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\DOI{10.5802/crgeos.249}
\datereceived{2023-05-20}
\daterevised{2023-11-17}
\dateaccepted{2023-12-01}
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\begin{document}

\begin{noXML}

\TopicEF{Research article}{Article de recherche}

\RubricEF{Hydrology, hydrogeology}{Hydrologie, hydrog\'eologie}

\title{Water--rock interaction in the geothermal systems related to
post-collision zone volcanism: A case study based on multivariate
statistical analysis from the Kavak geothermal field (Konya, Turkey)}

\alttitle{Interaction eau--roche dans les syst\`{e}mes g\'{e}othermiques
li\'{e}s au volcanisme de zone post-collision : Une \'{e}tude de cas
bas\'{e}e sur l'analyse statistique multivari\'{e}e du champ
g\'{e}othermique de Kavak (Konya, Turquie)}

\author{\firstname{Mesut} \lastname{G\"{u}nd\"{u}z}\CDRorcid{0000-0003-2526-4806}\IsCorresp}
\address{Graduate School of Natural and Applied Sciences, Mu\u{g}la
S\i{}tk\i{} Ko\c{c}man University, TR-48000, Mu\u{g}la, Turkey}
\email[M. G\"{u}nd\"{u}z]{mesutgunduz24@hotmail.com}

\author{\firstname{Ayla} \lastname{Bozda\u{g}}}
\address{Geological Engineering Department, Konya Technical University,
TR-42250, Konya, Turkey}

\author{\firstname{Ali Ferat} \lastname{Bayram}}
\addressSameAs{2}{Geological Engineering Department, Konya Technical University,
TR-42250, Konya, Turkey}

\author{\firstname{Ali} \lastname{Bozda\u{g}}}
\addressSameAs{2}{Geological Engineering Department, Konya Technical
University, TR-42250, Konya, Turkey}

\author{\firstname{K\"{u}r\c{s}ad} \lastname{Asan}}
\addressSameAs{2}{Geological Engineering Department, Konya Technical
University, TR-42250, Konya, Turkey}

\author{\firstname{Paul} \lastname{Sardini}}
\address{Institut de Chimie des Milieux et Mat\'{e}riaux de Poitiers
(IC2MP), CNRS, (E2-HydrASA), Universit\'{e} de Poitiers, F-86073,
Poitiers, France}

\shortrunauthors

\begin{abstract}
Water--rock interaction is the focus of geothermal energy studies and
can be documented by traditional geochemical methods such as ion ratio
method and hydrogeochemical modelling etc. Statistical approaches are
also vital for the quantitative models, and mainly combined with the
traditional methods. In this study, we re-evaluate the published data,
including water chemistry and volcanic and metamorphic whole-rock
geochemistry from the Kavak geothermal field (Konya, Turkey) by using
multivariate statistical analysis (e.g. factor analysis and clustering
analysis) to research possible interaction between the thermal waters
and surrounding rocks. 

The Kavak geothermal field (KGF) overlies a metamorphic basement
composed of the Paleozoic metacarbonates and metaclastic rocks, yet is
located near the Erenlerda\u{g}--Alacada\u{g} volcanic complex (ErAVC).
An example of unimodal orogenic volcanism in an extensional geodynamic
setting, the Neogene ErAVC is composed of widespread high-K
calcalkaline andesite to rhyodacite lavas with enclaves and their
pyroclastic counterparts. The Kavak geothermal field covers a small
area (${\sim}$7.5~km$^{2}$) and lies along the Seydi\c{s}ehir fault zone
in the southeast of the ErAVC. The Kavak thermal waters are meteoric in
origin and peripheral waters (Ca--Na--HCO$_{3}$) in the geothermal system
related to the orogenic volcanism. The Kavak thermal waters are
characterised by high K$^{+}$ and Na$^{+}$ cations, and low pH (between
6.4--6.9~pH) values relative to the cold waters around the KGF. Two
types of thermal waters were identified in the KGF based on the slight
difference in their hydrochemistry and discharge temperature. The first
type thermal water (${\sim}$22~\textdegree C) has higher TDS and Cl/Br
ratio and lower dissolved silica and Br content relative to the second
type of water (up to 45~\textdegree C). The chemical relationship
between the KGF and high-K ErAVC is clearly seen in the cation-based
diagrams. Multivariate statistical analysis confirms that first type
and second type thermal waters identified based on their hydrochemistry
formed two separate statistical groups, and suggests that the chemistry
of the KGF waters was mainly controlled by the composition of the ErAVC
rather than those of the basement metamorphic rocks as a result of
water--rock interaction.
\end{abstract}

\begin{altabstract}
L'interaction eau--roche est au centre des \'{e}tudes sur l'\'{e}nergie
g\'{e}othermique et peut \^{e}tre document\'{e}e par des m\'{e}thodes
g\'{e}ochimiques traditionnelles telles que la m\'{e}thode du rapport
d'ions et la mod\'{e}lisation hydrog\'{e}ochimique, etc. Les approches
statistiques sont \'{e}galement essentielles pour les mod\`{e}les
quantitatifs, et principalement combin\'{e}es aux m\'{e}thodes
traditionnelles. Dans cette \'{e}tude, nous r\'{e}\'{e}valuons les
donn\'{e}es publi\'{e}es, y compris la chimie de l'eau et la
g\'{e}ochimie des roches volcaniques et m\'{e}tamorphiques du Champ
g\'{e}othermique de Kavak (Konya, Turquie) \`{a} l'aide d'une
analyse statistique multivari\'{e}e (telle que l'analyse factorielle,
et l'analyse de regroupement) afin de rechercher des indices
d'interaction possible entre les eaux thermales et les roches
environnantes.

