New Stratigraphic and Palaeogeographic Results from the Palaeozoic and Early Mesozoic of the Middle Pontides (Northern Turkey) in the Azdavay, Devrekani, Küre and Inebolu Areas: Implications for the Carboniferous-Early Cretaceous Geodynamic Evolution and Some Related Remarks to the Karakaya Oceanic Rift Basin

The Küre Complex of the Middle Pontides, northern Turkey, is not a remnant of the Palaeotethys but consists of three different units with differing geological history, the Küre Ridge Unit, the Küre Ocean Unit and the Çalça Unit. The Küre Ridge Unit consists of the Serveçay Group, a pre-Permian, low-grade metamorphic Variscan oceanic sequence, and the Sirçalik Group, a Lower and Middle Triassic shallow-water sequence of North Alpine facies and event succession which disconformably overlies the Serveçay Group. Following a hiatus, the Sirçalik Group is overlain by marginal parts of the Akgöl Group with olistoliths of local origin which were derived mainly from the Sirçalik Group. The Küre Ocean Unit consists mostly of the Akgöl Group (siliciclastic turbidites and olistostromes of the Karadagtepe Formation, which is a middle Carnian to Middle Jurassic accretionary complex from the southern, active margin of the Küre Ocean, and mainly Middle Jurassic molasse type shallow-water sandstones, siltstones and shales of an unnamed formation) and of thick oceanic basalts (Ipsinler Basalt). Tectonic slices of Middle Triassic to lower Carnian ophiolites and basalts are also present. The Karadagtepe Formation contains numerous Middle Triassic exotic olistoliths and blocks of shallow-water and predominantly slope and basinal limestones, ocean-floor deep-sea sediments (shales and radiolarites), basalts and small clasts of ophiolites or ophiolitic detritus. The Çalça Unit consists of deposits from the northern, passive margin of the Küre ocean with many Pelsonian to upper Norian Hallstatt Limestones and Rhaetian-Lower Jurassic (?Middle Jurassic) deep-water shales and marls. All three units are overlain following a period of non deposition by the Upper Jurassic Bürnük Formation (red conglomerate, sandstone) and Inalti Formation (shallow-water platform carbonates). The Küre Ridge Unit was split away from the Variscan Sakarya Continent by the opening of the Karakaya oceanic rift basin during latest Permian (Dorashamian) and became a continental splinter between the Karakaya oceanic rift basin and the Küre Ocean (opened during the late Scythian). Southward subduction began in the Küre Ocean during the middle Carnian (beginning of the Karadagtepe siliciclastic turbidites), whereas at the northern passive margin the deposition of Hallstatt Limestones continued until the latest Norian. The deposition of siliciclastic turbidites and olistostromes (Diskaya Unit) began in the entire Karakaya oceanic rift basin during the middle Carnian, and ocean basin deposits (radiolarites, pelagic limestones) and slope deposits form the passive margin (e.g., Hallstatt Limestones) are no more present in the Karakaya oceanic rift basin indicating that this basin was very narrow (only a few hundreds of kilometres). During the late Norian, the Karakaya oceanic rift basin closed, whereas subduction at the southern (active margin) of the Küre ocean continued. At the northern margin of the (Upper Triassic?) Jurassic-Lower Cretaceous Beykoz-Çaglayan turbidite basin (north of the Küre Complex) the accretionary complex of an older ocean, the Late Palaeozoic Paphlagonian Ocean, was exposed that yielded clasts in the Beykoz-Çaglayan turbidite basin. Among these clasts Carboniferous to Middle Permian (Capitanian) pelagic rocks (pelagic limestones, radiolarites) could be dated. A Middle to Late Permian southward-directed subduction is assumed for the Paphlagonian Ocean. Its closure occurred either at the end of the Permian or during the Scythian

Terlemez quartz monzonite of Central Anatolia (Aksaray-Sarikaraman): Age, petrogenesis and geotectonic implications for ophiolite emplacement

