Patent mantle-metasomatism: Inferences based on experimental studies     

Y Thibault  A D Edgar 《Journal of Earth System Science》1990,99(1):21-37

K, Na and Ca are the most common elements transported during mantle metasomatism and result in formation of phlogopite (K), amphibole (Na) and clinopyroxene (Ca) by various reactions. This review presents models for this type of metasomatism based on experiments on the pyrolite-K₂CO₃-H₂O, pyrolite-Na₂ CO₃-H₂O systems and on the pyrolite-CaCO₃ system. The addition of K₂CO₃ and Na₂CO₃ lowers the liquidus of pyrolite providing a low temperature, alkali-rich hydrous melt which may ascend and metasomatize overlying mantle regions. Several reactions are proposed for the formation of phlogopite and amphibole (pargasite-edenite) in these systems. The compositions of amphiboles correspond to those found in metasomatized mantle xenoliths. In contrast, Ca-metasomatism is considered to be mainly an anhydrous process in which orthopyroxene and carbonate react to produce clinopyroxene, olivine and CO₂. High pressure liquids in this model system are of carbonatitic composition and this low viscosity melt can ascend converting harzburgite mantle assemblages to olivine-rich wehrlite. Based on an inverse experimental approach, moderately high degrees of partial melting of a model metasomatized alkali clinopyroxenite xenolith yield liquids at 30kb which are very comparable in composition to the lavas enclosing such types of xenoliths. Experimental modelling of mantle metasomatism produces assemblages which are in good agreement with the mineral assemblages and textural relationships found in metasomatized mantle xenoliths from areas such as West Eifel and South-West Uganda.  相似文献   

Hydrous ferric oxide precipitation in the presence of nonmetabolizing bacteria: Constraints on the mechanism of a biotic effect     

Denis G. Rancourt  Pierre-Jean Thibault  Denis Mavrocordatos  Gilles Lamarche 《Geochimica et cosmochimica acta》2005,69(3):553-577

We have used room temperature and cryogenic ⁵⁷Fe Mössbauer spectroscopy, powder X-ray diffraction (pXRD), mineral magnetometry, and transmission electron microscopy (TEM), to study the synthetic precipitation of hydrous ferric oxides (HFOs) prepared either in the absence (abiotic, a-HFO) or presence (biotic, b-HFO) of nonmetabolizing bacterial cells (Bacillus subtilis or Bacillus licheniformis, ∼10⁸ cells/mL) and under otherwise identical chemical conditions, starting from Fe(II) (10⁻², 10⁻³, or 10⁻⁴ mol/L) under open oxic conditions and at different pH (6-9). We have also performed the first Mössbauer spectroscopy measurements of bacterial cell wall (Bacillus subtilis) surface complexed Fe, where Fe(III) (10^−3.5-10^−4.5 mol/L) was added to a fixed concentration of cells (∼10⁸ cells/mL) under open oxic conditions and at various pH (2.5-4.3). We find that non-metabolic bacterial cell wall surface complexation of Fe is not passive in that it affects Fe speciation in at least two ways: (1) it can reduce Fe(III) to sorbed-Fe²⁺ by a proposed steric and charge transfer effect and (2) it stabilizes Fe(II) as sorbed-Fe²⁺ against ambient oxidation. The cell wall sorption of Fe occurs in a manner that is not compatible with incorporation into the HFO structure (different coordination environment and stabilization of the ferrous state) and the cell wall-sorbed Fe is not chemically bonded to the HFO particle when they coexist (the sorbed Fe is not magnetically polarized by the HFO particle in its magnetically ordered state). This invalidates the concept that sorption is the first step in a heterogeneous nucleation of HFO onto bacterial cell walls. Both the a-HFOs and the b-HFOs are predominantly varieties of ferrihydrite (Fh), often containing admixtures of nanophase lepidocrocite (nLp), yet they show significant abiotic/biotic differences: Biotic Fh has less intraparticle (including surface region) atomic order (Mössbauer quadrupole splitting), smaller primary particle size (magnetometry blocking temperature), weaker Fe to particle bond strength (Mössbauer center shift), and no six-line Fh (6L-Fh) admixture (pXRD, magnetometry). Contrary to current belief, we find that 6L-Fh appears to be precipitated directly, under a-HFO conditions, from either Fe(II) or Fe(III), and depending on Fe concentration and pH, whereas the presence of bacteria disables all such 6L-Fh precipitation and produces two-line Fh (2L-Fh)-like biotic coprecipitates. Given the nature of the differences between a-HFO and b-HFO and their synthesis condition dependences, several biotic precipitation mechanisms (template effect, near-cell environment effect, catalyzed nucleation and/or growth effect, and substrate-based coprecipitation) are ruled out. The prevailing present view of a template or heterogeneous nucleation barrier reduction effect, in particular, is shown not to be the cause of the large observed biotic effects on the resulting HFOs. The only proposed mechanism (relevant to Fh) that is consistent with all our observations is coprecipitation with and possible surface poisoning by ancillary bacteriagenic compounds. That bacterial cell wall functional groups are redox active and the characteristics of biotic (i.e., natural) HFOs compared to those of abiotic (i.e., synthetic) HFOs have several possible biogeochemical implications regarding Fe cycling, in the photic zones of water columns in particular.  相似文献   

