Okan Tüysüz

Tethyan sutures of northern Turkey

Abstract The two main Tethyan sutures of Turkey, the İzmir-Ankara-Erzincan and the Intra-Pontide sutures, are reviewed through several well-studied transects crossing the suture regions. Both sutures have formed during the Early Tertiary continental collisions following northward subduction of Tethyan oceanic lithosphere. The İzmir-Ankara-Erzincan suture is represented along most of its c. 2000 km length by Paleocene and younger thrust, which emplace the upper crustal rocks of the northern continent over that of the southern continent with an intervening tectonic layer of Cretaceous subduction-accretion complexes. These thrusts constitutes a profound stratigraphic, structural, magmatic and metamorphic break, of at least Carboniferous to Palaeocene age and form the main boundary between Laurasia and Gondwana in the Turkish transect. Voluminous subduction-accretion complexes of Triassic and Cretaceous ages occur respectively to the north and south of the suture giving the antithetic subduction polarities during these two periods. This, and evidence for a major accretionary orogeny of Late Triassic age north of the İzmir-Ankara-Erzincan suture suggest that two separate oceanic lithospheres, of Carboniferous to Triassic (Palaeo-Tethys) and of Triassic to Cretaceous ages (Neo-Tethys) respectively have been consumed along the suture. The final continental collision along the İzmir-Ankara-Erzincan suture was slightly diachronous and occurred in the earliest Palaeocene to the west and in the Late Palaeocene to the east. The c. 800 km long Intra-Pontide suture is younger in age and have formed during the Early Eocene and younger continental collisions linked to the opening of the Western Black Sea Basin as an oceanic back-arc basin. At present the North Anatolian Fault, which came into existence in the Late Miocene, follows the course of the older Intra-Pontide suture.

Timing and climatic impact of Greenland interstadials recorded in stalagmites from northern Turkey.

A 50 kyr-long exceptionally well-dated and highly resolved stalagmite oxygen (δ 18O) and carbon (δ 13C) isotope record from Sofular Cave in northwestern Turkey helps to further improve the dating of Greenland Interstadials (GI) 1, and 3–12. Timing of most GI in the Sofular record is consistent within ±10 to 300 years with the “iconic” Hulu Cave record. Larger divergences (>500 years) between Sofular and Hulu are only observed for GI 4 and 7. The Sofular record differs from the most recent NGRIP chronology by up to several centuries, whereas age offsets do not increase systematically with depth. The Sofular record also reveals a rapid and sensitive climate and ecosystem response in the eastern Mediterranean to GI, whereas a phase lag of ∼100 years between climate and full ecosystem response is evident. Finally, results of spectral analyses of the Sofular isotope records do not support a 1,470-year pacing of GI.

Obduction, subduction and collision as reflected in the Upper Cretaceous-Lower Eocene sedimentary record of western Turkey

Late Cretaceous–Early Eocene Tethyan evolution of western Turkey is characterized by ophiolite obduction, high-pressure/low-temperature metamorphism, subduction, arc magmatism and continent–continent collision. The imprints of these events in the Upper Cretaceous–Lower Eocene sedimentary record of western Anatolia are studied in thirty-eight well-described stratigraphic sections. During the Late Cretaceous period, western Turkey consisted of two continents, the Pontides in the north and the Anatolide-Taurides in the south. These continental masses were separated by the Izmir-Ankara Neo-Tethyan ocean. During the convergence the Pontides formed the upper plate, the Anatolide-Taurides the lower plate. The arc magmatism in the Pontides along the Black Sea coast is biostratigraphically tightly constrained in time between the late Turonian and latest Campanian. Ophiolite obduction over the passive margin of the Anatolide-Tauride Block started in the Santonian soon after the inception of subduction in the Turonian. As a result, large areas of the Anatolide-Tauride Block subsided and became a region of pelagic carbonate sedimentation during the Campanian. The leading margin of the Anatolide-Tauride Block was buried deeply and was deformed and metamorphosed to blueschist facies during Campanian times. The Campanian arc volcanic rocks in the Pontides are conformably overlain by shaley limestone of Maastrichtian–Palaeocene age. However, Maastrichtian sedimentary sequences north of the Tethyan suture are of fore-arc type suggesting that although arc magmatism ceased by the end of the Campanian age, continent–continent collision was delayed until Palaeocene time, when there was a change from marine to continental sedimentation in the fore-arc basins. The interval between the end of the arc magmatism and continent–continent collision may have been related to a northward jump of the subduction zone at the end of Campanian time, or to continued obduction during the Maastrichtian.

