Middle Eocene paleomagnetic data from the eastern Sakarya Zoneand the central Pontides: Implications for the tectonic evolutionof north central Anatolia

Mualla Cengiz Çinku,1 Z. Mümtaz Hisarlı,1 Friedrich Heller,2 Naci Orbay,1

and Timur Ustaömer3

Received 17 March 2010; revised 19 October 2010; accepted 4 November 2010; published 17 February 2011.

[1] A paleomagnetic investigation has been carriedout on Middle Eocene volcanic rocks at 23 sites inthe eastern Sakarya Zone and the central Pontides ofnorth central Anatolia in order to better understandthe regional tectonic evolution of the main zones ofnortheastern Anatolia in the Middle Eocene. Theresults constrain the tectonic evolution of the areawhen evaluated in conjunction with earlier publishedpaleomagnetic directions from 92 localities. Smallcounterclockwise rotations in the range of R ± DR =−1.3 ± 1.4° to R ± DR = −17.2 ± 16.8°, with respectto Eurasia, are observed in the central Pontides on thenorthern side of the North Anatolian Fault (NAF).Clockwise rotations ranging between R ± DR =8.5 ± 15.1° and R ± DR = 29.7 ± 12.0° are observedbetween the NAF and the Sungurlu Fault (SF), in theeastern Sakarya zone. Counterclockwise rotations ofR ± DR = −18.9 ± 12.4° to R ± DR = −42.2 ± 6.9°are observed to the south of the SF. Our findings, com-bined with previous data, support the indentationmodel of Kaymakcı et al. (2000, 2003a, 2003b), whichpostulates the collision and northeast directed inden-tation of the Kırşehir Block into the Sakarya Zone.This model, which was developed to explain the evo-lution of the Çankırı Basin, can also explain the vari-able magnitudes of paleomagnetically determinedrotations, thrust directions, and the curvature of theNorth Anatolian ophiolite belt. Citation: Çinku, M. C.,Z. M. Hisarlı, F. Heller, N. Orbay, and T. Ustaömer (2011),Middle Eocene paleomagnetic data from the eastern SakaryaZone and the central Pontides: Implications for the tectonicevolution of north central Anatolia, Tectonics, 30, TC1008,doi:10.1029/2010TC002705.

1. Introduction[2] Present‐day Anatolia comprises several lithospheric

fragments, including the Arabian Platform, the Anatolide‐Tauride Platform, the Kırşehir Block, and the Pontides, allseparated by Late Mesozoic to Cenozoic Neotethyanophiolitic suture zones (Figure 1a). The Istranca Massif andthe İstanbul Fragment in the northwest Pontides are Var-iscan continental terranes. The rest of the Pontides is termedthe Sakarya Zone [Okay, 1989], which is characterized by aJurassic to Late Cretaceous platform with a sedimentarysuccession, deposited on a heterogeneous basement of high‐grade continental metamorphic rocks. Structurally it overliesPaleotethyan accretionary subduction complexes of Permo‐Triassic age. The Pontides are assumed to be part of Eurasiawhile the other continental pieces were detached fromGondwana and carried northward during the rifting andsubsequent spreading of the different branches of the Neo-tethyan ocean [Şengör and Yılmaz, 1981; Yılmaz et al.,1997a, 1997b; Okay and Tüysüz, 1999; Robertson et al.,2009]. During the Late Mesozoic and Cenozoic, the north-ern Neotethys oceanic basin was progressively closed bynorthward subduction. This subduction was marked by theformation of a magmatic arc and fore‐arc basins, and theemplacement of large ophiolitic mélanges that were thrustover the Taurides to the south and the Pontides to the north[Şengör and Yılmaz, 1981; Şengör, 1995; Okay and Tüysüz,1999; Rice et al., 2006, 2009; Robertson et al., 2009].[3] The remnants of the northern branch of the Neotethys

collectively are known as the Izmir‐Ankara‐Erzincan SutureZone (IAESZ). This zone separates the Pontides in the northfrom the various units of the Anatolide‐Tauride and Kırşehirblocks in the south [Okay and Tüysüz, 1999]. It is sharplyfolded into an W shape between the Kırşehir Block and thePontides (Figure 1a). The shape has been explained by thenorthward drift of the Kırşehir Block (which consists ofrigid crystalline rocks) and its eventual indentation into thePontides (foreland) continent [Kaymakcı et al., 2003a,2003b;Meijers et al., 2010]. This process produced a crustaldeformation defined by thrusts and reverse faults, mainlywithin the indenting Kırşehir Block [Kaymakcı et al., 2000].[4] The collision of the Kırşehir Block and the Pontides

caused the northern Neotethys oceanic basin to close com-pletely during the Early Cenozoic. Postcollisional magma-tism, produced a large belt of E‐W trending Eocenevolcanics along the IAESZ [Tüysüz et al., 1995; Okay andSatır, 2006; Keskin et al., 2008]. The Middle Eocene calc‐

1Department of Geophysical Engineering, Faculty of Engineering,Istanbul University, Avcılar, Turkey.

2Institute of Geophysics, ETH Zurich, Zurich, Switzerland.3Department of Geological Engineering, Faculty of Engineering,

Istanbul University, Avcılar, Turkey.

Copyright 2011 by the American Geophysical Union.0278‐7407/11/2010TC002705

TECTONICS, VOL. 30, TC1008, doi:10.1029/2010TC002705, 2011

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alkaline volcanic rocks have a distinct subduction signature[Keskin et al., 2004] and formed in a compressional regime[Bozkurt and Koçyiğit, 1995; Görür and Tüysüz, 1997;Okay and Satır, 2006] during a postcollisional event [Keskinet al., 2004; Altunkaynak and Dilek, 2006] related to slabbreak off or lithospheric delamination [Boztuğ, 2000;Düzgören‐Aydın et al., 2001; İlbeyli, 2005]. Deformationas a result of N‐S compression continued until the Mid‐Late Miocene, with the development of thrusting, nappeemplacement, and strike‐slip faulting [Tüysüz and Dellaloglu,1992; Yılmaz et al., 1995]. Hence, the paleotectonic phase ofdeformation was finally completed, whereas the neotectonicphase of deformation imparted by the continuing northwardmovement of Arabia, followed by westward extrusion ofthe Anatolian region (Figure 1b), by displacement along thenorthern and eastern Anatolian Transform Faults and their

second‐order faults [cf. Le Pichon and Angelier, 1979;Barka, 1992; Şengör et al., 2005].[5] In this paper, we present paleomagnetic results inves-

tigating the regional Middle Eocene tectonic evolution of theprincipal zones of north central Anatolia (NCA). We inte-grate the results with previously published paleomagneticdata in order to provide quantitative constraints on theproposed tectonic models. The results support the collisionand indentation model for the Kırşehir Block, as previouslysuggested by Kaymakcı et al. [2000, 2003a, 2003b].

2. Previous Paleomagnetic Studiesand Tectonic Models[6] Several earlier paleomagnetic studies of Eocene vol-

canic rocks in Anatolia have focused on understanding the

Figure 1. (a) The main tectonic units of North Anatolia. (b) Active tectonic features of Turkey [afterYılmaz et al., 1995; Stampfli, 2000]. EAF, East Anatolian Fault; SF, Sungurlu Fault; SLF, Salt LakeFault; AF, Almus Fault. Gray units show ophiolitic rocks. Arrows indicate the general directions of platemovements. Also shown is the shaded paleomagnetic sampling area in the central Pontides and the easternSakarya Zone.

