Central Pontides Research Articles

Geochemical evidence used to test alternative plate tectonic models for pre-Upper Jurassic (Palaeotethyan) units in the Central Pontides, N Turkey

East–west trending, inferred Palaeotethyan subduction–accretion complexes form much of the pre-Upper Jurassic basement of the Central Pontides. A number of specific tectonic units are present that include variably metamorphosed basic igneous rocks, as dismembered ophiolites, coherent stratigraphical successions, ordered thrust sheets, and blocks in melange. About 200 samples from a c. 200 km long N–S traverse were analysed by a high-precision X-ray fluorescence technique, supplemented by electron microprobe analysis. The basic igneous rocks have not experienced significant chemical mobility after formation and are thus useful for discrimination of tectonic settings of formation using well known binary and ternary plots and mid-ocean ridge basalt (MORB)-normalized ‘spidergrams’. From N to S the main results are that basalts of the Kure Complex were erupted in a subduction-influenced tectonic setting, favouring interpretation as a dismembered ophiolite formed in a marginal basin along the S Eurasian margin. Thick, mainly volcanic, successions of the Cangaldag Complex show a subduction-influenced calc-alkaline composition, above a basement varying from MORB/island arc tholeiite type to high-Mg (boninitic) type, with an inferred origin as an oceanic arc above forearc basement. Meta-basites from the adjacent Bayam Melange indicate a supra-subduction zone origin, possibly as a dismembered forearc ophiolite (possibly related to the Cangaldag). A large overriding thrust sheet of mainly ultramafic rocks, the Elekdag, is interpreted as a supra-subduction zone ophiolite, based on depleted chrome spinel composition (analysed by microprobe). Eclogitic blocks in structurally underlying melange are of mid-ocean ridge (MOR) type. Further south, a northward-dipping, inferred subduction–accretion complex, the Domuzdag–Saraycikdag Complex, includes MOR-type meta-basites in the north, and more ‘enriched’ compositions in the south, of within-plate origin. Lastly, the geochemistry of meta-basites in the south, within the Kargi Complex, suggests a plume-MOR to within-plate type eruptive setting, without continental crustal influence. The geochemical data mainly support a northward rather than southward subduction model for the Palaeotethyan assembly of the Central Pontides, particularly since the Kure ophiolitic basalts in the north exhibit a subduction-influenced chemical signature, in contrast to all the units in the south which lack any identifiable subduction component. Comparisons with published geochemical data from the Karakaya Complex in the SW Pontides reveal similar units, interpreted as accreted MORB lithosphere and oceanic seamounts, but emphasize that the Cangaldag arc is presently the only known Palaeotethyan subduction arc-related unit in Turkey. Copyright © 1999 John Wiley & Sons, Ltd.

Geology of the Cretaceous sedimentary basins of the Western Pontides

The southern passive margin of the oceanic Western Black Sea Basin consists of two tectonic units, the Istanbul Zone and the Central Pontides. These units are delimited by a fundamental, north–south Arac–Daday shear zone juxtaposing totally different basement rock groups and covering later Mesozoic sedimentary rocks. To the west of this shear zone the Istanbul Zone is covered by a sedimentary succession deposited in a southerly deepening continental margin basin. This basin was bisected lengthwise during the Maastrichtian forming the Zonguldak Basin in the northwest and the Ulus Basin in the southwest. Both of these basins were deformed in the Early Cainozoic. To the east of the Arac–Daday shear zone, the northerly deepening Sinop Basin dominates the architecture of the Pontides in the north. It began forming by extension in the Barremian and was destroyed by a single-phase north–south compression in the Late Eocene–Oligocene. After the juxtaposition of the Central Pontides and the Istanbul Zone, an E–W trending extensional magmatic arc was established on these sedimentary basins in response to northward-subducting Neotethys to the south. This magmatic arc, which began during the Turonian, gave rise to the Western Black Sea oceanic back-arc basin. None of the basins in the Pontides is simple. They show a complex evolution responding to different rifting and closure events with much, as yet unspecified, strike-slip movement. Copyright © 1999 John Wiley & Sons, Ltd.

