassy matrix (Helvacı et al.,

springs.Ilıksugeothermalspringislocatednorth-eastofGülbahc¸e 2009).TheunitinterfingerswiththeMiocenevolcano-sedimentary

Bayandapproximately6kilometersfromthenorthernborderof unitsandwaspreviouslydatedas16.6and17.3Ma(K-Arages)by

ourstudyarea.Thesetwogeothermalspringsarebothtectonically Borsietal.(1972)(Fig.2).Intheeastofthestudyarea,Urlavolcanics

controlledandhavedirectconnectionwithsea-waterintrusion. were emplaced with fine grained rhyolitic lavas and porphyritic

Thisstudypresentstheresultsofamultidisciplinaryapproach domeswithtrachyte-likeporphyriticrhyolitedomes(Kaya,1981;

aimedatunderstandingtherelationshipbetweentectonicsetting Helvacıetal.,2009).Theunitcutsandunconformablyoverliesthe

andgeothermalsystemsintheregionandtoevaluatehydrogeo- limestones of the Miocene volcano-sedimentary succession. The

chemicalfeaturesofgeothermalfluidinthisregion. UrlavolcanicshavebeendatedbyBorsietal.(1972)to11.7and

11.9Ma(K-Arages).

HigherinthesequencetheMiocenevolcano-sedimentaryunit
2. Geologicalsetting
contains thick-bedded white limestones and brown/gray mud-

stone, marl, interlayers and limestones crop out extensively in
2.1. Stratigraphy
south-eastern parts of Gülbahc¸e Bay (Kaya, 1981). The Miocene

deposits are unconformably overlain by Quaternary deposits;
The rock units exposed in the study area are divided into
Pleistocene Ballıkaya conglomerate, and Holocene deposits. In
two main groups for simplification in the study: basement and
Gülbahc¸esub-basin,Pleistoceneconglomerateshavewidespread
coverrocks.ThebasementismadeupofTriassic-Jurassicrocksof
distributionandthickentowardsBallıkayaHill,whereitexceeds
KaraburunPlatformCarbonatesandUpperCretaceoustoPaleocene
40–45m. The unit has clast-supported texture and alternating
rocksofBornovaFlyschZone(BFZ).Theunconformably-overlying
gravel grains of several different rock types interbedded with
cover rocks are Miocene volcano-sedimentary units and Quater-
claystone-mudstone-sandstone layers. The facies of the unit is
narydeposits.Basementrocksoutcroponthesouth-easternsideof
interpreted as channel-fill conglomerate. The unconformably-
thestudyareaandareboundedbytheGülbahc¸eFaultZone(GFZ).
overlyingHoloceneunitsaregenerallyalluvialfan/plaindeposits,
Regionally, cover rocks were deposited in Urla Basin, and were
colluvialdepositsnearsteepslopesoffaultscarpsandfan/deltato
accompanied by Miocene volcanic units which are the products
shallowmarinedepositsalongtheshorelineofGülbahc¸eBay.
oftwo-phasevolcanicactivity(Fig.2and3).

2.1.1. Basementrocks:Pre-Mioceneunits

Theoldestbasementrockunitsinthestudyareaarecarbon- 2.2. Tectonicframeworkoftheregion
atesof theKar aburunPla tform whi ch isal socall edth eKa raburun