Tectonic Evolution of the Central Anatolian Basins

The central Anatolian basins can be grouped into two basic types—arc-related (forearc and intra-arc) basins and collision-related (peripheral foreland) basins. The former began developing in the Late Cretaceous, whereas the latter started to form at the beginning of the Eocene. Both types of basins were filled until the Oligocene with turbidites overlain by shelf and nonmarine strata. During the Oligocene, all these basins were unified into a large epi-Anatolide molasse basin, in which widespread gypsiferous series were deposited together with abundant clastic deposits and volcanics. After the Oligocene, these basins evolved into an areally more extensive “intra-cratonic” basin that bears no relation to the earlier orogenic structures. This superposition of different types of basins makes the geology of central Anatolia extremely complicated. To date, no reliable evolutionary tectonic model for this region has been formulated. Considering that the hydrocarbon potential of these basins is largely unknown, ...

Cretaceous and Triassic subduction-accretion, high-pressure–low-temperature metamorphism, and continental growth in the Central Pontides, Turkey

Biostratigraphic, isotopic, and petrologic data from the Central Pontides document major southward growth of the Eurasian continental crust by subduction-accretion during the Cretaceous and Triassic Periods. A major part of the accreted material is represented by a crustal slice, 75 km long and up to 11 km thick, consisting of metabasite, metaophiolite, and mica schist that represent underplated Tethyan oceanic crustal and mantle rocks. They were metamorphosed at 490 degrees C and 17 kbar in mid-Cretaceous time (ca. 105 Ma). The syn-subduction exhumation occurred in a thrust sheet bounded by a greenschist facies shear zone with a normal sense of movement at the top and a thrust fault at the base. A flexural Foreland basin developed in front of the south-vergent high-pressure-low-temperature (HP-LT) metamorphic thrust sheet; the biostratigraphy of the foreland basin constrains the exhumation of the HP-LT rocks to the lbronian-Coniacian, similar to 20 m.y. after the HP-LT metamorphism, and similar to 25 m.y. before the terminal Paleocene continental collision. The Cretaceous subduction-accretion complex is tectonically overlain in the north by oceanic crustal rocks accreted to the southern margin of Eurasia during the latest Triassic-earliest Jurassic. The Triassic subduction-accretion complex is made up of metavolcanic rocks of ensimatic arc origin and has undergone a high pressure, greenschist facies metamorphism with growth of sodic amphibole. Most of the Central Pontides consists of accreted Phanerozoic oceanic crustal material, and hence is comparable to regions such as the Klamath Mountains in the northwestern United States or to the Altaids in Central Asia.

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

Geology of the Saros graben and its implications for the evolution of the North Anatolian fault in the Ganos–Saros region, northwestern Turkey

Abstract Palaeo- and neo-tectonic evolutions of the Gulf of Saros, northwestern Turkey, were investigated based on geological mapping, geomorphology, seismicity and GPS measurements. In this area three overlapping basins were differentiated: the Thrace, Enez and Saros basins. The Thrace basin opened during the middle Eocene on the continental Strandja Massif as a post-collisional, fault-controlled extensional basin after the closing of the Intra-Pontide Ocean to the south. This basin reached its greatest extent during the Late Eocene–Early Oligocene and then, turned into an intramontane terrestrial basin from the middle Miocene onwards. The Enez basin opened along the southern margin of the former Thrace basin as an E–W-trending half graben during the middle Miocene. The age and geometry of this basin corresponds to the extensional basins of the Aegean graben system to the south. Stratigraphy and structures related to the North Anatolian fault indicate that the fault started to be active since Pliocene and modified older structures. The fault zone evolved in two stages in and around the Gulf of Saros. During the initial stage the fault was trending as a single segment with a transpressional nature and without any stepping, and caused thrusting and folding subparallel to the main trace of the fault. Since the Late Pliocene the fault was left-stepping in the Saros area, giving rise to the Saros pull-apart basin. We modelled these two stages by using boundary element method, and found that there is a good correlation between the modelling results and geology and geomorphology.

