Quaternary Activity of the Cihanbeyli and Yeniceoba Fault Zones: ‹nönü-Eskiﬂehir Fault System, Central Anatolia

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Quaternary Activity of the Cihanbeyli and Yeniceoba Fault Zones: ‹nönü-Eskiﬂehir Fault System, Central Anatolia

ERMAN ÖZSAYIN & KAD‹R D‹R‹K

Hacettepe University, Department of Geological Engineering, Tectonic Research Laboratory, TR-06800 Ankara, TURKEY (e-mail: eozsayin@hacettepe.edu.tr)

Abstract: The ‹nönü-Eskiﬂehir fault system (‹EFS) is one of the most important fault systems in Central Anatolia and consists of a series of NW–SE- to WNW–ESE-trending fault zones extending from Uluda¤ (Bursa) in the northwest to Sultanhan› in the southeast. Between ‹nönü and Sivrihisar, the Eskiﬂehir fault zone of the ‹EFS trends WNW, but east of Sivrihisar the ‹EFS changes its direction to NW–SE and splays out into four fault zones, named the Il›ca, Yeniceoba, Cihanbeyli and Sultanhan› fault zones and extends to south of Tuzgölü in the east. The NW–SE- trending Yeniceoba fault zone (YFZ), exposed between Günyüzü in the west and Yeniceoba in the east, controls the northern margin of the Kelhasan horst and the southern margin of the Yeniceoba basin. Along this fault zone two sets of superimposed slickenlines indicate older pure right-lateral strike-slip faulting and younger normal faulting with a right-lateral component. The NW–SE-trending Cihanbeyli fault zone (CFZ) is well exposed between north of Sülüklü in the west and Cihanbeyli in the east. It controls the southern margin of the Kelhasan horst, and is marked by fault scarps, triangular facets, alluvial fans and alignment of springs. Recent detailed field mapping and kinematic analysis along the fault planes between Pliocene lacustrine carbonates and younger fluvial clastic rocks has shown that the CFZ consists of a series of parallel normal faults. However, kinematic analysis of the fault slip-plane data indicates that the fault planes cutting the Pleistocene–Holocene clastic sediments of the Cihanbeyli Graben at the southeastern tip of the CFZ are normal faults with a minor sinistral component. The kinematic analyses of fault-slip data clearly indicate that the area experienced NNE–SSW extension. Recent horizontal terrace deposits cut by a series of steeply-dipping normal faults with minor strike-slip component in ‹lhanyayla, Damlakuyu (Çorca) village and nearly 4 kilometres southeast of ‹nsuyu village, which are located on the YFZ and CFZ, indicate that the activity of both CFZ and YFZ continues, controlled by NNE–SSE-directed extension, in the Quaternary. The distribution of earthquake epicentres supports this view and suggests recent activity along the fault zones.

Key Words: Neotectonic, Quaternary activity, kinematic analysis, Tuzgölü, Central Anatolia, ‹nönü-Eskiﬂehir fault system, Cihanbeyli fault zone, Yeniceoba fault zone

Cihanbeyli ve Yeniceoba Fay Zonlar›’n›n Kuvaterner Aktivitesi:

‹nönü-Eskiﬂehir Fay Sistemi, Orta Anadolu

Özet: Bat›da (Uluda¤), güneybat›da Sultanhan› aras›nda yer alan, gidifli KB–GD ile BKB–DGD aras›nda de¤iflen bir dizi fay zonundan oluflan ‹nönü-Eskiflehir fay sistemi (‹EFS), Orta Anadolu’daki en önemli fay sistemlerinden birisidir. ‹EFS’nin en bat› ucundaki kolu olan Eskiflehir fay zonu ‹nönü ile Sivrihisar aras›nda BKB–DGD gidifllidir.

‹EFS, Sivrihisar civar›nda do¤rultular› KB–GD olan dört fay zonuna ayr›larak Tuzgölü’nün güneyine kadar devam eder. Bunlar Il›ca, Yeniceoba, Cihanbeyli ve Sultanhan› fay zonlar›d›r. Bat›da Günyüzü, do¤uda Yeniceoba aras›nda yüzeyleyen KB–GD gidiflli Yeniceoba fay zonu (YFZ) Kelhasan yükselimi’nin kuzey kenar›n› ve Yeniceoba Ovas›’n›n güney kenar›n› kontrol eder. Fay düzlemleri üzerinde üst üste (süperimpoze) gözlenen iki fay çizi¤i seti daha eski sa¤ yanal do¤rultu at›ml› bir faylanmay›, ve daha genç olan sa¤ yanal bileflenli normal bir faylanman›n varl›¤›na iflaret eder. KB–GD gidiflli Cihanbeyli fay zonu (CFZ) bat›da Sülüklü kuzeyi, do¤uda ise Cihanbeyli aras›nda çok belirgin olarak yüzeylenir. Kelhasan yükselimi’nin güney kenar›n› kontrol eden fay zonu, fay diklikleri, üçgen yüzeyler, alüvyon yelpazeleri ve su kayna¤› dizilimleri ile karakterize olur. Pliyosen gölsel kireçtafllar› ile daha genç akarsu klastikleri aras›ndaki fay düzlemlerinde yap›lan güncel ayr›nt›l› saha çal›flmalar› ve kinematik analizler CFZ’nun birbirine paralel ve tamamen normal fay karakterli fay serilerinden olufltu¤unu göstermektedir. Halbuki, CFZ’nun güneydo¤u ucunda yer alan Cihanbeyli Grabeni içinde yer alan Pleyistosen–Holosen yafll› klastikleri kesen faylardaki kayma düzlemi verileri bu faylar›n çok az sol yanal at›m bileflenli normal faylar oldu¤unu göstermifltir.