Beltintheliterature(Erdog˘an,1990;Kozur,1997;Robertsonand Therearecloserelationshipsbetweentectonicframeworkand
Pick ett ,200 0).TheKa raburunPl atform isone ofthem ostimpor tant hydrogeo che mical propertiesin localgeo thermal systemssuc has
tectonic beltsw est oftheMM CCandth e BFZ .R ock softh eKarabu- Gülbahc¸e.Moresp ecifically,w he reth egeotherma lsystem isco n-
runPlatf orma recl ose lyr elatedt oev olut iono ftheT et hya nOcean trolledb y secon darypermea bility, the studyofthe fractur e, joint
(Erd og˘an,199 0). andfau ltn etworkisi mportanttou nder stand un kno wnflowp ath-
In the study area, Karaburun Platform is represented by two way sinh ydrother m alsystems .T hereforethe geotherm alsy stem
forma tion s: Noh utala n and Güve rcinlik Fo rm ations. The latt er is wasi nve stigatedwith structura ldataforb ett erunderstan dingof
madeupof Carnian-Rh aetia nooliticlim estoneswith Me galodo n, theg eometryoft hesy stem.
and g ree n, yellow to red silts tone, s andstone a nd pi solitic con- T heGülbah c¸e ge othermalfieldislocatedonthewesternmar-
glom eratew ithiro na ndb auxite.Als oinsomea reas theform ation gin of Urla basi n , which is a depo si tional e nvi ronm ent bet ween
haslightg rayla mina ted dolomite and w hited olomi ticl imestones Kar abu run Platfor m and th e BFZ. Landfo rms in Urla B asin are
(Lec hner et al ., 1967; Br inkmann , 196 6; Bri nkmann e t al., 1972; mainlycon trolledby Gül bahc¸ eand Seferihisar Fa ultZo nes(S FZ),
C¸akmako g˘lu an d Bilgi n, 2006). Th ese sha llow marin e l ime stones at the western an d eastern m argin s of the b asin, respec tively.
h aveawides prea dsurfa ceand subsur facedist ribution inthearea Am ong them,D emir cili-Yag˘c ılar(DYFZ )a ndK us¸c¸ula r-Urla(KUFZ)
and a r e gradationa l with the N ohutalan Formation (F ig . 2). The fault zo nes ex tend between Gü lbahc¸e Bay and Sıg˘acık B ay, and
Noh utal anFormation isa unifo rmunitwi thlimeston es,do lom itic are p ossibly under the contr ol of str ik e-sli p fau lting of the I˙BTZ
limestones andlimest on e withClad ocor opsis sp.fossils(B rinkmann (Fig .3).Due tothe com binatio no fthesefau ltzones, fo urdiffer-
etal.,1972) .The formation isLi assic-Malmin age ,gray incolor,500 ent s ma ll su b-b asin s have been for med in Url a Basin ; the se are
th ick m and wa s deposite d in shallow m ari ne r eef e nv ironm ent I˙c¸m eler, T urasan, Kus ¸c¸ular and G ülbahc¸e su b-ba sins (F ig. 3). The
(C¸akm ak og˘lu and Bilgin,200 6). G ülbahc¸ esub-bas inis l ocat edon thesou th -westcoast ofGü lba hc¸e
TheBFZis atec tonicb eltlyingbetweentheMMCCandKarabu- Bay and i s tectonica ll y borde red by approxima tely N -S -trendin g
run Pla tfor m . The BFZ , wh ich i s also kn ow n as th e “ Bornova faul tsth at areconsiste ntwithits tra nstensionalori gin.TheN-S-
com plex” (Erd og˘an , 199 0), has a defo rmed U ppe r Cr etaceous- trendi ngsu b-b asinisabou t2km w ideand6kmlo ngand con tains
Paleocene aged mat rix. The ma tri x contains differe nt blocks of up to 70 0–800m t hi ck Mio c ene volc ano- se dim enta ry u nits and
various lit holog ies; Mes ozoi c limest ones, rad iolarites, ultraba sic Ple isto cenecon glo mera tes(Pamu kc¸uetal.,2014).
rocks,a ndalteredb asicvolcan icrocks.The BFZisunco nformably TheTura san,Kus¸c¸ulara ndI˙c¸mel er su b-b asinsarealsotectoni-
overla inby theMi ocene andQua ternar ycov eru ni ts. callyco ntrolled and b orde redby NW- SE-andN-S -tre ndin gfaults.

