Central Pontides Research Articles

Late Eocene evolution of the Çiçekdağı Basin (central Turkey): Syn-sedimentary compression during microcontinent–continent collision in central Anatolia

Abstract The Central Anatolian Crystalline Complex (CACC) exposes metasediment rocks overlain by Cretaceous ophiolites and intruded by granitoids. Following late Cretaceous exhumation of its high-grade metamorphic rocks, the CACC started to collide with the Central Pontides of southern Eurasia in the latest Cretaceous to Paleocene. Here, we present the sedimentary, stratigraphic and tectonic evolution of the Cicekdagi Basin, located in the northwest of the CACC. Magnetostratigraphic dating, supported by 40 Ar/ 39 Ar geochronology, shows a late Eocene basin age. The basin fill unconformably overlies metamorphic basement in the south and ophiolites of the CACC in the north. It consists of red conglomerates, sandstones and siltstones, which overlie a sequence of nummulitic limestones. In the south, these limestones are ~ 10 m thick, are underlain by a few meters of conglomerate unit unconformably covering the CACC metamorphics. In the north, the limestones are underlain by a ~ 200 m thick sequence of volcanics and fine-grained clastics intercalating with shallow marine black shales. The upper Eocene sediments of the Cicekdagi Basin were deformed into a syn-anticline pair. Progressive unconformities in the northern flank and a rapid and persistent ~ 180° switch in paleocurrent directions from southward to northward in the southern flank of the anticline demonstrate syn-sedimentary folding. We interpret the folding to result from a southward progression of the Cankiri foreland basin as a result of ongoing collision between the CACC and the Pontides.

Reply to Genç and Yürür’s comments on: “Late Cretaceous extensional denudation along a marble detachment fault zone in the Kırşehir massif near Kaman, Central Turkey”

We appreciate the interest of Dr. Yurdal Genc and Dr. Tekin Yurur in the work we carried out in central Turkey. In our paper, we presented a detailed structural study focused on one single fault zone located in the Kaman area, in the northwestern metamorphic massif of central Anatolia. The aim of our work was to provide clear structural evidence to assess the nature and kinematics of this fault zone, and to test whether it could be held responsible for part of the exhumation of the high-grade metamorphic rocks in the region. We demonstrated that the Kaman fault is an extensional detachment that was active in the late Cretaceous, and concluded that it was contemporaneous with late Cretaceous extension and exhumation of metamorphic rocks of the Central Anatolian Crystalline Complex (CACC) documented previously. This extensional phase has been discussed in numerous works such as the structural and metamorphic analysis from the southern Nigde crystalline massif ( [Gautier et al., 2002], [Whitney et al., 2003], [Whitney et al., 2007] and [Gautier et al., 2008]), structural and geochronological data from discrete shear zones across large magmatic intrusions in the north (Yozgat) and the west (Agacoren) of the CACC ( [Isik et al., 2008] and [Isik, 2009]), and the tectonic evolution of the large basins surrounding the CACC (e.g. the Tuzgolu and Sivas basins, ( [Cemen et al., 1999] and [Dirik et al., 1999]). Following extension, the region underwent compression during the Paleogene due to the convergence and consequent collision between the CACC and the central Pontides ( [Gorur et al., 1984], [Gorur et al., 1998], [Kaymakci et al., 2000], [Kaymakci et al., 2009] and [Meijers et al., 2010]). In contradiction to the generally accepted tectonic evolution for central Anatolia, Genc and Yurur (2010) recently proposed an alternative model based on inferences from digital elevation data and local field observations. They interpreted the Cenozoic tectonic regime of central Anatolia to be dominated by extension, associated with coeval compressional zones resulting from gravitational movements. Taking that into consideration, Genc and Yurur have in their discussion listed several points that they consider to be incoherencies. In this reply, we answer each point addressed in the comment, discussing the validity of our statements and data, and taking the opportunity to clarify the ideas that the authors of the comment may have misunderstood

Two-Dimensional Geothermal Modelling Along the Central Pontides Magmatic Arc: Implications for the Geodynamic Evolution of Northern Turkey

