G. Fiquet

Institut de Physique du Globe de Paris, Lutetia Parisorum, Île-de-France, France

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Publications (130)473.6 Total impact

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    ABSTRACT: [1] Sintered polycrystalline “rocks” of two-phase aggregate CaGeO3 perovskite (GePv) + MgO and single-phase GePv were deformed at pressure, temperature, and strain rates of 4–10 GPa, 600–1200 K, and ∼1–3 × 10−5 s−1, respectively, with maximum bulk strains up to ∼20%. The as-synthesized two-phase aggregate, produced from the reaction CaMgGeO4 (olivine) → GePv+MgO (MgO occupying ∼28% in volume), possessed a load-bearing framework (LBF) texture indistinguishable from that of (Mg,Fe)2SiO4 → (Mg,Fe)SiO3 perovskite + (Mg,Fe)O reported in previous studies. Stress states of the two phases in the deforming aggregate were evaluated based on systematic distortion of lattice spacings over the entire 360° diffraction azimuth angle. Compared with the single-phase GePv sample, stresses of GePv in the two-phase composite were about 10–20% higher at similar strain and strain rates. Stresses of MgO are about a factor of ∼2 lower than GePv in the same two-phased rock. Volumetrically averaged bulk stresses in the two samples were therefore virtually identical. Texture analyses showed that both samples deformed by dislocation glide, with the dominant slip systems {1 0 0}<1 1 0> (in cubic setting) for both GePv and MgO. These results show that, at low bulk strains up to ∼20%, the two-phase aggregate remains a LBF fabric, with rheological properties of GePv controlling those of the bulk. These experimental findings are in quantitative agreement with previous numerical simulations. Implications of the results to the silicate counterparts and dynamics of the lower mantle are discussed.
    Geochemistry Geophysics Geosystems 01/2013; · 2.94 Impact Factor
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    ABSTRACT: The structure and the polarized infrared absorption spectrum of OH-defects in wadsleyite (beta-Mg2SiO4) are studied, at 0 and 15 GPa, by first-principles calculations based on density functional theory (DFT). Four types of OH-defects are considered: fully protonated magnesium vacancies, fully protonated silicon vacancies, silicon vacancies compensated by a magnesium cation and two protons, and OH-defects associated with the migration of a silicon cation to a normally vacant site, as reported by Kudoh and Inoue (1999). The results suggest that the main absorption band constituted by a doublet (3326 and 3360 cm(-1)) corresponds to at least two types of OH-defects involving M3 vacancies with protonation of the O1-type O atoms along the O1 center dot center dot center dot O-4 edges. The main contribution of the less intense band at 3581 cm(-1) is likely related to the partial protonation of a silicon vacancy (protonation of the O3-type oxygen) associated with the migration of the silicon cation to the Si2 site. This assignment is consistent with several experimental constraints: wavenumber and pleochroism of infrared OH-stretching bands, pressure-dependence of the band wavenumber, evidence from X-ray diffraction of magnesium vacancies in M3 site, and increase of the b/a axial ratio with water content. The integrated absorption coefficients of the corresponding OH-defects are also calculated and thus complement the set of data obtained previously for forsterite and ringwoodite. Absorption coefficients of wadsleyite computed at 0 and 15 GPa indicate that for a precise quantification of the hydrogen content in in situ experiments, one must consider higher absorption coefficients than those determined at 0 GPa after quench. It is also shown that a single theoretical relation can account for the three Mg2SiO4 polymorphs at 0 GPa: K-int = 278.7 +/- 18.1 (3810 +/- 465 - x), where K-int is the integrated molar absorption coefficient of the OH stretching modes and x is the average wavenumber in cm(-1). Absorption coefficients are significantly lower than the general calibrations, the use of which would lead to an underestimation of the water concentrations.
    American Mineralogist 01/2013; 98(11-12):2132-2143. · 2.20 Impact Factor
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    ABSTRACT: We performed sound velocity and density measurements on polycrystalline hexagonal close-packed (hcp) iron at simultaneous high pressure and high temperature, up to 93 GPa and 1100 K, by inelastic x-ray scattering and x-ray diffraction. Our experimental results indicate that high-temperature anharmonic corrections are negligible at least up to 1100 K and that the aggregate compressional velocity VP scales linearly with density over the pressure and temperature range of the investigation (Birch's law). The new results are compared with literature studies and we discuss the extrapolation schemes commonly used in experimental mineral physics, with specific regard to extrapolations to the Earth's core conditions.
