Geology and Structural Evolution of the Tokat Massif (Eastern Pontides
Turkish Journal of Earth Sciences (Turkish J. Earth Sci.), Vol. 13, 2004, pp. 231-246. Copyright ©TÜB‹TAK
Geology and Structural Evolution of the Tokat Massif (Eastern Pontides, Turkey)
AL‹ YILMAZ1 & HÜSEY‹N YILMAZ2
1 Cumhuriyet Ünversitesi, Mühendislik Fakültesi, Çevre Mühendisli¤i Bölümü, TR-58140 Sivas - Turkey (e-mail: [email protected]) 2 Cumhuriyet Ünversitesi, Mühendislik Fakültesi, Jeofizik Mühendisli¤i Bölümü, TR-58140 Sivas - Turkey (e-mail: [email protected])
Abstract: The Tokat Massif consists of a pre-Jurassic metamorphic complex that crops out widely between Amasya and Refladiye in the western part of eastern Pontides, and which can be correlated with the Karakaya Complex of the western Pontides. This complex is named the Tokat Group, and is divided into two main units, namely, the Turhal Metamorphics and Devecida¤ Mélange. The Turhal Metamorphics form a volcano-sedimentary sequence in the northern part of the Tokat Massif. The lower level of the formation is made up of gneiss, amphibolite and mica schists, whereas the upper part is represented by an alternation of mica schist, phyllite, metaclastic rocks, metabasite and marble, which probably reflects an arc association. The Devecida¤ Mélange is characterised by a metavolcano-sedimentary olistostrome, which forms the southern part of the massif. This unit is quite heterogeneous and reflects, in places, a subduction mélange and/or a fore-arc sequence. The Devecida¤ Mélange may have formed in a setting between a subduction zone and a fore-arc. The units of the Tokat Massif can be traced along the eastern Pontides and also along the North Anatolian Ophiolitic Belt. These units have been accreted to the mélange prism as tectonic slices along the North Anatolian Ophiolite Belt before the Campanian. Some of Late Cretaceous ophiolitic mélange slices also crop out in the Tokat Group as E–W-trending tectonic slices. The ophiolites and ophiolitic mélange are believed to have been emplaced both to the north and to the south during the Late Cretaceous. The north-vergent thrusts have been later realigned into south-dipping thrusts during a neotectonic phase.
Key Words: Tokat Group, Karakaya Complex, structural evolution, eastern Pontides
Tokat Masifi'nin Jeolojisi ve Yap›sal Evrimi (Do¤u Pontidler, Türkiye)
Özet: Tokat Masifi, do¤u Pontidler’in bat› kesimini temsil eden ve Amasya ile Refladiye aras›nda genifl bir yay›l›m sunan Liyas öncesi yaflta metamorfik bir karmafl›k ile temsil edilir ve bat› Pontidler’deki Karakaya Karmafl›¤› ile korele edilebilir. Bu kompleks, Tokat yöresinde iki temel birime ayr›labilir. Bunlar, Turhal Metamorfitleri ve Devecida¤› Kar›fl›¤›’d›r. Turhal Metamorfitleri, masifin kuzeyini oluflturan metavolkano-tortul bir diziyi karakterize eder. Alt kesimi, gnays, amfibolit ve mika flistlerle, üst kesimi ise mika flist, fillit, metak›r›nt›l›, metabazit ve mermerin ardafl›m›ndan oluflan bu birim a¤›rl›kl› olarak bir yay istifinin özelliklerini yans›t›r. Devecida¤› Kar›fl›¤› ise masifin güneyini oluflturan ve yer yer olistostromal özellikte bloklu metavolkano-tortul istifi karakterize eder. Bu birim, kimi zaman yitim kar›fl›¤›, kimi zaman yay-önü istifinin özelliklerini yans›tan ve a¤›rl›kl› olarak yitim zonu ile yay-önü aras›nda geliflen heterojen bir kayatürü toplulu¤u ile temsil edilir. Tokat Masifi’ni oluflturan metamorfik birimler, do¤u Pontidler’in di¤er kesimlerinde ve Kuzey Anadolu Ofiyolit Kufla¤› boyunca da izlenmektedir. Bu birimler, daha güneydeki Kuzey Anadolu Ofiyolit Kufla¤›’na ait ofiyolitli melanj prizmas›na geç Kampaniyen öncesinde tektonik dilimler halinde eklenmifllerdir. Geç Kretase yafll› olan ofiyolitli melanj prizmas›na ait baz› dilimler de, Tokat Masifi aras›nda yaklafl›k do¤u–bat› uzan›ml› olarak yer almaktad›r. Dolay›s›yla, Tokat Masifi birimleri aras›nda yer alan ofiyolitler ve ofiyolitli melanjlar, ilksel yerleflim yerlerinde olmad›¤›ndan bunlar›n konumu gözetilerek kenet kuflaklar› çizilemez. Kuzey Anadolu Ofiyolit Kufla¤›’n› oluflturan ofiyolitli melanj prizmas› bafllang›çta hem kuzeye hem de güneye do¤ru yay›larak büyümüfl ve kuzeydeki yani masif taraf›nda yer alan melanj dilimleri daha sonraki s›k›flman›n güdümünde yükselip afl›nm›fl ve kal›nt› yüzeylemeler neotektonik süreçte retro- flaryajlarla terslenmifltir.
