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Fluids are a primary control on deformation processes, in particular in the upper, brittle portion of the crust. In the mechanical framework of poroelasticity or friction, used to describe brittle rock behavior, the influence of fluid is integrated through the fluid pressure. High fluid pressure reduce the deviatoric stress necessary for slip ; for example during seismic slip, the temperature rise due to frictional work in the fault core might result in a large drop in resistance to further slip and constitutes therefore a very efficient lubricating process. Another example of the influence of fluid pressure is observed in deep slow slip events in subduction zones, where the slipping portion of the plate interface and domains of high fluid pressure migrate conjointly.While models and observations highlight the large mechanical role of fluid pressure, measurements of fluid pressure below a few kilometers of depths are very indirect and plagued by large uncertainties. Veins constitute one of the ubiquitous by-products of the fluid-rock interaction during deformation at depths. Vein-forming mineral, such as quartz and calcite, trap, as inclusions, the fluid that was present during crystal growth. Fluid inclusions constitute therefore one of the very few record of the physicochemical conditions of the deep fluid.We examined in this work three examples of syn-deformation quartz veins, from a japanese accretionary complex. The crystals within veins show growth rims, bringing to light the time evolution of the rock-fluid system. Many fluid inclusions are trapped within the growth rims ; in particular methane-rich fluid inclusions, which minimize the problem of late-stage reequilibration and therefore unravel the fluid pressure at the time of trapping. In parallel, those growth rims can be divided into two types, with either low or large content in trace elements (in particular aluminum).We correlated the median fluid pressure recorded in fluid inclusions with the average Al concentration in quartz : High/low fluid pressure correspond to low/high Al concentration, respectively. Based on literature data about crystal growth in hydrothermal and magmatic contexts, it appears that the higher incorporation of impurities can be accounted for by rapid, out-of-equilibrium growth of quartz. We propose therefore a model of vein evolution with repetitions of large fluid pressure drop, where crystal grew rapidly and incorporated a large concentration in Al, alternating with longer period of slower growth, at higher fluid pressure, with a reduced incorporation of Al. The highest fluid pressure variations are of the order of 70MPa, and the corresponding Al concentration variations of the order of 0.28wt%.Quartz veins are abundant in most, if not all tectonic contexts. In addition, Al concentration in quartz is preserved throughout exhumation, unlike fluid inclusions signal, which is in many cases questionable because of reequilibration. In conclusion, quartz geochemistry can be considered as a promising sensor of fluid pressure variations, which can provide access to the conditions of the fluid attending deformation of the brittle crust.

Whether seismic rupture propagates over large distances to generate earthquakes or on the contrary slows down quickly, is heavily dependent on the slip processes operating within the fault core. One possible scenario is that during seismic slip, the frictional work induces a local and transient release of heat up to reach the melting of the rock. This melt-lubrication of the fault plane results in resistance drop and promotes further propagation of the fault. Nonetheless, assessing the occurrence of flash melting has turned problematic, especially in the metasediments that constitute a large fraction of seismically active collision or subduction zones.In this work, we explore the effects of short-lived intense heating on the crystallinity of the carbonaceous particles present in the fault core. For this purpose, we carried out flash-heating experiments on pellets of natural sediments. Using a pair of lasers, the sample temperature was raised to 1400°C for durations ranging from 0.5 to 60 seconds, resulting in partial to total melting. The carbonaceous particles were then analyzed by Raman Spectroscopy. The spectroscopic signal of particles intensely heated for a short period of time present an atypical shape, with a large D3 band centered around 1500cm-1. The D3/Gsl. ratio in Flash-heating experiments show an evolution from 0.2 for the starting material up to 0.7 after a couple of seconds of Flash-heating. Following this experimental work, we analyzed with Raman spectroscopy several independent examples of short-lived intense heating of carbon-bearing rocks: static heating, stick-slip, high-velocity-friction experiments, In all these cases, we observed the presence of a prominent D3 band and a D3/Gsl. ratio larger than reference material. Based on these observations, we established a new parameter, the D3/Gsl. ratio, as sensitive to short-lived intense heating.Finally, we applied this new Raman parameter in association with micro-structural observations to discriminate the formation process of five Black Fault Rocks (BFR) from the Shimanto and the Kodiak Accretionary Complex. Microstructures are in several cases ambiguous as to the occurrence of melting in the BFR. However, the D3/Gsl. ratio shows a large increase in the Kure and the Mugi BFR while the values are close to 0.2 in the host-rock. In contrast, Nobeoka, Okitsu and Kodiak BFR show similar values in comparing the BFR veins and the host-rocks. Accordingly, the Mugi and Kure BFR are associated with a molten origin when the three others BFR are the result of mechanical wear solely, without evidence for large temperature increase.In summary, the D3/Gsl. ratio is a parameter that can be easily retrieved in most fault rocks cutting across sediments and that efficiently tracks the occurrence of short-lived intense heating. The use of this parameter appears as a promising approach to decipher the dynamics of faulting and to discriminate faults with intense frictional work from faults where temperature increase was much more limited, either because of slow creep or inhibiting processes (e.g. fluid vaporization during slip).

Resume A l’encontre des modeles qui privilegient une approche bipolaire des rapports travail/hors travail et une conception individualisante de leurs mecanismes de regulation, nous proposons une definition systemique plurielle des domaines de vie et une approche relationnelle des processus d’elaboration de leurs eventuels conflits. L’analyse des contenus de discours de salaries confrontes a un plan social montre comment leurs strategies de reinsertion professionnelle passent toutes par une deliberation individuelle et collective sur le sens, la nature et la hierarchie des relations a etablir entre leurs differents domaines de vie. Dans chaque espace-temps de vie, passe, present et futur, des autrui, individuels et collectifs, cibles et supports de strategies de reconnaissance, sont materiellement et affectivement associes a ces deliberations.

International audience

Poster; International audience

International audience; In the frame of the development of uranium-plutoniummixed oxide fuels for Sodium-cooled Fast Reactors (SFRs),characterizing nuclear materials by various techniques isparamount.These fast neutron reactors imply the use of a (U,Pu)O$_{2-x}$ceramic fuel with a Pu/(U+Pu) content between 19 and30 mol.%. Furthermore, the physico-chemical andmicrostructural properties of such fuels, such as chemicalhomogeneity, oxygen stoichiometry (O/(U+Pu) ratio) andcrystallographic structure, have to meet precise criteria forbeing introduced in the reactor core.