Tüm fay düzlemlerinin kinematik analizi ise, bölgenin tansiyonel rejimin etkisi alt›nda oldu¤unu ve genifllemenin KKB–GGD do¤rultusunda geliflti¤ini göstermifltir. YFZ ve CFZ üzerinde yer alan ‹lhanyayla, Damlakuyu köyü ve

‹nsuyu köyünün yaklafl›k 4 km do¤usunda yüzeyleyen, yatay konumdaki güncel taraça çökellerini kesen oldukça dik e¤imli, az miktarda do¤rultu at›m bileflenine sahip normal faylar, Cihanbeyli ve Yeniceoba fay zonlar›n›n her ikisinin de Kuvaterner’de aktif oldu¤unu ve KKD–GGB yönlü bir aç›lman›n etkisinde olduklar›n› belirtir. Aletsel dönemde meydana gelen ve deprem d›fl merkezleri fay zonu üzerinde yer alan depremlerin varl›¤› ise, aktivitenin günümüzde de devam etti¤ini kan›tlamaktad›r.

Anahtar Sözcükler: güncel tektonik, Kuvaterner aktivite, kinematik analiz, Tuzgölü, Orta Anadolu, ‹nönü-Eskiﬂehir fay sistemi, Cihanbeyli fay zonu, Yeniceoba fay zonu

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Introduction

Four major neotectonic structures shape Turkey and adjacent areas. These are the right-lateral North Anatolian Fault System, the left-lateral East Anatolian and Dead Sea fault systems, and the Aegean-Cyprus active subduction zone. Besides these major structures, there are some second order structures which divide the Anatolian plate into smaller blocks. These second order structures are the left-lateral Central Anatolian Fault System, the right-lateral Tuzgölü Fault Zone, the ‹nönü- Eskiﬂehir fault system (‹EFS) and the Akﬂehir oblique-slip normal fault zones (Dirik & Göncüo¤lu 1996; Koçyi¤it &

Beyhan 1988; Koçyi¤it et al. 2000; Dirik 2001; Koçyi¤it 2003, 2005; Koçyi¤it & Özacar 2003; Dirik & Erol 2003). The North Anatolian and the East Anatolian fault systems are the intracontinental plate boundaries, active since the Late Pliocene, along which the Anatolian plate is escaping to the WSW onto the oceanic lithosphere of the African plate along the Aegean-Cyprus subduction zone (e.g., Koçyi¤it & Beyhan 1998; Koçyi¤it & Özacar 2003;

Yaltırak et al. 2005; Kaymakcı et al. 2006; Aksoy et al.

2007; Bektaﬂ et al. 2007).

Within these major structures four Neotectonic provinces can be defined, namely: East Anatolian contractional province, North Anatolian province, Central Anatolian province and West Anatolian province (ﬁengör et al. 1985; Bozkurt 2001). The East Anatolian contractional province is characterized by an N–S compressional tectonic regime. The North Anatolian Province, located north of the North Anatolian Fault System (NAFS), is characterized by numerous strike-slip faults with a strong E–W thrust component (ﬁengör et al.

1985). The West Anatolian Province is characterized by NNW–SSE continental extension; E–W-trending grabens and intervening horsts are its most prominent features (e.g., Bozkurt & Mittwede 2005; Erkül et al. 2005;

Tokcaer et al. 2005; Yücel-Öztürk et al. 2005; Ersoy &

Helvacı 2007 and references therein). The Central Anatolian Province, located between the NAFS in the north, the East Anatolian Fault System (EAFS) in the east, and a transition zone in the west, extends nearly N–S along the 37°30´ east meridian (Dirik & Göncüo¤lu 1996;

Koçyi¤it & Beyhan 1998; Dirik 2001; Koçyi¤it & Erol 2001; Dirik & Erol 2003; Koçyi¤it & Özacar 2003;

Koçyi¤it 2005). East of Tuzgölü it is mostly characterized by a contractional-extensional tectonic regime, and mainly strike-slip faults. Koçyi¤it & Erol (2001) stated that the

Konya-Eskiﬂehir neotectonic district west of Tuzgölü is the eastern continuation of extension in west-southwest Anatolia. The ‹nönü-Eskiﬂehir fault system is the most important shear zone in this district. Numerous previous studies pointed out the importance of this system (Ünalan

& Yüksel 1978; ﬁaro¤lu et al. 1987; Koçyi¤it 1991;

Koçyi¤it et al. 1991; Dirik & Göncüo¤lu 1995; Koçyi¤it &

Beyhan 1998; Altunel & Barka 1998; Bozkurt 2001;

Koçyi¤it & Erol 2001; Dirik & Erol 2003; Koçyi¤it 2003, 2005). The WNW–ESE-trending western part of the system is exposed between Uluda¤ and NW of Sivrihisar.

