Formation of the Late Palaeozoic-Early Mesozoic Karakaya Complex and Related Ophiolites in NW Turkey by Palaeotethyan Subduction-Accretion

Journal of the Geological Society, London, Vol. 153, 1996, pp. 995-1009,

Formation of the Late Palaeozoic-Early Mesozoic Karakaya Complex and related ophiolites in NW Turkey by Palaeotethyan subduction-accretion

ELIZABETH A. PICKETT’ & ALASTAIR H. F. ROBERTSON Department of Geology and Geophysics, University of Edinburgh, Grant Institute, West Mains Road, Edinburgh EH9 3JW, UK I Present address: British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, UK

Abstract: Several pre-Jurassic tectonic units in NW Turkey are crucial to the current debate regarding the timing and direction of subduction of Palaeotethys,a major ocean that separated Eurasiaand Gondwana in Late Palaeozoic-Early Mesozoic times. The most critical unit is the Karakaya Complex, a deformed, low-grade assemblage of oceanic origin which comprises a NW-verging, SE-dipping stack of tectonostratigraphic units, hereinterpreted asa Palaeotethyan accretionary complex. The units display lithologies consistent with origins in seamount, trench, abyssal and rifted carbonate platform settings. Clastic basin sequences developed on top of the complex. Other relevant tectonostratigraphic units in the area include ultrabasic rocks of supra-subduction zone affinity, which tectonically overlie Permian carbonate platform units with interveningmetamorphic soles and mklanges. Restored structural trends suggest the presence of a southward-dipping Palaeotethyan subduction zone border- ing Gondwana-related units during the Late Permian-Triassic. This was probably additional to more importantregional northward subduction along the southern margin of Eurasiafrom the Eastern Mediterranean to the Himalayas.

Keywords: Turkey, Tethys. subduction, accretion, ophiolites.

Turkey is a segment of the Alpine-Himalayan orogenic belt units. Extensive greenschistfacies metamorphism has that lies betweenthe cratons of Eurasia in thenorth and affected theKarakaya Complex, as clearly recorded by Gondwana in the south. Within this broad suture zone can mineral assemblageswithin spilitized volcanic rocks. The be found the remnants of oceanic basins known collectively Karakaya Complex is probably the most critical pre-Jurassic as the Tethys Ocean, of which the Eastern Mediterranean unit in NWTurkey, as its componentsrepresent Sea is the last surviving remnant. A general consensus exists Palaeotethyan ocean floor and illustrate the processes which that a large Palaeozoic ocean (‘Palaeotethys’) was succeeded subsequently incorporated this material into an accretionary by smaller, mainly Mesozoic ocean basins (‘Neotethys’). The complex. Several different tectonic models for the Karakaya evolution of Neotethys is now well documented, but that of Complexhave beenproposed in theliterature, and these Palaeotethys has remained poorly understood, due in most will betested and discussed here, using new field and part tothe fragmentary, deformed and metamorphosed geochemicalevidence. A new tectonicmodel will be nature of itsremains. One of the mostvigorous current proposed, which drawson information from other related debates in Tethyan geology concernsthe direction and units in NW Turkey. timing of subduction of Palaeotethys.Radically different published models canbe divided into‘southward subduction’ (e.g. Sengor et al. 1980, 1984; Okay et al. 1991; Tiiysiiz Regional setting 1990) and ‘northward subduction’ models (e.g. Adamia et al. The main area considered here is the Biga Peninsula and the 1981; Robertson & Dixon1984; Ustaomer & Robertson Bergama region in western Turkey (Figs 1 & 2). The units 1993).Until recently theremains of Palaeotethyswere discussed in this paper occur widely throughout these areas, sought well to the north, in theBlack Sea-Caucasus area. butoften as isolated outcrops separated by largeareas of However, ithas recently become clear that important youngercover or no exposure.Only parts of the overall evidence for subduction is present further south, principally tectonostratigraphyarepreserved locally, leading to in thenorthern and central regions of Turkey (e.g. the problems of regional correlation. The southern part of the northernAegean region, the Central Pontides and the Biga Peninsula is dominated by metamorphic rocks of the classic Ankara MClange of CentralAnatolia). Possible Kazdag Massif, trending NE-SW from the Bay of Edremit subduction-accretionunitsrelatedclosure to of (Fig. 2). The massifis flanked by smaller hills comprising Palaeotethysare especially widespread in theAegean deformed volcanic and sedimentary rocks of the Karakaya coastalregion of NW Turkey,the area discussed in this Complex andNeotethyana mClange (Cetmi Ophiolitic paper. The presentwork helps to resolve the current controv- MClange; Okay et al. 1991).In this area,the Karakaya ersy of the nature and timing of Palaeotethyan subduction Complex formsa SE-dipping stack of tectonostratigraphic in NW Turkey and its wider regional significance. units which arejuxtaposed against the Kazdag Massif by The main focus of this paper is the Karakaya Complex, a major low-angleextensional detachment faults (Fig. 3). In deformed, low-grade metamorphic assemblagecontaining the southeast part of the Biga Peninsula, around Balya (Fig. rocks of deep-sea origin disposed as a stack of thrust-bound 2), sequences of disruptedcarbonate platformrocks and 995

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Fig. 1. Tectonic map of Turkey, showing the location of the Biga Peninsula and Bergama areas (in box). The Karakaya Complex and related Palaeotethyan ophiolites and melanges are shown in black.

debris flows form the northern end of a belt of relatively discussedin this paper (Fig. l), thestructural trend is undeformed clastic rocksand PermiarI limestoneswhich approximately N-S. ThickTriassic carbonate platform extends southwestwards towards Bergama. sequences are exposed in both of these areas and overlie West of theKazdag Massif thestructural trend is melange containing blocks of volcanic rocks and Palaeozoic predominantly N-S to NNE-SSW, parallel to an elongate limestone (Papanikolaou & Sideris 1983). sliver of harzburgite(Denizgoren Ophiolite; Okay et al. Tertiary to Recent tectonics have played a major role in 1991); this has an along-strike equivalent further south, on thestructural arrangement of the Biga Peninsula and theGreek island of Lesbos (Fig. 2). Onthe Karaburun surrounding regions. The 'escape' of Anatolia towards the Peninsula and the Greek island of Chios, south of the area westas a result of movement along theNorth and East Anatolian Faults has resulted in N-S extension and graben formation in western Turkey (Sengor et al. 1985). Common NE-SW-trending normalfaults inthe Biga Peninsula probablyrepresent strands of theNorth Anatolian Fault whichsplay across the north and central part of the Biga Peninsula (Fig. 2).

