1,720,971 research outputs found
Caractérisation et interprétation de l'enregistrement métamorphique afin de définir les processus d'enfoncement et d'exhumation dans les orogènes (exemple du Massif de Bohême)
Full text linkA range of petrological and structural works carried in the Bohemian Massif largely contributed to establishment of the models of burial and exhumation mechanisms in the external and internal orogenic domains. The eastern margin of the Bohemian Massif is formed by the Brunia microcontinent that was underthrust below the westerly orogenic root of the Moldanubian-Lugian domain. The underthrusting produced in the Brunia basement approximately 50 kilometers wide zone of deformation and metamorphism, called the Moravo-Silesian zone. The Lugian-Moldanubian internal domain forms the core of the orogen and it is characterized by presence of high grade rocks, such as high-pressure felsic granulites, eclogites, garnetiferous and spinel peridotites and migmatites, low-grade rocks and magmatic bodies, preserving a complicated structural and metamorphic history of the deep orogenic root. The presence of high-pressure and low-temperature rocks in the Saxothuringian domain to the west is interpreted as a remnant of a subduction zone.At the south-eastern margin of the Bohemian Massif, two large tectonic windows of the Moravian zone are emerging through a migmatitic nappe of the Moldanubian domain. We have shown that Barrovian prograde metamorphism in these tectonic windows, ranging from chlorite to kyanite zone, is related to continental underthrusting below the orogenic root, and retrograde P−T evolution to nappe stacking and inversion of metamorphic isograds. Complex pattern of isograds that obliquely crosscut tectonic boundaries in a present section is interpreted as a result of late folding of crustal sheets. In the northeastern margin of the Bohemian Massif occurs the Silesian domain, characterized by Barrovian and Buchan type metamorphism. In the kyanite zone, we described eclogite lenses in the metapelite matrix and demonstrated their separate metamorphic histories, indicating mixing of rocks at the tip of the underthrust crustal wedge. Further east, based on chloritoid-staurolite equilibria, we distinguished a high geothermal gradient during prograde metamorphism that is probably associated with inherited heat from a Devonian intracontinental rift, which can also explain the development of Buchan-type metamorphism. In the north-eastern part of the contact between the Lugian domain and the Silesian zone occurs the Staré Město belt, composed of granodiorite, layered amphibolite, metagabbro and serpentinite. Combined structural and geochronological study revealed a structural unconformity between subhorizontal fabrics in the granulites and amphibolites dated at 500 Ma and fabrics of the granodiorite sheet that are parallel to steep foliations reworking the gabbros, dated at 340 Ma on zircon. This allowed distinguishing relics of subhorizontal Ordovician fabrics for the first time in the whole Variscan European belt and interpreting these lithologies as a Cambro-Ordovician intracontinental rift. The Variscan tectono-metamorphic event is manifested by syn-convergent intrusion of the Carboniferous granodiorite sill and by HT-MP compressional deformation of the gabbros that produces foliations parallel with the structure of the granodiorite. Based on these criteria we interpreted the Staré Město belt as a preserved example of an intracontinental Cambro-Ordovician rift that has been reactivated and exhumed during the Variscan orogeny.The studies in the Moldanubian-Lugian orogenic root domain shown that HP conditions are connected with early shallow-dipping fabric, and that HP rocks are exhumed during vertical crustal-scale folding that leads to extrusion of HP rocks along vertical channels. This produces a pattern of large-scale “synforms” cored commonly by HP granulites and large-scale “antiforms” dominated by metasediments. This model of crustal-scale folding and vertical extrusion is proposed as a possible major exhumation mechanism of HP rocks in hot orogens and a potential role of gravity in this process is discussed.Studies of HP granulites from the Moldanubian orogenic root pointed to a problem of interpretation of equilibrium metamorphic assemblages in high-grade rocks and consequently to a problem of determining the peak metamorphic conditions. Classic combination of high-grossular garnet and high-temperature ternary feldspar led to estimation of metamorphic conditions to >1000 °C and 18−28 kbar. Microstructural analysis has shown that mafic granulites contain several generations of garnet, and that ternary feldspar and high-grossular garnet belong to two distinct episodes, and cannot be combined to infer metamorphic conditions. Detailed study of a Morb-type eclogite shows unusually hot prograde conditions that are interpreted as a result of Devonian thermal rejuvenation of continental back arc domain that was responsible for softening of a future orogenic root domain. The steep foliations in the Lugian-Moldanubian domains are to a different degree reworked by shallow-dipping fabrics. At the eastern margin of the Bohemian Massif, kilometre-scale crustal boudins of HP granulites and eclogites enclosed in migmatites are present. The HP lenses experienced first burial to 20 kbar and than exhumation to 10–7 kbar and the mid-crustal rocks revealed increase of pressure to 10 kbar. All the system was re-equilibrated at 7 kbar where the high pressure rocks cooled while mid-crustal rocks became heated. We interpreted this metamorphic pattern as a result of vertically extruded lower-crustal rocks into the middle crust, then travelling as fragments in a subhorizontal hot migmatitic channel above a continental margin. This is interpreted as a continental channel flow domain that developed in the orogenic root above the underthrust Brunia basement, and which is eroded along its total width of 120 km and length of 200 km. A detailed petrological, microstructural and geochemical study of migmatites in the well developed shallow-dipping fabrics of the Moldanubian orogenic root allowed discussion about the evolution of the “channel flow” domain and about the melt migration in the crust. Four migmatite types collected in the steep and shallow-dipping structures show decreasing P−T conditions, indicating exhumation and cooling. Progressive changes in whole rock composition are interpreted in terms of open system behavior, caused by crustal-scale melt infiltration operating at grain boundaries. The mineral-equilibria modelling shown that such “metasomatism” by cirulating melt may cause the observed whole rock composition changes and was suggested as a new mechanism of melt transport in the crust. In order to discuss the effects of melting on large-scale rheology during orogenic root deformations, pseudosection modeling of melt quantities was done to evaluate deformation mechanisms in various high-grade orthogneisses. Simultaneous metamorphic and structural studies of lower- and middle crustal rocks permitted correlation of retrograde and very rarely preserved prograde metamorphic fabrics of the middle and lower orogenic crust, which started discussion of coupled and uncoupled mechanisms of burial and exhumation in the two crustal levels, but also with respect to the upper and lower plate
Thermomechanical evolution of collisional boundary during variscan convergence - eastern margin of the Bohemian massif.
No full textThe first part of the work deals with metamorphic and structural evolution of the Thaya window emerging through Moldanubian bloc below hot Variscan orogenic root associated with development of Barrovian metamorphic zonation was studied in detail. This research was completed by interpretation of dome-like structure of the Thaya window in terms of large-scale buckling of imbricated nappe sequence. The second part deals with the structural, petrological and geochronological study of the major collisional boundary between the Silesian block and westerly lying orogenic root - the Lugian domain.Available from STL, Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