Northwest of Sivrihisar, the system changes its trend to NW and splays into three branches, namely the Ilıca, Yeniceoba and Cihanbeyli fault zones (Koçyi¤it 1991;

Çemen et al. 1999; Dirik & Erol 2000, 2003; Koçyi¤it &

Özacar 2003; Koçyi¤it 2005). The shear zone merges with the Altınekin fault zone southeast of Cihanbeyli. This fault zone was first called the ‘Zıvarık Fault System’ by Erol (1969), but with the name change from Zıvarık to Altınekin, it has been renamed the ‘Altınekin fault zone’

by Dirik & Erol (2003, Figure 1). However, at the same time the fault zone was also named the ‘Konya-Bulok fault zone’ by Koçyi¤it (2003). In this study, we prefer to utilize the name ‘Altınekin fault zone’, as the type locality of this fault zone is in ‘Altınekin County’ where it is characterized by seismically active grabens, hence the priority of this terminology. The southeastern extension of the ‹EFS is the Sultanhanı fault zone (Figure 1). Altunel

& Barka (1998) stated that the western part of this zone consists of sinistral oblique faults with a normal component and separates the Aegean/Western Anatolian block from the Central Anatolian block. Koçyi¤it (2003) named the fault zone the ‹nönü-Eskiﬂehir fault zone and based on more recent studies (Koçyi¤it 2005) concluded that it is the north-northeast boundary of the southwest Turkey extensional province. Although the existence of the ‹EFS has been known for years and its western part is well defined, few kinematic studies have been made in the eastern part of this mega shear zone, and they cannot represent the whole character of, and deformation stages within the southeastern part of the fault system.

The main objective of this paper is therefore to present new kinematic field data from different locations along the southern branches of the shear zone, namely the Cihanbeyli and Yeniceoba fault zones (Figure 2), to determine their initiation times and to show the Quaternary–Recent tectonic activity of both the Cihanbeyli and Yeniceoba fault zones.

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Stratigraphy

The units exposed in the study area are subdivided into two main categories. The Oligo–Miocene and younger units are considered as cover units while older rocks are regarded as the basement units (Figure 3).

Basement Units

The oldest basement units exposed in the south of the area are the Kütahya-Bolkarda¤ı metamorphics (KBM) (Özcan et al. 1990), composed mainly of Palaeozoic–Mesozoic platform carbonates. In the north and west of the study area, ophiolitic rocks form the

basement and are covered by Paleocene red terrestrial clastic rocks. This unit grades up and laterally into Upper Paleocene–Lower Eocene shallow marine rocks. The latter sequence starts with sandy-clayey limestone at the base, overlain in turn by a marl-sandstone alternation and fossiliferous limestone. These carbonates are unconformably overlain by Eocene yellow nummulitic limestone and a greenish grey sandstone-shale alternation.

Cover Units

The Gökda¤ Formation (Göncüo¤lu et al. 1996), comprising the oldest cover rocks, consists entirely of terrestrial sediments and overlies basement rocks with

İnönü ESKİŞEHİR

Sivrihisar Günyüzü

Polatlı

Ilıca

Haymana Bala

ANKARA

KIRIKKALE Keskin

Akpınar Kaman

KIRŞEHİR Kulu

Ortaköy Akgöl

Yunak

Sandıklı

LakeEber AkşehirLake

Hoyran

TUZ GÖLÜ

3268 Ilgın

TUZ GÖLÜ

FAUL TZONE AKŞEHİR

FAUL T ZONE

32 00’⁰

31 00’⁰ 33 00’⁰

34 00’⁰ 34 00’⁰

37 30’⁰ 38 30’⁰ 39 30’⁰

Quaternary alluvial fan deposits and talus Pleistocene-Quaternary basin deposits Miocene-Quaternary volcanics

lake

strike-slip fault normal fault with shown hanging wall

oblique-slip fault study area

burried fault

N

Ş.Koçhisar

Sultandağı Çay

AFYON

Akşehir

Altınekin Sultanhanı

AKSARAY

HASANDAĞ 38 00’⁰

KARACADAĞ Ereğli Karapınar

33 00’⁰ KONYA

32 00’⁰

ALTINEKİN FAUL

TZONE

ALTINEKİN FAUL

TZONE SUL

TANHANI FAUL

T ZONE SUL

TANHANI FAUL

T ZONE ILICA

FAULT ZONE ILICA

FAULT ZONE ESKİŞEHİR

FAULT ZONE

Cihanbeyli CİHANBEYLİ

FAULT ZONE YENİCEOBA

FAULT ZONE ^Yeniceoba

0 60 km

Figure 1. Tectonic map of the study area and surrounding regions (modified from Dirik & Göncüo¤lu 1996; Göncüo¤lu et al. 1996; Dirik 2001; Dirik

& Erol 2003; Koçyi¤it & Özacar 2003).

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Hacıömeroğlu Tüfekçipınarı

Kandil Ortakışla Hatırlı SÜLÜKLÜ Zaferiye Harabe Böğrüdelik

Kelhasan

BüyükbeşkavakKüçükbeşkavak Kütükuşağı YENİCEOBA

Yeniceoba Ova Kuşça half-graben Damlakuyu (Çorca) CİHANBEYLİ

Tuğtepe

Kuşça Pınarbaşı Çıngırık İnsuyu İlhanyayla

C i h a n b e y l i

F a u l t

Z o n e

Y e n i c e o b a F a u l t

Z o n e

Kelhasan Horst

N

ab Figure 2. (a)Simplified map showing major neotectonic structures shaping Turkey. (b)Perspective relief map of the study area.

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AGE UNITTuzgölüCihanbeyli KuşçamemberGökdağ

L I T H O L O G Y D E S C R I P T I O N

Pliocene Pleistocene Holocene Oligo-Miocene basement rocks

angular unconformity

angular unconformity disconformity

greyish white Triassic crystalline limestone blocks and ophiolitic mélange

x: light brown-cream, unsorted, thick-bedded polygenetic conglomerate-coarse sandstone alternation

y: light brown, sandy claystone-mudstone alternation with conglomerate intercalations

z: light brown-cream, mudstone-tuffite alternation m: light brown-red, unsorted, carbonate cemented,

polygenic conglomete-sandstone alternation n: white-cream, porous, thick-bedded lacustrine

limestone and thin- to medium-bedded claystone alternation

a: grey gravel-sand facies b: silt-clay facies

tiltedslightly towardsTuzgölü c: lime-clay facies

d: sand-clay facies

e: carbonate, gypsum and sulphate facies A: terrace deposits

B: Recent alluvial fan deposits C: Recent alluvium

brick red, thick- to thin-bedded conglomerate-sandstone alternation

yellow to green claystone-mudstone-sandstone alternation

Kütahya-Bolkardağı metamorphics ophiolitic mélange

Paleocene terrestrial clastics

Paleocene-Eocene shallow-marine carbonates a

x m

n y

z

b c

d e

B C

palaeotectonicperiod (contractionalregime)neotectonicperiod (extensionalregime) A

?

