Observatoire Des Science Of Lunivers Of Grenoble


Observatoire Des Science Of Lunivers Of Grenoble

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Dublet G.,CNRS Institute of Mineralogy, Materials Physics and Cosmochemistry | Dublet G.,Aix - Marseille University | Dublet G.,Ecole Polytechnique Federale de Lausanne | Juillot F.,CNRS Institute of Mineralogy, Materials Physics and Cosmochemistry | And 11 more authors.
Geochimica et Cosmochimica Acta | Year: 2017

Because they can host significant amounts of Co, the Mn-oxides are commonly considered as the major Co-bearing mineral species in lateritic environments. However, little is known about the process leading to the formation and/or the weathering of these Co-rich Mn-oxides. This lack of knowledge is mainly due to the fact that Co concentrations are too low in primary silicates for classical speciation analysis. In this study, we investigated both Co and Mn speciation in a 64 m thick lateritic regolith developed upon peridotites in New Caledonia, by combining High Energy Resolution Fluorescence Detection X-ray absorption Near Edge Structure (HERFD-XANES) spectroscopy at the Co K-edge with classical XANES spectroscopy at the Mn K-edge, bulk chemistry (ICP) and mineralogy (XRD). The results obtained provide new insights into the evolution of Co and Mn speciation as a function of the weathering stages. Co and Mn primarily occur as Co(II) and Mn(II,III) in olivine and serpentine in the bedrock. During the first weathering stage, these forms of Co and Mn are progressively oxidized toward Co(III) and Mn(III,IV), which occur mainly as Co(III)-bearing Mn(III/IV)-oxides in the transition between the saprolite and the laterite. In the uppermost lateritic horizons, long-time weathering resulted in a strong leaching of Co and Mn, and the remaining of these elements occurs as Co(II) and Mn(III) substituting for Fe(III) in goethite. This latter scavenging process emphasizes the importance of Fe-oxides for the long-term stabilization of Co and Mn in such deeply weathered laterites. © 2017 Elsevier Ltd

Etschmann B.E.,University of Adelaide | Etschmann B.E.,University of Melbourne | Etschmann B.E.,South Australian Museum | Liu W.,University of Melbourne | And 9 more authors.
Geochimica et Cosmochimica Acta | Year: 2010

Chloride and hydrosulfide are the principal ligands assumed to govern transport of copper in hydrothermal fluids. Existing solubility experiments suggest that Cu(I)-hydrosulfide complexes are dominant compared to chloride complexes at low salinities in alkaline solutions (H2S(aq)/HS- pH buffer), and may be important in transporting Cu in low density magmatic vapors, potentially controlling the liquid-vapor partitioning of Cu. This study provides the first in situ evidence of the solubility of copper sulfides and the nature and structure of the predominant Cu species in sulfur-containing fluids at temperatures up to 592°C and pressures of 180-600bar. XANES and EXAFS data show that at elevated T (≥200°C), Cu solubility occurs via a linear Cu complex. At 428°C in alkaline solutions, Cu is coordinated by two sulfur atoms in a distorted linear coordination (angle ∼150-160°). This geometry is consistent with the species Cu(HS)2- predicted by earlier solubility studies. In addition, in situ measurements of the solubility of chalcocite in 2m NaHS solutions performed in this study are in remarkably good agreement with the solubilities calculated using available thermodynamic data for Cu(I)-hydrosulfide complexes, also supporting the interpretation of speciation in these studies and validating the extrapolation of low-T thermodynamic properties for Cu(HS)2- to high P-T. Data on phase separation for the 2m NaHS solution show that while significant amounts of copper can be partitioned into the vapor phase, there is no indication for preferential partitioning of Cu into the vapor. This is consistent with recent partitioning experiments conducted in autoclaves by Pokrovski et al. (2008a) and Simon et al. (2006). XANES data suggest that the species present in the low density phase is very similar to that present in the high density liquid, i.e., Cu(HS)2-, although Cu(HS)(H2S)0 cannot be excluded on the basis of XAS data. © 2010 Elsevier Ltd.