The wider context of the Lower Jurassic Toarcian oceanic anoxic event in Yorkshire coastal outcrops,UK     

Nicolas Thibault  Micha Ruhl  Clemens V. Ullmann  Christoph Korte  David B. Kemp  Darren R. Gröcke  Stephen P. Hesselbo 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(3):372-391

The Toarcian Oceanic Anoxic Event (T-OAE, ～183 Ma) was characterized by enhanced carbon burial, a prominent negative carbon-isotope excursion (CIE) in marine carbonate and organic matter, and numerous geochemical anomalies. A precursor excursion has also been documented at the Pliensbachian/Toarcian boundary, but its possible causes are less constrained. The T-OAE is intensively studied in the Cleveland Basin, Yorkshire, UK, whose sedimentary deposits have been litho-, bio- and chemostratigraphically characterised. Here, we present new elemental data produced by hand-held X-ray fluorescence analysis to test the expression of redox-sensitive trace metals and detrital elements across the upper Pliensbachian to mid-Toarcian of the Cleveland Basin. Detrital elemental concentrations (Al, Si, Ti, Zr) are used as proxies for siliciclastic grain content and thus, sea-level change, which match previous sequence stratigraphic interpretations from the Cleveland Basin. The timescale of the event is debated, though our new elemental proxies of relative sea level change show evidence for a cyclicity of 350 cm that may be indicative of ～405 kyr eccentricity cycles in Yorkshire. Trends in total organic carbon and redox-sensitive elements (S, Fe, Mo, As) confirm scenarios of widespread ocean deoxygenation across the T-OAE. The correlation of comparable trends in Mo across the T-OAE in Yorkshire and the Paris Basin suggests a similar oceanic drawdown of this element accompanying widespread anoxia in the two basins. Data from Yorkshire point to a transgressive trend at the time of the Mo drawdown, which contradicts the “basin restriction” model for the euxinic conditions that characterise the CIE interval.  相似文献   

Reduction of Manganese Oxides: Thermodynamic,Kinetic and Mechanistic Considerations for One- Versus Two-Electron Transfer Steps     

George W. LutherIII  Aubin Thibault de Chanvalon  Véronique E. Oldham  Emily R. Estes  Bradley M. Tebo  Andrew S. Madison 《Aquatic Geochemistry》2018,24(4):257-277

