1,720,998 research outputs found
Mineralogia química dos anfibolitos da Região de Morretes-Antonina, Paraná
No full textNão informado pelo autor.Não informado pelo autor
Petrology of potassic alkaline ultramafic and carbonatitic rocks from Planalto da Serra (Mato Grosso State), Brazil
No full textThe Planalto da Serra lithotypes are represented by 600 Ma plugs and necks of glimmerites and carbonatites. Phlogopite and/ or tetraphlogopite are the most abundant minerals of the glimmerites. Carbonatites comprise granular hypidiomorphic alvikites and brecciod beforsites. Diopside and melanitic garnet are restricted to the glimmerites, whereas pyroclore occur only in carbonatites. Perovskite, tremolite, magnetite, pyrite, apatite, titanite, chlorite and serpentine are common accessories of both lithologies. Under high CO2 and H2O activity glimmerites and carbonatites gave rise to hydrotermalites, in which chlorite and serpentine are the predominant minerals (up to 70%).They derived from tremolite, diopside and sometimes from olivine. Pyrite is a common accessory. Glimmerites, alvikitic dykes and hydrotermalites have kamafugitic affinity. Sr-Nd isotopes and incompatible trace-element data, characterized high LREE/HREE fractionation suggest that the K-ultramafic alkaline and carbonatite rocks originated from a varied metasomatized source mantle, characterized by Sr radiogenic enrichment. Crustal contamination is negligible or absent. Geochronological data of the Planalto da Serra rocks and its relationship with the low-grade metamorphic rocks of the Cuiabá Group make improbable the presence of the Clymene Ocean in this area. The age determination also rules out the geochronological relationship between the Planalto da Serra intrusions and the Mesozoic alkaline bodies from the Azimuth 125° lineament, and makes possible to relate its emplacement with to one of the most important extensional periods of Neoproterozoic times, which is characterized by the separation of Laurentia and the Amazonian Craton. The TDM model ages suggest that the Planalto da Serra melts derived from the remobilization of subcontinental lithospheric mantle that had been enriched by small-volume K-rich melt fractions at the Early to Late Neoproterozoic, which makes highly improbable the hypothesis of mantle plume tail, given that a subcontinental mantle enrichment, controlled by an Early Neoproterozoic event, produced similar ultramafic alkaline products at 600 and 80-90 Ma
Petrography and mineral chemistry of carbonatites and mica-rich rocks from the Araxá complex (Alto Paranaíba Province, Brazil)
No full textThe Araxá complex (16 km²) comprises carbonatites forming a central core and a complex network of concentric and radial dykes as well as small veins; additionally, it includes mica-rich rocks, phoscorites and lamprophyres. Fenites also occur and are represented by Proterozoic quartzites and schists of the Araxá Group. The petrographic study of 130 borehole samples indicates that the complex is basically made up by two rock-types, carbonatites and mica-rich rocks, and subordinately by a third unit of hybrid composition. Carbonatites range chemically in composition, the most abundant type being magnesiocarbonatites. Dolomite and calcite correspond to the chief constituents, but other carbonate phases, including the Ce-group RE minerals, are also recognized. Phosphates and oxides are widespread accessories whereas silicate minerals consist of olivine, clinopyroxene, mica and amphibole. Mica-rich rocks are represented by abundant glimmeritic rocks and scarce cumulitic phlogopite-, olivine- and diopside-bearing pyroxenites. Hybrid rocks mainly contain phlogopite and tetraferriphlogopite as cumulus and intercumulus phases, respectively; carbonate minerals may also be found. Chemical data indicate that the carbonatites are strongly enriched in REE and have lower contents of Nb, Zr, V, Cr, Ni and Rb compared to the mica-rich rocks. The higher K, Nb and Zr contents of the latter rocks are believed to be related to metasomatic processes (glimmeritization) of the pyroxenites. Similar REE patterns for carbonatites and mica-rich rocks seem to suggest that they are related to a single parental magma, possibly of ijolitic composition. Steep LREE/HREE fractionation and high sigmaREE content of some carbonatite samples would be explained by hydrothermal and supergenic processes.O complexo de Araxá (16 km²) é constituído por carbonatitos na forma de um núcleo central e de complexa rede de diques concêntricos e radiais, além de pequenos veios; adicionalmente, ele contém rochas ricas em mica, foscoritos e lamprófiros. Fenitos também ocorrem e estão representados principalmente por quartzitos e xistos proterozóicos do Grupo Araxá. O estudo petrográfico de 130 amostras de testemunhos de sondagem indica que o complexo reúne basicamente dois tipos litológicos, carbonatitos e rochas ricas em mica, e, subordinadamente, um terceiro de composição híbrida. Carbonatitos apresentam composição química variável e têm magnésiocarbonatitos como o tipo mais abundante. Dolomita e calcita são os seus principais constituintes, mas outras fases carbonáticas, incluindo as pertencentes ao grupo dos carbonatos ricos em ETR, são também reconhecidas. Fosfatos e óxidos diversos caracterizam os acessórios mais comuns enquanto que os minerais silicáticos consistem de representantes dos grupos da olivina, clinopiroxênio, mica e anfibólio. As rochas ricas em mica reúnem abundantes glimmeritos e escassos piroxenitos cumuláticos portadores de quantidades variáveis de flogopita, olivina e diopsídio. As rochas híbridas contêm principalmente flogopita e tetraferriflogopita, respectivamente, como fases cumulus e intercumulus; minerais carbonáticos podem também estar presentes. Dados químicos indicam que os carbonatitos são fortemente enriquecidos em ETR e possuem teores mais baixos em Nb, Zr, V, Cr, Ni e Rb em relação às rochas mais ricas em mica. As concentrações mais altas em K, Nb e Zr dessas últimas poderiam ser atribuídas a processos metassomáticos (glimeritização) que teriam afetado os piroxenitos. O comportamento similar dos ETR nos carbonatitos e nas rochas ricas em mica parece sugestivo de que essas litologias estão relacionadas a um mesmo magma parental, possivelmente de composição ijolítica. O pronunciado fracionamento ETRL/ETRP e os elevados teores em ETR de algumas amostras de carbonatitos poderiam estar ligados a processos de natureza hidrotermal ou mesmo supergênicos
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Nepheline syenites to syenites and granitic rocks of the Itatiaia Alkaline Massif, Southeastern Brazil: new geological insights into a migratory ring Complex
No full textABSTRACT: The Itatiaia Alkaline Massif comprises some of the largest meso-cenozoic alkaline igneous occurrences in Brazil, covering over 215 km2 between the states of Minas Gerais and Rio de Janeiro. It appears as an elongated, 30-km long and 4.5-11.5-km wide SE-NW-trending body emplaced along accommodation zones of the Continental Rift of Southern Brazil, intruding metapelites, orthogneiss and granites of the Brasília and Ribeira fold belts. New data and geological mapping suggest that the massif evolved from a migratory magmatic center manifested as ring structures and successive moon-shaped intrusions from SE to NW in three sectors of distinct lithological and geomorphological characteristics: Southeastern, Central and Northwestern. The lithological variants in the three sectors present themselves as discrete intrusive bodies, comprising feldspathoid-bearing and quartz-bearing syenites, porphyritic to breccioid trachytes, granite, monzonite, gabbro and trachybasalt, which can be grouped into 21 units. These rocks occur in five petrographical sets: plagioclase-free nepheline syenites, plagioclase-bearing nepheline syenite and pulaskites, nordmarkite-granite series, anti-rapakivi associations and basic rocks. Sin- to tardi-plutonic dykes of nephelinites, phonolites, trachytes and rhyolites are also present
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
- …