    Earth and Planetary Science Letters 05/2012; s 331–332:210–214. · 4.72 Impact Factor
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    E Boulard, F Guyot, G Fiquet
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    ABSTRACT: Characterization of a set of iron-magnesium carbonate mineral samples was done by Raman spectroscopy, X-ray diffraction and electron microprobe. The evolution of unit cell parameters and of the Raman peak positions of the three vibrations modes T, L and 2 nu(2) are reported as a function of the Fe content. Fourteen samples spanning the compositional range from FeCO3 siderite to MgCO3 magnesite were used for this calibration. Such a calibration provides a non-destructive and rapid method for extracting mineral chemistry, suitable for samples that cannot be moved and need immediate analysis or for samples that cannot be destructed or that are in small quantities.
    Physics and Chemistry of Minerals 03/2012; 39(3):239-246. · 1.30 Impact Factor
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    ABSTRACT: The fate of carbonates in the Earth's mantle plays a key role in the geodynamical carbon cycle. Although iron is a major component of the Earth's lower mantle, the stability of Fe-bearing carbonates has rarely been studied. Here we present experimental results on the stability of Fe-rich carbonates at pressures ranging from 40 to 105 GPa and temperatures of 1450–3600 K, corresponding to depths within the Earth's lower mantle of about 1000–2400 km. Samples of iron oxides and iron-magnesium oxides were loaded into CO 2 gas and laser heated in a diamond-anvil cell. The nature of crystalline run products was determined in situ by X-ray diffraction, and the recovered samples were studied by analytical transmission electron microscopy and scanning transmission X-ray microscopy. We show that Fe (II) is systematically involved in redox reactions with CO 2 yielding to Fe (III) -bearing phases and diamonds. We also report a new Fe (III) -bearing high-pressure phase resulting from the transformation of FeCO 3 at pressures exceeding 40 GPa. The presence of both diamonds and an oxidized C-bearing phase suggests that oxidized and reduced forms of carbon might coexist in the deep mantle. Finally, the observed reactions potentially provide a new mechanism for diamond formation at great depth.
    Journal of Geophysical Research 02/2012; 117. · 3.17 Impact Factor
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    ABSTRACT: Among the volatile elements present in our solar system, iodine is involved in mechanisms of primary importance during planet's evolution. The different isotopic signatures of 129Xe/132Xe for mantle and atmosphere between the Earth and Mars may reflect an early fractionation of xenon with respect to iodine. The role of fluids and more especially water is seriously envisaged to generate such a fractionation because whereas iodine is hydrophilic, xenon is not. Therefore iodine's early degassing with a water-rich fluid from a magma ocean is a good hypothesis to explain iodine, but also chlorine and bromine losses during early differentiation stages of the Earth. It was also shown that iodine is involved in natural ozone destruction in the Earth's atmosphere. Today we are able to detect iodine in volcanic emissions. The intensive subduction-zones volcanic degassing may explain the presence of iodine in the atmosphere if degassed together with water. The combination of synchrotron X-Ray characterization with diamond anvil cells, applied as magmatic and mantelic reactors to simulate pressure and temperature conditions of the planet interiors allows: (1) the characterization of fluids (aqueous, melt, supercritic) existing in the Earth; (2) element transfers via such fluids from depths to planets surfaces. Here, we have experimentally monitored iodine degassing from high pressure hydrous melts in situ in diamond anvil cells DAC by measuring iodine partitioning between aqueous fluids and hydrous melts during decompression. DAC experiments have been combined with high energy Synchrotron X-Ray Fluorescence at the beam lines Id27 and FAME from ESRF. Partition coefficients (D(I)fluid/melt = (I)fluid/(I)melt ) have been measured in situ from 500 to 900 °C and from 0.1 to 1.8 GPa. First results show that they are ranging from 1.9 (1.4 GPa) to 60 (0.1 GPa) and seem to tend to unity close to total miscibility between melts and aqueous fluids. At low pressure conditions (lower than 0.5 GPa) iodine partition coefficients are higher than those of bromine [Bureau et al., 2010, CGA 74, 3839-3850] confirming the higher affinity of iodine for water. These results are in agreement with the hypothesis of iodine early magmatic degassing process to generate I fractionation from Xe. They may also be useful to explain the bulk Earth's halogen elements abundances.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Detailed knowledge of the high pressure melting relations is essential for constructing and validating models of materials behavior under extreme conditions for fields ranging from geophysics and planetary sciences to fundamental and applied physics. In the present work, melting and solid-solid phase transitions of several materials have been precisely followed using an original in-situ synchrotron time-resolved x-ray diffraction method. The real-time detection of the x-ray signal scattered by the liquid is used as an objective criterion for melting. The principle and potential of this method will be illustrated in three important cases, i.e. lead, and tantalum melting curves (physics) and the melting of peridotite (geophysics).