Manganese oxides, typically similar to δ-MnO₂, form in the aquatic environment at near neutral pH via bacterially promoted oxidation of Mn(II) species by O₂, as the reaction of [Mn(H₂O)₆]²⁺ with O₂ alone is not thermodynamically favorable below pH of ~?9. As manganese oxide species are reduced by the triphenylmethane compound leucoberbelein blue (LBB) to form the colored oxidized form of LBB (λ_max?=?623 nm), their concentration in the aquatic environment can be determined in aqueous environmental samples (e.g., across the oxic–anoxic interface of the Chesapeake Bay, the hemipelagic St. Lawrence Estuary and the Broadkill River estuary surrounded by salt marsh wetlands), and their reaction progress can be followed in kinetic studies. The LBB reaction with oxidized Mn solids can occur via a hydrogen atom transfer (HAT) reaction, which is a one-electron transfer process, but is unfavorable with oxidized Fe solids. HAT thermodynamics are also favorable for nitrite with LBB and MnO₂ with ammonia (NH₃). Reactions are unfavorable for NH₄⁺ and sulfide with oxidized Fe and Mn solids, and NH₃ with oxidized Fe solids. In laboratory studies and aquatic environments, the reduction of manganese oxides leads to the formation of Mn(III)-ligand complexes [Mn(III)L] at significant concentrations even when two-electron reductants react with MnO₂. Key reductants are hydrogen sulfide, Fe(II) and organic ligands, including the siderophore desferioxamine-B. We present laboratory data on the reaction of colloidal MnO₂ solutions (λ_max?~?370 nm) with these reductants. In marine waters, colloidal forms of Mn oxides (<?0.2 µm) have not been detected as Mn oxides are quantitatively trapped on 0.2-µm filters. Thus, the reactivity of Mn oxides with reductants depends on surface reactions and possible surface defects. In the case of MnO₂, Mn(IV) is an inert cation in octahedral coordination; thus, an inner-sphere process is likely for electrons to go into the empty e _g ^* conduction band of its orbitals. Using frontier molecular orbital theory and band theory, we discuss aspects of these surface reactions and possible surface defects that may promote MnO₂ reduction using laboratory and field data for the reaction of MnO₂ with hydrogen sulfide and other reductants.  相似文献   

Formation of phyllosilicates in a fault zone affecting deeply buried arkosic sandstones: their influence on petrophysic properties (Annot sandstones, French external Alps)     

Henri Leclère  Martine Buatier  Delphine Charpentier  Jean-Pierre Sizun  Pierre Labaume  Thibault Cavailhes 《Swiss Journal of Geoscience》2012,105(2):299-312

The Restefond fault, located in the Late Eocene-Early Oligocene Alpine foreland basin, affects the well lithified and low porosity Grès d??Annot. The fault core zone is characterized by the occurrence of highly deformed sandstone lenses. Deformation inside the lenses corresponds to mm to sub-mm-spaced cleavage planes rich in phyllosilicates and up to cm-thick and dm-long quartz-calcite pure extensional veins. The cleavages are mostly composed of newly-formed synkinematic white mica and chlorite. By using thermodynamic thermometers based on the chemical composition of chlorite, a temperature of 200?±?20?°C of fault activity was computed. This temperature shows that the Restefond fault was active at burial conditions comprised between 6.5 and 8?km, assuming a mean geothermal gradient between 25 and 30?°Ckm^?1. The petrophysic properties of sandstones from the core zone and in the hanging and foot wall of the fault were determined on drilled plugs following three spacial directions. The permeability of the highly deformed sandstone from the core zone is about one order of magnitude higher than in the host rock. This increase in permeability occurs in the direction parallel to the S?CC structures and is explained by the occurrence of well-connected micropores localized between platy phyllosilicates. This study shows that the fault petrophysic properties are mostly controlled by the precipitation of synkinematic phyllosilicates under deep burial conditions.  相似文献   

Upper Campanian-Maastrichtian nannofossil biostratigraphy and high-resolution carbon-isotope stratigraphy of the Danish Basin: Towards a standard δC curve for the Boreal Realm     

Nicolas Thibault  Rikke HarlouNiels Schovsbo  Poul SchiølerFabrice Minoletti  Bruno GalbrunBodil W. Lauridsen  Emma SheldonLars Stemmerik  Finn Surlyk 《Cretaceous Research》2012,33(1):72-90

