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Origin of 'ultra' - rocks
No full textAfter decades of studies, it seems generally accepted that the Earth’s lithospheric mantle cannot be characterized by a homogeneous composition, either from a mineralogical, geochemical and isotopic point of view. It would rather be affected by re-fertilization and metasomatic processes. Indeed, the constant subduction and the recycling of crustal material, either continental and oceanic, triggered by the Plate Tectonics, would cause a local enrichment of the previously depleted peridotitic mantle (Stracke, 2021). The upper mantle heterogeneity is clearly reflected in the variegated igneous lithologies that crop out on the surface of our planet, which show a wide chemical compositional range, as their formation would be related to partial melting events, resulting after a long interaction and assimilation among these different lithologies (Stracke, 2021). In particular, partial melting of veined lithospheric mantle sources may explain the presence of exotic liquids, whose formation cannot be ascribed to a classical four-phase mantle assemblage (olivine, orthopyroxene, clinopyroxene, spinel or garnet; Foley, 1992a). Indeed, Davis et al. (2011) demonstrated that low degree of partial melting of a lherzolite source, which did not undergo any metasomatic events, cannot lead to the generation of melts with total alkalis content higher than 3-4 wt%.
Even if the rocks produced by these exotic melts have always attracted the attention of the scientific community, today many rare lithologies represent matter of discussion, as their mantle sources, their petrogenesis, and even their classification and nomenclature, are only poorly constrained. A detailed and systematic study of these debated rocks might allow to reach a better knowledge of the mantle conditions, i.e., its thermal and chemical state, and of the processes responsible for their formation.
The goal of this thesis is to gain a deeper understanding of different groups of exotic and peculiar lithologies, mainly ultrabasic to basic, ultramafic and/or ultra-alkaline in composition, through a multidisciplinary investigation, based on petrographic, mineral chemical (SEM-EMP analyses), whole-rock geochemical data, together with isotopic analyses (either on radiogenic systematics, as Sr-Nd-P, plus conventional, as C and O, and unconventional stable isotopes, as B) and petrological experiments at different pressure (from 1 to 5 GPa) and temperature (from sub-solidus to supra-liquidus T) conditions.
The three main rock-types that have been accurately analysed are kamafugites, carbonatites and ultramafic lamprophyres. In particular, kamafugite samples come from south-eastern Brazil (Alto Paranaiba Igneous Province), central Italy (Intra-Apennine Province) and Uganda (Toro Ankole Volcanic Province); carbonatites from Uganda (Toro Ankole Volcanic Province) and from western Germany (Eifel Volcanic Field); and ultramafic lamprophyres are from eastern Antarctica (Beaver Lake). Together with these samples, minor melilitites (Montefiascone Volcanic Complex, central Italy), leucitite and nephelinite (Toro Ankole Volcanic Province) have been also studied.
Exotic samples have been collected from many sampling sites found in different geodynamic environments, and they have been chosen with variable petrographic, geochemical and isotopic characteristics, as we believe that a detailed comparison would highlight similarities and differences helpful to infer the reason of such heterogeneities, but also to better constrain the mantle sources and processes involved in their formation.
All the analyses that have been carried out highlight the exotic nature of the samples. Petrography and mineral chemistry point out the presence of rare phases, as primary carbonate (found not only in the carbonatite samples, but also in the groundmass of kamafugites, ultramafic lamprophyres and melilitites), kalsilite, melilite and perovskite (diffuse in kamafugite, ultramafic lamprophyres and melilitite samples). Whole-rock geochemistry indicates strongly ultrabasic (carbonatites), ultrabasic (Ugandan and Brazilian kamafugite, ultramafic lamprophyres) and basic (Italian kamafugites) compositions, mostly characterized by a potassic or ultrapotassic affinity (K2O up to 8.36 wt% in Italian kamafugites, K2O/Na2O < 34). Moreover, all samples show a variable, but often marked, enrichment in trace elements. Also the isotopic data indicates strongly radiogenic 87Sr/86Sr and 206Pb/204Pb, coupled with low values of 143Nd/144Nd isotopic ratios. Only two carbonatites represent an exception, having 87Sr/86Sr < BSE (present-day Bulk Silicate Earth). 11B values roughly fall in the mantle range (-8.3 to -3.3 ‰; Agostini et al., 2021), with the exception of few Ugandan rocks, having heavier values (11B = -1.9 to 6.6 ‰).
Even if samples cover a large compositional spectrum, multi-stage refertilization events must have occurred and must have strongly modified all the lithospheric mantle sources. Recycling of various lithologies, as marine limestone, caused by more or less old subductions, could explain either the carbonated metasomatism, necessary in all the analysed volcanic districts, but also the phlogopite and diopsitic clinopyroxene-rich veins, necessary in the formations of kamafugites, ultramafic lamprophyres and melilites
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
Infrared spectroscopy of natural Type Ib diamond: insights into the formation of Y-centers and the early aggregation of nitrogen
No full textVariations 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
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