Anahtar Sözcükler: Tokat Grubu, Karakaya Kompleksi, yap›sal evrim, do¤u Pontidler
231 GEOLOGY OF THE TOKAT MASSIF
Introduction It has also been suggested that, at least, the Devecida¤ Complex is the equivalent of the Karakaya Complex of the The E –W-trending Pontide orogenic belt in northern Turkey, bounded to the south by the North Anatolian western Pontides (Bingöl et al. 1975), and that it Ophiolite Belt (Figure 1, Ketin 1966), is commonly represents a subduction-accretion complex (Tekeli 1981). divided into the western, central and eastern Pontides (Y. The Tokat Massif as a whole is placed into the Sakarya Y›lmaz et al. 1997a, b). In this classification, the Tokat Zone of the Pontides (Okay 1989; Okay et al. 1991; Okay Massif lies in the eastern Pontides. Parts of the Tokat & fiahintürk 1997). Y. Y›lmaz et al. (1997a, b), who have Massif have been studied by various authors (Alp 1972; studied the whole of the Tokat Massif, have renamed the Öztürk 1979; Özcan et al. 1980; Bektafl et al. 1984; rock-stratigraphic units without proper consideration of Özcan & Aksay 1996; Seymen 1991, 1993; A. Y›lmaz the previous stratigraphic nomenclature in the Tokat 1980, 1981a, b, 1982a, b, 1985; Okay 1983, 1996; Massif. They claimed that an ophiolite outcrop, extending Okay & fiahintürk 1997). These studies have in an E –W direction in the centre of the Tokat Massif, demonstrated that the Tokat Massif consists of represents an old suture, and that the rocks to the north heterogeneous pre-Jurassic rock associations. The pre- and south of this “suture” belong to different former Jurassic rock association in the Tokat Massif has been plates. subdivided into a lower metamorphic unit and an upper The different tectonic interpretations, outlined above, blocky unit (Özcan et al. 1980; A. Y›lmaz 1980, 1982a, reflects the scarcity of geological data from the Tokat b). The lower unit, consisting of metaclastic and Massif. In this study we aim to rectify this situation by metabasic rocks, phyllite and marble is named the Turhal providing detailed geological data from the massif. These Metamorphics, and the overlying metavolcaniclastic unit data include the descriptions, characteristics, distribution, with exotic blocks of the Devecida¤ Complex; these contact relations, ages, depositional environments, and stratigraphic names have been confirmed by the metamorphic grades of the rock units within the Tokat Stratigraphy Committee of Turkey (TSK 1987). Massif. We also provide information on the little known
W
28e 32 36 40 W Black Sea Fault s R N t SE C BLACK S US ri SEA LE AS m UC
e
a A
n C F
a Figure 2 u l S KAM E S D E Ýstanbul Zone DE TM EA TI R NTI Tokat STERN PON U 40 RN PO T 40 WESTE SU N KIM AM IA A UT Sivas NORTH ANATOL KAR S UR AN E IAN S R- OL UT Ý S AT URE M D IT AN ÝZ M AN ST TFOR EA IDE PLA TH TAURIDE-ANATOL ENTS U PLATFO UIVAL O AN RM METAMORPHIC EQ S BI RA A KAM:Kargý Massif TM:Tokat Massif 36 28 32 36 AM:Akdaðmadeni Massif
Figure 1. Simplified tectonic divisions of Turkey. The Pontides (shaded region) (after Ketin 1966 and general evaluations). Abbreviations : KAM– Karg› Massif, TM– Tokat Massif, AM– Akda¤madeni Massif. Inset shows the location of the map displayed in Figure 2 (after Okay 1 989; Okay & Tüysüz 1999 and personal evaluations).
