Éditeur(s) : HAL CCSD Springer-Verlag
Résumé : The seismology is the most effective method to explore the Structure of subduction zones to great depth. The distinguishing feature of the mantle in the subduction regions is the presence of hydrated phases, which transport water into the Earth's interior and release it with dramatic local consequences, triggering earthquakes and melting. The seismological detection of these hydrous phases and geo-dynamic interpretation of flow in the hydrous mantle depend on knowledge of the anisotropic elastic properties and the characteristics of the wave propagation in anisotropic media. In this paper we briefly recall the distinguishing features of anisotropic wave propagation and the observable parameters. We suggest the Vp/Vs ratio is a physically sound parameter than can be observed by seismology in anisotropic regions of the Earth, whereas the Poisson's ratio, which is often quoted, is not directly observable and does not correspond to the characteristics of wave propagation in an anisotropic or isotropic medium. We report for the first time the ratios of Vp/Vs1 and Vp/Vs2, where Vs1 is the fastest and Vs2 slowest S-wave velocities of an anisotropic media. We present the current knowledge of the anisotropic seismic properties of hydrous minerals in the upper mantle, transition zone, and lower mantle that are stable along low temperature geotherms associated with subduction, and identify which minerals are likely to influence seismological observations because they have very high volume fractions, or very high anisotropies, or both of these.;In the upper mantle antigorite and talc are exceptionally anisotropic (Vp 71% Vs 68% and Vp 65%, Vs 68%, respectively) and chlorite is also very anisotropic for S-waves (Vp 35%, Vs 76%). Comparatively less anisotropic are hornblende (Vp 27%, Vs 31%), used as proxy for tremolite in subduction zones, and clinohumite (21.8%, Vs 15.9%). Brucite at 4 GPa (Vp 26.5%, Vs 30.9%) and the dense hydrogen magnesium silicate (DHMS) phase A at 9GPa (Vp 9.3%, Vs 17.6%) are the only hydrous minerals stable in the upper mantle that have had their elastic properties measured at in situ mantle pressures. Except for the phase A, all these minerals are more anisotropic than olivine for at least one parameter (Vp, Vs, Vp/Vs1, or Vp/Vs2). In the transition zone the major phases hydrous wadsleyite and ringwoodite C have moderate to weak anisotropies (Vp 16.3%, Vs 16.5%, and Vp 1.9%, Vs 4.4%, respectively). The DHMS Superhydrous B has a moderate anisotropy (Vp 6.9%, Vs 11.6%). At greater depth the DHMS phase D Lit 24 GPa (Vp 10.8%, Vs 18.0%) is the only hydrous phase that can transport hydrogen from the transition zone into the lower mantle. The phase D is more anisotropic for S than P waves like many of the hydrous phases. From these data it is clear that hydrous phases are in general very anisotropic. However, pressure can play a strong role in reducing anisotropy. It is the case for brucite and talc, in which increasing pressure from ambient to 4 GPa reduces the anisotropy by about 50% for both P and S waves. In contrast, the anisotropy of the DHMS phase A does not change significantly with pressure.;Our picture of the seismic anisotropy of hydrated minerals remains incomplete; the elastic properties of many have not been measured even at ambient conditions (e.g., 10 angstrom phase and phase E) or not measured in their true elastic symmetry (e.g., clinochlore). The majority of hydrous minerals have not been measured at high pressure. and none related to hydrated mantle have been measured at elevated temperature. We have shown in the few cases where hydrous minerals have been measured as a function of pressure, that this variable has an important effect oil the velocity distribution and in most cases reduces the degree of anisotropy, hence we Would expect seismic anisotropy to play a key role in the determination of the shallow structure of subduction zones in the upper mantle.
Subduction zone geodynamics

hal-00420893
https://hal.archives-ouvertes.fr/hal-00420893

Éditeur(s) : HAL CCSD American Physical Society
Résumé : We study the equilibrium properties of a liquid phase condensed at the nanoscale between the surfaces of a sharp crack in fused silica in a moist controlled atmosphere. The extension of the condensed phase along the fracture is measured by in situ atomic force microscopy phase imaging and it is shown to be determined by a critical distance between the opposite crack surfaces, which is an increasing function of humidity. The present technique is very promising for measuring the properties of confined liquids at the nanoscale as well as for modeling the physics and chemistry of slow crack propagation in glasses.
ISSN: 0031-9007

hal-00411946
https://hal.archives-ouvertes.fr/hal-00411946
DOI : 10.1103/PhysRevLett.100.165505

