Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We compare a global compilation of shear-wave splitting measurements with azimuthal seismic anisotropy parameters inferred from surface-wave tomography. The currently available splitting dataset is taken from a novel comprehensive collection of available publications that is updated interactively online. The comparison between the two types of data is made by calculating predicted splitting parameters from the anisotropic tomography model. Comparing these predicted splitting parameters with the observed ones, we find a considerable correlation between the two datasets at global scale. This result is noteworthy, since such correlation did not seem to exist in previous studies. The spatial resolution associated with the two types of methods is rather different. While surface waves have good vertical resolution and poor lateral resolution of several hundreds of kilometers, SKS splitting measurements have good lateral, but poor vertical resolution. The correlation can be understood in light of recent propositions that anisotropy seen by SKS splitting constrains mostly the upper mantle, and therefore a similar depth region as surface waves. The correlation also confirms the generally good quality of the shear-wave measurements, as well as that of the anisotropic tomography model.
ISSN: 0031-9201

hal-00429396
https://hal.archives-ouvertes.fr/hal-00429396
https://hal.archives-ouvertes.fr/hal-00429396/document
https://hal.archives-ouvertes.fr/hal-00429396/file/Wuestefeld_SKS_SW_correlation_PEPI2009-hal.pdf
DOI : 10.1016/j.pepi.2009.05.006

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Grain deviations and high extractives content are common features of many tropical woods. We aimed at clarifying their respective impact on vibrational properties, referring to African Padauk (Pterocarpus soyauxii Taub.), a species selected for its interlocked grain, high extractives content, and uses in xylophones. Specimens were cut parallel to the trunk axis (L), and local variations in grain angle (GA), microfibril angle (MFA), specific Young's modulus (E'L/ρ, where r stands for specific gravity) and damping coefficient (tanδL), were measured. GA dependence was analyzed by a mechanical model which allowed to identify the specific Young's modulus (E'3/ρ) and shear modulus (G'/ρ) along the grain (3), as well as their corresponding damping coefficients (tanδ3, tanδG). This analysis was done for native and then for extracted wood. Interlocked grain resulted in 0-25° GA and in variations of a factor 2 in E'L/ρ and tanδL. Along the grain, Padauk wood was characterized, as compared to typical hardwoods, by a somewhat lower E'3/ρ and elastic anisotropy (E'/G'), due to a wide microfibril angle plus a small weight effect of extracts; and a very low tanδ3 and moderate damping anisotropy (tanδG/tanδ3). Extraction affected mechanical parameters in the order: tanδ3 ≈ tanδG > G'/ρ >> E'3/ρ. That is, extractives' effects were nearly isotropic on damping but clearly anisotropic on storage moduli.
ISSN: 0043-7719

hal-00544382
https://hal.archives-ouvertes.fr/hal-00544382
https://hal.archives-ouvertes.fr/hal-00544382/document
https://hal.archives-ouvertes.fr/hal-00544382/file/Identification_anisotropic_vibrational_properties_Bremaud_al.pdf
DOI : 10.1007/s00226-010-0348-0

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We investigated the structure of the upper mantle beneath southeastern Brazil using teleseismic shear wave splitting measurements. Measurements were performed on seismic data recorded in the Ribeira and Brasilia Neoproterozoic belts, which wrap around the southern termination of the São Francisco craton and disappear westward under the Paraná basin. In the northern Ribeira belt, dominated by thrust tectonics, the fast shear wave polarization planes trend on average N080°E, whereas in the central domain, dominated by strike-slip tectonics, fast shear waves are polarized parallel to the structural trend (N065°E). Stations located above the main transcurrent fault display large delay times (> 2.5 s). Such values, among the largest in the world, require either an unusually large intrinsic anisotropy frozen within the lithosphere, or a contribution from both the lithospheric and asthenospheric mantle. Within the southern Brasilia belt, fast split shear waves are polarized parallel to the structural trend of the belt, at a high angle from the APM. Although part of our data set strongly favors an origin of anisotropy related to a fabric frozen in the lithospheric mantle since the Neoproterozoic, a contribution of the asthenospheric flow related to the present day plate motion is also required to explain the observed splitting parameters.
ISSN: 0012-821X

hal-01389116
http://hal.univ-reunion.fr/hal-01389116
http://hal.univ-reunion.fr/hal-01389116/document
http://hal.univ-reunion.fr/hal-01389116/file/Heintz_SKS_Brazil_EPSL2003_hal.pdf
DOI : 10.1016/S0012-821X(03)00163-8