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tectonic evolution of the Anatolian plate, as well as theblock rotations caused by tectonic deformation across thevarious fault zones [Sarıbudak, 1989; Platzman et al., 1994;Tatar et al., 1995, 1996; Piper et al., 1996, 1997; Kaymakcıet al., 2003a; İşseven and Tüysüz, 2006].[7] The first of these studies, that of Sarıbudak [1989],

sought to evaluate the paleotectonic evolution of thePontides in the Eocene and Upper Cretaceous. Later studiesfocused on detecting the deformation that occurred close tothe North Anatolian Fault (NAF) [Kissel and Laj, 1988;Morris and Robertson, 1993; Gürsoy et al., 1999; Kaymakcıet al., 2007; Çinku and Orbay, 2010; Piper et al., 2010].Platzman et al. [1994] provided paleomagnetic data fromNiksar, along a transect across the NAF, that indicateapproximately 30° of counterclockwise (CCW) rotation. Inthe Pontides, Piper et al. [1996, 2010] detected CCW rota-tions in Middle Eocene lavas on both sides of the NAF. Theyinterpreted their results in terms of block rotations onsecond‐order faults that splayed westward from the NAFduring the neotectonic period.[8] Two different tectonic models have been developed to

explain the rotations observed in the Middle Eocene vol-canics. Kaymakcı et al. [2003a] proposed that the shape ofthe Çankırı Basin (Figure 2) is a result of northeastwarddirected indentation of the northward migrating KırşehirBlock into the Pontides during closure of the northernNeotethys. The authors concluded that the indentation beganprior to the Eocene and ended before the Middle Miocene.The accompanying deformation would explain the con-trasting range of rotations indicated by the Middle Eocenepaleomagnetic data. In contrast, İşseven and Tüysüz [2006],based on paleomagnetic data from 46 sites in the Eocenevolcanics, provided evidence for clockwise rotations offault‐bounded blocks about vertical axes within the right‐lateral NAF zone. They also documented CCW rotations,and related these to the CCW rotation of the AnatolianBlock during the neotectonic period. They assumed that theeastern Pontides consisted of individual blocks that repre-sent segments of a dextral shear zone. Their model however,does not adequately explain the CCW rotations.[9] It remains uncertain whether the paleomagnetic rota-

tions observed in the Anatolian tectonic zones are the resultof rotations of fault‐bounded blocks, which accompaniedthe dextral motion of the NAF, or whether they are a con-sequence of the differential rotation of the Anatolian Block.

3. Middle Eocene Volcanics3.1. Regional Geology

[10] The present study area includes the main zones of thecentral Pontides, the eastern Pontides, and the KırşehirBlock (Figure 1). The central Pontides, situated between theKırşehir Block to the south and the Black Sea to the north(Figure 1), are made up of Paleotethyan accretionary sub-duction complexes which are unconformably overlain byUpper Jurassic to Oligocene sedimentary and volcanic rocks[Yılmaz and Tüysüz, 1984; Tüysüz, 1990; Ustaömer andRobertson, 1999]. A magmatic arc and a mélange com-plex were formed during the Upper Cretaceous as a result ofsubduction of the northern Neotethys ocean [Tüysüz, 1990;

Ustaömer and Robertson, 1997; Yılmaz et al., 1997a; Riceet al., 2006].[11] Metamorphic and granitic rocks of Cretaceous age

are exposed in the Kırşehir Block [Seymen, 1982;Göncüoğlu,1986; İlbeyli, 2005; Boztuğ et al., 2007]. The block isgenerally regarded to be separated from the Anatolide‐Tauride Block by the Inner Tauride Suture [Şengör et al.,1984; Robertson et al., 2009]. The metamorphic rocks inthis block are tectonically overlain by an unmetamorphosedLate Cretaceous accretionary complex, and this complex, aswell as the metamorphic rocks, are intruded by graniticrocks that are exposed over large areas [Okay et al., 1998].[12] The Çankırı Basin in the northern part of the Kırşehir

Block separates the Pontides and the Kırşehir continentalfragments from each other. The basin is surrounded by theNorth Anatolian Ophiolitic Belt, and has an W shape andimbricated structure. Thrusts and faults which developedduring collision between the Kırşehir Block and thePontides, are the main structures that define the western andnorthern rims of the basin [Kaymakcı et al., 2000].

3.2. Sampling and Petrology

[13] Samples for paleomagnetic analysis were taken fromthe main zones of the central Pontides and the eastern part ofthe Pontides. A total of 794 minicore samples (diameter2.54 cm) were collected from 23 different sites (Figure 2).Volcanic rocks of the Middle Eocene succession were takenfrom 5 sites around Kastamonu, and at 18 sites fromOsmancık to the Merzifon area. The Middle Eocene volca-nic succession comprises basaltic andesitic lavas, tuffs,agglomerates, and volcanoclastic sediments. The lavas atKastamonu overlie sediments discordantly. Around Çorum,the lavas are intercalated with Eocene sedimentary rocks,and continental volcanism continued contemporaneouslywith the Oligocene to Early Miocene sedimentation. At mostof the sampling sites, the boundary between the flat lyinglavas and the underlying highly deformed ophiolites ismarked by a regional unconformity [Keskin et al., 2004].Paleontologic and radiometric data suggest that the volcanicrocks were emplaced during the Lutetian‐Bartonian. K/Arages in the range of 45.3 ± 3.1 to 41.8 ± 1.3 Myr have beenreported by Yılmaz et al. [1993a] and Platzman et al. [1994].Ketin [1962] determined a Lutetian age for lavas aroundOsmancık and Çorum, whereas Yılmaz and Tüysüz [1984]identified Nummulites sp. Group uroniensis in the tuffs,suggesting an Early Lutetian age (∼46–48 Myr).[14] Petrographic analyses were carried out on 23 thin and

polished sections. The dominant lithologies range from basaltto dacite in composition. The basalts have porphyritic oramygdoidal intersertal textures, dominated by plagioclaseand pyroxene, with chlorite and epidote as alteration products.Amphiboles are very rare in the basalts. In some samples, thepyroxenes are altered and transformed to chlorite, and inothers to uralite. Magnetite, hematite, and pyrite are the mainopaque minerals. The andesites and trachyandesites havetrachytic, porphyritic, hyalopoikilitic, and poikilitic textures.The groundmass usually includes microlithic plagioclase andalkalifeldspar crystals. Amphibole phenocrysts are uncommon.Microcrystalline feldspar, hornblende, epidote, biotite, chlorite,

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calcite, and rare quartz are accessory minerals. Blackopaque minerals are identified as magnetite, hematite, andilmenite, together with limonite, which appears as a decom-position product. The dacites have porphyritic textures withphenocrysts of plagioclase, hornblende, and quartz, andsmall amounts of K‐feldspar. Plagioclase phenocrysts con-tain inclusions of apatite, magnetite, pyrite‐hematite, andamphibole.[15] The most abundant Fe‐Ti oxide mineral is titano-

magnetite (Fe3‐xTixO4, 0 < x < 1) transformed to Ti‐poortitanomagnetite. Titanomagnetites either show homoge-neous textures or are intergrown with ilmenite lamellae. Theamount of the ilmenite‐rich phase increases with increas-ing degree of high‐temperature oxidation. Titanohematite(Fe2‐yTiyO3, 0 < y < 1) is observed in a few samples. Themain magnetic minerals, described as titanomagnetite, areoctahedral in shape in the basalts, with grain sizes in therange 10–150 mm (Figures 3a and 3b), and rounded in formin the andesites and dacites, with grain sizes of 10–100 mm(Figures 3c and 3d).

3.3. Rock Magnetism

[16] High‐field thermomagnetic curves were used to helpidentifying the ferrimagnetic minerals in the various lithol-ogies (Figure 4). Measurements were made in air with avariable field translation balance (VFTB) in the range

18°C–700°C, and in an applied field of 100 mT. Theanalyses were undertaken in the Department of Earth andEnvironmental Sciences, Ludwig‐Maximilians‐University,München, Germany. Hysteresis loops were also measuredat room temperature using the VFTB.[17] Three different types of thermomagnetic curves, with

one or two ferromagnetic phases, are recognized. Reversiblethermomagnetic behavior is observed in unaltered basaltic‐andesitic samples, with Curie temperatures of around 580°Cindicative of magnetite (Figure 4a). A second group ofsamples shows irreversible curves where Curie temperaturesand magnetizations are lowered upon cooling (Figures 4band 4c). The original phase is thought to be Ti‐poor tita-nomaghemite that is converted to less magnetic hematite. Arelatively Ti‐poor titanomagnetite remains, as indicated bythe lower Curie temperature in the cooling curve. A thirdgroup, with nearly reversible curves, is characterized byCurie temperatures of 600°C–680°C (Figure 4d), taken asevidence for the presence of titanohematite.[18] Isothermal remanent magnetization (IRM) was

imprinted in magnetic fields increasing stepwise from 10 to1500 mT. This was followed by stepwise demagnetizationusing alternating fields (AF). The IRM acquisition curvesshow two different types of behavior (Figure 5a). The firstis dominated by a low‐coercivity phase with a saturationfield of 0.2–0.5 T, as seen in the andesites SY1‐3.2b andHV1.2a. Taking the thermomagnetic evidence into account,

Figure 2. Geological map of the eastern Sakarya Zone and the central Pontides, showing Mesozoic‐Cenozoic ophiolitic rocks, Eocene‐Oligocene sediments, and volcanics. The sampling sites within theMiddle Eocene volcanics are labeled and have been assigned to three regional groups (groups 1–3).

