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1.
Isotopic dilution technique and mass spectrometry are used in order to measure isotopic compositions and concentrations of some particular elements on the Oklo sample KN50-3548, which are interesting for describing the nuclear reaction. These analyses give coherent results leading to the determination of the following parameters: neutron fluence, spectrum index, total number of fissions relative to uranium, and percentage of238U and239Pu fissions. From the percentage of plutonium fissions, the duration of the nuclear reaction is estimated to be 800,000 years. The age of the nuclear reaction is measured from the lead analysis and from the number of uranium fissions; these two determinations give respectivelyd = 1730 ± 10m.y. andd = 2000 ± 100m.y. The second method, based on the assumption that uranium and rare earths have not migrated, could mean that the nuclear reaction might be older than the Francevillian. It is also shown that no contamination by natural elements has occurred for lead, rare earths, palladium and rare gases, after the reaction.  相似文献   

2.
We present an aeromagnetic survey of the Gulf of Valencia and the Balearic Islands (western Mediterranean). A total field anomaly map and a map of the anomalies reduced to the pole have been obtained. From these maps, it is apparent that there are two regions of opposing magnetic style: the Balearic archipelago which is magnetically very smooth, and the north Balearic basin (or Gulf of Valencia) where anomalies are in places very intense. From a comparison of these two domains, we conclude that the Valencian basin was created during an extensional tectonic phase.  相似文献   

3.
Uranium and thorium distributions are studied in top-oxidized, bottom-reduced cores. In sediments uranium is more abundant in the reducing zones than in the oxidized ones. In pore water also, uranium is more abundant in the reducing zones. In the cores studied, the Io/U chronology is completely disturbed.The general model of steady-state diagenesis cannot be applied to the uranium pattern.  相似文献   

4.
An experimental study is reported on the distributions of trace amounts of Rb and Cs between some trioctahedral micas and a hydrothermal solution at 600°C and 1000 bars. The equilibrium constant KXmin = (X/K)aq/(X/K)min varies considerably with the composition of micas. KCsmin is equal to 4.2 for phlogopite of theoretical composition, whereas it becomes equal to 8 for a mica close to eastonite. It reaches up to 17 for a mica in which Mg is largely substituted by Al. In annite, Fe(II) analogue of phlogopite, KCsmin becomes equal to 1.8. With Rb, the variations of the equilibrium constant are smaller than with Cs. KRbmin is 0.65 for phlogopite and increases up to 1.9 for a more aluminous mica. It is 0.44 for annite.The distributions depend very much on the ratios Mg/Fe and Si/Al of the trioctahedral micas. Consequences in geothermometrical interpretation of alkali trace element distributions in natural rocks are considered.  相似文献   

5.
After recalling briefly the major geological characters of the Nepal Himalayas and the global evolution of the Himalayan chain we stress the importance of three dominant and remarkably constant tectonic features in this chain: (1) a huge overthrust is seen everywhere to entail a visible throw of more than 100 km; (2) a shallow dipping cleavage develops over an observable thickness in excess of 15 km; and (3) in the underthrusting slab the stretching lineation keeps a similar direction constantly perpendicular to the local trend of the chain.We suggest that these features, especially the cleavage, can be explained in terms of a simple mechanical model, namely simple shear on a crustal scale. This clearcut case could be used as a model for the origin of flattish cleavages in many orogens. After discussing other modes of formation for such cleavages (diapiric intrusion, extension) we show that the Himalayan model could apply to other chains.  相似文献   

6.
The measurement of the176Lu/175Lu ratio in the Oklo uranium ore zones where nuclear reactions have been identified, can be related to the average equilibrium temperature of the neutrons at the time of the nuclear reactions; indeed, the effective neutron capture cross section of the isotope176Lu is particularly sensitive to temperature. A simple model has been developed to calculate the temperature. The results obtained on seven samples from three reactor zones are presented. From six samples an average value of280 ± 50°C is obtained, the corresponding integrated neutron flux τ varies from 0.06 × 1020 to 6 × 1020 n/cm2 and176Lu/175Lu from 0.0254 to 0.0054. From one sample a very high temperature is obtained:T > 1000°C, τ = 4.4 × 1020n/cm2,176Lu/175Lu= 0.0032. The validity of this result is sharply dependent on the relative stability of uranium and the rare earths during and after the nuclear reactions; so, it can be noticed that the two samples giving the highest temperatures present a surprisingly high enrichment in heavy rare earth elements.  相似文献   