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Predicting the impact of underground engineering on the environment requires the knowledge of natural media at different scales. In particular, understanding basic phenomena controlling the properties of rocks in the presence of complex fluids necessitates a detailed atomic description of the solid/fluid/solid contacts, the subject of Part I of the present study. First, building the solid interspace between two different crystals in a non-periodic situation is achieved using the ab initio and molecular mechanics code GenMol (TM). A description of the fluid confined within the interspace is then derived from the original genetic iterative multi-species (GIMS) algorithm implemented in the same code. This approach consists of equilibrating chemical potentials, cycle after cycle and species after species, between the confined fluid and the free natural fluid. An elementary iteration for a species k consists of different steps incrementing the number N-k of particles k, with other numbers N-k remaining constant. At each step, an optimum fluid composition is obtained by a genetic process distributing the fluid particles on a grid by stochastic shots, followed in fine by a refining process. The effectiveness of the GIMS approach is demonstrated in the case study of a fluid confined between two (0 0 1) kaolinite faces, with apertures h varying between 4 and 10 A. connected to a 9-species external solution [H2O, Cl-, Na+ CO2(aq), NaCl(aq), Ca2+, Mg2+, HCO3-, H3O+] where concentrations are ranging from 55 to 10(-4) mol/L. The results show a drastic variation in the solute/solvent and cations/ions ratios in the confined fluid when aperture h is lowered to less than 1 nm. These results obtained with a very rapid convergence of the iterative algorithm combined with a very competitive genetic optimizer are validated with high precision on a free solution. This description of contacts between crystals is original and unattainable by standard crystal interface approaches. It opens the way to understanding and/or predicting phenomena between crystals in a complex natural environment, such as adhesion or repulsion investigated in the Part II of this study.
ISSN: 0022-0248

hal-00544569
https://hal.archives-ouvertes.fr/hal-00544569
DOI : 10.1016/j.jcrysgro.2010.08.009

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé : International audience
*Context Increased knowledge on diversity in wood properties would have implications both for fundamental research and for promoting a diversification of uses as material. *Aims The objective is to contribute to overcoming the critical lack of data on the diversity of wood dynamic mechanical/viscoelastic vibrational properties, by testing lesser-known species and categorizing sources of variability. *Methods Air-dry axial specific dynamic modulus of elasticity (E'/γ) and damping coefficient (tanδ) were measured on a wide sampling (1792 specimens) of 98 wood types from 79 species. An experimental device and protocol was designed for conducting systematic (i.e. rapid and reproducible) characterizations. *Results Diversity at the specimens' level corroborates the "standard" relationship between tanδ and E'/γ, which is discussed in terms of orientation of wood elements and of chemical composition. Diversity at the species level is expressed on the basis of results for normal heartwood, with specific gravity (γ) ranging from 0.2 to 1.3. Axial E'/γ ranges from 9 to 32 GPa and tanδ from 4×10-3 to 19×10-3. Properties distribution follows a continuum, but with group characteristics. The lowest values of tanδ are only found in certain tropical hardwoods. Results can also suggest alternative species for musical instruments making.
Annals of Forest Science

hal-00808242
https://hal.archives-ouvertes.fr/hal-00808242
https://hal.archives-ouvertes.fr/hal-00808242/document
DOI : 10.1007/s13595-011-0166-z

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The lithospheric mantle is intrinsically heterogeneous and anisotropic. These two properties govern the repartition of deformation, controlling intraplate strain localization and development of new plate boundaries. Geophysical and geological observations provide clues on the types, ranges, and characteristic length scales of heterogeneity and anisotropy in the lithospheric mantle. Seismic tomography points to variations in geothermal gradient and hence in rheological behavior at scales of hundreds of km. Seismic anisotropy data substantiate anisotropic physical properties consistent at scales of tens to hundreds of km. Receiver functions imply lateral and vertical heterogeneity at scales < 10 km, which might record gradients in composition or anisotropy. Observations on naturally deformed peridotites establish that compositional heterogeneity and Crystal Preferred Orientations (CPOs) are ubiquitous from the mm to the km scales. These data allow discussing the processes that produce/destroy heterogeneity and anisotropy and constraining the time scales over which they are active. This analysis highlights: (i) the role of deformation and reactive percolation of melts and fluids in producing compositional and structural heterogeneity and the feedbacks between these processes, (ii) the weak mechanical effect of mineralogical variations, and (iii) the low volumes of fine-grained microstructures and difficulty to preserve them. In contrast, olivine CPO and the resulting anisotropy of mechanical and thermal properties are only modified by deformation. Based on this analysis, we propose that strain localization at the plate scale is, at first order, controlled by large-scale variations in thermal structure and in CPO-induced anisotropy. In cold parts of the lithospheric mantle , grain size reduction may contribute to strain localization, but the low volume of fine-grained domains limits this effect.
ISSN: 0040-1951