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Geodetic data support a short-term continental deformation localized in faults bounding lithospheric blocks. Whether major "faults" observed at the surface affect the lithospheric mantle and, if so, how strain is distributed are major issues for understanding the mechanical behavior of lithospheric plates. A variety of evidence, from direct observations of deformed peridotites in orogenic massifs, ophiolites, and mantle xenoliths to seismic reflectors and seismic anisotropy beneath major fault zones, consistently supports prolongation of major faults into the lithospheric mantle. This review highlights that many aspects of the lithospheric mantle deformation remain however poorly understood. Coupling between deformation in frictional faults in the uppermost crust and localized shearing in the ductile crust and mantle is required to explain the post-seismic deformation, but mantle viscosities deduced from geodetic data and extrapolated from laboratory experiments are only reconciled if temperatures in the shallow lithospheric mantle are high (> 800 °C at the Moho). Seismic anisotropy, especially shear wave splitting, provides strong evidence for coherent deformation over domains several tens of km wide in the lithospheric mantle beneath major transcurrent faults. Yet it cannot detect narrow strain localization zones or shallowly dipping faults. Seismic profiling images shallow-dipping seismic reflectors in the lithospheric mantle interpreted as the continuation of normal or, less frequently, inverse faults in the mantle. However the nature of these reflectors is poorly understood. There is a large discrepancy between the scale at which deformation processes are studied (a few kilometers, at most, due to the limited size of continuous mantle exposures at the Earth's surface) and the scale inferred for strain localization in the mantle from geophysical observations (tens of kilometers). Combining data on deformation microstructures and crystal preferred orientations in naturally deformed peridotites and seismologic observations allows nevertheless discussing strain localization processes that may play a role on the development of mantle shear zones.
ISSN: 0040-1951

hal-00750314
https://hal.archives-ouvertes.fr/hal-00750314
DOI : 10.1016/j.tecto.2012.06.006

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We have analyzed the microstructures and crystal preferred orientations (CPO), and calculated the seismic properties of 53 mantle xenoliths from four localities within the North Tanzanian Divergence of the East African rift: two within the rift axis and two in the transverse volcanic belt. Olivine OH concentrations were measured in 15 xenoliths.Most samples have harzburgitic to dunitic compositions and high olivine Mg#. Microstructures and olivine CPO patterns vary strongly depending on the location. In-axis peridotites display mylonitic to porphyroclastic microstructures, which record recent deformation by dislocation creep. Highly stretched orthopyroxenes in mylonites indicate that the deformation was initiated under high stress and probably low temperature. Orthopyroxene replacement by olivine in mylonitic and porphyroclastic peridotites suggest syn-kinematic melt–rock reactions and further deformation under near-solidus conditions. Exsolutions in orthopyroxene imply significant cooling between melt-assisted deformation and xenolith extraction. Late metasomatism is evidenced by the occurrence of veins crosscutting the microstructure and interstitial clinopyroxene and phlogopite. Axial-[100] olivine CPOs predominate, suggesting activation of the high temperature, low pressure [100] {0kl} slip systems and, probably, transtensional deformation. In the volcanic belt, Lashaine peridotites display very coarse-granular textures, indicating deformation by dislocation creep under low deviatoric stress conditions followed by annealing. Axial-[010] olivine CPOs are consistent with transpressional deformation or simultaneous activation of the [100](010) and [001](010) slip systems. Intermediate microstructures and CPOs in Olmani suggests heterogeneous deformation within the volcanic belt. Olivine OH concentrations range between 2 and 12 ppm wt. H2O. No systematic variations are observed between in- and off-axis samples. Maximum P wave azimuthal anisotropy (AVp) ranges between 3.3 and 18.4%, and the maximum S wave polarization anisotropy (AVs) between 2.3 and 13.2%. Comparison between seismic properties of in-axis peridotites and SKS splitting data suggests transtensional deformation in the lithospheric mantle beneath the rift.
ISSN: 0040-1951

hal-01121552
https://hal.archives-ouvertes.fr/hal-01121552
DOI : 10.1016/j.tecto.2014.11.011

