126 research outputs found
Experimental deformation of olivine single crystals at lithospheric temperatures
No full textInternational audienceRheological 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
Control of intestinal hyperplasia by the PAR-4/LKB1 kinase in Caenorhabditis elegans
No full textLa protéine de polarité et suppresseur de tumeur PAR-4/LKB1 est considérée comme un régulateur majeur de la physiologie intestinale. Son activation ectopique est suffisante pour induire la formation de microvillosités apicales dans des lignées cellulaires intestinales cancéreuses, tandis que des mutations du gène lkb1 sont responsables du syndrome de Peutz-Jeghers (PJS) dans lequel les patients développent des polypes intestinaux bénins. Il est crucial de mieux caractériser son rôle dans les entérocytes in vivo. Pour ce faire, nous avons utilisé la microscopie confocale et électronique pour observer l'épithélium intestinal chez les embryons C. elegans mutants par-4. De manière surprenante, PAR-4 n'est pas strictement requise pour la polarité intestinale et la formation de microvillosités. Cependant, les embryons par-4 présentent des entérocytes supplémentaires, ce qui entraîne des défauts dans l'architecture du tissu, notamment des déformations de la lumière. Des expériences de lignage ont révélé que le nombre excessif d’entérocytes présents dans les embryons par-4 n’est pas induit par une hyperprolifération cellulaire, mais par des défauts de spécification. Alors que dans les embryons contrôles, les entérocytes proviennent tous du blastomère E, dans les embryons par-4, des entérocytes supplémentaires naissent également à partir du blastomère C. Ce travail révèle une nouvelle fonction nécessaire de PAR-4 pour restreindre l’acquisition du destin intestinal au lignage E.The polarity and tumor suppressor protein PAR-4/LKB1 is thought to be a major regulator of intestinal physiology. Its ectopic activation is indeed sufficient to induce apical microvilli formation in intestinal cancer cell lines. Moreover, mutations in the lkb1 gene are responsible for the Peutz-Jeghers syndrome (PJS) in which patients develop benign intestinal polyps. As this master kinase acts via various signaling pathways, it is crucial to better characterize its role in enterocytes in vivo. To do so, we used confocal and electron microscopy to observe the intestinal epithelium in C. elegans par-4 mutant embryos. Surprisingly, PAR-4 is not strictly required for intestinal polarity and microvilli formation. However, par-4 mutant embryos display extra enterocytes, which lead to striking defects in tissue architecture, notably to strong lumen deformations. Lineage experiments revealed that PAR-4 does not control the number of enterocytes by regulating cell proliferation, but rather by controlling cell fate specification during embryogenesis. While in wild type embryos intestinal cells exclusively arise from the E blastomere, in par-4 mutants additional enterocytes arise from the C blastomere. Thus, PAR-4 prevents intestinal specification in the C lineage of wild type embryos. This work reveals a novel function of PAR-4 in the regulation of cell fate specification during embryogenesis. This appears to be essential to prevent intestinal hyperplasia in C. elegans
Contrôle de l’hyperplasie intestinale par la kinase PAR-4/LKB1 chez Caenorhabditis elegans
No full textThe polarity and tumor suppressor protein PAR-4/LKB1 is thought to be a major regulator of intestinal physiology. Its ectopic activation is indeed sufficient to induce apical microvilli formation in intestinal cancer cell lines. Moreover, mutations in the lkb1 gene are responsible for the Peutz-Jeghers syndrome (PJS) in which patients develop benign intestinal polyps. As this master kinase acts via various signaling pathways, it is crucial to better characterize its role in enterocytes in vivo. To do so, we used confocal and electron microscopy to observe the intestinal epithelium in C. elegans par-4 mutant embryos. Surprisingly, PAR-4 is not strictly required for intestinal polarity and microvilli formation. However, par-4 mutant embryos display extra enterocytes, which lead to striking defects in tissue architecture, notably to strong lumen deformations. Lineage experiments revealed that PAR-4 does not control the number of enterocytes by regulating cell proliferation, but rather by controlling cell fate specification during embryogenesis. While in wild type embryos intestinal cells exclusively arise from the E blastomere, in par-4 mutants additional enterocytes arise from the C blastomere. Thus, PAR-4 prevents intestinal specification in the C lineage of wild type embryos. This work reveals a novel function of PAR-4 in the regulation