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: We examine flow properties and deformation-induced fabric evolution in two-phase composites using the deformation DIA (D-DIA) and the high-pressure x-ray tomography microscope (HPXTM) with monochromatic synchrotron radiation. Stress-strain curves were determined on an analog lower mantle material CaGeO3 perovskite (GePv) plus MgO. The sintered polycrystalline rock was synthesized from the disproportionation reaction of CaMgGeO4 (olivine) - GePv+MgO at 12 GPa and 1573 K for 4 h. The sample contains 28 vol% MgO, and is an excellent analog material for the lower mantle. Scanning electron microscopy showed that the average grain size was about 1 micron. The sample was deformed in the D-DIA at pressures from 4 to 12 GPa, temperatures 600 to 1200 K, and strain rates from 1x to 3x10-5 s-1. The maximum axial strain was 16 %. Elastic constants for GePv were calculated using first-principles with the generalized gradient corrections (GGC) technique. In order to examine effects of the second phase on flow properties, a pure GePv sample was deformed under identical conditions. Flow properties of MgO are available from our previous studies [1]. The relative stress levels in GePv and MgO in the composite sample are in general agreement with numerical simulations [2]. Another analog, a mixture of San Carlos olivine and Fe-S, was examined in the HPXTM. The strength contrast of two phases is similar to that of perovskite and ferropericlase. The initial texture was of the load-bearing framework (LBF) type, with isolated "weak" Fe-S grains sounded by "strong" silicate framework. During shear deformation, a strong shape preferred orientation began to develop in the sample at shear strains above 300%, forming an interconnected weak layer (IWL) texture. The development of deformation fabric was continuously monitored by tomographic imaging under high pressure to a maximum shear strain of 1300%. Applications of these results to dynamics of the lower mantle are discussed. [1] Uchida, T. et al. (2004) Earth Planet. Sci. Lett., 226, 117-126. [2] Madi, K., et al. (2005) Earth and Planetary Sci. Lett., 237, 223-238.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: The physical properties of iron at high pressure and high temperature have unique relevance for geophysics and are crucial in the attempt to refine the chemical composition and dynamics of the Earth's core. In this respect, compressional-wave (VP) and shear-wave (VS) sound velocities play a fundamental role, as two of the few parameters that can be directly compared with the seismic observations. Experiments probing sound velocities, in particular those of opaque metallic samples are at the cutting edge of modern techniques. These experiments are very challenging even when only involving high pressure, and presently very few results exist at simultaneous high pressure and high temperature. None of these experiments however was capable to reach P-T conditions relevant for the Earth's core, and thus the results need to be extrapolated. Currently, velocities extrapolation is made according to the Birch's law, which assumes a linear dependence of the longitudinal acoustic sound velocity on density, or, in more general terms, that the elastic properties of a compressed material are well described within a quasi-harmonic approximation. The validity of this semi-empirical relationship is argument of debate, with theoretical models suggesting anharmonic high-temperature corrections to become eventually significant at very high temperature. Here we present sound velocity and density measurements on polycrystalline hcp-Fe at simultaneous high pressure and high temperature conditions, up to 93 GPa and 1100 K. We directly determined the compressional sound velocity VP from the initial slope of the aggregate longitudinal acoustic phonon dispersion probed by momentum resolved, high resolution inelastic x-ray scattering. In parallel, densities were measured by x-ray diffraction. Our results indicate that high-temperature anharmonic correction are negligible at least up to 1100 K and that VP scales linearly with density irrespectively of specific pressure and temperature conditions over the investigated pressure and temperature range. These new results will be compared with literature studies, and limitations of extrapolation schemes commonly used in experimental mineral physics will be discussed in order to further constrain geophysical models of the Earth's inner core.