ThesethreeadjacentbasinscontainrecentalluviumandMiocene
2.1.2. Coverrocks:Mioceneandquaternaryunits volcan o-sed imentary unitsn earthe surface .I˙c¸melera ndG ülbahc¸e
Th e Mioc ene v olcano-s edim entary un it is composed of con- sub-basinsaresepara tedb yana rro wridgem adeup of basemen t
glomer ates, sand stone and mudstone alte rna tions, follo we d by limestones .Th eridgecou ld p ossibly havef ormed by u pliftingof
yellow/whit ethinbedd edan dweather edfresh-wate rlimeston es. basementro cks simila rtoth eformat iono ftheTur asa n,Kus¸c¸u lar
Duringdepos ition ,twovo lcani cunitswer eemplaced inthestudy andI˙c¸mele rsub -basins, wh ich aresepara ted by upliftedl imes t one
areain theearlyM ioce ne.Inth ewes ternp artofthe st udy area; outcro psof Mioceneun its(Fig .4).
70 T.Uzellietal./Geothermics68(2017)67–85

Fig.2. Stratigraphiccolumnarsectionoftheunitsinthestudyareawithlithologydefinitionsandhydrogeologicalproperties(compiledfromErdog˘anetal.,1990;Filizand

Tarcan,1990;C¸akmakog˘luandBilgin,2006;Helvacıetal.,2009andthisstudy).

2.3. Structuralgeology mentsenterGülbahc¸esub-basinnearSög˘ütköyRiverandformthe

boundariesofthebasin.Althoughsegmentshavestrike-slipchar-

ThedominantstructuraltrendintheGülbahc¸eareaisN-Sand acterinthesouth,theyshowoblique-sliptonormalslipcharacter

manyfaultsaremappedaspartsoffaultzonesandindividualseg- wheretheyenterGülbahc¸esub-basininthenorth.TheSög˘ütköy

ments in this study. Kinematic studies were carried out at nine fault(Station8),whichtakesitsnamefromSög˘ütköystream,has

differentstations.Datawasalsocollectedfromjoints(Station6) approximately N-S strike and steeply dips towards the W, sepa-

nearthegeothermalspring(Fig.4).Allofthefaultsandjointsare ratesbasementunitsfromQuaternarydepositsandalsocontrols

groupedunderthreeheadingsbasedontheirstrikes;N-S,NE-SW themorphologyofstreamsaroundtheGGF(Fig.4).

andNW-SEtrendingfaults. TheotherimportantstructureistheN-Sorientednormalfault

segment (Station 1) with 5–6km length. The fault plane can be

observed in the Gülbahc¸e sub-basin around the eastern bound-
2.3.1. N-S-trendingfaults
aryoftheKocadag˘volcanics.NearBallıkayaHill,itjumpstowest,
TheGFZstartsatthesouthwithtwoparallelsegmentsthatcan
where talus breccias cover the fault plane and then continues
be followed along mountain ranges for nearly 10km. Fault seg-
T.Uzellietal./Geothermics68(2017)67–85 71

Fig.3. GeologicalmapofGülbahc¸eandUrlaareawithmaintectonicstructures(SFZ:SeferihisarFaultZone,KUFZ:Kus¸c¸ular-UrlaFaultZone,DYFZ:Demircili-Yag˘cılarFault
Zon e,G FZ:Gülbah c¸eFa ul tZone,I˙S B :I˙c¸m eler Sub- basin ,TSB: Turasan Sub-basin, GSB: Gülbahc¸eS ub-ba sin,K SB:Kus ¸c¸ul a rSub-bas in,com piled from; C¸akmakog˘luandB ilgin,

2006;Helvacıetal.,2009;Uzeletal.,2012,2013andthisstudy).
72 T.Uzellietal./Geothermics68(2017)67–85

Fig.4. Detailedgeologicalmapandlower-hemisphereequal-areaprojectionoffaultplanesandjointsetsfrom10differentstations(compiledfrom;FilizandTarcan,1990;

C¸akmakog˘luandBilgin,2006;andthiswork).

to the north before disappearing below the sea in Gülbahc¸e Bay NohutalanandGüvercinlikformations.Thegeneraltrendofthese

(Figs.4and5).Thisstep-overstructureformedapossiblerelay- smallscalefaultsandjoint-setsappeartobeN-Sdirectedbutin

rampgeometrywhichisveryimportantforgeothermalfluidsrising local areas detached limestone blocks have distinct jointing and

throughgeothermalsystems. deformationpattern.

