Adsorption mechanisms of trivalent gold on iron- and aluminum-(oxy)hydroxides. Part 1: X-ray absorption and Raman scattering spectroscopic studies of Au(III) adsorbed on ferrihydrite, goethite, and boehmite     

Ingrid Berrodier  François Farges  Marc Benedetti  Gordon E. Brown Jr  Michel Deveughèle 《Geochimica et cosmochimica acta》2004,68(14):3019-3042

Gold adsorption products on powdered ferrihydrite, goethite, and boehmite samples, prepared by reacting Au(III)-Cl solutions ([Au] = 4.2 × 10⁻⁵-9.0 × 10⁻³ M; [Cl] = 0.017-0.6 M) with these adsorbents at pH values of 4 to 9 and Au adsorption densities ranging from 0.046 to 1.53 μmol/m² were characterized using Au-L_III XAFS spectroscopy. The solutions (before and after uptake) were investigated by Raman scattering to determine speciation and by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) to determine solution composition. We present an analysis of several effects that are observed in the Au L_III-edge XAFS spectra, including X-ray beam-induced photo-reduction, multi-electronic excitations, disorder effects, and multiple scattering, that would complicate interpretation of the spectra if not accounted for. A combination of methods (spectral deconvolution, principal component analysis, spectral inversion, and wavelet analysis) was used to identify and quantify these effects, to characterize the nature of mixed ligands around gold, and to distinguish between multiple-scattering features and features due to next-nearest neighbors in the XAFS spectra.Analysis of the Au-L_III XAFS spectra showed that Au(III) is present as square-planar Au(III)(O,Cl)₄ complexes in the aqueous solutions and on the surfaces of the Al/Fe-(oxy)hydroxide adsorption samples with dominantly O ligands at pH > 6 and mixed O/Cl ligands at lower pH values. The EXAFS-derived Au-O and Au-Cl distances are 2.00(2) and 2.28(2) Å, respectively, and the magnitudes of the Debye-Waller factors and third cumulants from anharmonic analyses indicate very little thermal or positional disorder around Au(III) in the adsorption samples. Iron second neighbors are present around Au in the Au(III)/ferrihydrite and Au(III)/goethite adsorption samples, with Au-Fe distances of 3.1(1) and 3.3(1) Å. In boehmite, two sets of Au-Al distances were detected at 3.0(1) and 3.2(1) Å. A reverse Monte Carlo study of the XAFS spectroscopic data suggests the presence of a continuum of edge-shared AuO₄-FeO₆ distances, which cannot be described correctly by a classical model of these data in which only a mean distance (although severely under-estimated) is derived.  相似文献   

From rifting to spreading in the eastern Gulf of Aden: a geophysical survey of a young oceanic basin from margin to margin   总被引：1，自引：0，他引：1  

Sylvie Leroy  Pascal Gente  Marc Fournier  Elia d'Acremont  Philippe Patriat  Marie-Odile Beslier  Nicolas Bellahsen  Marcia Maia  Angelina Blais  Julie Perrot  Ali Al-Kathiri  Serge Merkouriev  Jean-Marc Fleury  Pierre-Yves Ruellan  Claude Lepvrier  Philippe Huchon 《地学学报》2004,16(4):185-192

A geophysical survey in the eastern Gulf of Aden, between the Alula–Fartak (52°E) and the Socotra (55°E) transform faults, was carried out during the Encens–Sheba cruise. The conjugate margins of the Gulf are steep, narrow and asymmetric. Asymmetry of the rifting process is highlighted by the conjugate margins (horst and graben in the north and deep basin in the south). Two transfer fault zones separate the margins into three segments, whereas the present‐day Sheba Ridge is divided into two segments by a transform discontinuity. Therefore segmentation of the Sheba Ridge and that of the conjugate margins did coincide during the early stages of oceanic spreading. Extensive magma production is evidenced in the central part of the western segment. Anomaly 5d was identified in the northern and southern parts of the oceanic basin, thus confirming that seafloor spreading in this part of Gulf of Aden started at least 17.6 Ma ago.  相似文献   

Interpreting the clustering of radio sources     

Catherine M. Cress  & Marc Kamionkowski 《Monthly notices of the Royal Astronomical Society》1998,297(2):486-492

