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New 187Re-187Os, 87Rb-87Sr, triple O-isotope isotope, bulk rock highly siderophile- (HSE: Os, Ir, Ru, Pt, Pd, Re), major- and trace-element abundance data are reported for a variety of carbonaceous, ordinary and enstatite chondrite meteorites. In addition, new mineral chemical data are reported for the Chelyabinsk LL5 ordinary chondrite fall for comparison with existing chondrite data and to investigate element sequestration into metal and mineral phases within some chondrites. The focus of the study is to link the variations observed in the HSE abundances and Re-Os isotopes with other isotopic and elemental data to explore the relative roles of sample sizes, terrestrial alteration and parent body processes more fully on chondrite meteorite compositions. Trace element variations in Chelyabinsk silicate, oxide and metal grains highlight the importance of geochemical heterogeneity imparted by mineralogical variations and mode effects, as well as sample size. Using a range of sample powder aliquot sizes, it is possible to show that this becomes significant for the HSE at

Ferrous oxide (FeO)-rich asteroid achondrites can be defined as asteroid-derived samples that experienced incipient partial melting processes in the early Solar System (>4.5 Ga) leading to melt-residues and cumulate and melt rocks that have high FeO in silicate grains (molar Mg/[Mg + Fe]

International audience; 16 Evaporites play a major role on the structuration of collisional orogens especially when they 17 act as décollement units. However, their exact pressure-temperature-deformation (P-T-d) paths 18 are poorly documented. In this study, the first direct P-T-d constraints of the "Nappe des 19 Gypses" formation (western French Alps) have been established. An innovative association of 20 structural geology, petrography, crystallochemistry, and detailed study of both fluid inclusions 21 and stable isotopes (C, O) analysis has been applied to this evaporitic facies. Geochemical 22 analysis shows that the "Nappe des Gypses" formation has recorded the three typical 23 metamorphic and deformational events of the Alps (namely D1, D2 and D3). These different 24 constraints allow the determination of the first determination of the P-T path for this unit. 25 Metamorphic peak conditions of the "Nappe des Gypses" are at 16.6 ± 2.3 kbars and 431°C ± 26 28°C. This formation was buried at similar conditions than the oceanic units. During the 27 exhumation path, the D1-D2 transition is reached at 350°C ± 20°C and 6.5 ± 1.8 kbars and the 28 D2-D3 transition is assumed to be at 259°C ± 24°C and 2.0 ± 1.0 kbars (Strzerzynski et al., 29 2012). Peak P-T conditions overlap those of the median Liguro-Piemontese units but are 30 different from those of the Briançonnais units. It implies 1) an active and crucial role of the 31 "Nappe des Gypses" during the exhumation of the Alpine oceanic complex. And 2) confirms the 32 allochthonous and more distal origin of the European Thetysian passive margin of the "Nappe 33 des Gypses" formation. Consideration of sulfates dehydration probably between 15.0 and 16.6 34 kbars and 200 and 300°C, allows to discuss pore pressure excess and its mechanical 35 consequences on the exhumation process. This process is very likely to amplify the 36 "décollement" effect of the evaporites and allow the nappe stack formation. 37 This illustrates the role of this formation as a décollement surface. This difference of 38 evolution highlights the major role of the evaporitic formations on the exhumation and 39 structuration of a collisional chain. Such methodology could contribute to decipher the role of 40 evaporites in the structural context of other collisional chains such as Himalaya, Pyrenees or 41 Zagros. 42

Modern anthropogenic aerosols usually exhibit low but significant Δ33S signatures (−0.6 to 0.5‰) whose origin still remains unclear. While isotope fractionation factors associated with the oxidation of SO2 by O2+TMI (Transition Metal Ion), H2O2 or OH cannot lead to such extreme Δ33S-values, an increasing number of studies points to the significant role of NO2 as a contributing oxidant, especially in the urban environment. To address the possible relation between atmospheric NO2 and observed Δ33S-values in aerosols, we carried out laboratory experiments oxidizing SO2 by NO2 at temperatures ranging between −7 and 52 °C. Our results show that at temperatures ≥10 °C SO2 oxidation by NO2 is characterized by 1) a 34α-value whose temperature dependence (0.2437/T+0.0457) is distinct from those related to oxidation by O2+TMI, H2O2 and OH oxidation pathways and 2) 33β (0.514 ± 0.0003) and 36β (1.90 ± 0.002) values that are closer to the mass dependent values (0.515 and 1.89 respectively) than those reported for the other oxidation pathways. This implies that the NO2 oxidation pathway cannot explain the extreme Δ33S-values measured in urban aerosols. Our data show that if atmospheric SO2 oxidation by NO2 is neglected, both the O2+TMI and OH oxidation pathways would be overestimated in urban areas. Finally, we conclude that another oxidation reaction is responsible for the high Δ33S-values measured in urban aerosol samples.

