1,720,985 research outputs found
Metasediments covering ophiolites in the hp internal belt of the western alps: Review of tectono‐stratigraphic successions and constraints for the alpine evolution
Full text linkOphiolites of the Alpine belt derive from the closure of the Mesozoic Tethys Ocean that was interposed between the palaeo‐Europe and palaeo‐Adria continental plates. The Alpine orogeny has intensely reworked the oceanic rocks into metaophiolites with various metamorphic im-prints. In the Western Alps, metaophiolites and continental‐derived units are distributed within two paired bands: An inner band where Alpine subduction‐related high‐pressure (HP) metamorphism is preserved, and an outer band where blueschist to greenschist facies recrystallisation due to the decompression path prevails. The metaophiolites of the inner band are hugely important not just because they provide records of the prograde tectonic and metamorphic evolution of the Western Alps, but also because they retain the signature of the intra‐oceanic tectono‐sedimentary evolution. Lithostratigraphic and petrographic criteria applied to metasediments associated with HP met-aophiolites reveal the occurrence of distinct tectono‐stratigraphic successions including quartzites with marbles, chaotic rock units, and layered calc schists. These successions, although sliced, de-formed, and superposed in complex ways during the orogenic stage, preserve remnants of their primary depositional setting constraining the pre‐orogenic evolution of the Jurassic Tethys Ocean
Fossil mantle-sediments interface recognized in the Western Alps metaophiolites : a key to unravel the accretion mechanism of the Jurassic Tethys ocean
No full textABSTRACT
In the southern Aosta Valley (Italian Northwestern Alps), meta-ophiolites are mainly composed of serpentinized mantle-derived peridotites intruded by gabbros and rodingitic dykes, well exposed in the Mount Avic area, and of smaller amounts of mafic rocks and metatrondhjemite. This rock assemblage recalls the "slow-spreading" lithosphere created at modern mid-ocean ridges. Meta-ophiolites show a dominant early Alpine subduction-related metamorphic imprint under eclogite/blueschist facies conditions, variously retogressed under greenschists facies conditions. In the high Champorcher Valley (SW of Mount Avic) serpentinites are directly covered by a serpentinite mélange followed by flysch-like calcschists with detrital ophiolitic interbeds. Despite the pervasive Alpine tectonic deformation and metamorphic recrystallization through subduction-related stretching and boudinage and collision-related folding, the mélange internal fabric still retains records of a block-in-matrix structure, well consistent with mass-transport processes related to an active oceanic tectonic setting in which mantle rocks were progressively and continuously exhumed by faulting. The products of mass-transport processes and faulting are unconformably sealed by flysch-type calcschists embedding cm-sized clasts of actinolite/tremolite-schists interpreted as detrital ophiolitic material. The serpentinite mélange is interpreted as syn-extensional sedimentary rocks produced at the mantle-sediments interface on the Jurassic Tethys ocean floor and subsequently overprinted by subduction zone tectonics
Geology of the Fontane talc mineralization (Germanasca valley, Italian Western Alps)
Full text linkThe 1:5000 scale Geological Map of the Fontane talc mineralization (FTM) aims to give new information about the origin and geological structure of an important talc mineralization occurring in the axial sector of the Italian Western Alps. The FTM is hosted within a pre-Carboniferous polymetamorphic complex which was deformed and metamorphosed during both Variscan and Alpine orogenesis, and is part of the Dora-Maira continental crust. Field mapping and underground investigations highlight that the talc bodies (i) never crop out but occur at depth along a well-defined lithostratigraphic association between micaschist, marble and gneiss and (ii) were deformed during different Alpine-related deformation phases (i.e. D1, D2 and D3 syn-metamorphic phases and post-metamorphic extensional faulting). The here defined lithostratigraphic and structural characterization of talc bodies, is an input for further research into the geodynamic context of where talc forms and for new mineral exploration outside the mapped area
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
Different types of HP mélange and broken formation in the northern Monviso Meta-ophiolite Complex (Inner Western Alps, NW Italy)
No full textIn the Western Alps the superposition of tectonic and/or tectonometamorphic events, and mineral transformations, strongly concur in obscuring the original prevailing processes of formation of block-inmatrix structures. We document in this study the occurrence and nature of different types of block-in-matrix structures (i.e. sedimentary and tectonic mélanges, and broken formations), formed at the plate interface between continental (i.e. the Dora Maira Unit) and oceanic (i.e. the Monviso Metaophiolite Complex) units, that experienced the overprint of different tectonic stages from subduction to collision. A Sedimentary Mélange characterizes the metasedimentary cover of the Dora Maira Unit and consists of exotic blocks (i.e., olistholits and blocks of marble) gravitationally collapsed from the margins of the Triassic-to Jurassic carbonate platform of the European continental margin. The Broken Formation is obtained thanks to the superposition of two deformation phases that, during exhumation stages, dismembered the original coherent stratigraphic succession. The Tectonic Mélange started to be formed during the subduction via offscraping of exotic blocks from the heterogeneous oceanic seafloor. The superposition of exhumation-related deformation contributed to form its final "structurally ordered" block-inmatrix fabric. Our findings may provide better constraints for the tectonometamorphic evolution of the northern sector of the Monviso Metaophiolite Complex and its pre-orogenic physiography. © Società Geologica Italiana, Roma 2013
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