Previous research The Karakaya Complex was first described from the Kazdag area of the Biga Peninsula by Bingol et al. (1973). Predominantly Permo-Triassicages have beendetermined for the complex (e.g. Bingol et al. 1973; Okay et al. 1991; Kaya & Mostler1992). Thepresence of adepositionally overlying Upper Triassicclastic sequence in the Biga

dlrabaSICS 8 amPhlDOl~lCSlDelllzgorerl a LeWsOphKhIe51 Fig. 3. Schematic cross-section of the Edremit-Havran region, Fig. 2. Generalized geological map of the Biga Peninsula and showing the juxtaposition of the Karakaya units and their surrounding regions. Line A refers to the schematic cross-section in relationship with the Kazdag Massif and the overlying Upper Fig. 3. Compiled from maps by Bingol (1989), Katsikatsos et al. Triassic-Jurassic sedimentary sequence. Line B refers to the (1982) and Okay er al. (1991). (NAF North Anatolian Fault.) schematic succession in Fig. 4.

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Peninsula (near Havran: Fig. 2) confirms a pre-Late Triassic & Yllmaz (1981) in which the Karakaya Complex formed as agefor theKarakaya Complex. Two maincategories of a back-arc basin behind a southward-dipping Palaeotethyan hypotheses have beenproposed for the formation of the subduction zone.In morerecent work, following their Karakaya Complex:those(i) involving sedimentary, discovery of Middle Carboniferousand LowerPermian relatively in situ, basinal processes, and (ii) those involving pelagic sedimentary blockswithin theKarakaya Complex, tectonicjuxtaposition and imbrication of deep-sease- Okay & Mostler (1994) suggestedthat the Karakaya quences. The sedimentary option was initiated by Bingo1 et Complexrepresents accreted active margin and oceanic al. (1973) with a model of gravitysliding in EarlyTriassic units of Permo-Triassic age (but including material as old as extensional basins, and was subsequently developed by Kaya theCarboniferous). Closure of theKarakaya basin is et al. (1986,1989), who postulated formation by apurely relatively well constrained in the west of Turkey by the Late depositionalrepetition of olistostromeswithin an overall Triassicage of theoldest unconformably overlying layer-cake sequence.The alternative, tectonic, hypothesis sediments (Tekeli 1981). Further east, the oldest unconfor- began with Tekeli's(1981) description of theKarakaya mable cover sequencesare of lateEarly Jurassic age, Complex (part of his 'NorthAnatolian MClange') asa possibly representing diachronous closure from west to east subduction-accretion complex which formed in the fore-arc (Tekeli 1981). region of anactive margin. Ugiimezsoy (1987)also placed the Karakaya Complexwithin an accretionary complex, in this case above a northward-dipping subduction zone. Okay Tectonostratigraphy et al. (1991)postulated formation of aLate Permian- Several major tectonostratigraphic units are present in the Triassic Karakaya riftbasin aboveasouthward-dipping area studied: Palaeotethyan subduction zone: in their model the Karakaya (1) ultrabasicunit with ametamorphic sole (Denizgoren Complex represents an entire active margin tectonostratig- Ophiolite), emplaced onto Permian platform carbonate raphy,including back-arc rift, intra-arc, fore-arc and rocks (Karadag Unit); accretionary units. This model is broadly in agreement with (2) amphibolite gneisses and marbles (Kazdag Massif): the plate reconstructions of Sengor et al. (1980) and Sengor (3) Permo-Triassiclow-grade meta-sedimentaryand meta- volcanicrocks (KarakayaComplex) (Fig.4) with an Upper Triassic-Jurassic sedimentary cover - this is the

voicanic cisats in caiclte matrix main focus of the paper: (4)a disrupted succession of clasticrocks depositionally U. Permian limeatone blocks in clastic matrix overlain by Permian carbonate platformrocks (also sheared phyilites interpreted as part of the Karakaya Complex). Based on new data collectedduring this study, the major units of the Karakaya Complex in NW Turkey are outlined dlsrupted basaic-chert-sandstone sequence below, from the deepest structural unit upwards.

The Niliifer Unit spliitized voicanics and voiceniciastics (lowgreenschist) The NiliiferUnit (Okay et al. 1991) comprisesathick sequence of green spilitic basalts, volcaniclastic debris flows, ignimbrites and volcanogenic sedimentary rocks.It iswell sheared debris flows exposed in the Edremit and Bergama regions (Figs 5 & 6). purple volcanic8 and volcaniciastics A distinctive feature is thepresence, within volcanogenic with limestone debris flows rocks, of redeposited,recrystallized limestone, forming derivedclasts and discrete beds, locally dated as Middle recrystallized limestone Triassic in the Bergamaregion on the basis of conodonts (Kaya & Mostler 1992). Limestone blocks up to 10 m across, spilite (high greenschist) limestonedebris flows and calciturbiditesform horizons within the volcanic pile. The lower parts of the unit consist serpentinite silvers of massivebasalts andignimbrite-related debris flows. Whole-rockgeochemical analysis of basaltsfrom the v) 0 marble with amphibolite horizons Edremit, Bergama and Bursa regions reveals a within-plate I P basalt (WPB) signature (Table 1 & Fig. 7). Data plotted on a 0 amphibolite, feldspathic gneiss and marble the clinopyroxene discrimination diagrams of Leterrier et al. I (1982) suggest thatthe basalts arepredominantly non- 4 c E alkalineand non-orogenic, which isin accordance with a W X v) I h WPB setting (Pickett 1994). The unit becomes progressively marble 0 moresediment-rich towardsits upper levels, with the 4 P appearance of volcanogenic sandstonesand chertymudst- N 4 sheared amphiboiite ones.However, continent-derived clastic material is Y serpentinized harzburgite noticeablyabsent, apart fromrare occurrences within tectonicslivers of clasticdebris flows in the NiliiferUnit. (K. Unit = Kalabsk Unit) These debris flows are locally seen only in the Edremit area Fig. 4. Tectonostratigraphic summary of the Kazdag Massif and (Fig. S), where they are lithologically similar to the overlying Karakaya Complex in the Edremit-Havran region. Ortaoba Unit (see below).

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Fig. 5. Geological map of the area 5 km NNW of Edremit. From our fieldwork and an unpublished map by Okay.