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Figure 4. Typical Curie curves for representative samples. (a) Reversible thermomagnetic curve ofsample OS2.3a showing only one magnetic phase with a Curie temperature around 580°C. (b, c) Partlyreversible thermomagnetic curves of samples HO1.14c and HV2.14b indicate Curie points at490°C–580°C, with mineralogical alteration upon heating (transformation of maghemite/magnetite to tita-nohematite). (d) Sample IG 1.23b shows a Curie temperature clearly above 600°C, indicating the presenceof titanohematite.

Figure 3. Photomicrographs of representative samples. Titanomagnetite observed as the white‐coloredmineral in samples (a) GH1.1, (b) OS1.1, (c) OG1, and (d) IG1.2. Hematite crystals are scattered through-out the matrix in Figures 3b–3d. Fine ilmenite lamellae in Figure 3d indicate high‐temperature oxidation.

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the low‐coercivity mineral is likely to be titanomagnetiteor titanomaghemite. Samples such as OS5.23b, DO1.42a,KY2.41a, OG‐1.22a (Figure 5a) are typical of the secondtype, showing a slow IRM increase in low fields, oftenwithout complete saturation at 1500mT. This high‐coercivityphase is most likely (titanohematite) hematite. AF demag-netization indicates the presence of a low‐coercivity compo-nent in samples HV1.2a, OS5.23b, DO1.42a, and SY‐1.32b(Figure 5b), and a high‐coercivity component for KY 2.41aand OG1.22a with medium destructive field (MDF) valuesof 20–30 mT and 50–90 mT, respectively.[19] Magnetic grain sizes were estimated from the hys-

teresis properties. Most of the samples are saturated between0.2 and 0.5 T. Saturation remanence versus saturation mag-netization ratios (Mrs/Ms) of about 0.4–0.7, and coercivity ofremanence versus coercivity ratios (Hcr/Hc) of about 1.4–2.7place the magnetic grains into the pseudo‐single‐domain(PSD) size on a Day plot [Day et al., 1977].

3.4. Regional Paleomagnetism

[20] The directions and intensities of the natural remanentmagnetization (NRM) were measured with a Molspinspinner magnetometer in the Yılmaz Ispir PaleomagnetismLaboratory of Istanbul University, Turkey. Both thermal andalternating field demagnetization were applied to isolate thecharacteristic remanent magnetizations (ChRM) in stepsbetween 50°C and 700°C or 2.5–150 mT, respectively, usinga Schonstedt MTD‐80 oven and 2G600 AF demagnetizer.Principal component analysis was used to calculate the direc-tions of individual NRM components.[21] Two NRM components are generally recognized

during demagnetization (Figure 6). Low unblocking tem-peratures or low‐coercivity components that record a weakviscous magnetization are removed between 50°C and 300°Cor 5–10 mT, respectively. After this treatment, the intensitydecays linearly to the origin of the orthogonal vector plots[Zijderveld, 1967]. In many samples, the maximum unblock-

ing temperatures of 500°C–580°C, or median destructivealternating fields of 10–40 mT, are consistent with the pres-ence of PSD magnetite (titanomagnetite). AF demagnetiza-tion was effective in demagnetizing the low‐coercivitycomponent, whereas thermal demagnetization was successfulin isolating the hard component.[22] Different paleomagnetic components could be dis-

tinguished, in general agreement with the rock magneticresults. A high‐stability characteristic remanence (ChRM)component is identified in samples GH1.12a, OS3.46b,and SY2.12b with maximum unblocking temperatures of500°C–580°C (Figures 6a, 6f, and 6h), or at alternatingdemagnetization fields up to 100 mT (Figures 6i, 6j, 6k, and6l), indicating the presence of magnetite (titanomagnetite).Samples HV2.14a, IG1.22b, and OG2.33b reveal unblock-ing temperatures above 600°C, corresponding to titanohe-matite (Figures 6b, 6c, and 6g). A soft component isidentified in samples such as HV1.13b, with an unblockingtemperature of ∼400°C, indicating that the remanence iscarried by Ti‐rich titanomagnetite (Figure 6d).[23] According to the geographic distribution of the sample

localities, we can assign the paleomagnetic directions to thefollowing three regional groups (Figure 2 and Table 1):Group 1, with 11 sites, is situated in the south of the NAF, andcovers the central part of the investigation area; Group 2 isfurther east, with 7 sites; and Group 3, with 5 sites, is locatednorth of the NAF.[24] The ChRM site mean directions group very well,

yielding a95 = 2.7°–7.3° and k = 18.8–80.1 (Table 1). Themean ChRM direction of Group 1 is calculated as D = 26.9°and I = 43.7° (k = 44.7, a95 = 6.9°) in stratigraphic coor-dinates, with three normal‐polarity and eight reversed‐polarity sites. Group 2 comprises five directionally consistentsites, with three normal‐polarity and two reversed‐polaritysites that yield a mean ChRM of D = 325.3°, I = 38.6°, k =36.0, and a95 = 12.9° in stratigraphic coordinates. The meandirections of sites HV1 and HV2 show consistent inclina-tions, but the declinations diverge clockwise from the mean

Figure 5. (a) Normalized IRM acquisition curves indicate the presence of low‐coercivity minerals(titanomagnetite or maghemite) and an additional high‐coercivity mineral (hematite). (b) AF demagne-tization curves after IRM was acquired in a maximum field of 1500 mT.

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Figure

6.(a–l)NRM

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westerly declination of the remainder of Group 2. These twosites are closer to the NAF and located further east withinGroup 2; they are not included in the regional group meandirection. Group 3 is characterized by four normal‐polaritysites, all in flat‐lying flows, and with a ChRMmean direction

of D = 11.6°, I = 40.2°, k = 120.1, and a95 = 8.4° in geo-graphic coordinates (Table 1 and Figure 7). Site KY1, with aCCW‐rotated mean declination of ∼34°W, deviates distinctlyto the west of the mean direction, and is therefore excludedfrom the statistical analysis of Group 3. The excluded sites

Figure 7. Tilt‐corrected site mean directions of the regional groups 1 to 3 (crosses) with a95 confidencecircles, plotted on equal area projection. Solid (open) symbols on the lower (upper) hemisphere. CompareTable 1 for ChRM mean directions.

