La vague de chaleur de l'été 2003 et sa prévision saisonnière     

Jean-Claude André  Michel Déqué  Philippe Rogel  Serge Planton 《Comptes Rendus Geoscience》2004,336(6):491-503

The main features of the heat wave that has affected western Europe during the summer 2003 are first recalled, with particular concern to analogies and differences with previous warm-summer episodes. The skills of the various operational and pre-operational seasonal forecasting models in use at that time are evaluated. None of them has been able to consistently forecast the heat wave three month in advance. The meteorological and climatic situation prevailing during spring 2003 is then analysed. A strong sea-surface-temperature (SST) anomaly is found to have developed over North Atlantic a few months before the heat wave. The particular mechanism at work to explain the occurrence of the heat wave is not a ‘simple downwind influence’ of the SST anomaly. It very likely involves complex ocean–atmosphere interaction phenomena of a kind that is not properly taken into account in today's seasonal forecasting models. To cite this article: J.-C. André et al., C. R. Geoscience 336 (2004).  相似文献   

Les sillons plissés du Burundien supérieur dans la chaı̂ne Kibarienne d'Afrique centrale     

Michel Villeneuve  Jean Chorowicz 《Comptes Rendus Geoscience》2004,336(9):807-814

The Kibaran belt that extends all over the central Africa, from the Katanga to the southern Uganda, straddles the African great lakes area. The Kibaran stratigraphy is one of the most debated questions. Some geologists favoured two different systems: the Ruzizian system (1800–2000 Ma) and the Burundian or Kibaran system (1600–960 Ma). Some others favoured a single Burundian system with large areas granitised and metamorphosed during several Burundian tectonic events and with a lot of sedimentary fold belts of the Burundian age. Recent geological data and new remote sensing interpretations allow us to favour the second hypothesis but with a major disconformity within the Burundian system which is separating the Upper and the Lower Burundian. To cite this article: M. Villeneuve, J. Chorowicz, C. R. Geoscience 336 (2004).  相似文献   

Ennoyage des mines de fer lorraines : impact sur la qualité de l'eau     

Pauline Collon  Robert Fabriol  Michel Buès 《Comptes Rendus Geoscience》2004,336(10):889-899

The flooding of the abandoned iron mines of Lorraine leads to a degradation of the groundwater quality. Laboratory experiments allowed us to build a kinetic chemical model based on simple chemical mechanisms. During mining operations, pyrite oxidation and carbonate dissolution lead to the precipitation of gypsum. The local decrease of pH favours local dissolutions of minerals and releases ions that are fixed on cationic exchange sites. During the flooding of the mine workings, the dissolution of the newly precipitated gypsum, the precipitation of carbonates and cationic exchange reactions are responsible for the increase of the concentrations of sulphate, magnesium, sodium, potassium and strontium in water. Thereafter, these concentrations would decrease with the natural leaching of the mining reservoir. To cite this article: P. Collon et al., C. R. Geoscience 336 (2004).  相似文献   

Experimental sorption of Ni, Cs and Ln onto a montmorillonite up to 150°C     

Emmanuel Tertre  Gilles Berger  Michel Loubet 《Geochimica et cosmochimica acta》2005,69(21):4937-4948

The effect of temperature on the sorption of cations onto a dioctahedral smectite was investigated by running batch experiments at 25, 40, 80 and 150°C. We measured the distribution coefficient (Kd) of Cs⁺, Ni²⁺ and 14 lanthanides (Ln³⁺) between solutions and the montmorillonite fraction of the MX80 bentonite at various pH and ionic strengths. Up to 80°C we used a conventional experimental protocol derived from Coppin et al. (2002). At 150°C, the experiments were conducted in a PTFE reactor equipped with an internal filter allowing the sampling of clear aliquots of solution.The results show a weak but measurable influence of the temperature on the elements sorption. Kd’s for Ni²⁺ and Ln³⁺ increase by a factor 2 to 5 whereas temperature raises from 25 to 150°C. This effect seems higher at high ionic strength. The estimated apparent endothermic sorption enthalpies are 33 ± 10 kJ.mol⁻¹ and 39 ± 15 kJ.mol⁻¹ for Ni²⁺ and Eu³⁺, respectively. On the other hand, the temperature effect on Cs⁺ sorption is only evidenced at low ionic strength and under neutral conditions where the Kd decreases by a factor 3 between 25 and 150°C. Apparent exothermic sorption enthalpy for Cs⁺ on the montmorillonite is −19 ± 5 kJ.mol⁻¹.Experiments conducted at the four temperatures with the coexistence of all of the cations in the reacting solution (100 ppb of each element in the starting solution) or only one of them, produced similar values of Kd. This suggests the absence of competition between the sorbed cations, and consequently a low degree of saturation of the available sites. A fractionation of the lanthanides spectrum is also observed at high pH and high ionic strength whatever the temperature.The conclusion of this study is that the temperature dependence on sorption reflects, as the fractionation of REE or the pH and ionic strength effects, the chemical process which controls the overall reaction. In the case of an exchange dominated reaction (low pH and low ionic strength), the temperature effect is negligible. In the case of surface complexation (high pH and high ionic strength), the observed increase of Kd with temperature reflects either an increase of the sorption equilibrium constant with temperature or an endothermic property for reactions describing the montmorillonite surface chemistry.  相似文献   