of cell fate specification during embryogenesis. This appears to be essential to prevent intestinal hyperplasia in C. elegans.La protéine de polarité et suppresseur de tumeur PAR-4/LKB1 est considérée comme un régulateur majeur de la physiologie intestinale. Son activation ectopique est suffisante pour induire la formation de microvillosités apicales dans des lignées cellulaires intestinales cancéreuses, tandis que des mutations du gène lkb1 sont responsables du syndrome de Peutz-Jeghers (PJS) dans lequel les patients développent des polypes intestinaux bénins. Il est crucial de mieux caractériser son rôle dans les entérocytes in vivo. Pour ce faire, nous avons utilisé la microscopie confocale et électronique pour observer l'épithélium intestinal chez les embryons C. elegans mutants par-4. De manière surprenante, PAR-4 n'est pas strictement requise pour la polarité intestinale et la formation de microvillosités. Cependant, les embryons par-4 présentent des entérocytes supplémentaires, ce qui entraîne des défauts dans l'architecture du tissu, notamment des déformations de la lumière. Des expériences de lignage ont révélé que le nombre excessif d’entérocytes présents dans les embryons par-4 n’est pas induit par une hyperprolifération cellulaire, mais par des défauts de spécification. Alors que dans les embryons contrôles, les entérocytes proviennent tous du blastomère E, dans les embryons par-4, des entérocytes supplémentaires naissent également à partir du blastomère C. Ce travail révèle une nouvelle fonction nécessaire de PAR-4 pour restreindre l’acquisition du destin intestinal au lignage E
Contrôle de l’hyperplasie intestinale par la kinase PAR-4/LKB1 chez Caenorhabditis elegans
No full textThe polarity and tumor suppressor protein PAR-4/LKB1 is thought to be a major regulator of intestinal physiology. Its ectopic activation is indeed sufficient to induce apical microvilli formation in intestinal cancer cell lines. Moreover, mutations in the lkb1 gene are responsible for the Peutz-Jeghers syndrome (PJS) in which patients develop benign intestinal polyps. As this master kinase acts via various signaling pathways, it is crucial to better characterize its role in enterocytes in vivo. To do so, we used confocal and electron microscopy to observe the intestinal epithelium in C. elegans par-4 mutant embryos. Surprisingly, PAR-4 is not strictly required for intestinal polarity and microvilli formation. However, par-4 mutant embryos display extra enterocytes, which lead to striking defects in tissue architecture, notably to strong lumen deformations. Lineage experiments revealed that PAR-4 does not control the number of enterocytes by regulating cell proliferation, but rather by controlling cell fate specification during embryogenesis. While in wild type embryos intestinal cells exclusively arise from the E blastomere, in par-4 mutants additional enterocytes arise from the C blastomere. Thus, PAR-4 prevents intestinal specification in the C lineage of wild type embryos. This work reveals a novel function of PAR-4 in the regulation of cell fate specification during embryogenesis. This appears to be essential to prevent intestinal hyperplasia in C. elegans.La protéine de polarité et suppresseur de tumeur PAR-4/LKB1 est considérée comme un régulateur majeur de la physiologie intestinale. Son activation ectopique est suffisante pour induire la formation de microvillosités apicales dans des lignées cellulaires intestinales cancéreuses, tandis que des mutations du gène lkb1 sont responsables du syndrome de Peutz-Jeghers (PJS) dans lequel les patients développent des polypes intestinaux bénins. Il est crucial de mieux caractériser son rôle dans les entérocytes in vivo. Pour ce faire, nous avons utilisé la microscopie confocale et électronique pour observer l'épithélium intestinal chez les embryons C. elegans mutants par-4. De manière surprenante, PAR-4 n'est pas strictement requise pour la polarité intestinale et la formation de microvillosités. Cependant, les embryons par-4 présentent des entérocytes supplémentaires, ce qui entraîne des défauts dans l'architecture du tissu, notamment des déformations de la lumière. Des expériences de lignage ont révélé que le nombre excessif d’entérocytes présents dans les embryons par-4 n’est pas induit par une hyperprolifération cellulaire, mais par des défauts de spécification. Alors que dans les embryons contrôles, les entérocytes proviennent tous du blastomère E, dans les embryons par-4, des entérocytes supplémentaires naissent également à partir du blastomère C. Ce travail révèle une nouvelle fonction nécessaire de PAR-4 pour restreindre l’acquisition du destin intestinal au lignage E
