1,720,979 research outputs found
Exhumation history of the Red River shear zone in northern Vietnam: New insights from zircon and apatite fission-track analysis
No full textA new set of zircon and apatite fission-track ages from the Ailao Shan and Day Nui Con Voi (DNCV) metamorphic massifs of the Red River shear zone (RRSZ) and neighboring rocks in northern Vietnam is presented. A complex, along-strike diachronous, denudation history is revealed. The southern sector of the DNCV cooled to about 100 °C by the Late Oligocene, whereas its central compartment was affected by the later thermotectonic evolution of the Song Chay dome to the E of the RRSZ, whose final exhumation occurred during the Early Miocene. The northern sector of the RRSZ is characterized by the 35 Ma Phan Si Pang pre- to synkinematic intrusion. Fission-track ages from a vertical section within the Phan Si Pang granite indicate rapid exhumation and cooling. The Paleozoic tectonic block to the west of the RRSZ (fission-track ages between 40 and 30 Ma) was exhumed and cooled earlier than the fault mylonite belt (fission track ages of 30 Ma and younger) and also than the eastern block. Its structural level is consistent with field observations that suggest the RRSZ in northern Vietnam to be a transtensional system, with a regional NE-SW oriented extension component. © 2007 Elsevier Ltd. All rights reserved
Exhumation history of subcontinental, garnet pyroxenite-bearing mantle from the External Liguride ophiolites (Northern Apennine, Italy): implications for rifting and mantle exhumation processes at ocean-continent transition
No full textStructure and shearing conditions in the Day Nui Con Voi massif: Implications for the evolution of the Red River shear zone in northern Vietnam
Full text linkThe Day Nui Con Voi massif bears a record of the Red River shear zone (RRSZ) activity in North Vietnam. It forms a large-scale antiformal "core complex"-type structure, bounded by the Song Hong and Song Chay faults. The kinematics of both faults are identical and reflect transtensional shear initiated under upper amphibolite facies conditions and propagated into greenschist facies. Microfabric analysis establishes that both extensional and strike-slip shearing initiated between 700 and 500°C. The RRSZ evolved from a single, subvertical fault, which, due to strike-perpendicular extension, underwent progressive dilation. The created space was "intruded" by already metamorphosed and deformed ductile middle crust in the form of a gneissic "dome." Both strike-slip and extensional shearing were accommodated in the limbs of the antiform, while its core was uplifted from midcrustal level bearing only a minor record of sinistral shear. Copyright 2007 by the American Geophysical Union
Exhumation history of a garnet pyroxenite-bearing mantle section from a continent-ocean transition (Northern Apennine ophiolites, Italy)
No full textGarnet clinopyroxenite and garnet websterite layers occur locally within mantle peridotite bodies from the External Liguride Jurassic ophiolites (Northern Apennines, Italy). These ophiolites were derived from an ocean–continent transition similar to the present day western Iberian margin. The garnet clinopyroxenites are mafic rocks with a primary mineral assemblage of pyrope-rich garnet + sodic Al-augite (Na2O ca. 2.5 wt %, Al2O3 ca.12.5 wt %), with accessory graphite, Fe–Ni sulphides and rutile. Decompression caused Na-rich plagioclase (An50–45) exsolution in clinopyroxene porphyroclasts and extensive development of symplectites composed of secondary orthopyroxene + plagioclase (An85–72) þ Al-spinel ± clinopyroxene ± ilmenite at the interface between garnet and primary clinopyroxene. Further decompression is recorded by the development of an olivine + plagioclase-bearing assemblage, locally under syn-kinematic conditions, at the expense of two-pyroxenes þ Al-spinel. Mg-rich garnet has been also found in the websterite layers, which are commonly characterized by the occurrence of symplectites made of orthopyroxene þ Al-spinel ± clinopyroxene. The enclosing peridotites are Ti-amphibole-bearing lherzolites with a fertile geochemical signature and a widespread plagioclase-facies mylonitic foliation, which preserve in places a spinel tectonite fabric. Lu–Hf and Sm–Nd mineral isochrons (220 ± 13 Ma and 186.0 ± 1.8 Ma, respectively) have been obtained from a garnet clinopyroxenite layer and interpreted as cooling ages. Geothermobarometric estimates for the high-pressure equilibration have yielded T ca.1100°C and P ca. 2.8 GPa. The early decompression was associated with moderate cooling, corresponding to T ca. 950°C, and development of a spinel tectonite fabric in the lherzolites. Further decompression associated with plagioclase–olivine growth in both
peridotites and pyroxenites was nearly isothermal. The shallow evolution occurred under a brittle regime and led to the superposition of hornblende to serpentine veining stages. The garnet pyroxenite-bearing mantle from the External Liguride ophiolites represents a rare tectonic sampling of deep levels of subcontinental lithosphere exhumed in an oceanic setting. The exhumation was probably accomplished through a two-step process that started during Late Palaeozoic continental extension. The low-pressure portion of the exhumation path, probably including also the plagioclase mylonitic shear zones, was related to the Mesozoic (Triassic to Jurassic) rifting that led to continental break-up. In Jurassic times, the studied mantle sequence became involved in an extensional detachment process that resulted in sea-floor denudatio
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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