1,721,012 research outputs found
Topographic expressions of mantle dynamics in the Mediterranean
No full textThe surface of the Earth is the ever-changing expression of the dynamic processes occurring at depth and at or above its surface. However, our ability to “read” landscapes in terms of their underlying tectonic or climatic forcing remains rudimentary. During the last decade, particular attention has been drawn to the deep dynamic contributions to topography, related to the stresses that are produced at the base of the lithosphere by mantle convection, and their relevance compared to the (iso)static component of topography. Here, we use examples from the Mediterranean and estimate residual and dynamic topography. We then compare those with surface uplift from geology for specific regions to disentangle the dynamic from the static components. Considering the different topographic signatures of tectonic processes (e.g. actual, residual, and dynamic topography as well as uplift rates) jointly provides a powerful way to distinguish between the contributions of mantle, crustal, and surface processes. Such an approach might bring us closer to reading topographic expressions in terms of their geological cause
Shaping mobile belt by small scale convection
No full textMobile belts are long-lived deformation zones composed of an
ensemble of crustal fragments, distributed over hundreds of kilometres
inside continental convergentmargins1,2.TheMediterranean
represents a remarkable example of this tectonic setting3: the region
hosts a diffuse boundary between the Nubia and Eurasia plates
comprised of a mosaic of microplates that move and deform independently
from the overall plate convergence4. Surface expressions
of Mediterranean tectonics include deep, subsiding backarc basins,
intraplate plateaux and uplifting orogenic belts. Although the
kinematics of the area are now fairly well defined, the dynamical
origins ofmany of these active features are controversial and usually
attributed to crustal and lithospheric interactions. However, the
effects of mantle convection, well established for continental
interiors5–7, should be particularly relevant in a mobile belt, and
modelling may constrain important parameters such as slab coherence
and lithospheric strength. Here we compute global mantle
flow on the basis of recent, high-resolution seismic tomography to
investigate the role of buoyancy-driven and plate-motion-induced
mantle circulation for theMediterranean.Weshowthatmantle flow
provides an explanation for much of the observed dynamic topography
and microplate motion in the region. More generally,
vigorous small-scale convection in the uppermost mantle may also
underpin other complex mobile belts such as the North American
Cordillera or the Himalayan–Tibetan collision zone
A review of the role of subduction dynamics for regional and global plate motions
No full textSubduction of oceanic lithosphere and deep slabs control several aspects
of plate tectonics. We review models of subduction dynamics that have been studied
over the last decade by means of numerical and analog experiments. Regional models
indicate that trench rollback, trench curvature, and back-arc deformation may be
explained by fl uid slabs that are ~250–500 times stiffer than the upper mantle. Slab
width and, more importantly, rheology determine the role of viscous bending, poloidalsinking
fl ow and toroidal-rollback stirring, and interactions of the slab with the
higher viscosity lower mantle. Several of these contributions can be represented by
a local sinking velocity. Back-arc deformation may then result from an imbalance if
larger-scale plate forcing leads to deviations of the convergence rate from the local
equilibrium. Lateral viscosity variations (LVVs) are also key for understanding plate
driving forces. The realism of global circulation computations has advanced and
such models with weak zones and other LVVs have lead to an improved match to
observed plate tectonic scores. Those include the correlation with plate motions, the
magnitude of intraplate deformation, and oceanic to continental plate velocity ratios.
Net rotation of the lithosphere with respect to the lower mantle may be caused
jointly by regional slab forcing and the stirring effect of cratonic keels. However,
slab models have so far only produced net rotations that are small compared to
recent hotspot reference-frame models. Progress in the next years will likely come
from a better understanding of slab strength, which is still uncertain since large-scale
subduction zone observables and laboratory results do not put strong constraints on
slab rheology. Importantly, circulation models with an improved representation of
convergent margins will help to close the gap between regional and global approaches
to subduction, and to better understand the potential role of the overriding plate
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
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