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The Arkot Dag Melange Central Turkey: Evidence for the geodynamic evolution of the Intra-Pontide Suture zone.
No full textThe geological setting of Turkey (figure 1)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 (figure 2). 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 (figure 3)
The intra-pontide suture zone, northern turkey: an updated view
No full textThe tectonic setting of Turkey can be described as a puzzle where several continental terranes are boubded by ophiolite-bearing suture zones (Sengör and Yılmaz, 1981). Among these suture zones, the Intra-Pontide Suture Zone (IPSZ) is probably the less known one. The IPSZ is an east-west trending, suture zone that stretches for about 600 km dividing the Istanbul-Zonguldak terrane, in the north, from the Sakarya terrane, in the south. This suture zone is well exposed along the Daday-Arac-Kursunlu and Tosya – Emirköy geotraverses in northern-central Turkey where its tectonic features can be fully reconstructed.
The study of the two geotraverses indicates that the imbricate stack of the IPSZ consists of several distinct tectonic units, all characterized by the occurrence of mafic rocks. These units include the Aylı Dağ ophiolite Unit, the Arkot Dağ Mèlange and three metamorphic units (the Daday, Domuz Dağ and Devrekani Units). This imbricate stack is probably the result of several episodes of out-of-sequence thrusts that affected the whole IPSZ.
The Aylı Dağ Unit (Göncüoglu et al., 2012) includes an about 5 km-thick, not metamorphic ophiolite sequence topped by the middle Bathonian to early Callovian radiolarian cherts. In addition, a metamorphic sole is present at the base of the serpentinized peridotites. The geochemical evaluation of pillow-basalts and dykes highlights subduction-related characteristics, similar to IAT- and BABB-type lavas generated in a back-arc oceanic basin.
The Arkot Dağ Mèlange (Göncüoglu et al., 2014) consists of an assemblage of slide-blocks, with different size and lithology, enclosed in a Late Santonian sedimentary matrix. The slide-blocks also include ophiolitic lithologies, mainly represented by basalts, but gabbros and peridotites are also found. The slide-blocks of basalts display affinites to IAT- and BABB-type magmas, signifying the involvement of subduction component, whereas no MORB-like basalt have been found. The age of the radiolarian chert blocks ranges between Middle-Late Triassic (Tekin et al., 2012) to Late Cretaceous.
The Daday unit (cf. Martin Unit by Okay et al., 2013) is characterized by metasedimentary and metabasic slices deformed under low-grade blueschist metamorphic facies conditions (in the Early Cretaceous (ca. 110 Ma; Rb–Sr method on mica; Okay et al., 2012). The metasedimentary rocks include mica-bearing schists, fine-grained marbles and quartzites, which inclue detritial zircons mainly derived from an Early Carboniferous felsic magmatic source. The metabasic lithologies, on the other hand, comprise actinolite-bearing schists and Na-amphibole-bearing varieties possibly derived from basaltic and gabbroic protoliths. The metabasic rocks have a wide range of chemical compositions, displaying N-MORB-, E-MORB-, OIB- BABB- and IAT-type signatures.
The Devrekani Unit is represented by an assemblage of amphibolites, marbles and micaschists showing a metamorphic climax developed under upper amphibolite facies in the Late Jurassic time (ca. 163 Ma; mica Ar-Ar geochronology; Marroni et al., 2014). Amphibolites recorded pressures of ~0.80–0.99 GPa and temperatures of ~600°C. Comparable P-T conditions were obtained for the micaschist (P ~0.86 GPa and T ~ 640°C)(Marroni et al., 2014). The amphibolites display E-MORB-, OIB- BABB- and IAT-type signatures.
The Domuz Dağ Unit is in turn mainly represented by eclogites and amphibolites with minor micaschist, gneisses and marbles deformed under eclogite facies metamorphism (490°C and 1,7 Gpa; Okay et al., 2006) of Early Cretaceous age (ca. 105 Ma; mica Ar-Ar geochronology; Okay et al., 2006).