Le champ g\'{e}othermique de Kavak (KGF) repose sur un socle
m\'{e}tamorphique compos\'{e} de m\'{e}tacarbonates
pal\'{e}ozo\"{i}ques et de roches m\'{e}taclastiques, situ\'{e}
pr\`{e}s du complexe volcanique d'Erenlerda\u{g}--Alacada\u{g} (ErAVC).
En tant qu'exemple de volcanisme orog\'{e}nique unimodal dans un
cadre g\'{e}odynamique extensionnel, l'ErAVC du N\'{e}og\`{e}ne est
majoritairement compos\'{e} d'and\'{e}site calcoalcaline \`{a} haute
teneur en potassium, ainsi que de rhyodacite \`{a} enclaves et leurs
produits pyroclastiques associ\'{e}s. Le champ g\'{e}othermique de
Kavak (KGF) couvre une petite superficie (${\sim}$7,5 km$^{2}$) et se
situe le long de la zone de faille de Seydi\c{s}ehir au sud-est de
l'ErAVC. Dans ce syst\`{e}me g\'{e}othermique li\'{e} au volcanisme
orog\'{e}nique, les eaux thermales de Kavak ($T \sim22$--45~\textdegree
C) sont d'origine m\'{e}t\'{e}orique et p\'{e}riph\'{e}rique
(Ca--Na--HCO$_{3}${). Ces eaux sont caract\'{e}ris\'{e}es par des
teneurs en cations K}$^{+}$ {et Na}$^{+}$ \'{e}lev\'{e}es et un pH bas
(entre 6.4--6.9) relatif aux eaux froides autour du KGF. Deux types
d'eaux thermales ont \'{e}t\'{e} identifi\'{e}s dans le KGF,
gr\^{a}ce \`{a} de l\'{e}g\`{e}res diff\'{e}rences
hydrog\'{e}ochimiques et de temp\'{e}ratures de sortie. Le premier type
d'eau thermale ($T \sim 22$~\textdegree C) poss\`{e}de une TDS et un
rapport Cl/Br relativement \'{e}lev\'{e} ainsi que des teneurs plus
faibles en silice dissoute et en Br ($T > 45$~\textdegree
C), ceci vis-\`{a}-vis du second type d'eau. La relation
g\'{e}ochimique liant le KGF et les formations riches en potassium de
l'ErAVC sont clairement mises en \'{e}vidence par des diagrammes
bas\'{e}s sur les cations. L'analyse statistique multivari\'{e}e
confirme que les deux types d'eaux thermales forment deux groupes
s\'{e}par\'{e}s statistiquement. Ceci sugg\`{e}re que la chimie des
eaux du KGF est principalement contr\^{o}l\'{e}e par le biais de
l'interaction eau-roche avec l'ErAVC plut\^{o}t qu'avec les roches
m\'{e}tamorphiques du socle.
\end{altabstract}

\keywords{\kwd{Kavak geothermal field}
\kwd{Water--rock interaction}
\kwd{Hydrogeochemistry}
\kwd{Data analysis of the thermal waters}
\kwd{Silicate weathering}}

\altkeywords{\kwd{Champ g\'{e}othermique de Kavak}
\kwd{Interaction eau--roche}
\kwd{Hydrog\'{e}ochimie}
\kwd{Analyse des donn\'{e}es des eaux thermales}
\kwd{Alt\'{e}ration des silicates}}

\maketitle

{\vspace*{6pt}}

\twocolumngrid

\end{noXML}

\section{Introduction}\label{sec1}
Water--rock interaction (WRI), one of the most important factors that
deeply control the geochemistry of thermal waters is a prime interest
in geothermal energy studies. Although this phenomenon has been known
for many years by earth scientists, its nature has always been debated
\citep{WohletzHeiken1992}. WRI encompasses primarily three types of
reactions, namely adsorption, dissolution, and precipitation that take
place at the mineral-fluid interfaces \citep{Teng2005}. WRI can be
documented by theoretical, experimental, field, and laboratory studies,
based mainly on the geochemical and isotopic data. After the
acquisition data, WRI can be studied by traditional methods such as ion
ratio method and hydrogeochemical modelling software (e.g. PHREEQC).
Multivariate statistical analysis techniques have recently been
combined with these methods. Factor analysis and principal component
analysis (PCA) are commonly used multivariate statistical analysis
techniques \citep{Poznanovic-Spahicetal2023,Zhangetal2022}. These
statistical methods are useful to analyse all parameters in a large
dataset as a whole, which allows practically to screen, reduce and
classify the data. Compared to the traditional methods, they serve as a
more powerful tool on the deciphering origin, interaction with the
rocks and circulation pathway of thermal waters
\citep{Haoetal2020,Yidanaetal2012}.

The Kavak geothermal field (KGF) is a fault-controlled thermal system
of meteoric origin located in the southwest of the
Erenlerda\u{g}--Alacada\u{g} volcanic complex 
\citep{Bayram1992,Bozdag2016,Burcaketal2002,Davrazetal2022a,Davrazetal2022b,Gocmezetal2005,GocmezSen1998}
(Figures~\ref{fig1} and~\ref{fig2}). Using traditional methods,
previous studies emphasised that water--rock interactions and
decomposition processes, and argued the interaction between the thermal
waters and metamorphic basement rocks played an important role in the
KGF
\citep{Bozdag2016,Davrazetal2022a,Davrazetal2022b,KaraisaogluOrhan2018}. 
However, the possible interaction between the \mbox{thermal} waters and
volcanic rocks of the Erenlerda\u{g}--Alacada\u{g} volcanic complex
(e.g. ErAVC) as a geothermal heat source in the KGF was not evaluated
in the previous studies. Hence, we here reprocess the published
geochemical data from the thermal waters, volcanic and metamorphic
rocks in the KGF using multivariate statistical analysis (e.g. factor
analysis and clustering analysis) and evaluate whether interactions
between the Kavak thermal waters and volcanic rocks in the ErAVC play a
decisive role in water chemistry.\looseness=-1 

\begin{figure*}
\includegraphics{fig01}
\caption{\label{fig1}Simplified tectonic map of Turkey showing the
major suture zones \citep{OkayTuysuz1999}, arc systems (red
lines), continental blocks (black lines), and distribution of the main
Post-Collision (Late Cenozoic) volcanic fields \citep{MTA2013}.
\.{I}AESZ: \.{I}zmir-Ankara-Erzincan Suture Zone, BSZ: Bitlis Suture
Zone, ASZ: Antalya Suture Zone, NAF: North Anatolian Fault, EAF: East
Anatolian Fault, DSF: Dead Sea Fault, AF: Afyon Fault, EAVP: East
Anatolian volcanic provence, KV: Karacada\u{g} volcanics, CAVP: central
Anatolian volcanic provence, GVP: Galatian volcanic provence, ErAVC:
Erenlerda\u{g}--Alacada\u{g} volcanic provence, KAIVP:
K\i{}rka-Afyon-Isparta volcanic provence, WAVP: West Anatolian volcanic
provence.\vspace*{-4pt}}
\end{figure*}


\begin{figure*}
\includegraphics{fig02}
\caption{\label{fig2}Simplified geological map of the west of Konya
[\citealp{Kelleretal1977}; General Directorate of Mineral Research and
Explorations 1/100,000 geology map] from  \citet{Gunduz2023}.}
\end{figure*}

\section{Geological and hydrogeological setting} \label{sec2}

Located in the Central Taurus, the KGF is in the Bey\c{s}ehir Basin
characterised by a graben-like structure, including several units with
different stratigraphic, lithologic, tectonic, volcanic, and
metamorphic features (Figure~\ref{fig2}). The Bey\c{s}ehir Basin, which controls
the morpho-tectonic structure of the Kavak geothermal field, is mostly
related to the northwest--southeast trending (sub) parallel normal
faults. The Mio-Pliocene fluvio-lacustrine deposits around the KGF are
proof of the fault-controlled intermontane basin in the region 
\citep{Kocetal2017,Kocetal2018}. In addition, this graben system
(i.e. Bey\c{s}ehir Basin) is surrounded by the Taurus belt from the SW
and the Afyon zone from the NE. It is also separated from the Konya
graben in the north. The morpho-tectonic structures of the study area
and seismic activities in recent years indicate that the faults in the
region (i.e. Abazda\u{g}\i{}, Bey\c{s}ehir, and Seydi\c{s}ehir fault
zones, etc.) are a part of the active-neotectonic structure
\citep{Aksoy2019}. The Kavak geothermal field is an example of the
fault-controlled spring system \citep{Keegan-Treloaretal2022} and
thermal water springs of the KGF discharge along a fault in the north
(e.g. TS4 and TS5 thermal waters) and fault in the south (e.g. TS1, TS2
and TS3 thermal waters) parallel to the Seydi\c{s}ehir Fault Zone
(Figures~\ref{fig2},~\ref{fig3}). The southern fault acts actually as a structural
(semi) barrier, leading to the existence of two types of thermal waters
in terms of their chemical compositions, surface temperatures and
location.