7.
A 1-month pumping test has been carried out during the summer of 1970 in order to study the desaturation of the cone of depression and the restoration of the water level and the re-wetting during the recovery phase. The observations were continued in order to evaluate the water movements during an annual cycle.The water flux resulting from a potential difference was evaluated. A slow and long-continued drainage is due to the low permeability of the water-bearing formations. Less than half the gravitational water was removed. The specific yields obtained from nuclear methods and other more classical methods based on transient flow formulae are quite different, being, in the latter case, 10–15 times smaller.The interaction between the saturated and unsaturated zones has been determined: contrary to what we would expect, in the unsaturated zone the capillary fringe has contributed only a small part to the water flux. Measurements of soil-water content show that in the cone of depression the resaturation is not complete.During the recharge period, we have noticed a water-level rise in the absence of vertical fluxes, due to an increase of the level in the river; the water movement is controlled by the nature of the formation and the influence of the water content on the permeability. The water balance obtained from the water content measurements is close to that found by the generalized Darcy law and it gives an acceptable approximation of infiltration and evapotranspiration components. The evapotranspiration estimated by this method is, however, very different from that derived from the climatic method.A continuous inflow to the water table has been determined, but it is often insignificant. Most of the groundwater recharge is obtained by a few periods of intense precipitation during which the daily fluxes reach values 100 times higher than normal inflow. Summer rains can reach the groundwater table when their intensity and timing create conditions favourable for downward flow in the upper soil horizons.  相似文献   

8.
Microscopic investigations have been done on the chondrites Sena and Nadiabondi (H5, not shocked), Ste. Marguerite en Comines (H4, very slightly shocked), Allegan (H5, slightly shocked). Only in such cases can the matrix be easily observed and compared to those of type 3 chondrites. The <100 μm debris found in types 4 and 5 that we have observed are not the result of the metamorphism of type 3 fines.The abundance of tiny debris is in direct relation with the intensity of the shock though this shock was insufficient to provoke either the induration of the stones or a significant loss of rare gases. The bulk of the fines are the result of local disaggregation of the most brittle parts from chondrules and fragments.A low-temperature matrix has not been observed in these meteorites but only in H3 chondrites, as a coating around the chondrules. The accretion modelists should take into account the absence or the scarcity of fine particles in their calculations.  相似文献   

9.
Summary The hydrologic study, by the mean of tritium of Taurus karst (Turkey), has shown two kinds of underground circulations: aconstant circulation whose waters have a mean residence time of one year andstill waters, several years older, found in a deeper karst. Moreover the averge time of renewal of Lake Beysehir has been put in evidence. The results have very important consequences on the future development of this area and the harnessing of its potentials.   相似文献   

10.
Résumé A partir de sismogrammes enregistrés dans deux stations sismologiques longues périodes identiques (WWSSS) installées à Machhad (36°1840N, 59°3516E) et à Chiraz (29°3040N, 52°3134E), la vitesse de phase des ondes de Rayleigh a été calculée dans cette région. D'après les résultats obtenus par l'étude des ondes de volume dans cette même région des modèles ont été établis. Le modèle s'accordant le mieux avec les résultats expérimentaux a une croûte d'environ 50 km d'épaisseur et comporte une couche à faible vitesse située entre 100 et 200–250 km de profondeur.  相似文献   

11.
Concentrations in uranium, thorium and potassium were determined by gamma spectrometry in more than 100 samples of volcanic rocks from the material obtained during the French-Italian expedition in Dankalia (Afar-Ethiopia) (December 1967 – February 1968). These samples were taken from two geographically distinct areas:
  1. the danakile depression (Erta Ale range, Pierre Pruvost massif, Alayta, Afdera, Borawlu).
  2. Ethiopian high lands (Adigrate — Axum).
The values we obtained give the following contents:

