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161.
Jean‐Pierre LORAND Jean‐Alix BARRAT Vincent CHEVRIER Violaine SAUTTER Sylvain PONT 《Meteoritics & planetary science》2012,47(11):1830-1841
NWA 2737, a Martian meteorite from the Chassignite subclass, contains minute amounts (0.010 ± 0.005 vol%) of metal‐saturated Fe‐Ni sulfides. These latter bear evidence of the strong shock effects documented by abundant Fe nanoparticles and planar defects in Northwest Africa (NWA) 2737 olivine. A Ni‐poor troilite (Fe/S = 1.0 ± 0.01), sometimes Cr‐bearing (up to 1 wt%), coexists with micrometer‐sized taenite/tetrataenite‐type native Ni‐Fe alloys (Ni/Fe = 1) and Fe‐Os‐Ir‐(Ru) alloys a few hundreds of nanometers across. The troilite has exsolved flame‐like pentlandite (Fe/Fe + Ni = 0.5–0.6). Chalcopyrite is almost lacking, and no pyrite has been found. As a hot desert find, NWA 2737 shows astonishingly fresh sulfides. The composition of troilite coexisting with Ni‐Fe alloys is completely at odds with Chassigny and Nahkla sulfides (pyrite + metal‐deficient monoclinic‐type pyrrhotite). It indicates strongly reducing crystallization conditions (close to IW), several log units below the fO2 conditions inferred from chromites compositions and accepted for Chassignites (FMQ‐1 log unit). It is proposed that reduction in sulfides into base and precious metal alloys is operated via sulfur degassing, which is supported by the highly resorbed and denticulated shape of sulfide blebs and their spongy textures. Shock‐related S degassing may be responsible for considerable damages in magmatic sulfide structures and sulfide assemblages, with concomitant loss of magnetic properties as documented in some other Martian meteorites. 相似文献
162.
Peter Stille Anne-Désirée Schmitt François Labolle Marie-Claire Pierret Sophie Gangloff Florian Cobert Eric Lucot Florence Guéguen Laure Brioschi Marc Steinmann François Chabaux 《Comptes Rendus Geoscience》2012,344(5):297-311
The combination of the Sr, Nd and Pb isotope systems, recognized as tracers of sources, with the Ca isotope system, known to reveal biology-related fractionations, allowed us to test the reliability of spruce (Picea abies) growth rings as environmental archives through time (from 1916 to 1983) in a forest ecosystem affected by acid atmospheric deposition. Sr and Pb isotopes have already been applied in former tree-ring studies, whereas the suitability of Nd and Ca isotope systems is checked in the present article. Our Sr and Nd isotope data indicate an evolution in the cation origin with a geogenic origin for the oldest rings and an atmospheric origin for the youngest rings. Ca isotopes show, for their part, an isotopic homogeneity which could be linked to the very low weathering flux of Ca. Since this flux is weak the spruces’ root systems have pumped the Ca mainly from the organic matter-rich top-soil over the past century. In contrast, the annual growth rings studied are not reliable and suitable archives of past Pb pollution. 相似文献
163.
Ralf Gertisser Nigel J. Cassidy Sylvain J. Charbonnier Luigia Nuzzo Katie Preece 《Natural Hazards》2012,60(2):623-648
Merapi, an andesitic volcanic complex in Central Java, is one of the most frequently erupting volcanoes in Indonesia and poses
a permanent threat to the surrounding population of over 1 million people. With frequently recurring volcanic activity, the
sixty or so reported eruptions since the mid-1500s have caused ~7,000 fatalities and destroyed numerous villages in the region.
In June 2006, an eruption affected the densely populated area on the volcano’s southern and south-eastern flanks for the first
time in almost a century. The resultant block-and-ash flows (BAFs) travelled down an incised river valley (Kali Gendol) to
a distance of 7 km from the source, breaking out of the main channel at four main locations. Unconfined (overbank) BAFs were
generated, which covered the interfluve regions on either side of the main valley and buried buildings and other infrastructure
features in the village of Kaliadem, situated on the western bank of the Gendol valley ~5 km from the summit of Merapi. Using
traditional volcanological field-based methods and non-invasive, high-resolution ground-penetrating radar techniques, the
morphology and internal architecture of these overbank deposits were studied in detail in order to evaluate the destructive
impact of these flows in a local context. The results show that complex, local-scale variations in flow dynamics and deposit
architectures are apparent and that BAFs are capable of transporting significant numbers of large blocks (>1–2 m) out of the
valley confines. We propose a conceptual model for the escape of these channelised BAFs onto the interfluvial terrace at Kaliadem
and show, through a stratigraphic analysis of the pyroclastic successions underlying the village and adjacent areas on the
volcano’s southern flank, that the area has been affected repeatedly by overbank BAFs and explosive eruptions over the past
few 100 years (and more). 相似文献
164.