Figure 3. Generalized tectono-stratigraphic columnar section of the study area.

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angular unconformity (Figure 3). A basal alternation of grey conglomerate and sandstone is overlain by a red conglomerate-mudstone alternation. Gypsum occurs in the upper levels of the formation occasionally.

The Pliocene Cihanbeyli Formation overlies the Gökda¤ Formation and older units with angular unconformity (Figure 4) and is composed of very thick- bedded white to cream, porous limestone and claystone.

In the southern part of Yeniceoba, the formation is characterized by grey, well-sorted, polygenetic conglomerate and a light grey, coarse- to medium- grained sandstone alternation at the base, overlain by a grey-red mudstone-tuffite alternation, named here the Kuﬂça member. The most diagnostic character of the Kuﬂça member is its tuffite content. The following Ostracoda fauna were found in this formation by Tuno¤lu et al. (1995): Cyprideis torosa Jones, 1850; Candona (Candona) neglecta Sars, 1888; Candona (Candona) paralella pannonica Zalanyi; Candona (Candona) altoides Petkovski, 1961; Candona (Pseudocandona) compressa Koch 1837; Heterocypris ponticus Krstic, 1973. Based on these fauna present in limestone levels of the sequence, a Pliocene age was assigned to the Cihanbeyli Formation by Tuno¤lu et al. (1995) and Beker (2002).

The Cihanbeyli Formation grades up into the Pleistocene Tuzgölü Formation (Ulu et al. 1994), comprising poorly consolidated conglomerates and sandstones with carbonate, gypsum and sulphate deposits in the upper levels. The unit dips gently to the E/ESE towards Tuzgölü; cross bedding in sandy beds is the most important syn-sedimentary structure.

Quaternary alluvial fans adjacent to fault scarps of the Cihanbeyli fault zone, terrace deposits, slope debris, sodium sulphate deposits around Bolluk Lake, and recent alluvial deposits of the ‹nsuyu stream are the youngest lithologies in the study area. They all unconformably overlie the older rocks (Figure 3).

‹nönü-Eskiﬂehir Fault System

An approximately 470-km-long and WNW–ESE- to NW–SE-trending active mega shear zone is exposed between Uluda¤ in the west and Sultanhanı in the east.

This mega shear zone forms a transitional boundary between continental extension in the south and strike- slip faulting in the north (Koçyi¤it 2003). This structure was simultaneously named the Eskiﬂehir-Sultanhanı

Fault System by Dirik & Erol (2003) and the ‹nönü- Eskiﬂehir Fault Zone by Koçyi¤it (2003). The type locality of this shear zone is ‹nönü County (Koçyi¤it 2003), and it has therefore been named the ‘‹nönü- Eskiﬂehir fault zone’. Detailed field studies have shown that this mega shear zone includes four fault zones, namely the Ilıca, Yeniceoba, Cihanbeyli and Sultanhanı fault zones (Çemen et al. 1999; Dirik & Erol 2003;

Özsayın & Dirik 2005). Therefore, the rank of ‹nönü- Eskiflehir fault zone is shifted up to ‘system’ and renamed as ‘‹nönü-Eskiflehir fault system’ (‹EFS) in this paper. The WNW–ESE-trending western part of the system, the Eskiflehir fault zone, is exposed between Uluda¤ and NW of Sivrihisar, where it controls the southern margins of the incipient Eskiflehir graben (Koçyi¤it 2003). According to Koçyi¤it (2003), two sets of superimposed slickensides indicate older dextral strike-slip faulting (contractional phase) and younger normal faulting (extensional phase). Northwest of Sivrihisar, the system changes its trend to SE and splays into three branches, namely the Ilıca, Yeniceoba and Cihanbeyli fault zones. The southeastern extension of the ‹EFS is the Sultanhanı fault zone (Figure 1). The present study is concerned with the Cihanbeyli fault zone and the eastern part of the Yeniceoba fault zone.

Cihanbeyli Fault Zone

The Sivrihisar-Cihanbeyli branch of the fault system was first named the Sivrihisar-Cihanbeyli fault zone by Dirik &

Göncüo¤lu (1995). But, as it is well exposed between Sülüklü and Cihanbeyli, and the type locality is west of Cihanbeyli county, it was renamed the Cihanbeyli fault zone by Çemen et al. (1999). The Cihanbeyli fault zone (CFZ) is about 80 km long and well exposed between Cihanbeyli in the east and northwest of Sülüklü in the west (Figures 1, 2 & 5). It is the southern branch of the

‹EFS and consists of a set of parallel faults. The fault zone trends approximately N50°W between Cihanbeyli and Sülüklü, then changes its direction to N25°W. The central and western faults of this zone have south dipping fault planes whereas the eastern faults have both north- and south-dipping planes which form a very characteristic extensional structure first described by (Erol 1969, figures 8 & 9) as the ‘Cihanbeyli-‹nsuyu fault valley’

(Figure 6). This extensional structure, later described as a graben and named the ‘Cihanbeyli graben’ by Koçyi¤it (2005), is an approximately 0.4-km-wide and 15-km-

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long and NW–SE-trending Quaternary depression located between the Cihanbeyli and Çıngırık fault zones (Figures 5 & 6). The graben affects the Pliocene Cihanbeyli formation and is filled by Pleistocene–Holocene fluvial sediments. Beyond Çıngırık, the fault zone controls the southern margin of the Kelhasan horst, and is characterized by fault scarps, triangular facets, alluvial fans and alignment of springs (Figure 2).