hal-01277174
https://hal.archives-ouvertes.fr/hal-01277174
DOI : 10.1016/j.tecto.2015.07.026

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Seismic tomography and high surface heat flow models indicate an anomalously thin and hot lithospheric mantle beneath the Canadian Cordillera. To understand the thermal and deformational history of the lithospheric mantle under these conditions, we performed a study of the microstructures, crystal preferred orientations (CPO), and seismic anisotropy of mantle xenoliths collected in the Summit Lake volcano in the southern Canadian Cordillera. The xenoliths vary in composition between spinel lherzolites, cpx-rich lherzolites, and wehrlites. All samples are coarse-grained and show clear evidence for annealing, but deformation microstructures are well-preserved in the spinel lherzolites. Olivine CPO is characterized by a strong point-maximum of [100] and by a girdle distribution of [010[ and [001] axes normal to it; CPO strength is variable, spinel-lherzolites have the strongest CPO. Some samples show a weak orthopyroxene CPO consistent with the olivine one. However most pyroxenes have random CPO, interstitial shapes and undeformed appearance, which suggest a secondary origin by reactive melt percolation under static conditions, leading to crystallization of cpx + sp +/- opx at the expenses of olivine, followed by crystallization of cpx + sp +/- ol at the expenses of opx to produce the wehrlites. The studied xenoliths have typical upper mantle seismic properties patterns with fastest propagation of P-waves and polarization of S-waves parallel to the olivine [100] maxima. Maximum P- and S-waves anisotropy for lherzolites are 8 and 5% respectively. Dispersion of the olivine CPO due to neocrystallization of olivine results in weaker anisotropies (6.5 and 3.5%) in wehrlites. Seismic velocities calculated using a geotherm consistent with the equilibrium temperatures of the Summit Lake xenoliths are 3-4% lower than those expected in a normal, 100 km-thick lithosphere, consistent with seismic tomography models for the region. This high geothermal gradient may be partially explained by considering the anisotropy of thermal conductivity of olivine and subhorizontal foliations in the lithospheric mantle, which result in a decrease by up to 15% of the thermal conductivity in the vertical direction.
ISSN: 0040-1951

hal-00618332
https://hal.archives-ouvertes.fr/hal-00618332
DOI : 10.1016/j.tecto.2011.04.014

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 American Geophysical Union
Résumé : International audience
Rheological properties of mantle minerals and rocks at temperatures (T) appropriate to much of Earth's lithosphere have remained poorly constrained, even though past experimental studies on olivine single crystals and polycrystalline aggregates have quantified the high-temperature creep mechanisms (T > 1200 degrees C). Consequently, we have performed deformation experiments on crystals of San Carlos olivine at lower temperatures, from 900 degrees to 1200 degrees C, in triaxial compression along the [101](c) direction. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at differential stresses of 100 to 500 MPa. Several samples were deformed at constant displacement rate and others at constant load, in order to provide insight into possible effects of work-hardening. Under the deformation conditions investigated, little evidence of work-hardening was observed. The data follow a power-law dependence on stress, as in previous high-temperature deformation studies. The samples were, however, considerably weaker than predicted by the experimentally determined high-temperature constitutive equation for olivine crystals of this orientation from the study of Bai et al. (1991). The mechanical behavior correlates instead with the weaker of the two mechanisms (flow laws) that contribute to the high-temperature constitutive equation. Thus, our experiments demonstrate that published high-temperature constitutive equations overestimate the strength of lithospheric mantle and that the transition to low-temperature creep occurs at lower temperatures than previously inferred. Citation: Demouchy, S., S. E. Schneider, S. J. Mackwell, M. E. Zimmerman, and D. L. Kohlstedt (2009), Experimental deformation of olivine single crystals at lithospheric temperatures, Geophys. Res. Lett., 36, L04304, doi: 10.1029/2008GL036611.
ISSN: 0094-8276

hal-00420070
https://hal.archives-ouvertes.fr/hal-00420070
DOI : 10.1029/2008GL036611

