Retrogressive hydration of calc-silicate xenoliths in the eastern Bushveld complex: evidence for late magmatic fluid movement     

T. Wallmach  C.J. Hatton  S.A. De Waal  R.L. Gibson 《Journal of African Earth Sciences》1995,21(4)

Two calc-silicate xenoliths in the Upper Zone of the Bushveld complex contain mineral assemblages which permit delineation of the metamorphic path followed after incorporation of the xenoliths into the magma. Peak metamorphism in these xenoliths occurred at T=1100–1200°C and P <1.5 kbar. Retrograde metamorphism, probably coinciding with the late magmatic stage, is characterized by the breakdown of akermanite to monticellite and wollastonite at 700°C and the growth of vesuvianite from melilite. The latter implies that water-rich fluids (X_CO2 <0.2) were present and probably circulating through the cooling magmatic pile. In contrast, calc-silicate xenoliths within the lower zones of the Bushveld complex, namely in the Marginal and Critical Zones, also contain melilite, monticellite and additional periclase with only rare development of vesuvianite. This suggests that the Upper Zone cumulate pile was much ‘wetter’ in the late-magmatic stage than the earlier-formed Critical and Marginal Zone cumulate piles.  相似文献   

Glacial-Geological/Geomorphological Research in West Greenland Used to Test an Ice-Sheet Model     

Frank G. M. van Tatenhove  Jaap J. M. van der Meer  Philippe Huybrechts 《Quaternary Research》1995,44(3)

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Results Of An Artificial Recharge Test And A Double Pumping Test As Preliminary Studies For Optimizing Water Supply In The Western Belgian Coastal Plain     

L. Lebbe  J. Tarhouni  E. Van Houtte  W. De Breuck 《Hydrogeology Journal》1995,3(3):53-63

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RESUMEN: En la planicie costera occidental de Bélgica, la mayor parte de la demanda de agua se abastece mediante captaciones en lentejones de agua dulce, bajo el cordón de dunas. Debido a la sobreexplotación, especialmente durante el verano, las captaciones están amenazadas por intrusiones de agua salada. Existe la posibilidad de utilizar recarga artificial, ya que en invierno una gran cantidad de agua dulce superficial se vierte al mar. Se presenta una propuesta para mejorar la gestión del agua en dicha región. Los estudios preliminares han consistido en dos ensayos: uno de recarga artificial en la zona de las dunas, y uno de doble bombeo en un cordón arenoso cerca de un canal de drenaje en la zona pantanosa de la planicie costera. La interpretación de los ensayos se realizó mediante modelación inversa. Los resultados del ensayo de recarga artificial han demonstrado la posibilidad de usar recarga artificial en la zona de captación de Koksijde. El ensayo de doble bombeo ha demonstrado que el cordón arenoso de Avekapelle, situado en la zona pantanosa, se puede utilizar como zona de captación.

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RéSUMé: Dans la partie occidentale de la plaine c?tière belge, la demande en eau est pour la plupart satisfaite par des captages d'eau souterraine. Les puits captent l'eau d'une lentille d'eau douce sous le cordon dunaire. Par suite d'une surexploitation, surtout pendant l'été, ces captages d'eau sont menacés par une intrusion d'eau salé. La recharge artificielle de la nappe peut être envisagée parce que, pendant l'hiver, de grandes quantités d'eau douce sont évacuées vers la mer. Une amélioration de la gestion de la ressource en eau est donc proposée. Deux essais ont été réalisés pour une étude préliminaire: un essai de recharge artificielle dans la région des dunes et un essai de double pompage prés d'un canal de drainage dans les polders. Ces deux essais ont été interprétés grace à une méthode inverse. L'essai de recharge artificielle a démontré les possibilités de recharge de la nappe pour le site de captage de Coxyde. L'essai de double pompage a montré que le d?me sableux d'Avekapelle, dans les polders, est une région de recharge qui convient.