Yeniceoba Fault Zone

The Yeniceoba fault zone (YFZ) (Çemen et al. 1999), exposed between the southeastern part of Yeniceoba in the east and Günyüzü town in the west, is about 130 km long (Figures 1 & 5). Like the CFZ, this zone consists of

NW–SE-trending faults. Fault planes of this zone are steeper than those of the CFZ and have both NE and SW dip directions. The YFZ controls both the northern margin of Kelhasan horst and the southern margin of Yeniceoba basin (Figure 2). This fault zone is characterized by linear valleys, fault scarps in the middle and northwestern and alignment of alluvial fans in the southeastern parts. In the southeast of this zone, there is a suspended basin named the Kuﬂça half-graben (Figure 2).

A fault plane, seen west of Kütükuﬂa¤ı village, displays two different sets of slickenlines (Figure 7). The first set of slickenlines are horizontal and give right-lateral movement, while the second set show normal fault movement with right-lateral component. The oblique slickenlines cut the horizontal ones (Figure 7). This

Paleocene-Eocene shallow-marine carbonatesPaleocene-Eocene shallow-marine carbonates Cihanbeyli Formation

Kuşça member Cihanbeyli Formation

Kuşça member ophiolitic mélange

ophiolitic mélange

Paleocene terrestrial clastics Paleocene terrestrial clastics Gökdağ

FormationGökdağ Formation

Recent alluvion Recent alluvion

NE NE SW

SW

330⁰ 330⁰ 15 NE⁰ 15 NE⁰ S45 W⁰ S45 W⁰

b a

33 cm 33 cm

Figure 4. (a) General view showing the compressional low-angle tectonic boundary (thrust) between the basement rocks and Gökda¤ Formation, and Pliocene Kuﬂça member of Cihanbeyli Formation sealing this compressional regime. (b) Close-up view of the tectonic boundary between ophiolitic mélange and Gökda¤ Formation.

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situation represents a two-stage deformation on this fault zone. A stereographic plot of the first set of fault slip-plane data indicates that they are right-lateral strikeslip fault with N–S-directed compression on them (Figure 7).

Besides, some fault slip-plane data are measured from a road cut near Damlakuyu village (north of Cihanbeyli). The host unit is the fluvial clastics of the Tuzgölü Formation and Quaternary deposits. These sediments are cut by NW–SE-trending and steeply north-dipping normal faults.

A stereographic plot of these fault slip-plane data indicates a NNE–SSW-directed extension (Figures 8 & 10j).

Deformation on the Yeniceoba fault zone around Kuflça village was also carefully investigated. Basement rocks are thrust onto the Gökda¤ Formation and the Kuflça member of Cihanbeyli Formation overlies this thrust belt with angular unconformity (Figure 4). Beds of the Kuflça member are horizontal and show no evidence of N–S compression. Hence, this is important evidence for showing that the compressional-contractional regime (palaeotectonic period) ended at the end of Miocene.

Kinematic Analysis

During field work in the summers of 2004, 2005, 2006 and 2007 we mapped the fault zone in detail. Special attention was given to fault planes with slip lines. The data was acquired from 10 stations, namely Hacıömero¤lu, Kuﬂça, Tu¤tepe, Pınarbaﬂı, Çıngırık,

‹nsuyu, 4 km east of ‹nsuyu, ‹lhanyayla (2 stations) and Damlakuyu (Figures 5; Table 1).

Hacıömero¤lu

Hacıömero¤lu is at the northwestern end of the Cihanbeyli fault zone (Figure 9a). 28 fault-slip data were taken from this location. Slickenlines are the main indicators (Figure 9b, c). The host unit is the Gökda¤

Formation. The principal stress distribution is σ1= 013°/75°, σ2= 105°/01° and σ3=195°/15° (Figure 10a, b).

Cihanbeyli İnsuyu

İlhanyayla Cihanbeyli graben

Pınarbaşı Tuğtepe Böğrüdelik

Harabe Sülüklü

Hatırlı

Hacıömeroğlu

Kandil

Kelhasan

Kütükuşağı

Yeniceoba

Kuşça

Damlakuyu Çıngırık

sites of stations where slip data were measured sites of stations where photos were taken

Figure 9

Figure 6

Figure 8

Figure 7 Figure 11

Figure 12

Figure 13 Figure 15

Figure 16

Figure 5

N

0 10 km

Ortakışla

normal fault with shown hanging wall

Zaferiye C İ H

A NB E

Y Lİ FA U

L T Z O N E C İ H

A NB E

Y Lİ FA U

L T Z O N E Y EN İ C

E OB A

F AU LT

Z ON E Y EN İ C

E OB A

F AU LT

Z ON E

Figure 5. The map of Cihanbeyli and Yeniceoba fault zones illustrating their segments and sites of observations where slip-data were measured.

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Kuﬂça

Kuﬂça village is southwest of Yeniceoba. 4 fault-slip data were taken, and slickenlines were the main indicators.

The host unit is the Kuﬂça member of Cihanbeyli Formation. The principal stress distribution is σ1= 098°/77°, σ2= 323°/09° and σ3= 232°/09° (Figure 10a, c).

