1,721,018 research outputs found
Age and geochemistry of the early Mesoproterozoic A-type granites in the southern margin of the North China Craton: Constraints on their petrogenesis and tectonic implications
No full textA-type granites are a spectrum of especial felsic rocks that are produced commonly within an extensional environment. They are rare before middle Paleoproterozoic but present abundantly since the late Paleoproterozoic, probably indicating a causal change of tectonics and geodynamic mechanism in the continental evolution of the Earth. An early Mesoproterozoic A-type granite belt was recognized in the southern margin of the North China Craton (NCC) in recent decades. The occurrence of this type of rocks indicates a possible spatial-temporal link between the tectonic evolution of the NCC and the breakup of the Columbia supercontinent during the Mesoproterozoic. The Zhangjiaping granitic pluton is located in the southern margin of the NCC and one part of the A-type granite belt. It can be divided into three zones according to their textural and compositional differences of the rocks with a gradually increasing degree of evolution inwards: wall zone, intermediate zone and core zone. LA-ICP-MS zircon U-Pb dating shows that it was emplaced at ca. 1.53 Ga. Petrologically, the Zhangjiaping granites contain perthite and calcic amphibole but are lack of alkali mafic minerals. Geochemically, all the Zhangjiaping granitic rocks show an affinity to fractionated aluminous A-type granites, with enrichment in silicon and total alkali, and depletion in MgO, CaO and P2O5 with negative Eu, Sr and Ti anomalies, as well as high FeOt/MgO, TiO2/MgO and Ga/Al ratios and high HFSEs (i.e., Zr, Nb, Ce, Y) concentrations. Such signatures, along with their low epsilon(Hf)(t) values (-12.5 to -4.0) of all the granites from the Zhangjiaping pluton, obviously indicate that the Zhangjiaping aluminous A-type granites were derived from partial melting of the crustal calc-alkaline granitoids (i.e., the granodiorites of the Taihua Complex in the study area) and experienced fractional crystallization during magmatic evolution. Their generation would be related to the underplating of mafic magmas in an extensional regime. Integrated with regional data, the Zhangjiaping aluminous A-type granites were the products of anorogenic magmatism likely corresponding to the breakup of the Columbia supercontinent. (C) 2016 Elsevier B.V. All rights reserved
Using detrital zircons from river sands to constrain major tectono-thermal events of the Cathaysia Block, SE China
No full textDetrital zircons from the Minjiang and Zhujiang Rivers in SE China have been analyzed for U/Pb ages and Lu-Hf isotopic compositions to constrain their provenance and the growth history of the continental crust of the Cathaysia Block. Zircon U/Pb ages show five major populations at 90-250 Ma, 400-500 Ma, 0.7-1.2 Ga, 1.6-2.0 Ga and 2.3-2.6 Ga. Proterozoic zircons have Hf isotopic signatures consistent with the remelted ancient crust and the involvement of juvenile crust. However, Phanerozoic zircons have Hf isotopic signatures indicative of reworked or recycled ancient crust. Crustal growth rates based on the two-stage Hf model ages of the detrital zircons indicate that 30% and 90% of present crust in the northeastern Cathaysia Block was formed by 2.5 Ga and 1.6 Ga, respectively, whereas <20% continental crust was formed by 2.5 Ga, and 80% by 1.6 Ga in the southwestern Cathaysia Block. Therefore, Neoarchean and Paleoproterozoic were two major periods of crustal growth of the Cathaysia Block. Our results also reveal that the tectono-thermal events at similar to 370 Ma and similar to 117 Ma may have occurred to the Wuyishan terrane in the northeastern Cathaysia Block. Jurassic zircon grains have Hf isotopic compositions more variable than Cretaceous grains, which may have been derived from different source rocks. The 140-120 Ma tectono-thermal events were likely related to the change of the subduction direction of the Paleo-Pacific plate from northward to northwestward at 140 Ma. The 112-90 Ma tectono-thermal events may be correlated with the rollback of the subducted paleo-Pacific plate at similar to 110 Ma. (C) 2016 Elsevier Ltd. All rights reserved
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
Geochronology and geochemistry of the late Paleoproterozoic aluminous A-type granite in the Xiaoqinling area along the southern margin of the North China Craton: Petrogenesis and tectonic implications
No full textThe occurrence of extensional-related A-type granites with a high-K nature in some early Precambrian blocks hints a possible link with the orogeny, and may imply the ending of the orogenic processes and the beginning of craton stabilization. The newly recognized late Paleoproterozoic A-type granite, the Guijiayu pluton composed of monzogranites in the Xiaoqinling area of the southern margin of the North China Craton (NCC), is a promising locus to investigate the late Paleoproterozoic tectonic evolution of the NCC. LA-ICP-MS zircon U-Pb dating shows that the Guijiayu pluton was emplaced at similar to 1.80 Ga. Petrologically, the Guijiayu granites contain perthite, annite and calcic amphibole but are lack of alkali mafic minerals. Geochemically, all the rocks are enriched in silicon and total alkali, and depleted in MgO, CaO and P2O5, with high FeOt/MgO, TiO2/MgO and 10,000 Ga/Al ratios and high HFSEs (i.e., Zr, Nb, Ce, Y) concentrations, as well as negative Eu, Sr, P and Ti anomalies. They are also characterized by high melting temperatures and metaluminous to weakly peraluminous natures. Taken together, the Guijiayu granites show an affinity to aluminous A-type granite. Their geochemical characteristics (e.g., obviously negative Eu and Sr anomalies), along with the low zircon epsilon(Hf)(t) values (-13.9 to -7.0) and whole-rock epsilon(Nd)(t) values (-5.81 to -5.65), indicate that the Guijiayu aluminous A-type granite was derived from partial melting of the crustal talc-alkaline granitoids dominated by the granodiorite of the Taihua Group in the study area. Combined with the regional data, especially for the identification of the clockwise P-T paths of Paleoproterozoic metamorphism in the southern margin of the NCC, even coeval granites and regional retrograde metamorphism in other areas in the NCC, it is most likely that the peak of continent-continent collision had finished in the study area at least before similar to 1.80 Ga, and that the generation of the Guijiayu aluminous A-type granite was related to the underplating of mafic magmas in a post-collisional regime. (C) 2016 Elsevier B.V. All rights reserved
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
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
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