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : We have applied transmission electron microscopy (TEM) analyses coupled with viscoplastic self-consistent (VPSC) numerical modelling to identify the active slip systems and to better understand the crystal preferred orientation (CPO) development of the Torridon quartz mylonite (NW Scotland). TEM analyses showed evidence of activation of 1/3〈a〉{π′}, 1/3〈a〉{z} and possible 〈a〉(c) slip systems, as well as dislocation climb and dynamic recrystallization. All the CPOs generated by VPSC models share common characteristics with the Torridon quartz mylonite, but only Models 2 and 3 reproduce the [c]-axes maxima at low angle (<20°) to the foliation pole along the YZ plane, as observed in the mylonite. In Model 2, this concentration only occurs at γ≥2.6, whereas in Model 3 this maxima occurs at lower shear strains. The models that start with a previous preferred orientation acquire very strong CPOs after small-imposed strains, followed by the rapid rotation of the fabric in relation to the new imposed finite strain axes. The combined activation of 〈a〉{π′}, 〈a〉{z} and possibly 〈a〉(c) slip systems, as demonstrated by TEM analyses, suggests that the VPSC model that best predicts CPO development in the Torridon quartz mylonite is Model 2, where the critical resolved shear stress (CRSS) of 〈a〉{π/π′} is assumed to be slightly stronger than 〈a〉(c).
Deformation Mechanisms, Rheology and Tectonics: Microstructures, Mechanics and Anisotropy

hal-00688840
https://hal.archives-ouvertes.fr/hal-00688840

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We have analyzed shear wave splitting recorded by portable and permanent broadband and long-period stations located in the eastern United States. Teleseismic shear waves (SKS, SKKS, and PKS) were used to retrieve the splitting parameters: the orientation of the fast wave polarization plane ϕ and the delay time δt. In total, 120 seismic events were processed, allowing for more than 600 splitting measurements. Within the Appalachians, stations located in the western (external) part are characterized by δt≈1s and ϕ trending N50°– 70°E in the south and central regions and N30°–40°E in the north, closely following the trend of the orogenic belt in these areas. The transition region between north and central is characterized by δt≈1–1.3 s and by E-W trending ϕ that are at a high angle to the regional geologic trend. Measurements at two stations located in the eastern (internal) part of the belt indicate very weak anisotropy. The large-scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate. Splitting along the southern and eastern margins of the continent is consistent with that expected for Grenvillian deformation, an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out. Within the cratonic core, the correlation between δt and lithospheric thickness suggests a lithospheric anisotropy. Smaller-length-scale variations also argue for a significant contribution of lithospheric structures. The fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern United States, i.e., the Grenville and Appalachian orogenies and the subsequent rifting of the North Atlantic Ocean. Our observations in the western Appalachians suggest that the anisotropy may be preserved since the Grenvillian orogeny. The absence of detectable splitting in the two stations in the eastern Appalachians is attributed to the igneous intrusions related to the Atlantic rifting. The measurements in the transition between the northern and central southern Appalachians, constitute an intriguing anomaly, whose E-W ϕ have little obvious relation to the regional surface geology. We suggest two possible causes: (1) the local dominance of asthenospheric flow, motivated by the proximity of a pervasive low-velocity anomaly and (2) lithospheric deformation in a transcontinental strike-slip fault zone active during the Appalachian collision.
ISSN: 2169-9313

hal-01388859
http://hal.univ-reunion.fr/hal-01388859
http://hal.univ-reunion.fr/hal-01388859/document
http://hal.univ-reunion.fr/hal-01388859/file/Barruol_JGR_1997.pdf
DOI : 10.1029/96JB03800

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The anisotropic single crystal seismic properties are reviewed in the light of recent experimental and theoretical determinations. Although considerable progress has been made on the determination of single crystal properties, data are still lacking, particularly for the temperature derivatives of transition zone and lower mantle phases. The common types of LPO of olivine, opx and cpx are presented together with their associated seismic properties. It is emphasized that simple seismic symmetry pattern of upper mantle rocks are a direct result of the interaction of olivine, opx and cpx. Using the standard structural frame (X lineation, Z pole to foliation) for typical LPOs of olivine, opx and cpx have the maximum Vp parallel to X, in the XZ plane and parallel to Y respectively. Destructive interference occurs between these minerals and hence P-wave anisotropy should be sensitive to the aggregate composition. For shear wave splitting (dVs) typical olivine and opx LPOs result in similar patterns with the maximum dVs in the YZ plane and the fast split shear wave (Vs1) polarized parallel to the foliation. A typical cpx LPO on the other hand produces destructive interference as the max dVs is close to X. By comparison with experiments and numerical simulations, it is estimated that upper mantle samples have an olivine LPO strength which recorded shear strain gamma of between 0.25 and 2.0. Pyrolite and piclogite models are compared with global transverse isotropic models. The slowly reducing P-wave anisotropy in the first 200 km can be explained by a model with constant composition and LPO strength. The sharp decrease in the observed anisotropy in the global models cannot be explained by the transformation of opx to cpx at 300 km, it is proposed that this decrease is due to a reduction in LPO strength from 200 to 350 km at the base of the lithosphere.
Earth's Deep Interior: Mineral Physics and Tomography From the Atomic Scale to the Global Scale

