Synthesis of Fluid Inclusion Reference Materials in the H2O–NaCl–CH4 System

In this study, we detail procedures to synthesise inclusions of fluids of known composition under diagenetic conditions – low temperatures (50–180 °C) and pressures (2–25 MPa) – hosted by quartz. Pre‐existing microcavities in polished quartz chips were used, decrepitated and rinsed before being healed in an autoclave. Each synthesis required around 4 weeks. A range of biphase liquid–vapour inclusions in the H₂O–CH₄–NaCl system, similar to natural ones, were synthesised in quartz, varying the content of all three components. The quartz chips were checked before and after synthesis by optical microscopy, microthermometry and Raman spectroscopy. The method was used to build a series of calibration curves relating methane‐to‐water count ratios to the methane content of aqueous fluid inclusions. Good correlation was obtained between Raman band area ratios and the expected CH₄ solubilities from equations of state. The chosen procedure's main advantages, compared with other published methods, are as follows: quicker healing of the microfractures at lower temperatures, larger inclusions, simple quartz sample preparation, control of fluid inclusion composition and the use of commercial reactors. Such reference material inclusions allow the calibration of Raman microspectrometers with the objective of PTX reconstruction of palaeofluid migration in petroleum reservoirs.     

Comparaison des méthodes d'interpolation pour l'é laboration de modèles numé riques d'é lé vation de haute pré cision dans la repré sentation micro-topographique des plaines inondables

Résumé

La micro-topographie des zones inondables influence l'étendue des nappes d'eau des secteurs submergés lors des crues. Cette analyse vise à comparer des méthodes d'interpolation pour la réalisation de modèles numériques d'élévation (MNE) de haute précision représentant la micro-topographie des plaines d'inondation. Ces méthodes ont été comparées au moyen d'un système d'information géographique (SIG) afin d'identifier lesquelles apparaissent les plus efficaces dans l'élaboration de l'image micro-topographique des sites, et ce en fonction d'un nombre restreint de données d'élévation. L'efficacité de chacune des méthodes d'interpolation a été validée au moyen du calcul de l'erreur quadratique moyenne, de tests statistiques, de cartes de l'erreur et d'une évaluation visuelle en trois dimensions. Il ressort que les méthodes d'interpolation du krigeage simple, de la fonction radiale, du réseau de triangles irréguliers et du krigeage ordinaire sont celles qui représentent le plus adéquatement la micro-topographie des sites, alors que les méthodes d'interpolation de l'inverse de la distance et du krigeage universel produisent des erreurs élevées.

Citation Drouin, A. & Saint-Laurent, D. (2010) Comparaison des méthodes d'interpolation pour l'élaboration de modèles numériques d'élévation de haute précision dans la représentation micro-topographique des plaines inondables. Hydrol. Sci. J. 55(4), 526?539.     

Impact de la variabilité climatique et du barrage Nangbéto sur l'hydrologie du système Mono-Couffo (Afrique de l'Ouest)

Résumé

En Afrique tropicale, de nombreuses études sur la variabilité climatique montrent qu'une tendance à la sécheresse s'est manifestée à partir de la fin des années 1960. Cette sécheresse a affecté aussi l'hydrosystème Mono-Couffo, en Afrique de l'Ouest, avec une persistance remarquable qui s'est répercutée sur les écoulements. Depuis 1988, avec la mise en eau du barrage de Nangbéto, qui coïncide avec une légère reprise pluviométrique dans les années 1990, on assiste à une modification du régime hydrologique du Mono à Athiémé. Les méthodes statistiques appliquées aux données mensuelles de pluie et débit de la période 1961–2000 ont permis de constater que les déficits pluviométriques des décennies 1970 et 1980 ont engendré des déficits de l'écoulement. Mais, avec la légère reprise pluviométrique (2%) de 1988 à 2000, on assiste à un excédent d'écoulement de 37% sur le Mono à Athiémé à régime « artificiel » depuis 1988; et, par contre, pas d'excédent (0,1%) sur le Couffo à Lanta à régime « naturel ».

Editeur Z.W. Kundzewicz

Citation Amoussou, E., Camberlin, P. et Mahé, G., 2012. Impact de la variabilité climatique et du barrage Nangbéto sur l'hydrologie du système Mono-Couffo (Ouest Afrique). Hydrological Sciences Journal, 57 (4), 805–817.     