We develop the formalism required to interpret, within a CDM framework, the angular clustering of sources in a deep radio survey. The effect of non-linear evolution of density perturbations is discussed, as is the effect of the assumed redshift distribution of sources. We also investigate what redshift ranges contribute to the clustering signal at different angular scales. Application of the formalism is focused on the clustering detected in the FIRST survey, but measurements made for other radio surveys are also investigated. We comment on the implications for the evolution of clustering.  相似文献   

Highly Robust Variogram Estimation   总被引：5，自引：0，他引：5  

Marc G. Genton 《Mathematical Geology》1998,30(2):213-221

The classical variogram estimator proposed by Matheron is not robust against outliers in the data, nor is it enough to make simple modifications such as the ones proposed by Cressie and Hawkins in order to achieve robustness. This paper proposes and studies a variogram estimator based on a highly robust estimator of scale. The robustness properties of these three estimators are analyzed and compared. Simulations with various amounts of outliers in the data are carried out. The results show that the highly robust variogram estimator improves the estimation significantly.  相似文献   

Melting and metasomatism in the continental lithosphere: laser ablation ICPMS analysis of minerals in spinel lherzolites from eastern Australia   总被引：28，自引：0，他引：28  

Marc D. Norman 《Contributions to Mineralogy and Petrology》1998,130(3-4):240-255

Olivine, low-Ca pyroxene, diopside, and spinel from a suite of protogranular lherzolite xenoliths from southeastern Australia have been analysed for their major and trace element compositions using electron microprobe and laser ablation ICPMS. Bulk compositions of the lherzolites range from fertile (12–13% modal diopside) to depleted (2–3% modal diopside), with equilibration temperatures of 850–900 °C indicating entrainment of these lherzolites from relatively shallow depths (probably ≤ 35 km) within the lithosphere. Mineral compositions and abundances indicate a primary control by partial melting, with decreasing abundance of modal diopside accompanied by increasing Mg# of olivine and pyroxene, decreasing Al and Ti contents of diopside, increasing Ni contents of olivine, and increasing Cr/Al of spinel. HREE, Y, and Ga in diopside also follow melting trends, decreasing in concentration with increasing Mg#. In contrast, highly incompatible elements such as LREE, Nb, and Th reveal divergent behaviour that cannot be ascribed entirely to partial melting. Diopsides from the fertile lherzolites have mantle-normalized patterns that are depleted in Th, Nb, and the LREE relative to Y and the HREE, whereas, diopsides from the cpx-poor samples are strongly enriched in Th, Nb and the LREE, and have elevated Sm/Hf and Zr/Hf, and low Ti/Nb. All diopsides have strongly negative Nb anomalies relative to Th and the LREE. Trace element patterns of diopside in the fertile lherzolites can be reproduced by ≤ 5% batch melting of a primitive source. The negative Nb anomalies are a consequence of this melting, and do not require special conditions or tectonic environments. The low concentrations of Y and HREE in diopside from the cpx-poor lherzolites cannot be produced by realistic degrees of batch melting, but can be accomplished by up to ∼20% fractional melting, suggesting multiple episodes of melt depletion. Os isotopic compositions of these lherzolites show that the melt depletion events occurred in the middle and late Proterozoic, demonstrating the long-term stability of lithospheric mantle beneath regions of eastern Australia. The LREE-enriched diopsides are well equilibrated and record metasomatic enrichment events that pre-date the magmatism that entrained these xenoliths. Trace element patterns of these pyroxenes suggest a carbonatitic melt as the metasomatic agent. Received: 24 September 1996 / Accepted: 12 August 1997  相似文献   

Airborne remote sensing of cloud radiative smoothing during the Baltex Bridge Cloud campaign     

Marc Schrder  Ralf Bennartz  Jürgen Fischer  Thomas Ruhtz 《Atmospheric Research》2004,72(1-4):107

Based on airborne observations during the Baltex Bridge Cloud (BBC) campaign in September 2001, the impact of two layer cloud systems, gas absorption and surface albedo on cloud radiative smoothing is investigated. Multispectral nadir radiance measurements have been conducted which cover the visible and near infrared wavelength range. The observed radiances are transformed into Fourier space where ranges of scale-invariance are identified. Associated slopes and scale breaks are determined and used to characterize the impacts on cloud radiative smoothing. The results reveal that an increase of gas absorption reduces the small scale slope and the scale break due to a decreasing likelihood of horizontal photon transport. Another impact is that the increasing gas absorption reduces the cloud surface interaction, which is indicated by an increase of the large scale slope. An increasing surface albedo results in large scale cloud radiative smoothing and is associated with a decrease of the large scale slope. This effect depends on the cloud height and the cloud morphology. Two layer cloud systems exhibit a similar behaviour in Fourier space as large surface albedos beneath a single cloud deck. It is argued that the impact of two layer cloud systems on large scale cloud radiative smoothing may not be typical for two layer clouds.  相似文献   

