1,721,049 research outputs found
Shear deformation in mafic-ultramafic complex in north-western Elba island (Northern Tyrrhenian Sea)
Full text linkThe Cotoncello shear zone is developed in the mafic and ultramafic rocks cropping out in the north-western Elba island (northern Apennines). The mylonitic fabrics documented in the field, are highlighted by a pervasive mylonitic foliation and by cm- to dm-thick high-strain transpressive shear zones with a top-to-the S/SE sense of shear. At the microscopic scale, the mylonitic foliation in the highstrain shear zones is made exclusively by isoriented Mg-hornblende and tremolite. In the less deformed domains, Mg-hornblende and tremolite rich-layers enveloped small domains preserving igneous fabric and/or older mylonitic fabric. Mineral assemblage on the amphibolitic-bearing mylonitic foliation indicates that the youngest mylonitic fabric occurred under amphibolites facies condition (T > 550°C, P: 0.6-0.8 GPa). © Società Geologica Italiana, Roma 2013
Coexistence of contractional and extensional tectonics during the northern Apennines orogeny: The late Miocene out-of-sequence thrust in the Elba Island nappe stack
No full textIn the northern Tyrrhenian Sea, the Elba Island is one of the westernmost portions of the northern Apennine inner belt. One of its noteworthy features is the anomalous tectonic repetition of continental-derived (Tuscan Unit) and oceanic-derived (Ligurian units) thrust sheets, lately intruded by late Miocene granitoids. Moreover, in detail, a slice of strongly deformed Ligurian peridotites results tectonically sandwiched between two thrust sheets of Tuscan units. This tectonic setting results from a middle Miocene folding and thrusting of the Apenninic nappe stack with development of large-scale antiform and out-of-sequence thrust. In central-eastern Elba Island, the folding of an imbricate stack is bracketed between Langhian (middle Miocene) and Messinian (late Miocene). Consequently, the anomalous repetition of Tuscan and Ligurian units thrust sheets gives evidence of middle-late Miocene shortening deformation post-dating nappe stack and pre-dating late Miocene-Pliocene granite emplacement. We suggest that the architecture of the Elba Island nappe stack documents the coexistence of early-middle Miocene contractional and extensional tectonics in an overall convergent tectonic setting in the westernmost zone of northern Apennines. Extensional tectonics in the upper portion of the wedge, balancing transient gravitational instabilities due to over-thickened conditions, were followed by a renewal of contractional deformation leading to development of large-scale out-of-sequence thrust responsible for inversion of the stack order
Fluid transfer and vein thickness distribution in high and low temperature hydrothermal systems at shallow crustal level in southern Tuscany (Italy)
Full text linkGeometric analysis of vein systems hosted in upper crustal rocks and developed in high and low temperature hydrothermal systems is presented. The high temperature hydrothermal system consists of tourmaline-rich veins hosted within the contact aureole of the upper Miocene Porto Azzurro pluton in the eastern Elba Island. The low temperature hydrothermal system consists of calcite-rich veins hosted within the Oligocene sandstones of the Tuscan Nappe, exposed along the coast in southern Tuscany. Vein thickness distribution is here used as proxy for inferring some hydraulic properties (transmissivity) of the fluid circulation at the time of veins’ formation. We derive estimations of average thickness of veins by using the observed distributions. In the case of power law thickness distributions, the lower the scaling exponent of the distribution the higher the overall transmissivity. Indeed, power law distributions characterized by high scaling exponents have transmissivity three order of magnitude lower than negative exponential thickness distribution. Simple observations of vein thickness may thus provides some clues on the transmissivity in hydrothermal systems
Introduction: Anatomy of rifting: Tectonics and magmatism in continental rifts, oceanic spreading centers, and transforms
Full text linkResearch at continental rifts, mid-ocean ridges, and transforms has shown that new plates are created by extensional tectonics, magma intrusion, and volcanism. Studies of a wide variety of extensional processes ranging from plate thinning to magma intrusion have helped scientists understand how continents are broken apart to form ocean basins. However, deformation processes vary significantly during the development of continental rifts and mid-ocean ridges. In addition, ocean ridges are offset along their length by major transform faults, the initiation of which is poorly understood. Data documenting active processes have proven difficult to obtain because most ridges are submerged with only rare portions of the divergent plate boundary being exposed on land. Therefore our current knowledge about the length and time scales of magmatism and faulting during rift evolution as well as the mechanisms of initial development of mid-ocean ridges and transforms is limited. In this themed issue we present contributions that document the wide variety of processes acting at divergent plate boundaries and transforms in order to synthesize some of the most relevant research topics about plate extension and to identify the important questions that remain unanswered. <br/
Control of gravitational potential energy on the distribution of off‐rift volcanic activity in the Turkana depression, East African rift
No full textThe distribution and alignment of volcanism in continental rifts is controlled by regional extensional stresses modulated by several factors such as structural inheritance, volcano edifice loading, and rift architecture. These interactions result in complex characteristics of rift-related volcanic features, which may be difficult to interpret considering the different controlling processes. The Turkana Depression (East Africa) exemplifies these complexities, showing an anomalous location of volcanic fields (outside the area of ongoing extension), with variable vent orientation. We analyze vent distribution in the Turkana Depression and calculate the stresses resulting from Gravitational Potential Energy (GPE). Our results show that West to East variations in topography and (subordinately) crustal thickness give rise to extensional GPE-related stresses East of Lake Turkana, where recent off-rift volcanism is localized. Within each different volcanic field, local GPE-related stresses control the arrangement of volcanic vents, which therefore do not respond to the regional (plate motion-driven) stress field
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
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