ISBN : 9780875909752
hal-01391524
http://hal.univ-reunion.fr/hal-01391524
http://hal.univ-reunion.fr/hal-01391524/document
http://hal.univ-reunion.fr/hal-01391524/file/Mainprice_AGUmonog_DM_GB_WBI_2000.pdf

Éditeur(s) : HAL CCSD Springer
Résumé : International audience
Thermoelastic behavior of different marble types was analyzed using computational modeling and experimental measurements. Eight marble samples with different composition, grain size, grain boundary geometry, and texture were investigated. Calcitic and dolomitic marbles were considered. The average grain size varies from 75 μm to 1.75 mm; grain boundary geometry differs from nearly equigranular straight grain boundaries to inequigranular-interlobate grain boundaries. Four typical marble texture types were observed by EBSD measurements: weak texture; strong texture; girdle texture and high-temperature texture. These crystallographic orientations were used in conjunction with microstructure-based finite element analysis to compute the thermoelastic responses of marble upon heating. Microstructural response maps highlight regions and conditions in the marble fabric that are susceptible to degradation phenomena. This behavior was compared to the measured thermal expansion behavior, which shows increasing residual strains upon repetitive heating-cooling cycles. The thermal expansion behavior as a function of temperature changes can be classified into four categories: (a) isotropic thermal expansion with small or no residual strain; (b) anisotropic thermal expansion with small or no residual strain; (c) isotropic thermal expansion with a residual strain; and (d) anisotropic thermal expansion with residual strain. Thermal expansion coefficients were calculated for both simulated and experimental data and also modeled from the texture using the MTEX software. Fabric parameters control the amount and directional dependence of the thermal expansion. Marbles with strong texture show higher directional dependence of the thermal expansion coefficients and have smaller microstructural values of the maximum principal stress and strain energy density, the main precursors of microcracking throughout the marble fabric. In contrast, marbles with weak texture show isotropic thermal expansion behavior, have a higher propensity to microcracking, and exhibit higher values of maximum principal stress and strain energy density. Good agreement between the experimental and computational results is observed, demonstrating that microstructure-based finite-element simulations are an excellent tool for elucidating influences of rock fabric on thermoelastic behavior.
ISSN: 1866-6280

hal-00858095
https://hal.archives-ouvertes.fr/hal-00858095
DOI : 10.1007/s12665-013-2406-z

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
The way faults control upward fluid flow in nonmagmatic hydrothermal systems in extensional context is still unclear. In the Eastern Pyrénées, an alignment of twenty-nine hot springs (29 ∘ C to 73 ∘ C), along the normal Têt fault, offers the opportunity to study this process. Using an integrated multiscale geological approach including mapping, remote sensing, and macro-and microscopic analyses of fault zones, we show that emergence is always located in crystalline rocks at gneiss-metasediments contacts, mostly in the Têt fault footwall. The hot springs distribution is related to high topographic reliefs, which are associated with fault throw and segmentation. In more detail, emergence localizes either (1) in brittle fault damage zones at the intersection between the Têt fault and subsidiary faults or (2) in ductile faults where dissolution cavities are observed along foliations, allowing juxtaposition of metasediments. Using these observations and 2D simple numerical simulation, we propose a hydrogeological model of upward hydrothermal flow. Meteoric fluids, infiltrated at high elevation in the fault footwall relief, get warmer at depth because of the geothermal gradient. Topography-related hydraulic gradient and buoyancy forces cause hot fluid rise along permeability anisotropies associated with lithological juxtapositions, fracture, and fault zone compositions.
ISSN: 1468-8115

hal-01582968
https://hal-brgm.archives-ouvertes.fr/hal-01582968
https://hal-brgm.archives-ouvertes.fr/hal-01582968/document
https://hal-brgm.archives-ouvertes.fr/hal-01582968/file/Taillefer_et_al_Geofluids_2017.pdf
DOI : 10.1155/2017/8190109

