Search

The reactivity of ultramafic rocks under hydrothermal conditions controls chemical fluxes at the interface between the internal and external reservoirs of silicate planets. On Earth, hydration of ultramafic rocks is ubiquitous and operates from deep subduction zones to shallow lithospheric environments where it considerably affects the physical and chemical properties of rocks and can interact with the biosphere. This process also has key emerging societal implications, such as the production of hydrogen as a source of carbon-free energy. To date, the chemical model systems used to reproduce olivine hydrothermal alteration lead to the formation of serpentine with sluggish reaction rates. Here, we use in situ diamond-anvil cell experiments and show that the presence of aluminum in hydrothermal fluids increases the rate of olivine serpentinization by one to two orders of magnitude. Aluminum increases the solubility of olivine and enhances the precipitation of aluminous serpentine. After two days, olivine crystals were fully transformed to aluminous serpentine under conditions typical for natural hydrothermal environments, i.e., 200 and 300 °C, 200 MPa. This result motivates a re-evaluation of the natural rates of olivine serpentinization and of olivine hydrolysis in general in a wide range of settings. This discovery also opens the potential of the serpentinization reaction for industrial scale production of hydrogen at economically feasible timescales and temperature.

The influence of sodium chloride salt on the liquidus of ice VI and ice VII has been measured for concentrations ranging between 0.01 and 4 mol kg−1 NaCl. Dissolved NaCl significantly increases the melting pressure or decreases the melting temperature as a function of the salt concentration and induces a density crossover between ice VI and the brine. For NaCl concentrations higher than 2.5 mol kg−1 ice VI is more buoyant than the brine. The liquidus points are fitted to a second order polynomial law and a model is provided to predict the melting pressures of ice VI and ice VII (Pm,VI and Pm,VII), respectively as a function of temperature T (K) and NaCl concentration XNaCl (mol kg−1): P m , VI ( T , X NaCl ) = 9.27 + 0.996 X NaCl - ( 6.99 × 10 - 2 + 7.6 × 10 - 3 X NaCl ) · T + ( 1.414 × 10 - 4 + 1.541 × 10 - 5 X NaCl ) · T 2 P m , VII ( T , X NaCl ) = - 0.133 + 0.122 X NaCl - ( 1.28 × 10 - 4 + 4.17 × 10 - 4 X NaCl ) · T + ( 1.86 × 10 - 5 + 8.56 × 10 - 7 X NaCl ) · T 2 The temperature of the triple point between ice VI, ice VII and the brine shifts of −7 K/XNaCl along the 2.17 GPa isobar. The consequences of potentially dissolved NaCl for the internal structure of water rich planetary bodies are discussed. The density crossover between ice VI and brines suggests that migration of brines through a deep ice VI layer is enhanced for high thermal profiles and is unlikely for colder thermal conditions. It also suggests that patches of brines may actually be gravitationally stable at the interface between the bedrock and a deep ice VI basal layer allowing for a potential new class of exobiological habitat.

Water-rich planetary bodies including large icy moons and ocean exoplanets may host a deep liquid water ocean underlying a high-pressure icy mantle. The latter is often considered as a limitation to the habitability of the uppermost ocean because it would limit the availability of nutrients resulting from the hydrothermal alteration of the silicate mantle located beneath the deep ice layer. To assess the effects of salts on the physical properties of high-pressure ices and therefore the possible chemical exchanges and habitability inside H 2 O-rich planetary bodies, we measured partitioning coefficients and densities in the H 2 O–RbI system up to 450 K and 4 GPa; RbI standing as an experimentally amenable analog of NaCl in the H 2 O-salt solutions. We measured the partitioning coefficient of RbI between the aqueous fluid and ices VI and VII, using in-situ Synchrotron X-ray Fluorescence (XRF). With in-situ X-ray diffraction, we measured the unit-cell parameters and the densities of the high-pressure ice phases in equilibrium with the aqueous fluid, at pressures and temperatures relevant to the interior of planetary bodies. We conclude that RbI is strongly incompatible towards ice VI with a partitioning coefficient K d (VI-L) = 5.0 ( ± 2.1 ) ⋅ 10 − 3 and moderately incompatible towards ice VII, K d (VII-L) = 0.12 ( ± 0.05 ) . RbI significantly increases the unit-cell volume of ice VI and VII by ca. 1%. This implies that RbI-poor ice VI is buoyant compared to H 2 O ice VI while RbI-enriched ice VII is denser than H 2 O ice VII. These new experimental results might profoundly impact the internal dynamics of water-rich planetary bodies. For instance, an icy mantle at moderate conditions of pressure and temperature will consist of buoyant ice VI with low concentration of salt, and would likely induce an upwelling current of solutes towards the above liquid ocean. In contrast, a deep and/or thick icy mantle of ice VII will be enriched in salt and hence would form a stable chemical boundary layer on top of the silicate mantle. Such a contrasted dynamics in the aqueous–ice VI–ice VII system would greatly influence the migration of nutrients towards the uppermost liquid ocean, thus controlling the habitability of moderate to large H 2 O-rich planetary bodies in our solar system (e.g., Ganymede, Titan, Calisto) and beyond.

By the end of the 19th century British and French oceanographic expeditions had shown that life exists in the deepest ocean trenches. Since then, microorganisms have been found to thrive in diverse environments characterized by a wide range of pressure-temperature-composition ( P - T - X ) conditions (Rothschild and Mancinelli 2001). The range of physicochemical conditions under which microbial life has been observed has continued to expand with greater access to extreme environments and greatly improved tools for sampling and assessing the diversity and physiology of microbial communities. This exploration now includes examination of subseafloor and continental subsurface settings—key goals of the Deep Life Directorate within the Deep Carbon Observatory (DCO) Program. Bacterial metabolic activity has been described at temperatures as low as −40 °C (Rivkina et al. 2000; Price and Sowers 2004; Panikov and Sizova 2007; Collins et al. 2010) and a methanogen has been cultured at 122 °C under hydrostatic pressure (Takai et al. 2008). Moreover, bacteria can withstand ionizing radiation levels up to 30,000 grays (Rainey et al. 2005), and can grow over a pH range between 0 and 12.5 (Takai et al. 2001; Sharma et al. 2012), at salinities up to 5.2 M NaCl (Kamekura 1998), and at hydrostatic pressures up to 130 MPa (Yayanos 1986). Bacterial survival has also been demonstrated up into the GPa range (Sharma et al. 2002; Vanlint et al. 2011). Because of the difficulty to access deep pressure-affected environments compared to most other extreme environments, less is known about deep-sea and deep-continental microbial communities and their physiological adaptation to high hydrostatic pressure, even though high-pressure environments are more voluminous in nature than other extreme environments. Our current knowledge about life at high pressure currently derives from studies of deep-sea microorganisms that possess adaptations for growth …

The mechanism and kinetics of the a-b transformation in San Carlos olivine a- Mg1.8Fe0.2SiO4 containing ca. 526 wt.ppm H2O were studied in situ by time-resolved synchrotron X-ray diffraction (XRD) in the range 12.5 - 14.5 GPa and 870 - 1150 K. Time series of XRD spectra reveal the early formation of an intermediate phase that further transforms to wadsleyite (b-phase). This intermediate phase may be either a metastable ringwoodite (g-phase) or the disordered spinelloid phase proposed in the pseudomartensitic reaction model. Both microstructural and kinetic data suggest that the transformation rates are controlled by growth processes after the early saturation of nucleation sites along olivine grain boundaries. Growth rates in the range 1.7 10 12 - 2.1 10 9 m.s 1 are estimated by fitting the transformation-time data to the Cahn rate equation and define an activation enthalpy for growth ΔHa = 204(55) kJ/mol. Compared to the previous studies performed on pure forsterite Mg2SiO4, these new kinetic results point out an increase of transformation rates with the iron content. Hence, the persistence of a metastable olivine wedge to depths > 660 km might be restricted to even colder and/or dryer subduction zones than previously estimated.