Résumé : Le fluide chaud produit par les forages de la centrale géothermique de Bouillante (Guadeloupe) est enrichi en espèces dissoutes telles que la silice qui peuvent précipiter sous forme de dépôts solides lors de son refroidissement et gêner fortement la production électrique. L’un des principaux objectifs de ce travail de thèse a donc été d’améliorer l’état des connaissances sur les conditions physiques, chimiques et cinétiques de la précipitation de la silice amorphe à Bouillante. Après une étude des caractéristiques physico-chimiques des fluides et des dépôts associés au champ de Bouillante, des expériences sur la cinétique de précipitation de la silice, sur site, pour une large gamme de température (25 - 90°C) et de pH (4 - 12) ont été menées et analysées en détail.Pour l’ensemble de ces expériences, seule la polymérisation (réversible) de la silice dissoute, sous forme de suspensions colloïdales très stables en solution, a été observée. La modélisation des données expérimentales de cinétique montre que la vitesse de polymérisation de la silice suit une loi d’ordre 2 vis-à-vis de la silice dissoute jusqu’à l’équilibre en accord avec une dimérisation de la silice. Par contre, durant l’étape initiale de la réaction, une loi d’ordre 4 semble mieux adaptée, suggérant des réactions de polymérisation plus complexes avec formation de tétramères. La température a un effet limité sur la cinétique de polymérisation de la silice comparé à l’effet du pH qui est beaucoup plus important. L’énergie d’activation de la réaction globale est de 41 - 54 kJ pour des pH compris entre 5 et 8.La caractérisation de la silice précipitée a mis en évidence des différences notables entre la structure poreuse de la silice solide prélevée sur les installations de surface et celle de la silice colloïdale obtenue par polymérisation lors des expériences de cinétique, ce qui semble indiquer que des mécanismes différents interviennent dans ces deux contextes de précipitation de la silice dissoute.Le deuxième objectif de cette thèse était d’évaluer la possibilité de valoriser la silice extraite de l’eau géothermale de Bouillante dans un procédé de traitement des eaux naturelles par adsorption. Pour cela, les propriétés d’adsorption de la silice géothermale brute et fonctionnalisée par le poly(ethylèneimine) (ou PEI) ont été étudiées pour deux polluants : un colorant, le bleu de méthylène et un métal lourd, le plomb. Les résultats obtenus montrent que la silice brute possède une grande capacité d’adsorption vis-à-vis du bleu de méthylène. En outre, la fonctionnalisation de la silice par le PEI permet d’améliorer sa capacité d’adsorption vis-à-vis du plomb en solution, en accord avec un modèle cinétique du pseudo-second ordre suggérant une chimisorption. Le modèle d’isotherme de Redlich-Peterson est également en très bon accord avec les données expérimentales.
The hot geothermal fluid produced by the geothermal power plant of Bouillante (Guadeloupe) contains various dissolved components such as silica that can precipitate as solid deposits during their cooling and cause serious problems on the electricity generation. One of the aim of this study is to improve the understanding on the physical, chemical and kinetics conditions of the amorphous silica precipitation in the Bouillante geothermal field. After a study on the physical and chemical characteristics of the Bouillante fluids and deposits which can form during their exploitation, experiments on the kinetics of silica precipitation, on site, under a large range of temperature (25 – 90°C) and pH (4 – 12) have been carried out and analyzed in detail.During on site kinetics experimentations only dissolved silica polymerization (reversible) as colloidal gel, very stable in solution, was observed. Modeling of the experimental data showed that the kinetics polymerization is characterized by a 2-order kinetic law relative to dissolved silica until the equilibrium that is consistent with silica dimerization. On the other side, the initial stage of the reaction is better characterized by a 4-order kinetic law that suggested more complex polymerization reactions with tetramers formation.Temperature has a little effect on the polymerization kinetics compared with the pH which has an effect more important. The activation energy of silica precipitation calculated between 25 and 90°C, is about 41 - 54 kJ for pH ranging to 5 - 8.The characterization of the silica precipitate reveals significant differences in the porous structure of the silica collected on the surface installations and the one obtained from kinetic experiments that suggests different precipitation mechanisms. The second objective of this thesis was to evaluate the possibility to promote geothermal silica for the treatment of natural waters containing contaminants by adsorption. Adsorption properties of the untreated and functionalized by poly(ethylèneimine) (ou PEI) geothermal silica have been investigated for two pollutants: a colorant, the methylene blue and a heavy metal, the lead.Results showed that untreated silica has a great adsorption capacity concerning the methylene blue. Besides, silica functionalization by the PEI allows improving the adsorption capacity for lead in solution. The adsorption kinetics curves followed a pseudo-second order model consistent with a chimisorption. The isotherm model of Redlich-Peterson fitted well the experimental data.