\begin{figure*}
\includegraphics{fig03}
\caption{\label{fig3}Geology map of the study area and location of
thermal springs and drilling wells  \citep{Bozdag2016}.}
\end{figure*}

The Central Tauride is an assemblage of various autochthonous and
allochthonous crystalline-metamorphosed basement rocks
\citep{DeanMonod1970,Goncuogluetal2007,GoncuogluKozlu2000,Gursuetal2003,Moixetal2008,Ozgul1976,Robertsonetal2013,Sengoretal2019,Turan2010}. 
The basement rocks around the KGF consist of Paleozoic metacarbonates
and metaclastic rocks intercalated with metamarls \citep{Karadag2014}.
These basement rocks are unconformably overlain by the
Neogene-Quaternary sedimentary and volcanic rocks 
\citep{Eren1996,Hakyemezetal1992,Kocetal2012,OzkanSogut1998,Turan2020}.

The Neogene volcanic rocks (ErAVC) cover approximately 1500~km$^{2}$
area (SW-Konya) and are separated from the Sulutas volcanic complex
(SVC) by the Anatolide (Afyon zone) \citep{Asanetal2021}
\mbox{(Figure~\ref{fig2})}. The ErAVC rocks are characterised by a large
compositional range (53 wt\% to 72 wt\% SiO$_{2}$) and a unimodal
distribution \citep{Asan2017,Asanetal2021} in the TAS diagram
(Figure~\ref{fig4}), and they were plotted into basaltic andesite
represented by enclaves to rhyolite fields \citep{LeBasetal1986}. The
ErAVC rocks are calc-alkaline in the AFM diagram of
\citet{IrvineBaragar1971}, and have high-K content (Figures~\ref{fig5}
and~\ref{fig6}). These volcanic rocks were first described as
calc-alkaline andesite and dacite, rarely basaltic andesite and
rhyolitic composition, and they were suggested to be related to
subduction-related magmatism by \citet{Kelleretal1977}. The authors
presented the first geological, geochemical (major oxides, very limited
trace element, and Sr isotopes), and geochronological (K/Ar radiometric
age) data of these rocks by \citet{Besangetal1977}. In these studies, it
was shown that volcanic products are composed of lava domes/lava flow,
pyroclastic fall and flow (e.g.~block-and ash flows and ignimbrites)
deposits \citep{Kelleretal1977}. It was stated by the researchers that
the volcanism prolonged a wide period from Miocene ($11.95\pm0.02$~Ma) 
to Pliocene ($3.35\pm0.08$~Ma). \mbox{Sr--Nd} isotopic data of the ErAVC
presented by \citet{Temeletal1998} show that the intermediate and felsic
volcanic rocks have high Sr and low Nd isotopes. The authors conclude
that the rocks were \mbox{related} to the subduction of the African plate
under the Anatolian plate. On the other hand,  \citet{KocakZedef2016}
divided Konya volcanics into eight different lithological units and
stated that these lithological units mainly contain mafic minerals
(Mg\# 0.69--0.71) (e.g. pyroxene ``augite and enstatite'', calcic
amphibole, biotite, opaques) and felsic minerals (e.g. plagioclase
``An$_{30\ndash 86}$'' and fewer quartz phenocryst)
(Figure~\ref{fig7}). 

\begin{figure}
\includegraphics{fig04}
\caption{\label{fig4}Geochemical classification diagrams of the ErAVC;
pointed \citep{Kelleretal1977}, gray dashed-line
\citep{Temeletal1998}, pink-colored \citep{Asan2017,Asanetal2023}:
Total-Alkali Silica (TAS) diagram of \citep{LeBasetal1986}.
Alkaline-sub alkaline division (dashed line)  from
\citet{IrvineBaragar1971}. All analyses were recalculated to 100\% on a
water-free basis for TAS classification.\vspace*{-4pt}}
\end{figure}

\begin{figure}
\includegraphics{fig05}
\vspace*{-3pt}
\caption{\label{fig5}Sub-alkaline ErAVC rocks; pointed
\citep{Kelleretal1977}, gray dashed-line \citep{Temeletal1998},
pink-colored \citep{Asan2017,Asanetal2023} on the AFM diagram
\citep{IrvineBaragar1971}.\vspace*{-6pt}}
\end{figure}

\begin{figure}
\includegraphics{fig06}
\caption{\label{fig6}Plot of SiO$_{2}$ vs. K$_{2}$O (wt\%)
illustrating andesite types of \citet{Gill1981}; pointed
\citep{Kelleretal1977}, pink-colored arrow
\citep{Asan2017,Asanetal2023}.}
\end{figure}

\begin{figure*}
\includegraphics{fig07}
\caption{\label{fig7}Microphotos of main mineralogical and textural
features of the ErAVC rocks; (a) orthopyroxene, (b) clinopyroxene, (c)
amphibole (hornblende), (d) biotite, (e) plagioclase, (f) K-feldspar
(sanidine), (g)~quartz and (h) opaque minerals (ilmenite or magnetite).}
\end{figure*}

The Paleozoic metacarbonates that seem to be the main reservoir in the
KGF have high permeability because of their highly fractured and
karstified characteristics. Fractured quartzites of the Paleozoic
metaclastic rocks are permeable whereas phyllite, clay, and
metasiltstone within the Paleozoic metaclastics are relatively
impermeable. Basin-filling limestones, conglomerates, and sandstones of
the Neogene-Quaternary sedimentary deposits are permeable, but silty
and clayey layers are impermeable  \citep{Bozdag2016}. Andesitic to
rhyodacitic lavas from the ErAVC rocks acting as possible caprocks is
impermeable whereas their pyroclastics (e.g. tuff, lapilli tuff and
breccia, etc.) are permeable. The ErAVC pyroclastics serving as
possible geothermal reservoir or aquifer are widespread from the
central to distal facies where they are interbedded with basin-filling
fluvio-lacustrine deposits (Figures~\ref{fig2} and~\ref{fig3}).