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Experiments of dissolution of siderite (FeCO3) in pure water and in saline aqueous solution (“seawater” composition) have been performed at temperatures of up to 400 °C in a maximum pressure range of 720–1150 MPa, using an hydrothermal diamond anvil cell (HDAC). The reaction products were characterized in situ by Raman spectroscopy. At 250 °C, in pure water system, we document formation of formaldehyde (HCOH) near the surface of siderite. At 250 °C and above, formic acid (HCOOH) and carbon monoxide (CO) were detected in the bulk fluid. The reduction of oxidized carbon to HCOH and HCOOH is coupled to conversion of ferrous iron (FeII) from siderite to ferric iron (FeIII). We thus provide experimental evidence of FeII–CO2 oxido-reductive coupling using a single mineral, siderite, in pure water and in saline solution. The presence of NaCl in the fluid enhances the kinetics of oxido-reductive dissolution of siderite, with formation of organic chlorinated molecules. The results suggest that in geological situations, especially in accretion prisms or active hydrothermal systems developing on ultrabasic rocks in which fluids may be transferred with relatively short residence times, formic acid and formaldehyde might be important metastable storage forms of hydrogen. Moreover, thermal dissolution of siderite may account for at least some of the reduced carbon observed in chondrites bearing traces of hydrothermal activity and in metasedimentary rocks from the early Earth.
    Chemical Geology. 11/2011; 290(s 3–4):145–155.
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    ABSTRACT: The global geochemical carbon cycle involves exchanges between the Earth's interior and the surface. Carbon is recycled into the mantle via subduction mainly as carbonates and is released to the atmosphere via volcanism mostly as CO(2). The stability of carbonates versus decarbonation and melting is therefore of great interest for understanding the global carbon cycle. For all these reasons, the thermodynamic properties and phase diagrams of these minerals are needed up to core mantle boundary conditions. However, the nature of C-bearing minerals at these conditions remains unclear. Here we show the existence of a new Mg-Fe carbon-bearing compound at depths greater than 1,800 km. Its structure, based on three-membered rings of corner-sharing (CO(4))(4-) tetrahedra, is in close agreement with predictions by first principles quantum calculations [Oganov AR, et al. (2008) Novel high-pressure structures of MgCO(3), CaCO(3) and CO(2) and their role in Earth's lower mantle. Earth Planet Sci Lett 273:38-47]. This high-pressure polymorph of carbonates concentrates a large amount of Fe((III)) as a result of intracrystalline reaction between Fe((II)) and (CO(3))(2-) groups schematically written as 4FeO + CO(2) → 2Fe(2)O(3) + C. This results in an assemblage of the new high-pressure phase, magnetite and nanodiamonds.
    Proceedings of the National Academy of Sciences 03/2011; 108(13):5184-7. · 9.81 Impact Factor
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    ABSTRACT: We report the preparation of the starting material reflecting the complex composition of the Earth's mantle. With this aim, we synthesized two types of material: sol–gel and glass obtained by aerodynamic levitation. Thanks to their high homogeneity and reactivity, these materials are suitable for experimental petrology under extreme conditions, conducted in laser-heated diamond anvil cell. We then used this mantle analog to investigate the iron partitioning between high pressure phases under lower mantle conditions during solid-state reaction and partial melting of the material. Iron preferentially partitions into the (Mg,Fe)O, but the presence of aluminum slightly enriches iron in the silicate phase (Kpv−fp=0.41±0.04) compared to similar experiments in an Al-free system.
    High Pressure Research 03/2011; 31(1):199-213. · 0.90 Impact Factor
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    ABSTRACT: Seismic discontinuities in Earth typically arise from structural, chemical, or temperature variations with increasing depth. The pressure-induced iron spin state transition in the lower mantle may influence seismic wave velocities by changing the elasticity of iron-bearing minerals, but no seismological evidence of an anomaly exists. Inelastic x-ray scattering measurements on (Mg(0.83)Fe(0.17))O-ferropericlase at pressures across the spin transition show effects limited to the only shear moduli of the elastic tensor. This explains the absence of deviation in the aggregate seismic velocities and, thus, the lack of a one-dimensional seismic signature of the spin crossover. The spin state transition does, however, influence shear anisotropy of ferropericlase and should contribute to the seismic shear wave anisotropy of the lower mantle.
