Mantle Heterogeneity from the Mantle Plume Perspective: Sources vs. Processes

Oceanic island basalts (OIB) which are derived from mantle plumes sample a compositionally heterogeneous mantle, as revealed by their radiogenic isotope systematics. Isotope compositions recurring in distinct hotspots have been used to characterize the composition and heterogeneity of the mantle as well as the thermochemical structure of upwelling plumes, with the assumption that the isotope composition of erupted lavas directly reflects that of their mantle source. Here I test how source transport, melting and hybridization in the upper mantle through space and time control the expression of deep mantle sources in erupted lavas. This work is focused on the Azores and Hawai‘i hotspots, which erupt in two distinctly different tectonic settings: at a triple divergent plate boundary for Azores and under a thick, fast moving plate for Hawai‘i. I demonstrate that Azores lavas sample mantle sources of distinct age and composition, including two generations of recycled oceanic crust. Τhe spatial distribution of these components in erupted lavas is controlled by the tectonic structure of the lithosphere, which is in turn controlled by the interaction of the ultraslow Terceira Rift and the adjacent Mid-Atlantic Ridge. This peculiar tectonic setting generates small-scale (70 km) westwards migration of mantle asthenosphere under a thinning lithosphere, as evidenced by the decrease in enriched components in lavas from east to west over ~ 70 km. The spatial expression of mantle sources in Azores lavas is therefore controlled by the tectonic features of the Azores Plateau, and not uniquely by the spatial distribution of mantle sources in the upwelling plume. Hafnium isotope data for shield and rejuvenated Hawaiian lavas reveal a switch from a spatially homogeneous expression of mantle sources in lavas across the plume track to a bilateral isotope zonation in both shield and rejuvenated lavas after 3.5 [Ma]. This transition coincides in time with a change in direction of the Pacific Plate’s motion, which has been theorized by geodynamicists to produce isotope gradients in lavas due to acrossplume gradients in melting conditions affecting a plume source heterogeneous on a small scale (veins, minerals). Our data therefore suggest plume–lithosphere dynamical interaction in Hawai‘i is the cause of bilateral isotope zonation in lavas, rather than a bilateral source zonation in the upwelling plume. A major conclusion of this work is that the structure and motion of the lithosphere in Azores and Hawai‘i exerts a first order control on the spatiotemporal systematics of isotope signatures in erupted lavas. Therefore, mantle plume-related erupted lava compositions do not necessarily reflect the chemical structure of the underlying mantle plume. Another contribution of this work is the development of new isotope tracers of mantle sources and processes. I present radiogenic cerium isotope measurements (138La decay to 138Ce) for a selection of Azores and Hawai‘i lavas. This technique is of interest as La and Ce are as robust to fluid interaction as Sm, Nd, Lu and Hf, while also decoupling from Sm/Nd and Lu/Hf during melting and in sediments. I demonstrate the coupled Ce- Nd-Hf isotope systematics of OIB lavas is more sensitive to the sampling of recycled oceanic crust and sediments compared to Nd-Hf alone, and the occurrence of curved mixing in Ce-Nd and Ce-Hf isotope space can be used as a proxy for the modalities of source melting and hybridization. Finally, I present a method to measure the stable Fe isotope signature of OIB lavas using a Thermo Neptune MC-ICP-MS with a precision of 0.02‰, on par with the most accurate published data, however through a significantly more time and cost-efficient method. This procedure uses the double-spike technique to monitor instrumental mass fractionation. I demonstrate that the condition of the source defining slit and the ability to move detectors are the most important factors influencing data quality. The iron isotope signature of erupted lavas is a direct tracer of the lithology of their source, which when compared with time-integrated tracers (radiogenic isotopes) can constrain the lithology of recycled sources in the convecting mantle, and the formation of hybrid sources prior to eruption. Preliminary data on Hawaiian shield lavas are at odds with the presence of a mafic component in the plume (shield source), while suggesting rejuvenated lavas sample a mafic or hybridized source. Inverse correlations between 87Sr/86Sr and 56Fe/54Fe in both shield and rejuvenated lavas go against the paradigm of recycled differentiated material existing under the form of mafic lithologies in the convecting mantle

De la centralisation à la contribution: proposition de modèle de design de service pour une gestion responsable des données