\section{Material and methods} \label{sec3}

The published geochemical data from water and whole-rock samples in the
KGF were used in this study. The water samples (e.g. thermal wells,
springs, and cold waters) were analysed by  \citet{Bozdag2016} for
major anion--cation, trace elements, and isotope compositions in
different geochemical laboratories (see the given reference for the
detailed analytical methods of water samples). Metamorphic rock samples
(e.g. metaclastics and metacarbonate) from the basement 
\citep{Karadag2014} and volcanic rock samples (e.g. lava flows, domes,
enclaves and their pyroclastic equivalents) from the ErAVC
\citep{Asan2017,Asanetal2023,Karakaya2009,Kelleretal1977,Temeletal1998}
were analysed for major oxide and trace elements using XRF, ICP-OES or
ICP-MS (see the given references for the detailed analytical methods of
whole-rock samples).

In this study, cluster analysis and factor analysis were chosen as data
analysis methods using GEOstats \citep{GunduzAsan2022}, a
statistical data analysis program to perform these complex multivariate
analyses. Using a class of cluster analysis designed to find groups of
similar items within a data set, hierarchical cluster method produces a
hierarchy of clusters, ranging from small clusters of very similar
items to larger clusters of increasingly dissimilar items. The data
matrix of cluster analysis is to be in standard form, $n\times p$
matrix with \textit{n} rows of samples (e.g. sampling locations) and
\textit{p} columns of variables (e.g. geochemical data, discharge
temperature, EC etc.). Computation may be in ``Q-mode analysis (e.g.
matrix size $n\times n$)'' or ``R-mode analysis (e.g. matrix size
$p\times p$)''. R-mode analysis calculates distances (similarities)
among all pairs of variables whereas Q-mode analysis calculates a
matrix of distances between all pairs of samples. The hierarchical
cluster analysis produces a graph known as a dendrogram. In dendrogram,
the most similar two samples (e.g. A and B) are joined to form the
first cluster, followed by another similar sample(s) (e.g. C or D)
forming the second cluster, and so on. In this study, we first used
``R-mode'' to classify and characterise the KGF thermal waters based on
the geochemical data, leading to the identification of homogeneous
groups or subgroups in the data set. This grouping has the advantage to
compare between water chemistry and rock or mineral chemistry,
simplifying to interpret water--rock interactions. For
example, if K, Na and Ba analysis results from thermal waters form a
cluster, this can be interpreted to the interaction of thermal waters
with a rock including alkali feldspar. On the other hand, Q-mode
analysis was used to classify sampling locations into similar groups,
and to identify thermal water types contributing to these groups. In
this study, water samples taken along the KGF from 12 locations of
which 4 locations are from cold waters and 8 locations from thermal
waters (e.g. Cold Waters: CW1, CW2, CW3, CW4; Thermal Springs: TS1,
TS2, TS3, TS4, TS5; Thermal Wells: TW1, TW2, TW3). These waters were
evaluated by Q-mode analysis to identify water origins and tectonic
(e.g. fault) control (e.g. spatial distribution) on their chemistry.
For example, if springs are aligned along a lineament, sampling
locations are to form a cluster in dendogram as expected from
fault-controlled springs. To test the grouping in the cluster analysis,
we finally used factor analysis which is designed to reduce a large
number of variables into fewer numbers of factors. Factor analysis
collects variables into groups termed ``factors'', which seem to behave
similarly. Factor analysis is computed by ``R-mode analysis'' or ``Q-mode
analysis''. Therefore, it is anticipated that ``factor analysis'' and
``cluster analysis'' produce similar groups as they do in this study.

\section{Results}\label{sec4}
\subsection{Hydrochemical characteristics of the Kavak thermal waters}\label{sec41}
In this study, the Piper diagram was used to assess the main chemical
composition of the Kavak thermal waters. In addition, thermal water
samples from the Pamukkale geothermal field  [e.g. an example of
interactions mainly with metamorphic rocks, 
\citealp{Alccicceketal2019}] and Varto geothermal field [e.g. an
example of interactions mainly with volcanic rocks, 
\citealp{Karaogluetal2019}] were selected to compare with the Kavak
thermal waters (Figure~\ref{fig8}). 

\begin{figure*}
\includegraphics{fig08}
\vspace*{-1pt}
\caption{\label{fig8}Piper plot showing the chemical composition of
thermal waters in the Kavak geothermal field  \citep{Bozdag2016}.
Pamukkale thermals from \citet{Alccicceketal2019} and Varto themals
from \citet{Karaogluetal2019}.}
\vspace*{-2pt}
\end{figure*}

The KGF can be characterised by two types of thermal waters based on
the slight difference observed in their hydrochemistry. The first type
thermal waters including TS1, TS2 and TS3 have higher TDS (up to 
3200~mg/l) and Cl/Br ratio (950--1215), and lower dissolved silica 
(22--23~mg/l) and Br content (234--268~mg/l) relative to the second type water
including TS4, TS5, TW1, TW2 and TW3 (TDS: 1850--2490~mg/l; Cl/Br ratio:
300--465; dissolved silica: 39--44~mg/l and Br content: 408--614~mg/l).
Li, Cs, Rb, Mn, Fe, Cu, and As are also slightly higher, but Cl, Na, K,
Ca, Mg, B, Ba, Sr and Zn concentrations are lower in second type
thermal water than those of the first type. In addition, outlet
temperatures of these thermal waters discharging along two different
faults in north and south are also slightly different (e.g.
${\sim}$22~\textdegree C for the first type of thermal waters and 25 to
46~\textdegree C for the second ones), and discharge along two
different faults in north and south (see Figure~\ref{fig3}).

Both type thermal waters in the KGF are chemically of Ca--Na--HCO$_{3}$
type although they show slight difference in their hydrochemistry.
Also, they have higher total dissolved solids (TDS) values (average of
2566~mg/l) than those of cold waters (average of 359~mg/l) which
probably offer long flow pathways, long residence times and intensive
water--rock interactions  \citep{Bozdag2016,ErbasandBozdag2022}.
Dissolution of the Paleozoic carbonates forming the main reservoir of
thermal waters in the KGF is the reason for the high Ca$^{2+}$
(283.1--549.4~mg/l) and HCO$_{3^-}$ (1445--2687~mg/l) concentrations.
Although the source of Mg$^{2+}$  in Kavak thermal waters is mainly the
dissolution of dolomite and dolomitic limestone in the main aquifer in
KGF, it is not the dominant cation. The reason for the low Mg values
(average 72~mg/l) in thermal waters can be explained by the Mg
depletion in the formation of phyllosilicates (e.g. clay minerals,
chlorite and micas) in the Paleozoic metamorphics forming the secondary
aquifer and/or ion exchange process. Na$^{+}$ (232--387~mg/l) is the
second common cation in the thermal waters and K$^{+}$ (average
86~mg/l) is reached considerable values. Accordingly, the high Na$^{+}$
and K$^{+}$ in the Kavak thermal waters may be assumed to be derived
from the decomposition mostly of intrusions of the ErAVC and regional
metacrystalline rocks, progressive reactions with feldspar in the
Paleozoic metamorphics and ion exchange process. As also seen in the
diagram, the similarity of the main ion concentrations of the Kavak
thermal waters with that of the Varto thermal waters located in the
south of the Varto caldera ``alkaline and calc-alkaline volcanic
rocks'' \citep{BuketTemel1998} may be important for a better
understanding of the relationship between regional geology and
water--rock interaction. 

