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Boron isotope compositions (δ 11 B) and B concentrations of rains and snows were studied in order to characterize the sources and fractionation processes during the boron atmospheric cycle. The 11 B/ 10 B ratios of instantaneous and cumulative rains and snows from coastal and continental sites show a large range of variations, from −1.5 ± 0.4 to +26.0 ± 0.5‰ and from −10.2 ± 0.5 to +34.4 ± 0.2‰, respectively. Boron concentrations in rains and snows vary between 0.1 and 3.0 ppb. All these precipitation samples are enriched in 10 B compared to the ocean value (δ 11 B = +39.5‰). An empirical rain-vapour isotopic fractionation of +31‰ is estimated from three largely independent methods. The deduced seawater–vapour fractionation is +25.5‰, with the difference between the rain and seawater fractionations principally reflecting changes in the speciation of boron in the liquid with ∼100% B(OH) 3 present in precipitations. A boron meteoric water line, δD = 2.6δ 11 B − 133, is proposed which describes the relationship between δD and δ 11 B in many, but not all, precipitations. Boron isotopic compositions of precipitations can be related to that of the seawater reservoir by the seawater–vapour fractionation and one or more of (1) the rain-vapour isotopic fractionation, (2) evolution of the δ 11 B value of the atmospheric vapour reservoir via condensation–precipitation processes (Rayleigh distillation process), (3) any contribution of vapour from the evaporation of seawater aerosols, and (4) any contribution from particulate matter, principally sea salt, continental dust and, perhaps more regionally, anthropogenic sources (burning of biomass and fossil fuels). From the δ 11 B values of continental precipitations, a sea salt contribution cannot be more than a percent or so of the total B in precipitation over these areas.

International audience; The Karakorum Range comprises a crustal section of marbles and metapelites providing an opportunity to study the extent of high-temperature metamorphic reequilibration in an active orogen. Metamorphism culminated during the Mio-Pliocene, at 6-7 Ma. Peak metamorphic conditions increased from south to north, i.e. from (1) the Upper Anchizone grade (lawsonite, chlorite-smectite) to (2) lower granulite migmatite grade (HT∼800°C) conditions along strike of a 30-km section perpendicular to the structural fabric of the rocks. The metamorphic section can be separated into two domains: 1. A domain with low to transitional metamorphic conditions, with respect to the HT zone, where initial bedding is preserved. These moderate PT conditions prevailed during the main tectonic stacking event (50-37 Ma), prior to the Mio-Pliocene event. In this domain, metamorphism is governed by fluid-assisted grain-scale diffusion, as suggested by the progressive coarsening of minerals with increasing metamorphic grade and the preservation of sedimentary δ13C signatures in carbonates. A low thermal gradient (17°C/km) is derived from P-T estimates of the prograde metamorphic sequences. 2. A higher-grade metamorphic domain where, by contrast, the metamorphic style is dominated by advection of heat with magmatic intrusions involving mantle melts during the recent tectonic history (20-3 Ma). Strong devolatilisation of CO2 and partial melting of the metapelites triggered mixing up of carbonated and pelitic lithologies resulting in ultramafic restites and calc-silicate mobilisates. The δ13C isotopic composition of carbonates is widely modified, though locally preserved.

International audience; The Bolivian previous termSub-Andean Zonenext term (SAZ) corresponds to a Neogene previous termthrustnext term system that affects an about 10-km thick Palaeozoic to Neogene siliciclastic succession. The analysis of macro and microstructures and cement distribution previous termin thrust fault zonesnext term shows that they are sealed by quartz at depths >not, vert, similar3 km, due to local silica transfer by pressure-solution/precipitation activated at temperatures >70–90 °C. At shallower depths, previous termfaultsnext term have remained open and could be preferential drains for lateral previous termflownext term of carbonate-bearing previous termfluids,next term as shown by the occurrence of carbonate cements previous terminnext term fractures and their host-previous termsandstone.next term Due to decreasing burial, resulting from foothill erosion during previous termfaultnext term activity, critically buried previous termfaultnext term segments can be affected by non-quartz-sealed structures that post-date initial quartz-sealed structures. The integration of textural, previous termfluidnext term inclusion and isotopic data shows that carbonates precipitated at shallow depth (