Table 1. Paleomagnetic Results for Middle Eocene Samplesa

Lat., Long. N/n

In Situ Tilt Corrected

Dg

(deg)Ig

(deg)a95

(deg) kDs

(deg)Is

(deg)a95

(deg) kTilt

CorrectionSF(deg)

SP(deg)

SL(deg)

SU(deg)

Site OS1 (B) 40°46′, 33°56′ 36/31 30.3 46.6 4.3 35.4 HorizontalSite OS2 (TA) 40°42′, 33°48′ 36/36 42.8 45.5 4.4 31.2 HorizontalSite OS3 (B) 41°02′, 34°45′ 46/46 23.9 41.3 3.5 37.3 HorizontalSite OS4 (H) 40°58′, 34°54′ 36/24 193.4 −41.2 6.3 23.3 HorizontalSite OG1 (A) 40°40′, 34°45′ 38/38 215.1 −40.2 4.1 34.4 HorizontalSite OG2 (BA) 40°45′, 34°40′ 37/35 207.3 −41.6 2.7 80.1 HorizontalSite DO1 (D) 40°50′, 34°50′ 9/9 218.5 −44.3 6.8 26.6 HorizontalSite DO2 (A) 40°48′, 34°52′ 37/26 222.6 −40.8 7.3 22.6 214.3 −55.7 180/24Site OS5 (T) 40°40′, 34°44′ 38/33 198.5 −43.6 5.2 21.8 HorizontalSite OS6 (M) 40°45′, 34°45′ 27/27 221.2 −39.2 6.4 19.7 HorizontalSite OS7 (A) 41°00′, 34°58′ 27/27 175.2 −31.9 7.2 18.1 HorizontalMean group 1 11/11 27.8 42.4 6.8 46.2 26.9 43.7 6.9 44.7 16.19 16.2 14.7 17.8Site HO (B) 40°48′, 35°07′ 36/35 241.8 −66.7 2.9 69.8 158.6 −41.3 220/54Site GH1 (B) 40°54′, 35°13′ 47/47 335.3 36.3 3.3 40.1 HorizontalSite GH2 (B) 40°54′, 35°13′ 34/31 124.2 −47.2 4.2 38.6 HorizontalSite SY1 (A) 40°58′, 35°10′ 28/28 322.5 27.0 4.9 26.2 333.8 31.0 340/20Site SY2 (A) 40°56′, 35°08′ 27/27 311.9 34.1 4.8 33.9 HorizontalSite HV1 (A) 40°55′, 35°38′ 36/36 25.7 32.9 2.9 67.5 HorizontalSite HV2 (TA) 40°55′, 35°38′ 36/33 25.1 24.5 3.1 64.4 HorizontalMean Group 2except HV1,2

7/5 326.2 46.5 7.7 29.4 325.3 38.6 12.9 36.0 15.66 15.7 13.6 17.0

Site KY1 (A) 41°16′, 33°45′ 38/37 326.2 42.2 5.4 18.0 HorizontalSite KY2 (A) 41°16′, 33°45′ 27/23 4.7 42.6 2.3 174.7 HorizontalSite KY3 (A) 41°16′, 33°45′ 29/23 15.2 47.1 4.7 42.6 HorizontalSite IG1 (D) 41°11′, 33°38′ 43/38 14.1 31.7 2.2 111.0 HorizontalSite IG2 (H) 41°11′, 33°34′ 36/27 12.3 39.3 2.7 110.5 HorizontalMean Group 3except KY1

5/4 11.6 40.2 8.4 120.1 9.27 9.3 8.5 10.3

aN, number of samples per locality; n, number of samples used for site mean calculation. Here a95 is the 95% confidence circle, and k is the precisionparameter [Fisher, 1953]. Declination Dg(s) and inclination Ig(s) describe the mean directions in geographic (before tilt correction) and stratigraphiccoordinates (after tilt correction), respectively. Lat., latitude; Long., longitude. SF is the paleosecular variation of the virtual geomagnetic pole (VGP)distribution, SP defines the total angular dispersion, and SL and SU are the lower and upper 95% confidence limits of SF, respectively. Lithologicaldescriptions are provided after site names in parentheses: B is for basalt, H is for hawaiite, M is for mugearite, BA is for basaltic andesite, A is for andesite,TA is for trachyandesite, T is for trachyte, and D is for dacite.

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HV1 and HV2 of Group 2, and site KY1 of Group 3, arediscussed later when considering the earlier publishedpaleomagnetic studies.[25] Group 1 passes the reversal test with Class C

[McFadden and McElhinny, 1990]. The normal‐polaritysites (N = 3) give a positive rotation angle (resultant vectorof length R = 2.98 and k = 119.3), while the reversed sites(N = 8) give resultant R = 7.8 and k = 35.7, in stratigraphiccoordinates. The observed angular distance g = 5.5° issmaller than the critical angle gc = 16.0°. The volcanic flowsat all Group 1 sites, with the exception of one, are hori-zontal. Hence, no meaningful paleomagnetic fold test can beapplied to test for the age of magnetization.[26] For Group 2, the observed angular distance g = 11.9°

is smaller than the critical angle gc = 28.9°, but an inde-terminate Class I [McFadden and McElhinny, 1990] wasobserved because of the low number of reversed directionsin stratigraphic coordinates. The McElhinny [1964] fold testprecision parameter increases to a value of 4.6 at the 95%confidence level during progressive unfolding (criticalvalues at 95% = 3.44; 99% = 6.03). In theMcFadden [1990]fold test, the precision parameter reaches a maximum at109% of unfolding that indicates evidence of a more com-plex structure rather than a simple cylindrical fold, or somemagnetic alterations of the ChRM. However, with two tilt‐corrected sites out of five sites in Group 2, the bedding‐corrected mean directions cluster more tightly than thosewithout bedding correction, indicating that the ChRM wasacquired before deformation.[27] A fold test could not be performed in Group 3,

because the lavas are flat lying. The mean direction ofGroup 3 was calculated as D/I = 11.6°/40.2° and couldpossibly have been remagnetized. However, a mean direc-tion of D/I = 10.9°/53.3° is expected at the mean location ofGroup 3 when referring to the contemporaneous referencepaleomagnetic pole for Eurasia [Besse and Courtillot, 2002].The effect of overprinted directions as means of a remag-netization component can be identified and dated whencompared the calculated mean directions with respect to theEurasian direction. According to our paleomagnetic analy-sis, the samples display single component on remanenceafter removal of relatively small viscous components,whereas further secondary overprints are not observed. Theexpected inclination values in Middle Eocene continuedincreasing inclination values until the present day with amean direction of D = 0°, I = 59.6°, whereas those of theobserved inclination values are significantly shallower thanthe expected ones in this time interval (Table 1). Since themeasured and expected inclinations for sites in Group 3differ by about 13° and 18° from the Middle Eocene and thepresent‐day inclination values, respectively, we exclude theremagnetization hypothesis at last at any time intervalbetween the Middle Eocene and present.[28] Paleosecular variation (PSV) should be averaged out

in paleomagnetic studies. To test the angular standarddeviation of the virtual geomagnetic poles of the data, wefirst calculated the total angular dispersion SP to define thescatter of N virtual geomagnetic poles (VGP) using the

formula Sp = ( 1N�1

PN

i¼1Di

2)1/2 where N is the number of

observations and D is the angular between ith VGP and thespin axis [McElhinny and McFadden, 1997]. The dispersion(SF) produced by paleosecular geomagnetic field variationsis derived by subtracting the within‐flow circular standarddeviation of the VGP (SW) which arises due to the randomerrors in the paleomagnetic direction at the correspondingsite, from the total dispersion (SP) using the formula SF

2 =SP2 − SW

2 /N [Cox, 1969]. The virtual geomagnetic poles ofgroups 1, 2, and 3 give angular standard deviations of SF =16.19°17.8

14.7, SF = 15.66°17.013.6, and SF = 9.27°10.3

8.5 , respectively(Table 1), using PMAG software [Tauxe, 1998]. Thesevalues are similar to the observed standard deviation valueof 16.12°16.46

15.08 from global PSV data sets for the latitudeof 40.0°.[29] From the collective evidence of the positive reversal

test, the fold test, and the analysis of angular dispersion, weconclude that secondary overprints have been successfullyremoved, and that the geomagnetic secular variation hasbeen averaged out.