The concentration of prebiotic organic building blocks may have promoted the formation of biopolymers in the environment of the early Earth. We therefore studied the adsorption of RNA monomers AMP, GMP, CMP, and UMP, and DNA monomers dGMP, dCMP, and TMP, on minerals that were abundant in the early Earth environment as the result of aqueous or hydrothermal alteration of the primitive oceanic crust. We focused our study on swelling clays, i.e. nontronite and montmorillonite, and non-swelling phyllosilicates, i.e. pyrophyllite, chlorite, lizardite and chrysotile suspended in an aqueous saline solution analog to seawater. In this reference study, adsorption experiments were carried out under standard conditions of pressure and temperature and controlled pH. Under such conditions, this work is also relevant to the preservation of nucleic acids in Fe–Mg-rich terrestrial and Martian soils. We compared the adsorption of the different monomers on individual minerals, as well as the adsorption of single monomers on the whole suite of minerals. We found that DNA monomers adsorb much more strongly than RNA monomers, and that any monomer containing the G nucleobase adsorbed more strongly than one containing the C nucleobase. At high surface loadings (greater than about 1 mM monomer in aqueous solution) we also found a dramatic increase in the slope of adsorption isotherm on the swelling clays, leading to large increases in the amounts adsorbed. Data were processed in order to understand the adsorption mechanism of nucleotides onto mineral surfaces. We infer that all nucleotides behave as homologous molecules in regard to their adsorption onto the studied mineral surfaces. At low to moderate surface loadings, their adsorption is best explained by a single mechanism common to the suite of minerals of the present study. At pH 7, adsorption certainly proceeds by ligand exchange between the phosphate group and the hydroxyls of the broken edges of phyllosilicates leading to the saturation of lateral surfaces. Below pH 4, swelling clays also adsorb nucleotides through cation exchange on basal surfaces, whereas non-swelling phyllosilicates do not. However, at high surface loadings an additional mechanism stabilizing adsorption occurs. Given the proposed adsorption mechanisms, the possibility of a favorable polymerization at the mineral–water interface is discussed. We propose that Fe–Mg rich phyllosilicates tightly bind nucleotides, under ambient conditions, and concentrate them up to 1000 times the solution concentration upon saturation. Nontronites have the most diverse and favorable adsorption behaviors and could have helped to the concentration and polymerization of nucleotides under primitive Earth-like conditions.

International audience; The impact of deep-subsurface pressure conditions on microbial activity is still poorly constrained. In particular it is unknown how pressure of deep environments affects microbial transformations of iron. We investigated the effects of high hydrostatic pressure (HHP) on the rate and the extent of bacterial dissimilatory iron reduction (DIR). We employed a novel experimental setup that enables in situ monitoring of Fe oxidation state and speciation in bacterial cultures in an optimized HHP incubation system using X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The iron-reducing bacterium Shewanella oneidensis MR-1 was incubated at 30 degrees C with Fe(III) citrate and tryptone at pressures between 0.1 and 100 MPa. For pressures up to 70 MPa strain MR-1 (10(8) cells ml(-1)) was able to reduce all 5 mM Fe(III) provided. Above 70 MPa, the final amount of Fe(III) that MR-1 could reduce decreased linearly and DIR was estimated to stop at 109 +/- 7 MPa. The decrease in the reduction yield was correlated with the dramatic decrease in survival (as determined by CFU counts) above 70 MPa. The initial rate of DIR increased with pressure up to 40 MPa, then decreased to reach zero at about 110 MPa. Increased rates of DIR activity and relatively high growth rates for pressures below 40 MPa would potentially ensure the maintenance of MR-1 in most of deep subsurface environments where moderate pressures occur, i.e. deep-sea environments. This study not only provides the first in situ quantitative results for microbial iron metabolism under HHP conditions but also sets the stage for future investigations of deep-sea pressure-adapted iron reducers. Moreover it demonstrates for the first time that XANES at the Fe K-edge is a powerful probe for in vivo monitoring of iron transformations in living microbial cultures. (C) 2012 Elsevier Ltd. All rights reserved.

Until recently, monitoring of cells and cellular activities at high hydrostatic pressure (HHP) was mainly limited to ex situ observations. Samples were analyzed prior to and following the depressurization step to evaluate the effect of the pressure treatment. Such ex situ measurements have several drawbacks: (i) it does not allow for kinetic measurements and (ii) the depressurization step often leads to artifactual measurements. Here, we describe recent advances in diamond anvil cell (DAC) technology to adapt it to the monitoring of microbial processes in situ. The modified DAC is asymmetrical, with a single anvil and a diamond window to improve imaging quality and signal collection. Using this novel DAC combined to Raman and X-ray spectroscopy, we monitored the metabolism of glucose by baker's yeast and the reduction of selenite by Agrobacterium tumefaciens in situ under HHP. In situ spectroscopy is also a promising tool to study piezophilic microorganisms.

In regions of the mantle where multi-phases coexist like at the olivine–wadsleyite–ringwoodite transitions, the stress induced by the seismic waves may drive a mineralogical reaction between the low to high pressure phases, a possible source of dissipation. In such a situation, the amount of attenuation critically depends on the timescale for the phase transformations to reach equilibrium relative to the period of the seismic wave. Here we report synchrotron-based measurements of the kinetics of the olivine to ringwoodite transformation at pressure-temperature conditions of the co-stability loop, for iron-rich olivine compositions. Both microstructural and kinetic data suggest that the transformation rates are controlled by growth processes after the early saturation of nucleation sites along olivine grain boundaries. Transformation-time data show an increase of reaction rates with temperature and iron content, and have been fitted to a rate equation for interface-controlled transformation: G = k 0 ⋅ T ⋅ exp ⁡ [ n ⋅ X Fa ] ⋅ exp ⁡ [ − ( Δ H a + P V ⁎ ) / R T ] × [ 1 − exp ⁡ ( Δ G r / R T ) ] , where X Fa is the fayalite fraction, the exponential factor n = 9.7 , ln ⁡ k 0 = − 9.1 m s − 1 . X Fa − 1 and Δ H a = 199 kJ / mol , assuming V ⁎ = 0 cm 3 / mol . Including these new kinetic results in a micro-mechanical model of a two-phase loop ( Ricard et al., 2009 ), we predict Q K − 1 and Q μ − 1 significantly higher than the PREM values for both body waves and normal modes. This attests that the olivine–wadsleyite transition can significantly contribute to the attenuation of the Earth's mantle transition zone.

