Assessing Pesticide Contamination to Ground Water: A Rapid Approach   总被引：1，自引：0，他引：1  

Majid Ehteshami  Richard C. Peralta  Hubert Eisele  Howard Deer  Terry Tindall 《Ground water》1991,29(6):862-868

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Convective instabilities in a variable viscosity fluid cooled from above     

Claude Jaupart  Barry Parsons 《Physics of the Earth and Planetary Interiors》1985,39(1):14-32

Whether in the mantle or in magma chambers, convective flows are characterized by large variations of viscosity. We study the influence of the viscosity structure on the development of convective instabilities in a viscous fluid which is cooled from above. The upper and lower boundaries of the fluid are stress-free. A viscosity dependence with depth of the form ν₀ + ν₁ exp(?γ.z) is assumed. After the temperature of the top boundary is lowered, velocity and temperature perturbations are followed numerically until convective breakdown occurs. Viscosity contrasts of up to 10⁷ and Rayleigh numbers of up to 10⁸ are studied.For intermediate viscosity contrasts (around 10³), convective breakdown is characterized by the almost simultaneous appearance of two modes of instability. One involves the whole fluid layer, has a large horizontal wavelength (several times the layer depth) and exhibits plate-like behaviour. The other mode has a much smaller wavelength and develops below a rigid lid. The “whole layer” mode dominates for small viscosity contrasts but is suppressed by viscous dissipation at large viscosity contrasts.For the “rigid lid” mode, we emphasize that it is the form of the viscosity variation which determines the instability. For steep viscosity profiles, convective flow does not penetrate deeply in the viscous region and only weak convection develops. We propose a simple method to define the rigid lid thickness. We are thus able to compute the true depth extent and the effective driving temperature difference of convective flow. Because viscosity contrasts in the convecting region do not exceed 100, simple scaling arguments are sufficient to describe the instability. The critical wavelength is proportional to the thickness of the thermal boundary layer below the rigid lid. Convection occurs when a Rayleigh number defined locally exceeds a critical value of 160–200. Finally, we show that a local Rayleigh number can be computed at any depth in the fluid and that convection develops below depth z_r (the rigid lid thickness) such that this number is maximum.The simple similarity laws are applied to the upper mantle beneath oceans and yield estimates of 5 × 10¹⁵?5 × 10¹⁶ m² s^?1 for viscosity in the thermal boundary layer below the plate.  相似文献   

Petrology of the mafic rocks of the Xigaze ophiolite,Tibet   总被引：2，自引：0，他引：2  

Jacques Girardeau  Jean Claude C Mercier  Wang Xibin 《Contributions to Mineralogy and Petrology》1985,90(4):309-321

The Xigaze ophiolite (Yarlung-Zangbo suture zone, Southern Tibet, China) shows an unusual crustal sequence characterized by a lack of large masses of cumulate gabbros, by dolerites intrusive throughout the whole ophiolite sequence, and by the injection of dolerites in already serpentinized peridotites. The abyssal tholeiitic nature of all the mafic rocks indicates that they have been generated at an oceanic ridge. All the geological arguments and petrological and textural data on the mafic rocks point to very low heat production and large heat losses through widespread intensive sea-water circulation, for the spreading centre in which they have been formed, in good agreement with a slow-spreading ridge origin.  相似文献   

The mechanical state of the lithosphere in the Altiplano-Puna segment of the Andes     

Claude Froidevaux  Bryan L. Isacks 《Earth and Planetary Science Letters》1984,71(2):305-314

Information about topography, the shape of the geoid, seismicity, Neogene deformation and volcanism in the region of Altiplano-Puna of western South America is used to analyse the state of stress across the convergent plate margin in terms of the effects of topography and simple models of its compensation. An average elevation near 4 km is consistent with compensation by a yet unresolved combination of crustal root and hot uppermost mantle producing a geoid high of 22–27 meters, average horizontal compressive stress (in excess of a reference sea level lithostatic value) of 390 bars in a 150 km thick lithosphere, and an average shear stress of 170 bars along a 30° dipping interplate boundary. The basis for these estimates is evidence for a neutral to extensional stress regime within the high plateau contrasted with a compressional regime on the eastern slopes and along the interplate boundary itself. Comparison with other plateaus in a convergent plate tectonic setting suggests an evolutionary sequence from compressional to extensional tectonics as elevation of the plateau increases.  相似文献   