http://www.theses.fr/2014AGUY0698/document

Éditeur(s) : HAL CCSD
American Geophysical Union, Fall Meeting 2009
San Francisco, United States

hal-00483586
https://hal.archives-ouvertes.fr/hal-00483586

Éditeur(s) : HAL CCSD
Résumé : International audience
In many geological reservoirs, open fractures or fault zones generally induce high spatial variability of hydrodynamical properties and shape the main deep-seated flow paths. It is of crucial interest to determine their structure and properties in order to achieve a sound and sustained exploitation of resources or to estimate the risk of failure of any underground storage. Tiltmeters have emerged as new tools to observe deformation generated by groundwater flow. As such instruments are highly sensitive to pressure gradients, they are perfectly suited for monitoring channelized flow in connected fractures and fault zones. Hence, they provide a unique insight of these reservoirs' geometry and dynamics over broad time scales. Here we demonstrate that continuous tilt data from surface long baseline tiltmeters (LBT) can be used alone to evaluate the general functioning of a fractured hardrock system and estimate the hydraulic properties of its main conductive features. The study is applied to the pumping site of Ploemeur observatory (Brittany, France) which is well documented and instrumented, and therefore forms a convenient setting for introducing LBT as tools for fractured media hydrology. On the short term, tilt signals are strongly correlated with pumping cycles and associated head level changes in well-connected boreholes. Besides, when pumps are stopped the maximal tilt direction is systematically perpendicular to a subvertical fault zone whose azimuth of strike has thereby been refined down to degree precision. By using a semi-analytical model of deformation, we establish the link between tilt and pressure change during pumping interruptions which then allows for hydraulic properties estimation from tilt measurements only. Finally, we validate our results with previous estimates obtained from other studies and discuss the orientation of future work that could enhance these estimates.
AGU Fall Meeting 2014
San Francisco, United States

insu-01093437
https://hal-insu.archives-ouvertes.fr/insu-01093437

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Functional ecology has long considered the support function as important, but its biomechanical complexity is only just being elucidated. We show here that it can be described on the basis of four biomechanical traits, two safety traits against winds (SW) and self-buckling (SB), and two motricity traits involved in sustaining an upright position, tropic motion velocity (MV) and posture control (PC). All these traits are integrated at the tree scale, combining tree size and shape together with wood properties. The assumption of trait constancy has been used to derive allometric scaling laws, but it was more recently found that observing their variations among environments and functional groups, or during ontogeny, provides more insights into adaptive syndromes of tree shape and wood properties. However, over-simplified expressions have often been used, possibly concealing key adaptive drivers. An extreme case of over-simplification is the use of wood basic density as a proxy for safety. Actually, since wood density is involved in stiffness, loads and construction costs, the impact of its variations on safety is non-trivial. Moreover, other wood features, especially the microfibril angle (MFA), are also involved. Furthermore, wood is not only stiff and strong, but it also acts as a motor for MV and PC. The relevant wood trait for that is maturation strain asymmetry. Maturation strains vary with cell wall characteristics such as MFA, rather than with wood density. Finally, the need for further studies about the ecological relevance of branching patterns, motricity traits and growth responses to mechanical loads is discussed.
ISSN: 0022-0957

hal-00909904
https://hal.archives-ouvertes.fr/hal-00909904
https://hal.archives-ouvertes.fr/hal-00909904/document
https://hal.archives-ouvertes.fr/hal-00909904/file/Integrative_biomechanics_for_tree_Fournier_al.pdf
DOI : 10.1093/jxb/ert279

