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Géochimie de l'île de la Martinique aux Petites Antilles
No full textMartinique Island has recorded the most complete history of the Lesser Antilles arc, from 25 Ma to present. The chemical and isotopic heterogeneity of the lavas is very large compared to other islands from the same arc and compared to other intra-oceanic arcs. The aim of this study is to explain the chemical and isotopic variability of Martinique lavas and to constrain the processes that took place during the genesis of volcanic products. We did a detailed geochemical study (major elements, minor elements and Pb, Sr, Nd and Hf isotopic ratios) of samples collected all over Martinique Island. Our geochemical study was coupled to precise dating of the same lavas by the K-Ar method through a collaboration with Aurélie Germa and Xavier Quidelleur from the University of Orsay-Paris XI. Martinique lavas define mixing trends between depleted and enriched end-members. Two significantly different trends can be distinguished, one defined by “old” lavas (between 25 and 7 Ma) and one defined by “recent” lavas (between 5 Ma and present). Both depleted and enriched end-members involved in the source of magmas differ before and after 6 Ma. The change of source most probably occurred when the subduction of an aseismic ridge shifted to the West the northern part of the arc. We evaluate the origin of the crustal signature of Martinique lavas through (a) a mixing model between slab sediments and mantle wedge and (b) a crustal assimilation model in which mantle-derived magmas are contaminated by the arc crust. The crustal-contamination model does not reproduce the trends defined by the Martinique lavas whereas the mixing model succeeds. A comparison between crustal end-members as constrained by the mixing trends, and local subducted sediments indicates that there is no decoupling between Pb, Sr, Nd and Hf implying that sediments are added to the mantle wedge through fusion and not dehydration. The La/Yb ratio is a proxy of the proportion of sediments involved in the genesis of the lavas. It is not governed by the melting degree or the nature of the residual aluminous phase in the mantle, even though lavas are generated by approximately 10% partial melting of a garnet-bearing mantle source. We show that La/Yb defines a spatial gradient in the island, suggesting a geographical gradient of the proportion of sediments.L'île de la Martinique a connu l'histoire volcanique la plus complète de l'arc des Petites Antilles, de 25 Ma à l'actuel. L'hétérogénéité chimique et isotopique des laves de l'île est très importante non seulement par rapport aux autres îles de l'arc mais aussi par rapport aux autres arcs intra-océaniques. L'objectif de ces travaux est d'expliquer la variabilité géochimique des laves de la Martinique et de caractériser les processus de genèse des produits volcaniques émis sur l'île. Pour cela, nous avons effectué une étude géochimique approfondie (éléments majeurs, éléments traces, rapports isotopiques du Pb, Sr, Nd et Hf) sur des échantillons de laves représentatifs de toute l'histoire volcanique de la Martinique. Grâce à une collaboration avec Aurélie Germa et Xavier Quidelleur de l'université Orsay - Paris XI, l'étude géochimique a été couplée à une datation des laves par méthode K-Ar. Les laves martiniquaises forment des droites et hyperboles de mélanges entre pôles appauvris mantelliques et pôle enrichis crustaux. Il apparaît que deux mélanges distincts sont visibles, un premier mélange est formé par les laves « anciennes » (entre 25 et 7 Ma) et un deuxième mélange est formé par les laves « récentes » (entre 5 Ma et l'actuel). Les pôles mantelliques et les pôles crustaux impliqués dans les sources des magmas ne sont pas les mêmes avant et après 6 Ma. Ce changement de source est probablement lié au passage de la ride asismique qui a décalé la moitié nord de l'arc des Petites Antilles. L'origine de la signature crustale des laves martiniquaises est testée en comparant un modèle de mélange à la source entre des sédiments de la plaque plongeante et le coin mantellique et un modèle d'assimilation de la croûte de l'arc par les magmas mantelliques ascendants. Le modèle d'assimilation intra-crustale ne peut pas reproduire les tendances décrites par les laves alors que le modèle de mélange à la source le fait parfaitement. La comparaison entre les pôles crustaux impliqués dans les mélanges et les sédiments entrants dans la subduction indique qu'il n'y a pas de fractionnement entre le Pb, le Sr, le Nd et l'Hf ce qui implique que les sédiments sont probablement ajoutés à la source par fusion partielle et non par déshydratation. Le rapport La/Yb des laves martiniquaises apparait comme un proxy de la proportion de sédiments dans la source des magmas et non du taux de fusion partielle ou de la nature de la phase alumineuse du manteau bien que la fusion, de l'ordre de 10%, ait lieu dans la zone de stabilité du grenat. Le gradient géographique du rapport La/Yb au sein de l'île traduit donc un gradient géographique de la proportion de sédiments, et montre que la proportion de sédiments dans la source augmente avec l'éloignement à la fosse
Géochimie de l'île de la Martinique aux Petites Antilles