Dash

  • in the Erta Ale range, for basalts, K: 0,5%, U: 1,3 ppm, Th: 3,3 ppm, Th/U: 2,6.
  • for alkaline rhyolites, U: 4,1 ppm, K: 2,3%, Th: 15,2 ppm, Th/U: 3,7.
  • in the Pierre Pruvost massif, for acid rocks, K: 3,9%, U: 3,6 ppm, Th: 13,5 ppm, Th/U: 3,8.
  • in the Borawlu centre, K: 2,8%, U: 4,6 ppm, Th: 14,7, Th/U: 3,4 for the rhyolites, K: 0,6%, U: 0,9 ppm, Th: 3,1 ppm for the basalts.
  • on the Ethiopian high lands, for the Adigrate basaltic trap rocks, K: 0,6%, U: 0,6 ppm, Th: 1,1 ppm, Th/U: 1,7 and for the Axum zone of phonolitic pinnacles, K: 3,9%, U: 2,7 ppm, Th: 14,9 ppm, Th/U: 4,9.
    • The Th/K and U/K ratios are particularly high compared with the usual data, except for the Pierre Pruvost massif which seems to be different from the others. The difference of Th/U ratios for basic rocks and acid rocks is meaningful. For the magma which gave the volcanism of the studied area, one can think of an evolution more especially connected with transfers of volatile elements. The strong correlations existing between potassium, uranium and thorium probably indicate the presence of groups which are distinct from a geochemical point of view in the Dankalia lavas.  相似文献   

    12.
    Summary The Lac de Bret, formerly an “oligotrophic” lake, has by several artificial risings of its level become “eutrophic” with the drawbacks of that state during the summer stagnation. A plant of partial underwater aeration has improved the situation and has been described in this Review (11, 423 [1949]). The above study compares the zooplancton of this lake in the years 1902/03 when it was yet oligotrophic with its plancton in the year 1943 during the investigations in the lake become eutrophic and finally in the year 1951 when it had again grown sound after five seasons of estival acration.   相似文献   

    13.
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    14.
    A method is established for computing the daily potential evapotranspirations of an entire hydrographic basin. It is based on the energy balance method. Its particularity lies in the fact that the daily values of the transfer factor between the evaporation of a virtual free water surface and the evapotranspiration of a vegetation cover are determined as a function of meteorological variables by means of a precise analytical expression.The potential evapotranspirations computed by this method are in very good accordance with the potential evapotranspirations deduced from water balances. Five watersheds in Belgium were chosen for testing the method.The daily values of the numerous meteorological elements which are taken into account by the computer method and the corresponding values of the potential evapotranspirations of different natural surfaces are grouped in two tables given as examples. These ones show how the transfer factors and the potential evapotranspirations of different natural surfaces react to the complex interactions between the different meteorological elements and namely to the heat transfer between surface and ground.  相似文献   

    15.
    Refilling of undifferentiated magma at high temperature in the shallow chamber of Stromboli volcano induces both partial gas release of the crystallizing shoshonic liquid and a beginning of melting of salite-augite megacrysts in equilibrium with the liquid. In the new magma, crystallization of pyroxenes resumes with a chrome-diopside composition. The study of silicate melts inclusions in pyroxenes reveals the importance of refilling processes in the evolution products stored in the magma reservoir.  相似文献   

    16.
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    17.
    The age and growth of adult Lake Geneva trout (Salmo trutta lacustris L.) caught from 1964 to 1974 for mark-and-recapture experiments was studied by scale analysis. The median lengths of 3 years and older fish were fitted to Von Bertalanffy growth curves. Their growth rates are higher than those of the fish younger than 3 years. It is conculded that this increase of growth rate concides with beginning of life in the lake, after the downstream migration of the juvenile trout which probably takes place in the second and third summer. No general increase of growth rates between cohorts could be detected from the beginning to the end of the period studied, in spite of a serious increase of eutrophication of Lake Geneva during the same time.   相似文献   