4. Discussion4.1. Synthesis of Cenozoic Paleomagnetic DataFrom North Central Anatolia

[30] In order to evaluate the rotational history of the studyarea since the Middle Eocene, a large database was com-piled using not only our paleomagnetic results, but also theearlier data of Sarıbudak [1989], Tatar et al. [1995], Piperet al. [1996], and İşseven and Tüysüz [2006], as obtainedfrom 92 different sites (Appendix A).[31] Sampling localities distributed along the major faults

or within thrust sheets have been grouped so as to differ-entiate between the influences of fault‐bounded blocks andthrust slices (Table 2 and Figure 8). At least four sites foreach group, with the exception of group G11, which is basedon only two sites in the northern part of the Pontides, wereselected (Table 1 and Appendix A). Mean directions withvery low inclination values, or incompatibility with othermean directions of the same group, were discarded. ReversedNRM directions have been inverted to normal polarity foreasier comparison. Twelve groups were identified across thestudy area (Table 2 and Figure 8).[32] Because the lavas are flat lying over most of the study

area, only a restricted number of sites with tectonic tiltcorrection could be used to perform a fold test following themethod of Watson and Enkin [1993] (see Appendix B).Some neighboring groups were joined together because oflow tilts. Insufficient tilt‐corrected data were available forgroups G4 and G6. After progressive bedding corrections,the best grouping of directions was found at 60–109%unfolding for the different groups (see Appendix B). Theseresults suggest that the natural remanent magnetization wasacquired before or during deformation.[33] The paleomagnetic mean directions of each group

were compared with those derived from the coeval paleo-magnetic pole for stable Eurasia (78.8°N and 160.2°E, witha95 = 7.3° [Besse and Courtillot, 2002]) using R. Enkin’s(unpublished data, 2004) PMGSC (version 4.2) software(Table 2). The difference between the observed poles(lobs, �obs) and the reference pole (lref, �ref), computed

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using the pole‐space method of Beck [1980], defines theamount of vertical axis rotation (R) and poleward transport(F). The confidence limits DR and DF were determinedafter Demarest [1983].[34] The group mean declinations suggest the following:

(1) groups G1, G9, G10, G11, and G12, located to the northof the NAF, show only small rotations that could not becorrelated with any geological structure, except G9, whichshows a CCW rotation of R ± DR = –38.6° ± 9.9° withrespect to Eurasia; (2) at the eastern margin of the ÇankırıBasin, between the NAF and the SF, clockwise rotations areobserved with R ± DR = 8.5 ± 15.1° to R ± DR = 29.7 ±12.0° for groups G2, G3, G4, and G6, R ±DR = −24.0 ± 8.6for G5; and (3) to the south of the SF, group means G7 andG8 have been rotated CCW with R ± DR = –18.9 ± 12.4°and R ± DR = –42.2 ± 6.9°, respectively (Figure 8).[35] The observed inclination values from the group

means (Table 2) could be considered with respect to thereference inclination value of Eurasia. The discrepancybetween the observed and expected inclinations differssignificantly at −0.3 ± 11.7 for site G3 to +19.7 ± 11.9 forsite G11, probably because of local tectonic events, whereasprevious paleomagnetic studies from Middle Eocene rocksindicate similar inclination values in the Pontides and sur-rounding [Van der Voo, 1968; Tatar et al., 1995, 1996;Kissel et al., 2003].

4.2. Age of Magnetization and Tectonic Deformation

[36] We now explore possible reasons for the contrastingsenses of rotations. The complex tectonic evolution of the

study area is a result of three successive tectonic regimes(herein referred to as (a) to (c)) associated with the paleo-tectonic and the neotectonic periods.[37] The oldest compressional regime (a) was the result of

collision between the Pontides, Taurides, and the KırşehirBlock in the Early Cenozoic, after the Kırşehir massifindented northward into the Pontides, and following thefinal closure of the Neotethys Ocean in early Eocene timesapproximately 50Myr ago [Şengör and Yılmaz, 1981; Tüysüzand Dellaloglu, 1992; Tüysüz et al., 1995; Kaymakcı et al.,2000, 2003a, 2003b; Rice et al., 2006, 2009]. The mostimportant deformation stage is related to large‐scale ophio-lite emplacement, thrust faulting, and transpression. Thesouth vergent, highly deformed ophiolitic slivers wereimbricated with the basement metamorphic rocks [Yılmazet al., 1993a]. Their outcrops are found largely in the areasaround Çorum, Amasya, Turhal, Çamlıbel, and Erzincan[Yılmaz et al., 1997a] (see also Figures 1, 2, and 8). The thrustsystem, named the Central Anatolian Thrust Belt [Tatar,1982], developed in response to regional ENE‐WSW short-ening. It surrounds the Çankırı Basin and extends approxi-mately in an E‐W direction toward Reşadiye [Şengör andYılmaz, 1981; Tüysüz and Dellaloglu, 1992, 2001; Tüysüzet al., 1995; Kaymakcı et al., 2000, 2003a, 2003b]. Furthernorth, in the KargıMassif, ophiolitic mélanges of Campanianage occur as thin thrust slices [Yılmaz and Tüysüz, 1984,1988; Tüysüz, 1990; Yiğitbaş et al., 1990; Rice et al., 2006,2009].[38] The second tectonic regime (b) involved pulses of

postcollisional extension, mainly during the Mid‐Eoceneand Miocene [Yılmaz et al., 1997a; Karadenizli et al., 2003;

Table 2. Mean Directions for Different Site Groups G1 to G12Which Were Defined According to Common Location, Tectonic Structures,and Geological Featuresa

Group Reference N D (deg) I (deg) a95 (deg) k R + DR (deg) F + DF (deg)

G1 Piper et al. [1996] (32, 34, 35),this study (KY1, KY2, KY3, IG1, IG2)

8 356 39 11 26.2 −12.3 ± 8.5 +13.4 ± 7.8

G2 This study (OS1, 3, 4, OG1, 2, DO1, 2);İşseven and Tüysüz [2006](OSM4‐7, OSM12‐14)

14 29.7 41 7.5 29.2 +21.3 ± 6.4 +11.5 ± 5.7

G3 İşseven and Tüysüz [2006] (OSM8, COM1‐5) 6 20.8 54.5 13.2 26.8 +12.4 ± 14.3 −0.3 ± 11.7G4 İşseven and Tüysüz [2006] (SU1‐4) 4 38.1 44.3 14.3 42.3 +29.7 ± 12.0 +8.5 ± 10.7G5 İşseven and Tüysüz [2006]

(KAM1‐3, OSM1, 10, 11, GHK1, 2, 3, 5, 6),this study (OS5, 7, HO1, GH1, 2, SY1, 2)

18 344.4 46.1 9.6 14.8 −24.0 ± 8.6 +7.4 ± 7.6

G6 İşseven and Tüysüz [2006](MER1, 4, 5, 7, 9), Piper et al. [1996] (24),

this study (HV1, 2)

8 17.0 39.7 20 8.6 +8.5 ± 15.1 +12.5 ± 13.9

G7 İşseven and Tüysüz [2006] (ORT1‐4),Piper et al. [1996] (11‐14; 18‐22)

13 169.6 −50.5 12.7 11.6 −18.9 ± 12.4 +3.4 ± 10.6

G8 Tatar et al. [1995] (50‐56; 61),Platzman et al. [1994] (TV1, 2)

10 146.5 −48.3 7 48.8 −42.2 ± 6.9 +5.6 ± 5.9

G9 Platzman et al. [1994] (TV6, 8, 11, 14, 16);Piper et al. [1996] (33‐42)

15 150.5 −41.9 9.6 16.7 −38.6 ± 9.9 +6.7 ± 7.1

G10 Piper et al. [1996] (1‐10, except 8) 9 9.9 48.6 15.2 12.5 −1.3 ± 1.4 +5.6 ± 12.1G11 Sarıbudak [1989] (BF01, BF02) 2 357.6 30.1 19.2 171.4 −11.1 ± 12.5 +19.7 ± 11.9G12 Platzman et al. [1994] (TV9, 10, 14, 15) 4 171.5 −67.4 9.5 168.3 −17.2 ± 16.8 −15.1 ± 10.8

aN, number of paleomagnetic sites. D and I indicate declinations and inclinations after tectonic correction, respectively. Here k and a95 are statisticalparameters after Fisher [1953]. R and F are the angles of vertical axis rotation (positive indicates clockwise rotation) and flattening of inclination(±, northward/southward) with respect to the direction computed from the stable Eurasia paleomagnetic pole with 95% confidence limits DR and DF,respectively [after Demarest, 1983].

