1,720,957 research outputs found
Apatite (U-Th)/He and Fission Track thermochronometry in the Northern Patagonian Andes: New insights into the exhumation history of the thrust belt foreland sector
Full text linkThe study of the Cretaceous–Cenozoic evolution of the North Patagonian Andes represents a great opportunity to investigate the effects of coupling between deep lithospheric processes and near-surface deformation. Despite the general along-strike continuity, this mountain belt is characterized by a pronounced internal tectonic segmentation (marked by the variable position of the magmatic arc and of the deformation front to the east). Thus, this plate margin results in a more complex configuration with respect to the simplified notion of “Andean-type” subduction system.
Being located in the retro-wedge of the Andes, this sector of the Southern Cordillera experienced a complex evolution characterized by alternating flat- and steep-slab subduction stages, which controlled shortening and extension episodes in the overriding plate. Furthermore, the deformation in this whole retroarc sector varied not only in time (i.e. with major 'cycles' of mountain building and orogenic collapse), but also in space, due to the variable transmission of horizontal compressive stress away from the orogen, that produced an irregular unroofing pattern, recorded by obtained low-temperature (low-T) thermochronometric ages. Indeed, low-T thermochronological systems are ideally suited for detecting events involving rocks in the uppermost part of the crust because they record time and rates of cooling related to exhumation of the top few kilometers of the crust.
In this study, apatite (U-Th)/He (AHe) and apatite fission track (AFT) dating are integrated with structural methods in the region located between 40° and 44°S. Two fieldwork periods were carried out throughout the Neuquén, Rio Negro, and Chubut Provinces in order to sample for thermochronological analyses and conduct structural surveys. These methods allowed us comparing the exhumation patterns both between the frontal part of the orogen and its adjacent foreland, and in the same morpho-structural domain at different latitudes.
A total of 48 samples have been collected, processed and analyzed. AHe dating was performed at the University of Paris Sud, while AFT dating was done at the University of Padua. Detailed structural surveys were mainly conducted in the less studied zones of the foreland, and in the entire studied area to check major structures. Integrating the different methods allowed us to unravel the complex tectonic scenario characterizing the study area. Three balanced and sequentially restored cross-sections have been integrated with thermochronological information in order to produce a thermo-kinematic model along two different transects located at 40° and 42°S. To do this, the analyzed transects were processed with FetKin, a dedicated software for forward modeling of thermochronometric ages and age prediction along the present-day profile. This in turn, was used to validate the proposed tectonic scenario. New AFT and AHe data obtained in this study highlight two major tectonic events that occurred in North Patagonia: a Late Cretaceous to Paleogene inversion and exhumation stage, that involved the entire fold-and-thrust belt–foreland basin system, and a Miocene-Pliocene inversion stage of focused exhumation in the Andean fold-and-thrust belt. The suggested tectonic scenario was successfully tested with FetKin along the two transects, allowing us to unravel the role and extent of each tectonic stage that occurred since the Mesozoic.
The recorded pattern may be interpreted as the result of a variable degree of propagation of the deformation from the Andean chain to the foreland. This appears to be controlled by two main parameters: (i) slab configuration (i.e. steep- vs. flat-subduction, which plays a fundamental role in foreland deformation), and (ii) convergence rate between the Pacific and South-America plates, which rules shortening and exhumation processes in the fold-and-thrust belt
Quartz fabric variations across the greenschist facies shear zone separating the zermatt-saas and combin ophiolitic zones, upper val gressoney, western alps
Full text linkThe Gressoney Shear Zone (GSZ) consists of a ca. 500 m thick, intensely deformed rock panel located at the top of the high-pressure ophiolitic rocks of
the Zermatt-Saas Zone in the Western Alps. This greenschist-facies shear zone accommodated multiple non-coaxial deformation events with contrasting kinematics.
In this study, detailed field mapping and structural analysis were integrated with the study of crystallographic preferred orientation (CPO) from mylonites
associated with the GSZ. Quartz CPO displays a systematic variation across the shear zone: moving from the basal shear zone boundary, the c-axes
pattern changes from type II cross-girdle distribution, to an asymmetric pattern characterized by clustering of c-axes on one side of the Z-direction (inclined
single girdle), to a central cluster in the Y-direction. The observed CPO patterns are consistent with increasing shear strain toward the basal contact, which
probably controls the transition from broad peripheral maxima indicative of basal slip to an inclined single girdle with no maxima, which is indicative of
prism slip, and finally an elongate single maximum at the girdle centre produced by a combination of prism and rhomb slip. Our results further
indicate that basal slip is dominant in pure quartz domains, whereas with increasing proportion of second phases, prism slip is activated. These features
confirm that CPOs obtained from the almost pure quartzites analysed in most published studies, and generally associated with the activation of distinct
slip systems controlled by temperature, cannot be straightforwardly applied to the analysis of heterogeneous shear zones and/or polymineralic mylonites.
From a regional point of view, the structures observed in the field and the fabric analyses are consistent with top-to-the-SE extension post-dating subductionrelated
high-pressure metamorphism and collisional nappe stacking in the studied sector of the Western Alps
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