232 A. YILMAZ & H. YILMAZ
relation of the Tokat Massif to the ophiolitic belt to the This age corresponds to the period when the ophiolitic south. This relationship is important for understanding mélange prism was thrust bilaterally to the north and to the place of the Tokat Massif in the regional tectonic the south. The metamorphic rocks of the Akda¤madeni framework. Group, which bear traces of the Alpide orogeny (fiengör 1987), are regarded as the metamorphic equivalents of the Anatolide-Tauride Platform (A. Y›lmaz et al. 1993). It Regional Geology has been suggested that the upper parts of the The rocks in the Tokat Massif and in the surrounding Akda¤madeni Group represent north-facing Atlantic-type, region belong to one of the following three basic tectonic passive continental-margin deposits (Seymen 1985). units: these are the Tokat, Yeflil›rmak and Akda¤madeni The Yeflil›rmak Group consists of ophiolitic mélange, groups (Figure 2; Özcan et al. 1980; A. Y›lmaz 1980, represented by the North Anatolian Ophiolite Belt, and of 1982a, b). The Akda¤madeni Group, which structurally fore-arc sequences, which lie unconformably over the forms the lower rock association (Figure 3), is part of the mélange. This belt starts in ‹zmir, and continues K›rflehir Massif (Seymen 1985), and consists of gneiss, eastwards in the direction of Ankara-Erzincan and joins to amphibolite, schist, quartzite and marble (Figure 3). the Lesser Caucasus ophiolitic belt (Zakariadze et al. These rocks, which are of continental crustal origin, have 1983). The Upper Cretaceous ophiolitic mélange has been been regionally metamorphosed in the amphibolite facies, thrust along the North Anatolian Ophiolite Belt northward and later were affected by cataclastic metamorphism and southward over other tectonic units (A. Y›lmaz 1980, (Alpaslan 1993). The age of the cataclastic 1982a, b, 1985, 1989; A. Y›lmaz & Özer 1984; A. metamorphism, determined by the K/Ar method, falls Y›lmaz et al. 1985). In the region between Tokat and into the Santonian–Maastrichtian (Alpaslan et al. 1996). Sivas, the present structure is characterised by north-
40 36 Samsun 37 38 39 N BLACK SEA 41 Ordu 41 0 20 km T M aþova A G M A T Amasya I C Niksar B E L T Figure 4 Gümüþhane Turhal Reþadiye Koyulhisar
Tokat Pulur Figure 6 Suþehri Agvanis Kelkit Köse daðý 40 40 Yýldýz Daðý
Erzincan Evliya Tepe Kýzýldað Figure 5 36 37 Sivas 38 39 40
Tokat Akdaðmadeni Yeþilýrmak Group: mainly Yeþilýrmak Group: mainly Jurassic Group Group undivided ophiolites ophiolitic mélanges rocks
Jurassic to Quaternary contacts overthrusts strike-slip settlements Tertiary rocks deposits faults
Figure 2. Simplified geological map of the area between Tokat, Sivas and Erzincan (after A. Y›lmaz 1980, 1982b; Özcan et al. 1980; Özcan & Aksay 1996; and our own observations). Insets show the location of the maps displayed in the following figures.
233 GEOLOGY OF THE TOKAT MASSIF
N S
1500 m 1500 m
0 m 0 m Approximate scale
Turhal Metamorphics, representing 020km metavolcano-sedimentary sequence
Devecidað Mélange, including Permian Yeþilýrmak Group, representing ophiolitic Akdaðmadeni Group, including gneiss, and Triassic limestone blocks and in mélange prism including ophiolites and amphibolite, schist, quartzite and marble places Permian and Triassic limestone ophiolitic mélanges alternations Tokat Group Tokat lenses
Figure 3. Columnar section indicating structural relationships between Yeflil›rmak group, Tokat Group and Akda¤madeni group. dipping thrusts. This may be related to the rotation of the been differentiated. The Cenci Group shows earlier south-dipping thrusts, or later backthrusting as a metamorphism in the granulite facies, whereas the Hasso result of continuing contraction following the Group is represented by greenschist-facies metavolcano- emplacement of the ophiolitic mélange. sedimentary rocks, and has been correlated with the The Tokat Group, which constitutes most of the A¤vanis and Tokat massifs (Okay 1996). The Upper Tokat Massif (Blumenthal 1950), consists of a lower Carboniferous–Lower Permian shallow-marine to coherent metamorphic sequence and an upper blocky terrigeneous sedimentary sequence in the Pulur region volcano-sedimentary series. It has undergone low-grade (Akdeniz 1988) contains well-rounded clasts derived greenschist facies metamorphism, and bears imprints of from the Cenci Group of the Pulur Massif, and represents the Alpide and Cimmeride orogenies (fiengör 1987). a molasses-type deposition at the end of the Hercynian orogeny (Khain 1975; Okay & Leven 1996; Çapk›no¤lu 2003). Similar lithologies and contact relations are The Pre-Jurassic Units of the Eastern Pontides, and observed in the Greater Caucasus and in the Khrami the Tectonic Setting of the Tokat Group Massif of the Lesser Caucasus (Adamia et al. 1982, 1983; The pre-Liassic basement of the eastern Pontides consists A. Y›lmaz 1989; Okay & Leven 1996). A further of various units with different lithologies and tectonic important pre-Jurassic rock association in the eastern features. These include high-grade metamorphic rocks, Pontides is the Lower Carboniferous Gümüflhane and Lower Carboniferous granitoids, Upper Carboniferous– Köse plutons (Zankl 1962; Y. Y›lmaz 1974; Bergougnan Lower Permian shallow marine to terrigeneous deposits, 1987). The presence of pre-Liassic ophiolites has long and Permo–Triassic low-grade metavolcano-sedimentary been claimed in the Tokat Massif and along the North rocks. The relations between these units are poorly Anatolian Ophiolite Belt (Blumenthal 1950; Koçyi¤it known because of the overlying Mesozoic–Tertiary cover, 1991a; Seymen 1991, 1993; Y. Y›lmaz 1997a, b). This and because of the interference of the Alpide orogeny. short discussion illustrates that the pre-Jurassic basement of the eastern Pontides forms a complex mosaic, with the The Permo–Triassic low-grade metavolcano- Tokat Massif having a key role in our understanding of sedimentary rock association between Amasya and the pre-Jurassic evolution of the region. Suflehri is known as the Tokat Massif. Figure 2 shows the outcrops of the Tokat Massif, and the neighbouring metamorphic massifs that can be correlated in part with The Tokat Group the Tokat Group. In the Pulur Massif, two metamorphic In this study, the name Tokat Group (Özcan et al. 1980; rock associations, separated by a tectonic contact, have A. Y›lmaz 1982a, b) has been used for the pre-Liassic