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Figure

8.Normal

polarity

declinations

ofsite

means

derivedfrom

this

stud

yandfrom

Sarıbu

dak[198

9],Piper

etal.

[1996],Tatar

etal.[1995],andİşsevenandTüysüz[2006].Site

groups

G1to

G12

asdefinedin

Table

2.Thrusts

are

draw

nafterYılm

az[1982],Y

ılmaz

etal.[1993b],Ö

zcan

etal.[1996],Hakyemez

andPapak

[2002],U

ğuzetal.[2002],and

Kaymakcı

etal.[2009].

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Figure

9.Distributionof

GPSvelocity

vectorsin

northcentralA

natolia.V

elocity

vectorsaredraw

nfrom

Yavaşoğ

luetal.

[2004,

2010],andthrustsareafterYılm

az[1982],Y

ılmaz

etal.[1993b],Ö

zcan

etal.[1996],Hakyemez

andPapak

[2002],

Uğu

zet

al.[2002],andKaymakcı

etal.[2009].

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Kaymakcı et al., 2000, 2001, 2003a, 2003b; Vincent et al.,2005]. The third regime (c) is represented by the develop-ment of the dextral NAF system [Şengör, 1995; Şengör et al.,2005; Yılmaz et al., 1997a; Tüysüz and Dellaloglu, 1992].[39] The three regimes were also documented by

Kaymakcı et al. [2000, 2003a, 2003b] on the basis ofpaleostress data. These authors found that the Çankırı Basinhad been affected by four principal deformational eventsduring the Cenozoic: (1) pre–Late Paleocene NW‐SEthrusting and folding; (2) late Paleocene to pre‐Burdigaliantranspression, correlated with collision between the Pontidesand the Taurides (regime a); (3) Burdigalian to Serravallianextension (regime b); and (4) transcurrent motion of theNAF Zone (regime c).[40] We consider the characteristic paleomagnetic directions

determined during this study to be of primary origin. This hasbeen confirmed by both stable paleomagnetic vectors and rockmagnetic properties, showing that the main magnetic carriersare mainly PSD magnetite but also partly titanohematite thathas been subjected to high‐temperature oxidation.[41] Paleomagnetic fold tests associated with progressive

unfolding [Watson and Enkin, 1993] were applied both tothe individual regional groups of this study and to the wholedata set available from previous studies. Almost all paleo-magnetic groups in NCA are carriers of a prefolding rem-anent magnetization, although the means of some groupscluster best after untilting at 60%, suggesting a syntectonicdeformation. The dual polarity in regional groups 1 and 2(Table 1) passes the reversal test, suggesting the data are ofhigh quality and of early magnetization origin. Moreover,the angular dispersion of all the mean directions has beenconfirmed to average out paleosecular variation. Thus, thecollective evidence suggests that the ChRM age correspondsto a period between the compressional regime in the MiddleEocene and the transcurrent deformation along the NAFduring the neotectonic era.

4.3. Influence of the NAF Deformationon Tectonic Rotations

[42] Several lines of argument, as follows, suggest that thepaleomagnetic rotations are not primarily induced by dextralstrike‐slip motion on the NAF.

[43] 1. Similar CCW rotations have been observed onboth sides of the NAF, e.g., in group G9 to the north of theNAF and in group G8 south of the SF (Figure 8). Tectonicblock rotations, caused by dextral motion on the NAF andits branches, would have been expected to cause distinctdifferences between groups G8 and G9.[44] 2. Groups G2, G3, G4, and G6 are situated between

the NAF and the SF. Tectonic rotation with respect toEurasia is determined as R ± DR = 29.0° ± 12.0° for G4,which lies in the southernmost part of the Çankırı Basin.However, closer to the NAF, rotations decrease down toR ± DR = 8.5° ± 15.1° for G6.[45] 3. The distances between the NAF and groups G5 and

G6 are much the same. However, G5 has been rotatedcounterclockwise by R ± DR = –24.0° ± 8.6°, whereas asmall clockwise rotation of R ±DR = 8.5° ± 15.1° applies toG6. These contrasting rotations cannot be explained in termsof dextral movement on the NAF.[46] 4. The nature of present‐day deformation of the NCA

block can be determined from GPS data, revealing a CCWrotation due to the westward escape of the Anatolian Platesince the neotectonic period [Yavaşoğlu et al., 2004, 2010].The aim of the study by Yavaşoğlu et al. [2004] was toidentify block movements between the Sungurlu, Merzifon,and Laçin faults, which are the most important splays of theNAF in central Anatolia (Figure 9). The authors proposedthat the velocity vector directions and magnitudes of theGPS vectors are in harmony with escape of the AnatolianPlate toward the west along the North and eastern Anatolianfaults. From their observed and modeled GPS data theyindicated that the residual velocity vectors in some blocks,such as Osmancık and Gümüşhacıköy diverge from east–west direction which can be interpreted as an ongoing rota-tion. However, when considering the GPS velocity vectors inthe whole investigation area (Figure 9), it seems unlikely tointerpret the paleomagnetic rotations (Figure 8) with respect toa small block rotation model, since the velocity vectors showno significant deviations from the general trend.

4.4. Tectonic Aspects of the Indentation Model

[47] Given the above arguments, we cannot connect therotations of the Middle Eocene volcanics to motion along

Figure 10. Results of sandbox experiments according to the indentation model. (a) Displacement vectorsparallel to the indentation direction during frontal imbrication. (b) Changes in displacement vectors due tochanges in the strike of thrusts during oblique indentation [after Zweigel, 1998] (with permission fromElsevier).

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Figure 11

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the NAF. The tectonic deformation that produced thecontrasting rotations in the study area must predate NAFactivity. Since the age of the NAF is Mio‐Pliocene [Şengöret al., 2005], the paleomagnetically documented rotationsmust have occurred under earlier tectonic regimes.[48] We propose to explain the observed rotations by an

indentation process during the Eocene, similar to that pro-posed by Kaymakcı et al. [2000, 2003a, 2003b]. Althoughthe indentation model was developed solely to explain theevolution of the Çankırı Basin, it is also able to explain thetectonic evolution of the main tectonic zones of Anatolia.[49] Zweigel [1998] performed sandbox indentation

experiments in which the deformation depends on thegeometry of a rigid indentor. The movement of the particlesin front of the indentor results in a deformation with crustalthickening and shortening across the faults. The simulationdemonstrates that the widths of the lateral and frontalwedges increase with increasing indentation angles. Whenthe indentor moves at low angle, parallel thrusts developalong its frontal face, and inclined strike‐slip faults along itslateral margins. New thrusts form sequentially, and olderthrusts are rotated to higher angles in response to the inden-tation (Figure 10).[50] The ophiolites near Çorum and Çankırı form a

scallop‐like structure, and then continue eastward towardReşadiye (Figure 8). This tectonic feature provides evi-dence of the continuity of the indentation of the KırşehirBlock into the Pontides. The ophiolite zone in the Çankırı‐Reşadiye region makes an W‐shaped loop near the ÇankırıBasin, consistent with the high‐angle indentation model ofZweigel [1998], whereas the ophiolites to the east areconsistent with a low‐angle indentor model.[51] Hence, we propose an indentation model with a

combination of high‐ and low‐angle movements of theindentor (Figure 11a). The W‐shaped thrust traces becomesmoother as one moves north of the ophiolites in the colli-sional zone. The directions of thrusting in the eastern andwestern areas are different. Likewise, thrust directions in theAmasya, Tokat, and surrounding areas are quite differentfrom those in the Çankırı Basin. Figures 11a, 11b and 11calso prove that the modeled structures developed afterindentation are in good agreement with the actually observedpaleomagnetic directions. The shapes of the thrust curves,which become quite smooth to the north, reflect the rotationof the paleomagnetic vectors. Therefore, the paleomagneticdeclinations further north (G1, G10, G11, and G12) areaffected by small rotations only (Figure 8). These conclu-sions are also supported by the Paleocene and Eocene paleo-magnetic data of Meijers et al. [2010], who reported norotations in central and eastern Pontides.[52] The structure of the thrust sheets resembles an

E‐W trending Greek v letter that is asymmetrical in shapeand oriented in an oblique NE‐SW direction (Figures 11aand 11b). If a line is plotted through the center of the vshaped area, one can recognize that clockwise rotations

occur in the eastern part of the Çankırı Basin, between theNAF and this line. The line corresponds to a fold axis thatformed during indentation of the Sakarya zone by theKırşehir Block (Figures 11b and 11c). In the area betweenthe southern part of this fold axis and the northern part of theophiolites, CCW rotations occur depending on the shape ofthe thrusts. The hypothetical fold axis is close to the presentSungurlu Fault. However, the indentation process and thecausative deformation were active prior to the evolution ofthe NAF and its side splays.

