1,721,048 research outputs found
The origin and evolution of Hercynian crustal fluids, South Cornwall, England
No full textCrustal fluids, mobilised in Devonian metasediments during and subsequent to the Hercynian orogeny in South Cornwall, have been investigated by a detailed study of fluid inclusions present in vein material. Four stages of vein formation are distinguished, related to the three main deformation events which affected the area. Within each stage, up to four different vein types are recognised, occurring in distinct structural and/or lithological settings. Fluid inclusion data, in combination with pumpellyite-actinolite mineral assemblages and vitrinite reflectance data indicate that low grade regional metamorphism in south Cornwall occurred at 330 ± 30^oC and 3.4 ± 0.5 kbar. Dense (0.95 ± 0.3 g cm^-3), low salinity (1-4.5 wt% NaCl equivalent), H_2O-rich (X_H2O> 0.986), peak metamorphic fluids were evolved via prograde devolatilisation reactions, contemporaneous with the first compressional deformation event (D1). The major element compositions of these fluids were buffered by quartz + albite + K-mica + chlorite ± paragonite assemblages in greywacke and slate host rocks. Thermodynamic calculations suggest that the peak metamorphic fluids could have transported significant (ppm) quantities of base metals and silver as chloro-complexes, and tin as hydroxy-complexes. High temperature metamorphic fluids migrated up imbricate thrusts to shallower crustal levels during the second deformation event (D2). These fluids caused limited sericitic and chloritic alteration of wallrocks, and became increasingly saline (up to 8 wt% NaCl equivalent) as a result of hydration reactions. CO2 and N2 contents increased, possibly as a result of oxidation of organic carbon and ammonium in the wallrocks due to cooling and decreasing oxygen fugacity. Lower ore mineral solubilities in these fluids may have resulted in precipitation, producing low-grade metal enrichment in the upper crust. Fluid inclusion data indicate that fluid temperatures and pressures did not fall below 200oC and 500 bars respectively, during D2. CO2(+ N2+ CH4)-bearing fluids, possibly generated by mixing of approximately equal proportions of magmatic and contact metamorphic fluids, were mobilised up to 5 km laterally from the roof zone of the Cornubian granite batholith during emplacement. These fluids unmixed at 400-200oC and 1000-500 bars to produce low density CO2-rich vapour and high density, moderately to highly saline, aqueous fluids (8-42 wt% NaCl equivalent). Up to 28 ppm tin could have been transported in the hypersaline fluids, primarily as chloro-complexes. High density, CO2-rich fluids (up to 85 mol% CO2) were produced in distal parts of the contact aureole, probably as a result of condensation of low density vapours. Low salinity (1-5 wt% Na Cl equivalent), H2O-rich fluids separated from the Megilliggar pegmatites during crystallisation. These fluids unmixed at ≈400^oC to produce a low density, CO_2(±CH4±N_2)-bearing vapour and moderately saline (8-10 wt% NaCl equivalent) aqueous liquid. Magmatic fluids of this type, possibly in combination with contact metamorphic fluids, were responsible for high temperature mineralisation phenomena. The initiation of convective fluid circulation, and dilution of magmatic±metamorphic fluids with meteoric water at or below ≈300^oC, resulted in the formation of the bulk of the Sn-W-polymetallic sulphide deposits observed in the province. Basinal brines migrated along wrench faults into the Cornubian peninsula and mixed with convecting meteoric fluids at structural intersections on the southern flank of the granite batholith at 140-200^oC and < 500 bars. Mixing caused base metal deposition by increasing pH and decreasing salinity.</p
Copper- and cobalt-rich, ultrapotassic bittern brines responsible for the formation of the Nkana-Mindola deposits, Zambian Copperbelt
No full textThe Central African Copperbelt (CACB) is Earth’s largest repository of sediment-hosted copper and cobalt. The criticality of these elements in battery technology and electricity transmission establishes them as fundamental components of the carbon-free energy revolution, yet the nature and origin of the hydrothermal fluids responsible for ore formation in the CACB remain controversial. Here, we present microthermomet-ric, scanning electron microscopy and laser ablation–inductively coupled plasma–mass spectrometry analyses of fluid inclusions from the Nkana-Mindola deposits in Zambia. We find that base metal concentrations vary by one to two orders of magnitude between “barren” and “ore” fluids, with concomitant distinctions in major salt chemistry. Primary fluid inclusions, hosted by pre- to synkinematic mineralized quartz veins, are character-ized by high homogenization temperatures (∼200–300 °C) and salinities, with K/Na >0.8 and elevated metal concentrations (102 to 103 ppm Cu and Co). Conversely, barren, post-kinematic vein quartz contains lower homogenization temperature (∼110–210 °C) and lower-salinity primary inclusions, characterized by K/Na <0.8 with low metal contents (<102 ppm Cu and Co). We propose a model in which high-temperature, sulfate-deficient, metalliferous, potassic residual brines, formed during advanced evaporation of CaCl2-rich, mid-Neoproterozoic seawater, were responsible for ore formation. During basin closure, lower-temperature, halite-undersaturated fluids interacted with evaporites and formed structurally controlled, sodic metasomatism. Reconciliation of these fluid chemistries and base metal concentrations with reported alteration assemblages from a majority of Zambian Copperbelt deposits suggests highly evolved, residual brines were critical to the formation of this unique metallogenic provinc
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
Mapping geologic features onto subducted slabs
Get PDFEstimating the location of geologic and tectonic features on a subducting plate is important for interpreting their spatial relationships with other observables including seismicity, seismic velocity and attenuation anomalies, and the location of ore deposits and arc volcanism in the over-riding plate. Here we present two methods for estimating the location of predictable features such as seamounts, ridges and fracture zones on the slab. One uses kinematic recon- structions of plate motions, and the other uses multidimensional scaling to flatten the slab onto the surface of the Earth. We demonstrate the methods using synthetic examples and also using the test case of fracture zones entering the Lesser Antilles subduction zone. The two methods produce results that are in good agreement with each other in both the synthetic and real examples. In the Lesser Antilles, the subducted fracture zones trend northwards of the surface projections. The two methods begin to diverge in regions where the multidimensional scaling method has its greatest likely error. Wider application of these methods may help to establish spatial correlations globally
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
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