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This study is focused on slide blocks including oceanic lavas associated with pelagic sediments within the eastern part of the Ankara Mélange. A detailed petrological characterization of the volcanic rocks and a detailed biochronological investigation of the associated radiolarian cherts in eight sections (east of Ankara) was carried out. The volcanic rocks are largely represented by basalts and minor ferrobasalts and trachytes. They show different geochemical affinities and overlapping ages including: (a) Late Jurassic – Early Cretaceous garnet-influenced MORB (middle late Oxfordian to late Kimmeridgian–early Tithonian and early–early late Tithonian; late Valanginian–early Barremian); (b) Early Cretaceous enriched-MORB (middle late Barremian–early early Aptian; Valanginian to middle Aptian–early Albian); (c) Middle Jurassic plume-type MORB (early–middle Bajocian to late Bathonian–early Callovian); (d) Late Jurassic – Early Cretaceous alkaline basalts (middle–late Oxfordian to late Kimmeridgian–early Tithonian; late Valanginian to late Hauterivian). All rock types show a clear garnet signature, as testified to by their high MREE/HREE (middle rare earth element/heavy rare earth element) ratios. The coexistence of chemically different rock types from Middle Jurassic to Early Cretaceous times suggests that they were formed in a mid-ocean ridge setting from partial melting of a highly heterogeneous mantle characterized by the extensive occurrence of OIB-metasomatized portions, which were likely inherited from Triassic mantle plume activity associated with the continental rift and opening of the Neotethys branch. [ABSTRACT FROM AUTHOR]

Newly discovered K-bentonite beds, interstratified with limestones/dolomitic limestones of the Upper Devonian-Lower Carboniferous Yılanlı Formation, are exposed in the northwestern Black Sea region of Turkey, around Zonguldak and Bartın. K-bentonite samples collected from four different locations: the Gavurpınarı and Yılanlı Burnu quarries from the Bartın area, the Çimşir Çukurları 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 Yılanlı 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 Bartın (Gavurpınarı and Yılanlı 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 Bartın 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 (Bartın 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] This paper bears new data on the Arkot Dağ Mélange, Intra-Pontide suture zone, Turkey. [•] The results allow to outline the tectonic history of the Intra-Pontide suture zone. [•] The Arkot Dağ Mélange is a Late Cretaceous obduction-related sedimentary deposits. [•] A geodynamic scenario from Triassic to Tertiary is attempted for the northern Turkey. [ABSTRACT FROM AUTHOR]

Abstract: The Karakaya Complex in the pre-Liassic basement of the Sakarya Composite Terrane includes relicts inherited from the closure of the Palaeotethys. The interpretations regarding its origin are still controversial. The main reason for these controversies is largely due to the mélange character of the complex and the misidentification and misinterpretation of the tectonostratigraphic units that make up the complex. Kocyigit (1987) subdivided the complex into the Upper and Lower Karakaya Nappes. This tentative division assumes that the Upper Karakaya Nappe (Lower Karakaya Complex) is composed of rock assemblages metamorphosed under greenschist/blueschist facies. In contrast, the Lower Karakaya Nappe (Upper Karakaya Complex) is thought to be composed of relatively unmetamorphosed, yet deformed rock lithologies. In this study, our detailed geological and petrological observations show that subdivision of the Karakaya Complex based on differences in metamorphism does little to decipher the geological evolution of the complex. Supported by our recent findings (Sayit et al., 2010), however, we suggest that the mafic rocks in both Karakaya Nappes are actually similar to each other in terms of metamorphism and tectonic setting. We also propose that in classifying such chaotically mixed units, tectonomagmatic origin (together with age data) should be taken as the primary criterion, rather than metamorphism and deformation. [Copyright &y& Elsevier]