International audience; Heterococcoliths are micron-scale calcite platelets produced by coccolithophores. They have been the most abundant and continuous fossil record over the last 215 million years (Myr), offering great potential for geochemical studies, although the heterococcolith fossil record remains underutilised in this domain. We have mapped heterococcoliths' composition using X-ray fluorescence (XRF) with a 100-nm resolution beam to decipher element distributions in heterococcoliths and to investigate the potential development of geochemical proxies for palaeoceanography. The study presents two Middle Jurassic Watznaueria britannica heterococcoliths from Cabo Mondego, Portugal. XRF analysis was performed with a 17 keV incident energy beam at the European Synchrotron Radiation Facility ID22NI beamline to study elements from Sr down to S. Ca, Sr and Mn are distributed following the heterococcolith crystalline arrangement. Cl, Br and S display an homogeneous distribution, whereas K, Fe, Cu, Zn and Rb are concentrated at the edges and in the central area of the heterococcoliths. Distributions of K, Fe, Ti, Fe, Cu, Zn, Rb and to a lesser extent V and Cr are highly influenced by clay contamination and peripheral diagenetic overgrowth. Mn is related to diagenetic Mn-rich CaCO3 overgrowth on top of or between heterococcoliths shields. Cl and Br are likely to be present in heterococcoliths inside interstitial nano-domains. We assume that the cytoplasm [Cl−] and [Br−] are mediated and constant during heterococcolithogenesis. Assuming a linear correlation between cytoplasm [Cl−] and sea water [Cl−], heterococcolith Cl may have potential as a salinity proxy. As S is incorporated into heterococcoliths by sulphated polysaccharides, our study suggests a role for such polysaccharides in heterococcolithogenesis for at least 170 Myr. The low Sr/Ca in the W. britannica specimens studied here may either highlight an unusual cellular physiology of Mesozoic coccolithophores or result from low growth rates in oligotrophic environments.

Olivine and pyroxene are the major minerals of ultramafic rocks. The hydrothermal alteration of these rocks leads to the serpentinization reaction that mainly forms serpentine and variable amounts of talc, brucite and magnetite, as well as hydrogen. The serpentinization kinetics of pyroxene under hydrothermal conditions has been very little studied in comparison with olivine, and both have been evaluated experimentally only in simple aqueous fluids. Here, we evaluate the effect of aluminum on the serpentinization rate of olivine and orthopyroxene at 200 degrees C, 340 degrees C and 200 MPa to simulate natural hydrothermal conditions. We used low-pressure diamond-anvil cells (lp-DAC) and time-resolved X-ray diffraction to monitor in situ the progress of the serpentinization reaction in four experiments. We also performed two long-lasting additional experiments with orthopyroxene for six days at 340 degrees C and 200 MPa, for which in situ monitoring was not possible. At 340 degrees C in presence of Al, olivine conversion into lizardite is extremely fast (half-time reaction t(1/2) = 7 h) while orthopyroxene did not react much even after 6 days (11%). In contrast to olivine, orthopyroxene conversion to serpentine was faster without Al (48% in 6 days). Magnetite was also observed in the run with olivine only at 340 degrees C. In experiments run with orthopyroxene only, we observed the exclusive formation of proto-serpentine instead of lizardite. We propose that the contrasted effect of Al on the serpentinization rate of olivine and orthopyroxene results from the complexation of Al in the solution that reacts differently with the different mineral surfaces during their dissolution. The positively charged olivine surface allows the adsorption of the dominant negatively charged Al(OH)(4)(-) complex, while the neutral surface of orthopyroxene does not. This adsorption process could facilitate both the dissolution of olivine and the nucleation-growth of an Al-enriched lizardite. (C) 2016 Elsevier B.V. All rights reserved.

International audience; We have designed a new low-pressure Diamond Anvil Cell (DAC), calibrated two novel pressure calibrants and validated the use of semi-quantitative Raman and Xray spectroscopies to monitor the fate of microbes, their metabolism or their cellular components under controlled pressures and temperatures in the 0.1-1.4 GPa and 20°-300°C P,T range. The low-pressure DAC has a 250-600 µm thick observation diamond window to allow for lower detection limits and improved microscopic imaging. This new design allows the determination of cellular growth parameters from automated image analysis, which can be correlated with the spectroscopic data obtained on metabolism, ensuring high quality data collection on microbial activity under pressure. The novel pressure sensors offer the ease of use of the well-known ruby scale, while being more sensitive and reacting to pressure variations instantaneously.

A (Ca,Na)-hexaluminosilicate, whose Ca end member was previously synthesized in numerous high-pressure experiments, has been identified by Raman spectroscopy in heavily shocked Martian meteorites. This mineral has a structural formula close to (CaxNa1-x)Al3+xSi3-xO11 and is similar to the calcium aluminum silicate phase previously synthesized in high-pressure experiments performed on anorthite and rocks of basaltic composition. This new mineral occurs in shock melt pockets in two distinct settings and is intimately intergrown with SiO2-stishovite. The first setting, encountered in Zagami, consists of idiomorphic equant crystals overgrown by acicular stishovite that crystallized from a melt of labradorite composition. The second setting contains the (Na, Ca)-hexaluminosilicate phase intergrown with stishovite and hollandite and was formed during partial melting at high pressures. The mineralogical association (Na,Ca)-hexaluminosilicate+stishovite was observed in shock melt pockets, which have distinct bulk compositions in seven Martian shergottites. This new mineral represents, after majorite, the second natural occurrence of a silicate mineral with silicon in both four and six coordination. The assemblage stishovite+(Na,Ca)-hexalummosilicate sets constraints on the pressure and temperature conditions that prevailed during shock in some of the studied meteorites. The (Na, Ca)-hexaluminosilicate mineral is a potential carrier of Al and Na during subduction of oceanic crust in the lower mantle of the Earth. (C) 2003 Elsevier B.V. All rights reserved.

International audience; The kinetics of the quartz-coesite phase transition has been studied in situ by X-ray diffraction in the 2.1-3.2 GPa, 5001010 C pressure-temperature range. Analysis of the data within Cahn's model of nucleation and growth at grain boundaries reveals that the prograde and retrograde reactions have different kinetics. The quartz --> coesite transformation is one order of magnitude faster than coesite --> quartz. Both reactions are characterized by high nucleation rates, so that the overall reaction kinetics is controlled by crystal growth processes. For the coesite --> quartz transformation, growth rates are extrapolated using Turnbull's equation with an activation energy for the transition of 163 +/- 23 kF/mol. This kinetic law is combined with an 'inclusion in a host' elastic model to study the contribution of kinetics in coesite preservation. This numerical modelling shows that above 400degreesC retrograde transformation of coesite to quartz is mainly controlled by the 'pressure vessel' effect of the host phase, whereas reaction kinetics is the controlling factor at lower temperatures. The influence of the shape of the P-T path and the exhumation rate upon the retrogression of coesite to quartz are investigated to use the percentage of unretrogressed coesite inclusions to constrain P-T-t paths.