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Homogenization models are widely used to predict the evolution of texture (crystal preferred orientations) and resulting anisotropy of physical properties in metals, rocks, and ice. They fail, however, in predicting two main features of texture evolution in simple shear (the dominant deformation regime on Earth) for highly anisotropic crystals, like olivine: (1) the fast rotation of the CPO towards a stable position characterized by parallelism of the dominant slip system and the macroscopic shear and (2) the asymptotical evolution towards a constant intensity. To better predict CPO-induced anisotropy in the mantle, but limiting computational costs and use of poorly-constrained physical parameters, we modified a viscoplastic self-consistent code to simulate the effects of subgrain rotation recrystallization. To each crystal is associated a finite number of fragments (possible subgrains). Formation of a subgrain corresponds to introduction of a disorientation (relative to the parent) and resetting of the fragment strain and internal energy. The probability of formation of a subgrain is controlled by comparison between the local internal energy and the average value in the polycrystal. A two-level mechanical interaction scheme is applied for simulating the intracrystalline strain heterogeneity allowed by the formation of low-angle grain boundaries. Within a crystal, interactions between subgrains follow a constant stress scheme. The interactions between grains are simulated by a tangent viscoplastic self-consistent approach. This two-level approach better reproduces the evolution of olivine CPO in simple shear in experiments and nature. It also predicts a marked weakening at low shear strains, consistently with experimental data.
ISSN: 0012-821X

hal-01243503
https://hal.archives-ouvertes.fr/hal-01243503
DOI : 10.1016/j.epsl.2015.08.018

Éditeur(s) : HAL CCSD
Résumé : This work provides new constraints on the interactions between deformation and percolation of melt or fluids, as well as on the implications of these processes for the seismic properties of the mantle wedge. It is based on the analysis of spinel peridotites from the massif of Ronda (Spain) and two xenolith suites from active subduction zones (Kamchatka, Papua New Guinea). A coupled structural, petrological and geochemical study of these samples shows that they underwent a reactive percolation of melts or Si-rich fluids, which was synchronous to a deformation event occurring under high temperature and low stress conditions, consistent with the PT conditions at the base of the lithosphere or in the asthenosphere. This reactive percolation is responsible for enrichment in pyroxenes, mainly orthopyroxene, which is often localized in bands parallel to the high-temperature foliation. This enrichment is associated with grain size reduction and dispersion of the crystallographic orientation of olivine. The dominant slip system in olivine is {0kl}[100], which results in fast S-wave polarization parallel to the flow direction in the mantle. The decrease in the intensity of the olivine crystal preferred orientations associated with the enrichment in pyroxene results in significant decrease of the anisotropy that may induce an underestimation of the thickness of the anisotropic layer by up to 33%. The observed orthopyroxene enrichment also lowers the Vp/Vs ratio, but cannot explain Vp/Vs < 1.7 mapped locally in the fore-arc mantle in Japan and the Andes. Such low Vp/Vs ratios may however be explained by considering the intrinsic anisotropy of the peridotites, which is generally ignored in large-scale Vp/Vs ratio mapping of the mantle wedge. Infrared analyses show that olivine from the both xenolith collections contains less water than the theoretical saturation calculated for their estimated equilibrium temperature in the spinel stability field. These low water content are similar to those observed in spinel peridotites from other subduction zones and probably record both the low solubility of water in olivine at relatively low pressure and dehydration during exhumation of the xenoliths. These measured water contents as well as theoretical saturation estimations are not sufficient to change the dominant slip direction of in olivine from [100] to [001].
Ce travail apporte de nouvelles contraintes sur les interactions entre déformation et processus d'hydratation et de percolation de magma ou de fluides dans le manteau à l'aplomb d'une zone de subduction et leurs implications sur les propriétés sismiques dans le coin mantellique. Il se base sur l'analyse de péridotites à spinelle provenant du massif de Ronda (Espagne) et deux séries de xénolites issues de zones de subduction actives (Kamchatka, Papouasie-Nouvelle-Guinée). L'étude structurale, pétrologique et géochimique de ces échantillons montrent qu'ils ont subit une percolation réactive de magma ou de fluide synchrone d'une déformation de haute température basse contrainte cohérente avec les condition PT de la base de la lithosphère ou de l'asthénosphère. Cette percolation réactive est responsable d'un enrichissement en pyroxènes, qui est souvent localisé dans des bandes parallèles à la foliation. Cet enrichissement est associé à une dispersion de l'orientation cristallographique de l'olivine. Les systèmes de glissement dominant dans l'olivine sont dans tous les cas {0kl}[100], ce qui implique que la direction de polarisation rapide des ondes S dans la partie supérieure du coin mantellique est parallèle à la direction d'écoulement dans le manteau. La décroissance de l'intensité des OPR de l'olivine associée à l'enrichissement en pyroxènes a pour conséquence une réduction non négligeable de l'anisotropie sismique qui peut induire jusqu'à 33% d'erreur sur l'interprétation de l'épaisseur de la couche anisotrope. Un enrichissement en orthopyroxène peut aussi entraîner une baisse du rapport Vp/Vs, mais ne peut expliquer les rapports Vp/Vs <1,7 cartés dans certains avant-arcs. Cependant de telles valeurs peuvent être expliquées si l'anisotropie des péridotites du coin mantellique est prise en compte. Les analyses par spectroscopie infra-rouge montrent que les olivines des deux séries de xénolites étudiées contiennent moins d'eau que la saturation théorique calculée pour leurs températures d'équilibre dans le domaine du spinelle. Ces faibles concentrations en eau sont similaires à celles observées dans les olivines des péridotites à spinelle des autres zones de subduction. Elles enregistrent probablement la faible solubilité de l'eau dans l'olivine à des pressions relativement basses et la déshydratation au cours de l'exhumation des xénolites. Ces teneurs en eau mesurées ainsi que les estimations de la saturation théorique ne sont pas suffisantes pour changer la direction de glissement dominante dans l'olivine de [100] à [001].
https://tel.archives-ouvertes.fr/tel-00689832

