Histoire de l’immigration en Auvergne

Jusqu’à la Seconde Guerre mondiale, la main-d’œuvre locale n’a pas manqué en Auvergne. L’immigration y a donc été plutôt tardive et modérée, et très inégale suivant les départements. L’immigration espagnole – d’exil – a joué un rôle prépondérant durant la Résistance, mais c’est l’immigration portugaise qui a été la plus massive, convoitée notamment par les industries du caoutchouc, dont Michelin

Etude de la croissance des sous-grains dans des alliages binaires aluminium-manganèse

L évolution de la microstructure a été étudiée sur deux alliages modèles Al-0,1wt%Mn et Al-0,3%wtMn lors de recuits réalisés après compression plane à froid ( VM=1,8). Les différents états recuits, ainsi que l état déformé, ont ensuite été analysés à l aide de la technique EBSD, couplée à un MEBFEG. Une nouvelle méthode de reconstruction des cartes EBSD, appelée SRM (Subgrain Reconstruction Mapping), basée sur l analyse d images, a été développée pour permettre d obtenir précisément les distributions de taille des sous-grains et des désorientations. Les cinétiques de croissance ont ainsi été déterminées et la mobilité des sous-grains estimée, apportant ainsi des données expérimentales importantes. Ces cinétiques de croissance ont été confrontées à deux lois théoriques : -la relation standard pour la croissance des grains, -la relation proposée par Nes. Si les deux approches ont permis de simuler les courbes expérimentales, la deuxième apparaît comme la plus efficace.Two, high purity, Al-0.1 and 0.3wt%Mn alloys have been cold deformed in plane strain compression to strains of order 1.8 and the kinetics of subsequent recovery by sub-grain coarsening during annealing at 150-300C measured by high resolution FEG-SEM EBSD. The technique for size measurement involves applying image analysis procedures to the EBSD orientation and band quality maps. This subgrain reconstruction map method (SRM) allows to obtain accurate sub-grain size distributions and misorientation angle distributions. The average growth rates are then used to estimate the sub-grain boundary mobilities. Growth is analyzed by two well-known growth laws for the average sub-grain size (t)i)ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

B-type olivine fabric induced by low temperature dissolution creep during serpentinization and deformation in mantle wedge

International audienceThe B-type olivine fabric (i.e., the [010] axes subnormal to foliation and the [001] axes subparallel to the lineation) has been regarded as an important olivine fabric for interpreting global trench-parallel S-wave polarization in fore-arc regions. However, strong serpentinization and cold temperature environment in the mantle wedge should inhibit development of the B-type olivine fabric that requires high temperature to activate solid-state plastic deformation. Here we report fabrics of olivine and antigorite generated at low temperatures (300–370 °C) during serpentinization in a fossil mantle wedge of the Val Malenco area, Central Alps. Olivine in the serpentine matrix develops a pronounced B-type fabric, while antigorite in the same matrix displays a strong crystallographic preferred orientation (CPO) with the (001) planes and the [010] axes subparallel to foliation and lineation, respectively. The following evidence leads to the conclusion that the B-type olivine fabric results from dissolution creep assisted by grain boundary sliding (GBS) and grain rotation, rather than solid-state plastic deformation: (1) serpentinization took place at low temperatures and a fluid-enriched environment, ideal for dissolution-precipitation creep; (2) the voids and zigzag boundaries along the interface between antigorite and olivine suggest a fluid dissolution reaction; (3) the primary coarse olivine develops a nearly random fabric, indicating the B-type fabrics in the fine-grained olivine may not be inherited fabrics. These results document for the first time the B-type olivine CPO formed by dissolution creep at low temperatures during serpentinization and provide a mechanism to reconcile petrofabric observations with geophysical observations of trench parallel fast S-wave seismic anisotropy in fore-arc mantle wedge regions

Plastic deformation of plagioclase in a gabbro pluton accreted at a slow-spreading ridge (Hole U1473A, Atlantis Bank, Southwest Indian ridge)

International audienc

Filtered EBSD dataset in slow spread oceanic gabbros, IODP Expedition 360

The dataset contains the electron backscattered diffraction (EBSD) filtered data acquired on samples collected on cores from IODP Hole U1473A. A suite of 102 samples in gabbroic lithologies was analyzed through 116 EBSD maps of variable area width, generally 1-2 cm², and 3-3.5 cm² in coarse-grained samples. The scanning resolution was chosen as a function of the average minimum grain size of each analyzed sample and varies from 2.5 µm to 30 µm (average resolution: 10 µm). Raw pixel data was filtered with the Channel 5 analysis suite from HKL Technology (Oxford Instruments) and consists in a noise reduction followed by a wild spikes extrapolation (level 6)

Textural insights into the significance of ophiolitic chromitites, with special reference to Oman