MIDDLE JURASSIC-LOWER CRETACEOUS BIOSTRATIGRAPHY IN THE CENTRAL PONTIDES (TURKEY): REMARKS ON PALEOGEOGRAPHY AND TECTONIC EVOLUTION

The deposition of Jurassic-Lower Cretaceous carbonates in the Pontides was controlled mainly by the evolution of an Atlantic-type continental margin in the Tethys. The study of several stratigraphic sections from allochthonous slices and blocks of the North Anatolian Ophiolitic Melange provided insight into the Middle Jurassic-Early Cretaceous paleogeographic evolution of the Central Pontide Belt. The Callovian-Aptian successions span the Globuligerina gr. oxfordiana, Clypeina jurassica (equivalent of the Tubiphytes morronensis zone), Protopeneroplis ultragranulata (with the Haplophragmoides joukowskyi subzone), Montsalevia salevensis , Hedbergella delrioensis - Hedbergella planispira - Leupoldina - Globigerinelloides and Globigerinelloides algerianus biozones. Two major stratigraphic gaps corresponding to the pre-Callovian and Hauterivian-Early Aptian ages are recognised within the successions. Lithostratigraphic and biostratigraphic studies indicate strong similarities in the evolution of the successions in the Amasya region (Central Pontides) and Biga-Bursa-Bilecik (BBB ) Platform (North-western Anatolia).

The Kazova basin: an active negative flower structure on the Almus Fault Zone, a splay fault system of the North Anatolian Fault Zone, Turkey

The Kazova basin is located within the Almus Fault Zone (AFZ), a splay fault system of the North Anatolian Fault Zone, in the central Pontides, Turkey. It is a 0.7–10-km-wide, 60-km-long, wedge-shaped right-lateral strike-slip depression bounded by the Mercimekdaǧi-Çamdere fault set in the north and the Tokat fault set in the south. The Kazova basin is superimposed on pre-Pliocene basement rocks while its basin fill comprises the Pliocene to lower Quaternary Kizkayasi and Çerçi formations, and Quaternary alluvials. The Mercimekdaǧi-Çamdere and Tokat fault sets of the AFZ, the basin-margin faults of the Kazova basin have a considerable amount of normal separation, and show a divergent character. Here, the Kazova basin is interpreted as an active negative flower structure, where the combination of normal movement (extension) along the different segments of the AFZ, and the oblique extension between its branching splays resulted from a natural response to the anticlockwise rotation along the AFZ are suggested basin-forming mechanism. This kind of basin is first from Turkey although different types of strike-slip basins, such as fault-wedge, pull-aparts, composite pull-aparts, are widely represented and well-known.

Late Palaeozoic marginal basin and subduction-accretion: the Palaeotethyan Küre Complex, Central Pontides, northern Turkey

The Küre Complex, located in the Central Pontides of northern Turkey, is a c . 20 km thick pile of thrust-imbricated deep-sea sediments, intercalated with a dismembered ophiolite. The ophiolitic rocks include serpentinized harzburgite, massive gabbro (cumulate and isotropic), sheeted dykes and basic volcanic rocks. The extrusive rocks are mainly pillow lavas, sheet flows and lava breccias. Geochemical evidence of immobile major- and trace-elements and pyroxene chemistry indicate mid-ocean ridge (MOR) and volcanic arc basalt (VAB) compositions, and suggest that the Küre Ophiolite was generated above a subduction zone. Chrome spine1 analysis also supports this interpretation. In some thrust sheets the extrusives are depositionally overlain by hemi-pelagic shales, passing up into terrigenous turbidites and shales, which are up to several hundred metres thick in intact successions. Cyprus-type massive sulphides, interpreted as precipitates from black smokers, are located along the lava-sediment contact. Individual, intact sediment units, up to several kilometres thick within the Küre Complex are separated by narrow (up to 10 m wide) zones of intense shearing, layer-parallel extension and melange formation. Asymmetrical folds, reverse faults, thrusts and duplex structures throughout the Küre Complex indicate mainly northwards emplacement. The Küre Complex is thought to have opened in the late Palaeozoic, as a marginal basin above a northward-dipping Palaeotethyan subduction zone, located along the southern margin of Eurasia. The Küre marginal basin later closed, in response to inferred southward subduction, leading to development of an accretionary prism, prior to late Jurassic time. The Küre Complex is unlikely to represent the main Palaeotethyan suture, as has been suggested in some earlier tectonic reconstructions. Regional comparisons with Dobrogea, Crimea and Caucasus suggest the Küre basin opened, then closed, along a south Eurasia active margin.

