1,720,982 research outputs found
Metasomatic reaction bands at the Mt. Hochwart gneiss-peridotite contact (Ulten Zone, Italy): insights into fluid-rock interaction in subduction zones
No full textWe investigated the contact zone between peridotite
lenses and host gneisses located on the northern side of the
Hochwart peak, also known as Vedetta Alta (Ulten Zone, Alto
Adige -Südtirol) where metasomatic contact bands occur. The
country rocks are gneisses consisting mainly of quartz, Kfeldspar,
garnet, kyanite, biotite and muscovite. The ultramafic
body consists of a hectometre-sized garnet peridotite and
harzburgite lens. The reaction zone shows mineralogic zoning
from phlogopite-rich to tremolite-anthophyllite-talc-rich rocks
from the host gneiss towards the peridotite. In some cases,
lenses of serpentine and talc in association with chlorite, and
trondhjemitic pods develop at the ultramafic rocks border to
the gneisses. Trondhjemite dikes with pegmatoid texture also
crosscut the peridotite body. Phlogopite aggregates with
accessory zircon, Cl-apatite and tourmaline and phlogopitehornblende
aggregates also occur. The combination of
petrography, mineral chemistry and mass balance calculations
constrains the gains and losses of elements during metasomatism.
Reaction zone formation involved extensive addition of
H2O, K2O and LILE from the fluid, whereas MgO, CaO and
Al2O3 were removed from the peridotite. Thus, the formation
of the reaction zones between the mantle rocks and the
gneisses was triggered by considerable fluid/melt circulation,
causing crystallisation of mainly phlogopite, anthophyllite
and talc, and the release of a trondhjemitic residual melt.
Field mapping provides evidence that the internal structures
of the host migmatites (folds) and those of the peridotites
(foliation, fluid texture) are discordant. Pseudosection calculations
give insights into the P-T conditions (T 660–700°C; P
0.5–0.7 GPa) of metasomatism responsible for the formation
of reaction zones, which is related to the retrograde path of
the Ulten Zone peridotites. Our results suggest that the
redistribution of major and trace elements in subduction
zones is strongly influenced by metasomatic reactions
occurring at the slab-mantle interface
Eckerite, Ag2CuAsS3, a new Cu-bearing sulfosalt from Lengenbach quarry, Binn valley, Switzerland: Description and crystal structure
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
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
Amphibole and phlogopite in “hybrid” metasomatic bands monitor trace element transfer at the interface between felsic and ultramafic rocks (Eastern Alps, Italy)
No full textUltramafic rocks in the Mt. Hochwart HP mélange (Eastern Italian Alps) preserve a series of metasomatic mineral zones generated by infiltration of hydrous fluids at T of 660-700°C and P<1.2 GPa, which occurred at the gneiss-peridotite interface. We present the results of in situ LA ICP-MS trace element analysis of minerals from contact lithologies (metasomatic zones and phlogopitite). Trace element composition of hydrous phases (phlogopite and amphibole) in different
metasomatic zones indicate mobility of many elements, including elements such as Ta, which are considered to show scarce mobility in fluids. Trace element composition of accessory minerals such as apatite in the phlogopite-rich zone suggests that the trace element signature of subduction zone fluids may be fractionated in this zone. The progressive depletion in some trace elements (LREE and LILE) and the enrichment in Li from the gneiss towards the peridotite suggest a strong influence of bulk composition on the trace element budget of hydrous minerals. Since these metasomatic zones represent geochemical processes occurring at the slab-mantle
interface, we can infer that metasomatic reactions between slab derived fluids and ultramafic mantle wedge will follow a specific series of reactions, creating mineral zones similar to those observed in this study. We stress the importance of phlogopite crystallization at the slab-mantle interface as an efficient mechanism to filter LILE from the fluid. Our results further favour the evidence that the primary composition of subduction zone fluids reaching the source region of arc magmas is substantially modified by metasomatic reactions occurring in the mantle wedge
In situ Sr isotope analysis of mantle carbonates: Constraints on the evolution and sources of metasomatic carbon-bearing fluids in a paleo-collisional setting
Full text linkCarbonate-bearing wedge peridotites attest the mobilization of carbon (C) by slab fluids/melts circulating in a subduction setting. In general, COH fluids are thought to derive from the dehydration/partial melting of the crustal portions of slabs, especially during the exhumation of crust-mantle mélanges along continental subduction channels. In this study we combined textural observations with in-situ Sr isotope analyses of mantle carbonates occurring in different microstructural sites to test whether the fluids responsible for the carbonation of a mantle wedge are derived from the subducted continental crust or not. We focus on the Ulten Zone peridotites (Eastern Italian Alps) associated with high-grade felsic rocks, where carbonates occur mainly as dolomite and minor magnesite and calcite. In situ laser MC-ICP-MS analysis of peridotites representing different episodes of a complex metasomatic history, indicates that Sr isotopic variations can be linked to the different microstructural positions of carbonates. The C-metasomatism of the UZ peridotites is proposed to have occurred in two stages. The first stage is the HP‐carbonation at peak (eclogite-facies) conditions, with formation of interstitial matrix dolomite in textural equilibrium with hornblende to pargasite amphibole and Cl-apatite. This dolomite exhibits relatively unradiogenic 87Sr/86Sr present day values of 0.70487±0.00010, requiring different sources with respect to the associated migmatites and the overhanging mantle wedge. Carbonation continued during exhumation, with local injection of C-rich fluids forming a dolomite vein in association with tremolite and chlorite. The dolomite vein shows a wide range of 87Sr/86Sr (0.7036–0.7083), reflecting both the primary composition of carbonates and the consequent interaction with crustal fluids as expected in a crust-mantle mélange. The second stage is C-remobilization by dolomite dissolution and precipitation of brucite intergrowths with calcite during the final exhumation. This remobilization event has resulted in a similar Sr composition to the precursor dolomite. The mantle wedge is therefore capable of storing carbonates which have been shown to represent a complex metasomatic evolution from eclogite-facies conditions to very shallow structural levels. Therefore, fluids released from subducting slabs of continental lithosphere might be responsible for the crystallization of metasomatic minerals such as amphibole, phlogopite and zircon in the overlying ultramafic rocks. Conversely, the role of these metasomatic fluids on the carbonation of mantle wedge is likely overestimated. The combination of geochemical, isotopic and textural evidence suggests that dolomite inclusions and interstitial dolomite are derived in large part from a distinct source of C-bearing fluids that could be related to depleted mantle wedge sources and/or trondhjemitic igneous activity. In contrast, at the end of exhumation, residual COH-fluids released by the associated stromatic gneisses and orthogneisses resulted in late-stage dolomite veins having the highest Sr isotope values in the Ulten Zone peridotites
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