1,721,008 research outputs found
Trace element partitioning in zoned clinopyroxene as a proxy for undercooling. Experimental constraints from trachybasaltic magmas
No full textSector-zoned clinopyroxene records kinetic effects imposed by variable degrees of magma undercooling,
DT, and can be utilised to track the dynamics of magmatic systems. The partitioning of trace elements
into sectors grown in different crystallographic orientations can be used as a proxy for DT. However,
an experimental assessment of the relationship between trace element zoning and DT has been lacking
to date. Here we present trace element data from a series of undercooling crystallisation experiments on
a primitive trachybasalt from Mt. Etna (Italy), at conditions of crustal storage (400 MPa, NNO + 2), and DT
ranging from 23 to 173 C. Changes in DT were modulated by varying both resting and liquidus temperatures,
the latter via the melt-H2O content of the experiments. The resting temperature was retained for
24 h to ensure the attainment of near-equilibrium conditions.
High-resolution elemental mapping reveals the distribution of trace elements in individual clinopyroxene
zones. Increasing DT drives a shift from polyhedral morphologies with Al-rich prism and Al-poor
hourglass sectors (DT = 23–25 C), to skeletal (DT = 75–123 C) and dendritic (DT = 132–173 C) crystals
with Al-rich skeletons and Al-poor overgrowths. Aluminium-rich zones have higher concentrations of
rare earth elements (REE) and high field strength elements (HFSE) than Al-poor zones across all investigated
DT conditions, and overall, Al, REE and HFSE contents increase with DT. This indicates that tetrahedral
aluminium (TAl) and associated charge-balancing mechanisms govern the incorporation of REE
and HFSE within clinopyroxene. Lattice strain parameters for REE in the M2 site indicate the incorporation
of light relative to heavy REE in clinopyroxene is controlled by competing effects between the strainfree
partition coefficient, D0, and the optimum cation radius, r0. Critically, the middle and heavy REE
switch from incompatible to compatible with increasing DT. Used to model fractional crystallisation,
our data demonstrate that fractionation of clinopyroxene at low DT controls pre-eruptive melt evolution.
Importantly, this indicates crystallisation of clinopyroxene in the deep portions of Mt. Etna’s plumbing
system is not rapid and is unlikely to result in the early formation of dendrites.
We develop a parameterisation of DT based on REE partitioning between experimental clinopyroxene
and coexisting melt, which can be applied to sector-zoned augite crystallising from mafic alkaline magmas,
to reconstruct dynamic processes and thermal pathways during magma transport and storage.
Applied to sector-zoned clinopyroxene microphenocrysts and groundmass microcrysts from the 1974
eccentric eruption at Mt. Etna, our parameterisation tracks an increase in DT with magma ascent and
eruption, following recharge of Cr-rich mafic magma at depth. Sector-zoned clinopyroxene can track
DT variations leading to volcanism at Mt. Etna and could be applied to quantify magma dynamics in other
active volcanoes
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Melting experiments of an L6 ordinary chondrite: Implications for the formation of alkali-rich achondrites
No full textWe conducted high-pressure (1 GPa) melting experiments (1100–1400 °C) on the equilibrated ordinary chondrite DAV 01001 (L6) to investigate partial melting scenarios of planetary embryo in the early solar system. At 1100 °C, no melting of the silicate phase is observed, and the initial chondritic texture is preserved, but the metallic-sulphidic phases formed two immiscible Fe–Ni and S-rich liquids. Melting of silicate minerals began at 1200 °C, progressing from plagioclase to high-Ca and low-Ca pyroxene and olivine. As melting advanced, the formation of new olivine and low-Ca pyroxene resulted in the production of trachy-andesitic melt at 1200 °C, basaltic trachy-andesitic melt at 1300 °C, and andesitic melt at 1400 °C. These silicate melts have chemical similarities with some anomalous achondrites (e.g., GRA 60128/9). At the same time, minerals of new formation resemble those of primitive achondrites (e.g., brachinites, ureilites, IAB silicate inclusions, acapulcoites and lodranites). The rapid mineral-liquid re-equilibration suggests that basaltic liquids can form only above 1400 °C and that relatively high degrees of melting (>20 %) and crystallisation are necessary to explain the observed diversity of achondritic lithologies. These findings suggest that partial melting and recrystallization processes within planetary embryos could have played a critical role in the early solar system, contributing to the early differentiation of planetary bodies and the diversity of achondritic lithologies, including (but not limited to) alkali-rich achondrites
Magmatic evolution and architecture of an oceanic intraplate volcano: Vesteris Seamount, Atlantic Ocean
Full text linkVesteris is a large (33 x 27 km) and young (summit age: 0.65-0.010 Ma) intraplate seamount in the Greenland Sea, formed from ocean island basalt (OIB) magmatism. The volcano is composed of alkali basalt, basanite/tephrite, phonotephrite, mugearite, and benmoreite. Its phenocryst assemblage includes clinopyroxene, plagioclase, olivine, amphibole, rare ha & uuml;yne, and oxides (Ti-magnetite and Cr-spinel), with phenocrysts hosting inclusions of apatite, sulfides (pyrrhotite), and melt. Despite its geological significance, the processes governing magma storage, ascent, and eruption dynamics remain poorly understood. To address this, we conducted detailed micro-chemical analyses of phenocrysts, groundmass microcrysts, melt inclusions, and groundmass glass. Using mineral-melt thermobarometry, we characterized the pre- to syn-eruptive crystallization conditions and reconstructed the architecture of the volcanic plumbing system. Our findings indicate that basanite liquids were primarily stored in the upper mantle (similar to 6.4 kbar; similar to 22 km depth) with evidence of multi-level storage extending to similar to 9 kbar (similar to 30 km depth). Textural and compositional zoning in clinopyroxenes suggests rapid magma ascent, while mafic recharge emerged as a key mechanism for remobilizing evolved clinopyroxene mush. Mafic recharge magmas also introduced early olivine crystals, which were later overgrown by high-Mg clinopyroxene upon mixing with more evolved melts. These results demonstrate that major crystal fractionation occurs in the upper mantle beneath Vesteris, resembling processes observed in low-flux ocean island basalt volcanoes. The evidence for rapid magma ascent highlights the dynamic nature of magma movement within the plumbing system, driven by mafic recharge and crystal-melt interactions
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
Variations 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
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