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Metamorphic evolution of the Saka Unit (Central Pontides, Northern Turkey): new implications for the Mesozoic convergence-related processes in the Intra-Pontide suture zone
Full text linkIn Northern Turkey, the Intra-Pontide suture (IPS) zone represents an east-west trending belt of deformed and/or metamorphic rocks bounded by the Istanbul-Zonguldak Terrane (IZ) to the north and the Sakarya Composite Terrane (SK) to the south (e.g. Göncüoğlu et al., 1997). Despite its importance for the geodynamics reconstructions of the Black Sea and Eastern Mediterranean areas during the Mesozoic, the IPS zone has been poorly investigated; only recently the role of its metamorphic units during the syn-collisional evolution was explored (Marroni et al., 2014; Frassi et al., 2016; 2017)
In order to provide new insights on the Mesozoic-Tertiary geodynamic reconstruction of the southern margin of the Laurasia, we present new data from the Saka Unit from the eastern portion of the IPS. Using a multidisciplinary approach that includes lithological, structural, metamorphic and petrographic investigations, we constrained the P-T-t path during the Mesozoic subduction and consequent exhumation and accretion to Laurasia. Following the determination of mesostructures, we analysed a series of samples of metabasite and metapelite. Mineral chemistry of phases at equilibrium in the pervasive S2 foliation was determined, and PT determinations were performed through pseudosection calculation of three samples. PT conditions are within the epidote-amphibolite facies, with pressures of 1.2 ± 0.15 GPa and Temperatures 600 ± 50 °C, thus higher than those determined previously, suggesting that S2 could be a composite foliation where a progressive evolution acquired during onset of exhumation was recorded. A comparison with the PT evolutions of the nearby Daday and Domuz-Dag units, shows that they record lower T at D2 at different ages, and that the pre-D2 conditions, when they are preserved, are different in the three units.
References
Frassi C., Göncüoğlu M.C., Marroni M., Pandolfi L., Ruffini L. Ellero A., Ottria G. & Sayit K. 2016. The Intra-Pontide Suture Zone in the Tosya-Kastamonu area, Northern Turkey. J. of Maps. 12, 211-219
Frassi, C, Marroni, M., Pandolfi, L., Göncüoğlu, M. C., Ellero, A., Ottria, G., Sayit, K., McDonald, C.S., Balestrieri, M.L. & Malasoma, A. 2018. Burial and exhumation history of the Daday Unit (Central Pontides, Turkey): implications for the closure of the Intra-Pontide oceanic basin. Geol. Mag., 155, 356-376.
Göncüoğlu, M. C., Marroni, M., Sayit, K., Tekin, U. K., Ottria, G., Pandolfi, L. & Ellero, A., 2012. The Ayli Dag ophiolite sequence (central-northern Turkey): A fragment of middle Jurassic oceanic lithosphere within the Intra-Pontide suture zone. Ofioliti, 37, 77–91.
Marroni, M., Frassi, C., Göncüoğlu, C. M., Di Vincenzo, G., Pandolfi, L., Rebay, G., Ellero, A. & Ottria, G. 2014. Late Jurassic amphibolite-facies metamorphism in the Intra-Pontide Suture Zone (Turkey): an eastward extension of the Vardar Ocean from the Balkans into Anatolia? J. Geol. Soc., 171, 605–608
Burial and exhumation history of the Daday Unit (Central Pontides, Turkey)
Full text linkIn northern Turkey, the Intra-Pontide suture (IPS) zone divides the Istanbul-Zonguldak and the continental terranes (Göncüoğlu et al. 2000). It consists of an assemblage of several oceanic and continental units characterized by different age, metamorphic imprint and deformation history. In the Central Pontides, the IPS zone is a pre- late Paleocene imbricate stack where an ophiolite unit (Ayli Dağ ophiolite Unit) and an ophiolite-bearing mèlange (Arkot Dağ Mèlange), derived from a NeoTethyan oceanic basin (the Intra-Pontide oceanic basin: Göncüoğlu et al. 2008) are associated with four metamorphic units (i.e. Saka, Emirkoy, Daday and Domuz Dağ Unit) (Frassi et al., 2016).
