Boron isotopic fractionation between minerals and fluids: New insights from in situ high pressure-high temperature vibrational spectroscopic data     

Carmen Sanchez-Valle  Bruno Reynard  Christophe Lecuyer  Jean-Claude Chervin 《Geochimica et cosmochimica acta》2005,69(17):4301-4313

Equilibrium boron isotopic fractionations between trigonal B(OH)₃ and tetragonal B(OH)₄⁻ aqueous species have been calculated at high P-T conditions using measured vibrational spectra (Raman and IR) and force-field modeling to compute reduced partition function ratios for B-isotopic exchange following Urey’s theory. The calculated isotopic fractionation factor at 300 K, α_3/4 = 1.0176(2), is slightly lower than the formerly calculated value of α_3/4 = 1.0193 (Kakihana and Kotaka, 1977), due to differences in the determined vibrational frequencies. The effect of pressure on α_3/4 up to 10 GPa and 723 K is shown to be negligible relative to temperature or speciation (pH) effects. Implications for the interpretation of boron fractionation in experimental and natural systems are discussed. We also show that the relationship between seawater-mineral B isotope fractionation and pH can be expressed using two variables, α_3/4 on one hand, and the pK_a of the boric acid-borate equilibrium on the other hand. This latter value is given by the equilibrium of boron species in water for the carbonate-water exchange, but could be governed by mineral surface properties in the case of clays. This may allow defining intrinsic paleo-pHmeters from B isotope fractionation between carbonate and authigenic minerals. Finally, it is shown that fractionation of boron isotopes can be rationalized in terms of the changes in 1) coordination of B from trigonal to tetrahedral in both fluids and minerals; and 2) the ligand nature around B from OH⁻ in the fluid and some hydrous minerals to non-hydrogenated O in many minerals. Relationships are established that allow predicting the isotopic fractionation factor of B between minerals and fluid.  相似文献   

Recent advances in Alpine studies: tracking the Caledonian–Variscan belt in the internal western Alps     

André Michard  Bruno Goffé 《Comptes Rendus Geoscience》2005,337(8):715-718

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Possibilities and Limitations of Interdisciplinary, User-oriented Research: Experiences from the German Research Network Natural Disasters     

Bruno Merz  Jana Friedrich  Markus Disse  Jochen Schwarz  Johann G. Goldammer  Jochen Wächter 《Natural Hazards》2006,38(1-2):3-20

The German Research Network for Natural Disasters (DFNK) linked 15 partners with scientific expertise in the field of natural hazards. Main objectives were the development and provision of the scientific fundamentals for an advanced risk management of important natural disasters in Germany, i.e., floods, earthquakes, storms and wildland fires. This included risk analyses, the development of information systems for supporting disaster management, and recommendations for risk reduction measures. This paper gives an overview of DFNK and summarises its experiences concerning multidisciplinarity and user-orientation. It illustrates the concept of risk chains, causally linking the different processes from hazard to risk. The step from hazard to risk requires interdisciplinary research teams. The experiences show that integrative concepts allow results not achievable with mono-disciplinary approaches. Integrative approaches pave the way to harmonised safety considerations taking into account the different hazards in a region within a common framework. User-orientation, policy advice and development of operational tools are key issues of disaster research. The experiences of DFNK illustrate the limitations of a research network in bridging the gap between research and application within rather short-term projects. Successful cooperation with users could be established by those activities where, at the beginning of the project, a user was identified who had a strong interest in solving an urgent problem.  相似文献   

Experimental constraints on pre-eruption conditions of pantelleritic magmas: Evidence from the Eburru complex, Kenya Rift   总被引：1，自引：0，他引：1  

Bruno Scaillet  Ray Macdonald 《Lithos》2006,91(1-4):95-108

The phase relationships and compositions of a pantellerite from the Eburru complex in the Kenya Rift Valley have been determined at 150 MPa and under reducing conditions, 2 log units below the Ni–NiO solid buffer. The effects of temperature and melt water content on phase relationships have been explored. Alkali feldspar and quartz crystallise alone at temperatures above 700 °C, irrespective of melt water content. Below 700 °C, sodic amphibole and clinopyroxene also crystallise; the amphibole being the liquidus phase under water-rich conditions. The coexistence of amphibole phenocrysts with alkali feldspar and quartz in a crystal-poor pantellerite implies temperatures below 700 °C and melt water contents higher than 4 wt.%, possibly up to 5–6 wt.%. Pantellerites have lower liquidus temperatures than associated comendites, which supports a parent–daughter relationship between the two magma types. The melts produced in the experiments extend the compositional trend displayed by the natural rock series, and reproduce some extreme compositions occasionally observed in alkaline volcanic series, with FeO contents above 12 wt.% and Na₂O contents approaching 10 wt.%. Pantellerites are therefore the true near-minimum melt compositions of alkaline oversaturated magma series.  相似文献   

