1,720,957 research outputs found
TESTING THE TECTONOMAGMATIC SETTING OF MESOPROTEROZOIC METAVOLCANIC TUFFS IN THE PICURIS RANGE, NEW MEXICO
No full textThe Picuris Range of northern New Mexico has long been considered part of a typical convergent continental margin during Laurentian assembly. It is now known to result from an intraplate orogenic event ~500 km inboard of the convergent margin orogenesis at ca. 1.4 Ga. The mechanisms of intraplate orogenesis are enigmatic, in part due to associated deformation. Mesoproterozoic supracrustal rocks include phyllite, schist, and metatuffs, although tectonic reworking of these units has obscured aspects of their volcanic sources and depositional setting. It is well known that Mesoproterozoic plutonism emplaced a significant volume of anorogenic, “A-type” granitoids across the southwestern United States through Labrador, Canada. Exposures of A-type granitoids are poor in the Picuris Range, but may represent plutonic-volcanic pairs with a subset of metatuffs of similar age. Recent tectonic models have yet to integrate Mesoproterozoic magmatism, basin formation, and deposition along the southwestern accretionary margin of Laurentia.
Zircon trace element and whole rock geochemical analyses from the only exposed Mesoproterozoic volcanic rocks in New Mexico are used to evaluate the tectonomagmatic setting of emplacement. Whole rock major element geochemistry indicates that the metatuffs underwent low- temperature metasomatism, facilitating significant mass and volume loss, most likely via silica removal. Metasomatic alteration modeling suggests the metatuffs were primarily silica-rich and alkaline to calc- alkaline in composition. Zircon compositions further indicate that the metatuffs were derived from two sources: a continental-arc source and an enriched-mantle (possibly intraplate, plume-influenced) source. Combined zircon 207Pb/206Pb ages and trace element compositions demonstrate that both magmatic sources contributed to the depositional basin from ~1489–1471 Ma. These findings fit the most recently proposed tectonic model for Mesoproterozoic Laurentian assembly, in which continental-arc volcanic rocks are sourced from the distal convergent margin and enriched-mantle volcanic rocks are sourced from local extension, lithospheric thinning, and mantle underplating causing widespread A-type magmatism.
Alternative enriched-mantle sources include local extension due to flat-slab subduction and roll-back induced back-arc basin formation, or a distal mantle plume
Multiphase Petrochronology of Archean Gneiss Complexes Unraveling polymetamorphic records at the Acasta Gneiss Complex, Northwest Territories, Canada and the Watersmeet Gneiss Dome, MI, USA
No full textArchean gneiss complexes represent critical records of the formation and evolution of the continental crust. However, these records are commonly modified by multiple, post- crystallization tectonothermal events, especially during the Archean and Proterozoic. The U-Th- Pb isotope system in titanite and apatite should be advantageous for unraveling the polymetamorphic record within Archean gneiss complexes, but previous studies suggest that these chronometers are partially or fully reset by Paleoproterozoic tectonothermal overprints. This study integrates textures and petrologic context, EPMA WDS major, minor, and trace- element analysis/mapping, and in situ U-Th-Pb isotopic and trace-element LASS-ICPMS data to improve chronologic interpretations of titanite and apatite in Archean rocks with Paleoproterozoic overprints.
Titanite from the Acasta Gneiss Complex (AGC), Northwest Territories, Canada and the Watersmeet Gneiss Dome (WGD), MI, USA preserves information about Archean events and Proterozoic overprinting, but apatite is consistently reset by Proterozoic tectonothermal events. At the AGC, four Archean events spanning ~3.6-2.9 Ga are identified in titanite. At the WGD, titanite preserves evidence of metamorphism at ~2.64 Ga interpreted to record the timing of collision and suturing of the Watersmeet terrane to the southern margin of the Superior Province. In both localities, titanite compositions reflect a combination of metamorphic fluid-rock interactions and primary igneous host rock chemistry that can be distinguished through integration of petrologic-geochemical datasets and statistical analysis. These results demonstrate the utility of titanite as an Archean chronometer that can resist Proterozoic overprinting, as well as a petrologic tracer of metamorphic fluids.NSF/GSA Graduate Student Geoscience Grant #13123-21, which is funded by NSF Award # 1949901, OKD and funds from the University of Wisconsin-Madison
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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