Tu¤tepe

Tu¤tepe is located approximately 5 km SE of Bö¤rüdelik village (Figure 6), at the point where the normal fault stepped right. Fault breccia is the dominant indicator but only 4 slickenlines could be determined at this location.

The principal stresses are σ1= 036°/73°, σ2= 300°/02°

and σ3= 209°/17° (Figure 10a, d).

Pınarbaﬂı

22 measurements of fault slip data were taken from Pınarbaﬂı village. The dominant fault type is pure dip slip (Figure 11a). Slickenlines, fault breccia are the main indicators (Figure 11b) and a big spring supplying water to the ‹nsuyu Stream exists at this location (Figure 11c).

The principal stress distribution is σ1= 031°/71°, σ2= 293°/03° and σ3= 202°/19° (Figure 10a, e).

Çıngırık

23 measurements of fault-slip data were taken from the fault scarps north of Çıngırık village (Figure 5). The host unit is the Pliocene Cihanbeyli Formation. Slickenlines and fault breccia are the dominant indicators of the fault (Figure 12a, b). 21 slip data are pure dip slip and the NE

NE NE NE

SW SW SW SW Kale

Ortakale Kale Ortakale 1050 m

1050 m

b a

CİHANBEYLİ CİHANBEYLİ

Figure 6. Close-up (a) and general (b) views of the Cihanbeyli graben.

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other two are normal with a sinistral component. The principal stresses are σ1= 017°/75°, σ2= 110°/01° and σ3= 200°/15° (Figure 10a, f).

‹nsuyu

13 measurements of fault-slip data taken from north of

‹nsuyu village are shown in Figure 5. The host unit is the Cihanbeyli Formation. At this location most faults are normal faults with a dextral component (Figure 10). The main faulting and a splay fault intersect and form a fault wedge at ‹nsuyu (Figure 13). This wedge is a releasing wedge and the faults form a little graben structure.

Slickenlines, fault breccia and flat iron faces are the indicators. The principal stress distribution is σ1= 001°/69°, σ2= 153°/18° and σ3= 246°/09° (Figure 10a, g).

4 km East of ‹nsuyu

At this location, nearly 4 km east of ‹nsuyu village, the Cihanbeyli graben is located (Koçyi¤it 2005). A set of faults cuts Quaternary alluvium and the dominant fault type is normal with a minor sinistral component. The main indicators are the slickenlines. The strikes of the faults change between N30°W and N65°W. The displacements of the blocks are 30 cm to 60 cm (Figures 12 & 13). The principal stress distribution of the Quaternary faults are σ1= 202°/72°, σ2= 296°/01° and σ3= 026°/18°, respectively (Figure 10a, h).

first phase (right-lateral)first phase

(right-lateral) second phase (normal with right-lateral comp.)

second phase (normal with right-lateral comp.)

a

b

c

horizontal component of 3

horizontal component of 1

55mm 55mm

Figure 7. General (a) and close-up (b) views of the fault plane which have two superimposed slickenlines observed at the west of Kütükuﬂa¤ı village; (c) stereographic plots of fault-slip plane data on Schmidt lower hemisphere, σ1, σ2, σ3are principal, intermediate and least stress axes, respectively.

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a b

45 cm 45 cm

26 mm 26 mm

Figure 8. General (a) and close-up (b) views of the fault observed at Damlakuyu village near the road-cut.

Hacıömeroğlu Hacıömeroğlu

_ +

~N25W

~N25W N N W

W

b a

c

33 cm 33 cm

28 cm 28 cm

Figure 9. General and close-up views of Hacıömero¤lu station and fault planes.

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Hacıömeroğlu OrtakışlaOrtakışla Hatırlı SÜLÜKLÜ Zaferiye Harabe Böğrüdelik Pınarbaşı Çıngırık İnsuyu

Damlakuyu

Büyükkartal

YENİCEOBA Kuşça

Kütükuşağı CİHANBEYLİresidentials sitesofstationswhere slip-dataweremeasured

010km

(b)(j) (c)(h) (d)(e)(g)(i)(f)

n=28n=28 n=4 n=5n=22n=21n=12n=4n=8

a N

1 2 3

horizontal component

of3 Figure 10.Shaded relief map showing the sites of stations where slip-data were measured and stereographic plots of fault-slip plane data on Schmidt lower hemisphere, σ1, σ2, σ3are principal, intermediate and least stress axes, respectively.

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Table 1. Measurements of slickensides and slickenlines on Hacıömero¤lu, Kuﬂça, Tu¤tepe, Pınarbaﬂı, Çıngırık,

‹nsuyu, 4 km east of ‹nsuyu, ‹lhanyayla (2 stations) and Damlakuyu stations.

location no dip direction dip amount rake sense principal φ

(ºN) (º) (º) stress axes

1 115 34S 89S Normal

4 150 57S 20S Dextral

7 117 43S 89E Normal

10 118 73S 89S Normal

11 117 40S 89S Normal

12 132 80S 89S Normal

13 130 67S 89S Normal σ1= 013º / 75º

Hac›ömero¤lu 14 120 69S 89S Normal σ2= 105º / 01º 0.315

15 235 73N 30W Dextral σ3= 195º / 15º

16 140 79S 89S Normal

17 256 66N 40W Dextral

18 135 89S 89S Normal

19 120 15S 89S Normal

20 112 87S 50W Sinistral

21 124 70S 89S Normal

22 122 54S 60E Normal

23 110 64S 89S Normal

25 85 75S 89W Normal

26 120 88S 89S Normal

27 135 88S 89S Normal

28 112 70S 89S Normal

Tu¤tepe 2 320 60S 89S Normal σ1= 036º / 73º 0.185

3 310 78S 89S Normal σ2= 300º / 02º

4 295 72S 89S Normal σ3= 209º / 17º

2 95 78S 89E Normal

10 135 89S 89E Normal σ1= 031º / 71º

P›narbaﬂ› 11 140 70S 89E Normal σ2= 293º / 03º 0.167

12 135 65S 89E Normal σ3= 202º / 19º

13 130 89S 89E Normal

14 130 61S 89E Normal

15 140 60S 89E Normal

16 150 65S 89E Normal

17 130 68S 89E Normal

18 150 60S 89E Normal

19 115 65S 89E Normal

20 120 65S 89E Normal

21 122 66S 89E Normal

22 145 55S 89E Normal

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Table 1. Continued.