5. Conclusions[53] The paleomagnetic results from the eastern Sakarya

Zone and the central Pontides, based on our new datafrom 23 sites together with earlier data from 92 other sites,indicate contrasting senses of tectonic rotation between−42.2° and 29.7°. With the exception of G9 with its CCWrotation of R ± DR = –38.6 ± 9.9°, the mean directions ofgroups G1, G9, G10, G11, and G12, all located on thenorthern side of the NAF, show small rotations with respectto Eurasia. The mean declinations in the eastern ÇankırıBasin, at G2, G3, G4, G5, and G6, between the NAF and theSF, display clockwise and counterclockwise rotations rang-ing from R ± DR = 8.5 ± 15.1° to R ±DR = –24.0 ± 8.6. Tothe south of the SF, the means of G7 and G8 show CCWrotations of R ± DR = –18.9 ± 12.4° and R ± DR = –42.2 ±6.9°, respectively. The variable senses and degrees of rota-tion have major implications for the origin and tectonicevolution of the main tectonic zones of north central Anatoliain the Middle Eocene. Based on these data, we arrive at thefollowing conclusions.[54] 1. The thrust structures that developed as a result

of the indentation of the Kırşehir Block into the SakaryaZone are compatible with the senses of rotation derivedpaleomagnetically.[55] 2. The NAF was active during the Late Miocene and

Pliocene. It separates G8 from G9, which are located onopposite sides of the NAF. However, no rotation due tomovement along the NAF was detected. In fact, the paleo-magnetic mean declinations in groups G8 and G9 (to thenorth and south of the NAF, respectively) have been affectedto the same extent by the indentation process and the fol-lowing compression event.[56] 3. The mean declinations in G10, G11, and G12 show

no significant rotation, because the thrust structures areprogressively flattening toward the north.

Appendix A[57] The tilt corrected Middle Eocene paleomagnetic

mean directions from published studies in the Sakarya Zoneand in the Pontides are used for the average group directionsin Table 2 in order to better distinguish the influence betweenfault bounded blocks and the thrust slices. Mean directions

Figure 11. (a) Oblique indentation model and displacement vectors, modified from Zweigel [1998] with permission fromElsevier. The rotationmodel depends on thrust structures and thrust curvature. Observed ophiolite distribution and tectonically(b) expected and (c) obtained declination directions in the study area.

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Table A1. Paleomagnetic Site Mean Directions From Middle Eocene Rocks in Eastern Sakarya Zone and the Central Pontides, FromPrevious Studies

Site Age N/n D (tec. cor.) I (tec. cor.) a95 k Reference

Çankırı‐ÇorumKAM1 Mid‐Eocene 8/9 187 −39 8 4.2 İşseven and Tüysüz [2006]KAM2 Mid‐Eocene 6/8 162 −23 5.9 7.5 İşseven and Tüysüz [2006]KAM3 Mid‐Eocene 9/9 188 −39 8.5 13.1 İşseven and Tüysüz [2006]OSM1 Mid‐Eocene 6/10 149 −58 5.7 16.8 İşseven and Tüysüz [2006]OSM2a Mid‐Eocene 5/5 263 1 2.8 81.1 İşseven and Tüysüz [2006]OSM3a Mid‐Eocene 8/9 240 −14 7.8 10.1 İşseven and Tüysüz [2006]OSM4 Mid‐Eocene 9/9 239 −23 8.7 9.3 İşseven and Tüysüz [2006]OSM5 Mid‐Eocene 7/9 204 −25 6.8 11.7 İşseven and Tüysüz [2006]OSM6 Mid‐Eocene 7/9 219 −45 6.9 6.9 İşseven and Tüysüz [2006]OSM7 Mid‐Eocene 7/9 190 −47 5.8 11.7 İşseven and Tüysüz [2006]OSM8 Mid‐Eocene 9/9 212 −30 8.9 4.3 İşseven and Tüysüz [2006]OSM9a Mid‐Eocene 8/8 258 −27 7.9 5.7 İşseven and Tüysüz [2006]OSM10 Mid‐Eocene 6/7 196 −69 6 6.7 İşseven and Tüysüz [2006]OSM11 Mid‐Eocene 7/8 173 −22 6.9 7.5 İşseven and Tüysüz [2006]OSM12 Mid‐Eocene 8/8 192 −56 7.9 5.4 İşseven and Tüysüz [2006]OSM13 Mid‐Eocene 8/9 195 −25 6.8 12.5 İşseven and Tüysüz [2006]OSM14 Mid‐Eocene 9/9 231 −47 8.9 4.9 İşseven and Tüysüz [2006]SU1 Mid‐Eocene 9/9 214 −37 8.9 4.6 İşseven and Tüysüz [2006]SU2 Mid‐Eocene 9/9 224 −40 8.9 6 İşseven and Tüysüz [2006]SU3 Mid‐Eocene 9/9 212 −62 8.9 5.3 İşseven and Tüysüz [2006]SU4 Mid‐Eocene 7/9 220 −38 6.8 10.4 İşseven and Tüysüz [2006]COM1 Mid‐Eocene 5/7 202 −68 4.9 9.1 İşseven and Tüysüz [2006]COM2 Mid‐Eocene 9/9 213 −64 8.9 6.7 İşseven and Tüysüz [2006]COM3 Mid‐Eocene 5/8 188 −58 4.7 20.1 İşseven and Tüysüz [2006]COM4 Mid‐Eocene 9/9 206 −57 8.9 3.4 İşseven and Tüysüz [2006]COM5 Mid‐Eocene 7/9 184 −46 6.9 9.5 İşseven and Tüysüz [2006]ORT1 Mid‐Eocene 8/8 141 −39 7.9 6.3 İşseven and Tüysüz [2006]ORT2 Mid‐Eocene 8/8 162 −54 7.8 7.2 İşseven and Tüysüz [2006]ORT3 Mid‐Eocene 6/8 149 −29 5.9 7.7 İşseven and Tüysüz [2006]ORT4 Mid‐Eocene 8/9 184 52 6.9 23.8 İşseven and Tüysüz [2006]MER1 Mid‐Eocene 8/8 223 −48 7.9 7.6 İşseven and Tüysüz [2006]MER2a Mid‐Eocene 8/8 275 51 3.1 81.7 İşseven and Tüysüz [2006]MER3a Mid‐Eocene 8/8 82 −25 7.8 8.8 İşseven and Tüysüz [2006]MER4 Mid‐Eocene 7/8 156 −29 6.9 8.1 İşseven and Tüysüz [2006]MER5 Mid‐Eocene 5/8 42 25 4.8 17.2 İşseven and Tüysüz [2006]MER6a Mid‐Eocene 7/7 213 −23 4.2 54.7 İşseven and Tüysüz [2006]MER7 Mid‐Eocene 8/8 134 −53 7.8 8.7 İşseven and Tüysüz [2006]MER8a Mid‐Eocene 8/9 331 9 4.6 53 İşseven and Tüysüz [2006]MER9 Mid‐Eocene 8/8 45 10 8 4.4 İşseven and Tüysüz [2006]MER10a Mid‐Eocene 10/10 84 −35 5.2 52.2 İşseven and Tüysüz [2006]GHK1 Mid‐Eocene 7/7 157 −52 6.8 12 İşseven and Tüysüz [2006]GHK2 Mid‐Eocene 9/9 123 −47 8.9 5.4 İşseven and Tüysüz [2006]GHK3 Mid‐Eocene 9/10 149 −58 8.8 7.7 İşseven and Tüysüz [2006]GHK4a Mid‐Eocene 10/10 252 −55 9.7 9.5 İşseven and Tüysüz [2006]GHK5 Mid‐Eocene 6/9 196 −37 5.7 18 İşseven and Tüysüz [2006]GHK6 Mid‐Eocene 7/9 195 −52 6.8 9.9 İşseven and Tüysüz [2006]