In order to establish the role and expression of silicate-metal fractionation in early planetesimal bodies, we have conducted a highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundance and 187 Re- 187 Os study of acapulcoite-lodranite meteorites. These data are reported with new petrography, mineral chemistry, bulk-rock major and trace element geochemistry, and oxygen isotopes for Acapulco, Allan Hills (ALHA) 81187, Meteorite Hills (MET) 01195, Northwest Africa (NWA) 2871, NWA 4833, NWA 4875, NWA 7474 and two examples of transitional acapulcoite-lodranites, Elephant Moraine (EET) 84302 and Graves Nunataks (GRA) 95209. These data support previous studies that indicate that these meteorites are linked to the same parent body and exhibit limited degrees ( 2 × CI chondrite) HSE abundances in transitional acapulcoite-lodranite meteorites (EET 84302, GRA 95209). All of the meteorites have chondritic Re/Os with measured 187 Os/ 188 Os ratios of 0.1271 ± 0.0040 (2 St. Dev.). These geochemical characteristics imply that the precursor material of the acapulcoites and lodranites was broadly chondritic in composition, and were then heated and subject to melting of metal and sulfide in the Fe-Ni-S system. This resulted in metallic melt removal and accumulation to form lodranites and transitional acapulcoite-lodranites. There is considerable variation in the absolute abundances of the HSE, both among samples and between aliquots of the same sample, consistent with both inhomogeneous distribution of HSE-rich metal, and of heterogeneous melting and incomplete mixing of silicate material within the acapulcoite-lodranite parent body. Oxygen isotope data for acapulcoite-lodranites are also consistent with inhomogeneous melting and mixing of accreted components from different nebular sources, and do not form a well-defined mass-dependent fractionation line. Modeling of HSE inter-element fractionation suggests a continuum of melting in the Fe-Ni-S system and partitioning between solid metal and sulfur-bearing mineral melt, where lower S contents in the melt resulted in lower Pt/Os and Pd/Os ratios, as observed in lodranites. The transitional meteorites, EET 84302 and GRA 95209, exhibit the most elevated HSE abundances and do not follow modelled Pt/Os and Pd/Os solid metal-liquid metal partitioning trends. We interpret this to reflect metal melt pooling into domains that were sampled by these meteorites, suggesting that they may originate from deeper within the acapulcoite-lodranite parent body, perhaps close to a pooled metallic ‘core’ region. Petrographic examination of transitional samples reveals the most extensive melting, pooling and networking of metal among the acapulcoite-lodranite meteorites. Overall, our results show that solid metal-liquid metal partitioning in the Fe-Ni-S system in primitive achondrites follows a predictable sequence of limited partial melting and metal melt pooling that can lead to significant HSE inter-element fractionation effects in proto-planetary materials.

International audience; This study is aimed to evaluate the role played by the sulfur radical ions (S3− and S2−) and molecular sulfur (S0) on sulfur isotope fractionation and to investigate if these species may leave an isotope fingerprint in hydrothermal systems. For this purpose, we combined (i) experiments using a hydrothermal reactor with aqueous S3−(S2−)-S0-sulfate-sulfide fluids and pyrite across a wide range of temperatures (300–450 °C), pressures (300–800 bars), fluid acidity (4