The differences of major cations between Pamukkale and Varto thermal
waters and the Kavak thermal waters can also be seen in the Schoeller
diagram (Figure~\ref{fig9}). The Kavak thermal waters have very high
cation values compared to cold waters as a result of relatively deep
and long-term circulation and contact with mainly volcanic rocks and
partially crystalline basement or reservoir rocks. Additionally,
Giggenbach's triangular diagram is often used for \mbox{water} classification
in geochemical investigations performed in convergent-plate settings.
In the diagram (Figure~\ref{fig10}), the Kavak thermal water samples are
located in the area of peripheral waters and this type water generally
occurs at relatively shallow depths at some distance from the
geothermal field.\looseness=-1

\begin{figure}
\includegraphics{fig09}
\caption{\label{fig9}Semi-logarithmic Schoeller diagram, comparison of
the concentrations of the Kavak geothermal (red line), the Pamukkale
geothermal (darkblue line), and Varto (green line) samples. Pamukkale
thermals from  \citet{Alccicceketal2019} and Varto themals from
\citet{Karaogluetal2019}.}
\end{figure}

\begin{figure}
\includegraphics{fig10}
\caption{\label{fig10}A triangular diagram of major anions has been
suggested by \cite{Giggenbach1988} for thermal waters, symbols as
Figure 8. Pamukkale thermals from  \citet{Alccicceketal2019} and Varto
themals from  \citet{Karaogluetal2019}.}
\end{figure}

It is known that silicate weathering is effective in terms of
SiO$_{2}$, Ca$^{2+}$, Mg$^{2+}$, Na$^{+}$, and K$^{+}$ concentrations
in groundwater. On the other hand, carbonate dissolution is effective
in terms of Ca$^{2+}$, Mg$^{2+}$, and HCO$_{3^-}$ concentrations.
Accordingly, it is seen in the Ca/Na-Mg/Na diagram that the Kavak
thermal waters fall close to the silicate weathering area and to the
Varto thermal waters (Figure~\ref{fig11}). The
$(\mathrm{Na}^{+}{+}\mathrm{K}^{+})/(\mathrm{Na}^{+}{+}
\mathrm{K}^{+}{+}\mathrm{Ca}^{2+})$ ratios are higher than
0.45 indicating that the chemistry of the Kavak thermal waters is
mainly controlled by the water--rock interaction.
$(\mathrm{Na}^{+}{+}\mathrm{K}^{+}-\mathrm{Cl}^{-})/
(\mathrm{Na}^{+}{+}\mathrm{K}^{+}-\mathrm{Cl}^{-}
+\mathrm{Ca}^{2+})$ ratio
$<$ 0.20, and $\mathrm{Na}^{+}/(\mathrm{Na}^{+}{+}\mathrm{Cl}^{-})$ 
ratio $>$ 0.50 indicate that
the source of Na$^{+}$ ion is plagioclase decomposition and ion
exchange process \citep{Hounslow1995}. Additionally, SiO$_{2}$
content, which is generally between 1--30~mg/l in natural waters, is
higher than 30~mg/l in the Kavak thermal waters, indicating silicate
weathering. The ion exchange process can be indicated by
chloro-alkaline indices (CAI-1 and CAI-2) \citep{Schoeller1965}, and
negative CAI indices reflect the presence of ion exchange in the
system. The CAIs are calculated by the following equations (all ionic
concentrations are expressed by meq/L);
{\begin{eqnarray}\label{eq1}
\text{CAI-}1 &=& [\mathrm{Cl}^--(\mathrm{Na}^{+}+\mathrm{K}^{+})]/\mathrm{Cl}^-  \Seqnsplit
\text{CAI-}2 &=& [\mathrm{Cl}^--(\mathrm{Na}^{+}+\mathrm{K}^{+})]/ (\mathrm{HCO}^{3-}
+\mathrm{SO}_{4}^{2-}+\mathrm{NO}^{3-}).\nonumber\\
\end{eqnarray}}\unskip
The negative of CAI-1 and CAI-2 indicates that Ca$^{2+}$ or Mg$^{2+}$
ions in the groundwater have been replaced by Na$^{+}$ ion in a
hydrodynamic medium (Figure~\ref{fig12}). However, \citet{Sahinci1991}
specified that generally, the chloro-alkaline indices of water emerging
from igneous and metamorphic rocks are also negative because the
contribution of the alkali ions releasing from the decomposition of
silicates is much more than the chloride ion. Accordingly, the
hydrolysis of alkali feldspars in the Paleozoic metamorphics may be
main process for especially high Na$^{+}$ ion in the Kavak thermal
waters. However, the low Na$_{2}$O contents (${<}$1~wt\%) and the low
modal feldspar proportions of the Paleozoic metamorphites 
\citep{Karadag2014} indicate that neither ion exchange nor hydrolysis
of alkali feldspars could not provide high sodium ions to thermal
waters. 

\begin{figure}
\includegraphics{fig11}
\caption{\label{fig11}Ca$^{2+}$/Na$^{+}$ vs. Mg$^{2+}$/Na$^{+}$ diagram
showing end-members; Evaporite dissolution, Silicate weathering, and
Carbonate dissolution, symbols as  Figure~\ref{fig8}. Pamukkale thermals
from \citet{Alccicceketal2019} and Varto themals from
\citet{Karaogluetal2019}.}
\end{figure}

\begin{figure}
\includegraphics{fig12}
\caption{\label{fig12}Chloro-alkaline indices (CAI) of the Kavak
geothermal waters, symbols as Figure~\ref{fig8}.}
\end{figure}