The lead isotope systematics of ophiolite complexes     

Bruno Hamelin  Bernard Dupré  Claude J. Allègre 《Earth and Planetary Science Letters》1984,67(3):351-366

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Statistical analysis of isotopic ratios in MORB: the mantle blob cluster model and the convective regime of the mantle     

Claude J. Allègre  Bruno Hamelin  Bernard Dupré 《Earth and Planetary Science Letters》1984,71(1):71-84

A statistical examination of isotopic distributions for MORB from various ocean ridges leads to the “blob cluster model”, in which the oceanic crust accreting at ridges results from the mixing of two components within the ascending mantle. These are (1) upper mantle material and (2) discrete rising blobs of more radiogenic material. The blobs are fractionated to a variable degree and are distributed in the upper mantle circulation in a manner that is related to the spreading rate.(1) Themean values of the isotopic distributions allow us to calculate the probabilities of the two types of material within the mantle. The results show that theproportion of asthenospheric material in the mixtureincreases with the spreading rate, in agreement with the hypothesis of blob dilution within the upper mantle convection.Mass fluxes can be estimated for the rising blobs from these probabilities, which depend on the respective concentrations in the sources of the two types of material. If the blobs originate in the lower mantle, this flux estimation would suggest that a significant part of the lower mantle has been injected into the upper mantle during earth history.(2) Thestandard deviations of the distributions depend on the “efficiency” of the mixing process:the more imbricated are the asthenospheric and blob materials in the mixture,the smaller is theisotopic spread. This efficiency parameter is shown to increase with the spreading rate, as already suggested by previous comparisons between the East Pacific Rise and the Mid-Atlantic Ridge. Moreover, this feature may also be correlated with other data such as ridge bathymetric variations.  相似文献   

Photo-interprétation à différentes échelles et relevés de terrain: exemples de corrélations structurales dans le Bassin Méditerranéen et sur le socle Ouest africain     

Jean Claude Grillot 《International Journal of Earth Sciences》1984,73(2):787-808

Résumé L'interprétation structurale des linéaments, décelés sur clichés photographiques pris par satellite, est discutée sur les bases suivantes: d'une part en pratiquant au minimum un changement d'échelle (plus grande); d'autre part en utilisant les relevés de terrain. Des exemples pris dans le Bassin Méditerranéen sédimentaire et sur le socle cristallophyllien de l'Afrique de l'Ouest permettent de définir une méthodologie commune. Ainsi en région sédimentaire, partant de prises de vue par exemple au 1/2 500 000, les échelles au 1/15 000 et au 1/50 000 se révèlent être des compléments précieux en photo-interprétation. De la même façon en zone de socle, les échelles au 1/20 000 et au 1/50 000 sont complémentaires du 1/200 000. De plus grâce aux donnés de terrain, il est possible de qualifier l'information photogéologique et d'en exprimer sa nature. Enfin les problèmes de corrélations entre rhegmatisme de socle et fracturation de couverture sont abordés de façon préliminaire: la similitude directionnelle observée devrait orienter les futures recherches en ce domaine.

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The structural interpretation of disclosed lineaments on satellite's pictures ist discused on the following basis: first, with a minimum scale change (making it bigger); on the other hand using field plotting. The examples took from the Mediterranean sedimentary basin and from the western Africa crystalographic shield allow us to define a common methodology. Thus, in sedimentary area, through 1/2 500 000 scale aerial photographys, the 1/15 000 and 1/50 000 scales would be real valuable complements in photo-interpretation. Same way as, in shield zone, the 1/20 000 and 1/50 000 scales would be complements of the 1/200 000 one. More than that, because of field plotting utilisation is possible to quality photogeological information and even to explain its nature. In short correlation problems are exposed in a preliminary approach; the observed directional similitude could orientate the future research.