Ab initio quantum-mechanical modeling of pyrophyllite [Al2Si4O10(OH)2] and talc [Mg3Si4O10(OH)2] surfaces     

Marco Bruno  Mauro Prencipe  Giovanni Valdre’ 《Physics and Chemistry of Minerals》2006,33(1):63-71

Bulk and slab geometry optimizations and calculations of the electrostatic potential at the surface of both pyrophyllite [Al₂Si₄O₁₀(OH)₂] and talc [Mg₃Si₄O₁₀(OH)₂] were performed at Hartree–Fock and DFT level. In both pyrophyllite and talc cases, a modest (001) surface relaxation was observed, and the surface preserves the structural features of the crystal: in the case of pyrophyllite the tetrahedral and octahedral sheets are strongly distorted with respect to the ideal hexagonal symmetry (and basal oxygen are located at different heights along the direction normal to the basal plane), whereas the structure of talc deviates slightly from the ideal hexagonal symmetry (almost co-planar basal oxygen). The calculated distortions are fully consistent with those experimentally observed. Although the potentials at the surface of pyrophyllite and talc are of the same order of magnitude, large topological differences were observed, which could possibly be ascribed to the differences between the surface structures of the two minerals. Negative values of the potential are located above the basal oxygen and at the center of the tetrahedral ring; above silicon the potential is always positive. The value of the potential minimum above the center of the tetrahedral ring of pyrophyllite is ?0.05 V (at 2 Å from the surface), whereas in the case of talc the minimum is ?0.01 V, at 2.7 Å. In the case of pyrophyllite the minimum of potential above the higher basal oxygen is located at 1.1 Å and it has a value of ?1.25 V, whereas above the lower oxygen the value of the potential at the minimum is ?0.2 V, at 1.25 Å; the talc exhibits a minimum of ?0.75 V at 1.2 Å, above the basal oxygen.  相似文献   

Unusual variations of dissolved As, Sb and Ni in the Rhône River during flood events     

Patrick Ollivier  Olivier Radakovitch  Bruno Hamelin 《Journal of Geochemical Exploration》2006,88(1-3):394

Dissolved major and trace element concentrations were determined from November 2000 to December 2003 in the lower Rhône River (France). Subsurface water samples were collected about twice a month and more regularly during flood events. An unusual trend was observed for As, Sb, Ni and Ba concentrations which increased with river discharge at the beginning of the floods, in contrast with other elements. Variations of Sb/Na and As/Na molar ratios show that it is related to higher contributions of waters from western tributaries of the Rhône River enriched in As, Sb, Ni and Ba due to ancient mining activities. These unusual variations of dissolved element concentrations are thus interpreted as mark of a water mass origin within the watershed.  相似文献   

Determination of the orbit of a natural satellite with hyperbolic flybys     

Bruno Bertotti 《Celestial Mechanics and Dynamical Astronomy》2001,80(1):21-38

We show that, when a natural satellite like Titan is invisible (e.g., due to an opaque atmosphere) its planetary orbit and its mass can be determined by tracking a spacecraft in close flybys. This is an important problem in the Cassini mission to the Saturnian system, which will be greatly improved by a good astrometric model for all its main components; in particular, an accuracy of a few hundred meters for the orbit of Titan is necessary to allow a measurement of its moment of inertia. The orbit of the spacecraft is the union of elliptical arcs, joined by short hyperbolic transitions: a problem of singular perturbation theory, whose solution leads to a matching condition between the inner hyperbolic orbit and the elliptical orbital elements. Since the inner elements are given in terms of the relative position and velocity of the spacecraft, accurate Doppler measurements in both regions can provide a satisfactory determination of Titan's position and velocity, hence of its Keplerian elements. The errors in this determination are discussed on the basis of the expected Allan deviation of the Doppler method; it is found that the driving errors are those in the elliptical arcs; the fractional errors in Titan's orbital elements are expected to be 10^–7. It is also possible to measure the mass of the satellite; however, when the eccentricity e of the flybys is large, the mass and a scaling transformation are highly correlated and the fractional error in the mass is expected to be e times worse.  相似文献   