A Late Palaeozoic‐Early Mesozoic marginal basin along the actives sourthern continental margin of Eurasia: Evidence from the central Pontides (Turkey) and adjacent regions

AbstractRemnants of two ‘Palaeotethyan’ oceanic basins are exposed in the Central Pontides of northern Turkey, separated by a continental sliver and an oceanic arc. The southern basin corresponds to the main Tethys (‘Palaeotethys’), which partially closed in Early Mesozoic time following northward subduction under the southern, active continental margin of Eurasia.The northern basin (Küre Complex) opened above the ‘Palaeotethyan’ subduction zone as a marginal basin, following rifting of a continental fragment (Istanbul fragment) from Eurasia. Marginal basin opening apparently dates from the Late Palaeozoic in the east (Küre basin) and from the Triassic in the west (Kocaeli basin). Basin closure was achieved by southward subduction‐accretion, in pre‐Late Jurassic times, leaving ‘Neotethys’ open to the south.Counterparts of the Küre Complex are found in the adjacent Crimea (Taurian Series), Istranca (Zabernevo Complex), Dobrogea (Nalbant flysch) and Caucasus (pre‐Late Jurassic Southern Slope Basin) regions. Basin opening was accompanied by oceanic crust genesis, at least in the Pontides and Caucasus. Closure before Mid‐Jurassic time was achieved by subduction‐accretion processes, whereby oceanic crust and deep‐sea sediments (including sulphides) were detached and structurally assembled, while oceanic basement was subducted. Marginal basin opening and closure is seen as one in a series of events along a long‐lived, active south Eurasian continental margin.

Geological history of the northward arched segment of the North Anatolian Transform Fault Zone

AbstractThe study area is located in the southern part of the Central Pontides. The rocks exposed in this region have been divided into three major groups: basement, cover sequence and volcanic rocks. The basement rocks are composed of metamorphic units and a chaotic assemblage derived from an accretionary prism produced during the northward subduction of northern Neo‐Tethys during the Late Cretaceous. During the same period, the basal element of the cover sequence, a thick and coarsening upward flysch succession (Cankurtaran Formation) was deposited in a tectonically active forearc regime. Towards the end of the Early Palaeocene, the entire study area emerged and became the site of erosion. During the Late Palaeocene to Early Eocene, the northern and southern parts of the study area were invaded by a new transgressing sea. This period was followed by uplift, volcanic activity and the formation of regressive sequences, events resulting from continental collision between the Anatolian and Pontide blocks during Late Eocene to Early Miocene times.Continuing convergence between the Anatolian and Pontide blocks resulted in conversion of the compressional‐contractional regime into a compressional‐extensional regime and the inception of the North Anatolian strike‐slip system during the Late Miocene‐Early Pliocene period.

New results and a palaeomagnetic overview of the Pontides in northern Turkey

SUMMARY Palaeomagnetic results are reported from 16 sites within volcanic and volcano-sedimentary rocks of Cretaceous and Eocene age from the central Pontides in northern Turkey. The sampled area is bounded by the North Anatolian Fault (NAF) to the south and the Black Sea to the north. The palaeomagnetic data collected demonstrate the presence of both non-rotated and anticlockwise rotated regions; (i) declination directions including Lower–Upper Cretaceous and Eocene sites do not indicate any significant rotations north of where the NAF exhibits an arcuate shape, (ii) 20° anticlockwise rotation was observed in the Sinop peninsula, the northernmost extremity of the central Pontides, (iii) in the west of the central Pontides, two sites with normal and reversed antipodal directions indicate a 20° anticlockwise rotation and (iv) another region lies to the east of the study area and shows a rotation in an anticlockwise sense of about 5°–30°. The Upper Cretaceous and Eocene directions reported in this paper and other palaeomagnetic studies show that there is not much difference between the inclination values of the Upper Cretaceous (I= 40.1°, α95= 7.2°) and the Eocene sites (I= 39.6°, α95= 8.1°). Furthermore, the values of the inclination available from both sedimentary and volcanic Upper Jurassic–Lower Cretaceous formations are shallower than the Upper Cretaceous ones. This suggests that the entire Pontides have undergone a northward drift of over 2000 km since the Upper Jurassic.