International audience; Auguste Bravais by his fundamental work on lattice has pioneered modern crystallography. He was born in 1811 in Annonay (France) at a short distance from Lyon and Saint-Etienne. He was then educated at the College Stanislas in Paris and entered the École Polytechnique in Paris in 1829. In 1832, he joined the French Navy as an officer and took part at scientific explorations to the Algerian Coast and Northern Europe. In 1837 he defended a PhD in Astronomy at the Faculty of Sciences in Lyon where he became Professor in 1841 to teach mathematics in astronomy. Then, in 1845, he moved at Ecole Polytechnique in Paris to take the chair of Physics, which he held till 1856. He published his first studies dealing with crystal lattice in 1849 in a short paper [1] and later wrote a book where he developed his theory fully based on geometrical theorems [2]. He died prematurely in 1863 exhausted by the loss of his only son. Like many scientists of that time Auguste Bravais was universalist and has been successively astronomer, geologist, mathematician, physicist, mineralogist, and crystallographer as well as an explorer from Lapland to the top of Mont Blanc [3]. In this communication, the steering committee Lyon-Saint-Etienne will recall the contribution of Auguste Bravais to crystallography and will show some aspect of his life that may be less known in our community.

This paper presents the first documentation of coesite-bearing eclogites in the eastern French Massif Central (Monts du Lyonnais unit) and discusses the exhumation processes for these very high-pressure rocks. A combination of mineralogical and geochronological datasets allows us to quantify a depth-time path and related exhumation rates. High-pressure metamorphism is constrained to 400–420 Ma (minimum 28 kbar or ca. 90 km). By 360–380 Ma, the rocks were exhumed to 30 km depth. These kinetic results conform to the geological constraints extracted from the tectonic and sedimentary record of the eastern French Massif Central. These multidisciplinary approaches provide new information on Paleozoic orogeny and allow us to discuss the relative roles of subduction and collision in exhumation of very high-pressure rocks. We suggest that a significant amount of exhumation of these rocks occurred during subduction, prior to continental collision; continental collision itself was responsible only for the final stages of exhumation under a transpressive regime.

The structural behaviour of lawsonite CaAl2Si2O7(OH)2.H2O, has been studied under quasi-hydrostatic conditions in a diamond-anvil cell to 18 GPa at room temperature, using angle-dispersive X-ray powder diffraction and Raman spectroscopy. With increasing pressure, we observe a phase transition at P = 8.6(3) GPa, characterized by (1) the splitting of diffraction lines, (2) the emergence of new Raman bands, and (3) significant changes in the frequency shifts of the hydroxyl O-H stretching modes. The transition is displacive and fully reversible, without any detectable hysteresis. The high-pressure phase, referred to here as lawsonite III can be indexed into a monoclinic unit-cell, with a = 5.6833(3), b = 8.5944(4), c = 12.8773(5) A, Y = 91.42(4)° and V = 628.80(4) A3 at P = 10.6 GPa. The space-group of lawsonite III is likely to be C 1121/ m , which is the unconventional representation of P 21/ m related to the low-pressure Cmcm symmetry. Assuming the change in space-group from Cmcm to C 1121/ m , the resulting components of the spontaneous strain tensor are analyzed in terms of the change in point group from mmm to 2/ m . The pressure-dependence of the fourth power of the symmetry-breaking component e 64 is linear, indicating a tricritical character for the transition. Both X-ray diffraction and Raman spectroscopy indicate that the overall aluminosilicate framework of lawsonite is retained through the transition. However, monoclinic lawsonite III is ∼ 40% less compressible than the low-pressure orthorhombic polymorph. The Raman spectroscopic results, in good agreement with recent infrared ones reveal that this decrease in compressibility is likely to be related to the increase in the hydrogen bond strength involving the hydroxyl groups in the structure, whereas the hydrogen bond system around the water molecule does not appear to be modified at the transition.

Raman spectra of MgSiO3-perovskite (Mg-pv) were recorded at simultaneous high-pressure and low-temperature conditions. This allowed to estimate characteristic frequencies (nu(i)) and other mode parameters as a function of both pressure and temperature. The cross derivatives partial derivative(2)nu(i)/partial derivative T partial derivative P were measured for the first time, thus providing new insights into the lattice dynamics of Mg-pv. These parameters are negative for the two lowest frequency modes at 250 and 255 cm(-1) (approximate to-6 X 10(-4) cm(-1) GPa(-1) K-1) and positive for the other modes (+3 X 10(-4) to +5 X 10(-4) cm(-1) GPa(-1) K-1). These measurements were combined with previously published vibrational density of states (VDoS) for deriving entropy, specific heat, thermal pressure, equation of state (EoS), and various thermoelastic parameters of Mg-pv at mantle P-T conditions. The calculations were performed using a general anharmonic formulation including the spectroscopically measured parameters, It is shown that anharmonic effects are relatively small in this compound under geophysically relevant conditions especially for the EoS. The model is used to discuss the discrepancies in the pressure and temperature calibrations in diamond-anvil cells and multianvil presses. Finally, a complete thermodynamic data set for (Mg0.9Fe0.1)SiO3-perovskite is proposed along lower mantle geotherms, It is shown that a pure perovskite lower mantle is unlikely to exist. (C) 2000 Elsevier Science B.V, All rights reserved.

X-ray powder-diffraction measurements performed at the ESRF between 10(-4) and 22 GPa have been used to infer the equations of state (EOS) of both C-12 and C-13 diamonds. The experiments were carried out with a diamond-anvil cell and care was taken to obtain the most hydrostatic pressure conditions using nitrogen, argon, or ethanol:methanol:water mixtures as pressure transmitting media. The cell parameter determinations were precise enough to distinguish the small volume differences between the two isotopic end members. Fits of the data to Birch-Murnaghan EOS yield an isothermal bulk modulus of C-12 diamond [K-0T ,= 446(4) GPa for K'(0T) fixed to 4], in excellent agreement with the values inferred from ultrasonic and Brillouin scattering measurements. The EOS of C-13 is very close to that of C-12 diamond [K-0T =438(8) GPa for K'(0T)=4]. This result is at variance with previous acoustic measurements which suggested that the bulk modulus of C-13 diamond is 17% higher than that of C-12 diamond. [S0163-1829(99)03545-6].

