Laboratoire Geosciences Environnement Toulouse GET

Moncé-en-Belin, France

Laboratoire Geosciences Environnement Toulouse GET

Moncé-en-Belin, France
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Farla R.,University of Bayreuth | Rosenthal A.,University of Bayreuth | Rosenthal A.,Charles University | Rosenthal A.,University of Auvergne | And 7 more authors.
Earth and Planetary Science Letters | Year: 2017

The rheology of eclogite, garnetite and clinopyroxenite in the peridotitic upper mantle was experimentally investigated in a large volume press combined with in situ synchrotron X-ray diffraction techniques to study the impact on mantle convection resulting from the subduction of oceanic lithosphere. Experiments were carried out over a range of constant strain rates (2×10-6-3×10-5 s-1), pressures (4.3 to 6.7 GPa) and temperatures (1050 to 1470 K). Results show substantial strength variations among eclogitic garnet and clinopyroxene and peridotitic olivine. At low temperatures (<1200 K), eclogite is over 1 GPa stronger than dunite. On the other hand, at high temperatures (>1400 K) eclogite is weaker than dunite by 0.2 GPa or more. Garnetite and clinopyroxenite exhibit higher strength than dunite at approximately 1200 K. However, at higher temperature (1370 K), clinopyroxenite is significantly weaker than garnetite (and dunite) by more than a factor of five. We explain these observations by transitions in deformation mechanisms among the mineral phases. In clinopyroxene, high temperature dislocation creep resulting in a strength reduction replaces low temperature twinning. Whereas garnet remains very rigid at all experimental conditions when nominally anhydrous ('dry'). Microstructural observations show phase segregation of clinopyroxene and garnet, development of a crystallographic and shape preferred orientation in the former but not in the latter, suggesting an overall weak seismic anisotropy. Detection of eclogite bodies in the peridotite-dominated mantle may only be possible via observation of high VP/VS1 ratios. A comparable or weaker rheology of eclogite to dunite suggests effective stirring and mixing of eclogite in the convecting mantle. © 2017 Elsevier B.V.

Guignard J.,European Synchrotron Radiation Facility | Guignard J.,Laboratoire Geosciences Environnement Toulouse GET | Crichton W.A.,European Synchrotron Radiation Facility
Review of Scientific Instruments | Year: 2015

We report here the newly developed deformation setup offered by the 20MN (2000T) multi-anvil press newly installed at sector 7 of the European synchrotron radiation facility, on the ID06 beamline. The press is a Deformation-DIA (D-DIA) type apparatus, and different sets of primary anvils can be used for deformation experiments, from 6 mm to 3 mm truncations, according to the target pressure needed. Pressure and temperature calibrations and gradients show that the central zone of the assemblies is stable. Positions of differential RAMs are controlled with a sub-micron precision allowing strain rate from 10-4 to 10-6 s-1. Moreover, changing differential RAM velocity is immediately visible on sample, making faster reaching of steady state. Lattice stresses are determined by the shifting of diffraction peak with azimuth angle using a linear detector covering typically a 10° solid-angle in 2θ mounted on rotation perpendicular to the beam. Acquisition of diffraction pattern, at a typical energy of 55 keV, is less than a minute to cover the whole azimuth-2θ space. Azimuth and d-spacing resolution are respectively better than 1° and 10-3 Å making it possible to quantify lattice stresses with a precision of ±20 MPa (for silicates, which have typically high values of elastic properties), in pure or simple shear deformation measurements. These mechanical data are used to build fully constrained flow laws by varying P-T-σ-ε conditions with the aim to better understanding the rheology of Earth's mantle. Finally, through texture analysis, it is also possible to determine lattice preferred orientation during deformation by quantifying diffraction peak intensity variation with azimuth angle. This press is therefore included as one of the few apparatus that can perform such experiments combining with synchrotron radiation. © 2015 AIP Publishing LLC.

Souissi R.,Laboratoire Materiaux Utiles | Souissi F.,Laboratoire Materiaux Utiles | Souissi F.,Tunis el Manar University | Ghorbel M.,Tunis el Manar University | And 2 more authors.
Environmental Earth Sciences | Year: 2015

Pb-, Zn- and Cd-bearing particles from the flotation tailing heaps of Jebel Ressas mine are carried by wind and water toward the surrounding agricultural areas. These crop-producing areas are made of fersialitic soils and developed on carbonated bedrock. The risk of ecotoxicity depends on the bioavailability fraction of metals which is closely related to their physicochemical and biological environment. The objective of this study was to assess the contamination of the soils surrounding the waste dumps and to estimate the bioavailable fraction of metals present in these soils. The flotation tailings display big amounts of Zn, Pb and Cd, averaging 7.11 %, 2.30 % and 290 mg kg−1, respectively. The concentrations found in soils reach 6.3 % Zn, 2.3 % Pb and 290 mg kg−1 Cd. Analyses of the samples taken between surface and bedrock show that Pb and Zn may reach concentrations as high as 900 mg kg−1 2 m below surface. Simple extraction tests show that with deionized water only Zn is mobile, with 0.02–0.03 mmol l−1 released from soil. The mobilization of contaminants by organic acids, secreted by plants in the rhizosphere, is potentially higher than that achieved in the presence of percolating waters. © 2014, Springer-Verlag Berlin Heidelberg.

Ghorbel M.,Tunis el Manar University | Ghorbel M.,Laboratoire Geosciences Environnement Toulouse GET | Munoz M.,Laboratoire Geosciences Environnement Toulouse GET | Solmon F.,International Center for Theoretical Physics
Environmental Geochemistry and Health | Year: 2014

This work presents a modeling approach to simulate spatial distribution of metal contamination in aerosols with evaluation of health hazard. This approach offers the advantage to be non-intrusive, less expensive than sampling and laboratory analyses. It was applied to assess the impact of metal-bearing dust from mining wastes on air quality for a nearby community and agricultural lands in Jebel Ressas (Tunisia) locality. Dust emission rates were calculated using existing parameterization adapted to the contamination source composed of mining wastes. Metal concentrations were predicted using a Gaussian model (fugitive dust model) with, as input: emission rates, dump physical parameters and meteorological data measured in situ for 30 days in summertime. Metal concentration maps were built from calculated PM10 particle concentrations. They evidence the areas where Pb and Cd concentrations exceeded WHO guidelines (0.5 and 0.005 µg/m3, respectively). Maximum concentrations of Pb and Cd in PM10 are, respectively, of 5.74 and 0.0768 µg/m3 for measured wind speed values up to 22 m/s. Preferential areas of contamination were determined in agricultural lands to the NW from the source dump where Pb and Cd exceeded guidelines up to a distance of 1,200 m. The secondary spreading directions were SW and E, toward the village. Health hazard prospecting shown that a major part of the village was exposed to contaminated dust and that daily hazard quotient (HQ) values reached locally 118 and 158, respectively, for Pb and Cd during the study period. However, HQ variations in the village are high, both temporally and geographically. © 2014, Springer Science+Business Media Dordrecht.

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