Viscous and frictional strength of the lithospheric mantle : microstructural characterization of experimentally deformed polycrystalline Olivine
No full textLa convection dans le manteau terrestre est la principale force motrice du mouvement des plaques tectoniques. Alors que les parties inférieures du manteau supérieur se déforment de manière ductile, les plaques tectoniques sont rhéologiquement plus rigides que l'asthénosphère sous-jacente. Pour comprendre le couplage entre la convection profonde et les plaques tectoniques à la surface de la Terre, il est essentiel de comprendre les mécanismes de déformation visqueuse et frictionnelle du manteau lithosphérique. Mais à ce jour, la rhéologie du manteau supérieur juste au-dessous de la discontinuité de Mohorovicic est encore mal comprise. De plus, les premiers stades de la déformation viscoplastique à des températures intermédiaires (600-1000 ° C) pertinentes pour le manteau lithosphérique, ne sont ni bien documentés ni quantifiés. Dans le passé, la plupart des expériences de déformation étaient effectuées à des températures très élevées (> 1200 ° C). Pour fournir des valeurs mécaniques précises pour le manteau lithosphérique, nous avons besoin de données mécaniques mais aussi de la caractérisation de la microstructure associée pour comprendre la physique des mécanismes en jeu lors de la déformation permanente des roches riches en olivine. Dans cette thèse, nous avons réalisé des expériences de déformation en compression axiale à l'aide d'une presse Paterson (Géosciences Montpellier, Université de Montpellier, France) à haute pression et température (300 MPa, 1000-12000 ° C) et en torsion (‘rotary shear frictional testing machine’ au laboratoire de mécanique des roches, université de Durham, Royaume-Uni) à pression et température ambiantes. Les échantillons ont été caractérisés par microscopie électronique à balayage, diffraction d’ d'électrons rétrodiffusés et microscopie électronique en transmission. Après un chapitre d'introduction où l'état de l'art est détaillé et un chapitre consacré aux méthodes expérimentales et analytiques utilisées dans les projets scientifiques, la thèse s'organise en trois chapitres, chacun correspondant à trois articles scientifiques: le premier est publié (1) Évolution de la contrainte et des microstructures associées au fluage transitoire de l'olivine à 1000-1200 °C (Phys. Earth Planet. Int., doi: 10.1016/ j.pepi.2018.03.002. (https: //hal.archives- ouvertes.fr/hal-01746122) et les deux autres sont en préparation, (2) Densité de disclinaisons dans l'olivine polycristalline déformée expérimentalement à 1000 ° C et 1200 ° C (3) Déformation par cisaillement de l'olivine nano- et micro-cristalline. Le premier projet du chapitre III a montré que le durcissement mécanique observé ne peut pas provenir d'une simple augmentation de la densité de dislocations (e.g., la forêt) et que d'autres mécanismes doivent être mis en œuvre pour compenser les limites de glissements des dislocations. Dans le chapitre IV, les densités de dislocation géométriquement nécessaires (GND, défauts de translation) et les disclinaisons (défauts de rotation) sont quantifiées sur une série de roches déformées à différentes températures, déformations finies et niveaux de contrainte, mais aucune corrélation n'a été identifiée entre la densité de disclinaisons, et la contrainte, la déformation finie, ou la densité de GND. Le rôle des disclinaisons serait donc limité à la migration aux joints de grains, ce qui peut être suffisant pour débloquer les dislocations dans l'agrégat d'olivine polycristalline. Au chapitre V, les expériences de torsion ont confirmé l'effet négligeable de la taille du grain (olivine de 0,7 à 70 µm) sur la diminution drastique du coefficient de frottement, mais la caractérisation des échantillons n’a pas permis d'élucider le mécanisme principal de déformation. Cette thèse a permis de mieux caractériser la transition fragile-ductile d'une roche de type dunite à grains fins soumise à une déformation permanente aux températures du manteau sommitale.Convection in Earth’s mantle is the major driving force behind the movement of tectonic plates. While the lower parts of the upper mantle deform in a ductile way, the plates themselves are rheologically more rigid than the asthenosphere beneath. To understand how convection yields tectonic plates, it is vital to quantify the viscous and frictional strength of the lithospheric mantle. Yet to date, the rheology of the uppermost mantle just below the Mohorovicic discontinuity is still poorly understood. Furthermore, the early stages of visco-plastic deformation at intermediate temperatures (600 – 1000 °C) relevant of the lithospheric mantle are not well documented or quantified. In the past, most