A pressure-volume-temperature data set has been obtained for lawsonite [CaAl2Si2O7(OH)2.H2O], using synchrotron X-ray diffraction and an externally heated diamond anvil cell. Unit-cell volumes were measured to 9.4 GPa and 767 K by angle dispersive X-ray diffraction using imaging plates. Phase changes were not observed within this pressure-temperature range, and lawsonite compressed almost isotropically at constant temperature. The P-V-T data have been analyzed using a Birch

International audience; The survival of Shewanella oneidensis MR-1 at up to 1500 MPa was investigated by laboratory studies involving exposure to high pressure followed by evaluation of survivors as the number (N) of colony forming units (CFU) that could be cultured following recovery to ambient conditions. Exposing the wild type (WT) bacteria to 250 MPa resulted in only a minor (0.7 log N units) drop in survival compared with the initial concentration of 10(8) cells/ml. Raising the pressure to above 500 MPa caused a large reduction in the number of viable cells observed following recovery to ambient pressure. Additional pressure increase caused a further decrease in survivability, with approximately 10(2) CFU/ml recorded following exposure to 1000 MPa (1 GPa) and 1.5 GPa. Pressurizing samples from colonies resuscitated from survivors that had been previously exposed to high pressure resulted in substantially greater survivor counts. Experiments were carried out to examine potential interactions between pressure and temperature variables in determining bacterial survival. One generation of survivors previously exposed to 1 G Pa was compared with WT samples to investigate survival between 37 and 8 degrees C. The results did not reveal any coupling between acquired high pressure resistance and temperature effects on growth.

We determine the compressibility, the elasticity and the slip systems for ice X in the 100-350 GPa pressure range from first-principles calculations. Our results show that ice X has a high elastic anisotropy, which increases by more than two orders of magnitude over this pressure range. We use the Peierls-Nabarro model to compute the dislocation structure for the most likely glide systems. We obtain that the easiest slip systems are 111 \110\ at low pressures, and 100 \110\ at higher pressure. This suggests that the mantle of large icy planets may have different rheological properties at shallow and at deep conditions. In contrast the mantle of smaller icy planets would be more homogeneous from a rheological point of view. (C) 2014 Elsevier B.V. All rights reserved.

The analysis of ancient or processed DNA samples is often a great challenge, because traditional Polymerase Chain Reaction - based amplification is impeded by DNA damage. Blocking lesions such as abasic sites are known to block the bypass of DNA polymerases, thus stopping primer elongation. In the present work, we applied the SERRS-hybridization assay, a fully non-enzymatic method, to the detection of DNA refractory to PCR amplification. This method combines specific hybridization with detection by Surface Enhanced Resonant Raman Scattering (SERRS). It allows the detection of a series of double-stranded DNA molecules containing a varying number of abasic sites on both strands, when PCR failed to detect the most degraded sequences. Our SERRS approach can quickly detect DNA molecules without any need for DNA repair. This assay could be applied as a pre-requisite analysis prior to enzymatic reparation or amplification. A whole new set of samples, both forensic and archaeological, could then deliver information that was not yet available due to a high degree of DNA damage.

We present the results of a detailed study of the high-pressure behavior of anorthite (CaAl2Si2O8) between ambient pressure and 30 GPa under static conditions, using in situ Raman spectroscopy and energy-dispersive X ray diffraction. On increasing pressure under hydrostatic conditions, the transition occurs first at 2.6 GPa. At 10 GPa, a reversible polymorphic transition is observed which transforms the polymorph into a phase of higher symmetry. With further pressure increase, large changes occur in the Raman and X ray spectra between 14 and 16 GPa, premonitory to the onset of pressure-induced amorphization. Above 16 GPa, anorthite is fully amorphous. However, only samples pressurized to above 22 GPa remain amorphous on recovery to ambient conditions. The high-pressure behavior of anorthite is highly sensitive to deviatoric stresses. Under less hydrostatic conditions, the 10-GPa transition described above occurs below 9 GPa, amorphization begins below 11.2 GPa, and samples decompressed from peak pressures as low as 17 GPa are fully amorphous. We have also carried out a thermodynamic analysis of the pressure-induced amorphization of anorthite, using a two state model for the equation of state (EOS) of CaAl2Si2O8 glass in order to account for the increase in Al coordination. With this EOS, we calculate that the free energies of the crystalline and amorphous materials are equal at about 30 GPa, or slightly lower when effects of structural relaxation in the glass are taken into account, well above the observed crystalline-amorphous transition at 16 GPa.

The Raman spectrum of calcium aluminate (CaAl2O4) glass has been obtained as a function of pressure at ambient temperature to similar to 15 GPa, and as a function of temperature at room pressure to 1650 K. On increasing pressure at 300 K, the Raman spectrum changes drastically between 8 and 10 GPa. The intensity of the overall spectrum weakens, the intensity of the 580-cm(-1) band decreases markedly, and a new broad band centered near 750 cm(-1) begins to dominate the spectrum. We interpret these spectral changes as due to the formation of highly coordinated Al species through the involvement of bridging oxygens (i.e. formation of O-[3] species). Upon decompression, the pressure-induced spectral changes are mostly reversible. However, the decompressed samples do not relax completely to their normal ambient state, and the spectra reflect important changes in the inter-tetrahedral AlOAl linkages. These changes are consistent with some high-coordinate species being retained in the decompressed sample. On increasing temperature through the glass transformation range (T-g = 1178 K) at room pressure, our Raman spectra show evidence for important configurational changes, after vibrational effects are removed. The major spectral change consists of growth of a broad band between 600 and 1100 cm(-1), appearing immediately above T-g. We suggest that these configurational changes concern the removal of O2- ions from the fully polymerized aluminate framework, with the resulting formation at high temperature of O-[3] species (''triclusters''), coordinated by three tetrahedral aluminate groups.

High-temperature Raman spectroscopy and optical microscopic observations have revealed a new metastable polymorph of CaAl2Si2O8 composition, which brings to four the number of known crystalline phases in this system. Similar to the metastable monoclinic pseudo-orthorhombic and pseudo-hexagonal phases, the new polymorph nucleates prior to anorthite, at around 1545 K, and its pseudo-liquidus temperature is 1700 ± 10 K. It can also be formed from the transformation of the pseudo-hexagonal phase at 1050 K. The actual structure of this new crystalline form is unknown, but its Raman spectrum indicates that it is most likely a 6-membered alumino-silicate framework. We have obtained all three metastable phases as pure single crystals using wire loop heating techniques, and have studied their structures via Raman spectroscopy up to their metastable melting points or transformation temperatures.

We have developed a fully enzyme-free SERRS hybridization assay for specific detection of double-stranded DNA sequences. Although all DNA detection methods ranging from PCR to high-throughput sequencing rely on enzymes, this method is unique for being totally non-enzymatic. The efficiency of enzymatic processes is affected by alterations, modifications, and/or quality of DNA. For instance, a limitation of most DNA polymerases is their inability to process DNA damaged by blocking lesions. As a result, enzymatic amplification and sequencing of degraded DNA often fail. In this study we succeeded in detecting and quantifying, within a mixture, relative amounts of closely related double-stranded DNA sequences from Rupicapra rupicapra (chamois) and Capra hircus (goat). The non-enzymatic SERRS assay presented here is the corner stone of a promising approach to overcome the failure of DNA polymerase when DNA is too degraded or when the concentration of polymerase inhibitors is too high. It is the first time double-stranded DNA has been detected with a truly non-enzymatic SERRS-based method. This non-enzymatic, inexpensive, rapid assay is therefore a breakthrough in nucleic acid detection.