Caroline Avril Valérie Malavergne Razvan Caracas Brigitte Zanda Bruno Reynard Emeline Charon Ema Bobocioiu Fabrice Brunet Stephan Borensztajn Sylvain Pont Martine Tarrida François Guyot 《Meteoritics & planetary science》2013,48(8):1415-1426
Raman spectra were acquired on a series of natural and synthetic sulfide minerals, commonly found in enstatite meteorites: oldhamite (CaS), niningerite or keilite ((Mg,Fe)S), alabandite (MnS), troilite (FeS), and daubreelite (Cr2FeS4). Natural samples come from three enstatite chondrites, three aubrites, and one anomalous ungrouped enstatite meteorite. Synthetic samples range from pure endmembers (CaS, FeS, MgS) to complex solid solutions (Fe, Mg, Ca)S. The main Raman peaks are localized at 225, 285, 360, and 470 cm?1 for the Mg‐rich sulfides; at 185, 205, and 285 cm?1 for the Ca‐rich sulfides; at 250, 370, and 580 cm?1 for the Mn‐rich sulfides; at 255, 290, and 365 cm?1 for the Cr‐rich sulfides; and at 290 and 335 cm?1 for troilite with, occasionally, an extra peak at 240 cm?1. A peak at 160 cm?1 is present in all Raman spectra and cannot be used to discriminate between the different sulfide compositions. According to group theory, none of the cubic monosulfides oldhamite, niningerite, or alabandite should present first‐order Raman spectra because of their ideal rocksalt structure. The occurrence of broad Raman peaks is tentatively explained by local breaking of symmetry rules. Measurements compare well with the infrared frequencies calculated from first‐principles calculations. Raman spectra arise from activation of certain vibrational modes due to clustering in the solid solutions or to coupling with electronic transitions in semiconductor sulfides. 相似文献
165.
A Simple Mixing Length Formulation for the Eddy-Diffusivity Parameterization of Dry Convection 总被引:2,自引:1,他引:1
In this paper a simple mixing length formulation for the eddy-diffusivityparameterization of dry convection is suggested. The new formulation relates the mixinglength to the square root of the turbulent kinetic energy (e) and a time scale ( ):l = e. To close the parameterization the time scale is calculated as a functionof the boundary-layer height (h) and the convective velocity scale (w*), h/w*. Thesimpler approach of a constant time scale is also studied. The simulation of a case of dry atmosphericconvection with a one-dimensional boundary-layer model shows that the model with the new formulationreproduces quite well the main properties of the convective boundary layer. In particular,the entrainment is realistically represented by the new mixing length, which has the advantage of naturallydecreasing with the turbulent kinetic energy. Sensitivity studies to the surface flux and the lapserate, in the context of a simplified situation, show the robustness of the new formulation. 相似文献
166.
The impact of vegetation on fractionation of rare earth elements (REE) during water–rock interaction
P. Stille M. Steinmann M.-C. Pierret F. Gauthier-Lafaye D. Aubert A. Probst D. Viville F. Chabaux 《Journal of Geochemical Exploration》2006,88(1-3):341
Previous studies on waters of a streamlet in the Vosges mountains (eastern France) have shown that Sr and rare earth elements (REE) principally originate from apatite dissolution during weathering. However, stream water REE patterns normalized to apatite are still depleted in light REE (LREE, La–Sm) pointing to the presence of an additional LREE depleting process. Speciation calculations indicate that complexation cannot explain this additional LREE depletion. In contrast, vegetation samples are strongly enriched in LREE compared to water and their Sr and Nd isotopic compositions are comparable with those of apatite and waters. Thus, the preferential LREE uptake by the plants at the root–water–soil (apatite) interface might lead to an additional LREE depletion of the waters in the forested catchment. Mass balance calculations indicate that the yearly LREE uptake by vegetation is comparable with the LREE export by the streamlet and, therefore, might be an important factor controlling the LREE depletion in river waters. 相似文献
167.
Fanny Lasry Isabelle Coll Sylvain Fayet Maxime Havre Robert Vautard 《Journal of Atmospheric Chemistry》2007,57(2):107-134
In Europe, in case of the observation or the forecast of a photochemical event, punctual and local reductions in anthropogenic
emissions can be triggered at the regional scale. Although the necessity for the establishment of such measures appears to
be justified by bad air quality records over large European cities, individual short-term action plans (STAPs) have been blindly
elaborated by regional authorities. Moreover, as they impose industrial and road traffic emission restrictions, these measures
have an elevated economical cost. It is consequently crucial to determine their efficiency and potential for ozone peak reduction.
