1,721,012 research outputs found
REE distribution in Upper Cretaceous calc-alkaline and shoshonitic volcanic rocks from Eastern Srednogorie (Bulgaria)
No full textLa, Ce, Nd, Sm, Eu, Gd, Tb, Yb, Lu, Cr and Sc contents have been determined by instrumental neutron activation analyses (INAA) in high-K calc-alkaline and shoshonitic volcanic rocks from the Upper Cretaceous volcanic belt of Eastern Srednogorie (Bulgaria). The high-K calc-alkaline rocks are characterized by fractionated LREE and unfractioned HREE patterns. The shoshonitic rocks have higher overall REE abundance, higher La/Yb ratio and they display a variable degree of HREE fractionation. The absolute abundance of REE and their distribution patterns are consistent with the hypothesis that both calc-alkaline and shoshonitic magmas were derived by partial melting of mantle enriched in LREE. The flat HREE patterns of calc-alkaline rocks indicate that they represent magma formed by melting of spinel peridotite. The variable HREE fractionation of shoshonites can be explained by non-modal melting of a garnet peridotite with differing proportions of garnet in the residuum. The low Ni, Cr and Sc contents of the analyzed rocks indicate that the primary shoshonitic and calc-alkaline magmas underwent fractionation involving removal of olivine and some spinel and pyroxene during their ascent to the surface
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
Magmatic enclaves distribution within the Khaggiar lava dome (Pantelleria, Italy): implication for magma chamber dynamics and eruption
No full textA study integrating spatial distribution observations, petrographical and geochemical features of magma mixing structures occurring inside the Khaggtar endogenous lava dome outcropping on the island of Pantelleria (Italy) reveals that the intensity of magmatic interaction increases from the outer to the more internal layers of the dome. Based on these observations a model for a silicic magma chamber evolution, in which magmatic interaction processes occur, is advanced. During a first stage the magma chamber is characterized by the onset of plume like dynamics induced by the hotter and more volatiles-rich mafic magma leading to the eruption of the external layers of the dome. In this physical regime the magmatic interaction processes are limited by rheological contrasts and low velocity of ascending magma. Successively fluid dynamics and thermal perturbations induce more intense magmatic interaction processes leading to the eruption of the internal parts of the dome
Geodynamic evolution of the Aegean: constraints from the Plio-Pleistocene volcanism of the Volos-Evia area
No full textThe Plio-Pleistocene lava flows and domes of the Volos-Evia area were erupted between 3.4 and 0.5 Ma ago on the western continuation of the North Anatolian Fault, in a back-arc position with respect to the active arc. They are mainly high-K calc-alkaline trachyandesites. Based on their Sr-Nd-Pb isotopic compositions, the mantle source of the Volos-Evia area lavas is similar to that of a large volcanic belt that developed north of the Pelagonian-Attic-Cycladic-Menderes massifs, encompassing a 35 Ma timespan and widespread over a large area from NW Greece Macedonia to the Aegean western Anatolia. In contrast, southern Aegean arc rocks have a similar subduction fingerprint but distinctly lower Sr and higher Nd isotopic compositions. The geochemical and isotopic differences between southern and northern Aegean rocks may be ascribed to the different nature of the mantle wedge: depleted asthenosphere under the the southern Aegean, and lithosphere northward. The lack of an asthenospheric mantle wedge below the northern Aegean fits with the hypothesis of an almost horizontal subduction of the African slab. In the mantle reference frame the African slab is moving out of the mantle, and a slab-driven suction flow of the underlying mantle may be responsible for the recent development of a thin asthenospheric layer in the southern Aegean mantle wedge
South Aegean volcanic arc: Geochemical variations and geotectonic implications
No full textThe Aegean volcanic arc is one of the most important geological structure of the Mediterranean area. It is a belt of volcanic centers consisting of products ranging from basaltic, andesitic, dacitic to rhyolitic in composition, all of them displaying a typical calc-alkaline chemical character. The most abundant rock types are represented by andesites and dacites. Minor amounts of basalts and rhyolites occur mainly in the central-eastern sector of the arc. The REE, Rb, Sr, Ba, Th, Ta, Hf, Zr, Ni, Co, V and Cr abundances determined in 27 representative samples from different centers suggest that: 1) the intermediate and acidic terms are products of crystal/liquid fractionation processes starting from basic parent magmas: 2) large variations in incompatible elements occur in the most basic samples that are interpreted as evidence for heterogeneously LIL element-enriched mantle source; 3) plagioclase played a role in the evolution of the volcanic centers of the eastern and central arc different from that played in the volcanoes of the western sector. Along the arc, the differences in the distribution of lithological types, in the volumes of erupted material, in the volcanological characteristics of the different centers as well as in the patterns of trace element distribution in the volcanites are considered to be connected with the prevailing tectonic regime affecting the various sectors of the arc
Nature and geodynamic significance of the Miocene dyke swarm in North Yemen (YAR)
No full textThe results of mineralogical, geochemical and geochronological studies carried out on dyke swarms outcropping between the coastal plain (Tihama) and the western border of the highland in the Yemen Arab Republic (YAR) are reported. On the basis of field relations the dyke swarms have been grouped into a younger association (TDS) and an older one (ATD). The younger Tihama dyke swarm (TDS) represents the southern prolongation of the Tertiary Tihama-Asir Complex, which is well developed in the Jizan Region of Saudi Arabia (Coleman et al., 1979). K/ Ar ages obtained on TDS samples range from 20 to 23 m.y.; considerably higher ages (54-75 m.y.) were established for the ATD samples. Chemical and mineralogical data indicate that the Miocene TDS are transitional in nature and similar to basaltic dykes related to the Trap Series (PBD). A MORB-type magmatism can be excluded on the basis of the distribution of hygromagmatophile elements. Geochemical variations within the TDS and PBD samples can be related to different degrees of partial melting of a garnet-bearing mantle source. Our data agree well with the interpretation of the TDS magmatism as related to a continental rifting episode (Arno et al., 1980) closely following the Plateau magmatism, better than an early oceanization event in the evolution of the Red Sea system
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