International audience; In this study, we have applied Surface Enhanced Resonance Raman Scattering (SERRS) technology to the specific detection of DNA. We present an innovative SERRS sandwich-hybridization assay that allows specific DNA detection without any enzymatic amplification, such as is the case with Polymerase Chain Reaction (PCR). In some substrates, such as ancient or processed remains, enzymatic amplification fails due to DNA alteration (degradation, chemical modification) or to the presence of inhibitors. Consequently, the development of a non-enzymatic method, allowing specific DNA detection, could avoid long, expensive and inconclusive amplification trials. Here, we report the proof of concept of a SERRS sandwich-hybridization assay that leads to the detection of a specific chamois DNA. This SERRS assay reveals its potential as a nonenzymatic alternative technology to DNA amplification methods (particularly the PCR method) with several applications for species detection. As the amount and type of damage highly depend on the preservation conditions, the present SERRS assay would enlarge the range of samples suitable for DNA analysis and ultimately would provide exciting new opportunities for the investigation of ancient DNA in the fields of evolutionary biology and molecular ecology, and of altered DNA in food frauds detection and forensics.

International audience; X-ray absorption spectroscopy is a well-established method for probing local structural and electronic atomic environments in a variety of systems. We used X-ray absorption near-edge structure (XANES) spectroscopy for monitoring in real-time conditions selenium reduction in situ in live cultures of Shewanella oneidensis MR-1 under high hydrostatic pressure. High-quality XANES data show that Shewanella oneidensis MR-1 reduces selenite Se(IV) to red elemental selenium Se(0) up to 150 MPa without any intermediate redox state. MR-1 reduces all selenite provided (5-10 mm) between 0.1 and 60 MPa. Above 60 MPa the selenite reduction yield decreases linearly with pressure and the activity is calculated to stop at 155 +/- 5 MPa. The analysis of cultures recovered after in situ measurements showed that the decrease in activity is linked to a decrease in viability. This study emphasizes the promising potential of XANES spectroscopy for real-time probing in situ microbial redox transformations of a broad range of metal and metalloid elements in live samples, including under high hydrostatic pressure.

International audience; Properties of serpentine minerals are thought to influence the occurrence and location of intermediate‐depth seismicity in subduction zones, which is often characterized by two dipping planes separated by ∼30 km defining a double seismic zone. The seismicity of the lower plane is believed to be provoked by the dehydration of serpentine since the experimentally determined stability limit for antigorite matches hypocenter locations. This requires that the fluid produced by dehydration is released much faster than the typical time scale of ductile deformation mechanisms. Here we measured the kinetics of antigorite dehydration in situ at high pressure and high temperature by time‐resolved synchrotron X‐ray diffraction in a closed system. Antigorite dehydrates in two steps. During step 1 it partially breaks down into olivine and a hydrous phyllosilicate closely related to the 10 Å phase. The modal abundance of the intermediate assemblage is described by 66 wt % antigorite, 19 wt % olivine, 12 wt % 10 Å phase. During step 2 at higher temperature, the remaining antigorite and the 10 Å phase fully dehydrate. From the analysis of reaction progress data, we determined that the major release of aqueous fluid occurs during step 2 at a fast rate of 10−4 mfluid 3 mrock −3 s−1. This exceeds by orders of magnitude the typical time scale of deformation by ductile mechanisms of any mineral or rock in the subducting slab or in the overlying mantle wedge. These results suggest that the fast dehydration of antigorite may well trigger the seismicity of the lower plane of the double seismic zone.

A simple, rapid, and inexpensive heating‐wire technique is used for physical observations at high temperatures. The upper limit is 2000 K in air with platinum‐iridium or platinum‐rhodium wires and 2700 K with iridium; temperatures up to 3600 K can be achieved under an inert atmosphere with tungsten wires. Raman spectroscopy measurements made up to 1900 K by this technique suggest that the high‐temperature harmonic vibrational behavior of corundum (α‐Al2O3) results from the cancellation of anharmonic effects. Powder x‐ray diffraction experiments with synchrotron radiation show that perovskite (CaTiO3) changes from orthorhombic symmetry to cubic between 1330 and 1530 K, with an intermediate tetragonal phase likely, consistent with λ‐type transitions recorded by recent calorimetric measurements. Finally, observations of CaAl2Si2O8 polymorphism has shown the existence of a new metastable phase.

We present a new experimental set-up for studying minerals by Raman spectroscopy in-situ at simultaneously high pressures (up to 35 GPa) and high temperatures (up to 2000 K). High pressures are generated with a diamond anvil cell and local sample heating is obtained by focussing the beam of a CO2 laser on the pressurized sample through a type IIa diamond. The Raman spectrum and the thermal emission of the sample are collected on the same 2 mum-sized heated area, whereas the pressure can be measured simultaneously anywhere in the pressure chamber. Temperature in the central part of the heated spot is estimated from the thermal emission curves. Pressures are obtained by the classical fluorescence technique. Raman spectra of CaTiO3 perovskite, analogue of MgSiO3-perovskite, are presented at temperatures up to 1700 K at a pressure of 12 GPa. These data are compared with high temperature Raman data at ambient pressure. The spectral changes upon heating observed in both series of experiments are discussed.

International audience; The phase relations and density of a natural mid‐ocean ridge basalt (MORB) were investigated from 28 to 89 GPa and 1600 to 2700 K by in situ X‐ray diffraction measurements and chemical analysis of the quenched samples using transmission electron microscopy (TEM). We observed an assemblage of five phases up to 50 GPa, namely an aluminum‐bearing magnesium perovskite phase, a calcium perovskite phase, a stishovite phase, the new aluminum‐rich (NAL) phase, and a calcium ferrite‐type phase. The NAL phase was no longer observed above 50 GPa. The phase proportions were obtained by Rietveld refinement of the in situ X‐ray diffraction patterns. After the disappearance of the NAL phase beyond 50 GPa, the proportion of each phase remains constant up to 89 GPa. The density of MORB was calculated using the measured volumes, phase proportions, and chemical compositions of the coexisting phases. The thermoelastic parameters of the MORB sample were estimated from the fit of the measured densities at various pressure and temperature conditions. Resulting MORB density profiles were calculated for different subducting slab temperature profiles. MORB densities are 0.5% to 2% greater than those of the surrounding mantle over the entire lower mantle range, suggesting MORB likely subducts to the core-mantle boundary

Conference on Goldschmidt 2010 - Earth, Energy, and the Environment ; Knoxville, TN ; June 13-18, 2010; International audience

Until recently, monitoring of cells and cellular activities at high hydrostatic pressure (HHP) was mainly limited to ex situ observations. Samples were analyzed prior to and following the depressurization step to evaluate the effect of the pressure treatment. Such ex situ measurements have several drawbacks: (i) it does not allow for kinetic measurements and (ii) the depressurization step often leads to artifactual measurements. Here, we describe recent advances in diamond anvil cell (DAC) technology to adapt it to the monitoring of microbial processes in situ. The modified DAC is asymmetrical, with a single anvil and a diamond window to improve imaging quality and signal collection. Using this novel DAC combined to Raman and X-ray spectroscopy, we monitored the metabolism of glucose by baker's yeast and the reduction of selenite by Agrobacterium tumefaciens in situ under HHP. In situ spectroscopy is also a promising tool to study piezophilic microorganisms.