The study presented in this paper aims to draw up an expertise on standard European STAPs, through the example of a French
Mediterranean city. The objective is to determine and investigate the impact of current STAPs on ozone peak formation and
to test ways to optimise their efficiency. In this frame, a set of emission scenarios has been elaborated and tested with
the chemistry-transport model CHIMERE on the Berre–Marseille area. Simulations have shown that the tested action plans are
not sufficient to eradicate severe ozone peaks and that more drastic restrictions on emissions are required to significantly
affect ozone plumes. However, results also showed that the potential for ozone reduction remains small, with a maximum impact
of only 5 ppbv for feasible STAPs. Finally, a temporal analysis of the ozone-emission relationship was engaged in order to
optimise their application. 相似文献
168.
Philipp Steinmann Bernd Eilrich Markus Leuenberger 《Geochimica et cosmochimica acta》2008,72(24):6015-6026
Vertical profiles of concentration and C-isotopic composition of dissolved methane and carbon dioxide were observed over 26 months in the catotelm of a deep (6.5 m) peat bog in Switzerland. The dissolved concentrations of these gases increase with depth while CO2 predominates over CH4 (CO2 ca. 5 times CH4). This pattern can be reproduced by a reaction-advection-ebullition model, where CO2 and CH4 are formed in a ratio of 1:1. The less soluble methane is preferentially lost via outgassing (bubbles). The isotopic fractionation between CO2 and CH4 also increases with depth, with αC values ranging from 1.045 to 1.075. The isotopic composition of the gases traces the passage of respiration-derived CO2 (from the near surface) through a shallow zone with methanogenesis of low isotopic fractionation (splitting of fermentation-derived acetate). This solution then moves through the catotelm, where methanogenesis occurs by CO2 reduction (large isotopic fractionation). In the upper part of the catotelm the C-13-depleted respiration-derived CO2 pool buffers the isotopic composition of CO2; the δ13C of CO2 increases only slowly. At the same time strongly depleted CH4 is formed as CO2 reduction consumes the depleted CO2. In the lower part of the catotelm, the respiration-derived CO2 and shallow CH4 become less important and CO2 reduction is the dominant source of CO2 and CH4. Now, the δ13C values of both gases increase until equilibrium is reached with respect to the isotopic composition of the substrate. Thus, the δ13C values of methane reach a minimum at intermediate depth, and the deep methane has δ13C values comparable to shallow methane. A simple mixing model for the isotopic evolution is suggested. Only minor changes of the observed patterns of methanogenesis (in terms of concentration and isotopic composition) occur over the seasons. The most pronounced of these is a slightly higher rate of acetate splitting in spring. 相似文献
169.
Jacques Dorel Sylvain Eschenbrenner Michel Feuillard 《Pure and Applied Geophysics》1979,117(5):1050-1069
Summary In 1976 and 1977, seismic profiles were carried out in Guadeloupe. Two profiles were established in the area of La Soufriére volcano and one profile through the northern part of Guadeloupe and southern part of Grande Terre. The two first profiles were occupied from 1 to 30 km and the third profile between 5 and 50 km.The interpretation shows that the superficial structures are characterized by a three-layers model: the compressional velocity is about 2.7 to 3.0 km/s down to a depth from 1 to 3 km. Below this, the velocity is between 4.0 and 4.5 km/s in a layer whose thickness varies from 1 to 2.5 km. Under this layer we find a 6.0–6.1 km/s layer which is one of the two known crustal layer under Lesser Antilles. The boundary between the old and new are which form the Lesser Antilles arc, is marked by a thicker layer of sediments on the eastern flank of recent volcanic chain. 相似文献
170.
Stéphane Bodin Alexis Godet Virginie Matera Philipp Steinmann Jean Vermeulen Silvia Gardin Thierry Adatte Rodolfo Coccioni Karl B. Föllmi 《International Journal of Earth Sciences》2007,96(2):327-341
The Faraoni Level is a short-lived oxygen-deficient event that took place during the latest Hauterivian. In order to improve
our understanding of the palaeoenvironmental conditions that occurred during this event, we have analysed the contents of
several redox-sensitive trace elements (U, V, Mo, As, Co, Cd, Cu, Zn, Ni, Pb, Cr) from bulk limestone samples of late Hauterivian–early
Barremian age from three reference sections. U, V, Mo and As show consistent and significant enrichments during the Faraoni
event whereas the other redox-sensitive trace elements analysed here are not systematically enriched. In order to explain
this discrepant behaviour, we propose that the Faraoni Level was deposited during a period of anoxic conditions near the sediment–water
interface. The distinctive peaks in U, V, Mo and As contents are traceable throughout the three studied sections and represent
a good correlation tool which helps to identify the Faraoni Level and its equivalents in the western Tethyan realm and outside
of the Tethys. For example, a peak in U contents in upper Hauterivian sediments of the northwestern Pacific realm (ODP leg
185, site 1149) may well be an expression of the Faraoni event in this particular basin. 相似文献