According to magnetotelluric surveys (Pamukc¸u et al., 2014),

morphologicalinterpretationsandsatellitephotos,thereisastrong
2.3.2. NE-SW-trendingfaults
possibilityoftheexistenceofanotherfaultbetweenBallıkayaand
The NE-SW-trending faults are mainly strike-slip faults, with
C¸ ıtırlıalan Hills. It is also parallel to known fault segments and means trikeofN30◦Eobs erved ind ifferent partsofthe study area.
mappedasaprobablefaultinthisstudy.Inaddition,asseenfrom
NorthernsegmentsoftheGFZandtheDYFZmaybeconsideredas
Stations 3, 4 and 5; we detected many small E-W striking nor-
mal/obli qu es lipn orm alf aultsbetw eenGü lbahc¸ eand I˙c¸melerf aults part of this fault classification. In addition, we mapped two parallel
active strike-slip faults (Station 7) extending between C¸ıtırlıalan
andaroundBallıkayaHill.Thesefaultsreflecttheextensionalfault-
Hill and GGF, as shown in Fig. 4. The observed lengths of these
ingrelatedtothetranstensionalstrike-slipregimeintheGülbahc¸e
faultsareapproximately1.8kmandtheycutPleistoceneBallıkaya
sub-basin. The faults of this set are well exposed around the study conglo me rateandrecent all uviu m( Fig.6 ).F aultshaveN 10−25◦E
area.Forexample;thereisanothermajorN-Sstrikingfaultseg-
ment loca tedbetwe enI˙c¸m e lerandM alkac¸a dag˘ ıHills.Th atfa ultis strikes and high dip angles with nearly horizontal slicken sided
faultplanes.SubsidiaryantitheticRiedelshearfracturesobserved
acontinuationoftheDYFZ,cuttinganddisplacingbasementrocks
aroundthemainfaultareshownonlowerhemisphereequalarea
withright-lateralstrike-slipcharacter(Fig.4).Also,therearesev-
projectionwithmainfaultplanedatafromStation7.TheNE-SW
eralantitheticandsyntheticfaultsthatcutmainlylimestonesof
strike-slipfaultispossiblyresponsibleforsea-waterintrusioninto
T.Uzellietal./Geothermics68(2017)67–85 73

Fig.5. Fieldphotostakenfromnormalfaultsegment(Station1)onthecontactofKocadag˘volcanicswithrecenttalus/alluviumdeposits.

Gülbahc¸esub-basin,andalsoaffectsthemorphologyandstrength ary between Urla volcanics with Miocene and Quaternary units,

ofbarrierunitsaroundtheGGF,wheretheSög˘ütköystreamdis- anotherNW-SE-trendingleft-lateralstrike-slipfaultwasdetected

chargesintoGülbahc¸eBay. byanalyzingdrainagepatternanomaliesandsatelliteimages.

2.3.3. NW-SE-trendingfaults 3. Hydrogeologyandhydrogeochemistryofgeothermal

TheNW-SE-trendingfaultsegmentsarebasin-boundingstruc- fluid
tures o f Turasan and I˙c¸ meler sub-basin s. T he I˙c¸meler faul t, also

called the Ilıca fault in previous works (C¸etiner et al., 2000; 3.1. Hydrogeologicalpropertiesofstudyarea

C¸akmakog˘luandBilgin,2006),isoneofthefaultsthatboundsthe
w esternmar gino fI˙c¸me lerbasi n, cutt ing an ddispl acin gGüverc in- Knowledgeofthestratigraphy,permeabilityandfracturepat-
liklimes tones.I˙c ¸mel erfaul thasa norma lfau ltcharacte r;footwall tern of the st ud y ar ea are funda mental facto rs t o model the

blockisontheSWsideoffaultplane,thusthenorthernblockslid geothermal system. The hydrogeological properties of the study

downrelativetofootwalldevelopinglowrelieftopography.Also area were reviewed based on the above described stratigraphic

thefaultplaneinmassivelimestonescouldactasahydrogeolog- unitswiththeirhydrogeologicalrole.Thestudyindicatesthatfaults

icalbarrier,withsea-waterintrusionintothegeothermalsystem andfractureshavecreatedpredominantlyN-S,NE-SWandNW-SE