PubMed | Aix - Marseille University, Elettra - Sincrotrone Trieste, CNRS Research on Catalysis and Environment in Lyon and Observatoire Des Science Of Lunivers Of Grenoble
Type: | Journal: Environmental pollution (Barking, Essex : 1987) | Year: 2014

A multi-scale methodology was used to characterize the long-term behavior and chemical stability of a CeO2-based nanocomposite used as UV filter in wood stains. ATR-FTIR and (13)C NMR demonstrated that the citrate coated chelates with Ce(IV) through its central carboxyl- and its -hydroxyl- groups at the surface of the unaged nanocomposite. After 42 days under artificial daylight, the citrate completely disappeared and small amount of degradation products remained attached to the surface even after 112 days. Moreover, the release/desorption of the citrate layer led to a surface reorganization of the nano-sized CeO2 core observed by XANES (Ce L3-edge). Such a surface and structural transformation of the commercialized nanocomposite could have implications in term of fate, transport, and potential impacts towards the environment.

Westall F.,CNRS Center for Molecular Biophysics | Cavalazzi B.,CNRS Center for Molecular Biophysics | Cavalazzi B.,University of Johannesburg | Lemelle L.,Ecole Normale Superieure de Lyon | And 18 more authors.
Earth and Planetary Science Letters | Year: 2011

Timing the appearance of photosynthetic microorganisms is crucial to understanding the evolution of life on Earth. The ability of the biosphere to use sunlight as a source of energy (photoautotrophy) would have been essential for increasing biomass and for increasing the biogeochemical capacity of all prokaryotes across the range of redox reactions that support life. Typical proxies for photosynthesis in the rock record include features, such as a mat-like, laminated morphology (stratiform, domical, conical) often associated with bulk geochemical signatures, such as calcification, and a fractionated carbon isotope signature. However, to date, in situ, calcification related to photosynthesis has not been demonstrated in the oldest known microbial mats. We here use in situ nanometre-scale techniques to investigate the structural and compositional architecture in a 3.3. billion-year (Ga) old microbial biofilm from the Barberton greenstone belt, thus documenting in situ calcification that was most likely related to anoxygenic photosynthesis. The Josefsdal Chert Microbial Biofilm (JCMB) formed in a littoral (photic) environment. It is characterised by a distinct vertical structural and compositional organisation. The lower part is calcified in situ by aragonite, progressing upwards into uncalcified kerogen characterised by up to 1% sulphur, followed by an upper layer that contains intact filaments at the surface. Crystallites of pseudomorphed pyrite are also associated with the biofilm suggesting calcification related to the activity of heterotrophic sulphur reducing bacteria. In this anoxygenic, nutrient-limited environment, the carbon required by the sulphur reducing bacteria could only have been produced by photoautotrophy. We conclude that the Josfsdal Chert Microbial Biofilm was formed by a consortium of anoxygenic microorganisms, including photosynthesisers and sulphur reducing bacteria. © 2011 Elsevier B.V.

Ryder I.,University of Liverpool | Rietbrock A.,University of Liverpool | Kelson K.,Fugro | Burgmann R.,University of California at Berkeley | And 4 more authors.
Geophysical Journal International | Year: 2012