10 145 75S 89E Normal σ1= 017º / 75º

Ç›ng›r›k 11 175 75E 89S Normal σ2= 110º / 01º 0.233

12 150 51S 89E Normal σ3= 200º / 15º

13 140 66S 89E Normal

14 128 45S 89E Normal

15 135 66S 89E Normal

16 125 70S 89E Normal

17 150 59S 89E Normal

18 135 68S 89E Normal

19 155 60S 89E Normal

20 120 75S 89E Normal

21 125 85S 89E Normal

5 125 89S 89S Normal σ1= 001º / 69º

‹nsuyu 6 135 60S 55W Normal σ2= 153º / 18º 0.390

7 140 70S 71W Normal σ3= 246º / 09º

10 141 56S 70W Normal

11 179 62W 78S Normal

12 145 46S 58W Normal

1 300 80N 70W Normal

4 km east 3 330 67N 70W Normal

of ‹nsuyu 4 325 76N 70W Normal σ1= 242º / 68º

5 328 68N 75W Normal σ2= 099º / 18º 0.273

6 310 70N 72W Normal σ3= 005º / 12º

1 25 71B 89N Normal

‹lhanyayla 2 35 75B 89N Normal σ1= 140º / 69º

3 45 81B 80N Normal σ2= 256º / 10º 0.206

4 50 80B 80N Normal σ3= 349º / 18º

1 345 10D 89N Normal

Kuﬂça 2 325 30D 89N Normal σ1= 098º / 77º

3 335 15D 89N Normal σ2= 323º / 09º 0.498

4 310 30G 89N Normal σ3= 232º / 09º

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‹lhanyayla

At this location two different faults, approximately 400 m apart, cut the Quaternary units. Additionally, four measurements of fault-slip data could be taken from both locations (Figure 16), so the slip data are evaluated together. Slickenlines are the main indicators at two locations. The displacements of the blocks range from 10 cm to 120 cm. The principal stresses distribution of the

‹lhanyayla faults are σ1= 140°/69°, σ2= 256°/10° and σ3= 349°/18°, respectively (Figure 10a, i).

Damlakuyu

Damlakuyu is north of Cihanbeyli. Field work in 2006 included observation of a new road cut in which Tuzgölü Formation, Quaternary units and the NW–SE-trending faults can be seen clearly. The fault planes dip both NE and SW. There are also some second order conjugate faults. Slickenlines are the main indicators. The displacements on fault planes range from 5 cm to 40 cm (Figure 8). The principal stresses distribution the faults are σ1= 151°/77°, σ2= 272°/07° and σ3= 003°/11°, respectively (Figure 10a, j).

Table 1. Continued.

1 310 89K 2N Sinistral

2 320 89K 2N Sinistral

3 38 84G 10S Dextral

4 328 59G 89N Normal

5 313 75K 89N Normal

6 345 68D 89N Normal

7 280 56K 89E Normal

8 60 35G 80W Normal

9 50 30G 80W Normal

10 305 80G 2S Sinistral

11 280 79K 89E Normal

12 40 89K 1E Dextral σ1= 151º / 77º

13 100 71K 89E Normal σ2= 272º / 00º 0.425

Damlakuyu 14 85 33G 89E Normal σ3= 003º / 11º

15 315 60K 89E Normal

16 115 46K 70S Normal

17 125 44K 89E Normal

18 60 44G 80W Normal

19 70 30G 89E Normal

20 320 56K 89E Normal

21 345 43D 89N Normal

22 310 49K 89E Normal

23 80 45G 89E Normal

24 122 55G 60E Normal

25 110 35K 89E Normal

26 135 35K 89E Normal

27 90 82K 80E Normal

28 20 25G 45S Normal

1 320 80N 1W Dextral

Kütükuﬂa¤› 2 322 80N 1W Dextral σ1= 182º / 11º

bat›s› 3 315 80N 1W Dextral σ2= 068º / 65º 0.302

4 318 80N 1W Dextral σ3= 277º / 23º

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Pınarbaşı Pınarbaşı N

N SS

a b

c

85 mm 85 mm

250 cm 250 cm

Figure 11. General (a) and close-up (b) views of Pınarbaﬂı station; (c) fault plane and artificial pool in front of the Pınarbaﬂı spring.

Çıngırık Çıngırık

SS NN

b a

175cm175cm 6 cm

6 cm

Figure 12. General and close-up views of slickensides at Çıngırık station.

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N50W N50W

EW EW

İnsuyu İnsuyu

NW

NW SESE

SS NN

a

b c

175cm175cm

Figure 13. General (a) and close-up views of ‹nsuyu station and fault planes forming the fault wedge (b, c).

İnsuyu

a

Quaternary faults

SW

A B

NE

Not to scale

(b)

Cihanbeyli Formation location of Quaternary faults normal fault with shown hanging wall

talus alluvium

İnsuyu Stream

A B

Figure 14. (a) Shaded relief map of ‹nsuyu village and surroundings. (b) Sketched geological cross section showing the relationship between main fault and Quaternary faults.

