1,720,964 research outputs found
Apatite fission-track data for the Miocene Arabia-Eurasia collision
No full textThe collision between the Eurasian and Arabian plates along the 2400-km-long Bitlis-Zagros thrust zone isolated the Mediterranean from the Indian Ocean and has been linked to extension of the Aegean, rifting of the Red Sea, and the formation of the North and East Anatolian fault systems. However, the timing of the collision is poorly constrained, and estimates range from Late Cretaceous to late Miocene. Here, we report the fi rst apatite fissiontrack
(AFT) ages from the Bitlis-Zagros thrust zone. The AFT samples are distributed over the 450 km length of the Bitlis thrust zone in southeast Turkey and include metamorphic
rocks and Eocene sandstones. Despite the disparate lithology and large distance, the AFT ages point consistently to exhumation between 18 and 13 Ma. The AFT ages, along with a critical appraisal of regional stratigraphy, indicate that the last oceanic lithosphere between the Arabian and Eurasian plates was consumed by the early Miocene (ca. 20 Ma). The results imply that Aegean extension predated the Arabia-Eurasia collision
An oligocene ductile strike-slip shear zone: The Uludag Massif, northwest Turkey - Implications for the westward translation of Anatolia
No full textThe Uludağ Massif in northwest Turkey represents an exhumed segment of an Oligocene ductile strike-slip shear zone that is over 225 km long and has ~100 km of right-lateral strike-slip displacement. It forms a faultbounded mountain of amphibolite-facies gneiss and intrusive Oligocene granites. A shear-zone origin for the Uludağ Massif is indicated by: (1) its location at the tip of the active Eskişehir oblique-slip fault, (2) pervasive subhorizontal mineral lineation in the gneisses with a right-lateral sense of slip, (3) foliation with a consistent strike, (4) the presence of a subvertical synkinematic intrusion, and (5) the alignment of the Eskişehir fault, synkinematic metagranite, and the strike of the foliation and mineral lineation. The shear zone nucleated in amphibolite-facies gneisses at peak pressure-temperature (P-T) conditions of 7.0 kbar and 670 °C, and it preserves Eocene (49 Ma) and Oligocene (36–30 Ma) Rb/Sr muscovite and biotite cooling ages. The shear zone was active during the latest Eocene and Oligocene (38–27 Ma), as shown by the crystallization and cooling ages from synkinematic granite. A 27 Ma postkinematic granite marks the termination of shear-zone activity. The 20–21 Ma apatite fi ssion-track (AFT) ages indicate rapid exhumation during the early Miocene. A 14 Ma AFT age from an Uludağ gneiss clast deposited in a neighboring Neogene basin shows that the shear zone was on the surface by the late Miocene. Results of this study indicate that during the Oligocene, crustal-scale right-lateral strikeslip faults were transporting crustal fragments from Anatolia into the north-south– extending Aegean; this implies that the westward translation of Turkey, related to the Hellenic slab suction, started earlier than the Miocene Arabia-Eurasia collision
Thermal Evolution of the Permo-Triassic Karakaya Subduction-accretion Complex between the Biga Peninsula and the Tokat Massif (Anatolia)
No full textThe results of the combined application of a series of analytical methods (clay mineralogy, vitrinite reflectance, Raman microspectroscopy) placed tight constraints on the thermal evolution of the Karakaya Complex of northern Anatolia, a mostly Permo−Triassic subduction-accretion complex resulting from the progressive closure of the Palaeotethys. The thermal evolution of the Karakaya Complex is the result of Permian−Triassic subductionaccretion processes, and was not significantly affected by later Alpine-age tectonism, as shown by Liassic shallow-water siliciclastic and carbonate deposits overlying unconformably the Karakaya Complex which did not undergo any significant burial. The Lower Karakaya Complex, comprising metabasite and subordinate marble and phyllite, experienced maximum temperatures ranging from 340 to 497° C, in agreement with independently determined thermobarometric reconstructions. The entire Upper Karakaya Complex, previously considered unmetamorphosed or slightly metamorphosed, was affected by zeolite to lower greenschist facies metamorphism (120−376° C). The coherent results of this study show that Raman thermometry has great potential for palaeotemperature determination at low temperature ranges (200−350° C)
A precursor of the North Anatolian Fault in the Marmara Sea region
No full textApatite (U-Th)/He and fission-track analyses of both basement and sedimentary cover samples collected around the Marmara Sea point to the existence of a system of major E–W-trending structural discontinuities active at least from the Late Oligocene. In the Early Pliocene, inception of the present-day North Anatolian Fault (NAF) system in the Marmara region occurred by reactivation of these older tectonic structures. This is particularly evident across the Ganos fault in southern Thrace, as exhumation south of it occurred during the latest Oligocene and north of it during the mid-Miocene. In this area, large tectonic structures long interpreted as the results of Plio-Quaternary NAF-related transpressional deformation (i.e. the Ganos monocline, the Korudag ̆ anticline, and the Gelibolu folds) were in fact produced during the Late Oligocene – Early Miocene. The overall lack of significant (U-Th)/He age differences across the NAF indicates that the Early Pliocene inception of strike–slip motion in the Marmara region represents a relatively minor episode. At the scale of the entire Marmara region, the geographic pattern of exhumation ages shown in this study results instead from the complex superposition of older tectonic events including: (i) the amalgamation of Sakarya and Anatolide–Tauride terranes and (ii) Aegean-related extension
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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