    Science 01/2011; 331(6013):64-7. · 31.20 Impact Factor
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    ABSTRACT: We have examined the microstructural evolution of a two-phase composite (olivine + Fe-Ni-S) during large shear deformation, using a newly developed high-pressure X-ray tomography microscope. Two samples were examined: a load-bearing framework-type texture, where the alloy phase (Fe-Ni-S) was present as isolated spherical inclusions, and an interconnected network-type texture, where the alloy phase was concentrated along the silicate grain boundaries and tended to form an interconnected network. The samples, both containing [~]10 vol% alloy inclusions, were compressed to 6 GPa, followed by shear deformation at temperatures up to 800 K. Shear strains were introduced by twisting the samples at high pressure and high temperature. At each imposed shear strain, samples were cooled to ambient temperature and tomographic images collected. The three-dimensional tomographic images were analyzed for textural evolution. We found that in both samples, Fe-Ni-S, which is the weaker phase in the composite, underwent significant deformation. The resulting lens-shaped alloy phase is subparallel to the shear plane and has a laminated, highly anisotropic interconnected weak layer texture. Scanning electron microscopy showed that many alloy inclusions became film-like, with thicknesses <1 {micro}m, suggesting that Fe-Ni-S was highly mobile under nonhydrostatic stress, migrated into silicate grain boundaries, and propagated in a manner similar to melt inclusions in a deforming solid matrix. The grain size of the silicate matrix was significantly reduced under large strain deformation. The strong shape-preferred orientation thus developed can profoundly influence a composite's bulk elastic and rheological properties. High-pressure-high temperature tomography not only provides quantitative observations on textural evolution, but also can be compared with simulation results to derive more rigorous models of the mechanical properties of composite materials relevant to Earth's deep mantle.
    Geosphere 01/2011; 7(1):40-53. · 2.02 Impact Factor
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    ABSTRACT: Detailed studies of devolatilization reactions, fluid-rock interactions and metamorphic transformations occurring in subducting slabs play a key role in unraveling the complex physical-chemical transformations of crust and mantle at convergent margins and in the understanding of fluids and element fluxes involved. One of the main characteristics of subduction zones is the presence of water released from oceanic lithosphere that interacts with mantle wedge rocks. In particular, reaction of water with ferrous iron-rich minerals contained in ultramafic rocks can develop highly reducing conditions and generation of H2 during serpentinization. Fluids interacting with peridotite in this temperature range may have important biological implications and play a key role on metasomatism of the forearc mantle. In particular, the dissolution of Fe-bearing minerals can be responsible for the generation of reactive reduced species, as is the case, for example, of deep-sea hydrothermal systems (cf Seewald et al., 2006). For a better understanding of these processes, H2 and CO2 generation can be monitored by experiments at the P and T conditions expected during subduction and serpentinization at shallow levels. Experiments on dissolution of iron (II) carbonate (FeCO3 siderite) in aqueous fluids (pure water, saline solution and ammonium solution) have been performed at temperatures up to 400°C and pressures in the range 730-1150 MPa using an externally heated hydrothermal diamond anvil cell (HDAC). In situ Raman spectroscopy allowed direct characterization of the new phases and of the C-O-H-N species dissolved in the aqueous fluid. For the simplest C-O-H aqueous system (H2O and H2O-NaCl) we document reduction of oxidized carbon to organic molecules (formaldehyde and formic acid) and H2 production in the fluid. HDAC quenched samples characterized at room temperature and pressure by Raman spectroscopy and SEM (Scanning Electron Microscopy) have also revealed the occurrence of complex chlorinated organic molecules. In complex ammonium-bearing aqueous solutions (NH4Cl, NH4HCO3 and (NH4)2CO3) dissolution of siderite is coupled at temperatures above 300°C with conversion of NH4+ to ammonia (NH3), which in turn reacts at higher temperatures to form amide-types bonds (C=O and N-H stretching of amides). The results confirm that amines can be synthesized in high-temperature hydrothermal systems in the presence of carbonate and aqueous ammonium chloride solutions (cf Marshall, 1994). We provide experimental evidence of direct reduction of carbon from siderite in aqueous fluids with formation of organic molecules and amide bonds. Our results suggest that thermal dissolution of siderite may account for some of the reduced carbon observed in meteorites (cf McCollom, 2003) and in hydrothermal settings, with important implications for abiotic organic synthesis and speciation of hydrogen and nitrogen in geological systems. Marshall, W.L. (1994), GCA, 58, 1099-2106. McCollom, T.M. (2003), GCA, 67, 311-317. Seewald, J.S., Zolotov, M.Yu., McCollom, T.M. (2006), GCA, 70, 446-460.