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Zusammenfassung Die strukturelle Deutung von Lineamenten, die aus Satellitenphotos abzulesen sind, wird nach folgenden Voraussetzungen erörtert: zum einen wird zumindest eine Vergrößerung des Maßstabes vorgenommen, zum anderen werden Geländebefunde herangezogen. An Hand von Beispielen aus dem sedimentären Mittelmeerbecken sowie dem Kristallo-phyllitischen Sockel Westafrikas ist es möglich, eine gemeinsame Methodik zu definieren. So erweisen sich im sedimentären Gebiet die Maßstäbe 115 000 und 150 000 als wertvolle Ergänzungen zur Photointerpretation zum Beispiel einer Aufnahme von 12 500 000. Entsprechend ergänzen im Bereich des Sockels die Maßstäbe 120 000 und 150 000 die Aufnahme von 1200 000. Darüber hinaus ist es mit Hilfe von Geländedaten möglich, die photogeologische Information zu qualifizieren und zu beinhalten. Schließlich werden die Probleme der Korrelation zwischen Bruchbildung im Sockel und Brücken im Deckgebirge angesprochen: Die beobachtete Annäherung in der Ausrichtung soll zukünftige Untersuchungen auf diesem Gebiet orientieren.

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, , : , no- , , — . . , 1: 15.000 1:50.000 12.500.000. 1: 200.000 1: 20.000 1: 50.000. . . .

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A new parameterization of eddy diffusivities for nocturnal boundary-layer modeling     

Claude Estournel  Daniel Guedalia 《Boundary-Layer Meteorology》1987,39(1-2):191-203

Exchange coefficients and mixing lengths under stable stratification have been studied through measurements of mean wind velocity and temperature in the nocturnal boundary layer. For values of the gradient Richardson number lower than 0.15, our measurements fit well the relation of Delage (1974). Beyond Ri = 0.15, the decrease of mixing length is much slower. So a new parameterization of turbulent exchanges is suggested. When introduced in a model of the nocturnal boundary layer, it results in a thickening of the turbulent and inversion layers.  相似文献   

Helmut Erich Landsberg, 1906–1985     

Hubert H. Lamb 《Climatic change》1986,9(3):265-266

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Héritage et sources des métaux d'après la géochimie isotopique du plomb     

Eric Marcoux  Hubert Bril 《Mineralium Deposita》1986,21(1):35-43

Résumé Les galènes et sulfoantimoniures de plomb des filons quartzeux, barytiques et fluorés du Haut-Allier (district de Brioude-Massiac) ont fait l'objet d'analyses isotopiques du plomb. Les résultats montrent l'existence de deux populations de plomb appartenant à chacune des deux phases minéralisatrices reconnues dans la région.La première population (18,108<²⁰⁶Pb/²⁰⁴Pb<18,181) est rapportée à la phase mésothermale permienne. Elle comprend les sulfosels précoces des filons antimonifères ainsi que la galène des filons plombo-stannifères. L'homogénéité isotopique confirme la liaison génétique existant entre ces différents types filoniens et leur appartenance à un même processus métallogénique. Le socle métamorphique régional apparaît comme la source possible du plomb.La relative dispersion des valeurs isotopiques de la seconde population (18,215<²⁰⁶Pb/²⁰⁴Pb<18,472), d'âge liasique, est corrélable avec la situation géographique et géologique des filons. Elle est due à deux phénomènes complémentaires: le lessivage d'un segment crustal comprenant le socle métamorphique avec une participation graduée du granite uranifère de la Margeride et la réassimilation partielle du plomb des filons permiens. Ce dernier phénomène d'héritage métallique se traduit au niveau des paragenèses par la formation de filons à sulfosels dominants.

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Lead isotope analyses are reported for galena and lead sulfosalts from quartz, barite and fluorite vein deposits from the Haut-Allier (Brioude-Massiac district). The data define two lead populations reflecting the two mineralization episodes in this region.The first population (18,108<²⁰⁶Pb/²⁰⁴Pb<18,181) is related to the Permian mesothermal episode. It includes early sulfosalts from antimony veins and galena from lead-stanniferous veins. The Pb isotopic homogeneity confirms the relationship between the different vein types and their formation by a single metallogenic process. The metamorphic basement is the potential source of lead.The second population includes quartz-barite and fluorite veins. It shows much more isotopic variation (18,215<²⁰⁶Pb/²⁰⁴Pb<18,472) correlating with the geographical and geological location of the veins. Because the veins have a contemporaneous age, the isotopic dispersion therefore depends on two complementary phenomena: the leaching of a large volume of crust, including metamorphic basement, with a progressive contribution of the uraniferous granite of Margeride; and the partial remobilization of lead from Permian veins. The latter inheritance phenomena result in the genesis of major lead-sulfosalt vein deposits.

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