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Federico Caprilli e la svolta copernicana della monta naturale: da Tor di Quinto a Pinerolo
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Mapping of hydrogen and carbon in volcanic minerals: an infrared microspectrometry study
No full textThe analysis of volatile traces such as H2O and CO2 in volcanic minerals may provide significant constraints on the genesis and evolution of magmatic systems. The analysis of water in minerals (e.g. Libowitzky and Rossman, 1997) and glasses (Ihinger et al., 1994) using FTIR spectrometry is now a relatively routine technique, however still few data exist on the H2O content and distribution in nominally-anhydrous minerals (NAMs) from volcanic environments. On the contrary, the spectroscopic analysis of CO2 is common in glasses or fluid inclusions within minerals (e.g. Linnen et al., 2004), although work on minerals has been so far restricted on few cases (see Armbruster and Bloss, 1980, Komenko and Langer, Della Ventura et al., 2005, 2007 and references therein). One additional point of extreme interest in the study of volcanic materials, is the distribution of the volatile constituent across the crystal, which can provide insight into the evolution of the crystallizing system with time; such possibility is offered by modern microscopes and spectrometers where a good spatial resolutions (20-30 μm) is coupled with computer-controlled stages or focal-plane-array (FPA) detector systems.
In this work we explore the possibilities provided by the new facilities for microspectrometry recently made available at SIMBAD, INFN-LNF (Frascati, Rome), for the analysis of the distribution of water and carbon dioxide within some volcanic crystals. The specimens studied are from volcanic rocks spanning lava flows, pyroclastic deposits and volcanic ejecta, these latter representing fragments of the basement under the volcanic area (magmatic chamber or the volcanic conduct), scavenged during the explosive effusion and scattered on the surface. In particular we show here the data collected on several feldspathoids, clinopyroxenes, garnets, and cordierite.
References
Armbruster T. and Bloss F.D. (1980) Nature, 286, 140-141.
Della Ventura, G., Bellatreccia, F., Bonaccorsi, E. (2005) Eur. J. Mineral., 17, 847-851.
Della Ventura, G., Bellatreccia, F., Parodi, G.C., Cámara, F., Piccinini, M. (2007) Am. Mineral., in press.
Khomenko V.M. and Langer K. (2005) Am. Mineral., 90, 1913-1917.
Ihinger, P.D., Hervig, R.L., and McMillan. P.F. (1994) Rev. Mineral., 30, 67-121.
Linnen, B., Keppler, H. and Sterner, S.M. (2004) Can. Mineral., 42, 1275-1282.
Libowitzky, E. and Rossman, G.R. (1997) Am. Mineral., 82, 1111-1115
Metamorphic, metasomatic and instrusive xenotiths of the Colli Albani Volcano and their significance for the reconstruction of the volcano plumbing system
No full textCrystal structure and crystal chemistry of fluorannite and its relationships to annite
No full textWe present the crystal chemical characterization of fluorannite from Katugin Ta-Nb deposit, Chitinskaya Oblast’, Kalar Range, Transbaikalia, Eastern-Siberian Region, Russia. This mica belongs to 1M polytype (space group C2/m) with layer parameters a = 5.3454(2) Å, b = 9.2607(4) Å, c = 10.2040(5) Å, ? = 100.169(3)°. Structure refinement, using anisotropic displacement parameters, converged at R = 0.0384. Fluorannite shows a smaller cell volume (V = 497.19 Å3) than annite (V = 505.71 Å3) because of its smaller lateral dimensions and its reduced c parameter. The flattening of the tetrahedral basal oxygen atoms plane decreases with F content, together with the A-O4 distance (i.e., the distance between interlayer A cation and the octahedral anionic position) because of the reduced repulsion between the interlayer cation and the anion sited in O4
Metamorphic, metasomatic and intrusive xenoliths of the Colli Albani volcano and their significance for the reconstruction of the volcano plumbing system
No full textThis paper analyses the xenoliths found in the phreatomagmatic products of the most
recent Via del Laghi maar field at Colli Albani volcano in order to investigate the nature of the
substratum and its interaction with the magmatic system. The pre-volcanic sedimentary xenoliths
are from the same rock formations that form the pre-orogenic Mesozoic – Cenozoic carbonatic
pelagic succession cropping out in the nearby Apennine mountain belt, and the Pliocene post-
orogenic marine sedimentary succession. Along with the sedimentary xenoliths, a large variety
of thermo-metamorphic, metasomatic and magmatic xenoliths are present. Skarn xenoliths have
been studied to estimate peak metamorphic P – T conditions and assess the role of fluids during
prograde and retrograde metamorphism. The presence of hydrous minerals such as phlogopite
and amphibole and the carbonatic nature of the substratum suggest a binary H2O – CO2 mixture
as the dominant fluid. Microscale wollastonite filling fractures indicates a temporal link between
fracturing and fluid infiltration. The occurrence of retrograde hydrous textures superimposed on
anhydrous associations indicates at least a two step process: metamorphism with a T peak at dry
conditions (CO2 saturated), followed by fracturing of the substratum in the late stage, allowing
abundant aqueous fluids to penetrate the thermally modified rocks. A significative amount of
rare earth minerals crystallized in the late stage
Britholite - hellandite intergrowths and associated REE-minerals from the alkali-syenitic ejecta of the Vico volcanic complex (Latium, Italy): petrological implications bearing on REE mobility in volcanic systems
No full textThis paper describes the occurrence of Th-rich hellandite-(Ce) and britholite-(Ce) within a volcanic ejectum from a pyroclastic formation of the Vice volcanic complex, north of Rome, Italy. The host rock is a saturated alkali-syenite which consists mainly of potassium feldspar and plagioclase, together with fluor-biotite, plagioclase, titanite, clinopyroxene and magnetite. Hellandite-(Ce) and britholite-(Ce) are associated with this mineral assemblage which contains also several accessory phases including zircon, fluorapatite, allanite, and silico-phosphates of Th, U, REE close in composition to cheralite-brabantite. Hellandite-(Ce) and britholite-(Ce) are typically intergrown with hellandite in all case observed rimming britholite. These unusual REE, Th, U minerals are secondary to the formation of the host rock and the compositions of the associated minerals suggest that they originated from fluids rich in F, P and possibly S and C. The presence of fractures filled by clays containing dispersed REE-minerals, probably fluorocarbonates, suggests a very late-stage hydrothermal remobilization, transportation and redeposition of the REE. An important implication of such widespread secondary mineralization is that great care should be exerted when using bulk-rock trace-element data from these volcanic samples for geochemical modelling
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
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