deformation experiments were performed at high temperatures (> 1200 °C). To provide accurate mechanical values for the lithospheric mantle, we need mechanical data but also a characterization of the associated microstructure to understand the deformation mechanisms at play during permanent deformation of olivine-rich rocks. In this thesis, I have performed deformation experiments in axial compression using a Paterson press (at Géosciences Montpellier, University of Montpellier, France) at high pressure and temperature (300 MPa, 1000 -12000 °C) and in torsion using a low to high velocity rotary shear frictional testing machine (Rock Mechanics Laboratory, Durham University, UK) at room pressure and temperatures. The recovered samples were characterized using scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. After an introduction chapter where the state-of-the-art is detailed, and a chapter focusing on experimental and analytical methods used during scientific projects, the thesis is organized as three subsequent chapters, each of them corresponding to three scientific articles: one is published (1) Stress evolution and associated microstructure during transient creep of olivine at 1000-1200 °C (Phys. Earth Planet. Int., doi: 10.1016/j.pepi.2018.03.002.); and the two others are in preparation, (2) Disclination density in polycrystalline olivine experimentally deformed at 1000 °C and 1200 °C; and (3) Shear deformation of nano- and micro-crystalline olivine at seismic slip rates. Chapter III has shown that the observed mechanical hardening can not come from a simple increase in dislocation density (e.g., entanglement) and that other mechanisms must be at play to compensate for the limitations of dislocation slip. For the first time, in chapter IV the densities of geometrically necessary dislocations (GND, translational defects) and disclinations (rotational defects) are quantified on a series of rocks deformed at different temperatures, finite strains and stress levels. No correlation has been identified between disclination density and stress, strain or GND. The role of the disclinations will therefore be limited to migration at grain boundaries, which may be sufficient to unblock dislocations in the polycrystalline olivine aggregate. In chapter V, torsion experiments confirmed the negligible effect of grain size (olivine from 0.07 to 70 μm) on the drastic decrease of the coefficient of friction, but the characterization of the samples did permit to shed light on the main mechanism of deformation. Thanks to an experimental approach and up-to-date material characterization, this thesis permitted better characterization of the brittle-ductile transition of a fine-grained dunite-type rock subjected to permanent deformation at uppermost mantle temperatures
Diffusion of hydrogen in olivine grain boundaries and implications for the survival of water-rich zones in the Earth's mantle
No full textNominally anhydrous minerals (NAMs) of Earth's mantle can contain hydrogen as atomic impurity in their crystal structures. This hydrogen substantially modifies many physical properties of Earth's mantle rocks. Also, the Earth's deep interior is made of rocks where minerals are separated by nanometer-scale interfaces call grain boundaries and interphase boundaries. These grain boundaries should carefully be considered as a potential hydrogen reservoir as well. I report here an experimental investigation of hydrogen diffusion through grain boundaries in olivine polycrystalline aggregates. Hot-press and diffusion experiments were performed using a gas-medium high-pressure vessel at a confining pressure of 300 MPa, over a temperature range of 1000-1200 degrees C. The diffusion assembly consisted of a dense polycrystalline cylinder of natural olivine from San Carlos (Arizona) mixed with olivine singles crystals of millimeter size. This mixture was couple with a talc cylinder. Ni capsule were used to buffer the oxygen fugacity at Ni-NiO level. Experiment durations varied from 3 min to 4 h. The presence of hydrogen in the sample was quantified using Fourier transform infrared spectroscopy. The calculation of the diffusion coefficients was based on the estimation of the length of polycrystalline solid affected by the diffusion of hydrogen. The absence or presence of hydrogen was recorded by the large olivines behaving here as "hydrogen sensor", which are implanted in the aggregate. The results indicate that effective hydrogen diffusivity which includes grain boundaries effect in olivine aggregate is barely one order of magnitude faster than hydrogen diffusion in an olivine single crystal with a diffusivity similar to 8.5x 10(-10) m(2) s(-1) 1000 degrees C and only twice faster