δ13C variation of soil organic matter as an indicator of vegetation change during the Holocene in central Cameroon     

Thierry Desjardins  Bruno Turcq  Jean-Pierre Nguetnkam  Gaston Achoundong  Magloire Mandeng-Yogo  Fethyé Cetin  Anne-Marie Lézine 《Comptes Rendus Geoscience》2013,345(7-8):266-271

In order to better understand the dynamics of the forest–savanna mosaic from central Cameroon, we analyzed ¹³C and ¹⁴C profiles of six oxisols: two under forests and four under savannas. The δ¹³C soil profiles collected in the forests indicate that these environments are stable at least since the mid-Holocene, whereas the areas currently covered by savannas were formerly occupied by more forested vegetations. The ¹⁴C dating of organic matter indicate that the late extension of the savannas in central Cameroon date from the Late Holocene, starting from 4000–3500 ¹⁴C yr BP.  相似文献   

Millennial-scale shifts in microtidal ecosystems during the Holocene: dynamics and drivers of change from the Po Plain coastal record (NE Italy)     

Veronica Rossi  Giulia Barbieri  Stefano Claudio Vaiani  Marco Cacciari  Luigi Bruno  Bruno Campo  Marco Marchesini  Silvia Marvelli  Alessandro Amorosi 《第四纪科学杂志》2021,36(6):961-979

Framed into a robust stratigraphic context, multivariate analyses on the Holocene palaeobiological record (pollen, benthic foraminifers, ostracods) of the Po coastal plain (NE Italy) allowed the investigation of microtidal ecosystems variability and driving parameters along a 35-km-long land–sea transect. Millennial-scale ecosystem shifts are documented by coeval changes in the meiofauna, reflecting variations in organic matter–water depth (shallow-marine environments) and degree of confinement-salinity (back-barrier settings). In-phase shifts of vegetation communities track unsteady water-table levels and river dynamics in freshwater palustrine areas. Five environmental–ecological stages followed one another crossing four tipping points that mark changes in relative sea level (RSL), climate and/or fluvial regime. At the culmination of Mediterranean RSL rise, after the 8200 event, remarkable growth of peatlands took place in the Po estuary, while low accumulation rates typified the shelf. At the transgressive–regressive turnaround (~7000 cal a bp ), the estuary turned into a delta plain with tidally influenced interdistributary embayments. River flow regime oscillations after the Climate Optimum (post-5000 cal a bp ) favoured isolation of the bays and the development of brackish wetlands surrounded by wooded peatlands. The youngest threshold (~800 cal a bp ), which led to the establishment of the modern delta, reflects a major avulsion of the Po River.  相似文献   

Three-dimensional hydrogeological modeling to assess the elevated-water-table technique for controlling acid generation from an abandoned tailings site in Quebec,Canada     

Ethier  Marie-Pier  Bussière  Bruno  Broda  Stefan  Aubertin  Michel 《Hydrogeology Journal》2018,26(4):1201-1219

The Manitou Mine sulphidic-tailings storage facility No. 2, near Val D’Or, Canada, was reclaimed in 2009 by elevating the water table and applying a monolayer cover made of tailings from nearby Goldex Mine. Previous studies showed that production of acid mine drainage can be controlled by lowering the oxygen flux through Manitou tailings with a water table maintained at the interface between the cover and reactive tailings. Simulations of different scenarios were performed using numerical hydrogeological modeling to evaluate the capacity of the reclamation works to maintain the phreatic surface at this interface. A large-scale numerical model was constructed and calibrated using 3 years of field measurements. This model reproduced the field measurements, including the existence of a western zone on the site where the phreatic level targeted is not always met during the summer. A sensitivity analysis was performed to assess the response of the model to varying saturated hydraulic conductivities, porosities, and grain-size distributions. Higher variations of the hydraulic heads, with respect to the calibrated scenario results, were observed when simulating a looser or coarser cover material. Long-term responses were simulated using: the normal climatic data, data for a normal climate with a 2-month dry spell, and a simplified climate-change case. Environmental quality targets were reached less frequently during summer for the dry spell simulation as well as for the simplified climate-change scenario. This study illustrates how numerical simulations can be used as a key tool to assess the eventual performance of various mine-site reclamation scenarios.

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