\begin{table*}
\caption{\label{tab1}R-mode correlation matrix of the Kavak thermal
waters (for April 2015)}
\fontsize{10}{11}\selectfont
\begin{tabular}{cccccccccccccc}
\thead
 & {SiO}$_{2}$ & {Ca} & {Mg} & {Na} & {K} & {Fe} & {Li} & {P} & {Rb} & {Sr} & {Ba} & {Al} & {Cs} \\
\endthead
{SiO}$_{2}$ & 1 & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ \\
{Ca} & ${-}$0.86 & 1 & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ \\
{Mg} & ${-}$0.86 & \mn0.96 & 1 & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ \\
{Na} & ${-}$0.76 & \mn0.96 & \mn0.98 & 1 & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ \\
{K} & ${-}$0.84 & \mn0.82 & \mn0.94 & \mn0.86 & 1 & ~ & ~ & ~ & ~ & ~ & ~ & ~ & ~ \\
{Fe} & \mn0.72 & ${-}$0.28 & ${-}$0.31 & ${-}$0.11 & ${-}$0.44 & 1 & ~ & ~ & ~ & ~ & ~ & ~ & ~ \\
{Li} & \mn0.79 & ${-}$0.67 & ${-}$0.59 & ${-}$0.47 & ${-}$0.56 & \mn0.72 & 1 & ~ & ~ & ~ & ~ & ~ & ~ \\
{P} & ${-}$0.62 & \mn0.74 & \mn0.78 & \mn0.81 & \mn0.79 & ${-}$0.07 & ${-}$0.26 & 1 & ~ & ~ & ~ & ~ & ~ \\
{Rb} & \mn0.70 & ${-}$0.48 & ${-}$0.43 & ${-}$0.29 & ${-}$0.47 & \mn0.78 & \mn0.95 & ${-}$0.18 & 1 & ~ & ~ & ~ & ~ \\
{Sr} & ${-}$0.94 & \mn0.92 & \mn0.96 & \mn0.90 & \mn0.94 & ${-}$0.48 & ${-}$0.63 & \mn0.84 & ${-}$0.52 & 1 & ~ & ~ & ~ \\
{Ba} & ${-}$0.96 & \mn0.93 & \mn0.95 & \mn0.89 & \mn0.90 & ${-}$0.50 & ${-}$0.67 & \mn0.79 & ${-}$0.55 & \mn0.99 & 1 & ~ & ~ \\
{Al} & \mn0.12 & ${-}$0.18 & ${-}$0.09 & ${-}$0.16 & \mn0.12 & ${-}$0.12 & ${-}$0.25 & ${-}$0.01 & ${-}$0.36 & ${-}$0.08 & ${-}$0.14 & 1 & ~ \\
{Cs} & \mn0.40 & ${-}$0.19 & ${-}$0.08 & \mn0.05 & ${-}$0.06 & \mn0.69 & \mn0.81 & \mn0.34 & \mn0.80 & ${-}$0.12 & ${-}$0.17 & ${-}$0.23 & 1
\botline
\end{tabular}
\vspace*{-5pt}
\end{table*}


\subsection{Data analysis and geochemical origin of the Kavak thermal
waters}\label{sec42}

To better understand the details of the water--rock interaction and to
classify sampling locations into similar groups, and to identify two
types of thermal water contributing to these groups in the KGF, data
analysis methods were performed by using the published hydrochemistry
data from  \citet{Bozdag2016}. Firstly, cluster analysis was performed
by the method of shortest distance on the Kavak thermal waters to
reveal the relationship between thermal water and rocks/minerals based
on the R-mode analysis and to research spatial distribution of two
types of thermal waters (e.g. their relationship with the faults) based
on the Q-mode analysis. The clustering analysis and factor weights were
calculated for variables from thermal water taken from 8 different
locations (TS1, TS2, TS3, TS4, TS5; TW1, TW2, TW3) in the Kavak
geothermal field by using GEOstats  \citep{GunduzAsan2022}. 

\begin{figure}
\includegraphics{fig13}
\vspace*{-5pt}
\caption{\label{fig13}R-mode cluster analysis (Dendrogram) of the Kavak
thermal waters (single-linkage method).\vspace*{-5pt}}
\end{figure}

The hierarchical cluster analysis with R-mode is based on correlation
coefficients (Table~\ref{tab1}), producing dendrogram (Figure~\ref{fig13}). The
dendrogram consists of two main groups (Group I: K, Ba, Sr, Ca, Na, Mg,
Al, P; Group II: Cs, Rb, Li, Fe, SiO$_{2}$) and 4 sub-groups. These
groups may be attributed to rock-forming minerals especially in
volcanic rocks represented by the ErAVC and metamorphic rocks from the
basement. For example, Subgroup (1) Sr, Ba and K are important
components for biotite and K-feldspar: sanidine is modally rare in the
ErAVC rocks, but they have high normative orthoclase (Or;
KAlSi$_{3}$O$_8$ end-member) content (Table~\ref{tab2}). K may also be
associated with sericite, and other phyllosilicate minerals in the
crystalline basement rocks (e.g. phyllite, schist, etc.). On the other
hand, Sr is an important element for plagioclases as a result of Ca-Sr
substitution. Subgroup (2) Na, Ca and Mg may be interpreted to
plagioclase and mafic silicates (e.g. amphibole, pyroxene) in volcanic
rocks or calcite-dolomite in meta-carbonate rocks. Also, Al and P can
be accepted in the same group as plagioclase and apatite minerals,
respectively. Subroups (3) and (4) Li, Rb, Cs, Fe, and Si are important in
the crystal structure of amphiboles and biotites. 

\begin{figure}
\includegraphics{fig14}
\vspace*{-3pt}
\caption{\label{fig14}Q-mode cluster analysis (Dendrogram) of the Kavak
thermal waters (single-linkage method).}
\end{figure}

\begin{table}
\caption{\label{tab2}Results of CIPW norm calculation (\%) of the ErAVC
\citep{Asan2017,Asanetal2023}}
\begin{tabular}{cccc}
\thead
{~} & {Min} & {Max} & {Mean} \\
\endthead
{Quartz} & \00.99 & 27.75 & 13.27 \\
{Anorthite} & 13.02 & 28.52 & 21.21 \\
{Albite} & 20.90 & 34.19 & 27.80 \\
{Orthoclase} & \09.87 & 24.29 & 18.26 \\
{Pyroxene} & \06.88 & 30.43 & 16.24 \\
{Ilmenite} & \00.63 & \01.98 & \01.29 \\
{Magnetite} & \00.64 & \02.45 & \01.31
\botline
\end{tabular}
\end{table}

\begin{table*}
\caption{\label{tab3}Q-mode correlation matrix of the Kavak thermal
waters (for April 2015)}
\begin{tabular}{ccccccccc}
\thead
~ & {TS1} & {TS2} & {TS3} & {TS4} & {TS5} & {TW1} & {TW2} & {TW3} \\
\endthead
{TS1} & 1 &  &  &  &  &  &  &  \\
{TS2} & 0.997 & 1 &  &  &  &  &  &  \\
{TS3} & 0.999 & 0.999 & 1 &  &  &  &  &  \\
{TS4} & 0.763 & 0.808 & 0.785 & 1 &  &  &  &  \\
{TS5} & 0.801 & 0.844 & 0.822 & 0.995 & 1 &  &  &  \\
{TW1} & 0.813 & 0.855 & 0.830 & 0.973 & 0.986 & 1 &  &  \\
{TW2} & 0.849 & 0.884 & 0.865 & 0.975 & 0.987 & 0.990 & 1 &  \\
{TW3} & 0.845 & 0.881 & 0.861 & 0.977 & 0.989 & 0.993 & 0.999 & 1
\botline
\end{tabular}
\end{table*}

\begin{figure}
\includegraphics{fig15}
\caption{\label{fig15}R-mode factor weights of the Kavak thermal waters
on the diagram.}
\end{figure}