cited By 88; A crustal-scale ductile shear zone network in the Precambrian granulite-facies crust of Madagascar is examined to determine the nature of the connections between the mantle and lower crust. Based on three independent data sets - field and satellite mapping, C- and O-isotope geochemistry and gravimetry - this crust is divided into three zones: (1) outside of shear zones; (2) minor shear zones that are 350 km long (up to 1000 km) and 20-35 km wide. The mantle is uplifted by about 10 km beneath the major shear zones. The major shear zones are rooted in and are inferred to be controlled by the mantle; they directly tapped mantle-derived CO2. The small-scale minor shear zones were controlled by crustal processes and focused crustally derived H2O-rich±CO2 fluids. The regular distribution of the shear zones on a crustal scale is in agreement with models of buckling of the continental lithosphere in a compressional context. The propagation of these mechanical instabilities promoted and channelled fluid flow. These major Pan-African shear zones thinned the crust and were reactivated during the subsequent drifting of Madagascar and opening of the Indian Ocean during Jurassic to Cretaceous times. They also controlled many of the brittle fault zones in the overlying sedimentary basins. Mantle-rooted large-scale shear zones are inferred to be a general feature of cratonic areas reactivated by shear zone systems.

The P-T-t path has been determined for a vein and its tourmalinized metapelitic wall rocks from Walmes, central Morocco, by applying fluid-inclusion, chemical and isotopic (H-O) thermometers and mineral paragenesis analysis. Concordant temperatures have been derived from the tourmaline-biotite (Fe/Mg), tourmaline-muscovite (H-isotope) and quartz-muscovite-biotite (O-isotope isotherm) thermometers on the wall rocks. Biotite has undergone later H-isotope exchange in contrast to the more resistant muscovite and tourmaline. For the vein, concordant temperatures are given by the fluid-inclusion trapping temperatures, muscovite [Na/(Na+K)] and muscovite-H 2 O (H-isotope) systems

REE geochemistry and isotopic (Pb, Sr, Nd, O) compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in South Brittany. Ages decrease from 340 Ma in the north to 300 Ma in the south whereas initial 87 Sr/ 86 Sr ratios increase from 0.706 to 0.710–0.717. REE abundances are relatively low (La N ∼ 20–80 × chondrites) with a strong enrichment of LREE relative to HREE (La N /Lu N = 13.4–26.6). Pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 Ma ago. 18 O/ 16 O ratios are high and relatively uniform at 10.7 to 12.8, mean 11.9. U Pb studies on zircon indicate the presence of an inherited radiogenic Pb component and that the sediment-dominated source region had been metamorphosed during the Siluro-Devonian (Ligerian). Negativee Nd(T) values imply that the source region had been enriched in LREE prior to the melting episode. Based on the combined data, large-scale partial melting of crustal material, dominantly of sedimentary origin, is proposed. The model age of the source rocks is not very old (600–700 to 1200 Ma). The Pb and Sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites.

International audience; The sulphur isotope composition of the mantle has been generally considered to be 0±2‰. There is, however, considerable uncertainty in the mean δ34S value of the mantle and in its range because there have been very few analyses of unaltered sulphide phases of direct mantle origin and δ34S values of sulphides from large mafic intrusions range from –9 to +17‰. We report here ion microprobe δ34S determinations from two mantle derived sulphide inclusions (≈100 µm) preserved in a diamond (δ13C = –4.25‰) of peridotitic(?) paragenesis from Premier (South Africa) and in four diamonds of eclogitic paragenesis from Orapa (Botswana). Three octahedral sulphides have lower δ34S values (+2.3±1.4‰) than three platelet-like sulphides (+8.2±0.9‰). This evidence for mantle heterogeneity for sulphur is interpreted in terms of recycling of crustal material into the eclogitic region of diamond growth in the mantle.

