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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
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
Effect of undercooling on clinopyroxene crystallization in a high K basalt. Implications for magma dynamics at Stromboli volcano
Full text linkWe present undercooling (ΔT) experiments aimed at investigating the effect of growth kinetics on the textural
and compositional evolution of clinopyroxene crystals growing from a high-K basalt erupted during the 2003
paroxysm of Stromboli volcano (Italy). The experiments were performed at P = 350 MPa, T = 1050–1210 ◦C,
H2Omelt = 0–3 wt%, and fO2 = Ni-NiO + 1.5 buffer. An initial stage of supersaturation was imposed to the melt
under nominally anhydrous (ΔTanh = 10–150 ◦C) and hydrous (ΔThyd = 25–125 ◦C) conditions. Afterwards, this
supersaturation state was mitigated by melt relaxation phenomena over an annealing time of 24 h. Results show
that plagioclase is the liquidus mineral phase of the high-K basalt at ΔTanh = 10 ◦C and dominates the phase
assemblage as the degree of undercooling increases. Conversely, clinopyroxene and spinel co-saturate the melt at
ΔThyd = 25 ◦C, followed by the subordinate formation of plagioclase. At ΔTanh/hyd ≤ 50 ◦C, the textural maturation
of clinopyroxene produces polyhedral crystals with {- 111} (hourglass) and {hk0} (prism) sectors typical
of a layer-by-layer growth mechanism governed by an interface-controlled crystallization regime. At ΔTanh/hyd ≥
75 ◦C, the attainment of dendritic and skeletal morphologies testifies to the establishment of diffusion-limited
reactions at the crystal-melt interface. 3D reconstructions of synchrotron radiation X-ray microtomographic
data reveal a composite growth history for clinopyroxene crystals obtained at ΔTanh/hyd ≥ 95 ◦C. The early stage
of melt supersaturation produces rosette-like structures composed of dendritic branches of clinopyroxene radiating
from a common spinel grain, which acts as surface for heterogeneous nucleation. As diffusive relaxation
phenomena progress over the annealing time, the elongate dendrites that constitute the inner crystal domain are
partially infilled by the melt and develop skeletal overgrowths in the outer domain. With the increasing degree of
undercooling, TAl and M1Ti cations are progressively incorporated in the lattice site of clinopyroxene at the
expense of TSi and M1Mg cations. Because of the effect of H2Omelt on the liquidus depression and melt depolymerization,
crystals obtained at ΔThyd are also more enriched in TAl and M1Ti and depleted in TSi and M1Mg than
those growing at ΔTanh. The emerging picture is that the morphological and geochemical evolution of clinopyroxene
is mutually controlled by the combined effects of melt supersaturation and relaxation phenomena. A
new empirical relationship based on the cation exchange reactions in the lattice site of clinopyroxene is finally
proposed to estimate the degree of undercooling governing the crystallization of augitic phenocrysts erupted
during normal and violent explosions at Stromboli
Very Fast Magma Dynamics at Mt. Etna Revealed by Clinopyroxene Growth Rates
No full textWe present new high-pressure crystallization experiments carried out on one of the most primitive trachybasalt from Mt. Etna, at temperatures ranging from 1000 to 1250 °C and pressure ranging from 300 to 800 MPa. Experiments were designed to investigate the effect of undercooling (∆T = Tliquidus - Tcrystallization) on hydrous and anhydrous crystallization kinetics and to place constraints on magma dynamics. Undercooling experiments were conducted by heating the charge at the temperature of 1300 °C, cooling down to the final target temperature at a constant rate (80 °C/minute) and holding the temperature for 24 hours. Clinopyroxene and titanomagnetite are the dominant mineral phases. Plagioclase crystallizes under anhydrous conditions, amphibole forms in hydrous experiments at 800 MPa, and olivine saturate the melt only at 300 MPa. Clinopyroxene growth rates are maximum at very low degrees of undercooling (∆T 500 μm). In contrast, at moderate to high degrees of undercooling (∆T > 20 °C), skeletal crystal shapes prevail. Growth rates measured in undercooling experiments are orders of magnitude higher than those from equilibrium isothermal experiments (performed heating the charge to the target temperature and holding the temperature for 24 hours), where smaller ( 50 °C), accounting for a very fast (few minutes) growth of skeletal crystals followed by a slower (few hours) filling and coarsening of crystal mantle and rim. Undercooling experiments closely reproduce the liquid line of descent of magmas at Mt. Etna and set constrains on magma evolution and dynamics, indicating early crystallization of clinopyroxene ± amphibole at 800-400 MPa, followed by late crystallization of plagioclase and olivine at pressure below 400 MPa. The low water content (<2 wt.%) and the extremely fast growth rates imposed by the undercooling remark the “open system” conduit evolution and the extremely fast dynamics of magmas erupted at Mt. Etna
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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