High-resolution carbon isotope stratigraphy of the upper Campanian-Maastrichtian is recorded in the Boreal Realm from a total of 1968 bulk chalk samples of the Stevns-1 core, eastern Denmark. Isotopic trends are calibrated by calcareous nannofossil bio-events and are correlated with a lower-resolution δ¹³C profile from Rørdal, northwestern Denmark. A quantitative approach is used to test the reliability of Upper Cretaceous nannofossil bio-events and provides accurate biohorizons for the correlation of δ¹³C profiles. The Campanian-Maastrichtian boundary (CMB) is identified through the correlation of dinoflagellate biostratigraphy and δ¹³C stratigraphy between Stevns-1 and the Global boundary Standard Stratotype-section and Point at Tercis les Bains (SW France), allowing the identification of new chemical and biostratigraphic markers that provide a precise placement of the stage boundary on a regional scale. The boundary interval corresponds to the third phase of a stepwise 0.8‰ negative δ¹³C excursion, lies in calcareous nannofossil subzone UC16d^BP, and encompasses the last occurrence of nannofossil Tranolithus stemmerikii and first occurrence of nannofossil Prediscosphaera mgayae. Fifteen δ¹³C events are defined and correlated to sixteen reliable nannofossil biohorizons, thus providing a well-calibrated standard high-resolution δ¹³C curve for the Boreal Realm.  相似文献   

Geochemical Soil Survey of The Netherlands - By Grishja van der Veer     

Thibault  Sterckeman 《The Geographical journal》2008,174(2):191-191

  相似文献   

Integral wide-field spectroscopy in astronomy: the Imaging FTS solution     

J. P. Maillard  L. Drissen  F. Grandmont  S. Thibault 《Experimental Astronomy》2013,35(3):527-559

Long-slit grating spectrometers in scanning mode and Fabry–Perot interferometers as tunable filters are commonly used to perform integral wide-field spectroscopy on extended astrophysical objects as HII regions and nearby galaxies. The goal of this paper is to demonstrate, by comparison, through a thorough review of the imaging Fourier transform spectrometer (IFTS) properties, that this instrument represents another interesting solution. After a brief recall of the performances, regarding FOV and spectral resolution, of the grating spectrometer, without and with integral field units (IFU), and of the imaging Fabry–Perot, it is demonstrated that for an IFTS the product of the maximum resolution R by the entrance beam étendue U is equal to $2.6\,N\times S_I$ with $N\,\times \,N$ the number of pixels of the detector array and S $_I$ the area of the interferometer beamsplitter. As a consequence, the IFTS offers the most flexible choice of field size and spectral resolution, up to high values for both parameters. It also presents on a wide field an important multichannel advantage in comparison to integral field grating spectrometers, even with multiple IFUs. To complete, the few astronomical IFTSs, built behind ground-based telescopes and in space, for the visible range up to the sub-millimetric domain, are presented. Through two wide-field IFTS projects, one in the visible, the other one in the mid-infrared, the question is addressed of the practical FOV and resolution limits, set by the optical design of the instrument, which can be achieved. Within the 0.3 to $\sim $ 2.5 $\upmu$ m domain, a Michelson interferometer with wide-field diopric collimators provides the easiest solution. This design is illustrated by a $11^{\prime}\times 11^{\prime}$ -field IFTS in the 0.35–0.90 $\upmu$ m range around an off-axis interferometer, called SITELLE, proposed for the 3.6-m CFH Telescope. At longer wavelengths, an all-mirror optics is required, as studied for a spaceborne IFTS, H2EX, for the 8–29 $\upmu$ m range, a $20^{\prime} \times 20^{\prime}$ field, and a high resolution of $\simeq 3\times 10^4$ at 10 $\upmu$ m. To comply with these characteristics, the interferometer is designed with cat’s eye retroreflectors. In the same domain and up to the far infrared, if the instrument aims only at a low spectral resolution (few thousands) and a smaller field (few arcmins $^2$ ), roof-top or corner cube mirrors, as for the IFTS SPIRE on the Herschel space telescope, are usable. At last, perspectives are opened, behind an ELT in the visible and the near infrared with the SITELLE optical combination, in the 2–5 $\upmu$ m on the Antarctic plateau or in space up to longer wavelengths, with the H2EX design, to provide the missing capability of global high spectral resolution studies of extended sources, from comets to distant galaxy clusters.  相似文献   