No full textL'île de la Martinique a connu l'histoire volcanique la plus complète de l'arc des Petites Antilles, de 25 Ma à l'actuel. L'hétérogénéité chimique et isotopique des laves de l'île est très importante non seulement par rapport aux autres îles de l'arc mais aussi par rapport aux autres arcs intra-océaniques. L'objectif de ces travaux est d'expliquer la variabilité géochimique des laves de la Martinique et de caractériser les processus de genèse des produits volcaniques émis sur l'île. Pour cela, nous avons effectué une étude géochimique approfondie (éléments majeurs, éléments traces, rapports isotopiques du Pb, Sr, Nd et Hf) sur des échantillons de laves représentatifs de toute l'histoire volcanique de la Martinique. Grâce à une collaboration avec Aurélie Germa et Xavier Quidelleur de l'université Orsay - Paris XI, l'étude géochimique a été couplée à une datation des laves par méthode K-Ar. Les laves martiniquaises forment des droites et hyperboles de mélanges entre pôles appauvris mantelliques et pôle enrichis crustaux. Il apparaît que deux mélanges distincts sont visibles, un premier mélange est formé par les laves anciennes (entre 25 et 7 Ma) et un deuxième mélange est formé par les laves récentes (entre 5 Ma et l'actuel). Les pôles mantelliques et les pôles crustaux impliqués dans les sources des magmas ne sont pas les mêmes avant et après 6 Ma. Ce changement de source est probablement lié au passage de la ride asismique qui a décalé la moitié nord de l'arc des Petites Antilles. L'origine de la signature crustale des laves martiniquaises est testée en comparant un modèle de mélange à la source entre des sédiments de la plaque plongeante et le coin mantellique et un modèle d'assimilation de la croûte de l'arc par les magmas mantelliques ascendants. Le modèle d'assimilation intra-crustale ne peut pas reproduire les tendances décrites par les laves alors que le modèle de mélange à la source le fait parfaitement. La comparaison entre les pôles crustaux impliqués dans les mélanges et les sédiments entrants dans la subduction indique qu'il n'y a pas de fractionnement entre le Pb, le Sr, le Nd et l'Hf ce qui implique que les sédiments sont probablement ajoutés à la source par fusion partielle et non par déshydratation. Le rapport La/Yb des laves martiniquaises apparait comme un proxy de la proportion de sédiments dans la source des magmas et non du taux de fusion partielle ou de la nature de la phase alumineuse du manteau bien que la fusion, de l'ordre de 10%, ait lieu dans la zone de stabilité du grenat. Le gradient géographique du rapport La/Yb au sein de l'île traduit donc un gradient géographique de la proportion de sédiments, et montre que la proportion de sédiments dans la source augmente avec l'éloignement à la fosse.Martinique Island has recorded the most complete history of the Lesser Antilles arc, from 25 Ma to present. The chemical and isotopic heterogeneity of the lavas is very large compared to other islands from the same arc and compared to other intra-oceanic arcs. The aim of this study is to explain the chemical and isotopic variability of Martinique lavas and to constrain the processes that took place during the genesis of volcanic products. We did a detailed geochemical study (major elements, minor elements and Pb, Sr, Nd and Hf isotopic ratios) of samples collected all over Martinique Island. Our geochemical study was coupled to precise dating of the same lavas by the K-Ar method through a collaboration with Aurélie Germa and Xavier Quidelleur from the University of Orsay-Paris XI. Martinique lavas define mixing trends between depleted and enriched end-members. Two significantly different trends can be distinguished, one defined by old lavas (between 25 and 7 Ma) and one defined by recent lavas (between 5 Ma and present). Both depleted and enriched end-members involved in the source of magmas differ before and after 6 Ma. The change of source most probably occurred when the subduction of an aseismic ridge shifted to the West the northern part of the arc. We evaluate the origin of the crustal signature of Martinique lavas through (a) a mixing model between slab sediments and mantle wedge and (b) a crustal assimilation model in which mantle-derived magmas are contaminated by the arc crust. The crustal-contamination model does not reproduce the trends defined by the Martinique lavas whereas the mixing model succeeds. A comparison between crustal end-members as constrained by the mixing trends, and local subducted sediments indicates that there is no decoupling between Pb, Sr, Nd and Hf implying that sediments are added to the mantle wedge through fusion and not dehydration. The La/Yb ratio is a proxy of the proportion of sediments involved in the genesis of the lavas. It is not governed by the melting degree or the nature of the residual aluminous phase in the mantle, even though lavas are generated by approximately 10% partial melting of a garnet-bearing mantle source. We show that La/Yb defines a spatial gradient in the island, suggesting a geographical gradient of the proportion of sediments.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF
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
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