Upper Permian (Changxingian) Radiolarian Cherts within the Clastic Successions of the "Karakaya Complex" in NW Anatolia

The arkosic sandstones with olistostromes within the "Karakaya Complex" in NW Anatolia to the south of Geyve include a thin layer of green chert with radiolaria. Based on the composition of Albaillellids, the radiolarian assemblage corresponds to the Neoalbaillella ornithoformisassemblage, and its age is assigned to the Changxingian (Late Permian). This is the first finding of synsedimentary radiolarian cherts within the Karakaya units and the indication of latest Permian rifting of the Karakaya basin within the Midian carbonate platform and its pre-Permian basement in the Sakarya Composite Terrane

Early Paleozoic evolution of the NW Gondwanaland: data from southern Turkey and surrounding regions

The Lower Paleozoic assemblages in the E. Meditterranean comprise a Southern (Tauride-Anatolide,SE Anatolia and Central Iranian terranes) and a Northern (Carpathian-Balkan, Istanbul, Zonguldak and the Main Range terranes) Zone. A detailed stratigrapic account is given for these terranes for the Early Paleozoic and their paleogeographical settings are discussed to evaluate the Early Paleozoic geodynamic interpretation of this critical area between Gondwana-Perigondwana and Laurussia..Published315-323JCR Journalope

Pozzolanic activity of clinoptilolite: A comparative study with silica fume, fly ash and a non-zeolitic natural pozzolan

WOS: 000274869600006Pozzolanic activity of clinoptilolite, the most common natural zeolite mineral, was studied in comparison to silica fume, fly ash and a non-zeolitic natural pozzolan. Chemical, mineralogical and physical characterizations of the materials were considered in comparative evaluations. Pozzolanic activity of the natural zeolite was evaluated with various test methods including electrical conductivity of lime-pozzolan suspensions; and free lime content, compressive strength and pore size distribution of hardened lime-pozzolan pastes. The results showed that the clinoptilolite possessed a high lime-pozzolan reactivity that was comparable to silica fume and was higher than fly ash and a non-zeolitic natural pozzolan. The high reactivity of the clinoptilolite is attributable to its specific surface area and reactive SiO(2) content. Relatively poor strength contribution of clinoptilolite in spite of high pozzolanic activity can be attributable to larger pore size distribution of the hardened zeolite-lime product compared to the lime-fly ash system. (C) 2009 Elsevier Ltd. All rights reserved.Scientific and Technological Research Council of Turkey [104M393]This study was funded by The Scientific and Technological Research Council of Turkey under Project Number: 104M393. The instrumental analyses in this study were carried out in Middle East Technical University Central Laboratory. Acknowledgment is given to Emeritus Professor P. Kumar Mehta from the Civil and Environmental Engineering Department at the University of California, Berkeley, for his helpful comments during the investigation

Metamorphic imprint of ridge subduction on the Neo-Tethyan ophiolites from the Saka Unit (Central Pontides, northern Turkey)

The Intra-Pontide suture zone is the northernmost ophiolite suture zone exposed in the Anatolian peninsula. It consists of several variably deformed and metamorphosed tectonic units derived from the Neo-Tethyan Intra-Pontide oceanic (IPO) basin, and its continental margins that are currently represented by the Istanbul-Zonguldak and the Sakarya terranes. Recent data suggests that the IPO was a wide supra-subduction oceanic basin whose closure began in the uppermost Early Jurassic by a north dipping intra-oceanic subduction that divided the IPO into two different oceanic areas, namely IPO1 and IPO2. The Saka Unit is a small tectonic unit exposed in the eastern portion of the Intra-Pontide suture zone in the Central Pontides, which is interpreted as a tectonic mélange produced during the intra-oceanic subduction that led to the closure of IPO1. The unit was affected by polyphase deformation and epidote–amphibolite facies metamorphism peak conditions experienced during the uppermost Middle Jurassic. Metamorphic studies and thermodynamic investigations constrain the peak pressure conditions to T ≈ 650–700 °C and P ≈ 0.9–1.3 GPa. These conditions reveal a ‘hot’ and anomalous geothermal gradient (15–22 °C/km) with respect to those of the other ophiolite-bearing units of the Intra-Pontide suture zone involved in the subduction. This anomalous gradient was herein attributed to the thermal pulse produced by the subduction of the IPO1 mid-oceanic ridge. The final re-equilibration occurred under greenschist facies conditions during the Early Cretaceous exhumation, when the oceanic lithosphere of the IPO was completely consumed and the continental collision between the Istanbul-Zonguldak and Sakarya terranes occurred

Geological, Structural and Mineralogical Approach to Investigate the Evolution of Low- and very Low-Grade Metamorphic Units from the Intra-Pontide Suture Zone, Central Pontides, Turkey

A multidisciplinary approach combining multiscale geological-structural analyses (from field to microscale) and clay mineral transformations (clay mineralogy, illite and chlorite “crystallinity” and b cell dimension (b0) of K-white mica) was adopted to unravel the tectono-metamorphic evolution of low- and very low-grade tectono-metamorphic units from the Intra-Pontide suture zone in northern Turkey. The mineralogical study allowed to better evaluate the structural stacking outlined during the geological mapping, leading to distinguish three tectono-metamorphic units, two in epizone (Daday and Emirköy units) and one in anchizone (Çifter Unit) metamorphic conditions. The mesostructural and microstructural analyses suggest a polyphase tectonic-metamorphic evolution. The different macroscopic features observed between the two units characterized by the same epizone metamorphism, can be justified by the evidence that these metamorphic conditions were acquired during the last stages of exhumation in the Daday Unit, while they constrained the metamorphic-peak conditions in the Emirköy Unit. Contemporary analyses and comparison between structural and mineralogical data have thus proven to be a powerful tool to investigate the low-grade and very low-grade metamorphic environments, allowing at the same time to solve the apparent contradictions deriving from the mineralogical study and to significantly improve the detail of the geological mapping in the field