Ureilite meteorites are partially melted asteroidal-peridotite residues, or more rarely, cumulates that can contain greater than three weight percent carbon. Here we describe an exceptional C-rich lithology, composed of 34 modal % large (up to 0.8 mm long) crystalline graphite grains, in the Antarctic ureilite meteorite Miller Range (MIL) 091004. This C-rich lithology is embedded within a silicate region composed dominantly of granular olivine with lesser quantities of low-Ca pyroxene, and minor FeNi metal, high-Ca pyroxene, spinel, schreibersite and troilite. Petrological evidence indicates that the graphite was added after formation of the silicate region and melt depletion. Associated with graphite is localized reduction of host olivine (Fo88–89) to nearly pure forsterite (Fo99), which is associated with FeNi metal grains containing up to 11 wt.% Si. The main silicate region is typical of ureilite composition, with highly siderophile element (HSE) abundances ∼0.3 × chondrite, 187Os/188Os of 0.1260–0.1262 and Δ17O of −0.81 ± 0.16‰. Mineral trace-element analyses reveal that the rare earth elements (REE) and the HSE are controlled by pyroxene and FeNi metal phases in the meteorite, respectively. Modeling of bulk-rock REE and HSE abundances indicates that the main silicate region experienced ∼6% silicate and >50% sulfide melt extraction, which is at the lower end of partial melt removal estimated for ureilites. Miller Range 091004 demonstrates heterogeneous distribution of carbon at centimeter scales and a limited range in Mg/(Mg + Fe) compositions of silicate grain cores, despite significant quantities of carbon. These observations demonstrate that silicate rim reduction was a rapid disequilibrium process, and came after silicate and sulfide melt removal in MIL 091004. The petrography and mineral chemistry of MIL 091004 is permissive of the graphite representing late-stage C-rich melt that pervaded silicates, or carbon that acted as a lubricant during anatexis and impact disruption in the parent body. Positive correlation of Pt/Os ratios with olivine core compositions, but a wide range of oxygen isotope compositions, indicates that ureilites formed from a compositionally heterogeneous parent body that experienced variable sulfide and metal melt-loss that is most pronounced in relatively oxidized ureilites with Δ17O between −1.5 and ∼0‰.

Rationale: The O- and S- isotope compositions of sulfates can be used as key tracers of the fate and sink of sulfate in both terrestrial and extra-terrestrial environments. However, their application remains limited in those geological systems where sulfate occurs in low concentrations. Here we present a simple and reliable method to extract, purify and concentrate sulfate from natural samples. The method allows us to take into account the separation of nitrate, which is known to be an issue in O-isotope analysis. Methods: The separation and concentration of sulfate from other anions in any aqueous solution are performed within a few hours via anion exchange resin. The possible O- (δ 18 O and Δ 17 O) and S- (δ 34 S, Δ 33 S and Δ 36 S) isotope exchanges, fractionations and/or contaminations are for the first time monitored during the whole procedure using initial O- and S-mass-dependent and mass-independent sulfate solutions. Results: After elution in HCl, pure sulfate is fully retrieved and precipitated into BaSO 4 , which is suitable for O- and S- isotopic measurements using established techniques. The analysis of retrieved barite presents no variation within 2σ uncertainties: ± 0.5‰ and ± 0.1‰ in O (δ 18 O, Δ 17 O) and ± 0.2‰, ± 0.02‰ and ± 0.09‰ in S (δ 34 S, Δ 33 S and Δ 36 S) isotope ratios, respectively. Conclusions: This study shows for the first time that the resin method for sulfate extraction and purification, in addition to being cheap, simple and quick, is applicable for the measurements of all O- and S-isotopic ratios in sulfates (including the Δ 17 O, Δ 33 S and Δ 36 S values). Therefore, this method can be easily used for a high range of natural samples in which sulfate occurs in low concentration including aerosols, ice cores, sediments, volcanic deposits, (paleo)soils and rainwater and it can thus be a key to our understanding of the sulfur cycle on Earth.