The Pontides, which can be divided tectonically into three main segments as Eastern, Central, and Western Pontides, is one of the most complex geodynamic settings within the Alpine belt. The Central Pontides, where the Eastern and Western Pontides met and formed a tectonic knot, represent an amalgamated tectonic mosaic consisting of remnants of oceanic, continental, and island arc segments. Subduction polarity, which is responsible for the formation of the Pontides, is still under debate because of limited geological, geophysical, and geochemical data. Two-dimensional (2-D) thermal modelling studies along the Central Pontides magmatic arc (Northern Turkey), Sakarya and Kirsehir continents are investigated in order to delineate the crustal thermal structure and subduction polarity. The obtained numerical results indicate that arc and back-arc regions are hot because of the cooling effects of a subducting plate. Moho temperatures in the investigated region are found between 992°C in the south (back-arc) and 415°C in the north (arc). Moreover, mantle heat flow values vary from 57.2 mWm−2 in the south (back-arc) to 34.7 mWm−2 in the north (arc). It is shown from this study that the Eurasia plate had moved from north to south under the Anatolia plate along the south Black Sea coast.

Late Neogene and active orogenic uplift in the Central Pontides associated with the North Anatolian Fault: Implications for the northern margin of the Central Anatolian Plateau, Turkey

Surface uplift at the northern margin of the Central Anatolian Plateau (CAP) is integrally tied to the evolution of the Central Pontides (CP), between the North Anatolian Fault (NAF) and the Black Sea. Our regional morphometric and plate kinematic analyses reveal topographic anomalies, steep channel gradients, and local high relief areas as indicators of ongoing differential surface uplift, which is higher in the western CP compared to the eastern CP and fault‐normal components of geodetic slip vectors and the character of tectonic activity of the NAF suggest that stress is accumulated in its broad restraining bend. Seismic reflection and structural field data show evidence for a deep structural detachment horizon responsible for the formation of an actively northward growing orogenic wedge with a positive flower‐structure geometry across the CP and the NAF. Taken together, the tectonic, plate kinematic, and geomorphic observations imply that the NAF is the main driving mechanism for wedge tectonics and uplift in the CP. In addition, the NAF Zone defines the boundary between the extensional CAP and the contractional CP. The syntectonic deposits within inverted intermontane basins and deeply incised gorges suggest that the formation of relief, changes in sedimentary dynamics, and >1 km fluvial incision resulted from accelerated uplift starting in the early Pliocene. The Central Pontides thus provide an example of an accretionary wedge with surface‐breaking faults that play a critical role in mountain building processes, sedimentary basin development, and ensuing lateral growth of a continental plateau since the end of the Miocene.

Middle Eocene paleomagnetic data from the eastern Sakarya Zone and the central Pontides: Implications for the tectonic evolution of north central Anatolia

A paleomagnetic investigation has been carried out on Middle Eocene volcanic rocks at 23 sites in the eastern Sakarya Zone and the central Pontides of north central Anatolia in order to better understand the regional tectonic evolution of the main zones of northeastern Anatolia in the Middle Eocene. The results constrain the tectonic evolution of the area when evaluated in conjunction with earlier published paleomagnetic directions from 92 localities. Small counterclockwise rotations in the range of R ± ΔR = −1.3 ± 1.4° to R ± ΔR = −17.2 ± 16.8°, with respect to Eurasia, are observed in the central Pontides on the northern side of the North Anatolian Fault (NAF). Clockwise rotations ranging between R ± ΔR = 8.5 ± 15.1° and R ± ΔR = 29.7 ± 12.0° are observed between the NAF and the Sungurlu Fault (SF), in the eastern Sakarya zone. Counterclockwise rotations of R ± ΔR = −18.9 ± 12.4° to R ± ΔR = −42.2 ± 6.9° are observed to the south of the SF. Our findings, combined with previous data, support the indentation model of Kaymakcı et al. (2000, 2003a, 2003b), which postulates the collision and northeast directed indentation of the Kırşehir Block into the Sakarya Zone. This model, which was developed to explain the evolution of the Çankırı Basin, can also explain the variable magnitudes of paleomagnetically determined rotations, thrust directions, and the curvature of the North Anatolian ophiolite belt.