tel-00689832
https://tel.archives-ouvertes.fr/tel-00689832
https://tel.archives-ouvertes.fr/tel-00689832/document
https://tel.archives-ouvertes.fr/tel-00689832/file/These-Soustelle2010.pdf

Éditeur(s) : HAL CCSD CRC Press
Résumé : Among the ecosystem services provided by forests, wood provisioning takes a central position. Wood and derived products have played a critical role in the evolution of human kind and demand for raw material is increasing in a foreseeable future. Wood is used for energy production, construction and a wide variety of products for which different properties are required. Anatomical, chemical and physical properties of wood are determined through a complex process called xylogenesis controlled by internal and external signals and occurring during the life of the tree. In this chapter we describe i/how wood is formed and ii/the different factors controlling this developmental process with emphasis on the molecular machinery involved, iii/the functions of wood and iv/the biotechnology approaches developed to improve wood biomass production and properties genetically.
Tree Biotechnology

ISBN : 978-1466597143
hal-01032436
https://hal.archives-ouvertes.fr/hal-01032436

Éditeur(s) : HAL CCSD
Résumé : International audience
Some morphological and biochemical taxonomic markers are also affecting factors of dynamic mechanical properties of wood. Thus, could these properties reflect the classification/phylogeny of taxa? This work is a first insight into this question. It relied on the gathering (through experimental campaigns and exhaustive literature review) of a large database on the viscoelastic (i.e. including damping) vibrational properties of 445 woody species. relationship between damping was confirmed at a wide interspecific scale, but described no more than 40% of not in a way that could be easily related to the phylogenetic tree. Damping was a bit more -Papilionoideae and, to a lesser extent, Lauraceae, Cupressaceae and Moraceae) damping than average, independently While for some other families no clear characteristics could be observed at least with the present number of represented species. In the future, increasing the amount of data and compiling anatomical and chemical markers / affecting factors will allow further analysis at sub-family levels, and a better understanding of this wide topic.
6th Plant Biomechanics Conference PBM09
Cayenne, French Guiana

hal-00808398
https://hal.archives-ouvertes.fr/hal-00808398
https://hal.archives-ouvertes.fr/hal-00808398/document
https://hal.archives-ouvertes.fr/hal-00808398/file/Mechanical_damping_wood_Bremaud_al.pdf