possiblylimitedunderthisconditionandthepresentshorelineis orientedaperturesandpathwaysforwatercirculation.Thewater
shaped b y I˙c¸me ler fau lt. Se a-water in trus ion can be seen local ly frompre cipitation, surf acerun-off ,str eam-d rainagewat era ndsea

in the north-eastern part of Gülbahc¸e sub-basin where the NW- waterinfiltratethroughthisintenselyfracturedsystemandfeed
SE stri kingfaultsegm ents in tersectw i thNE-SW strikin gI˙c¸m eler thehy drotherm alsystem .
Fau lt.Easte rnbo undaryof theI˙c¸me lersu b-basin isunderc ontrol A lthough not having primary porosity, limestones of the

of another NW-SE-trending right lateral strike-slip fault (Station NohutalanandGüvercinlikformationshavekarstfeatures,fissures,

10)withminordipslipcomponent.Inthesamearea,theMiocene faults,jointsetsandopenfracturesthatarethemainfactorscon-
lim eston eoutcr ops bet weenI˙c¸mele ra nd Turas ansu b-b asinsare trollin g seco nda ry p ermea bility. Th e fra ctur ing and j ointing lead

deformed by four parallel faults with normal fault character as asecondarypermeabilitywithspacinggenerallybetween10and

detectedfromblockmovementsoflimestone-marl-tufflayers. 45cm and some variable openings so surface water could easily

TheTurasansub-basinisboundedbyNW-SE-trendingnormal infiltratethroughtheseunits(Fig.7(b)).Whenconsideringthesize

faultswhichcausedsignificantchangesintopography.However, ofthelimestoneoutcroppingintheregion,discontinuitiescould

faultplanescannotbeseendirectlyinthefieldbecauseofcover controltherechargeofhydrothermalfluidsandlimestonescould

units,alluviumandsettlements.Forthatreason,air-photos,satel- becomeareservoirforthegeothermalsystem.Actually,thereare
liteim ages,dra inag epatternsan d3 -Ddi gitalele vationmod elsof manyka r sticspring ss uch asI˙c¸melers pringw ith200lt /secfl ow

theareawereusedfordetectionoffaults.Likewise,atthebound- ratethatcanbeseenaroundthegeothermalfield(Fig.8).
74 T.Uzellietal./Geothermics68(2017)67–85

Fig.6. Fieldphotosofstrike-slipfaultsfromStation7onBallıkayaconglomeratedeposits.

Fig.7. FieldphotostakenfromGülbahc¸eGeothermalFielda)FaultplaneofSög˘ütköyfault(Station8)(b)Jointsonlimestoneswithwateremerging(Station6)c)Ancient

ruinsofRomanbathnearbyGülbahc¸ehot-spring.
T.Uzellietal./Geothermics68(2017)67–85 75

Fig.8. HydrogeologicalmapofGülbahc¸eandsurroundingareawithsamplelocations.

However, another basement unit, the Bornova flysch that is underground deformation zones may allow water circulation.

composedofsandstones,siltstones,shales,granodiorites,serpen- Accordingtoregionalperspectivesandabsenceofsufficientsub-

tinites,anddiabase,hasneitherpermeabilitynorporosity.Despite surfacedata,thisunitisconsideredahydrogeologically-confining,

nothavinganyprimaryporosityandpermeability,fracturesand non-aquiferousunit.
76 T.Uzellietal./Geothermics68(2017)67–85

The Miocene volcano-sedimentary succession comprises vol- (inductively coupled plasma mass spectrometer) at ACME Labs

canic and lacustrine units. The unit has variable permeability (Canada).Anon-acidifiedsamplewasusedforanionanalyses.Chlo-
featur es d ue to litho logy a ltern ation s suc h as cla ystone, sand- rineandH C O − werede termine dvo lume tri callya ndSO 2− bya
3 4
stone,lim esto ne ,tuffand marl.TheMio cene str atacontain many grav imet ricmethodin theI˙zmirIn stituteofTechn olog y(IIT).Als o,

layers,lensesofmarlandvolcanictuffswithlowhydrauliccon- SiO wasdeterminedspectrophotometricallyintheIIT.Samplesfor
2
ductivi tyand the yact aslo calconfi ning units betw eenuppe rand determin ationofdeu terium(2H),oxygen-18( 18 O)a nd tritium(3 H)

lowerpartsofthesuccession.Theunitcouldnotallowtheriseof analyseswereexaminedatHacettepeUniversity.

