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International audience; Several kaolinite occurrences of economic interest have been reported in Europe and are usually interpreted as resulting from weathering during the Paleogene tropical climate. However, a hydrothermal contribution is also recognized in some kaolinite occurrences. Such occurrences are common throughout the Hercynian Armorican Massif, where they are developed mostly on granitoids. The kaolin deposit of the Tertre Rouge pit, South Brittany (France), has been mined for the past 70 years. It is the only deposit developed from carbon-rich (~1% C) Ordovician schists affected by a low-grade metamorphic event during the late Hercynian orogeny. Herein, we report the results of a detailed field and petrological study combining optical microscopy with SEM investigation, XRD analyses, and ICP-OES and ICPMS geochemical data. A typical weathering profile was identified in the pit. It is marked from the bottom to the top by an increasing kaolinite volume (~45%) at the expense of muscovite/illite, a decreasing volume of chlorite and graphite, and numerous occurrences of Fe oxides/oxyhydroxides that replaced former pyrites or sulfates in veins. Despite this intense weathering, the analyzed Tertre Rouge schists preserved a black shale bulk chemical composition characterized by lithophile trace elements contents at 2× to 5× the Upper Continental Crust composition. This was made possible by accessory minerals inherited from the parent rock, especially Al phosphates, namely florencite (Ce), which were systematically identified as the main concentrators of LREE and Sr. Their occurrence in the Tertre Rouge kaolinized schist confirms the regional Sr and P geochemical anomalies previously reported in the Paleozoic sedimentary formations in this area of the Armorican Massif. High temperature clay minerals, pyrophyllite (>270 °C) and nacrite/dickite (generally considered to be high-T kaolinite polymorphs), were also identified inside the weathered zone, filling millimeter-thick veinlets cutting across or lying parallel to the cleavage plane S of the schist. We ascribe this high-temperature clay mineral assemblage to a hydrothermal event related to the numerous documented evidences of Late Hercynian fluid circulations in Central/South Armorican tectonometamorphic domains. Hence, we strongly favor a two-stage formation for the Tertre Rouge kaolin deposit, including a minor hydrothermal contribution to weathering-related kaolinite.

Can information on the Martian environmental conditions prevailing during the alteration of its basaltic crust be inferred from near-infrared (NIR) spectra? In order to determine whether basalts altered under arid conditions but different temperatures have different spectral signatures, NIR spectra of basalts altered in cold (Udokan volcanic field, Siberia) and hot (Ogaden Basin, Ethiopia) environments were obtained. The NIR spectra of the alteration rind surface and the internal part of the studied samples are similar, suggesting that the NIR spectra of Martian bulk rocks may be of limited help in identifying paleoenvironment conditions. Bulk rock spectra analysis reveals, however, that spectra of the least altered rocks display clear absorption bands of smectites, suggesting that a distinction between clay minerals in weakly weathered basalts and clay-rich formations cannot be based solely on analysis of infrared spectra obtained from orbit. Additional compositional information can be retrieved from rock powder spectra – zeolites present in the Udokan basalt spectra might be used to infer composition and temperature of the fluids from which they precipitated. The presence of calcite and iddingsite is ascertained by other methods, but they are not apparent in bulk rock spectra and only weakly apparent in powder spectra. The basalt samples studied display alteration products that reflect their different alteration histories; nevertheless no criterion has been found that would help in identifying the origin of the weathering water – subsurface, rainfall, or snowfall.

In situ interaction experiments over periods of 2, 6, and 10 years between Toarcian argillite and carbon steel discs were carried out in the Tournemire Underground Research Laboratory (URL), yielding a dataset of the materials’ geochemical evolution under conditions representative of the future geological disposal of high-level long-lived radioactive wastes. The carbon steel discs were exposed to corrosion due to trapped oxygen. The corrosion rates indicate that the oxidizing transient lasted between 2 and 6 years. A systematic dissolution of calcium phases (Ca- smectite sheets in I/S and calcite) was observed in the iron diffusion halos. The iron release induced mineralogical dissolution and precipitation reactions, which partly clogged the argillite porosity.

Notre sexualite est complexe, oscillant entre les influences de notre passe et celles des representations sociales. Elle l’est d’autant plus encore pour les personnes handicapees mentales pour lesquelles l’interdit social de procreation pese lourdement.Parler de sexualite voire de possible enfant pourrait nous permettre de revisiter notre fonctionnement / dysfonctionnement social par rapport aux personnes handicapees mentales afin d’ameliorer nos pratiques d’accompagnement, et ce, dans une dynamique beaucoup plus globale. Ce sont, en effet, les propos des personnes handicapees dans cette experience singuliere de parentalite qui viennent nous interroger.