The Ortaoba Unit unithas well-developeda foliation and displayssmall The Niliifer Unit is tectonicallyoverlain by a disrupted, asymmetricalfolds, shear zones and small-scaleduplex mainlyclastic sequence whichis named the Ortaoba Unit development. A similar phyllitic sequence is exposed further after a village 4 km NW of Edremit (Fig. 5). At the base, south, in the region north of Bergama. Northeast of local occurrences of pillowlava and hyaloclastite are Edremit, phyllites of theKalabak Unit are intruded by a overlain by siliceous mudstone, followed by approximately granitic pluton (the Camhk Metagranodiorite of Okay et al. 10m of bedded greychert and thickening-a and 1991) that is demonstrably of pre-Late Triassic age, since it coarsening-upward sandstone sequence. Whole-rock geoch- is unconformably overlain by an undeformed Upper Triassic emical analysis of the lava reveals a mid-ocean ridge basalt sequence(NE of Havran).Recent zircondating suggests (MORB) signature (Table 1 & Fig. 7). As with the Nilufer that the Camllk Metagranodiorite may be as old as 399 f 13 Unit basalts, the clinopyroxene phenocrystcompositions Ma (i.e. Early Devonian) (Okay et al. in press). In this case, suggest the basalts are non-alkali and non-orogenic, which is theKalabak Unit couldrepresent Palaeozoic,a pre- also in accordance with a MORB-type setting (Pickett 1994). Karakaya,sedimentary succession which becametectoni- When normalizedagainst theNorth American shale cally intercalated with the Karakaya units (Okay et al. 1991). composite (Gromet et al. 1984), mudstones interbedded with the cherts display terrigenous signatures (Pickett 1994). The The Gal Unit mudstonesplot predominantly in andaround the active Thestructurally highestunit is the CalUnit (Okay et al. continentalmargin field of discrimination diagramsfor 1991) which occurs in the Edremit, Can, Bergama and Balya clastic rocks (Fig. 8). The Ortaoba Unit is strongly disrupted regions(Figs 5, 6 & 9), and comprisesdebris flows and with considerable tectonic repetition. Chert and basalt are disrupted fragments of Upper Permian carbonate platform found only in rare tectonic slices, while most of the unit is sequences with basal clastic rocks. The unit is well exposed madeup of feldspathicsandstone and interbedded dark in theCan region(Fig. 9), where the base of the unit is shaleand mudstone. Strong layer-parallelextension and representedby medium-bedded micaceous sandstones and recrystallizationhave obliterated most sedimentarystruc- shales:these areseparated fromoverlyingan red tures,although normal grading, debris flow horizonsand mudstone-dominated sequence by a local, high-angle fault. slump folds can be observed locally. The red mudstones are interbedded with pelagic limestones and several thin (

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Fig. 6. Geological map of the area 25 km NE of Bergama. From our fieldwork and the Turkish Institute of Mineral Exploration map Bahkesir-G4.

material to flows containing only volcanic clasts. These clasts ones,containing Halobia,Daonella, Posidonomya, exhibit a WPB-type geochemistry (Table 1 & Fig. 7). In the Neritopsis (van derKaaden 1959) and Bositra buchii Edremit region, theCal Unit forms klippen of Upper (Altmer et al. 1991) are intercalated with units composed of Permianlimestone, associated with micaceous sandstone, indistinctly beddedsandstones up to 30m thick: thinner- basalt and red mudstone (e.g. Cigdem Tepe and Kir Tepe: beddedintervals up to 15 m thickdisplay partial Bouma Fig. 5). The lower contacts of the klippen dip much more sequences. ALate Triassic age(probably Norian) is shallowly thanthe characteristicallysteeply-dipping struc- assigned tothe mudstone-rich part of thesequence tures of theunderlying Kalabak Unit andare marked by (Krushensky et al. 1980). Nearthe top of thesequence, serpentiniticslivers. Siltstones from the Gal Unit north of sandstonesand mudstones contain shallow-watertrace Edremit exhibit typical terrigenous trace-element signatures fossils, suchas Thalassinoides and Skolithos. The clastic whennormalized against theNorth American shale rockspass upinto pink,nodular, pelagic limestones composite (Pickett 1994). containing ammonites, which form the base of the overlying Lower-Upper Jurassic Bilecik Limestone. The Triassic-Jurassic cover sequence TheKarakaya Complex is overlain by relatively a Structural summary undeformed,unmetamorphosed clasticsuccession, upto Inthe Edremit and Bergamaregions of NW Turkeythe 1OOOm thick,in the Edremit-Havran region (theHalllar Karakaya Complex comprises a stack of tectonically bound Formation of Krushensky et al. 1980) (Fig. 11). Near its base units which dipapproximately E toSE (e.g. Okay et al. thesequence comprises thick conglomeratesand arkosic 1991; Pickett 1994). Deformational features within the units sandstones,rich in plantfragments and bivalveshells. includefoliations, duplexes, shears, folds and strata1 Up-sequence, thickhorizons of dark, fossiliferous mudst- disruption. The boundaries between the individual units are

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Table 1 Representative geochemical analyses of basalts from the Karakaya Complex in the Biga Peninsula