Résumé : L’objet de cette thèse est l’étude des comportements mécanique et à la corrosion d’un nouveau système de fondation, dit pieux SPIRMEC, adapté aux structures légères. Le travail s’est focalisé sur deux grands aspects. Le premier aspect concerne l’analyse du comportement sous chargement axiale des pieux SPIRMEC sur la base de l’expérimentation et de la modélisation numérique dans un sol mou non cohésif. Quant au deuxième aspect, il traite du problème de la corrosion de l’acier constituant le pieu dans un environnement tropical humide. Le comportement des pieux SPIRMEC sous une charge axiale de traction, dans un sol fin non cohésif, a montré le développement d’une surface cylindrique de rupture. Celle-ci ne dépend pas de la configuration géométrique des pieux tel que : l’espacement S, le diamètre d’hélice Dh et le diamètre du tube d. En adoptant ce critère de rupture et à l’aide d’une analyse statistique des données, nous avons proposé quatre méthodes analytiques de prédiction de la capacité portante des pieux SPIRMEC à partir des essais in-situ et au laboratoire qui sont: •Méthode CPT basée sur la résistance de pointe pénétromètrique (essai CPT), •Méthode MPT basée sur la pression limite pressiomètrique (essai MPT), •Méthode du couple d’installation, •Méthode analytique basée sur les paramètres de cisaillement de sol notamment l’angle de frottement interne (essais triaxial et boîte de cisaillement). Ces méthodes tiennent compte de la géométrie du pieu, du procédé de mise en oeuvre et de la compacité du sol. L’analyse de performance des méthodes proposées a montré que les méthodes analytique et CPT représentent mieux le comportement des pieux testés. La modélisation numérique du comportement des pieux SPIRMEC sous charge axiale de traction a été également étudiée à l’aide du code de calcul Plaxis 2D. Un modèle axisymétrique a été adopté pour modéliser la géométrie de la structure. Le modèle de comportement hardening soil a été retenu pour modéliser le comportement élastoplastiq des couches de sol. Un modèle élastique linéaire a été retenu pour le pieu. Quant au comportement de l’interface sol-structure, il a été pris en compte par un modèle élastoplastique basé sur les critères de Mohr-Coulomb. L’expansion du sol résultant de l’installation des pieux a été approchée par une cavité cylindrique. Cette dernière a été modélisée par des déformations volumiques anisotropes. Nous avons constaté, qu’appliquer une déformation volumique de l’ordre de 40% permet une bonne concordance entre les résultats numériques et expérimentaux. L’étude paramétrique nous a également permis de constater l’existence d’une variation linéaire entre la capacité portante et l’espacement S. Le comportement de l’acier galvanisé dans le sol a été également étudié au moyen de trois approches: électrochimique, visuelles grâce au microscope électronique et gravimétrique. Les tests électrochimiques de corrosion du zinc ont été réalisés dans la solution de sol artificielle pour deux périodes bien distinctes : saison des pluies et après 8 mois de contact sol-pieu. Une forte dépendance est constatée de la vitesse de corrosion de zinc au pH et à la conductivité de la solution. La vitesse de corrosion est plus importante en saison des pluies qu’après 8 mois de contact de pieu avec le sol. Les fortes concentrations en sulfates semblent augmenter la vitesse de corrosion. Les analyses menées au MEB montrent que la zone de fluctuation de nappe et en surface externe (sol/air) sont les zones les plus corrodées. La comparaison entre les différentes techniques d’évaluation de la vitesse de corrosion a montré que l’eau de nappe peut être utilisée comme un milieu représentatif du profil chimique d’un sol non cohésif et légèrement granulaire.
The purpose of this thesis is to study the both behaviors mechanical and of the corrosion of a new foundation system, called spirec piles, for lightweight structures. The work was based on two main aspects. The first aspect concerns the analysis of behavior of the spirmec piles under axial loading on the basis of experimental and numerical modeling in a non-cohesive soft soil. On the second aspect, it addresses the problem of corrosion of steel forming the pile in a humid tropical environment. The behavior of the tested piles under axial traction load, in a non-cohesive soil, showed the development of a cylindrical surface of failure. This does not depend on the geometrical configuration of the tested piles such that: the spacing s, the helix diameter dh and the diameter of the shaft. By adopting this failure criterion and using statistical data analysis, we proposed four analytical methods for predicting the bearing capacity of the piles from in-situ and laboratory tests, which are: cpt method based on tip resistance penetrometer (cpt test), mpt method based on pressuremeter limit pressure (test mpt), method of installation torque and analytical method based on the shear parameters of soil (triaxial tests and shear box). These methods take into account the geometry of the pile, the method and implementation of soil compaction. Performance analysis of the proposed methods showed that the analytical methods and cpt represent better the behavior of piles tested. An axisymmetric condition was assumed to model this geometry in two-dimensional space. In this study, we proposed to model the pipe screw pile with plates elements available in plaxis 2d. The helixes were modeled as circular disks. Interface elements were incorporated along the pile to simulate the soil-pile interaction. Hardening soil model was chosen to describe the soil with drained behavior was assigned for all layers. Linear elastic for pile and elastic plastic model based on the mohr-coulomb criterion was used to describe the interface behavior. The lateral expansion generated by the pile shaft was modeled by anisotropic volumetric strains (ɛxx=ɛzz, ɛyy=0). The pile behavior under tensile loading at different volumetric strains, it is clear that the best fit was obtained at volumetric strain of 40%. The parametric study also allowed us to establish the existence of a linear variation between the bearing capacity and spacings. The behavior of the galvanized steel in the ground has also been studied using three approaches such as: electrochemical, microscopic imaging and gravimetrically. Electrochemical tests of the corrosion of the zinc have been made in artificial soil solution into two periods, the rainy season and after eight months of contact soil-pile. Is a strong dependence of the observed corrosion rate of the zinc at the ph and conductivity of the solution. The corrosion rate is higher in the rainy season compared to eight months of contact of the pile with soil. High sulfate concentrations increase the rate of corrosion. The meb analysis shows that the fluctuation zone of the water table is the most corroded area. Comparison between the different methods of evaluating the corrosion rate showed that the ground water may be used as a representative profile of the chemical environment of a non-cohesive soil and slightly granular.