In the Daday Massif, the Daday Unit is an assemblage of tectonic slices having a monogenic composition (micaschists, paragneisses, marbles, actinolite-bearing schists and quarzites) derived from a supra-subduction oceanic crust (Sayit et al., 2016) and related deep-sea sediments of Middle Jurassic age. Structural analyses, P-T estimates and Ar-Ar dating allow to elaborate a P-T-t-d path (Frassi et al., 2017) in which the D1 phase was acquired during the Late Jurassic by tectonic underplating at 35-42 km of depth. The following D2, D3 and D4 phases produced the exhumation up to shallower structural levels. The high geothermal gradient detected during the D2 phase indicates that the Daday Units was exhumed during a continent arc collisional setting. The structure of the IPS zone is unconformably sealed by the upper Paleocene - Eocene deposits and lately reworked by the North Anatolian Fault Zone (D5).
Göncüoğlu M.C., Turhan N., Senturk K., Ozcan A. & Uysal S. 2000. A geotraverse across NW Turkey: tectonic units of the Central Sakarya region and their tectonic evolution. In Tectonics and magmatism in Turkey and the surrounding area (eds E. Bozkurt, J. Winchester & J.A. Piper), Geol. Soc. Lond. Special Publ. 173, 139-161.
Göncüoğlu M.C., Gürsu S., Tekin U.K. & Koksal S. 2008. New data on the evolution of the Neotethyan oceanic branches in Turkey: Late Jurassic ridge spreading in the Intra-Pontide branch. Ofioliti, 33, 153–164.
Frassi C., Göncüoğlu M.C., Marroni M., Pandolfi L., Ruffini L. Ellero A., Ottria G. & Sayit K. 2016. The Intra-Pontide Suture Zone in the Tosya-Kastamonu area, Northern Turkey. J. of Maps, 12, 211-219.
Frassi C., Marroni M., Pandolfi L., Göncüoğlu M.C., Ellero A., Ottria G., Sayit K., McDonald C.S., Balestrieri M.L., Malasoma A., Crowley Q.G. 2017. Burial and exhumation history of the Daday Unit (Central Pontides, Turkey): implications for the closure of the Intra-Pontide oceanic basin. Geol. Mag., doi10.1017/S0016756817000176.
Sayit K., Marroni M., Göncüoğlu M.C., Pandolfi L., Ellero A., Ottri, G. & Frassi C. 2016. Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide suture zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys. Intern. J. Earth Sciences, 105, 39–64
Late Cretaceous arc magmatism in the southern Central Pontides: constraints for the closure of the northern Neotethyan branches.
Full text linkIn the southern Central Pontides in northern Turkey the remnants of two Neotethyan oceanic basins, currently represented by the Intra-Pontide and the Izmir-Ankara-Erzincan sutures, and the interposing continental microplate (i.e., the Sakarya Composite Terrane) are completely dissected by the North Anatolian Shear Zone (NASZ). Within the resulting kilometre-scale, strike-slip fault-bounded blocks, several Late Cretaceous arc-type magmatic units have been detected. In this paper, we present new geochemical data from one of these magmatic units, the Yerkuyu Unit, that forms an ENE-WSW trending 30-km long and 10-km wide lens-shaped body surrounded by the splays of the NASZ. The studied igneous lithologies have a subduction-related magmatic geochemical signature matching with another lozenge-shaped magmatic block: Tafano Unit. However, the tectonomagmatic characterization indicates that the Tafano Unit magmatism developed within a continental arc tectonic setting, while the volcanic rocks of the Yerkuyu Unit derived from oceanic arc magmatism. This finding indicates that the subducted oceanic lithosphere of the İzmir-Ankara-Erzincan branch of the Neotethys Ocean produced oceanic volcanic arcs close to the subduction zone (i.e., the Yerkuyu Unit) and beneath the Sakarya continental microplate (i.e.,
the Tafano Unit)
The Ayli Dağ ophiolite sequence (central-northern Turkey): a fragment of Middle Jurassic oceanic lithosphere within the Intra-Pontide suture zone
No full textThe 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
Paleothetys and Neothetys suture zones in northern Turkey:evidences from Daday-Arac-Kursunlu geotraverse
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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
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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