CNRS Georesources lab

Nancy, France

CNRS Georesources lab

Nancy, France

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Sevostianov I.,New Mexico State University | Giraud A.,CNRS Georesources lab
International Journal of Engineering Science | Year: 2013

The paper focuses on the reformulation of classical Maxwell's (1873) homogenization method for elastic composites. Maxwell's scheme that equates the far fields produced by a set of inhomogeneities and by a fictitious domain with unknown effective properties is re-written in terms of the compliance contribution tensors. Explicit formula for tensor of effective elastic compliances is derived for the case the ellipsoidal fictitious domain. The method is illustrated by four examples-material containing multiple identical spheroidal pores, material containing three families of inhomogeneities having different shapes and properties, material containing circular cracks that have preferential orientation with certain scatter, and material containing randomly oriented non-ellipsoidal (superspherical) pores. © 2013 Elsevier Ltd. All rights reserved.

Pokrovski G.S.,French National Center for Scientific Research | Dubessy J.,CNRS Georesources lab
Earth and Planetary Science Letters | Year: 2015

The interpretation of sulfur behavior in geological fluids and melts is based on a long-standing paradigm that sulfate, sulfide, and sulfur dioxide are the major sulfur compounds. This paradigm was recently challenged by the discovery of the trisulfur ion S3- in aqueous S-bearing fluids from laboratory experiments at elevated temperatures. However, the stability and abundance of this potentially important sulfur species remain insufficiently quantified at hydrothermal conditions. Here we used in situ Raman spectroscopy on model thiosulfate, sulfide, and sulfate aqueous solutions across a wide range of sulfur concentration (0.5-10.0 wt%), acidity (pH 3-8), temperature (200-500 °C), and pressure (15-1500 bar) to identify the different sulfur species and determine their concentrations. Results show that in the low-density (<0.2g/cm3) vapor phase, H2S is the only detectable sulfur form. By contrast, in the denser liquid and supercritical fluid phase, together with sulfide and sulfate, the trisulfur radical ion S3- is a ubiquitous and thermodynamically stable species from 200 °C to at least 500 °C. In addition, the disulfur radical ion S2- is detected at 450-500 °C in most solutions, and polymeric molecular sulfur with a maximum abundance around 300 °C in S-rich solutions. These results, combined with revised literature data, allow the thermodynamic properties of S3- to be constrained, enabling quantitative predictions of its abundance over a wide temperature and pressure range of crustal fluids. These predictions suggest that S3- may account for up to 10% of total dissolved sulfur (Stot) at 300-500 °C in fluids from arc-related magmatic-hydrothermal systems, and more than 50% Stot at 600-700 °C in S-rich fluids produced via prograde metamorphism of pyrite-bearing rocks. The trisulfur ion may favor the mobility of sulfur itself and associated metals (Au, Cu, Pt, Mo) in geological fluids over a large range of depth and provide the source of these elements for orogenic Au and porphyry-epithermal Cu-Au-Mo deposits. Furthermore, the ubiquity of S3- in aqueous sulfate-sulfide systems offers new interpretations of the kinetics and mechanisms of sulfur redox reactions at elevated temperatures and associated mass-dependent and mass-independent fractionation of sulfur isotopes. © 2014 Elsevier B.V.

Gunzburger Y.,CNRS Georesources lab | Magnenet V.,CNRS Computer Science and Engineering Laboratory
Tectonophysics | Year: 2014

We investigate the source of non-purely gravitational horizontal stresses in the Paris basin, a nowadays tectonically quiet intracratonic basin, in its eastern border of which outstandingly dense stress measurements are available. Based on a synthesis of published data, the stress state in the basin is first shown to be very close to the one that may be extrapolated for the underlying basement, in terms of principal stress orientations and horizontal to vertical stress ratios. This is in favour of a mechanical coupling between the basement and its sedimentary cover, which may seem contradictory to the presence of several weak rock layers in the basin fill, e.g. an argillite layer that was shown to bear low deviatoric stresses, and salt layers that are implicated in a major décollement elsewhere. To unravel this apparent contradiction, a 3D-numerical modelling is performed, following a rigorous inverse problem approach, to determine the long-term elastic properties of both the basement and the basin rocks. The objective is to find the set of elastic constants that provides the best fit between the calculated stress state in the basin and the in situ data, by assuming that the stress state in the basement is known. This methodology provides a realistic set of mechanical parameters, in agreement with previous studies, which leads to the conclusion that the horizontal stresses in the basin constitute its mechanical response to the stresses that developed in the underlying basement during and since the last tectonic event (Alpine phase). The fact that horizontal stresses could be transmitted across the weak horizons, contrary to what may be expected at first glance, is explained both by the geometry of the basin and the fact that, over the long term, the stiffnesses of the various sedimentary rocks are only slightly different from each other. © 2014 Elsevier B.V.