234 A. YILMAZ & H. YILMAZ
low-grade metavolcano-sedimentary rocks. Although tectonic slices with the North Anatolian Ophiolite Belt similar pre-Liassic units have been studied and named in (Figure 5). more detail in the western Pontides, the outcrops around This discussion shows that the Tokat Group extends Tokat are large and distinctive enough to warrant a eastward as far as the Pulur region. Furthermore, the different name. The Tokat Group has been divided into dyke complex in the Yusufeli region, and the metavolcanic two formations: the Turhal Metamorphics and the rocks in the Khrami Massif can easily be correlated with Devecida¤ Mélange (Figure 4). the Bayburt-Pulur region (A. Y›lmaz 1989; Okay & Leven 1996). In the northern parts of the eastern Pontides, in Lithological Features the region of Giresun, small outcrops of pre-Liassic metamorphic rocks have been mapped (S. Y›lmaz & The Turhal Metamorphics is a volcano-sedimentary Boztu¤ 1996). These outcrops of mica schist, phyllite and sequence metamorphosed in the greenschist facies. The calc-schist, extending in a NE –SW direction south of the rocks consist of an alternation of phyllite, schist, Dereli village of Giresun, are correlated with the Turhal metasiltstone, metasandstone, metatuff and metabasite. Metamorphics. Were it not for the Mesozoic–Tertiary In the lower parts of the section, these rock types are cover of the eastern Pontides and the Transcaucasus, the accompanied by gneiss, amphibolite, mica schist and Tokat Group would have most probably been seen to quartzite, and in the upper parts by calc-schist and extend north to the Dizi series of the Greater Caucasus marble. (Adamia et al. 1982; A. Y›lmaz 1989). However, because The Devecida¤ Mélange is made up of exotic blocks, of the presence of the Mesozoic–Tertiary cover, the including Silurian to Triassic limestone, and ophiolite isolated pre-Liassic outcrops have been interpreted blocks, in a metaclastic and metavolcanic matrix. It differs differently (fiengör 1987), although they in fact are part from the Turhal Metamorphics by the presence of the of the same tectonic unit. In conclusion, the Tokat Group exotic blocks. When examined in detail, the Devecida¤ has a very wide distribution in the eastern Pontides and Mélange can be observed to locally have an olistostromal in the Caucasus. or strongly mylonitised, sheared character. In areas of strong mylonitisation, the primary relationships between different rock types have been completely destroyed. The Contact Relations ophiolite blocks in the Devecida¤ Mélange, mainly The basal stratigraphic contact of the Tokat Group is not serpentinised peridotites, are interpreted as remnants of observed anywhere. It is unconformably covered by a a pre-Liassic oceanic crust. It has also been suggested that sedimentary sequence of Liassic to Cretaceous age (Özcan at least parts of the Devecida¤ Mélange represents a pre- et al. 1980; Seymen 1991, 1993). The Turhal Liassic accretionary complex (Tekeli 1981). Metamorphics of the Tokat Group crop out generally in the north, and structurally at a lower position than the Devecida¤ Mélange, which crops out in the south. The Distribution contacts between these two formations are generally The Tokat Group has a wide distribution to the south, tectonic, and only locally gradational. The Tokat Group east and southeast of Tokat (Figure 2). The outcrops of shows tectonic relations with the granulite facies the Tokat Group in the Amasya and Turhal regions (Özcan metamorphic rocks of the Pulur Massif. These two et al. 1980), west of Koyulhisar, and immediately south different metamorphic units probably were amalgamated of the North Anatolian Fault are those of the Turhal during the Cimmeride orogeny (Okay 1996). The Tokat Metamorphics. Furthermore, the outcrops north of Group also lies tectonically over the metamorphic rocks of A¤vanis, and parts of the Pulur Massif can be assigned to the Akda¤madeni Group, as observed in the region of the Turhal Metamorphics (Okay 1983, 1996). All the Evliya Tepe north of Sivas (Figures 2 & 6). This tectonic outcrops in these regions consist of greenschist-facies contact is unconformably covered by Eocene clastic rocks. metamorphic rocks without exotic blocks. In regions This shows that the oceanic lithosphere between the south of Tokat, and in the Refahiye area south of Tokat and Akda¤madeni groups was completely A¤vanis, pre-Liassic metavolcanic rocks crop out as subducted by the Eocene.
235 GEOLOGY OF THE TOKAT MASSIF
N 36 50/ 20 50 0 4 Kozalan Almus km 40 45 x Taktaklýk T. 30
15 Tokat 20
40 20/ 30 40 20/ Tavþanal T. 20 Çevreli x
30
35 35 40
37
35 xx Toraç daðý 35
40
/ / 40 15 40 15 70
80 30 35
Demirözü
Turhal Devecidað Yeþilýrmak Group Boztepe Metamorphics Mélange (ophiolitic mélange) Formation Tertiary Quaternary cover deposits contacts overthrusts
20 bedding foliation settlements highway
Figure 4. Geological map of the area between Tokat and Almus (after A. Y›lmaz 1980, 1982b; Özcan & Aksay 1996; and our own observations). For the location see Figure 2.