The M w 8.8 Maule earthquake occurred off the coast of central Chile on 2010 February 27 and was the sixth largest earthquake to be recorded instrumentally. This subduction zone event was followed by thousands of aftershocks both near the plate interface and in the overriding continental crust. Here, we report on a pair of large shallow crustal earthquakes that occurred on 2010 March 11 within 15 min of each other near the town of Pichilemu, on the coast of the O'Higgins Region of Chile. Field and aerial reconnaissance following the events revealed no distinct surface rupture. We infer from geodetic data spanning both events that the ruptures occurred on synthetic SW-dipping normal faults. The first, larger rupture was followed by buried slip on a steeper fault in the hangingwall. The fault locations and geometry of the two events are additionally constrained by locations of aftershock seismicity based on the International Maule Aftershock Data Set. The maximum slip on the main fault is about 3 m and, consistent with field results, the onshore slip is close to zero near the surface. Satellite radar data also reveal that significant aseismic afterslip occurred following the two earthquakes. Coulomb stress modelling indicates that the faults were positively stressed by up to 40 bars as a result of slip on the subduction interface in the preceding megathrust event; in other words, the Pichilemu earthquakes should be considered aftershocks of the Maule earthquake. The occurrence of these extensional events suggests that regional interseismic compressive stresses are small. Several recent large shallow crustal earthquakes in the overriding plate following the 2011 M w 9.0 Tohoku-Oki earthquake in Japan may be an analogue for the triggering process at Pichilemu. © 2012 The Authors Geophysical Journal International © 2012 RAS.

Liscio F.,Grenoble Institute of Technology | Liscio F.,Third University of Rome | Maret M.,Grenoble Institute of Technology | Meneghini C.,Third University of Rome | And 7 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We present a detailed analysis of the local ordering in CoPt3 nanostructures epitaxially grown on WSe2(0001) and NaCl(001) low-energy surfaces. Polarized extended x-ray absorption fine-structure measurements at the CoK -edge show a local structural anisotropy in fcc CoPt3 nanostructures grown at 300 K on WSe2. It is characterized by preferential Co-Co bonding along the in-plane direction balanced with preferential heteroatomic bonding along the out-of-plane direction and explains the unexpected perpendicular magnetic anisotropy. Such anisotropy almost vanishes in partially L 12 -ordered nanostructures grown at 700 K. In contrast, the short-range order is isotropic in CoPt3 nanostructures grown on NaCl(001) at 370 K. These different behaviors emphasize the favorable role of Se segregated atoms of WSe2 in the dynamic segregation of Pt atoms at the advancing surface during codeposition, which governs the local structural anisotropy. In the absence of Se, as previously observed in epitaxial CoPt 3 films grown on Ru buffer layers, the development of similar structural anisotropy requires higher growth temperatures (550-720 K). © 2010 The American Physical Society.

Jacques E.,CNRS Paris Institute of Global Physics | Kidane T.,Addis Ababa Institute of Technology | Tapponnier P.,CNRS Paris Institute of Global Physics | Manighetti I.,University of Nice Sophia Antipolis | And 5 more authors.
Bulletin of the Seismological Society of America | Year: 2011

In August 1989, an earthquake sequence including ten events with 6.3 ≥ M ≥ 5.5 in the first two days produced widespread ground deformation in the Dôbi graben of central Afar. Numerous surface breaks with complex geometry, including fresh scarplets with vertical throws up to 30 cm high and open fissures up to 30 cm wide, were observed. Coseismic slip incremented the deformation (normal faulting, block tilting, and counterclockwise rotation of basaltic slices) accumulated in the last 2 m.y. in the transfer zone between the Dôbi and Hanle grabens. By combining maps of surface ruptures, relative event relocations with the local Djibouti network, published focal mechanisms, and source sizes, we tentatively relate most of the mainshocks of the sequence to slip on individual faults. The largest shocks at 11h16 on 20 August 1989 (MS 6.2) and at 1h09 on 21 August 1989 (MS 6.3) ruptured southern segments of the southwestern bounding fault of the graben. A dozen other faults also slipped along the edges of, and inside, the graben. On average, triggered seismic faulting propagated about 35 km northwestward along the graben in about 20 hr. Slip on the main faults was coupled with slip on secondary antithetic faults branching from them at depth. Although the Dôbi earthquakes ruptured part of the fault array between the Asal rift (1978 sequence) and the Serdo region (1969 sequence), an approximately 50-km-long gap subsists along the Der'êla half-graben. We infer the patterns of surface faulting in the Dôbi sequence, which coinvolved bookshelf-faulting about both horizontal and vertical axes, to typify the complexity of coseismic stress release in central Afar and in other active zones of distributed extension (e.g., Iceland, Abruzzi, Basin and Range).