RATIONALE Multiple sulfur isotope compositions are usually measured on relatively large samples (in the range of micromoles); however, sometimes only small amounts are available and thus it is necessary to analyze small (sub-micromole) samples. We report an improved method to measure multiple sulfur isotope compositions: δ(33) S, δ(34) S and δ(36) S values on the SF6 molecule (m/z 127, 128, 129, 131) for quantities down to 0.1 micromole, and δ(33) S and δ(34) S values for quantities down to 20 nanomoles. METHODS Multiple sulfur isotope analyses including fluorination and purification of two international Ag2 S standards, IAEA-S1 and IAEA-S3, were carried out at various low concentrations on a dual-inlet isotope ratio mass spectrometer using a microvolume and modified resistor capacities. RESULTS The analyses yielded a narrow range of δ(34) S values vs CDT (the international standard), with an overall standard deviation of ±0.2 ‰, which was within the range of certified values. This demonstrates the feasibility of determining both Δ(33) S and Δ(36) S values on the sub-micromole scale, and Δ(33) S values on the nanomole scale with similar accuracy to conventional dual-inlet analyses. CONCLUSIONS The analysis of the three S-isotope ratios on the SF6 molecule using the so-called conventional fluorination method and dual-inlet ion ratio mass spectrometry is reliable for sample sizes down to ~20 nanomoles. Despite being close to the theoretical limits for maintaining the viscous flow regime of gas in the capillary, errors were not limited by counting statistics, but probably relate to sample gas purification. Copyright © 2016 John Wiley & Sons, Ltd.

We report in situ and bulk S-isotope analyses of the 3.2 Ga old barite deposit of the Sargur Group, Dharwar Craton, India. Compared with the two other coeval barite deposits in Western Australia (Pilbara Craton, Warrawoona and Sulfur Springs Group) and South Africa (Kaapvaal Craton, Onverwacht and Fig Tree Group), the rocks of the Sargur Group have experienced pervasive ductile deformation and equilibrated under high-grade metamorphic conditions, which could have caused partial S-isotope re-equilibration. However, in situ techniques revealed high spatial heterogeneities in δ 34 S of up to ∼18‰ in barite-bearing pyrites, as well as similar Δ 33 S anomalies compared to the associated sulfate indicating bacterial sulfate reduction isotope effects and a minor impact of the pervasive ductile deformation and metamorphism on the primary/diagenetic signatures. Our data in associated silicate rocks define consistent trends in Δ 33 S/δ 34 S and Δ 36 S/Δ 33 S reflecting metamorphic reworking of primary photolytic signatures with sulfide deriving from thermal reduction of the barite sulfate at >400 °C. Our results match the previous data obtained on other Early Archean barite deposits. This strongly suggests that similar sulfur sources were at play over the three continents during the production and preservation of atmospheric sulfate and elemental sulfur aerosols. This also confirms that the different Early Archean barite deposits known on Earth formed during periods of intense subaerial volcanism and record volcanic photolytic signatures different from those common in the Archean.

International audience; Kimberlites of the Udachnaya-East pipe (Siberia) include a uniquely dry and serpentine-free rock type with anomalously high contents of chlorine (Cl ≤ 6.1 wt%), alkalies (Na2O + K2O ≤ 10 wt%) and sulfur (S ≤ 0.50 wt%), referred to as a “salty” kimberlite. The straightforward interpretation is that the Na-, K-, Cl- and S-rich components originate directly from a carbonate-chloride kimberlitic magma that is anhydrous and alkali-rich. However, because brines and evaporites are present on the Siberian craton, previous studies proposed that the kimberlitic magma was contaminated by the assimilation of salt-rich crustal rocks. To clarify the origin of high Cl, alkalies and S in this unusual kimberlite, here we determine its sulfur speciation and isotopic composition and compare it to that of non-salty kimberlites and kimberlitic breccia from the same pipe, as well as potential contamination sources (hydrothermal sulfides and sulfates, country-rock sediment and brine collected in the area). The average δ34S of sulfides is − 1.4 ± 2.2‰ in the salty kimberlite, 2.1 ± 2.7‰ in the non-salty kimberlites and 14.2 ± 5.8‰ in the breccia. The average δ34S of sulfates in the salty kimberlites is 11.1 ± 1.8‰ and 27.3 ± 1.6‰ in the breccia. In contrast, the δ34S of potential contaminants range from 20 to 42‰ for hydrothermal sulfides, from 16 to 34‰ for hydrothermal sulfates, 34‰ for a country-rock sediment (Chukuck suite) and the regional brine aquifer. Our isotope analyses show that (1) in the salty kimberlites, neither sulfates nor sulfides can be simply explained by brine infiltration, hydrothermal alteration or the assimilation of known salt-rich country rocks and instead, we propose that they are late magmatic phases; (2) in the non-salty kimberlite and breccia, brine infiltration lead to sulfate reduction and the formation of secondary sulfides – this explains the removal of salts, alkali-carbonates and sulfates, as well as the minor olivine serpentinization; (3) hydrothermal sulfur was added to the kimberlitic breccia, but not to the massive kimberlites. In situ measurements of sulfides confirm this scenario, clearly showing the addition of two sulfide populations in the breccia (pyrite-pyrrhotites with average δ34S of 7.9 ± 3.4‰ and chalcopyrites with average δ34S of 38.0 ± 0.4‰) whereas the salty and non-salty kimberlites preserve a unique population of djerfisherites (Cl- and K-rich sulfides) with δ34S values within the mantle range. This study provides the first direct evidence of alkaline igneous rocks in which magmatic sulfate is more abundant than sulfide. Although sulfates have been rarely reported in mantle materials, sulfate-rich melts may be more common in the mantle than previously thought and could balance the sulfur isotope budget of Earth's mantle.