236 A. YILMAZ & H. YILMAZ
N 38 45/ A 01 km Biçer
50 35 35 35 30 25 25
Atakilise 30 35
45 Karasu 30 / 39 55/ 60 45 39 55 30 REFAHÝYE 25
25
45 DUMANLI DAÐ x B
NW SE 2000 2000
1000 1000
0 m 0 m A-B cross-section
Plio-Quternary Tokat Group Tokat Group Yeþilýrmak Group (greenschist) (marble) deposits
active strike-slip faults contacts of NAFZ (arrows show settlements overthrusts foliation direction of the relative movement)
Figure 5. Geological map of Dumanl› Da¤ of Refahiye area (after A. Y›lmaz et al. 1985b). For location see Figure 2.
In several localities, the Tokat Group lies tectonically 2 & 4). Of these tectonic contacts, those west and north over the ophiolite or ophiolitic mélange (Figures 2 & 3), of Tokat are young neotectonic thrusts. In the Refahiye or over the Jurassic to Tertiary cover sequence (Figures region, the Tokat Group occurs as a tectonic slice in the
237 GEOLOGY OF THE TOKAT MASSIF
A
37 15/ N 0 1 35 km 40 Kamýþlý 40 05 / 40 05 / Evliya Tepe 40 x 50
25 Esenli
Uzamýþ 37 15/ B SE NW 1500 1500
500 m 500 m A-B cross-section
Yeþilýrmak Group
Akdaðmadeni Tokat serpentinized diabase, ophiolitic Group Group peridodit volcanics mélange
Eocene Doðanþar Upper Miocene contacts pre-Eocene formation Üregil formation overthrusts faults post-Eocene overthrusts bedding foliation settlements
Figure 6. Geological map of the Evliya Tepe area showing relationship between Tokat Group, Akda¤madeni Group and Yeflil›rmak Group (after A. Y›lmaz 1982b). For location see Figure 2.
238 A. YILMAZ & H. YILMAZ
serpentinised Cretaceous peridotites (Figure 5). In this Triassic in age (Alp 1972; Özcan et al. 1980; Çapk›no¤lu region, actinolite in the metabasic rocks of the Tokat & Bektafl 1999) implying that the Devecida¤ Mélange is Group shows replacement by sodic amphibole along a Triassic in age. However, to the east of Toraç Mountain, tectonic contact north and northeast of Alakilise (A. south of Tokat, south of the Develiçal› Hill (Figure 4), Y›lmaz 1985). The oldest rocks, which cover the tectonic stratigraphic intercalation of limestone lenses occur contacts between the Devecida¤ Mélange of the Tokat within the Devecida¤› Mélange. In Figure 4, these Group, and the ophiolitic mélange, make up the Boztepe limestone lenses are exaggerated. These limestone lenses Formation (Figure 4). The pelagic foraminifera make up a few distinct stratigraphic levels and are folded determined from the Boztepe Formation by Ercüment with the intervening metaclastic horizons. Samples from Sirel include Globotruncana linneiana (De LAPP.), these limestone intercalations contain a Permian fauna as Globotruncana cf. arca (CUSH.), Globotruncana cf. determined by Ahmet Ifl›k and Ercüment Sirel: Pachyphlio calcarata (CUSH.) Globotruncana cf. coronata BOLL‹, sp., Glomospira sp., Nodariidae, Staffelliidae, Lagenidae, Globotruncana cf. tricarinata (QUE), Globotruncana sp., and Fusulininae. There is no unconformity between the and indicate a Late Campanian age. Farther west, the levels with the Permian limestone lenses, and the Boztepe Formation also lies unconformably over the overlying series with Triassic limestone blocks. These Cretaceous ophiolitic mélange. The Boztepe Formation data indicate that the Devecida¤ Mélange has an age consists predominantly of pelagic limestones but also range of Permian and Triassic. includes turbiditic clastic rocks, and olistostromes with The high-grade metamorphic rocks, which make up ophiolitic detritus. The Boztepe Formation is interpreted part of the Pulur Massif, and those into which the as a fore-arc basin developed on the ophiolitic mélange. Gümüflhane and Köse granitoids were emplaced are Similar fore-arc basins have been described in detail by considered outside the definition of the Tokat Group. On Koçyi¤it (1991b). The stratigraphic position of the the basis of the geochronological data and stratigraphic Boztepe Group, both above the Tokat Group and above relations with the Upper Carboniferous–Lower Permian the ophiolitic mélange, indicates that at least part of the molasse units, these metamorphic rocks are Early tectonic interslicing between the Tokat Group and the Carboniferous in age. ophiolitic mélange occurred in pre-late Campanian time during formation of the ophiolitic mélange. In the Tokat region, where the Tokat Group has Depositional Environment extensive outcrops, the ophiolitic mélange occurs as thin Different depositional environments have been proposed thrust sheets within the Tokat Group (Bozkurt et al. for the rocks of the Tokat Group and its equivalents in 1997). In contrast, in the south in the North Anatolian the western and central Pontides. The equivalents of the Ophiolite Belt, rocks of the Tokat Group occur as thin Tokat Group in the western Pontides have been thrust sheets within the ophiolitic mélange. In all these interpreted as deposits of a fore-arc or intra-arc basin regions, the thrusts trend E-W, parallel to the North (Okay et al. 1996). Similar units in the central Pontides Anatolian Ophiolite Belt, and dip N. In conclusion, the have been considered as products of a marginal back-arc rocks of the Tokat Group were probably injected as basin opened above the southward subducting Palaeo- tectonic slices in the mélange prism during the formation Tethys ocean (fiengör & Y›lmaz 1981; Tüysüz & Yi¤itbafl of the ophiolitic mélange. 1994). Equivalents of the Devecida¤› Mélange have been interpreted as deposits of a marginal basin (Özcan et al. Age 1980), or of a back-arc basin (Koçyi¤it 1991a), or a fore- arc basin (Okay et al. 1997) or that of a subduction zone There is no concrete data on the age of the Turhal (Tekeli 1981). The various interpretations on the Metamorphics of the Tokat Group. The recrystallised depositional setting of the Tokat Group are the result of limestone levels in the upper parts of the Turhal Metamorphics have speculatively been correlated with strong post-depositional tectonism, and the lack of age Triassic and Permian carbonates in the Devecida¤ and primary sedimentary data. Mélange. The Devecida¤ Mélange comprises limestone The lithologies of the Turhal Metamorphics and the blocks of Silurian, Devonian, Carboniferous, Permian and matrix of the Devecida¤ Mélange are fairly similar.
