1,721,071 research outputs found
A crystal mush perspective explains magma variability at la fossa volcano (Vulcano, Italy)
Full text linkThe eruptive products of the last 1000 years at La Fossa volcano on the island of Vulcano (Italy) are characterized by abrupt changes of chemical composition that span from latite to rhyolite. The wide variety of textural features of these products has given rise to several petrological models dealing with the mingling/mixing processes involving mafic-intermediate and rhyolitic magmas. In this paper, we use published whole-rock data for the erupted products of La Fossa and combine them in geochemical and thermodynamic modelling in order to provide new constrains for the interpretations of the dynamics of the active magmatic system. The obtained results allow us to pic-ture a polybaric plumbing system characterized by multiple magma reservoirs and related crystal mushes, formed from time to time during the differentiation of shoshonitic magmas, to produce latites, trachytes and rhyolites. The residing crystal mushes are periodically perturbated by new, fresh magma injections that, on one hand, induce the partial melting of the mush and, on the other hand, favor the extraction of highly differentiated interstitial melts. The subsequent mixing and mingling of mush-derived melts ultimately determine the formation of magmas erupted at La Fossa, whose textural and chemical features are otherwise not explained by simple assimilation and fractional crystallization models. In such a system, the compositional variability of the erupted products reflects the complexity of the physical and chemical interactions among recharging mag-mas and the crystal mushes
Tracking mineral evolution and element mobility during albitisation and subsequent kaolinisation of phyllite rocks: A case study from the Verrucano of Monti Pisani, Tuscany, Italy
No full textThis work describes the first occurrence of albitite rocks in the Middle Triassic Verruca Formation, Monti Pisani, Northern Apennines, northern Tuscany, Italy. The albitite formed by Na-metasomatism of phyllites ('potassic white mica' + quartz + 'chlorite' + hematite + albite) in an amagmatic environment. The albitisation process took place after the Miocene main phases of Apenninic deformation and was followed by the formation of veins of Fe-carbonate + quartz. Hydrothermal alteration progressed with the ingression, possibly favoured by the increase of permeability due to albitisation, of a slightly acidic, oxidising, aqueous fluid that led to the pervasive kaolinisation of the albitite and to the complete transformation of the Fe-carbonate of the veins into Fe-hydroxides. This stage was followed by supergene alteration that led to the formation of a pervasive network of halloysite veinlets and colloform (P-Al-Si)-bearing Fe-hydroxides. Finally, the hydrothermally altered rock underwent a localised brittle fracturing without new minerals being formed. The prominent compositional changes occurring during this multi-stage hydrothermal process were the inversion of the Na2O/K2O ratio of the whole rock (from 0.07 in the pristine phyllite to up to 200 for the kaolinised albitite), the loss of Fe and Mg, and the enrichment of Sb. The MREE were partially lost, whereas LREE and HREE behaved conservatively. Though pervasive hydrothermal alteration occurrences are common in central-southern Tuscany, mostly related to the post-collisional extensional regime, lithospheric thinning and emplacement of magmatic bodies in the crust, the rare Monti Pisani kaolinised albitite described in this investigation expands the effects of post-collisional hydrothermal activity in Tuscany northwards, far from potential magmatic sources
Hydric dilatation of ignimbritic stones used in the Church of Santa Maria di Otti (Oschiri, northern Sardinia, Italy)
No full textIn the historical buildings of eastern Logudoro (northern Sardinia),
as well as in large areas of western Sardinia, ignimbritic
rocks are widely used for ashlars and architectural elements as
architraves, pedestals, shafts and capitals of columns. The decay
processes affecting these rocks cause a progressive disintegration of
the stone ashlars, with loss of material by exfoliation and flaking
that determine a progressive retraction of the external profile of
the façade with obliteration of the decorative elements. New data on
the linear dilatation due to water absorption of these volcanic rocks
are presented in this study in order to contribute to the evaluation of
the impact of hydric dilatation in the stone degradation. The relationships
among linear hydric dilatation of ignimbritic samples and
petrographic and mineralogical characteristics as well as physical
properties (texture, welding degree, porosity) indicate that three
lithotypes with different behaviour in the water absorption can be
distinguished in the ignimbrite rocks used as building stones in
the church of Santa Maria di Otti (Oschiri, northern Sardinia,
Italy). Although the linear hydric dilatation of the ignimbrites is
moderate to low, we suggest that hydric dilatation may be an additional
factor in enhancing the decay of the stones of the Santa Maria
di Otti church
Geoscience knowledge in Italy at the end of high School
No full textA survey aimed at an assessment of geoscience understanding of Italian students at the end of high school has been carried out from 2015 to 2018 by means of the IMES (Individuation of Misconceptions in Earth Sciences) questionnaire. The survey, conducted on freshmen of several courses at the University of Pisa, has revealed the persistence of alternative conceptions about different geoscience topics. In this paper, the psychometric validation and the latest results of IMES are presented, together with an analysis of textbooks used in Italian high school, aimed at investigating if, besides other factors, the way geoscience concepts are presented in textbooks may contribute to the birth or confirmation of concepts alternative to those agreed upon by the scientific community
Petrololgy of volcanic products younger than 40 ka on the Lipari-Vulcano complex (Aeolian Islands, Italy): an example of volcanism controlled by tectonics
No full text
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
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