PubMed | Observatoire Des Science Of Lunivers Of Grenoble, CNRS Neel Institute, CNRS Georesources lab, University Pierre and Marie Curie and 2 more.
Type: Journal Article | Journal: Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

Current models of the formation and distribution of gold deposits on Earth are based on the long-standing paradigm that hydrogen sulfide and chloride are the ligands responsible for gold mobilization and precipitation by fluids across the lithosphere. Here we challenge this view by demonstrating, using in situ X-ray absorption spectroscopy and solubility measurements, coupled with molecular dynamics and thermodynamic simulations, that sulfur radical species, such as the trisulfur ion S3(-), form very stable and soluble complexes with Au(+) in aqueous solution at elevated temperatures (>250 C) and pressures (>100 bar). These species enable extraction, transport, and focused precipitation of gold by sulfur-rich fluids 10-100 times more efficiently than sulfide and chloride only. As a result, S3(-) exerts an important control on the source, concentration, and distribution of gold in its major economic deposits from magmatic, hydrothermal, and metamorphic settings. The growth and decay of S3(-) during the fluid generation and evolution is one of the key factors that determine the fate of gold in the lithosphere.

Navratil O.,Observatoire Des Science Of Lunivers Of Grenoble | Albert M.-B.,IRSTEA
Journal of Hydrology | Year: 2010

Reach-average hydraulic geometry (RHG) defines the relations between the average hydraulic variables estimated at river reach (water depth, velocity, channel width) and the discharge. Single log-linear models are classically used by fluvial geomorphologists, hydrologists and ecologists to represent these relations. In this paper, we show that these single log-linear models are not relevant in most of cases and so can lead to significant errors. RHG estimated on 15 alluvial river reaches (the catchment sizes vary from 10 km 2 to 1700 km 2) were found non-linear for two-thirds of the river reaches when considering discharges ranging from low to bankfull flows. So we propose using two power functions (or log-linear) to model these relations, i.e. the log piecewise linear model. This model can detect a discharge Qbreak, i.e. a physical transition or "break point" between both relations. From very low flows (about 30% of the median discharge) to Qbreak, a first relation is comparable to the RHG found in the literature for aquatic habitat analysis. The second relation is relevant for flows ranging from Qbreak to bankfull discharge, and therefore may be more useful for sediment transport and flood routing analysis. Averaging along a reach including several pool-riffle units makes it difficult to clearly ascribe the form of RHG to particular physical processes. The non-linearity of RHG may have multiple origins: the presence of lateral gravel bars, the hydraulic conditions of riffle cross-sections, a change in the resistance to flow with water depth (vegetation, sediment influences). Further research is needed to focus on the physical processes that govern the RHG non-linearity. © 2010 Elsevier B.V. All rights reserved.

PubMed | University of Rome Tor Vergata, University of Pittsburgh and Observatoire Des Science Of Lunivers Of Grenoble
Type: Journal Article | Journal: The journal of physical chemistry. B | Year: 2015

In this work we analyze at a structural level the mechanism by which Cu(II) and Zn(II) ions compete for binding to the A peptides that is involved in the etiology of Alzheimers disease. We collected X-ray absorption spectroscopy data on samples containing A with Cu and Zn at different concentration ratios. We show that the order in which metals are added to the peptide solution matters and that, when Zn is added first, it prevents Cu from binding. On the contrary, when Cu is added first, it does not (completely) prevent Zn binding to A peptides. Our analysis suggests that Cu and Zn ions are coordinated to different numbers of histidine residues depending on the [ion]:[peptide] concentration ratio.

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