The Cluster analysis based on the Q-mode forms two main groups (Group
I: TS1, TS2, TS3; Group~II: TW1, TW2, TW3, TS4, TS5) and three
subgroups {(Figure~\ref{fig14}, Table~\ref{tab3}).} The Group I,
including subgroup~1, is represented by the first type of thermal
waters (e.g. higher TDS and Cl/Br ratio, and lower dissolved silica and
Br content with discharge temperature of 22~\textdegree C) discharged
along the southern fault whereas the Group II includes the second type
thermal waters (e.g. lower TDS and Cl/Br ratio, and higher dissolved
silica and Br content with discharge temperature of 25 to
46~\textdegree C) discharged along the northern fault, which is close
to the ErAVC (see Figures~\ref{fig2},~\ref{fig3}). In the Group II,
well samples (e.g. Subgroup 2; TW1, TW2, TW3) and spring samples (e.g.
Subgroup 3; TS4, TS5) also form two separate sub-groups. \looseness=1

The grouping of elements resulted from R-mode and Q-mode factor
analysis is similar to hierarchical clustering analysis. In R-mode
factor analysis \mbox{(Figure~\ref{fig15},} Table~\ref{tab4}), K, Sr, Ba, Ca,
Na, Mg and P form a group similar to those of the Group I in the R-mode
cluster analysis, whereas SiO$_{2}$, Li, Rb, Fe and Cs form another
group similar to the Group II in the R-mode cluster analysis. On the
other hand, in Q-mode factor analysis (Figure~\ref{fig16},
Table~\ref{tab5}), TS1 TS2, TS3 samples from the first type thermal
waters and TW1, TW2, TW3, TS4, TS5 samples from the second type thermal
waters form two separate groups as in Q-mode cluster analysis.

\begin{table*}
\caption{\label{tab4}R-mode factor analysis and eigenvalue results of
the Kavak thermal waters for 13 variables}
\begin{tabular}{lccccc}
\thead
{Component}~ & {Factor 1} & {Factor 2} & {Factor 3} & {Factor 4} & {Factor 5} \\
\endthead
{SiO}$_{2}$ & ${-}$0.965 & \mn0.116 & \mn0.181 & \mn0.146 & \mn0.006 \\
{Ca} & \mn0.934 & \mn0.202 & ${-}$0.107 & \mn0.270 & ${-}$0.037 \\
{Mg} & \mn0.946 & \mn0.268 & \mn0.025 & \mn0.109 & \mn0.142 \\
{Na} & \mn0.872 & \mn0.420 & \mn0.017 & \mn0.234 & \mn0.090 \\
{K} & \mn0.917 & \mn0.177 & \mn0.223 & ${-}$0.149 & \mn0.219 \\
{Fe} & ${-}$0.561 & \mn0.661 & \mn0.168 & \mn0.464 & ${-}$0.064 \\
{Li} & ${-}$0.780 & \mn0.583 & ${-}$0.006 & ${-}$0.205 & \mn0.089 \\
{P} & \mn0.735 & \mn0.529 & \mn0.262 & ${-}$0.147 & ${-}$0.287 \\
{Rb} & ${-}$0.668 & \mn0.697 & ${-}$0.093 & ${-}$0.041 & \mn0.165 \\
{Sr} & \mn0.977 & \mn0.183 & \mn0.009 & ${-}$0.105 & ${-}$0.004 \\
{Ba} & \mn0.980 & \mn0.144 & ${-}$0.083 & ${-}$0.073 & ${-}$0.032 \\
{Al} & ${-}$0.004 & ${-}$0.427 & \mn0.900 & \mn0.025 & \mn0.056 \\
{Cs} & ${-}$0.311 & \mn0.896 & \mn0.180 & ${-}$0.237 & ${-}$0.058\vspace*{6pt} \\
{Eigenvalue} & \08.22 & \02.92 & \01.05 & \00.54 & \00.21 \\
{Cumulative eigenvalue} & \08.22 & 11.13 & 12.18 & 12.72 & 12.93 \\
{Variability (\%)} & 63.22 & 22.43 & \08.08 & \04.13 & \01.59 \\
{Cumulative variability (\%)} & 63.22 & 85.65 & 93.73 & 97.85 & 99.45 
\botline
\end{tabular}
{\vspace*{12pt}}
\end{table*}

\begin{figure}
\includegraphics{fig16}
\caption{\label{fig16}Q-mode factor weights of the Kavak thermal waters
on the diagram.}
\end{figure}

\begin{table*}
\caption{\label{tab5}Q-mode factor analysis and eigenvalue results of
the Kavak thermal waters for 8 variables}
\begin{tabular}{lccccc}
\thead
{Component} & {Factor 1} & {Factor 2} & {Factor 3} & {Factor 4} & {Factor 5} \\
\endthead
{TS1} & 0.920 & \mn0.392 & \mn0.004 & ${-}$0.004 & ${-}$0.001 \\
{TS2} & 0.947 & \mn0.322 & \mn0.007 & \mn0.020 & \mn0.004 \\
{TS3} & 0.933 & \mn0.360 & \mn0.019 & ${-}$0.004 & ${-}$0.001 \\
{TS4} & 0.951 & ${-}$0.288 & \mn0.110 & ${-}$0.004 & \mn0.021 \\
{TS5} & 0.970 & ${-}$0.233 & \mn0.061 & \mn0.026 & ${-}$0.027 \\
{TW1} & 0.972 & ${-}$0.205 & ${-}$0.096 & \mn0.059 & \mn0.009 \\
{TW2} & 0.986 & ${-}$0.148 & ${-}$0.049 & ${-}$0.056 & ${-}$0.002 \\
{TW3} & 0.985 & ${-}$0.158 & ${-}$0.051 & ${-}$0.035 & ${-}$0.002\vspace*{6pt} \\
{Eigenvalue} & \07.35 & \00.61 & \00.03 & \00.01 & \0\00.01 \\
{Cumulative eigenvalue} & \07.35 & \07.96 & \07.99 & \08.00 & \0\08.00 \\
{Variability (\%)} & 91.82 & \07.67 & \00.38 & \00.11 & \0\00.02 \\
{Cumulative variability (\%)} & 91.82 & 99.49 & 99.87 & 99.98 & 100.00 
\botline
\end{tabular}
{\vspace*{1pt}}
\end{table*}

\section{Water--rock interaction and conceptual model of the Kavak
geothermal field} \label{sec5}

Whole rock- and mineral chemistry of volcanic rocks are key features of
better understanding the water--rock interaction in geothermal fields
such as KGF where volcanic rocks act as a heat source. The relative
cation chemistry of waters is compared with rocks in Ca--Mg--Na${+}$K
triangular plot to research water--rock interaction in the KGF. In the
Ca--Mg--Na${+}$K triangular diagram, both the ErAVC volcanic rocks and the
Kavak thermal waters plotting close to the Na${+}$K field suggest that high
Na--K concentrations of the Kavak thermal waters can be related to the
ErAVC volcanic rocks and their intrusions. However, the cold waters
show a high tendency towards Ca and Ca${+}$Mg around the KGF 
(Figures~\ref{fig17} and~\ref{fig18}). 