The Terlemez quartz monzonite is one of the Central Anatolian Granitoids and is exposed to the east of one of the main granitoid belts trending in a NW-SE direction and situated at the western end of the Central Anatolian Crystalline Complex. The Terlemez quartz monzonite is medium- to coarse-grained with granoblastic texture. It is essentially composed of quartz, plagioclase, hornblende and K-feldspar and variable contents of biotite. It is mostly compact and massive, but close to the contact with the ophiolitic basic rocks it shows a chilled margin. It characteristically includes K-feldspar megacrysts up to 3 cm in width and 10 cm in length, and contains irregular, angular or sub-rounded micromafic granular enclaves as well as xenoliths and large 'roof-pendants' of gabbroic composition derived from the Sarikaraman Ophiolite, which is the most representative member of the supra-subduction zone type of Central Anatolian Ophiolites. The Terlemez quartz monzonite is a calc-alkaline, metaluminous intrusion. It typically displays moderately developed negative Ba and Nb trace element anomalies and enrichment in light rare earth elements relative to heavy rare earth elements without any significant Eu, Sr and Ti anomalies. On the basis of field, petrographic and geochemical data, the Terlemez quartz monzonite has been classified as H-type (hybrid type), which requires significant input from a mantle-derived mafic magma. The intrusion represents the advanced stage of the post-collisional magmatism of the Central Anatolian Crystalline Complex. Unlike the other Central Anatolian Granitoids, the Terlemez quartz monzonite has a clear intrusive contact with the well studied Middle Turonian-Lower Santonian Sarikaraman Ophiolite. The K-Ar hornblende age obtained from the quartz monzonite (81.5 ± 1.9 Ma) is interpreted as the intrusion age. These data suggest a post-Early Santonian to pre-Early Campanian emplacement age for the supra-subduction zone type of Central Anatolian Ophiolites. The data further suggest that the post-collisional magmatism in Central Anatolia post-dates the emplacement of fore arc-type ophiolites onto the passive margin of the Tauride-Anatolide platform. The very short time interval between the formation and emplacement ages of supra-subduction zone-type ophiolites seems to be a very typical feature of the fore arc-type Eastern Mediterranean Ophiolites

Geological features and geochemical characteristics of Late Devonian-Early Carboniferous K-bentonites from northwestern Turkey

Newly discovered K-bentonite beds, interstratified with limestones/dolomitic limestones of the Upper Devonian-Lower Carboniferous Yllanll Formation, are exposed in the northwestern Black Sea region of Turkey, around Zonguldak and Bartln. K-bentonite samples collected from four different locations: the Gavurplnarl and Yllanll Burnu quarries from the Bartln area, the Çimşir Çukurlarl quarry from the Şapça area, and the Güdüllü and Gökgöl highway tunnel section near Zonguldak city were investigated using optical microscopy,X-ray diffraction and inductively coupled plasma mass spectrometry in order to reveal their mineralogical and geochemical characteristics and understand their origin and evolution. The K-bentonites occur at different levels in the Yllanll Formation as 2-40 cm-thick, greenish to yellowish beds cropping out several hundred metres along strike. Preliminary biostratigraphic data suggest that the protoliths of the Bartln (Gavurplnarl and Yllanll Burnu) and Güdüllü K-bentonites were deposited at around the boundary between the Frasnian and Famennian, whereas those in the Şapça and Gökgöl sections are slightly younger (Devonian-Carboniferous boundary interval). The lithofacies types of the host carbonate rocks suggest an 'epeiric' shallow carbonate platform environment. Illite and mixed-layer illite-smectite were the major clay minerals in the K-bentonites. The K-bentonites from the Bartln area display a high degree of illitization and consist mainly of illite indicating high-grade diagenesis, whereas illite-smectite-rich samples from the Şapca and Gökgöl tunnel locations reflect relatively lower diagenetic conditions. According to their geochemical compositions, two groups of K-bentonites were distinguished, one with alkali basalt (Bartln area and Güdüllü locations) and one with trachyte affinities (Gökgöl tunnel and Şapça locations). Geochemical fingerprinting of K-bentonites by trace and rare earth element (REE) data suggest that tephras with alkali basalt composition have been derived by a source formed in a 'continental back-arc' setting, whereas the source of K-bentonites with trachytic precursors is related to 'continental within-plate rifting'. An evaluation of the global Late Devonian and Devonian-Carboniferous volcanism suggests that the bentonite precursors may be related to late-Variscan magmatism in Laurussia. © 2016 by Walter de Gruyter Berlin/Boston

The geodynamic evolution of the Intra-Pontide suture zone, Central Turkey: evidence from the ophiolite bearing Arkot Dağ Mélange