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: The global geochemical carbon cycle involves exchange between the Earth's mantle and the surface. Carbon (C) is recycled into the mantle via subduction and released to the atmosphere via volcanic outgassing. Carbonates are the main C-bearing minerals that are transported deep in the Earth's mantle via subduction of the oceanic lithosphere [1]. The way C is recycled and its contribution to the lower mantle reservoir is however largely unknown [ e.g 2, 3]. In this respect, it is important to assess if carbonates can be preserved in the deep mantle, or if decarbonatation, melting or reduction play a role in the deep carbon cycle. To clarify the fate of carbonates in the deep mantle, we carried out high-pressure and high-temperature experiments up to 105 GPa and 2850 K. Natural Fe-Mg carbonates or oxide mixtures of (Mg,Fe)O + CO2 were loaded into laser heated diamond anvil cells. In situ characterizations were done by X-ray Diffraction (XRD) using synchrotron radiation at the high-pressure beamline ID27 of the European Synchrotron Radiation Facility. A focused ion beam technique was then used to prepare the recovered samples for electron energy loss spectroscopy in a dedicated scanning transmission electron microscope (EELS-STEM) and scanning transmission X-ray microscopy (STXM). In situ XRD clearly shows the transformation of the initial carbonate phase into a new Mg-Fe high pressure carbonate phase at lower mantle conditions. We also provide direct evidence for recombination of CO2 with (Mg,Fe)O to form this new carbonate structure. In addition, subsequent EELS-STEM and STXM spectroscopies carried out on recovered samples yields C K-edge and stoechiometry characteristic to this new carbonate structure. This new high pressure phase concentrates a large amount of Fe(III), as a result of redox reactions within the siderite-rich carbonate. The oxidation of iron is balanced by partial reduction of carbon into CO groups and/or diamond. These reactions may provide an explanation for the coexistence of oxidized and reduced C species observed on natural samples [4, 5], but also a new diamond formation mechanism at lower mantle conditions. [1] Sleep, N. H., and K. Zahnle (2001) J. Geophys. Res.-Planets 106(E1), 1373-1399. [2] Javoy, M. (1997) Geophys. Res. Lett. 24(2), 177-180. [3] Lecuyer et al. (2000) Earth Planet. Sci. Lett. 181(1-2), 33-40. [4] Brenker et al. (2007) Earth Planet. Sci. Lett. 260(1-2), 1-9. [5] Stachel et al. (2000) Contrib. Mineral. Petrol. 140(1), 16-27.
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: The characterization of pressure- and temperature-induced transitions of mantle minerals, and their link with seismic discontinuities, is one of the most striking contributions provided by mineral physics for the understanding of Earth's interior. Emblematic in this sense is the series of phase transformations that occur in olivine, which ultimately define the main seismic discontinuities of the upper mantle. On the contrary, the spin transition in ferropericlase and perovskite has not yet been clearly associated to any seismic signature, even though effects on mantle's density and seismic wave velocity have been anticipated. With specific regard to ferropericlase, the spin transition occurs without change in the structure, but experimental [1-3] and theoretical studies [4] indicate large softening of all the elastic moduli and consequently significant softening of the aggregate sound velocities. Such an effect should result in a seismic discontinuity or anomaly, albeit broad, depending upon the range of the pressure and temperature over which the spin crossover occurs [5]. However, no seismic anomalies are observed at relevant depth. Here we present measurements of the complete elastic tensor of (Mg0.83Fe0.17)O ferropericlase up to 70 GPa by inelastic x-ray scattering. From the initial slope of the phonon dispersion of longitudinal and transverse acoustic modes, we directly derived the three independent elements of the elastic tensor. While a clear softening of the shear modulus C44 occurs across the spin transition, along with a small anomaly for C12, we observe no softening for the longitudinal modulus C11. As a direct consequence of the absence of anomalies in C11, the derived density dependence of the aggregate compressional and shear sound velocities does not show any significant deviation from a linear trend. This provides a clear explanation for the lack of any one-dimensional seismic signature in the lower mantle directly related to the spin crossover. Conversely, the elastic shear anisotropies of high-spin and low-spin ferropericlase are profoundly different, and may account for, if not control, the shear wave anisotropy within the lower mantle. [1] J.C. Crowhurst et al., Science 319, 451 (2008). [2] H. Marquardt et al., Science 324, 224 (2009). [3] H. Marquardt et al., Earth Planet. Sci. Lett. 287, 345 (2009). [4] R.M. Wentzcovich et al., PNAS 106, 8447 (2009). [5] J.F. Lin et al., Science 317, 1740 (2007).
