El BARIUM AND STRONTIUM CONCENTRATIONS IN PACIFIC AND MEDITERRANEAN SEA WATER PROFILES BY DIRECT ISOTOPE DILUTION MASS SPECTROMETRY

The determination of barium and strontium directly from sea water by isotope dilution mass spectrometry proves to be an efficient, precise, and virtual blank free procedure. Results for an eastern Pacific profile confirm a regularly increasing barium concentration from 5 to 23 ,clg/kg at 2500 m, but strontium concentrations appear to be nearly homogeneous below 50 m at 7.6 f 0.1 I;lg/kg with a single low value for the surface water. Results for a western Mediterranean profile show uniform concentrations for both barium and strontium, similar to the Atlantic. There appears to be a nearly conservative strontium-to-salinity ratio of 0.218 i 0.002 for sea waters below mixed surface zones. The barium salinity ratio for the Mediterranean and Atlantic is (0.30 f 0.01) X lo3 but the integrated Pacific profile shows a ratio almost twice as great

Systématique Re-Os dans les basaltes océaniques (implications sur la nature des hétérogénéités chimiques du manteau supérieur)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Géochimie isotopique du bore (érosion continentale)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

The nature of the KT impactor. A 54Cr reappraisal

International audienceAccording to the variations observed in the various meteorite classes, 54Cr represents an isotopic tool for planetary body discrimination. In the search for the nature of the Cretaceous-Tertiary (KT) impactor, Cr isotopic measurements were already performed at KT boundary. The current work is aimed to modernize Cr isotopic data with high-precision measurements to confirm a carbonaceous chondrite type infall, the contribution of which is also estimated. Isotopic signatures of two marine clays (Caravaca, Stevens Klint) exhibit an isotopic ratio which would represent a mixing of a carbonaceous chondrite of CM2 type with terrestrial material in a ratio 6% to 19%. A single impactor may account for both marine and continental Cr isotopic signatures

Etude sur la variabilité de la susceptibilité magnétique (le cycle érosion-transport-sédimentation)

La récurrence des corrélations observées entre les fluctuations du climat et les fluctuations du signal magnétique nous a incité à rechercher une cause générale.Notre modèle est basé sur l'étude du cycle érosion-transport-sédimentation du point de vue magnétique. Les deux approches adoptées sont : l'approche régionale reposant sur deux études de cas : l'une sur la conservation de propriétés magnétiques entre sables et roches(Martinique) et l'autre sur la manière dont le transport de sédiment transfère le signal magnétique (Cantal). L'approche globale a consisté en l'établissement d'une base de données des susceptibilités des roches, des sédiments de rivières, des sédiments marins. A partir de ces données, nous avons ensuite calculé des flux de particules magnétiques globaux. Les principaux résultats sont résumés en quatre points :1. L'étude des rivières volcaniques dans les zones volcaniques a révélé que la susceptibilité magnétique massique des sables volcaniques est équivalente à celle des roches. 2. L'étude des rivières à grande échelle montre que le signal de susceptibilitévolcanique est dilué par l'apport de matériaux continentaux. Cependant, une fois la dilution faite, le signal se dégrade très peu lors du transport en milieu continental.L'étude sur le Cantal a permis de montrer l'importance de la fraction fine des sables dans le transport du signal magnétique. 3. Les susceptibilités magnétiques des sédiments océaniques, corrigés de l'effet de dilution par les carbonates, sont comparables à celles des sédiments de rivières prélevés près des embouchures. Nous avons de plus commencé à montrer que les fluctuations géographiques observés dépendaient de l'importance relative des apports volcaniques. Enfin nous avons montré que les fluctuations de susceptibilité, synchrones avec les fluctuations du climat, sont préservées lorsque l'on applique une correction sur la susceptibilité magnétique pour tenir compte de l'effet de dilution par les carbonates. Le lien climat-signal magnétique serait dû à des fluctuations dans le régime d'érosion ou dans celui des apports de matériaux volcaniques et/ou détritiques. 4. L'examen global révèle la cohérence quantitative entre le modèle exploré, les vitesses relatives dérosion des diverses lithologies, et les flux d'érosion sédimentairePARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Seawater Nd isotope variation in the Western Pacific Ocean since 80 Ma (ODP 807, Ontong Java Plateau)

International audienc

Complex proterozoic to paleozoic history of the upper mantle recorded in the Urals lherzolite massifs by Re–Os and Sm–Nd systematics

Re-Os and Sm-Nd isotope systematics for the Nurali and the Mindyak lherzolite massifs have been determined in conjunction with their whole-rock major and trace element contents. The data suggest that the peridotites represent residues after the extraction of up to 25% of partial melt from the fertile mantle protolith. Later melt percolation and associated fluid-rock reaction events have modified the Sm/Nd, Re/Os and Pd/Os ratios of peridotites, but didn't affect significantly their major element compositions. The Re-Os and Sm-Nd isotope data strongly suggest that several magmatic events are involved in the evolution of these bodies. The mantle sections of these complexes formed during Proterozoic times, represent the first reported evidence for Precambrian peridotites in the Southern Urals. The oldest Re-Os age of 1250 +/- 80 Ma for the Nurali cumulates records the separation from the convective upper mantle. Multiple partial melting of the peridotites followed by fractional crystallisation produced layered cumulates which were subsequently stored in the sub-continental lithosphere over similar to 0.8 Ga. The age of the Nurali ophiolite coincides with the development of an epicontinental rift basin on the passive margin of the Baltica proto-continent. The younger Sm-Nd age of Mindyak peridotites (882 83 Ma) and Re-Os age of associated gabbros (804 +/- 37 Ma) record another tectonic event responsible for the separation of the Mindyak massif from convective mantle. Between similar to 850 and 650 Ma, the margins of the paleo-Asian ocean became the site of island-arc formation. This ophiolite then evolved in an intra-oceanic island-arc setting. The Mindyak lherzolite massif could be the first record of a Neoproterozoic Cadomian are in the Southern Urals. A later island-arc formation event has then affected both massifs in different ways. The Mindyak massif was incorporated into a rifting zone at similar to 500 Ma, producing a second partial melting event of peridotites, cross-cutted by mafic dykes. The Nurali massif has also been cross-cut by gabbro-diorite dykes at Devonian time during the subduction event leading to Urals island-arc formation. The combination of. Re-187-Os-187 and Sm-147-Nd-143 systematics for peridotites, mafic-ultramafic cumulates and mafic dykes reveals the complex history of ophiolite complexes, including isolation from the convective upper mantle at Proterozoic time, storage in sub-continental lithospheric mantle and re-activation during later tectonic events, such as island-arc formation. (c) 2007 Elsevier B.V. All rights reserved

Open system behaviour andearly chronologies in the Solar System

International audienc