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : This paper presents the background for the calculation of physical properties of an aggregate from constituent crystal properties and the texture of the aggregate in a coherent manner. Emphasis is placed on the important tensor properties of 2nd and 4th rank with applications in rock deformation, structural geology, geodynamics and geophysics. We cover texture information that comes from pole figure diffraction and single orientation measurements (electron backscattered diffraction or EBSD, electron channelling pattern, Laue pattern, optical microscope universal-stage). In particular, we provide explicit formulae for the calculation of the averaged tensor from individual orientations or from an orientation distribution function (ODF). For the latter we consider numerical integration and an approach based on the expansion into spherical harmonics. This paper also serves as a reference paper for the mathematical tensor capabilities of the texture analysis software MTEX, which is a comprehensive, freely available MatLab toolbox that covers a wide range of problems in quantitative texture analysis, for example, ODF modelling, pole figure to ODF inversion, EBSD data analysis and grain detection. MTEX offers a programming interface which allows the processing of involved research problems as well as highly customizable visualization capabilities; MTEX is therefore ideal for presentations, publications and teaching demonstrations.
Deformation Mechanisms, Rheology and Tectonics: Microstructures, Mechanics and Anisotropy

hal-00688833
https://hal.archives-ouvertes.fr/hal-00688833

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Radial trends of vibrational properties, including the specific dynamic modulus (E'/r) and damping coefficient (tand), were investigated for 3 tropical rainforest hardwood species, Simarouba amara, Carapa procera and Symphonia globulifera by free-free flexural vibration test. The microfibril angle (MFA) was estimated through X-Ray diffraction. Consistent patterns of radial variations were observed for all studied properties. E'/r was found to decrease from pith to bark, which is strongly related to the increasing pith-bark trend of MFA. The variation of tand along the radius can be partly explained by MFA, and partly by the gradient of extractives due to heartwood formation. The coupling effect of MFA and extractives could be separated through the analysis of log(tand) - log(E'/r) diagram. For the studied species, the extractive content putatively associated to heartwood formation generally tends to decrease the wood damping coefficient. However, this weakening effect of extractives was not observed for inner part of the heartwood, suggesting the mechanical action of extractives was reduced during their chemical ageing.
ISSN: 1435-0211

hal-00797055
https://hal.archives-ouvertes.fr/hal-00797055
https://hal.archives-ouvertes.fr/hal-00797055/document
https://hal.archives-ouvertes.fr/hal-00797055/file/Radial_variations_vibrational_Zhang_al.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Intrinsic tribological properties of lamellar compounds are usually attributed to the presence of van der Waals gaps in their structure through which interlayer interactions are weak. The controlled variation of the distances and interactions between graphene layers by intercalation of electrophilic species in graphite is used in order to explore more deeply the friction reduction properties of low-dimensional compounds. Three graphite intercalation compounds with antimony pentachloride, iron trichloride and aluminium trichloride are studied. Their tribological properties are correlated to their structural parameters, and the interlayer interactions are deduced from ab initio bands structure calculations.
ISSN: 1023-8883

hal-00767639
https://hal.archives-ouvertes.fr/hal-00767639
https://hal.archives-ouvertes.fr/hal-00767639/document
https://hal.archives-ouvertes.fr/hal-00767639/file/Delbe_6330.pdf
DOI : 10.1007/s11249-012-9981-0

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
A feasibility study of glulam was carried out in French Guiana using local wood species. The aim was to determine gluing parameters affording satisfactory behaviour to manufactured glulam in a tropical climate. Three abundant wood species, with special properties, were selected for the study and Resorcinol-Phenol-Formaldehyde resin was used for bonding. Three industrial parameters were considered: adhesive spread rate, closed assembly time and gluing pressure. Delamination and shearing tests were carried outin accordance with European Standards. The tests revealed the influence of wood properties and manufacturing parameters on joint resistance. In fact, the results showed that specific gravity and the shrinkage coefficientgreatly influenced the gluing step. Indeed, wood with a medium specific gravity needed more adhesive and more pressure than wood with a high specific gravity. In addition, planning and lamella thicknesswere found to affect glue joint resistance.
ISSN: 0018-3768

hal-00856933
https://hal.archives-ouvertes.fr/hal-00856933
https://hal.archives-ouvertes.fr/hal-00856933/document
https://hal.archives-ouvertes.fr/hal-00856933/file/Feasibility_glued_laminated_timber_Bourreau_al.pdf