239 GEOLOGY OF THE TOKAT MASSIF
Therefore, the depositional setting of the Tokat Group Correlation can be considered as a whole. Lithologically, the Turhal The Tokat Group and its Mesozoic–Tertiary cover can Metamorphics are dominated by metaclastic sedimentary confidently be correlated with the Sakarya Zone of Okay and volcaniclastic rocks. Basic lavas and other et al. (1996). However, there are problems in the sedimentary intercalations are rarely observed. correlation of the pre-Liassic units between the eastern Therefore, a palaeo-arc depositional environment can be and western Pontides. Some of the problems arise assigned to the Turhal Metamorphics. A more accurate because the pre-Liassic units in the eastern Pontides have depositional setting can be assigned to this formation not been studied in as much detail as in the western after the geochemistry of the volcanic rocks is known. Pontides. The different names given to the same unit by A fore-arc or a back-arc depositional setting, or a different geologists also create problems in correlation. combination of the two, is probably more appropriate for The Tokat Group is the equivalent of the Tozanl› the Devecida¤ Mélange. The presence of both blocks and Complex, Akda¤ Formation and the Karakaya Mélange of sedimentary intercalations of Permian and Triassic Seymen (1975, 1991, 1993). In more detail, the Turhal limestones argues for a back-arc setting, whereas intense Metamorphics correlate with the Tozanl› Complex and the deformation suggests a fore-arc to subduction-zone Akda¤ Formation, and the Devecida¤› Mélange with the setting. Karakaya Mélange. With limited data, Y›lmaz et al. Considering that an inactive fore-arc basin may (1997a, b) claimed that the different rock units in the contain blocks and intercalations, a fore-arc depositional Tokat Massif represent different geotectonic setting can be preferred for the Tokat Group. The locally environments; for example, the Turhal metaophiolite, strongly sheared matrix of the Devecida¤ Group, and the which extends through the centre of the Tokat Massif, local presence of ophiolite blocks, indicate the presence of was claimed to represent a palaeo-suture. The presence a subduction complex beneath the fore-arc basin. of Palaeozoic ophiolites in the Tokat region (Blumenthal Considering that the outcrops of the Turhal 1950; Koçyi¤it 1991a; Y. Y›lmaz et al. 1997a) and along Metamorphics are mainly in the north, and those of the the North Anatolian Ophiolite Belt (Tatar 1978; Devecida¤ Mélange are mainly in the south (Figures 2, 4 Zakariadze et al. 1983; A. Y›lmaz 1989) has long been & 7), an arc through fore-arc to subduction zone claimed. However, these ophiolite slices have been depositional setting can be envisaged for the pre-Liassic accreted to the Upper Cretaceous ophiolitic mélange time. This implies a system with the subduction zone in prism. In a similar manner, the ophiolites mapped by Y. the south and the arc in the north, contrary to the Y›lmaz et al. (1997a) between Turhal and Mamoda¤› presently accepted view. belong to the Upper Cretaceous ophiolitic mélange with Upper Jurassic limestone blocks (Özcan et al. 1980). As shown in Figures 2 & 4, the Tokat Group Metamorphic Grade comprises several E –W-trending Upper Cretaceous The Tokat Group as a whole has undergone regional ophiolite mélange slices. In the view of Y. Y›lmaz et al. metamorphism in greenschist facies (Özcan et al. 1980; (1997a, b) this would require several sutures within the A. Y›lmaz 1980, 1982a, b). The mineral paragenesis Tokat Massif. In conclusion, ophiolites of various ages suggests a metamorphic pressure of 3 to 6 kbar, and a occur in the Upper Cretaceous ophiolitic mélanges of the temperature of 300–500 °C, indicating burial to a depth North Anatolian Ophiolite Belt or within the Tokat Massif. of 10–18 km (Y. Y›lmaz et al. 1997a). However, it is However, especially the ophiolitic mélanges in the claimed that some outcrops of the Devecida¤ Mélange northern part of the Tokat Massif do not represent have undergone metamorphism in blueschist, greenschist sutures. and to amphibolite facies (Tekeli 1981). Especially in The Ilgaz-Karg› and the Devrekani massifs in the localities where ophiolites lie tectonically over the central Pontides (Tüysüz & Yi¤itbafl 1994; Ustaömer & greenschists, a change towards the glaucophanitic Robertson 1997) can be correlated with the Tokat greenschist facies has been observed, for example, to the Massif, and hence with the Tokat Group. The Permo– north of Alakilise in the region of Refahiye (A. Y›lmaz Triassic volcano-sedimentary sequence with exotic blocks 1985).
