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31.
Bernard MARTY Veronika S. HEBER Ansgar GRIMBERG Rainer WIELER Jean‐Alix BARRAT 《Meteoritics & planetary science》2006,41(5):739-748
Abstract— We report noble gas data for the second chassignite, Northwest Africa (NWA) 2737, which was recently found in the Moroccan desert. The cosmic ray exposure (CRE) age based on cosmogenic 3He, 21Ne, and 38Ar around 10–11 Ma is comparable to the CRE ages of Chassigny and the nakhlites and indicates ejection of meteorites belonging to these two families during a discrete event, or a suite of discrete events having occurred in a restricted interval of time. In contrast, U‐Th/He and K/Ar ages <0.5 Ga are in the range of radiometric ages of shergottites, despite a Sm‐Nd signature comparable to that of Chassigny and the nakhlites (Misawa et al. 2005). Overall, the noble gas signature of NWA 2737 resembles that of shergottites rather than that of Chassigny and the nakhlites: NWA 2737 does not contain, in detectable amount, the solar‐like xenon found in Chassigny and thought to characterize the Martian mantle nor apparently fission xenon from 244Pu, which is abundant in Chassigny and some of the nakhlites. In contrast, NWA 2737 contains Martian atmospheric noble gases trapped in amounts comparable to those found in shergottite impact glasses. The loss of Martian mantle noble gases, together with the trapping of Martian atmospheric gases, could have occurred during assimilation of Martian surface components, or more likely during shock metamorphism, which is recorded in the petrology of this meteorite. 相似文献
32.
Résumé Les espaces urbanisés soumis à des risques modérés d'inondation pour les vies humaines sont souvent peu considérés dans les études sur la vulnérabilité aux risques naturels en dépit des enjeux qu'ils représentent en termes de gestion de crise. Comment les riverains y font-ils face au danger et quelles sont leurs « bonnes raisons » d'agir? A partir de l’étude socio-géographique de deux inondations récentes (2000 et 2003) dans la périphérie toulousaine (Sud-Ouest de la France), nous montrons que les caractéristiques de l'aléa dans les vallées étudiées influencent les représentations du risque et par conséquent les motivations à se protéger. Face au risque majeur, la vulnérabilité sociale se trouve ainsi augmentée. Pour améliorer la résilience des populations, il convient d'adapter la communication sur les risques: personnaliser l'information, améliorer la compréhension de l’événement vécu et mobiliser de nouvelles formes de médiation entre gestionnaires et riverains. Editeur Z.W. Kundzewicz Citation Becerra, S., Peltier, A., Antoine, J.M., Labat, D., Chorda, J., Ribolzi, O., Daupras, F., et Dartus, D., 2013. Comprendre les comportements face à un risque modéré d'inondation. Etude de cas dans le périurbain toulousain (Sud-Ouest de la France). Hydrological Sciences Journal, 58 (5), 945–965. 相似文献
33.
Julia ROSZJAR Knut METZLER Addi BISCHOFF Jean‐Alix BARRAT Thorsten GEISLER Richard C. GREENWOOD Ian A. FRANCHI Stephan KLEMME 《Meteoritics & planetary science》2011,46(11):1754-1773
Abstract– We report on the bulk chemical composition, petrology, oxygen isotopic composition, trace element composition of silicates, and degree of self‐irradiation damage on zircon grains of the eucrite Northwest Africa (NWA) 5073 to constrain its formation and postcrystallization thermal history, and to discuss their implications for the geologic history of its parent body. This unequilibrated and unbrecciated meteorite is a new member of the rare Stannern‐trend eucrites. It is mainly composed of elongated, zoned pyroxene phenocrysts up to 1.2 cm, plagioclase laths up to 0.3 cm in length, and is rich in mesostasis. The latter contains zircon grains up to 30 μm in diameter, metal, sulfide, tridymite, and Ca‐phosphates. Textural observations and silicate compositions, coupled with the occurrence of extraordinary Fe‐rich olivine veins that are restricted to large pyroxene laths, indicate that NWA 5073 underwent a complex thermal history. This is also supported by the annealed state of zircon grains inferred from μ‐Raman spectroscopic measurements along with U and Th data obtained by electron probe microanalyses. 相似文献