* INRA Unité de Pathologie Végétale, Domaine St Maurice, BP94, 84143 Montfavet cedex Diffusion du document : INRA Unité de Pathologie Végétale, Domaine St Maurice, BP94, 84143 Montfavet cedex

Not available, Ce mémoire présente quelques exemples d'application de la géochimie des isotopes stables à l'étude des bassins sédimentaires : 1) la composition chimique et isotopique (H, O, Sr) des eaux de formation du delta de la Mahakam (Indonésie) et la composition isotopique des minéraux carbonatées (C, O) de l'un des champs étudiés (Handil) sont interprétés comme le résultat d'une importante contribution d'eaux météoriques avec un très faible taux de mélange avec l'eau de mer. Ces eaux peuvent s'être mises en place à des âges différents ou à partir de zones de recharge différentes. Leur présence jusqu'a 3000 m de profondeur implique un important lessivage des hydrocarbures ; 2) un protocole expérimental a été élaboré pour mesurer la composition isotopique de l'hydrogène et du carbone des sédiments argileux riches en matière organique et de déterminer par bilan de masse, la composition isotopique de la matière organique associée ; 3) une nouvelle équation de fractionnement de l'hydrogène entre la montmorillonite de l'eau est proposée. La droite des kaolinites de Savin et Epstein (1970) est reconsidérée comme la droite des kaolinites et montmorillonites continentales (KML1). Une nouvelle droite (KML2) est proposée pour tenir compte de la variation de la composition isotopique des eaux météoriques en fonction des températures moyennes annuelles de l'air; 4) une trentaine de mesures isotopiques de l'oxygène, faites sur des roches totales argileuses donnent une variation entre 15 et 20 %. Les carbonates associés sont marins ou dia génétiques et ne montrent pas d'évidence pour un échange isotopique de l'oxygène avec les minéraux silicates. Une approche combinée minéralogique et isotopique est proposée pour déterminer si les sources d'apport détritique des formations argileuses sont les mêmes pour une séquence donnée et pour mesurer le degré d'échange isotopique entre le quartz et les minéraux argileux

Cette thèse rassemble 4 publications originales relatives à différents aspects de l'interaction entre fluides et minéraux dans les contextes de marge passive et de cisaillements ductiles. Une approche cristallochimique démontre la présence d'associations à grenats et de pyroxènes non stœchiométriques, formes dans des conditions hyperréductrices dans des skarns à graphite (Sidi Bou Othmane, Maroc) et met en évidence des pressions de fluides anormales dans le gisement Zn-Pb des Malines (bordure cévenole, France). Les conditions thermiques de l'alimentation hydrothermale de la fosse à saumures d'Atlantis II (Mer Rouge) sont définies par l'étude des inclusions fluides primaires dans les cristaux d'anhydrite épigénétiques, et par l'évaluation du bilan de masse et de chaleur de la fosse. Une synthèse sur les mécanismes des circulations hydrothermales dans les marges passives est réalisée