http://www.theses.fr/2014AGUY0790/document

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
without abstract
ISSN: 0012-821X

hal-00413027
https://hal.archives-ouvertes.fr/hal-00413027
DOI : 10.1016/j.epsl.2008.07.061

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The easternmost part of the Neoproterozoic Araçuaí belt comprises an anatectic domain that involves anatexites (the Carlos Chagas unit), leucogranites and migmatitic granulites that display a well-developed fabric. Microstructural observations support that the deformation occurred in the magmatic to submagmatic state. Structural mapping integrating field and anisotropy of magnetic susceptibility (AMS) revealed a complex, 3D structure. The northern domain displays gently dipping foliations bearing a NW-trending lineation, southward, the lineation trend progressively rotates to EW then SW and the foliation is gently folded. The eastern domain displays E-W and NE-SW trending foliations with moderate to steeply dips bearing a dominantly NS trending lineation. Magnetic mineralogy investigation suggests biotite as the main carrier of the magnetic susceptibility in the anatexites and ferromagnetic minerals in the granulites. Crystallographic preferred orientation (CPO) measurements using the electron backscatter diffraction (EBSD) technique suggest that the magnetic fabric comes from the crystalline anisotropy of biotite and feldspar grains, especially. The delineation of several structural domains with contrasted flow fabric suggests a 3D flow field involving westward thrusting orthogonal to the belt, northwestward orogen-oblique escape tectonics and NS orogen-parallel flow. This complex deformation pattern may be due to interplay of collision-driven and gravity-driven deformations.
ISSN: 0191-8141

hal-00903878
https://hal.archives-ouvertes.fr/hal-00903878
DOI : 10.1016/j.jsg.2013.08.001

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Upper mantle structures and flow related to the South Pacific Superswell and to the associated short-lived hotspots are investigated using seismic stations deployed in French Polynesia. Beside island stations, broadband ocean bottom seismometers ( BBOBS) have been deployed between the various Polynesian archipelagos to investigate the oceanic upper mantle "unperturbed'' by thickened crust or hotspot activity. We investigate seismic anisotropy measured at BBOBS stations and found it rather similar to that from island stations. This confirms the ability of OBS to be used for anisotropy purposes and suggests some homogeneity in the upper mantle pervasive deformation. The two OBS installed on the head of the Society hotspot provide different anisotropy signatures than most of the other French Polynesian stations: one is "isotropic'' to SKS waves and the other provides a fast split direction normal to the average value observed in this area, suggesting a more complex mantle flow induced by the plume upwelling.
ISSN: 0094-8276

hal-00420907
https://hal.archives-ouvertes.fr/hal-00420907
https://hal.archives-ouvertes.fr/hal-00420907/document
https://hal.archives-ouvertes.fr/hal-00420907/file/Barruol_SKS_PLUME_BBOBS_GRL2009.pdf
DOI : 10.1029/2009GL038139