geothermalfluidsthroughcoverunitsbyseparatingthemfromcool

groundwater and sea-water in the geothermal system. Previous
3.2.2. Physicalpropertiesofwaterresources
studiesanddrillingsshowthatMiocenelimestoneshavethickness
In the study area, geothermal fluids have surface discharge
of 250–300 m in this region. However, apart from basement, the temp eratu res in the r ange of 32.5 –33.5◦ C, and cold w aters have
Miocene limestones have limited extent near the GGF and gen- temperature val ues betwe en 10.3 and 2 3.6◦ C (Ta ble 1). The
erallycropoutandcoverwideareasaroundtheeasterncoastof
Gülbahc¸esub-basin,whichhostsageothermalfield,hasthehigh-
Gülbahc¸eBay.Inthisstudy,Miocenestrataareconsideredalocally
estsurfacetemperatures(P5andP6)withIlıksuhot-spring(P34)
aqueous,water-bearing,semi-permeableunit.
onthenorthernarea.Theareaisalsocharacterizedbyshallowsea-
The volcanic units existing in the study area have similar
water and cooler meteoric water intrusion at the intersection of
hydrogeological properties because of their lithological properties theSö g˘ütk öyand I˙c¸melerFa ultsan dotherm in orpa rallelfractur es
andstructuralframeworks.Primaryporosityandpermeabilityof
andfaults.Electricalconductivity(EC)valuesofgeothermalfluid
Kocadag˘ volcanics are low because of matrix lithification of agglom- aren early3 7,200((cid:2)S /cm)andcol dwa terhas val uesranging from
erates, volcanic breccias and andesite lithology but secondary 145 to381 0((cid:2)S/c m)(Tabl e1).
permeability is an important factor for water circulation. These

volcanicshavewell-developedconnectedfracturenetworks,faults

andverticalcoolingjointsets.Therearemanylow-flowingsprings 3.2.3. Chemicalpropertiesofwaterresources

anddrillingupto100–120mwithflowratesaround1–3lt/sec.The The semi-logarithmic Schoeller diagram (Fig. 9) shows that

Kocadag˘ volcanics are considered a moderately productive, frac- geothermalfluidsamples(P5,P6andP34)haveasimilarcompo-
tured, fis sured aqu ifer in this stud y . Lavas and tuff layers o f the sition and i t can be seen from th e pl ots th at th ei r Sodiu m (Na+)
young ervolcan icunit, Ur lavo lcanics ,areim per viou sandc on sid- andC hlori de (Cl− )c oncen tratio nsa rerel ative lyhig herthan other

eredashydrogeologicallyconfinedunits.Coolingjointscanbea chemical constituents (Table 2). The composition of geothermal
good fa ctorforsecondper meability within theUrl avolca nics ,bu t fluid sam ples is simila r to se awa ter, but with incr eas ed Na+ and
close dfractu res andthi ckclayeyfaul tbrecci asca usel owsecond ary K+co ncentrat ion andso me depletion inM g2+a ndSO 2−. TheNa+
4

permeabilityinlocalareas.Duetosurfaceconditions,volcanicrocks isthemajorcationinthehot-springsofthestudyareawithconcen-

areintenselydeformedandalteredsotheybecamemoreconve- trationrangesfrom10,750to12,777mg/l.Also,itcanbeobserved
nien tforwat ercirculati on.A saresu lt ofdis continui ties,t heUrla thatma gnesiu m(M g2+)an dc alcium (Ca2+ )hav e high co ncentra-
volcan icu nitis considereda m od eratel yp roductive,fractu red ,fis- tions . The chlori de (Cl− ) con centrati on in the ge othe rmal fluids