H-, C-, and a-isotopes studies have been applied to characterize the nature and role of the fluids asssociated with the High Himalaya leucogranitic magmatism, its source rocks and the Main Central Thrust (MCT). 290 isotopic analyses of whole rocks, mineraIs and fluid inclusions coming from the sedimentary formations beneath (Midlands) and above (Tibet an Slab : the source of the Manaslu granite) the MCT and from the Manaslu granite define some of the metamorphic and magmatic processes. The O-isotope variations in the Midlands preclude major infiltration and circulation of fluids. As most of the rocks are very poor in carbon, the C02 -rich fluids observed in inclusions were generated at a deeper level. Dehydration of the schists with 2 to 5 wt% H2 O, liberated 20 to 40% of the initial water content in the region of the MCT where metamorphism was at a maximum, and &D decreased by about 15%0. At deeper levels, near the shear zone, devolatilization was probably more intense. For the granite, &D muscovite varies from -70 to -85%0 and &18 O whole rock from 10.9 to 12.8%0. H- and O-isotope fractionations among mineraIs are consistent with equilibrium at high temperatures. A few samples, especially from the Chhokang dyke swarm, have &D = > -180 %0 and disequilibrium muscovitebiotite fractionations. These rare samples are related to chloritization and late exchange with meteoric waters. Formation 1 gneisses of the Tibetan Slab (source of the granite) have &180 = 12 to 14.3%0, confirming its relationship with the granite. The &D values of Formation 1 are however about 20%0 higher than those of the granite. This difference is related to (1) magmatic degassing associated with a H-isotope fractionation, and (2) the infiltration of D-depleted fluids into the zone of anatexis. Fluids liberated from the underlying Midlands Formation, many of whose initial &D were, L'étude des isotopes stables H, C, 0, à été entreprise dans le but de préciser le rôle et la nature des fluides associés au magmatisme leucogranitique du Haut Himalaya, ses roches sources et le Grand Chevauchement Central Himalayen (MCT), 290 analyses isotopiques de roches totales, de minéraux et d'inclusions fluides provenant des formations chevauchées (Moyen Pays), des formations chevauchantes (source du granite, Dalle du Tibet) et du granite du Manaslu, apportent certaines contraintes sur les processus métamorphiques et magmatiques. Les Formations du Moyen Pays ont des compositions isotopiques variables impliquant l'absence de circulation massive et pénétrante. La nature des roches majoritaires, très pauvres en C, implique que les fluides riches en CO2 présent dans les inclusions fluides sont libérés dans des niveaux plus profonds puis infiltrés dans les niveaux étudiés. La déshydratation des schistes atteint 20 à 40% de l'eau initiale dans les niveaux proches du MCT (maximum du métamorphisme) et s'accompagne d'une diminution des &D des schistes de l'ordre de 15 %0. On peut prévoir des volatilisations plus intenses (2 à 5 % poids suivant les niveaux) dans les zones plus profondes du chevauchement. Pour le granite, les &D musc varient entre -70 et -85 %0 et les & 180 RT de 10.9 à 12.8. Les fractionnements entre minéraux de l'hydrogène comme de l'oxygène sont compatibles avec des températures d'équilibre élevées et, pour l'oxygène, avec des évolutions en système fermé. Quelques échantillons provenant surtout du Bras filonien de Chhokang ont des &D très négatifs (> -180 %0) et des fractionnements biot.-musc. trop importants. Ces rares déséquilibres sont liés à la chloritisation et à des circulations tardives de fluides d'origine météorique, Les gneiss de la Dalle du Tibet (Formation l, source du granite) ont des &18 Oquartz variant de 12 à 14.3 %0 qui confirment la filiation du granite à la Formation I. Par contre les &D sont environ 20 %0 plus élevés que ceux du granite. Deux processus sont proposés pour expliquer cette différence (1) le dégazage magmatique accompagné d'un fractionnement du deutérium, (2) l'infiltration de fluides pauvres en deutérium dans la zone de fusion. Les fluides libérés au niveau du Moyen Pays pourraient concorder avec ce dernier processus car de nombreux niveaux du Moyen Pays ont des &D initiaux < -80 %0. La combinaison des données chimiques et isotopiques O, Sr, Nd du granite et de la Formation 1 confirme que les variations isotopiques et les relations des systèmes isotopiques dans le granite sont héritées de celles de la Formation 1. De plus ces données dans la Formation 1 reflètent le stade sédimentaire des gneiss et pour l'oxygène et le Nd la proportion des minéraux détritiques et des phyllosilicates.