A l'ère de l'information, où tous les aspects de notre existence sont d'une façon ou d'une autre liés à Internet, notre société est de plus en plus surveillée et le marché des nouvelles technologies est tenu par quelques géants du net. Les citoyens sont dépossédés de leurs données, et la plupart des applications et services Internet sont construits sur une architecture centralisée, s'éloignant fortement de ce que le réseau des réseaux était à l'origine. Ce travail de Master réalisé sur un mandat de la fondation CINTCOM (Centre International de Compétences) propose un modèle de design de service distribué, pour une gestion responsable des données. Après un état des lieux retraçant l'histoire d'Internet, la montée en puissance des grandes entreprises du web et la gestion des réseaux, ce travail se penche sur le point de vue et les connaissances du grand public, recueillis à l'aide d'un questionnaire. Des entretiens avec des professionnels des nouvelles technologies complètent ce panorama, puis les différents modèles de design sont présentés, et le modèle distribué est étudié à partir deux cas d'utilisation

Les jeux vidéo dans les bibliothèques publiques de Suisse romande: pourquoi, comment ?

Alors que le jeu vidéo est présent depuis plusieurs années dans les bibliothèques françaises, américaines ou néerlandaises, la Suisse accuse un retard certain dans ce domaine. Bibliomedia, fondation de droit public active dans le développement des bibliothèques et la promotion de la lecture, est consciente de l’essor que connaît le jeu vidéo et de sa présence de plus en plus importante au sein des institutions culturelles des pays voisins. Elle considère donc ce média comme une thématique d’avenir pour les bibliothèques suisses. Ce travail, mandaté par Bibliomedia, propose un historique des jeux vidéo, un argumentaire sur la légitimité culturelle de ce média, un état des lieux de l’offre vidéoludique des bibliothèques publiques de Suisse romande et de quelques pays étrangers, et vise à sensibiliser et informer les bibliothécaires romands qui ne connaîtraient pas bien voire pas du tout les jeux vidéo

Genres discursifs et attentes rhétoriques en Faculté des lettres : de l'acquisition des littératies universitaires à leur évaluation

At the end of the Bachelor degree, students of a Faculty of Arts in Switzerland must master the diverse academic written discursive genres necessary to produce and to convey knowledge in the language they study. Teachers must provide them with keys to improve their writing skills – in terms of form as well as content – by a meaningful assessment. This paper presents the device set up at the Faculty of Arts of the University of Lausanne allowing both students' acquisition of written academic literacy and teachers' assessment. Mainly based on a set of descriptors that defines academic genres' main features, the device leads students to autonomously apprehend the notion of genre, to have specific goals in terms of academic writing, to practice self-assessment and to improve their skills through the revision and rewriting of their texts

Bases públicas de datos morfométricos en antropología biológica : nuevas prácticas, nuevos desafíos

Fil: González, Paula Natalia. División Antropología. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Béguelin, Marien. Instituto de Investigaciones en Paleobiología y Geología. Universidad Nacional de Río Negro; Argentin

Le statut des concessives en avoir beau du français: considérations synchroniques et diachroniques

Cet article traite d'un tour spécifique au français: la structure concessive avec avoir beau + infinitif (Il aura beau sonner, je ne lui ouvrirai pas (Riegel et alii 1996: 520), à comprendre comme: Il pourra bien sonner/Il pourra sonner autant qu'il veut, je ne lui ouvrirai pas). Nous nous y interrogeons sur la nature du lien syntaxique qui s'instaure, en français moderne, entre les deux membres de cette structure >. Nous commençons par un aperçu critique des descriptions dont la séquence a fait l'objet dans les grammaires du français contemporain; nous tirons ensuite quelques enseignements de l'évolution des emplois entre moyen français et français contemporain. Pour conclure cette étude à caractère préliminaire, nous formulons quelques hypothèses relatives au scénario diachronique de coalescence dans lequel notre structure semble engagé

sms4science: Korpusdaten, Literaturüberblick und Forschungsfragen

This paper discusses some methodological issues related to current research on SMS communication in Switzerland, an ambitious research project situated in the context of the international project sms4science. Thus far, the analyses of the Swiss data focus on numerous inner-linguistic features, variational aspects and language contact phenomena; each of which is of the utmost interest for multilingual Switzerland (cf. the five articles contained in this issue). In the following pages we first provide some background information about the project and the constitution of the Swiss SMS-corpus. We then present some methodological demands and problems, which are discussed on the basis of a dialogic sub-corpus. In the final paragraphs of this introductory article, we outline the state of affairs in the field of the linguistic study of SMS communication and highlight some research questions that would be of significant interest for the further analysis of the Swiss corpus