International audienceThis paper analyses the process and depth of formation of chromite crystals occasionally including ultrahigh pressure (UHP) minerals, recovered from some investigated ophiolites. We present direct microstructural evidence for crystallization of chromite ores from the Semail ophiolite, in place they are exposed. Similar crystal preferred orientation in olivine-rich layers and in septa from chromite layers indicate deformation of the olivine solid frame by dislocation creep at high temperature, synchronous with the crystallization of chromite. The preservation of the olivine framework throughout the development of joined chromite grains suggests that chromite replaced olivine. Chromite grains crystallized from a melt circulating in an open-system, stress-bearing network of dunitic aggregate, controlled by the olivine high-T slip system. The misorientation of joined crystals at grain boundaries define the ratio of twin vs. random boundaries that were closed to vs. open to fluid circulation, respectively, suggesting that chromite layers may represent planes of channelized melt circulation. The relationship of chromite deposits to ridge tectonics structures suggests that Cr-bearing melt was produced at the transition from an active spreading ridge to deep mantle shear zones acting as possible source of hydration. The occurrence of potential UHP inclusions in chromite crystals is assigned to continental contamination of melts ascending through the Arabian margin

Twinning in SnO 2 -based ceramics doped with CoO- and Nb 2 O 5 : morphology of multiple twins revealed by electron backscatter diffraction

International audienceElectron backscatter diffraction (EBSD) was used for the analysis of multiple cyclic twins in cassiterite (SnO2), which form during sintering of SnO2 with small additions of CoO and Nb2O5. Grain misorientation analysis has shown that about one third of all grains contain {101} twin boundaries (TBs). The majority of these grains are contact twins, whereas a small fraction of grains are multiple, mainly cyclic twins. A procedure was developed in MTEX [Bachmann, Hielscher & Schaeben (2010). Solid State Phenom. 160, 63–88] for automated identification of crystallographically different types of cyclic twins and found two main types: coplanar twins composed of three or four domains with a common [010] axis and alternating twins composed of three to seven domains oriented along the [111] axis. Both types of cyclic twins have a characteristic common origin (nucleus) of all TBs, which is positioned eccentric relative to the grain section and the cycle is closed with a shorter non-crystallographic contact between the first and the last twin domain. The morphology of cyclic twins suggests that they form by nucleation in the initial stages of grain growth. The average size of twinned grains increases with the number of twin domains indicating the influence of TBs formation on the growth of composite grains

Odorant-binding protein engineering: impact on binding properties

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Plastic Deformation of Plagioclase in Oceanic Gabbro Accreted at a Slow‐Spreading Ridge (Hole U1473A, Atlantis Bank, Southwest Indian Ridge)

International audienceCrustal architecture at slow-spreading oceanic ridges results from complex interactions between magmatism, hydrothermalism, and tectonics. IODP Hole U1473A was drilled during Expeditions 360 and 362T at the summit of the Atlantis Bank, a gabbroic massif exhumed at the Southwest Indian Ridge. In this study, we identify and quantify plastic deformation processes in gabbroic lithologies and active slip systems in plagioclase from 115 microstructural domains throughout Hole U1473A. We describe deformed zones using petrographic observations and electron backscattered diffraction analyses made all along the core. Ductile deformation is widespread, and in places strongly localized in mylonitic and ultramylonitic zones. Plagioclase represents ∼60% of rock's volume and is the dominant phase accommodating deformation in samples. It shows strong dynamic recrystallization accommodated by subgrain rotation in the dislocation creep regime, forming a fine-grained matrix. Electron backscattered diffraction analyses reveal weak to moderate crystallographic preferred orientations of plagioclase as a result of plastic deformation and strain localization, producing a fabric characterized by (010) parallel to the foliation plane and [100] parallel to the lineation. The fabric strength is first increasing from slightly deformed lithologies to mylonites before decreasing significantly in ultramylonites. This could be explained by orientation scattering after recrystallization, and a change of active slip systems. Subsequent granular flow has likely occurred in some samples. A detailed investigation of intracrystalline misorientations measured at plagioclase subgrain boundaries reveals the activity of four dominant slip systems: [001](010), [100](001), ½[110](001), and ½[111](001). These slip systems reflect decreasing temperatures during CPO development and subgrain wall formatio

Sub-boundary mobilities during recovery of binary Al-Mn alloys

Two, high purity, Al-0.1 and 0.3wt%Mn alloys have been cold deformed in plane strain compression to strains of order 1.8 and the kinetics of subsequent recovery by sub-grain coarsening during annealing at 150-300°C measured by high resolution FEG-SEM EBSD. Accurate sub-grain size and misorientation distributions and their evolution with time and temperature have been determined. The average growth rates are then used to estimate the sub-grain boundary mobilities. Growth is analyzed by two well-known growth laws for the average sub-grain size δ (t): i) the standard relation for grain growth: where the exponent n takes values of 2-8 and ii) the relation proposed by Nes for dislocation climb in sub-grain walls: It is shown that the latter relation gives a better fit with the data in terms of the time and temperature dependence of the sub-grain sizes. In particular the activation energies for the logarithmic law are much closer to the values expected for solute-controlled movement of sub-boundaries