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: Melting phase relations and major elements partitioning have been determined for a fertile peridotite (KLB-1) between 36 and 140 GPa. The experiments were conducted in diamond-anvil cells at the high-pressure beamline ID27 of the European Synchrotron Radiation Facility (ESRF) so as to use clear in situ melting criterion and to determine phase relationships from X-ray diffraction. Focused ion beam (FIB) sections of the recovered diamond-anvil cell samples were further investigated at the nano-scale by scanning and analytical transmission electron microscopy to check melting/crystallization sequences as well as variations of phase composition with temperature and pressure. Our results show that Mg-perovskite is the liquidus phase above 50 GPa, whereas ferropericlase is the solidus phase. Our results also yield strong constraints on the solidus curve of the lower mantle, which is measured at 4180 ± 150 K at core mantle boundary pressure. Since this value matches estimated mantle geotherms, molten regions may exist at the base of the present-day mantle. Melting phase relations and element partitioning data show that the produced liquids could be dense and host many incompatible elements at the base of the mantle. The data also allow us to constrain the way the putative magma ocean would have crystallized.
    AGU Fall Meeting Abstracts. 11/2010; -1:04.
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    ABSTRACT: Interrogating physical processes that occur within the lowermost mantle is a key to understanding Earth's evolution and present-day inner composition. Among such processes, partial melting has been proposed to explain mantle regions with ultralow seismic velocities near the core-mantle boundary, but experimental validation at the appropriate temperature and pressure regimes remains challenging. Using laser-heated diamond anvil cells, we constructed the solidus curve of a natural fertile peridotite between 36 and 140 gigapascals. Melting at core-mantle boundary pressures occurs at 4180 ± 150 kelvin, which is a value that matches estimated mantle geotherms. Molten regions may therefore exist at the base of the present-day mantle. Melting phase relations and element partitioning data also show that these liquids could host many incompatible elements at the base of the mantle.
    Science 09/2010; 329(5998):1516-8. · 31.20 Impact Factor
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    ABSTRACT: We performed room-temperature sound velocity and density measurements on a polycrystalline alloy, Fe0.89Ni0.04Si0.07, in the hexagonal close-packed (hcp) phase up to 108 GPa. Over the investigated pressure range the aggregate compressional sound velocity is ∼ 9% higher than in pure iron at the same density. The measured aggregate compressional (VP) and shear (VS) sound velocities, extrapolated to core densities and corrected for anharmonic temperature effects, are compared with seismic profiles. Our results provide constraints on the silicon abundance in the core, suggesting a model that simultaneously matches the primary seismic observables, density, P-wave and S-wave velocities, for an inner core containing 4 to 5 wt.% of Ni and 1 to 2 wt.% of Si.
    Earth and Planetary Science Letters 01/2010; · 4.72 Impact Factor

Publication Stats

2k Citations
473.60 Total Impact Points

Institutions

  • 1993–2013
    • Institut de Physique du Globe de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2010–2012
    • Paris Diderot University
      • Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC) UMR 7590
      Lutetia Parisorum, Île-de-France, France
    • Tokyo Institute of Technology
      Edo, Tōkyō, Japan
  • 2001–2012
    • Pierre and Marie Curie University - Paris 6
      • Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC)
      Lutetia Parisorum, Île-de-France, France
  • 2008–2011
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
    • Université des Sciences et Technologies de Lille 1
      Lille, Nord-Pas-de-Calais, France
  • 1993–2000
    • Ecole normale supérieure de Lyon
      Lyons, Rhône-Alpes, France
  • 1999
    • Claude Bernard University Lyon 1
      Villeurbanne, Rhône-Alpes, France
  • 1992
    • Université de Rennes 1
      Roazhon, Brittany, France