1,720,996 research outputs found
Cs-Rb-Ba systematics in phengite and amphibole: an assessment of fluid mobility at 2.0 GPa in eclogites from Trescolmen, Central Alps
No full textEclogites from Trescolmen that contain abundant hydrous minerals (phengite, amphibole, paragonite, zoisite, talc, apatite) show petrographic evidence for fluid infiltration under conditions of 2.0 to 1.8 GPa, 650 degreesC. Large ion lithophile elements (LILE, e.g. Cs, Rb, Ba and Sr) were analysed by in-situ techniques in all eclogite mineral phases in order to characterize the behaviour of fluid-mobile elements at high pressure. In-situ analysis of carefully-chosen metamorphic assemblages circumvents the problem of partial late-stage alteration, which can severely influence the calculated element budgets of whole-rock samples. Phengite is the dominant host for Cs, Rb, and Ba in both eclogite and adjacent garnet mica schist samples, and incorporates > 90% of the budgets of these elements in whole rocks. LILE contents of phengites in phengite-rich rocks are likely to record the Cs/Rb and Ba/Rb ratios of their host rock protoliths. The LILE patterns of eclogite are consistent with protoliths derived from basalt that underwent seafloor alteration, whereas those of mica schist are almost identical to average upper continental crust. In contrast, LILE patterns of eclogite samples that lack phengite, but do contain amphibole, are unlike any plausible protolith, but are identical to those of amphibole in phengite-bearing samples. This observation points to homogenization of the LILE in different lithologies, which we correlate with petrographic evidence for fluid infiltration. Because phengite in garnet mica schist has a strong capacity to buffer the fluid with respect to Cs, Rb, and Ba, homogenization of amphiboles is best explained by fluid infiltration from the surrounding metapelites into eclogite bodies, implying at least metre-scale fluid mobility. The amphibole homogenization can be most easily modelled by a pervasive open-system fluid flux through the eclogites, possibly facilitated by ductile deformation during the early stages of uplift. Simple calculations give minimum fluid-rock ratios of similar to0.001 to 0.004. Demonstration of the mobility of very small volumes of fluid through eclogite is an important prerequisite of many subduction zone models that try to explain across-are variations in trace element geochemistry. The low fluid-rock ratios from this study are not in contrast with oxygen isotope heterogeneities reported from other eclogite localities. Fluid mobile elements such as Cs, Rb and Ba are more sensitive indicators of small volume, fluid-rock interaction and are therefore potentially valuable for understanding fluid infiltration processes in systems where oxygen isotope shifts are not large enough to be detectable
Cs-Rb-Ba systematics in phengite and amphibole: an assessment of fluid mobility at 2.0 GPa in eclogites from Trescolmen, Central Alps
No full textEclogites from Trescolmen that contain abundant hydrous minerals (phengite, amphibole, paragonite, zoisite, talc, apatite) show petrographic evidence for fluid infiltration under conditions of 2.0 to 1.8 GPa, 650 degreesC. Large ion lithophile elements (LILE, e.g. Cs, Rb, Ba and Sr) were analysed by in-situ techniques in all eclogite mineral phases in order to characterize the behaviour of fluid-mobile elements at high pressure. In-situ analysis of carefully-chosen metamorphic assemblages circumvents the problem of partial late-stage alteration, which can severely influence the calculated element budgets of whole-rock samples. Phengite is the dominant host for Cs, Rb, and Ba in both eclogite and adjacent garnet mica schist samples, and incorporates > 90% of the budgets of these elements in whole rocks. LILE contents of phengites in phengite-rich rocks are likely to record the Cs/Rb and Ba/Rb ratios of their host rock protoliths. The LILE patterns of eclogite are consistent with protoliths derived from basalt that underwent seafloor alteration, whereas those of mica schist are almost identical to average upper continental crust. In contrast, LILE patterns of eclogite samples that lack phengite, but do contain amphibole, are unlike any plausible protolith, but are identical to those of amphibole in phengite-bearing samples. This observation points to homogenization of the LILE in different lithologies, which we correlate with petrographic evidence for fluid infiltration. Because phengite in garnet mica schist has a strong capacity to buffer the fluid with respect to Cs, Rb, and Ba, homogenization of amphiboles is best explained by fluid infiltration from the surrounding metapelites into eclogite bodies, implying at least metre-scale fluid mobility. The amphibole homogenization can be most easily modelled by a pervasive open-system fluid flux through the eclogites, possibly facilitated by ductile deformation during the early stages of uplift. Simple calculations give minimum fluid-rock ratios of similar to0.001 to 0.004. Demonstration of the mobility of very small volumes of fluid through eclogite is an important prerequisite of many subduction zone models that try to explain across-are variations in trace element geochemistry. The low fluid-rock ratios from this study are not in contrast with oxygen isotope heterogeneities reported from other eclogite localities. Fluid mobile elements such as Cs, Rb and Ba are more sensitive indicators of small volume, fluid-rock interaction and are therefore potentially valuable for understanding fluid infiltration processes in systems where oxygen isotope shifts are not large enough to be detectable
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
Cold subduction of oceanic crust: Implications from a lawsonite eclogite from the Dominican Republic
No full textLawsonite eclogite is a rare rock type that has been described from only five natural occurrences. In contrast, laboratory experiments and thermal models predict that lawsonite eclogite should be widespread in subducted oceanic crust deeper than 1.5 GPa. Here we report a new lawsonite eclogite find from the Dominican Republic that provides constraints on the conditions of subducted crust and on its return to the surface. In this sample, lawsonite coexisting with omphacite occurs as both inclusions in garnet and as porphyroblasts, the latter being partly replaced at their margins by epidote and zoisite. Peak pressure conditions estimated from lawsonite-phengite-omphacite-garnet assemblages were ca 1.6 GPa at a temperature of 360degreesC, implying formation under a geotherm of ca. 8degreesC/km. Peak temperature conditions of 410-450degreesC were in the zoisite eclogite field, suggesting that the sample crossed from the stability field of lawsonite eclogite into that of zoisite eclogite as a result of increasing temperature. A comparison with other reported occurrences indicates that most lawsonite eclogite exhumed at the Earth's surface formed in accretionary wedges. The rarity of lawsonite eclogite at the Earth's surface may be principally due to two factors: (i) that in 'normal' subduction settings lawsonite eclogite enters the subduction factory and hence is usually not exhumed; and (ii) that in accretionary wedge settings, where the PT path leaves the stability field of lawsonite eclogite due to heating, lawsonite eclogite is only preserved if the exhumation path is constrained to a narrow window where the terminal stability of lawsonite is not crossed
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
- …