International audience; The occurrence of Early Archean barite deposits is intriguing since this type of sediment requires high availability of dissolved sulfate (SO42-), the oxidized form of sulfur, although most authors argued that the Archean eon was dominated by reducing conditions, with low oceanic sulfate concentration (56Fe values varying between -2.04‰ in Fe sulfide-dominated barite beds, to +2.14‰ in Fe oxide-bearing cherts. δ34S values of sulfides vary between -10.84 and +3.56‰, with Δ33S in a range comprised between -0.35 and +2.55‰, thus supporting an O2-depleted atmosphere (-5 PAL). Iron isotope variations together with major element correlations show that, although the sediments experienced a pervasive stage of hydrothermal alteration, the rocks preserved a primary/authigenic signature predating subsequent hydrothermal stage. Highly positive δ56Fe values recorded in primary Fe-oxides from ferruginous cherts support partial Fe oxidation in a reducing oceanic environment (O2 < 10-4 μM), but are incompatible with a model of complete oxidation at the redox boundary of a stratified water column. Iron oxide precipitation under low O2 levels was likely mediated by anoxygenic photosynthesis, and/or abiotic photo-oxidation processes. Our results are consistent with global anoxic conditions in the 3.2 Ga-old sediments, implying that the barite deposits were most likely sourced by atmospheric photolysis of S gases produced by large subaerial volcanic events, and possibly SO42- produced by magmatic SO2 disproportionation in hydrothermal systems.

The O- and S-isotope compositions of sulfates can be used as key tracers of the fate and sink of sulfate in both terrestrial and extra-terrestrial environments. However, their application remains limited in those geological systems where sulfate occurs in low concentrations. Here we present a simple and reliable method to extract, purify and concentrate sulfate from natural samples. The method allows us to take into account the separation of nitrate, which is known to be an issue in O-isotope analysis.The separation and concentration of sulfate from other anions in any aqueous solution are performed within a few hours via anion-exchange resin. The possible O- (δAfter elution in HCl, pure sulfate is fully retrieved and precipitated into BaSOThis study shows that the resin method for sulfate extraction and purification, in addition to being cheap, simple and quick, is applicable for the measurements of all O- and S-isotopic ratios in sulfates (including the Δ

We report on improvements to the sulfur extraction method out of silicate glasses by the use of HF + CrCl2 solution for the precise determination of S multi-isotope compositions. This protocol has been designed to be sulfide specific and if needed, can be easily extended to oxidized sulfur. The complete method was validated on a synthetic powder and three laboratory mid-ocean ridge glassy internal standards (CH98 DR12, ED DR46 1-6 and ED DR26 type 1). S extraction yields of the three basalt glass standards were 100 ± 4% (1σ, n = 12), 102 ± 6% (1σ, n = 4) and 97 ± 6% (1σ, n = 4) respectively. Their δ34S show little variation, at − 1.20 ± 0.08‰, − 1.09 ± 0.14‰ and − 1.25 ± 0.12‰ (all 1σ) with respect to V-CDT. Δ33S and Δ36S are both negative with respect to our SF6 tank, between − 0.018 and − 0.021‰ (± 0.012‰ maximum 1σ) for Δ33S and between − 0.216 and − 0.282 (± 0.106 maximum 1σ) for Δ36S. The method was then applied to sixteen additional glasses from worldwide mid-ocean ridges, including three samples for which δ34S was reported previously. Our results show that previous data are affected by a systematic δ34S shift toward positive values, of ≃ 0.4 to 1.5‰. We infer that this shift originates from an incomplete S recovery when the Kiba extraction protocol is used. δ34S values range between − 1.80 and 0.02‰ with a mean value of − 0.91 ± 0.50‰ (1σ n = 19). Such negative values contrast with the positive range previously reported leading us to suggest a revised mantle δ34S, mainly dominated by negative values. Δ33S and Δ36S are strikingly homogeneous with mean respective values of − 0.019 ± 0.005‰ and − 0.193 ± 0.093‰ (1σ n = 19) versus our SF6 tank. These estimates are indistinguishable from our CDT measurements and define the best present-day upper mantle estimate.