Apport de la modélisation géophysique pour la compréhension de la structuration du pas de Calais     

Bruno Minguely  Jean-Louis Mansy  Michel Everaerts  Geoffrey M. Manby  Olivier Averbuch 《Comptes Rendus Geoscience》2005,337(3):305-313

This study is based on an analysis of seismic, gravimetric and magnetic data to model the structure of the Dover Straits area. The Dover Straits are set in a transitional position within the Brabant para-autochthon, which lies between the Ardennes allochthon to the south and the Brabant Massif to the north. The seismic profiles show that this area is characterised by several superimposed Mesozoic basins, whose evolution has been controlled by the reactivation of Lower Palaeozoic faults. In common with the adjacent Weald–Wessex and southern North Sea basins, the Dover Straits area records a Jurassic extensional phase and a post-Cretaceous tectonic inversion. The geophysical modelling reveals the presence of a basement to these Mesozoic basins that exhibits Ordovician to Silurian structures, which cannot be detected on the seismic reflection profiles. In contrast to earlier interpretations, the modelling presented here suggests that the Brabant Massif continues southward beyond the Dover Straits and under the Brabant para-autochthon. Gravity data also provides evidence for the presence of granitic body at depth, in the vicinity of Km 27 on the seismic profile, which may have driven the uplift of the Silurian rocks in the area of the Straits. Similar granitic intrusions have been proposed to explain gravity anomalies along the Rhenohercynian Margin in Belgium, eastern and southern England. The geophysical modelling demonstrates the continuity of the basement and Mesozoic basin structures across the Dover Straits, suggesting a common geological evolution of the adjacent southern England–northern France regions. To cite this article: B. Minguely et al., C. R. Geoscience 337 (2005).  相似文献   

Sur l'assimilation variationnelle de données par un modèle d'écosystème marin de type NPZ     

Yann Leredde  Christine Lauer-Leredde  Frédéric Diaz 《Comptes Rendus Geoscience》2005,337(12):1055-1064

A variational data assimilation method is applied to a simplified marine ecosystem model of NPZ (Nutrient Phytoplankton Zooplankton) type, which implies five parameters. The method allows us to optimise these parameters by an iterative process of minimisation of a cost function which quantifies the quadratic discrepancy between observations and simulation results. The first part of this note describes how to obtain the adjoint model of the NPZ model allowing us to compute the gradient of the cost function relative to the parameters. Two experiments of artificial data assimilation then show the efficiency of this method, but also its limitations because of non-linearities and sensitivity problems of the model relative to the parameters. To cite this article: Y. Leredde et al., C. R. Geoscience 337 (2005).  相似文献   

Sm–Nd isotopic compositions as a proxy for magmatic processes during the Neoproterozoic of the southern Brazilian shield     

Maria do Carmo P. Gastal  Jean Michel Lafon  Lo Afraneo Hartmann  Edinei Koester 《Journal of South American Earth Sciences》2005,18(3-4):255-276

Combined analyses of Nd isotopes from a wide range of Neoarchaean–Cretaceous igneous rocks provides a proxy to study magmatic processes and the evolution of the lithosphere. The main igneous associations include the Neoproterozoic granitoids from the southern Brazilian shield, which were formed during two tectonothermal events of the Brasiliano cycle: the São Gabriel accretionary orogeny (900–700 Ma) and the Dom Feliciano collisional orogeny (660–550 Ma). Rocks related to the formation of the São Gabriel arc (900–700 Ma) mainly have a depleted juvenile signature. For the Neoproterozoic collisional event, the petrogenetic discussion focuses on two old crustal segments and three types of mantle components. However, no depleted juvenile material was involved in the formation of the Dom Feliciano collisional belt (800–550 Ma), which implies an ensialic environment for the Dom Feliciano orogeny. In the western Neoproterozoic foreland, records of a Neoarchaean lower crust predominate, whereas a Paleoproterozoic crust does in the eastern Dom Feliciano belt. The western foreland includes two amalgamated geotectonic domains, the São Gabriel arc and Taquarembó block. In the collisional belt, the old crust was intensely reworked during the São Gabriel event. In addition to the Neoproterozoic subduction-processed subcontinental lithosphere (São Gariel arc), we recognize two old enriched mantle components, which also are identified in the Paleoproterozoic intraplate tholeiites from Uruguay and the Cretaceous potassic suites from eastern Paraguay. One end member displays the prominent influence of Trans-Amazonian (2.3–2.0 Ga) or older subduction events, whereas the other can be interpreted as a reenrichment of the first during the latest Trans-Amazonian collisional or younger events. This reenriched mantle is documented in late Neoproterozoic suites from the western foreland (605–550 Ma) and younger suites from the eastern collisional belt (600–580 Ma). The other enriched mantle component with an old subduction signature, however, appears only in older rocks of the collisional belt (800–600 Ma). The participation of the subduction-related Brasiliano mantle as an end member of binary mixing occurred in some early Neoproterozoic suites (605–580 Ma) from the western foreland, but the contribution of the Neoarchaean lower crust increased near the late igneous event (575–550 Ma).  相似文献   