suredaquifersimilartoKocadag˘volcanics. ranges from 19,632 to 23,418mg/l and other two major anions,
Re cent all uvium dep osits are exposed around Gülbahc¸e and sulfate (SO 2 −)and bic arbonat e(HC O − ),hav emu chlow ercon-
4 3
I˙c¸melerba sins,the shoreline ofG ülbahc¸e Bayand intopog r aph- centrat ions tha n Cl− . In the geo thermal fl uid, Cl− co ncentr ation
ic ally lo w strea m a reas. The un it comp ri ses alluv ial and fluvial ismuchmo reth an19 ,00 0m g/landbrom ine( Br−)concentration

sedimentsconsistingofgravel,sandandclaylayers.Alluviumhas rangesfrom2.55to79mg/l,whichishigherthanthatofothercold

a thickness of nearly 30m in Gülbahc¸e sub-basin and is thicker waterinthestudyarea.
a roundtheI˙ c¸m elersub -ba si n.T hereare m anydugan ddr ille dwells The h igh- flowin gcoldwaterspringformedinfracturedkarstic
located on a lluvial deposits a nd th ese wells are ver y impo rtant limesto nesatI˙c¸mele rSpr ing(P 8)has highcon ce ntrations ofNa+
dueto bein gawat ersupply for theUr lareg ion. Recen tdeposits and Cl−, w hich also e merges alon g th e NW -SE-trending I˙ c¸m eler
seem h ydrog eo logica lly poro us and gran ular un its. Add itionally, faul t.Thi sindica test hatthehi gherN a+a ndCl−concentratio nval-
despi te having good pe rmeabi lity and poro sity, n ear sea-level ueso fthe I˙c¸melerS prin gco uldbe related tosea-waterintru sion
areas,sa linitya ndsea -waterintrusi onis animport antis sueforall ink ars ticlim eston esalon gtheI˙ c¸m elerFau lt. Likewise,o thercold

water-supplywellslocatedinrecentdeposits. watersourceslocatedinalluviumdepositsneartheGülbahc¸eBay
have h igher c oncentra tio ns of Cl− and als o Ca2 + an d Na+. T h ese

3.2. Hydrogeochemicalpropertiesofthestudyarea wells have been affected by sea-water intrusion. Bicarbonate is

known as the typical main cation in most cold water samples.
3.2.1. Materialandmethods Conside rin g ob servati on of higher bic arbon ate v alues w ith Ca2+

For the investigation and comparison of hydrogeochemical in cold water samples, it can be clarified that the reservoir for

characteristics,threegeothermalsprings(P5,P6andP34)andthirty these samples are similar and water comes from the limestones

coldwatersamples(withP-numbers)weremonitoredfrom2009 anddolomitesoftheNohutalanandGüvercinlikformations.

to 2014 in the study area (Fig. 8). The concentrations of major InthePiperdiagram,thetotalcationandanionconcentrations

ions, some heavy metals and isotopes were determined in the are plotted as percentages of meq/l and it’s very useful to find

watersamples.Duringfieldsurveys,somephysicalparametersof detailed information about the concentration of the waters and
thege othermal fluid,in clud ingtemp eratu re(◦C),p H,andelect ri- hydroge ochemicalfac iescla ssifi cation.IntheP ipe rdi agrama dja-
cal conductivity (EC,(cid:2) S/cm),w eremeasured in-s ituw ith aWTW centandgroupedp lotssh owthatthese wa ter sampl eshaven early

Multi340i/SETS.ThepH-meterwascalibratedwithpH4,pH7,and similarcompositions.FollowingthePiper’sdiagram(Fig.10),the

pH10buffersolutionsbeforecommencingfieldwork.Inorderto waterplotsareinsidethenon-carbonateandhigh-alkalinitywater

determinethevariationinmineralcontentofthewatersamples, area.Allsampleplots(exceptforhotwater)indicatethatthewaters

theywerecollectedinunused50,500,and1000mLhard-plastic ofthestudyareahavemixedwatertypewithnoion(cation-anion)

bottles.Topreventtheformationofheavymetalcomplexeswith exceedingapercentageof50.Piperdiagramalsoshowsthathot-

oxygen,sampleswereacidifiedwithHNO topH2.Acidifiedsam- waterspringsinthestudyarea(P5,P6,P34)canbeclassifiedas
3

pleswereanalyzedformajorandtraceelementswithanICP-MS sodium-chlorideenrichedwaters.