Jurassic-Cretaceous paleomagnetism and paleogeography of the Pontides (Turkey)

Published paleomagnetic data from the Pontides indicate anomalously low Jurassic and Early Cretaceous paleolatitudes compatible with the southern Neo-Tethyan (African) continental margin and significantly different from paleolatitudes predicted for the northern (Eurasian) Neo-Tethyan margin. We present a new set of paleomagnetic data from 50 Late Cretaceous sites mainly from the Western Pontides and from the Eastern Pontides, and 11 Early Jurassic sites mainly from the Eastern Pontides. Fold tests indicate that the characteristic magnetization components predate Eocene folding. Late Cretaceous site mean declinations are northerly in the Eastern Pontides and rotated to the west by a few tens of degrees in the Western Pontides. Late Cretaceous site mean declinations are affected by local clockwise rotation in one sampling region close to the North Anatolian Fault. The mean Late Cretaceous inclinations and resulting paleolatitudes are 41.1° (23.5°N) and 43.7° (25.5°N) for the Western and Eastern Pontides, respectively. For the Eastern Pontides, the Early Jurassic (Liassic) mean inclination is 60.5°, yielding a paleolatitude of 41.4°N, considerably further north than previous paleolatitude estimates for the Eastern Pontides at this time. The paleolatitude estimates for the Western and Eastern Pontides are consistent with these units being close to the Eurasian continental margin during Liassic and Late Cretaceous time.

A MAGMATIC BELT WITHIN THE NEO-TETHYAN SUTURE ZONE AND ITS ROLE IN THE TECTONIC EVOLUTION OF NORTHERN TURKEY

Abstract The Sakarya and Kirsehir continental fragments of Northern Turkey were separated by the Ankara-Erzincan ophiolitic suture zone, which is the remnant of the northern branch of the Neo-Tethys, namely the Ankara-Erzincan Ocean. This ocean branch opened during the Lias between these two continental fragments and started to close at the beginning of the Late Cretaceous, by the consumption of its floor, along two north-dipping subduction zones. The northern one was along the southern margin of the Sakarya Continent. As a result of this subduction zone, an ensialic magmatic arc, some fore-arc basins and a melange belt developed from north to south on the Sakarya Continent. The second subduction zone, located to the south, gave rise to a melange belt and an island arc developed with and on it. Hot-spot magmatics (seamounts), which were scraped from the subducting oceanic crust, also accreted into this ophiolitic-volcanic belt. At the end of the late Cretaceous, the central part of the Ankara-Erzincan Ocean closed due to the collision of the Kirsehir and the Sakarya continents. As a result of this collision, melange belts and ensimatic arc volcanics formed the Ankara-Yozgat suture between these continental fragments.

Palaeostress analysis of Tertiary post-collisional structures in the Western Pontides, northern Turkey

Fingerprints of the opening of the Western Black Sea Basin and collision of Pontides and Sakarya Continent along the Intra-Pontide suture can be traced in the area between Cide (Kastamonu) and Kurucasile (Bartin) in northern Turkey, along the southern coast of the Black Sea. The Western Black Sea Basin is an oceanic basin opened as a back-arc basin of the northward- subducting Intra-Pontide Ocean. Basement units related to this opening are represented by Lower Cretaceous and older units. The first arc magmatism related to this subduction began during Turonian times. Coeval with this magmatism, back-arc extension affected the region and caused development of horst-graben topography. This extensional period resulted in the break-up of continental crust and the oceanic spreading in the Western Black Sea Basin during Late Santonian times. During the Late Campanian-Early Maastrichtian period, the Sakarya Continent and Pontides collided and arc magmatism on the Pontides ended. After this collision, the Western Pontides thickened, imbricated and developed a mainly N-vergent foreland fold and thrust belt character since Late Eocene- Oligocene times. The palaeostress directions calculated from thrust faults of this foreland fold and thrust belt are 4.6°/156.6° for σ1, 6.4°/66.1° for σ2, and 83.2°/261.9° for σ3. The nature of the imbrica- tion indicates that it was a northward prograding foreland system connected to a floor thrust (detach- ment) fault at the bottom. Field observations on curved slickenfibres support the theory that the thrust faults of this imbricated structure have transformed to oblique thrusts and strike-slip faults over time.