This article presents a constitutive model for the elastic–plastic, viscoplastic and damage behaviour of hard porous rocks. The main hypotheses of the model are based on a large set of experimental data which are also presented in the paper. This constitutive model is of the over-stress type and is formulated within the unified theory of inelastic flow. An energy-based failure surface was considered to describe both short- and long-term behaviours within the same formulation. The inelastic yield surface is of static nature while the failure and damage surfaces are of dynamic nature. The kinetic law is written in terms of internal state variables that allow the description of how the frictional and the cohesive internal strengths of the material evolves. The reversible inelastic behaviour is also modelled using the “under-stress” concept, and considering that, it depends explicitly on the locked energy during the inelastic flow. In addition, this model is adapted to the porous nature of rocks such as iron ore that exhibit strong volumetric deformations and mean stress dependence. A large fraction of the volumetric straining is explained by damage mechanisms that also allow the accelerated creep to be modelled. Model parameters can easily be identified in the laboratory with commonly used mechanical tests. The constitutive model was implemented in a numerical code, and some qualitative simulations and comparisons with experimental curves showed the suitability of the model to reproduce both short- and long-term behaviours of porous rocks similar to iron ore. © 2014, Springer-Verlag Berlin Heidelberg.

Vigneresse J.-L.,CNRS Georesources lab
Geoscience Frontiers | Year: 2015

Abstract Felsic intrusions present ubiquitous structures. They result from the differential interactions between the magma components (crystal, melt, gas phase) while it flows or when the flow is perturbed by a new magma injection. The most obvious structure consists in fabrics caused by the interactions of rotating grains in a flowing viscous melt. New magma inputs through dikes affect the buk massif flow, considered as global within each mineral facies. A review of the deformation and flow types developing in a magma chamber identifis the patterns that could be expected. It determines their controlling parameters and summarizes the tools for their quantification. Similarly, a brief review of the rheology of a complex multi-phase magma identifies and suggests interactions between the different components. The specific responses each component presents lead to instability development. In particular, the change in vorticity orientation, associated with the switch between monoclinic to triclinic flow is a cause of many instabilities. Those are preferentially local. Illustrations include fabric development, shear zones and flow banding. They depend of the underlying rheology of interacting magmas. Dikes, enclaves, schlieren and ladder dikes result from the interactions between the magma components and changing boundary conditions. Orbicules, pegmatites, unidirectional solidification textures and miarolitic cavities result from the interaction of the melt with a gaseous phase. The illustrations examine what is relevant to the bulk flow, local structures or boundary conditions. In each case a field observation illustrates the instability. The discussion reformulates instability observations, suggesting new trails for ther description and interpretation in terms of local departure to a bulk flow. A brief look at larger structures and at their evolution tries to relate these instabilities on a broader scale. The helical structures of the Říčany pluton, Czech Republic and by the multiple granitic intrusions of Dolbel, Niger illustrate such events. © 2014 China University of Geosciences (Beijing) and Peking University.

Kutsenko A.A.,CNRS Georesources lab
European Journal of Mechanics, A/Solids | Year: 2015

Abstract A closed-form expression for the amplitudes of waves passing through the discrete uniform lattice with local defects and local sources is presented. It allows us to recover the defect properties from the available information about the amplitudes of waves. Other applications, such as modeling of cloaking devices, are also considered. The stability of this method is demonstrated by several numerical examples. © 2015 Elsevier Masson SAS.

Scholtes L.,CNRS Georesources lab | Donze F.-V.,Joseph Fourier University
Journal of the Mechanics and Physics of Solids | Year: 2012