Niliifer Unit Ortaoba Unit CaI Unit

49C/90 56B/90 21/9/92-19a56B/9049C/90 22/10/91-9 18/10/91-9 LOG2/90 2218192-422218192-62218192-21

SiO, 45.78 44.82 46.1 1 46.47 47.34 47.17 46.67 44.34 45.58 A1*03 13.77 15.60 13.98 13.64 13.93 13.23 11.26 13.24 9.25 FeP, 12.95 14.50 13.76 13.48 9.93 14.2.5 10.60 13.37 11.48 MgO 7.53 7.70 7.29 6.48 6.30 6.30 7.96 6.40 6.06 CaO 9.50 4.32 7.98 9.54 11.09 9.41 11.01 6.77 12.40 Na,O 3.16 3.56 2.58 3.57 3.99 3.33 3.71 2.39 3.05 K20 0.448 0.849 2.350 0.085 0.022 0.202 0.649 3.055 0.627 TiO, 2.638 3.123 2.797 1.784 1.158 1.954 2.223 2.998 2.033 MnO 0.161 0.173 0.164 0.191 0.146 0.189 0.128 0.123 0.092 P,% 0.301 0.378 0.326 0.145 0.098 0.159 0.378 0.500 0.391 L01 4.02 4.56 2.54 4.23 6.00 4.00 5.62 6.25 8.76 Total 99.58100.26 99.88 99.62 100.00100.21 100.19 99.44 99.72 Nb 27.2 33.2 34.3 2.5 2.1 2.6 31.8 44.5 29.4 Zr 170.8 212.7 196.6 100.2 60.5 110.1 173.2 244.7 152.3 Y 24.8 33.5 29.4 42.5 20.2 28.5 46.9 31.7 21.4 Sr 456.2 258.1 221.3 273.8 230.1156.7 230.8 245.0 239.6 Rb 7.5 19.9 59.8 3.5 9.2 0.8 5.4 48.9 13.0 Th 1.3 2.8 5.1 0.7 0.9 0.0 0.7 4.7 1.6 Pb 0.9 1.6 2.0 1.1 0.2 0.0 0.3 1.1 3.3 Zn 117.8 145.2 123.3 125.9 75.1 88.4 130.5 104.1 85.0 cu 107.2 167.6 129.8 100.8 82.7107.5 103.6 62.7 95.9 Ni 141.7 128.0 92.4 76.4 76.9 59.7 86.8 54.0 344.7 Cr 386.8 334.1 151.5 139.5 108.9220.9 91.8 43.2 607.1 Ce 56.1 52.7 56.6 13.7 10.2 13.0 68.8 98.0 77.5 Nd 29.5 28.8 30.0 10.0 31.1 6.2 12.4 48.3 37.3 La 17.8 22.6 20.7 4.0 24.7 3.4 3.1 30.1 31.4 V 291.7 304.6 332.6 426.7 226.5345.3 458.1 200.3 263.3 Ba 114.2 195.4 151.0 41.3 111.429.7 28.6 153.5 70.8 sc 36.0 40.7 33.4 48.0 55.9 47.6 23.6 24.2 27.5

Analyses obtained by XRF method of Fitton & Dunlop (1985). (LOI: loss on ignition.)

mainly poorlyexposed and commonlyinclude slivers and Karakaya Complexcan be inferred as follows. The lowest imbricatedsegments of adjacentunits. The Karakaya unit, the Niliifer Unit, is interpreted as a Triassic seamount Complex has clearly undergone complex and heterogeneous sequence in which aninternal core of massive basalt is deformation.Numerous structural measurements (i.e.fold overlain by volcanic-sedimentary flank facies of debris flows vergence, foliation, shear sense) were made in the field, but andredeposited sedimentary rocks. The presence of an theintensity of shearingand the scarcity of way-up original carbonatecap to the seamount is indicated by structures make detailed structural interpretations difficult. horizons of redepositedlimestone and discrete limestone However, many individual outcrops in sandstones and shales blocksin thedebris flows. The absence of continental- of theOrtaoba and Kalabak units displayclear senses of derivedclastic rocks implies formation in an openocean, motionranging from top-to-the-north to top-to-the-west. away fromterrigenous sources. The structurally overlying TheKalabak Unit displays the mostconsistent results, OrtaobaUnit is interpretedas MORB-type oceanic crust, showing clear northward vergence of small-scale asymmetri- overlain by deep-searadiolarian sediments, now trans- calfolds, associated with NE-SW-trendinglineations, and formedinto chert. The depositionallyoverlying turbiditic SE-dipping foliations and shear zones (Fig. 12). sequence canmost readily be explainedas a subduction A pilot palaeomagneticstudy of theJurassic Bilecik zone trench-type succession. Slumping within this sequence Limestone in the Biga Peninsulasuggests post-Mid-a indicatesthat a significantslope was present, while the Jurassicanticlockwise rotation of 47" (Pickett 1994). This coarsening-upward nature of the succession is takento implies that the Karakaya Complex, which currently trends record progressive migration of the oceanic crust towards a NE-SW in the Biga Peninsula, trended approximately E-W trench.The fine-grainedphyllites of thestructurally in pre-Mid-Jurassictimes andthat tectonic transport was overlyingKalabak Unit could indicate hemipelagic deposi- approximately towards the north. tion on ocean floor, away from the supply of coarse clastic material tothe trench, although asnoted earlier this unit Genesis of the Karakaya Complex units and the may predate other Karakaya Complex units. Finally, the Cal sedimentary cover Unit is interpreted asan extensive Permiancarbonate platform which rifted to produceintra-platform basins in Onthe basis of thedata presented above, the tectonic which slope carbonates and debris flows accumulated. The setting of formation for the various units which make up the

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--t 22110191-9

01 """ 1 Sr K Rb Ba Th Nb Ce P Zr TI Y Sc Cr

Fig. 7. Ti-Zr plots (fields from Pearce 1982) and MORB-normalized multi- element variation plots (normalizing values from Pearce 1982, 1983) for basaltic rocks from the Karakaya Complex in the Biga Peninsula. (a) Nilufer Unit north of Edremit; (b) Ortaoba Unit north of Edremit; (c) Gal Unit in the Can region. Fields: MORB. mid-ocean ridge basalt; WPB, within- plate basalt; VAB. volcanic arc basalt.

basement, which is not now preserved, is assumed to have subduction/collisionsettings is extremelylow unless they beencontinental crust, as continental-derived clastic rocks become incorporated into an accretionary complex. are present at the base of the unit. The regionally overlying, Theoverall structural arrangement of theKarakaya relatively undeformedHalllar Formation (Upper Triassic- Complex is also suggestive of an accretionary origin. The LowerJurassic) is interpreted as a shallowing-up basin-fill units form a stack of tectonically-bound slices which are sequence, unconformably deposited on top of the Karakaya commonly imbricated with each other along their contacts. Complex. By theEarly Jurassic, tectonics related to the For example,tectonic slivers of the NiluferUnit deformation of the Karakaya Complex had ceased in NW seamount-type basalts are found within the oceanic Ortaoba Turkey and the establishment of stable conditions led to the Unit,and the contact between the Ortaoba and Kalabak build-up of a thick carbonate platform, the extensive Bilecik Units is a sheared zone containing elements of both. With Limestone (Lower-Upper Jurassic). theexception of theUpper Permian Gal Unitcarbonate platform at the top of the thrust stack, the contacts between the units andalso their internal structures are relatively The Karakaya Complex as a subduction-accretion steep, a characteristicfeature of manyaccretionary complex complexes. In addition,the assemblage of small-scale The Karakaya Complex is comparable withwell-preserved structures (e.g. layer-parallelextension, duplexes) is accretionarycomplexes from around the world. The characteristic of modernand ancient accretionary prisms lithologicalassemblages of the individual Karakaya units worldwide. and their structural juxtaposition suggest an origin involving Many sedimentary features of the Karakaya Complex, as subduction-accretion processes. The lithologies which make describedbelow, are alsoconsistent with anaccretionary up the various tectonostratigraphic units record sedimenta- origin.Soft-sediment deformation and sedimentary blocks tion in a variety of marinesettings, including seamount, within the Ortaoba Unit imply an unstable slope, as do the trench, abyssal plain and rifted platform. The preservation coarse polymict debris flows tectonically intercalated within potential of lithologies formed in thesesettings, within the NiluferUnit nearEdremit. The coarsening-upward