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Über die Installation einer Apparatur für die Analyse des atmosphärischen Kohlensäuregehalts     

Walter Bischof  Arturo De Maio 《Pure and Applied Geophysics》1964,58(1):204-207

Zusammenfassung Die im vorläufigen Bericht beschriebene Anlage für die Analyse von atmosphärischem CO₂-Gehalt wurde vervollständigt. Es können nunmehr kontinuierliche Analysen sowie Einzelanalysen mit Gaspipetten ausgeführt werden. Die Arbeitsweise wird beschrieben und einige Resultate werden mitgeteilt. Es kann mit einer Messgenauigkeit von ±0.3 ppm gerechnet werden.

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Summary The second and the third part of the installation of the equipment for measuring the CO₂ content in the atmospheric air has been accomplished. It is now possible to make continuous local air analysis, and of samples collected in pipettes. The procedure is described and a few results reported. The measurement accuracy lies to within ±0.3 ppm.

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Riassunto Sono state completate la seconda e la terza parte dell'apparecchiatura per la misura del CO₂ atmosferico. Esse permettono l'analisi continua dell'aria locale e l'analisi di campioni raccolti in pipette; di queste si riporta un esempio. La precisione della misura è di ±0.3 ppm.

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Meteorologisches Institut der Universität Stockholm. Contribution No. 164.  相似文献   

Educational Facilities in Ground-Water Hydrology and Geology Outside the U. S. A. and Canada, 1963     

Roger J. M. De  Wiest Member NWWA 《Ground water》1964,2(2):18-24

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Chemical Ozone Loss in the Arctic Winter 1994/95 as Determined by the Match Technique     

M. Rex  P. Von Der Gathen  G.O. Braathen  N.R.P. Harris  E. Reimer  A. Beck  R. Alfier  R. Krüger-carstensen  M. Chipperfield  H. De Backer  D. Balis  F. O'Connor  H. Dier  V. Dorokhov  H. Fast  A. Gamma  M. Gil  E. Kyrö  Z. Litynska  I.S. Mikkelsen  M. Molyneux  G. Murphy  S.J. Reid  M. Rummukainen  C. Zerefos 《Journal of Atmospheric Chemistry》1999,32(1):35-59

The chemically induced ozone loss inside the Arctic vortex during the winter 1994/95 has been quantified by coordinated launches of over 1000 ozonesondes from 35 stations within the Match 94/95 campaign. Trajectory calculations, which allow diabatic heating or cooling, were used to trigger the balloon launches so that the ozone concentrations in a large number of air parcels are each measured twice a few days apart. The difference in ozone concentration is calculated for each pair and is interpreted as a change caused by chemistry. The data analysis has been carried out for January to March between 370 K and 600 K potential temperature. Ozone loss along these trajectories occurred exclusively during sunlit periods, and the periods of ozone loss coincided with, but slightly lagged, periods where stratospheric temperatures were low enough for polar stratospheric clouds to exist. Two clearly separated periods of ozone loss show up. Ozone loss rates first peaked in late January with a maximum value of 53 ppbv per day (1.6 % per day) at 475 K and faster losses higher up. Then, in mid-March ozone loss rates at 475 K reached 34 ppbv per day (1.3 % per day), faster losses were observed lower down and no ozone loss was found above 480 K during that period. The ozone loss in hypothetical air parcels with average diabetic descent rates has been integrated to give an accumulated loss through the winter. The most severe depletion of 2.0 ppmv (60 %) took place in air that was at 515 K on 1 January and at 450 K on 20 March. Vertical integration over the levels from 370 K to 600 K gives a column loss rate, which reached a maximum value of 2.7 Dobson Units per day in mid-March. The accumulated column loss between 1 January and 31 March was found to be 127 DU (36 %).  相似文献   

Designing river water quality policy interventions with scarce data: the case of the Middle Tagus Basin,Spain     