Cold-water geysers at Green River, in east central Utah are sourced by natural springs situated along the Little Grand Wash and Salt Wash faults zones, as well as abandoned oil and water wells. The intermittent geysers are driven by degassing of CO2 from CO2-rich waters sourced from the Jurassic Navajo sandstone. Here we discuss use of δ13C analyses of water and gases to estimate the depth at which the ascending waters become CO2 saturated. This is a potentially important control in the unlikely event of rapid CO2 escape from CO2 reservoirs. In Green River, it is also important for calculation of the kinetics of fluid-mineral reactions in the Navajo sandstone as an analogue for predicting the fate of CO2 in carbon storage reservoirs.

International audience; Lac Pavin (French Massif Central) is a permanently stratified lake: the upper water layers (mixolimnion, from 0 to 60 m depth) are affected by seasonal overturns, whereas the bottom water layers (monimolimnion, from 60 to 90 m depth) remain isolated and are never mixed. Hence, they are capable of storing important quantities of dissolved gases, mainly CO2. With the aim of better constraining the water balance and of gaining new insights into the carbon cycle of Lac Pavin, an isotopic approach is used. The δ18OH2O profiles lead the authors to give a new evaluation of the evaporation flow rate (8 L s−1), and to propose and characterize two sub-surface springs. The sub-surface spring located at the bottom of the lake can be deduced from the 1% isotopic difference between the upper water layers (mean δ18OH2O value: −7.3‰) and the bottom water layers (δ18OH2O=-8.4‰). It is argued that this sub-surface spring has isotopic and chemical characteristics similar to those of the magmatic CO2-rich spring (i.e. Fontaine Goyon, δ18OH2O=-9.4‰), and we calculate its flow rate of 1.6 L s−1. The second sub-surface spring is located around 45 m depth, with a composition close to those of the water surface streams (δ18OH2O

Multiple sulfur isotope compositions are usually measured on relatively large samples (in the range of micromoles); however, sometimes only small amounts are available and thus it is necessary to analyze small (sub-micromole) samples. We report an improved method to measure multiple sulfur isotope compositions: δ(33) S, δ(34) S and δ(36) S values on the SF6 molecule (m/z 127, 128, 129, 131) for quantities down to 0.1 micromole, and δ(33) S and δ(34) S values for quantities down to 20 nanomoles.Multiple sulfur isotope analyses including fluorination and purification of two international Ag2 S standards, IAEA-S1 and IAEA-S3, were carried out at various low concentrations on a dual-inlet isotope ratio mass spectrometer using a microvolume and modified resistor capacities.The analyses yielded a narrow range of δ(34) S values vs CDT (the international standard), with an overall standard deviation of ±0.2 ‰, which was within the range of certified values. This demonstrates the feasibility of determining both Δ(33) S and Δ(36) S values on the sub-micromole scale, and Δ(33) S values on the nanomole scale with similar accuracy to conventional dual-inlet analyses.The analysis of the three S-isotope ratios on the SF6 molecule using the so-called conventional fluorination method and dual-inlet ion ratio mass spectrometry is reliable for sample sizes down to ~20 nanomoles. Despite being close to the theoretical limits for maintaining the viscous flow regime of gas in the capillary, errors were not limited by counting statistics, but probably relate to sample gas purification. Copyright © 2016 John WileySons, Ltd.