Late Cretaceous to Paleocene oroclinal bending in the central Pontides (Turkey)

[1] The Turkish Pontide fold-and-thrust belt formed since the Paleozoic and is an important element in the Africa-Eurasia convergence and the resulting closure of the Neo-Tethys ocean. It has a peculiar arc-shaped geometry in its central part, along the Black Sea coast, which may have resulted from oroclinal bending. We have determined the vertical-axis rotation history of this area using paleomagnetism on Cretaceous to Eocene rocks from 47 sites and critically analyzed previously published data. We applied the same reliability criteria to all data. Our results show that late Cretaceous sites have clockwise and counterclockwise rotations perpendicular to the structural trend in the central Pontides. In the eastern Pontides, they show only local rotations. Paleocene to Eocene rocks in the central and eastern Pontides show no rotation. We conclude that the central Pontide northward arc-shaped geometry results from oroclinal bending in latest Cretaceous to earliest Paleocene times. The timing and scale of geological processes that occurred in the region make it likely that orocline formation resulted from Neo-Tethys closure between the Pontides and the metamorphic promontory of the Anatolide-Tauride Block. Earlier studies on the southerly located Cankiri Basin reveal that clockwise and counterclockwise rotations occurred in Eocene-Oligocene times. This implies that the entire region underwent continuous deformation from late Cretaceous to Eocene, caused by convergence of the Pontides and the Anatolide-Tauride Block, with a southward moving deformation front. Deformation was first localized in the northern part of the central Pontides until the Paleocene, resulting in oroclinal bending, and from at least Eocene times it shifted toward the Cankiri Basin region.

Dating of the Black Sea Basin: new nannoplankton ages from its inverted margin in the Central Pontides (Turkey)

Abstract The Eocene uplift and inversion of a part of the Black Sea margin in the Central Pontides, allows us to study the stratigraphic sequence of the Western Black Sea Basin (WBS). The revision of this sequence, with 164 nannoplankton ages, indicates that subsidence and rifting started in the Upper Barremian and accelerated during the Aptian. The rifting of the western Black Sea Basin lasted about 40 Ma (from late Barremian to Coniacian). In the inner, inverted, Black Sea margin, the syn-rift sequence ends up with shallow marine sands. The uppermost Albian to Turonian was a period of erosion or non deposition. This regional mid-Cretaceous stratigraphical gap might result from rift flank uplift, as expected in the case of a thick and cold pre-rift lithosphere. However, coeval collision of the Kargi Block, along the North Tethyan subduction zone at the southern margin of the Pontides, might also have contributed to this uplift. A rapid thermal post-rift subsidence of the margin occurred during the Coniacian–Santonian. Collision of the Kirşehir continental block commenced in Early Eocene time (zone NP12) giving rise to compressional deformation and sedimentation in piggyback basins in the Central Pontides, whereas the eastern Black Sea was still opening.

Cenomanian – Turonian Oceanic Anoxic Event (OAE2) in the Sakarya Zone, northwestern Turkey: Sedimentological, cyclostratigraphic, and geochemical records

The Cenomanian/Turonian oceanic anoxic event as recorded in many parts of the world is characterized by presence of black shales and global carbon isotope peaks. Cyclic variations within the anoxic event and association with pelagic red beds are indicated by many studies. Global tectonic/volcanic controls on the origin and the chronostratigraphic position of the anoxic event within the global sea-level changes are important for understanding the paleoceanographic and paleoclimatic conditions during the deposition of Cenomanian/Turonian sediments. Three measured stratigraphic sections in the Central Pontides and the Central Sakarya region of Turkey on the Sakarya Zone of the Pontides have been studied in detail. Cyclic facies alternations have been analysed and Ficher plot curves have been established for the measured sections. According to the cyclostratigraphic analysis, position of the C/T boundary with black shales/mudstones coincides with the global sea-level rise. This indicates that global sea-level change is one of the controlling parameters of black shale generation at the boundary and the long distance correlation between pelagic/hemipelagic successions of different parts of the Sakarya Zone and with global counterparts displays the effect of a large-scale event rather than local. A positive shift in the δ 13C curve has been obtained just below the C/T boundary similar to many curves obtained around the world. The depletion of Mn indicates oxygen-depleted bottom conditions. Parallel increase of Cd, P, Ba, and Fe indicates increased productivity. Increase in Zn, Cu, Pb and the presence of volcanoclastic sands just below the boundary indicate the fact that volcanism was present during the deposition of anoxic sediments and affected the productivity. TOC values of black shales reach up to 1, 95% at the boundary but drop suddenly after the boundary in parallel with other proxies. The Milankovitch-scale frequent rise and fall of the sea-level superimposed on larger cycles also triggered the nutrient enrichment and the ventilation of the basin resulting in the repetitive alternation of black shales and red marls or cherts. Therefore, this study indicates that the OAE2 including cyclic black shale and red marl/chert alternations on the Sakarya Zone was developed by the cooperation of volcanism, productivity and small and large-scale sea level changes.