\begin{figure}
\includegraphics{fig17}
\caption{\label{fig17}The relative cation chemistry of the Kavak
thermal and cold water \citep{Bozdag2016} and comparison with the ErAVC
rocks; pointed \citep{Kelleretal1977}, gray dashed-line
\citep{Temeletal1998}, pink-colored \citep{Asan2017,Asanetal2023} in
the (Na${+}$K)--Ca--Mg triangular plot. Altered volcanics are from
\citet{Karakaya2009}. Metamorphic rocks (metapelites, metapsammites, and
metamarls) are from  \citet{Karadag2014}.\vspace*{-5pt}}
\end{figure}

\begin{figure}
\includegraphics{fig18}
\caption{\label{fig18}The relative cation chemistry of the Kavak
thermal water and cold water  \citep{Bozdag2016} and comparison with
the ErAVC rocks; pointed \citep{Kelleretal1977}, gray dashed-line
\citep{Temeletal1998}, pink-colored \citep{Asan2017,Asanetal2023} in
the Na--K--(Ca$+$Mg) triangular plot. Altered volcanics are from
\citet{Karakaya2009}. Metamorphic rocks (metapelites, metapsammites, and
metamarls) are from  \citet{Karadag2014}.\vspace*{-5pt}}
\end{figure}


The Kavak geothermal field is recharged mainly by infiltrating of
meteoric waters, which go down through the faults and fracture/cracks
systems acting as hydrothermal conduits  \citep{Bozdag2016}. The
infiltrated waters are heated by the high thermal gradient of the
Neogene (Miocene--Pliocene) Erenlerda\u{g}--Alacada\u{g} volcanic rocks
in the deep, and then the density of these waters heated at the deep
decreases as a result of increasing temperature and pressure, and so
the thermal waters move up to the surface and/or shallower depths of
the hydrothermal pathways (Figure~\ref{fig19}). The low tritium values 
[${<}$1 TU;  \citealp{Bozdag2016}] of the Kavak thermal waters also
suggest deep circulation and longer residence times. The following
geological model of the region (Figure~\ref{fig19}) is also supported
by the ${\updelta}^{13}$C values in the Kavak travertines and thermal
waters because high ${\updelta}^{13}$C is revealed as a result of
reaching very deep the faults fractures in the region 
\citep{KaraisaogluOrhan2018}.\looseness=-1

\begin{figure*}
\includegraphics{fig19}
\caption{\label{fig19}Unscaled schematic illustration of the
Erenlerda\u{g}--Alacada\u{g} volcanic complex (ErAVC) and Kavak
Travertines modified from  \citet{Bozdag2016}. The geochemical
framework of the geothermal systems that are related to subduction zone
volcanism \citep{HenleyEllis1983}.}
\end{figure*}

Fractured and karstified Palaeozoic carbonates constitute the main
reservoir rocks for the Kavak geothermal waters and, pyroclastic rocks
of the ErAVC can be accepted as the secondary aquifer. Fine-grained
metasandstone, metasiltstone and phyllite in the Paleozoic
metamorphites and the clayey and silty levels of the Neogene units act
as cap rocks for the Kavak geothermal system. The chemical composition
of the Kavak thermal waters is mainly controlled water--rock
interactions including dissolution of the Paleozoic carbonates, and the
decomposition mostly of intrusions of the ErAVC. 

Based on the chemical and statistical data, it has been identified that
there are two distinct types of the thermal waters in the KGF. The
reason for the occurrence of two different types of thermal waters is
thought to be that the fault in the south, where the first type of
thermal waters (TS1, TS2 and TS3) are located, acts as a barrier or
semi-barrier. This is because faults act as a barrier and/or channel
for flow, depending on their composition and the stage of fault
evolution. In other words, a fault may act as a conduit immediately
after deformation and it can later act as a barrier due to the
precipitation of minerals \citep{Caineetal1996}. Therefore, the
partial interruption of the relationship between the first and second
types of the thermal waters due to the southern fault resulted in
slight differences, particularly in the minor ion contents and TDS
values. In addition, the mixing of the first type of thermal water with
colder water caused a greater decrease in temperature compared to the
second type of thermal water.

\section{Conclusions}\label{sec6}

In this study, the water--rock interaction mechanism was investigated
based on the multivariate statistical analysis (e.g. factor analysis
and clustering analysis) using the published water and whole rock
geochemical data from the Kavak Geothermal Field (Konya, Turkey). The
Kavak Geothermal Field (KGF) is controlled by the Seydi\c{s}ehir fault
that is a part of a graben-like structure in an extentional basin. The
KGF overlies a metamorphic basement, yet is located near the
Erenlerda\u{g}--Alacada\u{g} volcanic complex (ErAVC). The metamorphic
basement is \mbox{represented} by low-degree metaclastic and metacarbonate
rocks whereas the volcanic rocks are composed of orogenic-type high-K
calc-alkaline andesite and rhyodacite. The Kavak thermal waters are
meteoric in origin and peripheral waters (Ca--Na--HCO$_{3}$), and are
characterised by high K$^{+}$ and Na$^{+}$ cations, and low pH (between
6.4--6.9~pH) values relative to the cold waters. Two types of thermal
waters were identified in the KGF based on the slight difference in
their hydrochemistry. The first type thermal water has higher TDS and
Cl/Br ratio, and lower dissolved silica and Br content relative to the
second type water. These thermal waters lying along two different
faults allso have a slightly different discharge temperature. Q-mode
cluster and factor analysis confirmed that first type and second type
thermal waters formed two separate statistical groups, which is
compatible with the observed slight geochemical differences between two
types of thermal waters. The reason for the occurrence of two different
types of thermal waters is thought to be that the fault in the south,
where the first type of thermal waters (TS1, TS2 and TS3) are located,
acts as a barrier or \mbox{semi-barrier}. Mixing of the first type of thermal
water with colder water also caused a greater decrease in temperature
compared to the second type of thermal water. 

When compared, hydrochemical properties of the Kavak thermal waters are
similar to the ErAVC relative to the metamorphic basement rocks. R-mode
cluster and factor analysis performed in this study suggests that the
chemistry of the KGF waters was mainly controlled by the composition of
the ErAVC rather than those of the basement metamorphic rocks as a
result of water--rock interaction based on the quantitative of cation
exchanges. In this regard, the Kavak geothermal system was revised to a
new conceptual model considering the influence of the heat source on
the chemistry of the regional thermal waters as a result of water--rock
interaction. 

\section*{Declaration of interests}
The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Acknowledgments} 

This article is based on the first author's study at \mbox{University} of
Poitiers. The authors thank to the editor Dr. Fran\c{c}ois Chabaux and
an anonymous reviewer for their critical and constructive comments that
improved the quality of this paper. The first author also thanks to
Campus France for scholarships to foreign students in France.

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