Éditeur(s) : HAL CCSD Royal Society of Chemistry
Résumé : International audience
Abstract View references (60)Here we show the long term performance at high temperatures of a multi-tube module containing 8 membranes in 4 parallel lines with a total of 545 cm 2 area. The membranes were prepared via thin film dip coating of cobalt oxide silica (CoO xSi) sol-gel on tubular alumina supports. A preliminary study found that the sol-gel containing 20 mol% cobalt oxide formed the best microporous structure with the highest surface area and pore volume. All resulting membranes delivered permeances of ∼1 × 10 -7 mol m -2 s -1 Pa -1 at 500 °C, indicating a high repeatability for the membrane fabrication process. The permselectivities of helium (He) and hydrogen (H 2) over carbon dioxide (CO 2) and nitrogen (N 2) increased from 10-20 at 100 °C to values close to 1000 at 500 °C. Additionally, the apparent energies of activation (E act) for the smaller kinetic diameter gases He and H 2 at 12.2 and 19.5 kJ mol -1 were high and contrary to the negative values for larger gases N 2 and CO 2 at -1.8 and -7.4 kJ mol -1. These remarkable results were attributed to the molecular sieving mechanism of the microporous silica which was enhanced by the embedding of cobalt oxide into the matrix, delivering structural control with an average pore size of 3 Å. The E act for H 2 permeance was higher than that of He, indicating that the cobalt oxide played an important role in H 2 transport. Two membrane lines performed exceptionally well for binary gas mixture processing with H 2 purity reaching values close to 100% in the permeate stream for argon (Ar) concentrations of up to 80% in the retentate stream. A major finding here is that the binary gas selectivity was independent of temperature, contrary to the permselectivity observed for single gas permeance. Further, the H 2 flow rate was greatly affected by the concentration of Ar in the mixture, while the temperature dependency played only a marginal role. In particular, competitive adsorption in the percolative pathways containing pore constrictions or bottlenecks of the anisotropic CoO xSi matrix allowed Ar to impede H 2 diffusion. Finally, the CoO xSi membranes proved thermally stable and robust for 2000 h of testing for various thermal cycles up to 500 °C. © The Royal Society of Chemistry 2012.
Energy & Environmental Science

hal-01683199
https://hal.univ-antilles.fr/hal-01683199
DOI : 10.1039/c2ee03247c

Éditeur(s) : HAL CCSD
Résumé :  
The main aspects of wood mechanics are approached through the role played by wood as the building material of the tree. The main concepts used by nature: progressive setting up of tree weight and architecture, multifunctional role of wood and adaptability to hazard and long-term evolution, are clarified together with their consequence on the multilayered, anisotropic nature of wood. The technological choices of the plant world as the cellular structure, the use of composite with oriented fibres and hydro-carbonated polymers, as well as the systematic prestressing of every new layer, bear obvious consequences on the type of mechanical behaviour of wood. The local control of the level of prestressing through minor modifications of the cell-wall biosynthesis allows the tree to adapt to conditions of light exploration that will evolve according to time and risk occurrence. This analysis of wood genesis process permits in return to improve our understanding of the mechanical behaviour of the material in relation with the parameters of the microstructure.
Comptes Rendus de l'Académie des Sciences Série 2

hal-01032151
https://hal.archives-ouvertes.fr/hal-01032151
DOI : 10.1016/S1620-7742(01)01380-0

Éditeur(s) : HAL CCSD Elsevier
Résumé : We have studied the phase transformation of forsterite to wadsleyite under shear stress at the Earth's transition zone pressure and temperature conditions. Two-step experiments were performed using a multi-anvil press. First, we hot pressed iron-free forsterite at 6 or 11 GPa and 1100 degrees C. Then we deformed a slab of this starting material using a direct simple shear assembly at 16 GPa and 1400 degrees C for 1, 15, 35, 40, or 60 min. Both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations (CPO) by electron back scattered diffraction (EBSD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). The phase transformation occurs very rapidly, in less than 1 min, and metastable forsterite relics are not observed after deformation. The grain size of wadsleyite is slightly smaller than the forsterite starting material. The water contents obtained from FTIR analyses in forsterite and wadsleyite are 65-124 wt ppm H2O and 114-736 wt ppm H2O, respectively, which are well below water solubility at similar conditions in the presence of free water. Wadsleyite aggregates display weak CPO patterns with [1 0 0] axes concentrated at low angle to the shear direction, [0 1 0] axes perpendicular to the shear plane and nearly random [0 0 1] axes. Only a few dislocations were observed in wadsleyite with TEM. This observation is consistent with the assumption that most dislocations formed during the initial high-stress stages of these stress-relaxation experiments, were consumed in the phase transformation, probably enhancing the transformation rate. CPO patterns vary as a function of the water content: with increasing water content the density of [1 0 0] axes parallel to the shear direction decreases, and the density of [0 0 1] axes increases. Viscoplastic self-consistent modeling of CPO evolution using previously reported glide systems for wadsleyite, i.e., [1 0 0]{0 k 1} and 1/2 (1 1 1){1 0 1}, cannot reproduce the measured CPO, unless the [0 0 1](0 1 0) system, for which dislocations have not been observed by TEM, is also activated. In addition, wadsleyite grain growth suggests the participation of diffusion-assisted processes in deformation. Calculated anisotropies for P and S-waves using measured CPO are always below 1%. This very low anisotropy is due to both the low finite strain achieved in the experiments, which leads to weak wadsleyite CPO, and to the diluting effect of added majorite. The present experiments emphasize the importance of stress, grain size evolution and water content in the forsterite to wadsleyite phase transformation and subsequent deformation in the transition zone.
ISSN: 0031-9201

hal-00617430
https://hal.archives-ouvertes.fr/hal-00617430
DOI : 10.1016/j.pepi.2010.11.001