similar to 2.1 x10(-9) m(2) s(-1) 1200 degrees C. Calculations of the diffusion data in relation to the Arrhenius Law, yield an activation energy of similar to 70 +/- 10 kJ mol(-l) . From these effective diffusivities and combined with published diffusion data for olivine single crystals, hydrogen diffusion in grain boundaries is extracted and yield diffusivities almost three order of magnitude faster (similar to 5 x 10(-6) m(2) s(-1) at 1200 degrees C) than in an olivine single crystal at the equivalent high temperature. On geological scales and for coarse-grain rocks, hydrogen diffusivity in grain boundaries is not fast enough to compete with lattice diffusion. The relative large grain size of mantle rocks will ensure a very limited hydrogen transport by effective diffusion, and a good conservation of water-rich zones in the Earth's mantle
Stress evolution and associated microstructure during transient creep of olivine at 1000–1200 °C
No full textInternational audienceWe study the mechanical response and correlated microstructure of axial deformed fine-grained olivine aggregates as a function of incremental finite strains. Deformation experiments were conducted in uniaxial compression in an internally heated gas-medium deformation apparatus at temperatures of 1000 and 1200 °C, at strain rates of 10−6 s−1 to 10−5 s−1 and at confining pressure of 300 MPa. Sample volumes are around 1.2 cm3. Finite strains range from 0.1 to 8.6% and corresponding maximal (final) differential stresses range from 80 to 1073 MPa for deformation at 1000 °C and from 71 to 322 MPa for deformation at 1200 °C. At 1200 °C, samples approach steady state deformation after about 8% of strain. At 1000 °C, significant strain hardening leads to stresses exceeding the confining pressure by a factor of 3.5 with brittle deformation after 3% of strain. Deformed samples were characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD maps with step sizes as low as 50 nm were acquired without introducing analytical artifacts for the first time. The grain size of deformed samples ranges from 2.1 to 2.6 µm. Despite clear strain hardening, texture or microstructure do not change as a function of stress or finite strain. This observation is supported by a constant texture strength (J-index) and symmetry (BA-index), constant grain shape and aspect ratio, constant density of geometrically necessary dislocations, grain orientation spread, and constant subgrain boundary spacing and misorientation in between samples. TEM shows that all samples exhibit unambiguous dislocation activity but with a highly heterogeneous dislocation distribution. Olivine grains display evidence of [1 0 0] and [0 0 1] slip activity, but there is no evidence of interaction between the dislocations from the different slip systems. Several observations of grain boundaries acting as dislocation sources have been found. We find no confirmation of increasing dislocation densities as the cause for strain hardening during transient creep. This suggests other, yet not fully understood mechanisms affecting the strength of deformed olivine. These mechanisms could possibly involve grain boundaries. Such mechanisms are relevant for the deformation of uppermost mantle rocks, where the Si diffusion rate is too slow and dislocation glide must be accommodated in another way to fulfill the von Mises criterion
Hydrogen diffusion in spinel grain boundaries and consequences for chemical homogenization in hydrous peridotite
No full textInternational audienceHydrogen can be stored in the structure of nominally anhydrous minerals as point defects, and these impurities substantially modify many physical properties of Earth's mantle minerals. However, mantle rocks are composed of mineral grains separated by grain boundaries and interphase grains boundaries. Therefore, as a potential hydrogen reservoir, grain boundaries should be given proper attention. Here, I report an experimental investigation into hydrogen diffusion through grain boundaries in polycrystalline aggregates Sintering and diffusion experiments were performed using a gas-medium high-pressure vessel at under pressure of 300 MPa and over a temperature range of 900-1,250 degrees C. The diffusion assembly consisted of a polycrystalline cylinder of aluminous spinel + olivine crystals with a talc cylinder as the main hydrogen source. A Ni capsule was used to buffer the oxygen fugacity at Ni-NiO Experimental durations varied from 5 min to 5 h. The presence of hydrogen in the crystals was measured by Fourier-transform infrared spectroscopy. The calculation of the diffusion coefficients was based on the estimation of the characteristic distance. The absence or presence of hydrogen recorded by