240 A. YILMAZ & H. YILMAZ S km 20 S scale approximate 0 d of Late Cretaceous and/or earlier). Compression compression representing by horizontal arrows and vertical movements representing by vertical arrows, respectively Akdaðmadeni Group Yeþilýrmak Group Devecidað Mélange (a) Tokat Group Tokat N Turhal Metamorphics Cross-sections depicting structural relationships between Yeflil›rmak Group, Tokat Group and Akda¤madeni Group (A– Recent, B– en is represented by the horizontal arrows and vertical movements by the vertical arrows, respectively. (b) N Figure 7.
241 GEOLOGY OF THE TOKAT MASSIF
in the Ilgaz-Karg› Massif has even been named the Tectonic slices belonging to the Akda¤madeni Group, Karakaya Unit (Tüysüz & Yi¤itbafl 1994). and consisting of amphibolite-facies metamorphic rocks, The main problem in correlating the Tokat Group are observed in the North Anatolian Ophiolite Belt south with equivalents in the western Pontides lies in the fact of Y›ld›z Da¤ and at Evliya Hill (Figures 2 & 6; A. Y›lmaz that the pre-Liassic rocks have not been studied in as 1982 a, b). Furthermore, serpentinised peridotite and much detail as in the western Pontides. The Karakaya gabbro slices occur within the Akda¤madeni Group or above them (A. Y›lmaz 1980; A. Y›lmaz et al. 1995). Formation as defined by Bingöl et al. (1975) can be When the sizes and thicknesses of these tectonic slices correlated with the Tokat Group. However, a more have been studied, it has been found that the detailed study of the Karakaya Formation has resulted in Akda¤madeni slices are thin in the North Anatolian a change of the name to the Karakaya Complex (fiengör Ophiolite Belt, whereas the ophiolitic mélange slices are et al. 1984; Okay et al. 1996). Therefore, the Tokat thin in the main outcrop area of the Akda¤madeni Group Group can be used as the equivalent of the Karakaya (Figure 3). The relation between the Tokat Group and the Complex. In a more detailed study of the Tokat Massif, it Yeflil›rmak Group, which is the local name for the North would be possible to map the equivalents of the Nilüfer, Anatolian Ophiolite Belt, is shown in a cross-section in Çal and Hodul units, and the Orhanlar Greywacke, which Figure 3. As seen in this section, and also in Figure 6, the are defined on the Biga Peninsula in the western rocks of the Tokat Group and the Akda¤madeni Group Pontides. The correlation between the western and are locally in tectonic contact. A similar relation has also central Pontides becomes even easier when only the been described from the K›z›lda¤ region (A. Y›lmaz 1985; blocky and coherent pre-Liassic units are considered. In A. Y›lmaz et al. 1985). this case, the Turhal Metamorphics correlate with the Nilüfer Unit, and the lower parts of the Çal and Hodul Eocene clastic rocks lie unconformably over the Tokat units, and the Devecida¤ Mélange correlates with the Group in the north and over the Akda¤madeni Group in upper parts of the Çal and Hodul units, and the blocky the south, and also cover the tectonic contact between part of the Orhanlar Greywacke. these two groups (Figure 6). This suggests that the collision between these plates and the complete consumption of the oceanic lithosphere between these The Structural Evolution of the Tokat Group two groups occurred before the Eocene. The tectonic In order to understand the structural evolution of the contact between the Tokat Group and the ophiolitic rocks Tokat Group, it is necessary to study its contact relations of the Yeflil›rmak Group is unconformably covered by the with the North Anatolian Ophiolite Belt and the upper Campanian Boztepe Formation, as shown in Figure Akda¤madeni Group. The North Anatolian Ophiolite Belt 4. Therefore, the accretion of the various metamorphic represents a suture zone between the Pontides in the rock slices to the ophiolitic mélange occurred before the north and the Anatolide-Tauride Block in the south, late Campanian, possibly during the formation of the formed as a result of the closure of the northern branch ophiolitic mélange. of Neotethys (fiengör & Y›lmaz 1981). The North As stated above, all the present-day tectonic contacts Anatolian Ophiolite Belt comprises Upper Cretaceous dip to the north. It has been established that the thrusts mélanges, which include several different block in the south have had a northward dip at least since the lithologies. The blocks in the north are largely derived Late Cretaceous – since the formation of the ophiolitic from the Tokat Massif, whereas those in the south from mélange – and have preserved their northward dips the Akda¤madeni Group (A. Y›lmaz 1982a, b). Thin during Eocene movements (A. Y›lmaz & Özer 1984). In tectonic slices of Upper Cretaceous ophiolitic mélange addition, thrusts in the Tokat region are known to be occur within the Tokat Group (Figures 2 & 3). In rather young, and possibly active in a neotectonic phase. contrast, in the North Anatolian Ophiolite Belt in the For example, the extension of the thrusts north of the south, thin tectonic slices of the Tokat Group are found in Çevreli village in Figure 4 have been studied northeast of the Upper Cretaceous mélanges. As shown in Figures 4, 5 the Almus reservoir lake, and it has been found that the & 6, the tectonic slices and the thrusts dip to the north. Lower Miocene clastic and carbonates in the footwall of the thrusts are inverted (Terlemez & Y›lmaz 1980).