–Olivine-dominated (70–80 modal %) achondrite meteorite Lewis Cliff (LEW)88763 originated from metamorphism and limited partial melting of a FeO-rich parentbody. The meteorite experienced some alteration on Earth, evident from subchondritic Re/Os, and redistribution of rhenium within the sample. LEW 88763 is texturally similar towinonaites, has a D 17 O value of 1.19 0.10‰, and low bulk-rock Mg/(Mg+Fe) (0.39),similar to the FeO-rich cumulate achondrite Northwest Africa (NWA) 6693. The similarbulk-rock major-, minor-, and trace-element abundances of LEW 88763, relative to somecarbonaceous chondrites, including ratios of Pd/Os, Pt/Os, Ir/Os, and 187 Os/ 188 Os (0.1262),implies a FeO- and volatile-rich precursor composition. Lack of fractionation of the rareearth elements, but a factor of approximately two lower highly siderophile elementabundances in LEW 88763, compared with chondrites, implies limited loss of Fe-Ni-S meltsduring metamorphism and anatexis. These results support the generation of high Fe/Mg,sulfide, and/or metal-rich partial melts from FeO-rich parent bodies during partial melting.In detail, however, LEW 88763 cannot be a parent composition to any other meteoritesample, due to highly limited silicate melt loss (0 to <

This paper presents the initial results of a scientific drilling project to recover core and pressurized fluid samples from a natural CO2 reservoir, near the town of Green River, Utah. The drilling targeted a stacked sequence of CO2-charged Jurassic sandstone reservoirs and caprocks, situated adjacent to a CO2-degassing normal fault. This site has actively leaked CO2 from deep supercritical CO2 reservoirs at depth > 2 km within the basin for over 400,000 years. The project objectives were to gather samples to examine reactive fluid flow in the reservoirs, caprocks and faults, during migration of CO2 through the geological overburden from the deep supercritical CO2 reservoirs. Downhole fluid sampling and fluid element and isotope geochemistry show that the shallow reservoirs are being actively fed by inflow of CO2-saturated brines through the faults. Comparisons of shallow and deep fluid geochemistry suggest that: (i) CO2 and CO2-charged brines co-migrated from the deep reservoirs, (ii) the CO2-saturated brines migrating from depth interact with significant volumes of meteoric groundwater in aquifers in the shallower Permian and Jurassic sandstones, diluting the brine composition, and (iii) that a significant fraction of the CO2 migrating from depth is dissolved in these brine–meteoric water mixtures, with > 99% of the CO2 in fluids sampled from the shallow reservoirs being derived during fluid migration, after the fluids left their source reservoir. The 87Sr/86Sr ratio of the brine flowing through the faults is significantly elevated due to the addition of Sr from silicate mineral dissolution during fluid migration. The association of bleached sandstones in the core with CO2-rich fluids supports interpretations from elsewhere that CO2-charged brines with CH4 or H2S reductants can dissolve hematite present within the sediment. Analysis of fluid geochemistry and sandstone petrology suggests that the CO2-rich fluids dissolve carbonate, hematite and gypsum in the reservoirs, as they flow away from the faults. Element and isotope geochemistry of fluid samples from the drillhole and Crystal Geyser constrain mixing models which show that, within the Navajo Sandstone, the reservoir fluids are undergoing complex mixing of: (i) CO2-saturated brine inflowing from the fault, (ii) CO2-undersaturated meteoric groundwater flowing through the reservoir and (iii) reacted CO2-charged brines flow through fracture zones in the overlying Carmel Formation caprock, into the formations above. Such multi-scale mixing processes may significantly improve the efficiency with which groundwaters dissolve the migrating CO2.

International audience; In the inner part of the External Alps, inherited Liassic basins were buried and inverted during the Oligo-Miocene collisional phase of the Alpine orogeny. In northern Oisans, during crustal shortening, the basement was locally sheared while the cover was disharmonically folded above the main basement shear zones that did not propagate into the cover. In this contribution, we analyze the witnesses of paleo-␣uid circulations associated with these crustal deformations, focusing particularly on Bourg d'Oisans and Mizoën basins (external Western Alps). On the basis of structural and microstructural observations coupled to geochemical analyses (cathodoluminescence, O and C stable isotopes, trace elements) of vein versus host-rock minerals, we show that in the cover, ␣uids main- ly circulated over short distances (closed-system). However, trace element data also show that percolation of small amounts of basement-derived ␣uids occurred over several tens of meters in cover rocks right above base- ment shear zones. Indeed, the three successive vein sets recognized in the ␣eld display enrichments in basement- derived Ni, Co, and Cr, which indicate that ␣uid transfer from the basement was ef␣cient since the beginning of basin inversion, therefore con␣rming the synchronous deformation of cover and basement. Fluid temperatures and pressures are estimated (microthermometry coupled to à18O of vein minerals) to about 250-400 °C and 2-5 kbar for veins that most likely formed at or close to metamorphic peak conditions. These results coupled to literature data are ␣nally integrated into a model of ␣uid circulation evolution through progressive deforma- tion of the whole external Western Alps.