Abstract: Subduction/accretion complexes provide unique insight into the tectonic assembly of continental margins and oceanic basins, as they record the tectonic stacking and juxtaposition of materials derived from distinct tectonic environments. The Karakaya Complex, exposed throughout northern Turkey, is a good example of an ancient subduction/accretion complex that includes a number of pre-Liassic units that characterize the closure of Palaeotethys. Defining the components of this complex is of crucial importance to understanding the geodynamic evolution of Palaeotethys in the Eastern Mediterranean region. In this study, we explore the geochemistry of metabasic rocks within the Karakaya Complex, redefining and evaluating one of its main constituents, known as “the Nilüfer Unit”. New geochemical results combined with previously published data suggest that the Nilüfer Unit is dominated by oceanic-island basalt (OIB)- and enriched mid-ocean ridge basalt (E-MORB)-type metabasic rocks which are variably enriched in the most highly incompatible elements relative to normal MORB (N-MORB). Associated alkaline OIB-type basalts are characterized by highly fractionated and variable rare earth element (REE) patterns ([La/Yb] N =4.8–16.2), suggesting melting across the garnet–spinel transition, derivation from a heterogeneous mantle source, and/or dynamic melting of a homogeneous source. Similar Nb/Y–Zr/Y systematics of spatially associated OIB- and E-MORB-type samples may indicate involvement of a shared enriched mantle source(s). Combining both geological and geochemical evidence, we suggest that the OIB- and E-MORB-type assemblages defining the Nilüfer Unit represent seamounts and oceanic islands formed on Palaeotethyan oceanic crust, which was finally incorporated into a forearc accretionary prism during latest Triassic and became a component of the Karakaya Complex. [ABSTRACT FROM AUTHOR]

Abstract: The remnants of the Neotethyan Izmir–Ankara Ocean, the main branch of Neotethys in the eastern Mediterranean are represented by the Dagküplü Melange Complex in Central Sakarya, NW Turkey. It comprises several blocks or tectonic slices of pillow lavas, some of which include mudstones and radiolarian cherts as intra-pillow-fillings or interlayers. In the Igdecik area, a huge basaltic block has been studied in detail. Geochemical data reveal three distinct basalt types separated by sheared contacts. The first of these groups is an enriched mid-oceanic ridge basalt (E-MORB) type which is enriched in the most incompatible trace elements relative to normal MORB (N-NORB) in addition to having heavy rare earth elements (HREE) depletion, suggesting the influence of residual garnet in their mantle source region. The second is back-arc basin basalt (BABB) type with relatively depleted trace element compositions with respect to N-MORB together with a negative Nb anomaly, suggesting generation above an intra-oceanic subduction zone where partial melts are derived from a depleted (MORB-like) mantle. The final group is island-arc tholeiite (IAT) type, displaying the most depleted trace element abundances among the studied groups in addition to marked Nb depletion, reflecting intra-oceanic supra-subduction zone (SSZ) signatures similar to the BABB-type but requiring a depleted mantle source which has experienced a previous melt extraction. Combined with a previously ascribed Late Triassic age of (221Ma, Late Carnian; based on the radiolarian fauna found in a chert layer alternating with mudstones), the associated basalts with E-MORB-type geochemical signatures, suggest formation of oceanic crust as early as Late Carnian. This age is the oldest thus far obtained from the basalts of the Izmir–Ankara Ocean. This new data provides constraints on tectonic models for the opening the Izmir–Ankara Ocean and its relationship to other branches of the Neotethyan ocean in the Eastern Mediterranean area. [Copyright &y& Elsevier]

The Karakaya Complex in the Pontides consists of highly deformed and partly metamorphosed clastic and volcanic series of Permian and Triassic age. It is generally subdivided into two parts: The structurally lower part, called the Lower Karakaya Complex, consists of a mafic lava-mafic pyroclastite-shale-limestone succession metamorphosed in the greenschist and blueschist facies during the Late Palaeozoic or Triassic. The structurally upper part is made up of highly deformed Permian and Triassic clastic, volcaniclastic and volcanic rocks with exotic limestone blocks. There are currently two different models for the depositional setting and tectonic evolution of the Karakaya Complex. The rift model assumes that the Karakaya Complex was formed in a Late Permian rift, which developed into a marginal oceanic basin and closed by the latest Triassic. The subduction-accretion model regards the Karakaya Complex as subduction-accretion units of the Palaeo-Tethys. [ABSTRACT FROM AUTHOR]

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Pays tribute to Okan Tekeli, a prominent Turkish geologist, who died on August 6, 2001.

Introduces several articles featured in the August 2004 issue of the "Turkish Journal of Earth Sciences." Obituary of geologist Okan Tekeli; Geology of the Karakaya Complex in the Pontides.

The article focuses on the results analyzed by geological researchers Paquette and Le Pennec on zircon uranium-lead (U-Pb) dating data from the ignimbrites in Central Anatolia, Turkey. It also informs that the researchers detected zircons which reveal the geochronological results for Paleoproterozoic and Archean era for U-Pb ages ranging from 2.3 to 3.8 gigaampere. It mentions that research postulated the existence of an Archean basement terrane in lower parts of Central Anatolia.