We present a new diamond anvil cell (DAC), hereafter called the fluoX DAC, dedicated for x-ray fluorescence (XRF) analysis of trace elements in fluids under high pressure and high temperature to 10 GPa and 1273 K at least. This new setup has allowed measurement of Rb, Sr, Y, Zr, with concentrations of 50 ppm to 5.6 GPa and 1273 K. The characteristics of the fluoX DAC consist in an optimized shielding and collection geometry in order to reduce the background level in XRF spectrum. Consequently, minimum detection limits of 0.3 ppm were calculated for the abovementioned elements in this new setup. This new DAC setup coupled to the hard x-rays focusing beamline ID22 (ESRF, France) offers the possibility to analyze in situ at high pressure and high temperature, ppm level concentrations of heavy elements, rare earth elements, and first transition metals, which are of prime importance in geochemical processes. The fluoX DAC is also suitable to x-ray diffraction over the same high pressure-temperature range.

The process of dehydration embrittlement is usually proposed as an explanation for the presence of intermediate-depth earthquakes in subduction zones. It assumes that the release of water by hydrous mineral breakdown is fast enough to provoke brittle failure. We performed high-pressure, high-temperature, dehydration experiments of talc and 10 A phase coupled with in situ measurement of reaction kinetics using synchrotron X-ray diffraction. Newly developed, X-ray transparent, pressure-sealed, titanium capsule ensured a closed thermochemical environment. From isothermal kinetics data fitted to the Avrami's equation and from the texture of reaction products, we conclude that dehydration rates of these minerals are limited by diffusion. Predicted minimum rates of fluid release range from 10 − 4 to 9 × 10 − 6 m 3 fluid m − 3 rock s − 1 , and are fast enough to provoke hydraulic rupture since Maxwell relaxation rate of rocks relevant of subduction zones are slower than the rate of fluid release. These rates are comparable between talc, 10 A phase and antigorite also [Perrillat, J.-P., Daniel, I., Koga, K.T., Reynard, B., Cardon, H., Crichton, W.A., 2005. Kinetics of antigorite dehydration: a real-time X-ray diffraction study. Earth Planet. Sci. Lett. 236, 899–913]. Consequently, we suggest that the dehydration of hydrous minerals may eventually be fast enough to trigger the intermediate-depth earthquakes, and that the deepest among intermediate-depth earthquakes may actually locate the limits for dehydration of hydrous minerals in the downgoing lithosphere.

X-ray spectroscopies are very powerful tools to determine the chemistry of complex dilute solutes in abiotic and biotic systems. We have assayed their suitability to monitor the chemistry of complex solutions in a live biotic system. The impact of the probe on cells was quantified for 4 different cellular organisms differing in their resistance level to environmental stresses. We show that none of the organisms tested can survive the radiation doses needed for the acquisition of meaningful spectroscopic data. Therefore, on one hand, X-ray spectroscopy cannot be applied to the monitoring of single cells, and cellular damages have to be taken into account in the interpretation of the evolution of such systems. On the other hand, due to the limited extension of X-ray induced cellular damages in the culture volume, it is possible to probe a population of live cells provided that the culture to beam probe ratio is large enough to minimize the impact of mortality on the evolution of the biological system. Our results suggest that it could be possible to probe the volume in the close vicinity of a cell without affecting its activity. Using this setup we could monitor the reduction of selenite by the X-ray sensitive bacterium, Agrobacterium tumefaciens strain C58, for 24 h. This method has a great potential to monitor the respiration of various metals, such as iron, manganese and arsenic, in situ under relevant environmental conditions by live microorganisms.

International audience; Natural mid-ocean ridge basalt (MORB) samples recovered from diamond-anvil cell (DAC) experiments performed between 33 to 89 GPa and 1700 to 2600 K were studied with a transmission electron microscope (TEM). We used the focused ion beam (FIB) lift-out technique to prepare the recovered high-pressure, laser-heated samples for TEM study. Observations of TEM sections show the presence of five phases for samples transformed at pressures ranging from 33 to 45 GPa: Al-bearing Mg-perovskite, Ca-silicate perovskite, stishovite, and two Al-rich phases. The Al-rich phases were identified by selected area electron diffraction (SAED) patterns and chemical composition analysis, and include the new aluminous (NAL) phase with hexagonal structure and the calcium ferrite (CF) type phase. Chemical analyses obtained by analytical transmission electron microscopy (ATEM) show that Mg-silicate perovskite is the major host for Al, with significant amounts also distributed between the CF-type and NAL phases, and less than 1 wt% in stishovite. Beyond pressures of ~40 GPa (~1100 km depth), the Al content of Mg-perovskite and CF-type phase increases. Between 45 and 50 GPa, the NAL phase disappears. This mineralogical change may explain reported seismic anomalies in subduction zones at mid-mantle depths

The supposed low viscosity of serpentine may strongly influence subduction-zone dynamics at all time scales, but until now its role could not be quantified because measurements relevant to intermediate-depth settings were lacking. Deformation experiments on the serpentine antigorite at high pressures and temperatures (1 to 4 gigapascals, 200° to 500°C) showed that the viscosity of serpentine is much lower than that of the major mantle-forming minerals. Regardless of the temperature, low-viscosity serpentinized mantle at the slab surface can localize deformation, impede stress buildup, and limit the downdip propagation of large earthquakes at subduction zones. Antigorite enables viscous relaxation with characteristic times comparable to those of long-term postseismic deformations after large earthquakes and slow earthquakes. Antigorite viscosity is sufficiently low to make serpentinized faults in the oceanic lithosphere a site for subduction initiation.

We monitored alcoholic fermentation in Saccharomyces cerevisiae as a function of high hydrostatic pressure. Ethanol production from 0.15 M glucose was measured by Raman spectroscopy in situ in a diamond-anvil cell. At 10 MPa, fermentation proceeds three times faster than at ambient pressure and the fermentation yield is enhanced by 5% after 24 h. Above 20 MPa, the reaction kinetics slows down with increasing pressure. The pressure above which no more ethanol is produced is calculated to be 87 +/- 7 MPa. These results indicate that the activity of one or several enzymes of the glycolytic pathway is enhanced at low pressure up to 10 MPa. At higher pressures, they become progressively repressed, and they are completely inhibited above 87 MPa. Although fermentation was predicted to stop at ca. 50 MPa, due to the loss of activity of phosphofructokinase, the present study demonstrates that there is still an activity of ca. 30% of that measured at ambient pressure at 65 MPa. This study also validates the use of Raman spectroscopy for monitoring the metabolism of living microorganisms.