the 'hydrogen sensor' olivines embedded in the aggregate allows the estimation of bounds on this characteristic distance. Results presented here suggest that hydrogen effective diffusion coefficients are only one order of magnitude faster (similar to 10(-9) m(2)s(-1) at 1,000 degrees C) than in an olivine single crystal along the [100] axis. Resulting diffusion coefficients for hydrogen in grain boundary are four orders of magnitude faster than in a single crystal, but this diffusivity is not fast enough to affect hydrogen mobility in mantle rocks with grain sizes greater than similar to 1 mm. Thus, very limited chemical homogenization would occur using grain boundaries diffusion in mantle hydrous peridotite for incompatible and volatile element, such as hydrogen
Creep mechanisms in the lithospheric mantle inferred from deformation of iron-free forsterite aggregates at 900–1200 °C
No full textInternational audienceTo further constrain the plasticity of rocks in the uppermost lithospheric mantle, deformation experiments were carried out on forsterite aggregates using a gas-medium apparatus (Paterson press) at 300 MPa, 900–1200 °C and nearly constant strain rates of ~10−5 s−1. The starting material was a synthetic iron-free forsterite aggregate with an average grain size of ~2.8 μm and ~2–3% of iron-free enstatite. Eight deformation experiments were performed as well as an additional static annealing to characterize grain growth. The maximum stresses obtained range from ~480 to 1870 MPa. Below 1000 °C, where stress significantly exceeds confining pressure, and based on microstructural observations, grain boundary mediated creep is observed, with evidences of sliding and cavitation (gaping) at grain boundaries. At 1050–1200 °C, where pseudo-steady state could be achieved, the microstructures are very different and show evidences of dislocation activity, resulting from the activation of several dislocation slip systems with increasing temperature.When compared to rheology laws previously obtained from similar experiments, the temperature dependence of iron-free olivine creep is similar to the one of its iron-bearing counterpart at high temperature (∼1200 °C); at temperatures ≤ 1000 °C, however, the strength of iron-free olivine is higher than for iron-bearing olivine. The deformation-induced textures obtained show that grain boundary sliding (GBS) lead to cavitation, which was activated in response to large differential stresses, i.e., beyond the Goetze criterion. Given these high-stress conditions, our results cannot be directly applied to deformation of the Earth's mantle at large scale. Nevertheless, they highlight the key role played by grain boundaries in producing strain at lithospheric temperatures, when crystal-plastic mechanisms remain inefficient
Viscoplasticity of polycrystalline olivine experimentally deformed at high pressure and 900 degrees C
No full textInternational audienceWe have performed tri-axial compression experiments on olivine aggregates at 900 °C and at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus. Deformation at two different constant strain rates (1.1 × 10− 5 s− 1 and 3.4 × 10− 4 s− 1) yields continuous hardening, reaching maximal differential stresses of 930 and 1076 MPa, respectively, before sample failure at ca. 10% strain. The deformed samples were characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Crystallographic preferred orientations (CPO) are weak but reveal an alignment of the [010] axes around the compression direction and some concentration of [001] and [100] axes normal to it. TEM observations confirm plastic deformation by dislocation glide, with both [001] and [100] Burgers vectors. Electron tomography, performed for the first time on deformed fined-grained olivine, shows that [001] dislocations glide extensively on {110} and {130} planes, in complement to the (010) and (100) glide planes often reported at high temperatures. [100] dislocations glide mostly on (010), but {011} and {041} planes are also activated. The experimental CPO and relative activity of slip systems are well reproduced by viscoplastic self-consistent simulations in which all [100] and [001] slip systems have similar strengths. They are also consistent with olivine CPO from natural samples deformed at low temperature. Comparison of the present mechanical results to those obtained for olivine single-crystals at similar conditions shows that at low temperature (below 1100 °C) and high stress (> 300 MPa) polycrystalline olivine has a more complex mechanical behavior than single crystals. However, both datasets advocate for a much weaker dry mantle lithosphere than previously thought
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