Antonio Bolinches  Lucia De Stefano  Javier Paredes-Arquiola 《水文科学杂志》2020,65(5):749-762

ABSTRACT

Anthropic pressures deteriorate river water quality, so authorities need to identify their causes and define corrective actions. Physically based water quality models are a useful tool for addressing physicochemical pollutants, but they must be calibrated with an amount of data that is often unavailable. In this study, we explore the characterization of a model to design corrective interventions in a context of sparse data. A calibration indicator that is both simple and flexible is proposed. This approach is applied to the Middle Tagus Basin in central Spain, where the physicochemical concentration of pollutants is above legal standards. We quantify the effects of the main existing pressures (discharge from wastewater treatment plants, agricultural diffuse pollution and a major inter-basin water transfer) on the receiving waters. In particular, the study finds that wastewater treatment plant effluent concentrations should be reduced to up to 0.65 mg/L of ammonium and 0.55 mg/L of phosphate to achieve the environmental goals. We propose and prioritize a set of policy actions that would contribute to the good status of surface water bodies in the region.  相似文献   

The great 1983 floods in South American large rivers: a continental hydrological modelling approach     

Ayan Santos Fleischmann  Vinícius Alencar Siqueira  Sly Wongchuig-Correa  Walter Collischonn  Rodrigo Cauduro Dias De Paiva 《水文科学杂志》2020,65(8):1358-1373

ABSTRACT

This study provides a spatio-temporal analysis of the great floods that occurred in South America in 1983 using hydrometeorological data and outputs from a continental-scale hydrological-hydrodynamic model. In the extreme year 1983, there were three main flooding periods (February, June and July) in many South American river basins, such as the Araguaia, Tocantins, São Francisco, Uruguay, La Plata and its tributaries, resulting in high discharge of the Paraguay River for many months. Depth–area–duration curves show that 3-day precipitation events in northern regions of South America were among the largest 15 events in the period 1980–2015 but only for specific locations, whereas in southern areas, the most extreme events in the same period were for larger durations (≥7-day precipitation). Modelled total export of water volume to the oceans indicates that rivers draining to the South Atlantic reached an anomaly of 3.7 during 1983, followed by 1998 (1.9) and 1992 (1.1), all of them corresponding to El Niño years.  相似文献   

Revision of lunar Rb-Sr ages     

J.R De Laeter  M.J Vernon  W Compston 《Geochimica et cosmochimica acta》1973,37(3):700-702

Becalibration of ‘spikes’ using stoichiometric Rb and Sr salts recently issued by the National Bureau of Standards shows that our determinations of the ratio ${}^{87}\text{Rb}{}^{86}\text{Sr}$ in lunar samples have been low by 1.8 per cent, which we attribute to non-stoichiometry of the salts previously used for calibration, particularly RbCl. As a result, our lunar age-determinations must be decreased by this amount.  相似文献   

Volcanology and petrology of the Assab Range (Ethiopia)     

M. De Fino  L. La Volpe  L. Lirer 《Bulletin of Volcanology》1973,37(1):95-110

The results of petrological and volcanological investigations of the Assab area (Ethiopia) are reported. Fissure activity — which produced basaltic lava flows and several spatter cones — and central activity — represented by a cumulus dome and two explosive craters — have been recognized. The area is characterized by E-W and NE-SW tectonic trends, whereas the NNW-SSE « Eritrean trend » is absent. Transverse tectonics is limited to the blocks bordering the Danakil Depression, and never extends into the Depression itself. Mineralogical composition and chemical data point to an alkaline nature of the Assab lavas, which have been classified as: picritic basalts tending to ankaramites; alkali olivine basalts; hawaiites; and all the rock types ranging from mugearites to trachytes. Two rock groups have been identified which could be due to crystal fractionation processes controlled by different degree of oxidation. The petrological difference between the rocks from Afar proper and those from the Danakil block (unquestionably alkaline rock types in the Danakil block, and transitional rock types in Afar) is emphasized.  相似文献