Serpentines are hydrous phyllosilicates which form by hydration of Mg–Fe minerals. The reasons for the occurrence of the structural varieties lizardite and chrysotile, with respect to the variety antigorite, stable at high pressure, are not yet fully elucidated, and their relative stability fields are not quantitatively defined. In order to increase the database of thermodynamic properties of serpentines, the P–V Equations of State (EoS) of lizardite and chrysotile were determined at ambient temperature up to 10 GPa, by in situ synchrotron X-ray diffraction in a diamond-anvil cell. Neither amorphization nor hysteresis was observed during compression and decompression, and no phase transition was resolved in lizardite. In chrysotile, a reversible change in compression mechanism, possibly due to an unresolved phase transition, occurs above 5 GPa. Both varieties exhibit strong anisotropic compression, with the c axis three times more compressible than the others. Fits to ambient temperature Birch–Murnaghan EoS gave for lizardite V0=180.92(3) A3, K0 = 71.0(19) GPa and K′0=3.2(6), and for chrysotile up to 5 GPa, V0 = 730.57(31) A3 and K0 = 62.8(24) GPa (K′0 fixed to 4). Compared to the structural variety antigorite is stable at high pressure (HP) (Hilairet et al. 2006), the c axis is more compressible in these varieties, whereas the a and b axes are less compressible. These differences are attributed to the less anisotropic distribution of stiff covalent bonds in the corrugated structure of antigorite. The three varieties have almost identical bulk compressibility curves. Thus the compressibility has negligible influence on the relative stability fields of the serpentine varieties. They are dominated by first-order thermodynamic properties, which stabilizes antigorite at high temperature with respect to lizardite, and by out-of-equilibrium phenomena for metastable chrysotile (Evans 2004).

Antigorite, the high-pressure variety of serpentine, is a major water carrier in subduction zones. Its equation of state, which controls its stability field at high pressure, was determined at ambient temperature up to 10 GPa by in situ synchrotron X-Ray diffraction in a diamond-anvil cell. No amorphization, phase transition or hysteresis were detected during compression or decompression. Compression is anisotropic, with the c axis twice as compressible as the others. A fit to the second order Birch-Murnaghan equation of state gave V 0 = 2926.23(50) Å3 and K 0 = 67.27(123) GPa. In antigorite the atomic assemblage is denser than in lizardite, which may influence phase stability. The antigorite K 0 value obtained here is significantly higher than currently assumed in thermodynamic databases. Antigorite P-T stability field is re-evaluated, with major dehydration reaction (and associated potential earthquake) loci occurring at lower pressures, and is found to be consistent with the latest experimental results.

Life on Earth can be traced back to as far as 3.8 billion years (Ga) ago. The catastrophic meteoritic bombardment ended between 4.2 and 3.9 Ga ago. Therefore, if life emerged, and we know it did, it must have emerged from nothingness in less than 400 million years. The most recent scenarios of Earth accretion predict some very unstable physico-chemical conditions at the surface of Earth, which, in such a short time period, would impede the emergence of life from a proto-biotic soup. A possible alternative would be that life originated in the depth of the proto-ocean of the Hadean Earth, under high hydrostatic pressure. The large body of water would filter harmful radiation and buffer physico-chemical variations, and therefore would provide a more stable radiation-free environment for pre-biotic chemistry. After a short introduction to Earth history, the current tutorial review presents biological and physico-chemical arguments in support of high-pressure origin for life on Earth.

International audience; Phase relations in natural mid-oceanic ridge basalt (MORB) were investigated to depths of 700-1400 km in the lower mantle, using a laser-heated diamond-anvil cell and synchrotron X-ray diffraction (XRD). The crystalline phases, their unit-cell volumes and proportions were determined from Rietveld refinement of the in situ XRD spectra. At the top of the lower mantle, Mg-rich perovskite is the most abundant phase, followed by Ca-rich perovskite and stishovite. Two Al-rich phases occur in smaller amounts, the Ca-ferrite type and the new aluminum-rich phase (or NAL). This assemblage is stable down to 1150 km, approximately. At greater depths, the new aluminum-rich phase disappears, and the assemblage of Mg-rich perovskite, Ca-rich perovskite, stishovite and Ca-ferrite phase is stable up to at least 1400 km. In view of the present phase diagram, we discuss the nature and relations of the lower mantle Al-phases in MORB composition, and their bearing on the density evolution of the oceanic crust

International audience; High-pressure synchrotron infrared (IR) absorption spectra were collected between 650 and 4,000 cm−1 at ambient temperature for hydrous Mg-ringwoodite (γ-Mg2SiO4) up to 30 GPa. The main feature in the OH− stretching region is an extremely broad band centred at 3,150 cm−1. The hydrogen bond is strong for most protons and the most probable site for protonation is the tetrahedral edge. With increasing pressure, this band shifts downward while decreasing its integrated intensity until disappearance at a pressure of 25 GPa. Only one band at 2,450 cm−1 and an absorption plateau persist with a maximum wavenumber of 3,800 cm−1. This behaviour is reversible upon pressure release. We interpret this as a second-order phase transition occurring in hydrated Mg-ringwoodite at high pressure (beyond ∼ 25 GPa). This result is compatible with the observation by Kleppe et al. (Phys Chem Miner 29:473–476, 2002a) who suggested the presence of Si–O–Si linkages and/or partial increase in the coordination of Si. Beyond the phase transition, the protons are delocalized and their environment on the ringwoodite structure is probably quite different from that at low pressure. Data obtained in situ at high pressures and temperatures are needed to better understand the effect of protonation on the structure and to better constrain this phase transition.

A refined approach for the experimental determination of fluid composition at elevated pressure and temperature conditions is developed. It effectively determines partition coefficients of trace elements between aqueous fluid and minerals. This approach is developed on top of many previously known technical achievements. However, it differs from the previous ones by the use of calibrated base and acid leaching of quenched samples to strip off the precipitates formed from the fluid during the quench. This permits the reconstruction of a fluid composition from an experimental charge that consists of a complete mixture of solid and fluid phases. This is a significant difference from the previous analogous studies, in which the fluid was separated from the solids all through the experiment. Mass balance calculations and error propagation assess the merits of the present method applied to a fluid-antigorite system.

International audience; Antigorite dehydration has been studied in situ using time-resolved X-ray diffraction (XRD) in the 1.1-5.5 GPa pressure range. The sequence of XRD spectra reveals that: the high-temperature stability limit of antigorite is decreased by 50-100 degrees C under H2O-unsaturated conditions. The decomposition of antigorite into the high-temperature products, forsterite+enstatite, proceeds via an intermediate assemblage of forsterite and a "talc-like" phase, observed within a temperature interval of 130 +/- 20 degrees C. The analysis of the transformation-time data using the Avrami model suggests that the breakdown of antigorite and the "talc-like" phase is kinetically controlled by surface growth processes at the edges of grains. The overall transformation rates are 10 to 100 times faster than those observed in water-saturated experiments, and show that the H2O activity is a strong driving force for dehydration. The breakdown of antigorite in subducting oceanic mantle with such kinetics would result in a fluid discharge rate of the order of 10(-6) to 10(-8) s(-1). This is faster than the viscous relaxation of serpentinites, and could lead to brittle failure or weakening of pre-existing faults. This provides an explanation for the seismicity in the lower plane of double seismic zones.