Crustal Thermal Properties of the Central Pontides (Northern Turkey) Deduced from Spectral Analysis of Magnetic Data

The Pontides can be divided tectonically into three main sectors: Eastern, Central, and Western Pontides. Each of these represents an amalgamated tectonic mosaic consisting of remnants of oceanic, continental, and island arc segments. The Eastern and the Western Pontides meet in the Central Pontides, where they are structurally mixed and form a tectonic knot. The Central Pontides of northern Turkey is one of the best exposed segments of the southern margin of Eurasia adjacent to the Tethys Ocean. The study area also extends to parts of the Sakarya and Kırşehir continents. Magnetic spectral analysis, which has been used to estimate the Curie point depths and heat flow values, is employed to identify the thermal regime of the Central Pontides. The magnetic data of the region are separated into five subregions and the power spectra of each region is achieved by using 2D Fourier transform method to attain the average curie depth. The curie depth values changes across the studied region from 14.8 km in the south to 21.8 km in the north. The obtained results imply a high thermal gradient (39.2 °Ckm^{-1}) and corresponding heat flow values (94.1 mWm^{-2}) in the south of the research area. The northern part of the study area displays a low thermal gradient (26.6 °Ckm^{-1}) and low heat flow value (63.9 mWm^{-2}), corresponding to the Central Pontides consisting of accreted oceanic crustal material. The determined values show the heat flow decrease within the accretionary prism toward the island arc-like Pontides.

Apatite fission track data from central Anatolian granitoids (Turkey): Constraints on Neo‐Tethyan closure

Apatite fission track age versus elevation profiles and temperature‐time‐path modeling indicate an early to middle Paleocene (57–62 Ma) rapid exhumation of the Middle to Late Cretaceous granitoids in central Anatolia and an Oligocene (28–30 Ma) rapid exhumation of the Eocene Kösedağ batholith in the NE Sivas region, part of eastern central Pontides. The early to middle Paleocene rapid exhumation is thought to result from a regional compressional regime following the collision of the Eurasian Plate and the Tauride‐Anatolide Platform at the closure of the Izmir‐Ankara‐Erzincan branch of the northern Neo‐Tethys. The Oligocene accelerated exhumation of the Kösedağ batholith is contemporaneous with the Oligo‐Miocene closure of the southern Neo‐Tethys which juxtaposed the amalgamated Eurasian and Tauride‐Anatolide Platform and the African‐Arabian Plate along the Bitlis‐Zagros suture in southeast Anatolia. The compressional regime due to this collision affected a large area between the Greater Caucasus in the north and northern African‐Arabian Plate in the south.

Geochemical and isotopic constraints on the genesis of the Late Palaeozoic Deliktas and Sivrikaya granites from the Kastamonu granitoid belt (Central Pontides, Turkey)

The Late Palaeozoic Sivrikaya and Deliktas granitoids of the Kastamonu granitoid belt (KGB) are of sub-alkaline affi- nity, belong to the high-K calc-alkaline series and display features of transitional to S-type granites. Sivrikaya granitoid is host to biotite-hornblende granodiorite-tonalite and minor two-mica granites. The rocks are 303 - 300 Ma old, have low initial 87 Sr/ 86 Sr ratios (0.7041- 0.708), moderately low eNd(t) values (-1 to - 3.8) and young TDM model ages (0.75 to 1.08 Ga). All these charac- teristics, combined with low Al2O3/(FeO + MgO + TiO2) and (Na2O + K2O)/(FeO + MgO + TiO2) and δ 18 O values of 10-11.6 ‰ point to dehydration melting of heterogeneous protoliths dominated by amphibolite and greywackes-type sources with mantle contribution. Chondrite-normalized REE patterns of the Sivrikaya rocks are characterized by concave-upward patterns suggesting that amphibole played a more significant role than garnet during magma segregation. The main portion of the Deliktas granitoid consists of peraluminous muscovite-rich monzogranite. Compared to Sivrikaya, rocks from this pluton have higher initial Sr ra- tios (0.7109 - 0.7185), older Nd model ages (1.2 to 2.2 Ga) and similar eNd(t) values ( - 2.0 to - 4.7). U - Pb zircon analyses give an age range of 295 - 275 Ma. The nearly constant δ 18 O values (~ 11.5 to 11.7‰) in conjunction with the chemical characteristics in- dicate a predominantly pelitic source similar to the basement, which consists of felsic high-grade granulite-facies metasedimen- tary rocks, of continental origin.