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N

N SS N N SS

N N

SS N SS

a b

c d

e f

176cm176cm

6 cm 6 cm

26 mm 26 mm

Figure 15. General view of fault planes cutting Holocene deposits at 4 km east of ‹nsuyu village (a-d) and close-up view of fault seen on (d).

Slickenlines indicate normal faulting with a minor amount of sinistral strike-slip component.

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EE WW

b c

a

175cm175cm

Figure 16. Three photographs illustrating general (a, b) and close-up views (c) of the faulting in Quaternary alluvium at

‹lhanyayla village.

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There are no reported damaging historical earthquakes on the Cihanbeyli fault zone. But the epicentres of earthquakes with magnitudes ranging from 2 to 5 show the seismic activity of the zone in recent time (Figure 17).

Discussion and Conclusions

The mega shear zone extending from Uluda¤ in the west to Sultanhanı in the east is composed of a series of NW–SE- to WNW–ESE-trending fault zones, namely the Eskiﬂehir (EFZ), Ilıca (previously named the ‘Ilıca fault set’

by Koçyi¤it 1991), Yeniceoba (YFZ), Cihanbeyli (CFZ) and Sultanhanı (SFZ) fault zones. Since this mega shear zone is not a single fault zone, but composed of different fault zones, the rank of the ‹nönü-Eskiﬂehir fault zone was shifted up to ‘system’ and renamed the ‘‹nönü-Eskiﬂehir fault system’ (‹EFS). The YFZ controls both the northern margin of Kelhasan horst and the southern margin of

Yeniceoba basin. Recent field observations and kinematic analyses show the YFZ to have two stages of deformation. The first stage has right-lateral strike-slip faulting which must be evaluated by N–S compressional regime due to pure shearing. The second stage was normal faulting with right-lateral component. The latest faulting observed on the road-cut near Damlakuyu gives us the NNE–SSW-directed extension. This result reveals that the YFZ and EFZ were formed and evolved at similar times with similar character and consistent with Koçyi¤it’s results (2005).

The southern branch of the ‹EFS, the Cihanbeyli fault zone, between Sülüklü in the northwest and Cihanbeyli in the southeast, controls the southern margin of Kelhasan horst. Stereographic plots of the fault slip-plane data obtained from the southern margin-faults of Kelhasan horst, show that the CFZ movement was purely normal faulting. The zone trends N50°W, dips to the south, and its active extension direction is approximately NE–SW.

ANKARA

KIRIKKALE

AFYON

Polatlı

Bala

Keskin

Kaman ^Akpınar Kulu

Cihanbeyli Yunak

Akşehir

Ilgın Altınekin

F AU L T S YS

T EM A KŞ E

H İR F AU

L TZ ONE

32 00’⁰ 31 30’⁰

31 30’⁰ 31 00’⁰

39 30’⁰

38 30’⁰

33 00’⁰ 33 30’⁰ 34 00’⁰

ESKİŞEHİR ^{32 30’}

0

Haymana Sivrihisar

39 00’⁰

Bolvadin

Sultandağı

Sultanhanı AKSARAY

38 30’⁰ 39 00’⁰ Ş.Koçhisar

İ NÖN Ü-

ESK İ ŞEH

İ R

T UZ G ÖL Ü

F AU L TZ O

NE

32 30’⁰

32 00’⁰ 33 00’⁰ 33 30’⁰ 34 00’⁰

earthquake epicentres and magnitudes

5 > M > = 4 2 > M > = 3.9

6 > M > = 5 M > = 6

lake strike-slip fault normal fault with shown hanging wall normal fault with strike-slip component burried fault

Tuzgölü

0

N

50 km

Figure 17. Seismotectonic map of the Cihanbeyli and neighboring fault zones (modified from Dirik & Erol 2003).

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The Cihanbeyli graben, at the southeastern tip of the CFZ, is an important structure of this zone. Formed on the Pliocene Cihanbeyli formation, it was filled by Pleistocene–Holocene fluvial sediments. Kinematic analysis of the fault slip-plane data indicates that they are normal faults with a minor sinistral component with NNE–SSW-directed extension on them. However, based on his stereographic plot of fault slip-plane data, Koçyi¤it (2005, figure 40a) indicated the presence of NNW–SSE extension on margin-bounding faults of the graben and faults cutting Holocene graben fill. But, our results remain consistent with the regional results of Koçyi¤it (1991, 2005).

The above-mentioned situations reveal that the YFZ was initiated as a right-lateral strike-slip fault before the Pliocene and continues to move with dextral strike-slip deformation with N–S-directed compression. This compressional phase was followed by extensional faulting. However, only the CFZ shows NNE–SSW extension on every part of it. Comparison between the

final stage (NNE–SSW extension) of the YFZ and the whole character of the CFZ shows that the formation of CFZ is later than the formation of the YFZ. Fault trends in the Oligo–Miocene Gökda¤ Formation and Pliocene Cihanbeyli Formation are nearly parallel to Quaternary fault trends, and the kinematic results are similar. This indicates that the earliest initiation of motion along the CFZ is Late Pliocene and both the Cihanbeyli and Yeniceoba fault zones are active in the Quaternary. This result is also consistent with the results of Koçyi¤it (2003).

Acknowledgements

The field work was supported by Hacettepe University Scientific Research Fund project no 02 02 602 012.

Special thanks are due to Bülent Akıl for help during field studies. The authors also wish to express their thanks to two reviewers, for valuable and constructive comments and contributions. John A. Winchester helped with the English of the final text.

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