    18.
    A method is described for measurement of the magnetic viscosity of rocks, which is considered in its three forms: induced magnetization viscosity, remanent magnetization viscosity and viscous remanent magnetization. An application is then presented in the form of an experimental verification of the E. and O. Thellier test of approximate elimination of the viscous magnetization effect in rocks. It is shown that, used in the conventional manner, the employment of this test is fully justified, although not allowing measurement of the VRM, the values obtained being seriously underestimated.  相似文献   

    19.
    Old water-delivery tunnels can become leaky and produce water losses of some economic importance. The detection of solution cavities behind the concrete lining was the purpose of an investigation in a 2 km long part of a water-delivery tunnel in Switzerland. A gypsum zone of about 700 m length was considered to be especially critical. Two geophysical methods were used at the same time: resistivity profiling with three different array lengths, and ground-penetrating radar. The cavities were characterized by higher electrical resistivity, principally for the short array (AB = 3 m). Detailed measurements with a pole-dipole array were made for a better depth interpretation of anomalies in some critical zones. The GPR investigations were made with an antenna of 500 MHz. Some transverse profiles were carried out with GPR in order to better delineate the discovered cavernous or weathered zones. GPR located cavities up to a few meters in length, at depths between 0 and 4 m behind the lining. Anomalies found by one investigation method were often confirmed by the other one. Their complementarity thus allowed a more reliable interpretation of the gathered data. Verifying drillholes have mostly confirmed the good correlation between geophysical interpretation and drilling results. Endoscopic investigations in the drillholes enabled us to have a real vision of discovered cavities.Although GPR-profiling has the advantage of a continuous underground imaging and of greater efficiency during data acquisition (investigation speed) we consider the combination of both methods in the present study as a good example of an integrated geophysical survey, which enables a more reliable interpretation of the gathered data.

    Résumé

    Les galeries d'amenée d'eau d'un certain âge peuvent poser des problèmes à cause de pertes d'eau parfois importantes. L'objectif de cette étude a été la mise en évidence et le positionnement de cavités derrière le revêtement d'une galerie en Suisse, sur une longueur de 2 km. Une zone de gypse longue de 700 m était considérée comme particulièrement critique. Deux méthodes géophysiques ont été conjointement utilisées: le traîné électrique multiple avec trois longueurs de ligne d'envoi de courant et le géoradar. Les cavités, caractérisées par des résistivités élevées, ont surtout été mises en évidence par le dispositif le plus court (AB = 3 m). Des mesures de détail ont été réalisées dans les zones critiques avec un dispositif pôle-dipôle en vue d'une meilleure interprétation des anomalies en profondeur. Les mesures de géoradar ont été exécutées avec une antenne de 500 MHz. Quelques profils transversaux ont été effectués pour vérifier l'extension des zones d'altérations ou des cavités. Le géoradar a pu localiser des cavités mesurant jusqu'à plusieurs mètres en longueur à des profondeurs variant entre 0 et 4 m derrière le revêtement de la galerie. Les anomalies décelées par une méthode ont souvent pu être confirmées par l'autre et leur complémentarité a permis une interprétation plus sûre. Des forages carottés ont montré une bonne corrélation entre les anomalies géophysiques et la réalité. Des mesures de fibroscopie dans les forages nous ont permis de déterminer la géométrie des cavités.Le géoradar possède des avantages certains: imagerie continue du massif rocheux et grande rapidité dans l'acquisition des données. Néanmoins, nous considérons la combinaison des deux méthodes utilisées dans cette étude comme le bon exemple d'une investigation géophysique combinée permettant une interprétation optimale de tous les résultats.  相似文献   

    20.
    The study of the qualitative and quantitative distribution of macrophytic vegetation of Bienne lake is realized with the help of colour aerial photographies and verifications on the field. This distribution is discussed in relation to the trophic level of the lake and compared with that of the Geneva lake and Morat lake.  相似文献   

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