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Plagioclase as a tool for understanding magma dynamics - the 2001-2006 eruptive period at Mount Etna
No full textPlagioclase as a record of the magma ascent dynamics during 2001-2006 eruptions at Mt. Etna (Italy)
No full textThe 2001-2006 Eruptive Period at Mount Etna as Recorded in Plagioclase Phenocrysts: Implications for Magma Ascent Dynamics and Pre-Eruptive Conditions
No full textPetrological features of plagioclase as archive of magma ascent dynamics: the 2001-2006 eruptive period at Mount Etna
No full textSeveral studies are focused on textural and compositional features of plagioclase as an usefull tool to investigate magma chamber processes, ascent dynamics, and physico-chemical conditions. In particular water content, which plays a fundamental role in volcanic process, strongly affects plagioclase stability and, by conseguence, textural and compositional features. However, such reconstruction are usually biased by too many assumptions; particularly when dealing with past eruptions or remote volcanoes. Only few volcanoes provide an array of instrumental monitoring to constrain timing and modality of eruptive events. In this respect Mount Etna probably represents one of the most controlled volcano in the world and a great wealth of seismological and ground deformations data are available. In this work we present a textural and compositional study of plagioclases from lavas emitted during the 2001-2006 eruptive period on Mount Etna. Textural classification has been done on over 130 thin sections taking into account different portion of the crystals. This allow to recognize different types of core (ehuedral and rounded) and rims (dusty or with melt inclusion alignment) separated by oscillatory zoned overgrowth.
Oxygen fugacity in magmas has been calculated using the method of [1] and results has been used to reequilibrate the melts to mantle equilibrium, adding back the appropriate quantity of fractionated material. Water content of the melt has been estimated using the hygrometer of [2]. These data were used in the MELT model to estimate the plagioclase stability field and to calculate theoretic composition at different water content. Results were integrated with monitoring data acquired during the entire period under study with the aim to reconstruct magma ascent and storage conditions, as well as the mechanism of eruption triggering. Results indicate the 2001-2006 eruptive period involved magmas with quite similar major element composition but different dissolved H2O. Complex zoning such as dusty areas and alignments of melt inclusions in outer portion of the phenocrysts suggest two different trigger mechanism respectively: i) magma input and mixing with a more basic and volatile-rich magma; ii) fracture migration that induce decompression of shallow magma batches
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
Magma dynamics as inferred by plagioclase textural and compositional zoning at Mount Etna volcano
No full textA new perspective on the geochemical signature of Mt. Etna alkaline magmas
No full textThe occurrence of LREE enrichment and HREE
fractionation (LaN/YbN = 18) led many authors to hypothesize
the presence of residual phases in the source of Etnean
alkaline magmas that preferentially retain HREE, such as
garnet. The occurrence of garnet was commonly bounded to
lherzolites, thus implying the onset of partial melting at depth
greater than 80 km. This would indicate the occurrence of a
thermal regime related to an astenospheric plume-like
structure, whose evidence is still matter of debate. On the
other hand, if such a structure does not occur, the melting
process should be mainly under the control of slight pressure
changes induced by regional lithospheric stretching at more
shallow depth. Recent work has shown that partial melting of
a source composed of both spinel lherzolite and garnet
pyroxenite can produce sub-alkaline magmas, which can
preserve a garnet signature at more shallow depth. Here, we
investigate the role that partial melting of a heterogeneous
metasomatized source, constituted of spinel lherzolite and
garnet pyroxenite, can have in producing a trace element
signature consistent with that observed for Etnean alkaline
magmas. Xenoliths of deep provenance found in the Hyblean
area indicate that silicate melts, and related metasomatic
fluids, may have intruded a spinel lherzolite mantle to give
origin to a garnet-bearing pyroxenite. As a result, the spinel
lherzolite mantle is veined by garnet pyroxenite where phases
related to metasomatizing agents, such as amphibole and
phlogopite, have been stabilized. Mass balance calculations
have been performed for simulating partial melting of such a
source. Results have been compared with three representative
mantle-equilibrated magmas, calculated by adding an
ultramafic assemblage to compositions of the prehistoric lavas
of Mt. Maletto, and of the 1763 and 2005 eruptions. Different
proportions of spinel lherzolite and garnet pyroxenite, along
with variable modal contents of metasomatic phases, can
account for the trace element signature of the large spectrum
of Etnean alkaline magmas and for their geochemical
variability through time
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
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