The Discrete Element Method (DEM) is increasingly used to simulate the behavior of rock. Despite their intrinsic capability to model fracture initiation and propagation starting from simple interaction laws, classical DEM formulations using spherical discrete elements suffer from an intrinsic limitation to properly simulate brittle rock behavior characterized by high values of UCS/TS ratio associated with non-linear failure envelopes, as observed for hard rock like granite. The present paper shows that the increase of the interaction range between the spherical discrete elements, which increases locally the density of interaction forces (or interparticle bonds), can overcome this limitation. It is argued that this solution represents a way to implicitly take into account the degree of interlocking associated to the microstructural complexity of rock. It is thus shown that increasing the degree of interlocking between the discrete elements which represent the rock medium, in addition to enhancing the UCS/TS ratio, results in a non-linear failure envelop characteristic of low porous rocks. This approach improves significantly the potential and predictive capabilities of the DEM for rock modeling purpose. A special emphasis is put on the model ability to capture the fundamental characteristics of brittle rocks in terms of fracture initiation and propagation. The model can reproduce an essential component of brittle rock failure, that is, cohesion weakening and frictional strengthening as a function of rock damage or plastic strain. Based on model predictions, it is finally discussed that frictional strengthening may be at the origin of the brittle ductile transition occurring at high confining pressures. © 2012 Elsevier Ltd. All rights reserved.

Kutsenko A.A.,CNRS Georesources lab
Computational Mechanics | Year: 2014

The discrete periodic lattice of masses and springs with line and point defects is considered. The matrix integral equations of a special form are solved explicitly to obtain the Floquet–Bloch dispersion spectra for propagative, guided and localised waves. Explicit form of the dispersion equations makes possible detailed analysis of the position and other characteristics of the spectra. For example in the case of the uniform lattice with one line inclusion along with one single defect we obtain the sharp explicit upper bound (Formula presented.) for the mass of single defect for which there exist localised waves in the spectral gaps. The developed method can be applied to various problems in optics, solid-state physics, or electronics in which lattice defects play a major role. © 2014, Springer-Verlag Berlin Heidelberg.

Mejia-Herrera P.,CNRS Georesources lab | Royer J.-J.,CNRS Georesources lab | Caumon G.,CNRS Georesources lab | Cheilletz A.,CNRS Georesources lab
Natural Resources Research | Year: 2015

This work explains a procedure to predict Cu potentials in the ore-Kupferschiefer using structural surface-restoration and logistic regression (LR) analysis. The predictor in the assessments are established from the restored horizon that contains the ore-series. Applying flexural-slip to unfold/unfault the 3D model of the Fore-Sudetic Monocline, we obtained curvature for each restored time. We found that curvature represents one of the main structural features related to the Cu mineralization. Maximum curvature corresponds to high internal deformation in the restored layers, evidencing faulting and damaged areas in the 3D model. Thus, curvature may highlight fault systems that drove fluid circulation from the basement and host the early mineralization stages. In the Cu potential modeling, curvature, distance to the Fore-Sudetic Block and depth of restored Zechstein at Cretaceous time are used as predictors and proven Cu-potential areas as targets. Then, we applied LR analysis establishing the separating function between mineralized and non-mineralized locations. The LR models show positive correspondence between predicted probabilities of Cu-potentials and curvature estimated on the surface depicting the mineralized layer. Nevertheless, predicted probabilities are particularly higher using curvatures obtained from Late Paleozoic and Late Triassic restorations. © 2014, International Association for Mathematical Geosciences.

Tarantola A.,CNRS Georesources lab | Caumon M.-C.,CNRS Georesources lab
Journal of Raman Spectroscopy | Year: 2015

Salinity of fluid inclusions is usually determined by microthermometry, but it becomes unsuitable in case of metastability of the aqueous fluid because of thermodynamics indetermination. Raman microspectrometry of water in individual aqueous fluid inclusions can provide chemical information about fluid composition, in particular the concentration of chloride ions. The regular method consists in correlating the deformation of the OH stretching vibration band of liquid water in the region assigned to hydrogen-bonded OH groups, with chloride concentration. In order to evaluate the ability of Raman spectroscopy to determine salinity of metastable fluid inclusions, the Raman spectra of water trapped in two natural fluid inclusions were recorded at various temperatures in two physical states of the liquid phase, at equilibrium with vapor or metastable at negative pressure. The difference in salinity measured in the two states increased when temperature decreased, i.e. when the intensity of metastability increased. Metastability was then expressed in negative pressure scale (MPa) by thermodynamic modeling of the fluid trapped in the inclusions and correlated to salinity relative difference. The quantification of this effect led us to conclude that salinity expressed in mass% NaCleq. was overestimated of about 1% per 10-15 MPa of negative pressure. If the negative pressure can be quantified, it is thus possible to determine the salinity of metastable fluid inclusions by Raman spectroscopy. Copyright © 2015 John Wiley & Sons, Ltd. The Raman signal of water is a function of salinity The salinity of natural fluid inclusions is measured in stable and metastable equilibrium The value of salinity of metastable fluid inclusions measured by Raman spectroscopy is a function of negative pressure Copyright © 2015 John Wiley & Sons, Ltd.

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