International audience; Multiple pieces of geologic evidence suggest that interfaces between contrasted lithologies exert a strong control on the fate of volatiles in subduction zones. Here we present results from a contact between serpentinites and sediments, located in Corsica and metamorphosed in the blueschist facies during the alpine orogeny. It was shown previously that carbonates in the sediments have been reduced to graphitic carbonaceous material within a 5-10-cm-thick reaction zone at the contact with serpentinites. In an effort to investigate the mechanisms governing this unusual process, bulk rock geochemical analyses incorporating a statistical analysis of compositional data are presented. Observations show that the fate of C was decoupled from that of other elements such as O, H, and large-ion lithophile elements--e.g. K, Sr, Ba...,As--that were extensively leached from the reaction zone. Notably, Na is strongly enriched in the reaction zone and structurally linked to pectolite. Reducing conditions, manifested by the depletion of O in the reaction zone compared to the bulk metasediment, were likely maintained by the presence of Fe(II) in the serpentinite. Moreover, thermodynamic calculations show that the low solubility of carbon in COH fluids at high-pressure and low-temperature conditions was the main driver for graphite precipitation synchronously with carbonate destabilization. This may have been kinetically favored by the presence of already existing graphitized carbonaceous material and phengite in the metasediment. Limited lateral flow might have contributed as well to the geochemical and petrological patterns observed in these rocks.

International audience; We present here an improved and reliable method for measuring the concentration of dissolved inorganic carbon (DIC) and its isotope composition (delta C-13(DIC) in natural water samples. Our apparatus, a gas chromatograph coupled to an isotope ratio mass spectrometer (GCIRMS), runs in a quasi-automated mode and is able to analyze about 50 water samples per day. The whole procedure (sample preparation, CO2(g)-CO2(aq) equilibration time and GCIRMS analysis) requires 2 days. It consists of injecting an aliquot of water into a H3PO4-loaded and He-flushed 12 mL glass tube. The H3PO4 reacts with the water and converts the DIC into aqueous and gaseous CO2. After a CO2(g)-CO2(aq) equilibration time of between 15 and 24 h, a portion of the headspace gas (mainly CO2+He) is introduced into the GCIRMS, to measure the carbon isotope ratio of the released CO2(g), from which the delta C-13(DIC) is determined via a calibration procedure. For standard solutions with DIC concentrations ranging from 1 to 25 mmol (.) L-1 and solution volume of 1 mL (high DIC concentration samples) or 5 mL (low DIC concentration samples), delta C-13(DIC) Values are determined with a precision (1 sigma) better than 0.1 parts per thousand. Compared with previously published headspace equilibration methods, the major improvement presented here is the development of a calibration procedure which takes the carbon isotope fractionation associated with the CO2(g)-CO2(aq) partition into account: the set of standard solutions and samples has to be prepared and analyzed with the same 'gas/liquid' and 'H3PO4/water' volume ratios. A set of natural water samples (lake, river and hydrothermal springs) was analyzed to demonstrate the utility of this new method. Copyright

In order to study CO2-water-rock reactions relative to effectiveness of CO2 geological storage, small-scale CO2 injection experiments were performed, as single well push-pull tests, at the Lamont Doherty Earth Observatory test well site (New-York, USA). The injection interval was located at the contact zone between the chilled dolerite and the underlying metamorphosed sedimentary rocks. The variations of post-injection chemical and isotopic characteristics of retrieved water samples (major ions, DIC, 13CDIC) underline the CO2 reactivity in the aquifer and allow to identify reactions of the dissolved CO2 with the surrounding rocks, mainly the dissolution of carbonate minerals and complementary cation exchange.