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.

Late Cretaceous-Early Cenozoic tectonic evolution of the Eurasian active margin in the Central and Eastern Pontides, northern Turkey

Abstract The Izmir-Ankara-Erzincan suture zone (IAESZ) in the Central and the Eastern Pontides comprises a stack of thrust sheets of mainly Late Cretaceous-Early Cenozoic age that are restored as: (1) a subduction-accretion complex; (2) a continental-margin magmatic arc, plus an associated forearc basin; (3) a back-arc basin and its mainly sedimentary fill. Northward thrusting affected all of the Late Cretaceous units during latest Cretaceous (Campanian-Maastrichtian) time. This was followed by regional southward thrusting to form the present thrust stack during Mid-Eocene time. Alternative tectonic models are considered in the light of sedimentary, igneous geochemical and structural evidence, and global comparisons. We infer that the Northern Neotethys was subducted northwards beneath the Eurasian active margin during the Late Cretaceous. Subduction was associated with the genesis of a magmatic arc and a related forearc basin. The subduction zone retreated oceanwards, associated with the opening of a back-arc basin along the Eurasian margin, floored by oceanic crust and overlain by mixed terrigenous and volcaniclastic deep-marine sediments. Ophiolite genesis in a continental margin back-arc setting is suggested by the presence of screens of basement-type metamorphic rocks within an ophiolite-related sheeted dyke complex in the Eastern Pontides. During the latest Cretaceous closure of the inferred back-arc basin resulted in northward emplacement of ophiolitic and related units onto the Eurasian margin, as well exposed in the Central Pontides. In addition, accretionary mélange, volcanic arc, forearc and ophiolitic units were emplaced southwards onto the Tauride continent, represented by the Munzur platform in the Eastern Pontides, also during latest Cretaceous time. This incipient (‘soft’) collision was followed by widespread Paleocene-Early Eocene deposition of Nummulitic shelf carbonates and coarse clastic sediments on deformed and emplaced accretionary mélange, arc and ophiolitic units. Final closure (‘hard collision’) of the Northern Neotethys occurred during the Mid-Eocene, resulting in large-scale southward imbrication, together with northward backthrusting in some areas. Suture tightening and Plio-Quaternary strike-slip ensued.

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

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

Progressive left ventricular remodeling in patients with hypertrophic cardiomyopathy and severe left ventricular hypertrophy

The Central Pontides (Turkey) includes several igneous complexes, which are predominantly Permo-Carboniferous and Middle Jurassic in age. The Çangaldağ Pluton is one of the largest igneous bodies located in the northern Central Pontides, whose age and tectono-magmatic evaluation is important to constrain the geological evolution of the Northern Neotethys. The pluton tectonically overlies the Çangaldağ Metamorphic Complex, which represents an arc–back-arc complex of Middle Jurassic age. The Çangaldağ Pluton consists mainly of non-metamorphic gabbroic diorite, dacite porphyry, and lesser amount of granitic rocks. Geochemically, the various rock types are akin to volcanic arc magmas displaying Th/Nb and light rare earth element/heavy rare earth element enrichments. In-situ U–Pb age results of zircons from dacite porphyry and granite samples yield ages of 161 ± 5 Ma and 170 ± 2 Ma, respectively. Corresponding in-situ average 176Hf/177Hf initial ratios are 0.28287 ± 0.00004 and 0.28213 ± 0.00002 for the dacite porphyry and granite samples, respectively. These results are consistent with derivation from a subduction-modified mantle source. Based on Hf isotope compositions, TDM model ages vary between 624 and 1512 Ma and suggest that the arc magmatism associated with the Çangaldağ Pluton may have involved partial melting of Neoproterozoic/Mesoproterozoic crustal rocks, a common feature in Gondwana-derived terranes. The geochemical, Hf isotope, and geochronological data reported here confirm the presence of a continental arc system during the Middle Jurassic in the Central Pontides, and suggests that the Çangaldağ Pluton formed during northward subduction of the Intra-Pontide branch of the Northern Neotethys.