On the Lu-Hf Isotope Geochemistry of Silicate Rocks

This paper reviews the history (TIMS, hot‐SIMS, MC‐ICP‐MS), significance, geochemical behaviour and current uncertainties (λ¹⁷⁶ Lu, Hf‐Nd Bulk Silicate Earth) surrounding the Lu‐Hf isotope system, and thus marks two decades of its application to geochemical problems. An appendix further presents (a) improvements to the original chemistry protocol of Blichert‐Toft et al. (1997) for application to Mg‐rich samples and (b) a compilation of previously published and new Hf isotope determinations by MC‐ICP‐MS for a set of international rock reference materials. Prior to the advent of multiple‐collector plasma source mass spectrometry (MC‐ICP‐MS), routine analysis of the Lu‐Hf isotope system developed only slowly because of the extreme difficulty of measuring Hf isotope compositions with thermal ionisation mass spectrometry, caused by the very high first ionisation potential of Hf. However, Hf isotope compositions can be measured relatively easily using MC‐ICP‐MS and this new technique now provides reproducible measurements at high precision regardless of the matrix from which Hf is separated. Of the commonly used long‐lived radiogenic isotope systems, only the Sm‐Nd and Lu‐Hf isotope systems are unaffected by parent/daughter fractionations related to volatile nebular processes and core formation. While other systems (Rb‐Sr, U‐Th‐Pb, Re‐Os) may also be used to investigate the chemical evolution of the Earth, Moon, Mars and parent bodies of differentiated meteorites, the larger uncertainties in their bulk chemical and isotopic values limit their application to determine geochemical budgets and assess planetary mantle‐crust evolution. In the study of garnet‐bearing rocks, both for dating purposes and as an isotopic tracer for source provenance and mantle processes, the Lu‐Hf isotope system likewise is of major interest because of the high partition coefficient of Lu compared to Hf for garnet with respect to other minerals. Furthermore, the larger Lu/Hf fractionation compared to Sm/Nd during melting beneath ridges produces proportionally higher Lu/Hf in the residue and faster in‐growth of a radiogenic Hf isotopic signature (compared to Nd), which may help shed light on the dynamics of mantle melting. While the chemistry protocol and mass spectrometric technique for high‐precision Lu‐Hf isotope analysis have been resolved in satisfactory ways over the past five years, more accurate determination of the decay constant for ¹⁷⁶ Lu, at present known with a precision of only about 4%, still needs to be completed and a consensus reached on which value to use for future Lu‐Hf isotope studies. Although the current combined Lu‐Hf and Sm‐Nd Bulk Silicate Earth parameters are plagued by possible incompatibilities in chondrite selection and potential interlaboratory biases, a more accurate set of values may not be readily established owing to heterogeneities in the isotopic composition of chondrites that far exceed present analytical accuracy.     

浅析煤炭（田）地质勘探系统业务流程再造

流程再造(BPR)被认为是一种能显著提高企业业绩的根本性的管理理念,已被许多优秀的企业所运用,流程再造的作用越来越引起重视。由于煤田地质勘探系统逐步实施事转企,整个系统正处于发展的瓶颈期。因此,要想打破瓶颈,必须实施切实有效的变革,而变革的根本手段就是对业务流程进行再造。     

Les rhyolites hyperalcalines (pantellérites) du lac Tchad. Composition et signification tectonomagmatiqueThe peralkaline rhyolites (pantellerites) of the Lake Chad. Composition and tectonomagmatic significance

Remnants of rhyolite lava-dome and of alkaline microgranite extrusions emerge, as inselbergs, in the alluvial plain, south of Lake Chad. The peralkaline, arfvedsonite- and acmite-bearing rhyolites are determined as pantellerites. They can be related to a tectonomagmatic stage, dated of the Late Cretaceous, of the western central Africa rift system. They may constitute the NNE extension of a N50° to 30° elongated succession of small alkaline complexes, from the Gulf of Guinea to the North-Cameroon, which initiated the magmatic activity of the Cameroon Line. To cite this article: J.-P. Vicat et al., C. R. Geoscience 334 (2002) 885–891.     

Le magmatisme basique hercynien et post-hercynien du Système central espagnol : essai de caractérisation des sources mantelliques

Basic magmatism in central Spain occurred sporadically during a long period of ca. 140 Ma. The geochemical data on representative samples from the five igneous episodes show that different mantle reservoirs were tapped. Crustal involvement (via recycling in mantle sources or by hybridization at emplacement levels) was important in the basic magmas related to the Hercynian orogeny (Gb1 to Gb3 suites). Samples occurring as later dykes have signatures ranging from OIB-like values (Gb4 alkaline lamprophyres) to those of a formerly enriched subcontinental lithospheric mantle (tholeiites Gb5). To cite this article: C. Villaseca et al., C. R. Geoscience 336 (2004).     

Mise en évidence et analyse d'une structure atlasique ennoyée au front de la Chaîne alpine tunisienne

The eastern Tunisian Atlas shows major subsurface faults: the Kairouan–Sousse Fault (FKS), to the north, and the El Hdadja fault (FEH), to the south. The FKS is an inherited structural trend active since Late Cretaceous times. This fault is an eastern splay of the Chérichira–Labeïd fault. It separates a large northern diapiric structure (Ktifa Diapir) from a subsident domain (the Kairouan–El Hdadja rim-syncline), with a pull-apart configuration to the south. The latter area, which appears to be an inherited weakness zone at the range border, has recorded a series of tectonic events that characterizes the Alpine structural development in Tunisia. To cite this article: S. Khomsi et al., C. R. Geoscience 336 (2004).     

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

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).     

Numerical quantification of sources and phase partitioning of chemical species in cloud: application to wintertime anthropogenic air masses at the Puy de Dôme station

The Model of Multiphase Cloud Chemistry M2C2 has recently been extended to account for nucleation scavenging of aerosol particles in the cloud water chemical composition. This extended version has been applied to multiphase measurements available at the Puy de Dôme station for typical wintertime anthropogenic air masses. The simulated ion concentrations in cloud water are in reasonable agreement with the experimental data. The analysis of the sources of the chemical species in cloud water shows an important contribution from nucleation scavenging of particles which prevails for nitrate, sulphate and ammonium. Moreover, the simulation shows that iron, which comes only from the dissolution of aerosol particles in cloud water, has a significant contribution in the hydroxyl radical production. Finally, the simulated phase partitioning of chemical species in cloud are compared with measurements. Numerical results show an underestimation of interstitial particulate phase fraction with respect to the measurements, which could be due to an overestimation of activated mass by the model. However, the simulated number scavenging efficiency of particles agrees well with the measured value of 40% of total number of aerosol particles activated in cloud droplets. Concerning the origin of chemical species in cloud water, the model reproduces quite well the contribution of gas and aerosol scavenging estimated from measurements. In addition, the simulation provides the contribution of in-cloud chemical reactivity to cloud water concentrations.