On viscoplastic regularisation of strain-softening rocks and soils     

René de Borst  Thibault Duretz 《国际地质力学数值与分析法杂志》2020,44(6):890-903

Constitutive models for rocks and soils typically incorporate some form of strain softening. Moreover, many plasticity models for frictional materials use a nonassociated flow rule. Strain softening and nonassociated flow rules can cause loss of well-posedness of the initial-value problem, which can lead to a severe mesh dependence in simulations and poor convergence of the iterative solution procedure. The inclusion of viscosity, which is a common property of materials, seems a natural way to restore well-posedness, but the mathematical properties of a rate-dependent model, and therefore the effectiveness with respect to the removal of mesh dependence, can depend strongly on how the viscous element is incorporated. Herein, we show that rate-dependent models, which are commonly applied to problems in the Earth's lithosphere, such as plate tectonics, are very different from the approach typically adopted for more shallow geotechnical engineering problems. We analyse the properties of these models under dynamic loadings, using dispersion analyses and one-dimensional finite difference analyses, and complement them with two-dimensional simulations of a typical strain localisation problem under quasi-static loading conditions. Finally, we point out that a combined model, which features two viscous elements, may be the best way forward for modelling time-dependent failure processes in the deeper layers of the Earth, since it not only enables modelling of the creep characteristics typical of long-term behaviour but also regularises the initial/boundary-value problem.  相似文献   

Influence of glass composition and alteration solution on leached silicate glass structure: A solid-state NMR investigation     

Frédéric Angeli  Marina Gaillard  Thibault Charpentier 《Geochimica et cosmochimica acta》2006,70(10):2577-2590

A multinuclear solid-state NMR investigation of the structure of the amorphous alteration products (so called gels) that form during the aqueous alteration of silicate glasses is reported. The studied glass compositions are of increasing complexity, with addition of aluminum, calcium, and zirconium to a sodium borosilicate glass. Two series of gels were obtained, in acidic and in basic solutions, and were analyzed using ¹H, ²⁹Si, and ²⁷Al MAS NMR spectroscopy. Advanced NMR techniques have been employed such as ¹H-²⁹Si and ¹H-²⁷Al cross-polarization (CP) MAS NMR, ¹H double quantum (DQ) MAS NMR and ²⁷Al multiple quantum (MQ) MAS NMR. Under acidic conditions, ²⁹Si CP MAS NMR data show that the repolymerized silicate networks have similar configuration. Zirconium as a second nearest neighbor increases the ²⁹Si isotropic chemical shift. The gel porosity is influenced by the pristine glass composition, modifying the silicon-proton interactions. From ¹H DQ and ¹H-²⁹Si CP MAS NMR experiments, it was possible to discriminate between silanol groups (isolated or not) and physisorbed molecular water near Si (Q²), Si (Q³), and Si (Q⁴) sites, as well as to gain insight into the hydrogen-bonding interaction and the mobility of the proton species. These experiments were also carried out on heated samples (180 °C) to evidence hydrogen bonds between hydroxyl groups on molecular water. Alteration in basic media resulted in a gel structure that is more dependent on the initial glass composition. ²⁷Al MQMAS NMR data revealed an exchange of charge compensating cations of the [AlO₄]⁻ groups during glass alteration. ¹H-²⁷Al CP MAS NMR data provide information about the proximities of these two nuclei and two aluminum environments have been distinguished. The availability of these new structural data should provide a better understanding of the impact of glass composition on the gel structure depending on the nature of the alteration solution.  相似文献