Evolution of a tourmaline-bearing lawsonite eclogite from the Elekdağ area (Central Pontides, N Turkey): evidence for infiltration of slab-derived B-rich fluids during exhumation

An undated high-pressure low-temperature tectonic melange in the Elekdag area (central Pontides, N Turkey) comprises blocks of MORB-derived lawsonite eclogite within a sheared serpentinite matrix. In their outer shells, some of the eclogite blocks contain large (up to 6 cm) tourmaline crystals. ‘Prograde’ inclusions in poikiloblastic garnet from a well-preserved eclogite block are lawsonite, epidote/clinozoisite, omphacite, rutile, glaucophane, chlorite, Ba-bearing phengite, minor actinolite, winchite and quartz. In addition, glaucophane, lawsonite and rutile occur as inclusions in omphacite. These inclusion assemblages document the transition from a garnet-lawsonite-epidote-bearing blueschist to a lawsonite eclogite with the peak assemblage garnet + omphacite I + lawsonite + rutile. Peak metamorphic conditions are not well-constrained but are estimated approximately 400–430°C and >1.35 GPa, based on Fe–Mg exchange between garnet and omphacite and the coexistence of lawsonite + omphacite + rutile. During exhumation of the eclogite–serpentinite melange in the hanging wall of a subduction system, infiltration of B-rich aqueous fluids into the rims of eclogite blocks caused retrogressive formation of abundant chlorite, titanite and albite, followed by growth of tourmaline at the expense of chlorite. At the same time, omphacite I (XJd=0.24–0.44) became unstable and partially replaced by omphacite II characterized by higher XJd (0.35–0.48), suggesting a relatively low silica activity in the infiltrating fluid. Apart from Fe-rich rims developed at the contact to chlorite, tourmaline crystals are nearly homogeneous. Their compositions correspond to Na-rich dravite, perhaps with a small amount of excess (tetrahedral) boron (~5.90 Si and 3.10 B cations per 31 anions). δ11 B values range from −2.2 to +1.7‰. The infiltrating fluids were most probably derived from subducting altered oceanic crust and sediments.

Plate tectonic evolution of the southern margin of Eurasia in the Mesozoic and Cenozoic

Thirteen time interval maps were constructed, which depict the Triassic to Neogene plate tectonic configuration, paleogeography and general lithofacies of the southern margin of Eurasia. The aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework. The Hercynian Orogeny was completed by the collision of Gondwana and Laurussia, whereas the Tethys Ocean formed the embayment between the Eurasian and Gondwanian branches of Pangea. During Late Triassic–Early Jurassic times, several microplates were sutured to the Eurasian margin, closing the Paleotethys Ocean. A Jurassic–Cretaceous north-dipping subduction boundary was developed along this new continental margin south of the Pontides, Transcaucasus and Iranian plates. The subduction zone trench-pulling effect caused rifting, creating the back-arc basin of the Greater Caucasus–proto South Caspian Sea, which achieved its maximum width during the Late Cretaceous. In the western Tethys, separation of Eurasia from Gondwana resulted in the formation of the Ligurian–Penninic–Pieniny–Magura Ocean (Alpine Tethys) as an extension of Middle Atlantic system and a part of the Pangean breakup tectonic system. During Late Jurassic–Early Cretaceous times, the Outer Carpathian rift developed. The opening of the western Black Sea occurred by rifting and drifting of the western–central Pontides away from the Moesian and Scythian platforms of Eurasia during the Early Cretaceous–Cenomanian. The latest Cretaceous–Paleogene was the time of the closure of the Ligurian–Pieniny Ocean. Adria–Alcapa terranes continued their northward movement during Eocene–Early Miocene times. Their oblique collision with the North European plate led to the development of the accretionary wedge of the Outer Carpathians and its foreland basin. The formation of the West Carpathian thrusts was completed by the Miocene. The thrust front was still propagating eastwards in the eastern Carpathians. During the Late Cretaceous, the Lesser Caucasus, Sanandaj–Sirjan and Makran plates were sutured to the Iranian–Afghanistan plates in the Caucasus–Caspian Sea area. A north-dipping subduction zone jumped during Paleogene to the Scythian–Turan Platform. The Shatski terrane moved northward, closing the Greater Caucasus Basin and opening the eastern Black Sea. The South Caspian underwent reorganization during Oligocene–Neogene times. The southwestern part of the South Caspian Basin was reopened, while the northwestern part was gradually reduced in size. The collision of India and the Lut plate with Eurasia caused the deformation of Central Asia and created a system of NW–SE wrench faults. The remnants of Jurassic–Cretaceous back-arc systems, oceanic and attenuated crust, as well as Tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems.

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

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

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.