242 A. YILMAZ & H. YILMAZ
In conclusion, an investigation of the tectonic relations sequence is known from Gondwana. Furthermore, it is between the metamorphic units and the ophiolitic questionable as how representative this series is for the mélange suggests that initially the ophiolitic mélange was regional geology. Figure 4 shows one of the regions emplaced both northward and southward over the Tokat where this series has been described. Detailed mapping in and Akda¤madeni groups (Figure 7). The south-vergent this area has shown that the Geyraz Formation and the structure in the Tokat region developed later in a Çat Marble, which have been described as the lowermost neotectonic episode. If the initial tectonic picture had Gondwanian units, are in fact allochthonous within the been preserved, one would have expected a folded Permo–Triassic blocky series (A. Y›lmaz 1980). structure with the Akda¤madeni and Tokat groups below Furthermore, this blocky series also crops out north of and the ophiolitic mélange above, as illustrated in Figure the metaophiolite between Tokat and Mamoda¤› (Özcan 7b. Such a mechanism provides an explanation as to why et al. 1980). Therefore, this metaophiolite belt – with the thickness of the ophiolitic mélange slices decreases as similar sequences to the north and to the south – does not one goes to the north and to the south. represent a suture zone. The presence of north- and south-dipping thrusts Conclusions and Discussion along the North Anatolian Ophiolite Belt and the Lesser Caucasus, developed during Late Cretaceous ophiolite In the future, more detailed studies of the rocks of the obduction, are widely reported (Zakariadze et al. 1983; Tokat Group, which make up the Tokat Massif, would A. Y›lmaz 1985; Okay et al. 1996; Okay & fiahintürk allow a more thorough testing of theories concerning the 1997). However, because of subsequent deformation genesis and structure of this Massif, including that by Y. related to the North Anatolian Fault Zone, north-vergent Y›lmaz et al. (1997a) regarding the evolution of the structures cannot be seen clearly in the Tokat Massif. As Tokat Massif. However, at present it can be said that this shown in the model in Figure 7, in the Tokat region the model does not take into proper account some of the ophiolitic mélange was initially thrust both to the north previous data (Özcan et al. 1980; Tekeli 1981; A. Y›lmaz and to the south. The north-vergent thrusts were 1980, 1982 a, b, 1985, 1989). For example, the modified during a later period. presence of pre-Jurassic metaophiolite in the Tokat Massif does not necessarily indicate that the Massif is This study has shown that the Turhal Metamorphics divided by a Palaeozoic suture. The presence of pre- of the Tokat Group crop out mainly in the north, whereas Jurassic ophiolites is known from the North Anatolian the overlying Devecida¤ Mélange crops out in the south. Ophiolite Belt, and even from the Lesser Caucasus The Tokat Group formed in pre-Liassic time, probably (Blumenthal 1950; Tatar 1978; Zakariadze et al. 1983; during the Permian and Triassic in – from north to south A. Y›lmaz 1989; Koçyi¤it 1991a). However, these – an arc through fore-arc to subduction-zone setting, and ophiolites are accreted to the Upper Cretaceous ophiolitic this subduction complex was accreted to the ophiolitic mélange of the North Anatolian Ophiolite Belt, which mélange prior to the late Campanian. represents a suture zone of the northern branch of Neotethys. This belt does not represent a pre-Liassic Acknowledgements suture. The authors wish to thank Ercüment Sirel and Ahmet Ifl›k Y. Y›lmaz et al. (1997a) have described a series from for micropalaeontological determinations. Thanks also to the Tokat region consisting of Carboniferous –Permian Okan Tüysüz and Aral Okay for their advice and critical metapelites at the base, overlain by marble, and overlain reading of the manuscript. We also express our gratitude unconformably by the blocky Triassic sequence. They to Aral Okay for his translation of the manuscript from assigned this series to Gondwana. However, no such Turkish into English.
243 GEOLOGY OF THE TOKAT MASSIF
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Received 06 March 2003; revised typescript accepted 19 January 2004
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