1,720,964 research outputs found
Styles and regimes of orogenic thickening in the Peloritani Mountains (Sicily, Italy): new constraints on the tectono-metamorphic evolution of the Apennine belt
No full textThe Peloritani Mountains constitute the Sicilian portion of the Calabria–Peloritani Arc
(Italy), a tectono-metamor phic edifice recording the history of the subduction–exhumation cycle during
Tertiary convergence between the African and European plates. Here, we describe the kinematic and
the petrological characteristics of the major shear zones bounding the lowermost continental-derived
metamor phic units cropping out in the eastern portion of the Peloritani Mountains. Both meso-
and micro-scale shear sense criteria indicate a top-to-the-SSE tectonic transport, during a general
evolution from ductile to brittle deformation conditions. Quantitative thermobarometry on texturally
equilibrated phengite–chlorite pairs crystallized along the shear bands indicates pressure of 6–8 kbar
at temperatures of 360–440 ◦ C for the structurally highest units and 3–4 kbar at 380–440 ◦ C for the
lowest ones. This documents an overall inverse-type nappe ar rangement within the tectonic edifice
and a transition from an Alpine- (13–18 ◦ C km−1 ) to a Bar rovian-type (28–36 ◦ C km−1 ) geothermal
gradient during the progress of the Alpine orogenic metamor phism in the Peloritani Mountains. The
integration of these results allows the Peloritani Mountains to be considered as a constituent element
of the Apennine orogenic domain formed during the progressive space–time transition from oceanic
to continental subduction at the active convergent margin
A counter-clockwise P-T path for the Voltri Massif eclogites (Ligurian Alps, Italy)
No full textIntegrated petrological and structural investigations of eclogites from the eclogite zone of the Voltri
Massif (Ligurian Alps) have been used to reconstruct a complete Alpine P–T deformation path from
burial by subduction to subsequent exhumation. The early metamorphic evolution of the eclogites has
been unravelled by correlating garnet zonation trends with the chemical variations in inclusions found in
the different garnet domains. Garnet in massive eclogites displays typical growth zoning, whereas garnet
in foliated eclogites shows rim-ward resorption, likely related to re-equilibration during retrogressive
evolution. Garnet inclusions are distinctly different from core to rim, consisting primarily of Ca-,
Na/Ca-amphibole, epidote, paragonite and talc in garnet cores and of clinopyroxene ± talc in the outer
garnet domains. Quantitative thermobarometry on the inclusion assemblages in the garnet cores defines
an initial greenschist-to-amphibolite facies metamorphic stage (M1 stage) at c. 450–500 C and
5–8 kbar. Coexistence of omphacite + talc + katophorite inclusion assemblage in the outer garnet
domains indicate c. 550 C and 20 kbar, conditions which were considered as minimum P–T estimates
for the M2 eclogitic stage. The early phase of retrograde reactions is polyphase and equilibrated under
epidote–blueschist facies (M3 stage), characterized by the development of composite reaction textures
(garnet necklaces and fluid-assisted Na-amphibole-bearing symplectites) produced at the expense of the
primary M2 garnet-clinopyroxene assemblage. The blueschist retrogression is contemporaneous with the
development of a penetrative deformation (D3) that resulted in a non-coaxial fabric, with dominant topto-
the-N sense of shear during rock exhumation. All of that is overprinted by a texturally late
amphibolite/greenschist facies assemblages (M4 & M5 stages), which are not associated with a
penetrative structural fabric. The combined P–T deformation data are consistent with an overall
counter-clockwise path, from the greenschist/amphibolite, through the eclogite, the blueschist to the
greenschist facies. These new results provide insights into the dynamic evolution of the Tertiary oceanic
subduction processes leading to the building up of the Alpine orogen and the mechanisms involved in
the exhumation of its high-pressure roots
Pressure-Temperature-Deformation-time(P-T-d-t) exhumation history of the Voltri Massif HP-complex, Ligurian Alps, Italy
No full textAn integrated structural, petrological, and geochronological/thermochronological study was undertaken to constrain the tectonic controls on the exhumation of the Voltri Massif high-pressure (HP) complex, located in the Ligurian portion of the Western Alps (Italy). Petrotextural analyses were performed to identify the pressure-temperature interval of (1) peak metamorphism (the D1-M1 stage) to eclogitic/blueschist facies conditions and (2) the main retrogressive event (the D2-M2 stage) to greenschist facies conditions. U-Pb SHRIMP dating on a zircon rim (33.8 ± 0.8 Ma) and titanite grains (29 ± 5 Ma), coupled with 40Ar-39Ar analyses on phengite (∼64 Ma to ∼34 Ma) placed temporal constraints on the exhumation path from the D1-M1 to the D2-M2 stages at the Eocene-Oligocene boundary. Apatite fission track thermochronology, with older ages of 23.9 ± 4.9 Ma, confirms the existence of a regional, Late Oligocene to Miocene cooling/exhumation event for the Voltri Massif (the D3-M3 stage). The compilation of this pressure-temperature-deformation-time path supports a change in the exhumation history: (1) an initial stage, from the D1-M1 to the D2-M2, which was nearly isothermal with highly variable exhumation rates, and (2) a second stage, from D2-M2 to upper crustal levels, which was accomplished by cooling and moderate exhumation rates of ∼1–2 mm yr−1. This two-stage path can be reconciled with the dominant tectonic mechanisms responsible for exhumation of HP rocks in the Voltri Massif area. At the regional scale, this path is consistent with major geodynamic reorganization in the Mediterranean region at the Eocene-Oligocene time boundary, which involved a switch from synorogenic events during transpressive kinematics at the Alpine-Apennine plate boundaries, to postorogenic processes related to crustal thinning and opening of back-arc basins
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
Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)
Full text linkThe Iranian ophiolites are part of the vast orogenic suture zones that mark the Alpine-Himalayan convergence zone. Few petrological and geochronological data are available from these ophiolitic domains, hampering a full assessment of the timing and regimes of subduction zone metamorphism and orogenic construction in the region. This paper describes texture, geochemistry, and the pressure-temperature path of the Early Cretaceous mafic granulites that occur within the Tertiary Sabzevar ophiolitic suture zone of NE Iran. Whole rock geochemistry indicates that the Sabzevar granulites are likely derived from a MORB-type precursor. They are thus considered as remnants of a dismembered dynamo-thermal sole formed during subduction of a back-arc basin (proto-Sabzevar Ocean) formed in the upper-plate of the Neotethyan slab. The metamorphic history of the granulites suggests an anticlockwise pressure-temperature loop compatible with burial in a hot subduction zone, followed by cooling during exhumation. Transition from a nascent to a mature stage of oceanic subduction is the geodynamic scenario proposed to accomplish for the reconstructed thermobaric evolution. When framed with the regional scenario, results of this study point to diachronous and independent tectonic evolutions of the different ophiolitic domains of central Iran, for which a growing disparity in the timing of metamorphic equilibration and of pressure-temperature paths can be expected to emerge with further investigations
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
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