The three metamorphic units, referred by Okay et al (2006; 2013) as the Central Pontide Supercomplex, represent subduction-related mèlanges developed at different depths in a subduction zone during the Middle Jurassic-Early Cretaceous time span. This subduction zone probably developed since Early Jurassic in the Intra-Pontide oceanic basin (IPOB) as result of the convergence between Istanbul-Zonguldak and Sakarya continental margins. The occurrence of calc-alkaline volcanic rocks of Late Cretaceous in the sedimentary cover of Istanbul-Zonguldak terrane strongly suggests that the subduction was north-dipping. In this framework, the ophiolites from the Aylı Dağ Unit can be interpreted as the remnants of a Late Jurassic back-arc basin opened above this north-dipping subduction. As result of the continuous convergence, the back-arc basin started to close in the Late Cretaceous time leading to the obduction of the Aylı Dağ ophiolites onto the Sakarya continental margin. During the obduction, the Arkot Dağ Mèlange originated. In the Late Paleocene, the final closure of the IPOB led to development of the imbricate stack of tectonic units that characterizes the IPSZ, whose structures are sealed by the Early Eocene shallow-water deposits
Analysis of the North Anatolian Shear Zone in Central Pontides (Northern Turkey): insight for geometries and kinematics of deformation structures in a transpressional zone.
Full text linkThe western part of the North Anatolian Shear Zone at the southern boundary of the Central Pontides in Turkey, was investigated in the Kurşunlu-Araç area by means of a geological-structural field study. In this area the North Anatolian Shear Zone results in a transpressional deformation zone that extends between two master faults striking parallel to the main shear direction. The main systems of structures identified in the deformation zone appear to be oriented parallel to the directions predicted by Riedel theoretical model. Nevertheless, the strain partitioning is more complicated than predicted by theory. The structural analysis suggests a polyphase deformation characterized by a steady component of transcurrence associated with alternance of compression and extension. Along each of theoretical directions the combination of double verging structures can be observed, with folds and thrust surfaces root into high-angle shear zones, according to flower-type geometries. The discrepancies of directions, kinematics and geometries from theoretical models are due to transpressive and/or transtensive nature of the deformation. According to the observed outcropping structures, we propose a conceptual model for the North Anatolian Shear Zone, interpreting it as a crustal-scale positive flower structure
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The Intra-Pontide ophiolites in Northern Turkey revisited: From birth to death of a Neotethyan oceanic domain
Full text linkThe Anatolian peninsula is a key location to study the central portion of the Neotethys Ocean(s) and to understand how its western and eastern branches were connected. One of the lesser known branches of the Mesozoic ocean(s) is preserved in the northern ophiolite suture zone exposed in Turkey, namely, the Intra-Pontide suture zone. It is located between the Sakarya terrane and the Eurasian margin (i.e., Istanbul-Zonguldak terrane) and consists of several metamorphic and non-metamorphic units containing ophiolites produced in supra-subduction settings from the Late Triassic to the Early Cretaceous. Ophiolites preserved in the metamorphic units recorded pervasive deformations and peak metamorphic conditions ranging from blueschist to eclogite facies. In the non- metamorphic units, the complete oceanic crust sequence is preserved in tectonic units or as olistoliths in sedi- mentary m elanges. Geochemical, structural, metamorphic and geochronological investigations performed on ophiolite-bearing units allowed the formulation of a new geodynamic model of the entire “life” of the Intra- Pontide oceanic basin(s). The reconstruction starts with the opening of the Intra-Pontide oceanic basins during the Late Triassic between the Sakarya and Istanbul-Zonguldak continental microplates and ends with its closure caused by two different subductions events that occurred during the upper Early Jurassic and Middle Jurassic. The continental collision between the Sakarya continental microplate and the Eurasian margin developed from the upper Early Cretaceous to the Palaeocene. The presented reconstruction is an alternative model to explain the complex and articulate geodynamic evolution that characterizes the southern margin of Eurasia during the Mesozoic era
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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