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Th sc

Fig. 9. Geological map of the area SE of on. Modified after Okay et al. (1991).

slump unit. The Mino terrane is interpreted as remnants of Permian-Jurassic oceanic crust, including aseismic ridges of plume origin,dismembered seamounts, ocean-floorsedi- ments, trench turbidites and trench-slope debris flows (Sano et al. 1992: Jones et al. 1993).Processes of seamount dismembermentare illustrated by the Daiichi-Kashima seamount, an excellent modern analogue for the Karakaya seamount(s). A model for the subduction and accretion of seamounts,based on the Daiichi-Kashima seamount, is

Z'itOO shown in Fig. 13 (Taira et al. 1989). Having arrived at the Fig. 8. Tectonic discrimination diagrams for siltstone intercalations Japan Trench, the seamount is currentlybreaking up into in the Ortaoba Unit north of Edremit. (a) La-Th-Sc plot; (b) large blocks by processes of normal faulting and subsidence Th-Sc-Zr/lOO plot (fields from Bhatia & Crook 1986). into the trench (Fig. 13a). Its inferred fate as dismembered units within melange is shown in Figure 13c. Drilling by the Kaiko Project (Cadet et al. 1987) has also revealed extensive nature of siliciclastic turbiditesin the Ortaoba Unit is limestonetalus associated with these blocks, similar to consistent with an oceanic plate moving progressively closer limestone debris flows in the Karakaya Complex. to a trench. A debris flow in the Gal Unit near Can displays addition,In theKarakaya Complex showsmany twophases of conglomerateformation, possibly recording similarities with other mClange-type terranes in the Tethyan intra-platform rifting followed by subsequent disruption at a orogenicbelt (Robertson 1994). Specific examplesinclude subduction zone. Clastic sequences, interpreted as restricted, the Jurassic Avdella MClange of northern Greece (Jones & basindeposits which formed on an accretionarycomplex, Robertson 1991) and the Early Tertiary Ermioni Complex havealsobeen described elsewhere. Forexample, undeformed sandstones and mudstones in the Eastern Unit NE SW of theCoastal Belt of the FranciscanComplex, California

(Bachman 1982) may be analogous to the clastic succession pinklwhite limestone clasts in purple mudstone near Havran. .. Subduction-accretionsettings similar tothe Karakaya Complex are well documented, especially in circum-Pacific regions (e.g. Nankai Trough; Karig 1986) and on land (e.g. FranciscanComplex; Cloos 1984). Investigation of com- plexessuch asthose in Californiaand SW Japan, allows directcomparison with the Karakaya Complex. For , example, the Mino terrane, a Jurassic accretionary complex in SW Japan, is composed of units similar to those of the basaltblocks in greenvoicaniclastic matrix 0 m 2 KarakayaComplex in NWTurkey. These include a greenstone-carbonate-chert unit, a siliceouspelagite-distal Fig. 10. Field sketch of debris flows within the Cal Unit 0.5 km turbidite unit, a proximal turbidite unit and an olistostrome- south of Calkoy (see Fig. 9).

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m Poles to shear planes Lineations BilecikLimestone N N 1000

I ,. .*... ._..I

;l:Fold axes (+) and polesto axial planes (0) Poles to foliation N

600 Middle unit fi 8------Lower unit

\ + l 400

dp shallow-waterbivalves

U B plantfragments Fig. 12. Stereoplots of structural data from the Kalabak Unit NW CP tracefossils of Pagadag in the Edremit area (see Fig. 5), showing consistently m limestone SE-dipping shear planes, foliations and fold axial planes, and 200 NE-SW-trending lineations. [II calcareous sandslone

mudstonelsiltstone difficult to distinguish from a true oceanic setting, but even 0sandstone 0conglomerate

0 clay,f ,m,c,&,cg Fig. 11. Generalized stratigraphic column through the Hahlar Formation 9 km NE of Havran.

of SEGreece (Clift & Robertson 1989). Each of these includes basic volcanic components, interpreted as oceanic crust,including seamounts, withinhemipelagica and terrigenous matrix.

Palaeotethyan open ocean or back-arc basin? The question of whether the Karakaya Complex represents a fully oceanic basin (i.e. the Palaeotethys Ocean itself), or a smallerback-arc basin (i.e. marginal to Palaeotethys) is crucial tointerpretation of Palaeotethyan unitsin NW Turkey. Distinguishing betweenthese alternative tectonic settings is noteasy, especially as the rocks are highly dismembered withinanaccretionary complex. If the KarakayaComplex formed in anopen ocean setting, we would expect MORB/WPB-type igneous rocks, overlain by pelagic sedimentaryrocks (e.g. chert),without abundant continental-derived or volcanic sequences. If the Karakaya Complex represents a rifted back-arc setting, then extrusive rockswould be expectedto showasubduction-related .,,-;; ,.m: . ,c,\ - 1-l rc influence and could be associatedwith large volumes of arc-derivedvolcaniclastic sedimentary rocks and airfallash Fig. 13. Model for the arrival of a seamount at a trench and its as in the SW Pacific Lau Basin (Clift er al. 1995). Formation incorporation into an accretionary prism. Redrawn from Taira et al. in awider, moremature, back-arc basinwould be more (1989).

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in this case large volumes of airfall ash would be expected. TheKarakaya Complex displays MORB-type basalts, overlain by up to 10 m of chert (Ortaoba Unit), and thick seamount-typesequences of WPB-type (Niliifer Unit), featuresthat are consistent with anopen-ocean setting. Also, theKarakaya Complex lacks anyevidence of large volumes of arc-derived volcanogenic rocks, including airfall tuffs. Theavailable evidence favours an origin forthe Karakaya Complex in a relatively wide ocean basin, rather than as part of a small marginal basin developed above a subduction zone.

Associated units in NW Turkey Any regionaltectonic interpretation of NWTurkey must also takeaccount of severalother units exposed in the region.