The geological setting of Turkey can be described as an assemblage of continental terranes separated by ophiolitebearing suture zones that mark the areas where the PaleoTethyan and NeoTehyan oceanic basins were destroyed. In northern Turkey, one of the most important suture zone is represented by the Intra-Pontide one consisting of an eastwest trending belt of deformed and/or metamorphic units located at the boundary between the Istanbul-Zonguldak terrane to the north and the Sakarya terrane to the south. These units can be regarded as issued from the Intra-Pontide domain, whose geodynamic history is still a matter of debate. Along the Akpinar-Araç-Bayramoren geotraverse, located in central Turkey, an ophiolite-bearing mélange, known as the Arkot Dağ Mélange, is well-exposed along the Intra-Pontide suture zone. The Arkot Dağ Mélange can be described as a Late Santonian chaotic sedimentary deposit consisting of an up to 1000-m-thick succession of slideblocks of different sizes and lithologies enclosed in a sedimentary matrix consisting of shales, coarse-grained arenites, pebbly mudstones and pebbly sandstones. The slide-blocks, from a few meters to hectometers in size, are represented by metamorphic rocks (mainly micaschists and gneisses), by ophiolites (peridotites, gabbros, IAT and BAB basalts and cherts) and by sedimentary rocks (cherts, neritic and pelagic limestone, marly limestone and ophiolite-bearing turbidites). The youngest age among the slide-blocks has been provided by the ophiolite-bearing turbidites where a late Coniacian nannofossil assemblage has been found. The cherts have provided a wide range of ages from the Middle Trias to Late Cretaceous, whereas the fossils found in the limestone indicate Late Jurassic to Early Cretaceous ages. The matrix of the Arkot Dağ Mélange, even if unaffected by metamorphism, shows deformations represented by multiple meters-thick cataclastic shear zones at the boundaries of the mélange slices or inside of them. According to its features, the source area of the Arkot Dağ Mélange was most likely a stack of continental and oceanic thrust sheets emplaced in the Late Cretaceous onto a continental margin. The data collected from the different slide-blocks suggest that the Intra- Pontide domain was characterised by an oceanic basin opened at the latest in the Early Jurassic. The opening of the Intra-Pontide oceanic basin was followed by the development of a subduction zone with a subsequent opening of suprasubduction oceanic basin in the Middle Jurassic – Early Cretaceous. The convergence in this suprasubduction oceanic basin started at the Early/Late Cretaceous boundary by an obduction process, whereas its final closure can be regarded as Late Paleocene

Age and geochemistry of chert-basalt associations in the ophiolitic complexes of the Izmir-Ankara Mélange (East of Ankara, Turkey)

In this work, we present the preliminary age data of the radiolarian cherts deposited on the top of basalts belonging to the Eastern Ankara Mélange (part of the Izmir-Ankara Mélange). Petrological studies on basalts were carried out in order to constrain the tectonic setting of formation of the studied basalt-chert sequences. Nine sections were sampled to the East of Ankara and twenty seven samples were collected for biostratigraphic and geochemical analyses. The oldest radiolarian cherts dated in the present paper are referrable to Late Triassic (Section 6: late Norian) and are associated with basaltic rocks with OIB character. OIB type volcanic rocks are also found in other sections and are associated with cherts of Late Jurassic (Section 3: middle-late Oxfordian to late Kimmeridgian-early Tithonian) and Early Cretaceous (Section 1: late Valanginian to latest Valanginian-earliest Hauterivian) ages. E-MORB type rocks are associated with radiolarian cherts of Cretaceous age (Section 4: late Barremian and Section 7: Valanginian to middle Aptian-early Albian), whereas the oldest N-MORBs were found in a section of Late Jurassic age (Section 5: early-early late Tithonian). Other N-MORBs are associated with radiolarian cherts of Early Cretaceous age (Section 8: late Valanginian-early Barremian). P-MORBs type rocks were found only in a section of Middle Jurassic age (Section 2: early-middle Bajocian to late Bathonian-early Callovian age). In this work, we document the occurrence of OIB-type rocks of Late Triassic and of rocks showing different geochemical affinities (N-, E-, P-MORBs and OIB) generated in the same time span (Middle-Late Jurassic - Early Cretaceous). N-MORBs are compatible with composition of melts generated by partial melting of a depleted MORB mantle source. In contrast, OIBs are compatible with partial melting of enriched-type mantle source. E-MORBs may have derived from mantle source slightly enriched with respect to DMM source, whereas P-MORBs are compatible with melts generated from a mantle source significantly enriched, compared to DMM. The chemical differences shown by the distinct rock-types can be related either to differences in source composition or different tectonic settings of formation, which may have existed during the Late Jurassic - Early Cretaceous time span

The Arkot Dağ Mélange Central Turkey: evidence for the geodynamic evolution of the Intra-Pontide suture zone