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We determine the elasticity of FeSiO3 perovskite for various spin configurations using density-functional theory calculations. The elastic moduli and the bulk seismic wave velocities are weakly affected by the spin transition. However we show that the intrinsic differences in seismic anisotropy between the high-spin and low-spin phases of Fe-bearing perovskite coupled with lattice preferred orientation that can develop due and during the convection may lead to distinct seismic signatures between the top and the bottom of the lower mantle. These signatures should be detectable in observations and they need to be taken into account in tomographic studies of the Earth's lower mantle.
ISSN: 0094-8276

hal-00512662
https://hal.archives-ouvertes.fr/hal-00512662
DOI : 10.1029/2010GL043320

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
We present a new interpretation of anisotropy of magnetic susceptibility (AMS) fabrics in basaltic lava flows based on the detailed study of magnetic mineralogy and silicate crystallographic fabric of a Quaternary lava flow from the French Massif Central (La Palisse). We consider the model of AMS fabric imbrication between magnetic foliation and flow surface, as initially proposed for dykes. At the two sampling sites, the concordance between the flow direction deduced from the AMS foliation and that deduced from field observations indicates that the imbrication model could apply to the lava flows. However, the flow senses inferred fromAMSare systematically opposed between the two sampling sites suggesting permutations between K1 and K3 AMS axes, a configuration referred to as inverse fabric. Electron backscatter diffraction (EBSD) measurements show strong lattice-preferred orientations (LPO) for plagioclase, especially the (010) plagioclase plane, which tends to be parallel to the flow. Clinopyroxene LPO remains less marked than plagioclase LPO, whereas titanomagnetite does not display a significant LPO. Comparison between magnetic and crystallographic fabrics suggests that the AMS fabric of the lava flow results from the distribution of titanomagnetite grains, which is in turn controlled by the fabric of the silicate framework. Magnetic hysteresis parameters and anisotropy of remanent magnetization (ARM) measurements exclude a significant contribution from single-domain grains, often called upon to explain inverse magnetic fabrics. The origin of the observed inverse magnetic fabric may relate to the dip of the palaeosurface, which is the only remarkable difference between the two sampling sites. AMS appears as a good tool to determine the direction of basaltic lava flows and coupling with local crystallographic fabric data provides a valuable control of relationships between magnetic fabrics and flow and thus contributes to better constrain the AMS signature of lava flows.
ISSN: 0956-540X

hal-00903561
https://hal.archives-ouvertes.fr/hal-00903561
https://hal.archives-ouvertes.fr/hal-00903561/document
https://hal.archives-ouvertes.fr/hal-00903561/file/TB-GJI-193-2-Orig.pdf
DOI : 10.1093/gji/ggs115

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : This study describes normal fault zones formed in foreland arkosic turbidites (the Grès d'Annot Formation, SW French Alps) under deep diagenesis conditions (~200 °C) and highlights the occurrence of two markedly different fault-rock types: (1) the foliated fault rocks of the Moutière-Restefond area; and (2) the dilatant fault rocks of the Estrop area. The deformation of (1) is dominated by intra- and transgranular fracturing, pressure solution of quartz and feldspar grains and syn-kinematic phyllosilicate precipitation resulting from feldspar alteration. The combination of these mechanisms results in a strongly anisotropic strain with intense shortening normal to the foliation (pressure solution) and extension parallel to the foliation (quartz- and calcite-sealed extension veins). This deformation implies local mass transfer that may be achieved without (or with limited) volume change. The deformation of (2) is expressed as dilatant quartz-sealed veins and breccia textures in which the main mechanisms are transgranular fracturing and quartz precipitation. Type (2) implies fault volume increase, isotropy of deformation and mass transfer at distances larger than in type (1). This study discusses the origins of (1) and (2) and shows that the permeability of (1) is anisotropic, with higher values than the host rocks parallel to the Y main deformation axis (i.e. perpendicular to the slip vector), whereas the permeability of (2) is isotropic and equivalent to that of the host rocks.
ISSN: 0954-4879

hal-01115177
https://hal.archives-ouvertes.fr/hal-01115177
DOI : 10.1111/ter.12100