The Denizgoren and Lesbos Ophiolites The Denizgoren Ophiolite has an outcrop 2-3 km wide and 25-30 km long. It trends SSW-NNE and is almost entirely composed of serpentinized harzburgite (Figs 1 & 2). On its westernmargin, the ultrabasic thrust sheet tectonically overliesa Permian carbonate platform sequence (Karadag Fig. 15. Northwest-verging microfolds within sheared marbles Unit; Okay et al. 1991). Amphibolite forms a well-preserved beneath the Denizgoren Ophiolite metamorphic sole. metamorphic sole unitat the base of theslab (Fig.14). Geochemical analysis of the amphibolites reveals fractiona- tion trends suggesting that they were derived from gabbroic, ratherthan basaltic,precursors (Pickett 1994). The sole are similar to thosefrom supra-subduction-type ophiolites grades abruptly downwards into sheared meta-sedimentary around the Eastern Mediterranean (e.g. Troodos ophiolite, and meta-volcanic rocks which lie at the top of the Karadag Cyprus: Oman ophiolite: Pearce et al. 1984). The Unitand displaylocal top-to-the-north and northwest amphiboliteswhich form the metamorphic sole of both displacements (Fig.15). Tothe east, the Denizgoren ophioliteshad at least partly gabbroic precursors and are Ophiolitehas a steep, possiblystrike-slip, contact with a interpretedas fragments of oceaniccrust which were poorly exposed, monotonous sequence of mica-schists (the accreted tothe base of theophiolite prior to its final Camllca Micaschists; Okay et al. 1991). emplacement. Associated sedimentaryand extrusiverocks A similarultrabasic body and associated amphibolite within the underlying mClange are alsointerpreted as sole unit are exposed on the Greek island of Lesbos (Figs 1 material accreted to the base of the overriding ophiolite. & 2), alongstrike from the Denizgoren Ophiolite. The LesbosOphiolite and its metamorphic sole tectonically overlievolcanic-sedimentarya mdange whichcontains The Kazdag’ Massif crystalline carbonate intercalations of Lower-Middle Trias- sic age (Katsikatsos et al. 1982). The geographical position, The Kazdag Massif comprises metamorphic rocksfolded constituent lithologies and geochemistry of the Denizgoren into a broad antiform approximately 50 km long and 20 km and Lesbos ophiolites all suggest that they originally formed across (Figs 2 & 16). On its eastern side the Kazdag Massif part of the same ophiolitic body. Geochemical analyses of is tectonically juxtaposed againstvolcanic-sedimentary peridotitesfrom the Denizgoren Ophiolite (Pickett 1994) rocks of the Karakaya Complex. To the west it has a faulted

L I Fig. 14. Schematic cross-section through the Denizgoren Ophiolite Fig. 16. Schematic cross-section through the Kazdag Massif. 9 km NNE of Ezine. Modified after Dora (1971).

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contact with Upper Cretaceous Neotethyan melange (Cetmi accretionarycomplex shows clear southward vergence Ophiolitic MClange) and is intruded by anOligo-Miocene (Ustaomer & Robertson 1993). TheCentral Pontide area granodiorite. The base of the Kazdag Massif is not exposed formed close tothe Eurasian margin. By contrast,the and a totalstructural thickness of over 10 kmhas been KarakayaComplex lies furthersouthwest and reflects estimated (Bingo1 1969: Okay et al. 1991). tectonic events within the Palaeotethys Ocean, or towards The Kazdag Massif is interpreted as a metamorphic core itssouthern margins, i.e. close toGondwana. Thus, both complexthat was exhumedalong normal faults, detach- northwardand southward subduction of Palaeotethys are ments and extensional mylonite zones during the Miocene not precluded. (Okay et al. 1991: Pickett 1994). It provides a window into deeper structural levels and has modified the structure of the Karakaya Complex in its vicinity. Northward subduction of Palaeotethys The mostcommon lithologies arebanded quartzo- feldspathic gneiss intercalated with marble and amphibolite. Northward subduction of the Palaeotethys Ocean fits with Thebanded amphibolites andmarbles resemble a the broad picture of an active Eurasian margin and a passive metamorphosed form of interbedded spilites, volcaniclastic Gondwananmargin, extending from the Eastern Mediter- rocks and limestone debrisflows, similar to those seen in the ranean to the Himalayas and beyond (Dercourt et al. 1993). NiluferUnit. Radiometricdating of theKazdag gneisses Northwardsubduction of thePalaeotethys would also (Bingo1 1971)suggests a pre-LateTriassic agefor the explain the presence of Upper Permian Gondwana-derived protoliths of these rocks. The core of theKazdag Massif carbonateplatforms with clastic sedimentarybasements includesmeta-gabbro, meta-harzburgite, plagiogranite and found withinPalaeotethyan accretionary units in NW amphibolite, which havebeen interpreted as a meta- Turkey (e.g. KaradagUnit, Cal Unit). The Upper ophiolite of unknown age by Okay et al. (1991). Carboniferous-PermianKargl Complex inthe Central Pontides, which contains fusulinids of Gondwanan affinity, is alsothought torepresent a Gondwananfragment which Regional tectonic reconstructions driftednorthwards across Palaeotethys (Ustaomer 1993). Similar Gondwana-derivedcarbonate platforms withcon- The two main alternatives can be considered. tinental clastic basements are found as fragments within the Mesozoic Tethys (i.e.. Neotethys) (e.g. Robertson et al. 1991). However, a major problem with this latter model is that Southward subduction of Palaeotethys northwardsubduction cannot explain theubiquitous Northward-vergent structures within the Karakaya Complex northwardvergence of theKarakaya Complex and are ubiquitous in NWTurkey and strongly support a associatedunits, including theDenizgoren and Lesbos predominantlysouthward-directed subduction process dur- ophiolites. ing formation of thecomplex. The Denizgoren Ophiolite similarlyshows evidence of northwardemplacement. Exhumation of theKazdag Massif could locally have Discussion changed the dip of the Karakaya Complex, but not on the It seems likely thatelements of bothnorthward and scale of the entire Biga Peninsula and adjacent areas. southwardsubduction were involved in closure of the Inmodern subduction-accretion complexes significant PalaeotethysOcean NWin Turkey during the Late backthrusting (i.e. away fromthe trench) can take place Palaeozoic-EarlyMesozoic (Fig. 17). We proposethe (e.g. Barbados; Brown & Westbrook 1987). This would only following evolutionary interpretations for this area. tendpredominateto close thetobackstop of the The clear northward vergence of the Karakaya Complex accretionarywedge, far from the trench area. Similar requiresthat southward subduction wasprobably the backthrusting could explain local southward vergence in the predominantmechanism of its formation.However, this Karakaya Complex units, but is unlikely to have caused the doesnot preclude regionalnorthward subduction beneath overall northwardvergence, including that of themajor an active Eurasian margin further south. Northward drift of obducted Denizgoren and Lesbos ophiolitic thrust sheets. In carbonate-cappedcontinental slivers from the Gondwanan addition, the northward thrusting is not likely to have been margin andnorthward subduction at the Eurasian margin caused by a related collisionalprocesses. The Karakaya couldhave been followed by later,southward subduction Complextectonostratigraphy is not regionallyfolded, and and the formation of the Karakaya Complex, as closure of platform limestones to the south (e.g. Chios and Karaburun Palaeotethysproceeded. Oceanic crust, trench sequences, Peninsula)exhibit the Carboniferous toEarly Tertiary seamounts, abyssalsediments and intra-oceanic platforms without major hiatus or deformation (Chios: Erdogan 1990). were thereby accreted and incorporated into the Karakaya Emplacementhad ended by the latestTriassic when the Complex. A shallow-marine basin developed on top of the cover sediments (Hahlar Formation) began to accumulate. accretionary complex, depositing the Halllar Formation. A However,southward subduction cannot be easily cessation of northward-dipping subduction and the initiation reconciledwith the widely accepted view of an active of southward-dippingunderthrusting could have been Eurasianmargin and a passive Gondwanan marginduring caused by ‘jamming’ of the original trench by a large oceanic Late Palaeozoic-EarlyMesozoic time (e.g. Dercourt et al. plateau,seamounts (e.g. Nilufer-typeunits), or carbonate 1986, 1993: Robertson et al. 1996). In particular, a platforms (e.g. Cal/Karadag-type units]. Suchunits would southward-subductionreconstruction does not fit with occur to the north of the current position of the Karakaya evidence from the Central Pontides, approximately 600 km Complex in Turkey. An analogoussituation may have northeast of the field area,where a comparable, thick occurred in the SW Pacific during the Mid or Late Miocene,