Structure et caractérisation des matériaux utilisés dans la construction d'une mosaı̈que romaine de la cité de Volubilis (Maroc)     

Abdelilah Dekayir  Marc Amouric  Juan Olives  Claude Parron  Abdelilah Nadiri  Abdelkader Chergui  M.Abdeljalil El Hajraoui 《Comptes Rendus Geoscience》2004,336(12):1061-1070

In Volubilis, Roman mosaics are very beautiful and reveal, from the bottom to the surface, three layers: (i) ‘hedgehog’ layer, (ii) coarse grain mortar layer (rudus + nucleus) and (iii) tesselatum. Mineralogical analysis of coarse grain mortar sampled in Flavius Germanus mosaic shows that it consisted of quartz and calcite, with some feldspar and probably mica and dolomite. Fine-grained mortar in tesselatum is made from a mixture of calcite and quartz only. Limestone tesserae (white, pink and brown) show petrographic facies that change from micritic to oolithic limestone. Conversely, black and brick red tesserae are respectively made of marble, red sandstone and from fire clay. Other colours as yellow, blue, green and grey are obtained from artificial glass with different chemical compositions. To cite this article: A. Dekayir et al., C. R. Geoscience 336 (2004).  相似文献   

Large enigmatic crater structures offshore southern California     

Mark R. Legg  Craig Nicholson  Chris Goldfinger  Randall Milstein  Marc J. Kamerling 《Geophysical Journal International》2004,159(2):803-815

  相似文献   

How flat is the lower-mantle temperature gradient?     

Marc Monnereau  David A. Yuen 《Earth and Planetary Science Letters》2002,202(1):171-183

The temperature gradient in the lower mantle is fundamental in prescribing many transport properties, such as the viscosity, thermal conductivity and electrical conductivity. The adiabatic temperature gradient is commonly employed for estimating these transport properties in the lower mantle. We have carried out a series of high-resolution 3-D anelastic compressible convections in a spherical shell with the PREM seismic model as the background density and bulk modulus and the thermal expansivity decreasing with depth. Our purpose was to assess how close under realistic conditions the horizontally averaged thermal gradient would lie to the adiabatic gradient derived from the convection model. These models all have an endothermic phase change at 660 km depth with a Clapeyron slope of around −3 MPa K⁻¹, uniform internal heating and a viscosity increase of 30 across the phase transition. The global Rayleigh number for basal heating is around 2×10⁶, while an internal heating Rayleigh number as high as 10⁸ has been employed. The pattern of convection is generally partially layered with a jump of the geotherm across the phase change of at most 300 K. In all thermally equilibrated situations the geothermal gradients in the lower mantle are small, around 0.1 K km⁻¹, and are subadiabatic. Such a low gradient would produce a high peak in the lower-mantle viscosity, if the temperature is substituted into a recently proposed rheological law in the lower mantle. Although the endothermic phase transition may only cause partial layering in the present-day mantle, its presence can exert a profound influence on the state of adiabaticity over the entire mantle.  相似文献   

Active hydrate destabilization in Lake Baikal,Siberia?   总被引：1，自引：0，他引：1  

Marc De Batist  Jan Klerkx  Pieter Van Rensbergen  Maarten Vanneste  Jeffrey Poort  Alexander Y. Golmshtok  rei A. Kremlev  Oleg M. Khlystov  Petr Krinitsky 《地学学报》2002,14(6):436-442

ABSTRACT In this paper, we present new seismic and heat-flow data that show the base of the hydrate stability zone (BHSZ) in Lake Baikal to be locally characterized by abnormal variations in depth, with distinct regions of deeper-than-normal and regions of shallower-than-normal BHSZ. These variations are related to strong lateral variations in heat flow, and occur in close association with important rift-basin faults. Areas of shallow BHSZ are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor. We infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre-existing hydrates, in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the BHSZ. It thus seems that present-day hydrate dissociation in Lake Baikal is modulated by the tectonic activity in the rift rather than by – climatically controlled – changes in lake level or water temperature.  相似文献