The geological setting of Turkey can be described as an assemblage of continental terranes separated by ophiolite-bearing suture zones that mark the areas where the PaleoTethyan and NeoTehyan oceanic basins were destroyed. In northern Turkey, one of the most important suture zones is represented by the Intra-Pontide one consisting of an east-west trending belt of deformed and/or metamorphic units located at the boundary between the Istanbul-Zonguldak terrane to the north and the Sakarya terrane to the south. These units can be regarded as issued from the Intra-Pontide domain, whose geodynamic history is still a matter of debate. Along the Akpinar-Araç-Bayramoren geotraverse, located in central Turkey, an ophiolite-bearing mélange, known as the Arkot Dağ Mélange, is well-exposed along the Intra-Pontide suture zone. The Arkot Dağ Mélange can be described as an Upper Santonian chaotic sedimentary deposit consisting of an up to 1000-m-thick succession of slide-blocks of different sizes and lithologies enclosed in a sedimentary matrix consisting of shales, coarse-grained arenites, pebbly mudstones and pebbly sandstones. The slide-blocks, from a few meters to hectometers in size, are represented by metamorphic rocks (mainly micaschists and gneisses), by ophiolites (peridotites, gabbros, IAT and BAB basalts and cherts) and by sedimentary rocks (cherts, neritic and pelagic limestone, marly limestone and ophiolite-bearing turbidites). The youngest age among the slide-blocks has been provided by the ophiolite-bearing turbidites where a late Coniacian nannofossil assemblage has been found. The cherts have provided a wide range of ages from the Middle Triassic to Late Cretaceous, whereas the fossils found in the limestone indicate Late Jurassic to Early Cretaceous ages. The matrix of the Arkot Dağ Mélange, even if unaffected by metamorphism, shows deformations represented by multiple meters-thick cataclastic shear zones at the boundaries of the mélange slices or inside them. According to its features, the source area of the Arkot Dağ Mélange was most likely a stack of continental and oceanic thrust sheets emplaced in the Late Cretaceous onto a continental margin. The data collected from the different slide-blocks suggest that the Intra-Pontide domain was characterised by an oceanic basin that opened at the latest in the Early Jurassic. The opening of the Intra-Pontide oceanic basin was followed by the development of a subduction zone with a subsequent opening of suprasubduction oceanic basin in the Middle Jurassic – Early Cretaceous. The convergence in this suprasubduction oceanic basin started at the Early/Late Cretaceous boundary by an obduction process, whereas its final closure can be regarded as Late Paleocene

Age and geochemistry of basalt-chert associations in the ophiolites of the Izmir-Ankara mélange east of Ankara, Turkey: preliminary data

In this paper, we present the preliminary data on the age of the radiolarian cherts deposited on top of basalts belonging to the Eastern Ankara Mélange (part of the Izmir-Ankara Mélange). Petrological studies on the basalts were carried out in order to constrain the tectonic setting of the studied basalt-chert sequences. Nine sections were sampled East and Northeast of Ankara and twenty seven samples were collected for biostratigraphic and geochemical analyses. The oldest radiolarian cherts dated in the present paper are referable to the Late Triassic (Section 6: late Norian) and are associated with basaltic rocks of OIB character. OIB type volcanic rocks are also found in other sections, associated with cherts of Late Jurassic (Section 3: middle-late Oxfordian to late Kimmeridgian-early Tithonian) and Early Cretaceous (Section 1: late Valanginian to late Hauterivian) ages. E-MORB type rocks are associated with radiolarian cherts of Cretaceous age (Section 4: middle late Barremian-early early Aptian and Section 7: Valanginian to middle Aptian-early Albian), whereas the oldest N-MORBs were found in a section of Late Jurassic age (Section 5: early-early late Tithonian). Other N-MORBs are associated with radiolarian cherts of Early Cretaceous age (Section 8: late Valanginian-early Barremian). P-MORBs type rocks were found only in a section of Middle Jurassic age (Section 2: early-middle Bajocian to late Bathonian-early Callovian age). In this work, we document the occurrence of Late Triassic OIB-type rocks and of rocks showing different geochemical affinities (N-, E-, P-MORBs and OIB) generated within the same time span (Middle-Late Jurassic - Early Cretaceous). N-MORBs are compatible with composition of melts generated by partial melting of a depleted MORB mantle source. In contrast, OIBs are compatible with partial melting of an enriched-type mantle source. E-MORBs may have derived from mantle source slightly enriched with respect to a DMM source, whereas P-MORBs are compatible with melts generated from a mantle source significantly enriched, compared to DMM