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whenthe Ontong Java Plateau collidedwith theWest andthe subducting carbonate platforms to the north (i.e. Melanesian Trench (during SW subduction) in Mid- or Late KaradagUnit) (Model 1 in Fig. 17). Thisposition is Miocene, effectively blocking furthersubduction at this consistent with the absence of ophiolitic rocks overlying the trenchsystem (Weissel et al. 1982). As a result,plate Karakaya Complex and the absence of ophiolitic detritus in boundariesreadjusted and northeastward subduction was the unconformably overlying Upper Triassic-Lower Jurassic initiated along the SW margin of the New Ireland-Solomon Halllar Formation. In this reconstruction, one possibility is Islandarchipelago. A similar,although notidentical that a substantialcrustal unit (e.g. large volcanic edifice) situation is present south of Cyprus where the Eratosthenes collided with the trench, followed by its accretion and the Seamount is wedgedbetween the converging African and re-establishment of thesubduction zone in a more Eurasian plates.In this case, northward subduction of the oceanward position. Forexample, Tomoda & Fujimoto seamount was apparentlyaccompanied by southward (1983)suggested that large seamounts or rises which are underthrustingbeneath the Levantine Basin, owing to difficult to subductmay cause a newsubduction zone to collision-relatedcompression (Robertson et al. 1995).This form seaward of the original trench, as documented in the example shows how underthrusting can simultaneously take EarlyCretaceous Kamuikotan tectonicbelt of Hokkaido, place in opposing directions if oceanic/continental fragments Japan(Watanabe & Maekawa 1985). The collision of the impinge on a subduction zone. Niliifer ‘seamount(s)’could have caused this type of The presence of abundantterrigenous material within subduction ‘step-back’. The Karakaya Complex would then the Karakaya Complex implies that the inferred southward have become isolated from the trench and ceased to be an subduction occurred close to Gondwana-related units. The active accretionary complex. Subsidence of the accretionary regionalabsence of volcanic-arcsequences andrelated complex then led to deeper-water sediments being laid down sedimentary rocks implies that a major oceanic arc did not in a perched fore-arc basin. Arrival of a further Gondwanan develop.However, recent studies of the central Menderes platform (the clastic-carbonate Karadag Unit) at the trench Massif (interpretedas a largecontinental fragment rifted then initiatedemplacement of theophiolite over the from Gondwana), to the south of thestudy area (Fig. l), platform.Thrusting caused theincorporation of oceanic indicate the presence of large bodies of leucogranite which sediments, volcanics and gabbros into the metamorphic sole areinterpreted beingas intrusive into metamorphic beneaththe ophiolite. Northward emplacement of the basement lithologies of inferredLate Palaeozoic-Early ophiolite over the platform was accompanied by northward Mesozoic age (e.g. Durr et al. 1995; Dora et al. 1995). One thrusting of theKarakaya Complex as a whole.Tectonic possibility is thatthese granites developed in response to activity ceased by the Early-Mid-Jurassic when the Bilecik southward subduction of Palaeotethyan oceanic crust. Limestone shelf was laid down over much of NW Turkey. An important remaining question is how the Denizgoren Ophioliteformation in this setting would require a andLesbos ophiolites relate to closure of Palaeotethys in substantialelement of slab ‘roll-back’ to allow astheno- the north Aegean region. Two possibilities for their tectonic sphere uprise in the fore-arc region. However, recent studies setting of genesis and later emplacement can be considered, (e.g. Tongafore-arc) suggest that collision (or oblique given thatgeochemical evidence indicates a probable collision) of substantial edifices is more likely tolead to supra-subduction zone origin. In the first case, the ophiolites arc-rifting and back-arc initiation (Isacks & Barazangi 1977, are not substantially allochthonous and originated between Watts et al. 1988), rather than genesis of new ophiolites in theKarakaya Complex accretionary complex to the south thefore-arc region. Inthe Tonga area it appearsthat

S b-3 Late Permian EURASIA if: GONDWANA

Cangalda6 arc or equivalent /I carbonatedatforms on .\ / ondwanan c’ontinentalslivers ‘

MODEL 1 site of new subductlon zone MODEL 2

Karakaya Complex Karakaya Complex Early Triassic ophlolite formataon OphlolMe formaldon

(I.e. Chios. Karaburun) carbonate platform ophiolite emplaced directly on10 id ~~i~~~i~ophlolltethrust over bulld-up \ Karadag Carbonate platlorm Karakaya Complex A@qgz --l

Fig. 17. Alternative models for the tectonic evolution of the Palaeotethys Ocean in NW Turkey from the Late Palaeozoic to the Late Triassic. Model 2 is our preferred option. core complex.(l.e. Kardaii Massof)