The Ayli Dağ ophiolite sequence (central-northern Turkey): a fragment of Middle Jurassic oceanic lithosphere within the Intra-Pontide suture zone

The Ayli Dağ ophiolites occur as an independent tectonic unit within the Intra-Pontide suture zone, central-northern Turkey. They crop out, together with the other units of the Intra-Pontide suture zone, at the top of the Late Cretaceous-Middle Paleocene foredeep sediments of the Sakarya Terrane. The Ayli Dağ ophiolites sequence include in its lower part a mantle sequence consisting of not less than 2-3 km-thick peridotites, topped by 500-600 m-thick layered gabbros with alternating, dm- to m-thick layers of spinel-bearing dunites, melatroctolites, troctolites, ol-gabbros and leucogabbros. The gabbro sequence is overlain by a sheeted dyke complex, that shows a transition to 100-200 m-thick massive basaltic lava flows followed by 600-800 m-thick massive and pillow lavas and breccias alternating with ophiolite-bearing arenites and cherts. Geochemical evaluation of the mafic lavas and dykes reveals three distinct chemical groups that reflect melt generation within an intra-oceanic subduction system. Among these, the first group shows island-arc tholeiite (IAT)-like features, showing very-depleted characteristics (very high Zr/Nb, low Zr/Y and Nb/Y) ratios coupled with light rare-earth (LREE)-depleted chondrite-normalized patterns. The second group is more akin to back-arc basin basalts (BABB); it displays normal mid-ocean ridge basalt (N-MORB)-like high-field strength element (HFSE) distribution except for depletion in Nb, and flat REE patterns. The third group is somewhat similar to the second one, displaying BABB-like characteristics, but it is more enriched in terms of absolute trace element abundances. The radiolarian cherts sampled from the top of the pillow lavas yielded less-diverse but characteristic radiolarian assemblages indicating the middle Bathonian to early Callovian ages. The Ayli Dağ Ophiolite is the first finding of back-arc type oceanic lithosphere in the Intra-Pontide suture zone. Together with previous data obtained from basalts in the mélange from the Intra-Pontide suture zone, this finding represents a proof that an intra-oceanic subduction within the Intra-Pontide oceanic basin occurred in the Middle Jurassic time

The Intrapontide Suture zone in Turkey: the eastern extension of the Dinaric-Hellenic belt?

How the ophiolite-bearing suture zones documented in the Dinaric- Hellenic belt extend eastwards in Turkey is one of the most debated geological problems. Valuable insights can be provided by the eastern edge of the Intrapontide Suture Zone (Central Turkey) that consists of an assemblage of several units issued from a Neotethyan oceanic basin and its continental margins. Among these tectonic units, the Devrekani unit consists of a high-grade metamorphic mèlange where micaschists and amphibolites are found. New 40Ar-39Ar datings obtained through different extraction techniques on mineral phases with different crystal-chemical features, indicate that the Devrekani unit preserves the record of lowermost Late Jurassic amphibolite-facies metamorphism originated during the convergence-related processes leading to the closure of a Neotethyan oceanic basin. Coeval events have also been recognized in the Dinaric- Hellenic belt where the ophiolites are regarded as the remnants of the Neotethyan Vardar oceanic basin. The data provided in this paper strongly suggest that Intrapontide Suture Zone can be regarded as the most suitable candidate for the continuation of the Vardar oceanic basin in Turkey

The Arkot Dağ Mélange in Araç area, central Turkey: Evidence of its origin within the geodynamic evolution of the Intra-Pontide suture zone.

In northern Turkey, the IntraPontide suture zone is represented by 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 IntraPontide domain, whose geodynamic history is still matter of debate. Along the Akpinar-Araç-Bayramoren geotraverse, located in central Turkey, an ophiolite-bearing mélange known as Arkot Dağ Mélange, is well exposed along the IntraPontide suture zone. The Arkot Dağ Mélange, that plays a key role in the interpretation of the geodynamic history of the IntraPontide domain, can be described as a Late Santonian chaotic sedimentary deposits consisting of an up to 1000 m thick succession of slide-blocks, with different size and lithology, enclosed in a sedimentary matrix consisting of shales, coarse-grained arenites, pebbly-mudstones and pebbly-sandstones. The slide-blocks, from few meters to some hectometers in size, are represented by metamorphic rocks (mainly micaschists and gneisses), by ophiolites (peridotites, gabbros, IAT and BABB basalts and cherts) and by sedimentary rocks (cherts, neritic and pelagic limestones, marly-limestones 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 Middle Trias to Late Cretaceous, whereas the fossils found in the limestones indicate Late Jurassic to Early Cretaceous ages. The matrix of the Arkot Dağ Mélange, even if unaffected by metamorphism, shows deformations represented by multiple, m-thick cataclastic shear zones, recognized at the boundaries of the mélange slices or inside them. According to its features, the source area of the Arkot Dağ Mélange was probably represented by a 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 IntraPontide domain was characterized by an oceanic basin opened at least in the Early Jurassic. The opening of the IntraPontide oceanic basin was followed by the development of a subduction zone with a consequent opening of suprasubduction oceanic basin in the Middle Jurassic – Early Cretaceous time span. 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 in age