Multiple origin and regional significance of bedding parallel veins in a fold and thrust belt: The example of a carbonate slice along the Appalachian structural front     

Stephan Sjourn  Michel Malo  Martine M. Savard  Donna Kirkwood 《Tectonophysics》2005,407(3-4):189-209

The development and evolution of bedding parallel veins (BPV) are investigated in the Saint-Dominique carbonate slice (southern Québec Appalachian structural front), in order to emphasize the regional significance of BPV in a fold and thrust belt and their importance in establishing its structural and diagenetic evolution. Structural and microstructural analyses reveal that most BPV display a laminated structure locally crosscut by a massive one. Both structures show mutual crosscutting relationships with bedding parallel or bedding perpendicular stylolites and with bedding perpendicular veinlets, indicating that BPV cementation and deformation are continuous processes. Opening both sub-parallel and sub-perpendicular to the BPV walls are documented. Early BPV are planes of weakness that focus later reactivation, and evidence of successive and sometimes opposite senses of opening are locally preserved within a single BPV. The bedding parallel orientation of these veins proved particularly helpful in establishing the structural evolution of an area mostly characterized by front parallel structures with little crosscutting relationships otherwise. Petrographic and geochemical (δ¹⁸O _VPDB and δ¹³C) analyses of structural cements suggest a common, locally derived source for the fluids that percolated through BPV, non-bedding parallel veins and faults. The isotopic ratios also reveal a significant enrichment in ¹⁸O and ¹³C through time. This evolution is tentatively correlated with tectonic, syn-convergence exhumation of the Saint-Dominique slice during its imbrication along the Appalachian structural front, after its burial under Taconian thrust sheets.  相似文献   

Multiple-mineral inclusions in diamonds from the Snap Lake/King Lake kimberlite dike, Slave craton, Canada: a trace-element perspective     

Prinya Promprated  Lawrence A. Taylor  Mahesh Anand  Christine Floss  Nikolai V. Sobolev  Nikolai P. Pokhilenko 《Lithos》2004,77(1-4):69-81

Multiple inclusions of minerals in diamonds from the Snap Lake/King Lake kimberlites of the southeastern Slave craton in Canada have been analyzed for trace elements to elucidate the petrogenetic history of these inclusions, and of their host diamonds. As observed worldwide, the harzburgitic-garnet diamond inclusions (DIs) possess sinusoidal REE patterns that indicate an early depletion event, followed by metasomatism by LREE-enriched, HREE-depleted fluids. Furthermore, these fluids appear to contain appreciable concentrations of LILE and HFSE, based on the increasing abundances of these elements in the olivine inclusion that occurs at the outer portion of a diamond compared to that near the core. The compositions of these fluids are probably a mixture of hydrous-silicic melt, carbonatitic melt, and brine, similar to the compositions of micro-inclusions in diamonds reported by Navon et al. (2003). Comparison between the compositions of majoritic and normal harzburgitic garnets shows that the former are more depleted in terms of major/minor elements (higher Cr#) but significantly more enriched in the REE (up to 10×). This characteristic may indicate the higher susceptibility for metasomatic enrichment of previously more depleted garnets. Garnets of eclogitic paragenesis show strong LREE-depleted patterns, whereas the coexisting omphacite inclusion has relatively flat light- and middle-REE but depleted HREE. Whole-rock reconstruction from coexisting garnet and omphacite inclusions indicates that the protolith of these inclusions was probably the extrusive section of an oceanic crust, subducted beneath the Slave craton.  相似文献   

Surface Moisture Availability and Rock Weathering in Cold Climates     

Christine Elliott 《New Zealand geographer》2004,60(1):44-51

The importance of moisture in determining which rock weathering processes may operate, as well as the rate at which rock weathering occurs, has long been recognised. However, little is known about how often or when moisture is available to the rock surface, or for how long the surface may be wetted. This paper gives some initial results from current research on granite rocks in Antarctica. Recordings of surface moisture, for two aspects and three locations in Victoria Land, show that moisture reaches the rock surface more frequently than might initially have been expected in this dry climate. The number of occasions the surface is wetted, and the quantity of moisture the surface received, varied with aspect and time of year. Rock surfaces could be wet for up to 40% of the time during the summer months. This has important implications for rock weathering where some processes are deemed not to operate, or to operate in very restricted locations, due to the apparent absence of moisture.  相似文献