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oblique subduction of the Louisville Ridge seamount chain Conclusions against theTonga Trench is responsible for initiating (1) The Karakaya Complex in NW Turkey is a Palaeoteth- seafloor spreading in the back-arc (Clift et al. 1995; Parson et yan accretionary complex. Tectonostratigraphic units within al. 1990). the complexinclude Triassic seamount(s) (NiliiferUnit), Asecond possibilityis thatthe Denizgoren-Lesbos trenchsequences (Ortaoba Unit), abyssalplain deposits ophiolite formed during the initial stages of fore-arc genesis, (KalabakUnit) and Permian carbonate platforms with prior to formation of the Karakaya Complex as a substantial intra-platform rifts (Gal Unit). The dismembered seamounts subduction-accretion complex (Model 2 in Fig. 17). In this andintra-platform rift lavas exhibit WPB geochemical regardit would be similar in origin tothe Eocene crust signatures, whereas basalts flooring the trench sequence are forming the Mariana fore-arc and many large ophiolites in predominantly of MORB-type. thestratigraphic record, including the Oman ophiolite (2) Thetectonostratigraphic units of the Karakaya (Lippard et al. 1986), Pindos ophiolite (Jones et al. 1991) and Complex are tectonically juxtaposed to form a SE-dipping, anumber of theIapetus ophiolites (Pearce et al. 1984). NW-verging stack. Northwestward vergence is also a feature Similarly,in theCentral Pontides thePalaeotethyan of the Denizgoren and Lesbos ophiolites. Elekdagophiolite occurs structurally above a substantial (3) The clasticHalllar Formation accumulated in small accretionarycomplex interpreted asa phase of fore-arc basins in the Late Triassic-Early Jurassic after accretion of spreadingalong the south Eurasian margin, followed by the Karakaya Complex. northward-directedsubduction-accretion of Palaeotethyan (4)Ultrabasic rocks forming large thrust sheets in the material (Ustaomer 1993). Biga Peninsula (DenizgorenOphiolite) and on the Greek However,for this setting to apply in NWTurkey, the island of Lesbos(Lesbos Ophiolite) formed by supra- ophioliteswould require to besubstantially allochthonous subduction zone spreading, based on geochemical evidence. and have been thrust over the Karakaya Complex by around Theseophiolites weredisplaced relatively northwards, 100-150 km and then been eroded over a large area without accompanied by metamorphic sole formation and develop- traceprior to the Late Triassic.Studies of other Tethyan ment of melange, interpretedas oceanic and sedimentary areas (e.g. thePelagonian Zone of theHellenides) do material accreted to the base of the ophiolites prior to their indeed show thatfar-travelled ophiolites can bealmost final emplacement. completely eroded, leavingonly remnantsfar from the (5) Twoalternative settings for supra-subduction zone originalroot zones (e.g. Beotiaarea of centralsouthern genesis and emplacement were considered. In the first, the Greece:Robertson et al. 1991). A 20-40 Matime gap ophiolitesformed north of theKarakaya Complex,their separatesthe youngest Karakaya lithologies(e.g. Mid- presentposition. However, comparisons with tectonic Triassic conodonts in the Niliifer Unit; Kaya & Mostler settings of comparable ophiolites suggest the ophiolites may 1992)from theLate Triassictransgressive Halllar Forma- have beenformed during the initiation of southward tion. We have noted the local strong reddening in the lower subductionand only reachedtheir finallocation after Halllardeposits and the uppermost Karakaya unit (Gal 100-150 km northwardthrusting over subsequentlya Unit), suggesting that a substantial subaerial erosional hiatus formed Karakaya accretionary complex. may be present. (6) The genesis of the Karakaya Complex and related units In summary, while field evidence remains ambiguous the probablyrelates bothto north- andsouth-directed southerly,more allochthonous, origin forthe ophiolites subduction. Northward subduction beneath Eurasia shaped seemsmore consistentwith our understanding of modern thelarge-scale plate tectonic framework of theEastern andancient ophiolite analogues and at present this is our Mediterranean region. Theinferred continental fragments preferredoption. Thefurther possibility of large-scale within theKarakaya Complexrifted fromthe north strike-slip displacement of units cannot be ruled out but is Gondwanan margin anddrifted northwards towards not at present supported by our field evidence. Eurasia.However, the regional northward vergence that The Palaeotethys Ocean is viewed here as an essentially characterises the pre-Jurassic of NW Turkey is interpreted Palaeozoicocean which only finally closed by northward to reflecta subsequentsouthward subduction episode. A subduction along the Izmir-Ankara-Erzincan Suture Zone switch in subduction from north to south could have resulted in Late Mesozoic-Early Tertiary times (Robertson & Dixon from collision of seamounts/continental fragments with the 1984). Duringthe Triassic thenorthern margin of trench along the south Eurasian margin. Gondwana rifted toform several small ocean basins, representing ‘Neotethys’, separated by carbonate platforms (e.g. Tauride-Anatolideplatform) (e.g.Sengor & Yllmaz E.A.P.acknowledges support from NERC duringresearcha 1981: Robertson et al. 1991). These basinswere destroyed studentship at the University of Edinburgh. We would like to thank only in Late Mesozoic-EarlyTertiary times, coeval with A. I. Okay for help and logistical support in Turkey, J. E. Dixon, 1. final closure of the last remnants of the Palaeotethyan ocean Sharp and T. Ustaomer for useful discussions, and E. S. Platzman basin.Forceful suturing of Palaeotethysinthe Early for making the palaeomagnetic study possible. We thank P. D. Clift, Mesozoic,asinferred by Sengor & Yllmaz(1981), is G. Jones. P. Stoneand J. D. Floyd forconstructive reviews and suggestions. CorrespondencePickettA. (e-mailE. to unlikely,as relatively little deformation is recorded in the [email protected]). neighbouring Triassic carbonateplatforms (i.e. Chiosand Karaburun Peninsula), which show affinities with the rifted Tauride-Anatolideplatforms to the south. The area of References northward emplacement of the Denizgoren-Lesbos ophiol- ADAMIA,SH. A., CHKHOTIJA.T., KEKELIA, M., LORDKIPANIDZE,M,, itesand the Karakaya Complexduring the Triassicthus SHAvIsHILI, 1. & ZAKARIADZE,G. 1981. Tectonics of theCaucasus and occurred north of the final suture zone, while Palaeotethys adjoiningregions: implications for the evolution of theTethys ocean. remained at least partly open to the south. Journul of Srructurul Geology. 3,437-447.

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Received 22 January 1996; revised typescript accepted 4 June 1996. Scientific Editing by Alex Maltman.

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