Erbaa1 Mid‐Eocene 8/8 206.3 −52.5 5.1 118.6 İşseven and Tüysüz [2006]2 Mid‐Eocene 7/4 205.8 −59.3 14.2 42.7 İşseven and Tüysüz [2006]3 Mid‐Eocene 7/7 177.3 −24.0 11.1 30.6 İşseven and Tüysüz [2006]4 Mid‐Eocene 7/4 206.6 −71.5 7.4 154.8 İşseven and Tüysüz [2006]5 Mid‐Eocene 8/8 340.0 22.1 9.4 35.3 İşseven and Tüysüz [2006]6 Mid‐Eocene 7/6 346.4 62.5 9.9 46.6 İşseven and Tüysüz [2006]7 Mid‐Eocene 8/8 228.4 −45.8 5.4 105.2 İşseven and Tüysüz [2006]9 Mid‐Eocene 8/8 184.0 −48.9 9.2 37.5 İşseven and Tüysüz [2006]10 Mid‐Eocene 7/6 195.9 −30.9 6.8 99.2 İşseven and Tüysüz [2006]

SW Amasya11 Mid‐Eocene 10/9 143.9 −50.5 3.3 331.2 Piper et al. [1996]12 Mid‐Eocene 6/6 131.9 −28.7 4.1 266.0 Piper et al. [1996]13 Mid‐Eocene 6/6 146.8 −35.8 4.6 211.6 Piper et al. [1996]14 Mid‐Eocene 7/6 188.8 −47.1 5.3 160.6 Piper et al. [1996]18 Mid‐Eocene 8/7 160.4 −51.0 5.2 136.2 Piper et al. [1996]19 Mid‐Eocene 9/9 199.6 −65.1 4.8 116.1 Piper et al. [1996]20 Mid‐Eocene 9/8 211.7 −53.5 4.8 133.4 Piper et al. [1996]

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with very low inclinations or anomalous declinations are notconsidered further (see Table A1).

Appendix B[58] The fold test after Watson and Enkin [1993] has been

performed on the different groups in Table 2 to constrain the

age of magnetization. The optimal unfolding between 80.2%and 109.1% for groups G2+G3, G5, and G8−10 shows thatfolding occurs before deformation, whereas G4 and G6 werenot considered because of insufficient tilt corrected data (seeTable B1).

Table A1. (continued)

Site Age N/n D (tec. cor.) I (tec. cor.) a95 k Reference

21 Mid‐Eocene 7/7 235.5 −52.0 6.2 95.4 Piper et al. [1996]22 Mid‐Eocene 7/6 204.2 −41.1 3.2 435.1 Piper et al. [1996]

NW Amasya24 Mid‐Eocene 8/6 184.4 −55.2 14.2 23.3 Piper et al. [1996]29a Mid‐Eocene 7/7 1.7 55.1 12.4 24.6 Piper et al. [1996]30a Mid‐Eocene 7/5 161.9 −9.8 17.7 19.7 Piper et al. [1996]

SW Kastamonu (North NAFZ)32 Mid‐Eocene 8/8 157.8 −31.6 7.0 63.0 Piper et al. [1996]34 Mid‐Eocene 7/7 165.8 −26.6 4.3 198.2 Piper et al. [1996]35 Mid‐Eocene 7/6 169.1 −36.5 12.1 31.4 Piper et al. [1996]

Almus (South NAFZ)50 Mid‐Eocene 8/8 141.2 −40.4 4.0 177.3 Tatar et al. [1995]51 Mid‐Eocene 8/7 151.1 −57.3 10.0 39.4 Tatar et al. [1995]52 Mid‐Eocene 9/9 141.6 −47.2 8.0 42.2 Tatar et al. [1995]53 Mid‐Eocene 10/10 132.0 −49.0 6.0 57.0 Tatar et al. [1995]54 Mid‐Eocene 8/8 154.0 −55.2 5.0 124.0 Tatar et al. [1995]55 Mid‐Eocene 8/6 132.3 −54.7 15.0 22.1 Tatar et al. [1995]56 Mid‐Eocene 9/9 154.9 −44.4 6.0 70.6 Tatar et al. [1995]61 Mid‐Eocene 7/6 145.8 −28.9 13.0 27.7 Tatar et al. [1995]62a Mid‐Eocene 6/5 38.1 39.8 11.0 51.5 Tatar et al. [1995]

NiksarTV1 Mid‐Eocene 9 144 −59 4.0 127 Platzman et al. [1994]2 Mid‐Eocene 7 166 −43 5.0 119 Platzman et al. [1994]6 Mid‐Eocene 10 158 −46 3.0 175 Platzman et al. [1994]8 Mid‐Eocene 10 158 −63 4.0 146 Platzman et al. [1994]9 Mid‐Eocene 8 126 −61 6.0 91 Platzman et al. [1994]11 Mid‐Eocene 10 142 −31 3.8 165.6 Platzman et al. [1994]13a Mid‐Eocene 8 116 −16 3.7 229.1 Platzman et al. [1994]14 Mid‐Eocene 9 145 −44 3.5 211.3 Platzman et al. [1994]15 Mid‐Eocene 8 181 −70 7.3 58.8 Platzman et al. [1994]16 Mid‐Eocene 7 165 −26 7.5 65.1 Platzman et al. [1994]

SamsunBF01 Mid‐Eocene 5/5 182.0 −28.0 5.5 194.0 Sarıbudak [1989]BF02 Mid‐Eocene 5/5 172.7 −32.3 4.9 243.6 Sarıbudak [1989]

aSite means which are not considered.

Table B1. Syntilting Fold Test After Watson and Enkin [1993]a

Group N Dg (deg) Ig (deg) k Ds (deg) Is (deg) k Max. Unfolding (%)

G1 3 194.5 −48.9 84.8 173.0 −40.7 197.04 60.4G2 4 199.7 −39.1 19.3 204.0 −42.3 31.84 64.6G2+3 7 194.3 −41.6 16.1 201.8 −45.2 23.27 80.2G5 4 158.1 −54.4 4.5 158.0 −40.3 16.27 109.1G7 11 142.5 −45.5 8.1 165.4 −52.5 10.46 60.9G8 10 123.2 −34.6 25.4 144.2 −47.7 49.68 92.7G9 12 146.4 −26.8 6.2 151.8 −41.8 21.91 99.4G10 8 179.3 −45.7 5.7 191.9 −46.4 12.38 97.5G1+10+11+12 14 177.9 −48.8 7.9 178.5 −43.2 14.08 74.2

aThe maximum unfolding percentage values are shown with declination, inclination, and dispersion parameter k before and after tectonic correction ingeographic and stratigraphic coordinates.

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[59] Acknowledgments. The authors would like to thank ValerianBachtadse for his generous help in providing the rock magnetic measure-ments at the Department of Earth and Environmental Sciences, Ludwig‐Maximilians‐University, München, Germany. We thank Hasan Emre

for help with petrographic examinations. The initial submission of this paperwas reviewed by Nuretdin Kaymakcı. Useful comments were received fromanonymous reviewers.

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M. C. Çinku, Z. M. Hisarlı, and N. Orbay, Faculty ofEngineering, Department of Geophysical Engineering,Istanbul University, 34320 Avcılar, Istanbul, Turkey.(mualla@istanbul.edu.tr)

F. Heller, Institute of Geophysics, ETH Zurich,CH‐8092, Zurich, Switzerland.

T. Ustaömer, Department of Geological Engineering,Faculty of Engineering, Istanbul University, 34320Avcılar, Istanbul, Turkey.

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