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131.
Souad Boubekraoui Michel Courteaud Maurice Aubert Yves Albouy Jean Coudray 《Journal of Applied Geophysics》1998,40(4):165-177
In order to investigate aquifers, several geophysical surveys have been carried out in the Baril area of the southern flank of Piton de la Fournaise volcano on Reunion in the Indian Ocean using audiomagnetotelluric (AMT), very-low-frequency (VLF) and self-potential (SP) methods. We present the results with emphasis on a comparison between SP data and the findings of geoelectric surveys. AMT soundings have indicated, from the surface downward, three layers: (i) resistive volcanic rocks, (ii) an intermediate resistivity layer, and (iii) a conductive basement attributed to a seawater-bearing aquifer. VLF measurements allow the mapping of the first layer apparent resistivity, and therefore its bottom, when the true resistivity is supposed to be isotropic and homogenous. When this assumption does not hold, only the SP method permits the mapping of this bottom. Because of the good agreement between the SP and electromagnetic results, we propose the SP method as the first tool that should be used in studying shallow hydrogeological structures in volcanic areas. 相似文献
132.
The meta-igneous granulite xenoliths from Kerguelen Archipelago: evidence of a continent nucleation in an oceanic setting 总被引:1,自引:1,他引:0
Michel Grégoire Jean Yves Cottin André Giret Nadine Mattielli Dominique Weis 《Contributions to Mineralogy and Petrology》1998,133(3):259-283
Xenoliths of meta-igneous origin occur as one of the two main types of ultramafic and mafic xenoliths entrained by alkaline
lavas of the Kerguelen islands. These are designated type II xenoliths and are subdivided into three mineralogical groups.
Subtype IIa and IIc xenoliths are interpreted as crystallisation products of basaltic melts that were emplaced near the crust-mantle
boundary during the early tholeiitic–transitional magmatic activity of the Kerguelen islands. Younger magmatism became more
alkaline and subtype IIb xenoliths were formed as high-pressure alkaline cumulates related to the last alkaline volcanic stage.
Subsequently, the plagioclase-bearing type II rocks have been re-equilibrated under granulite facies conditions. This addition
of mafic material around the crust-mantle boundary is consistent with seismic evidence for crustal thickening to 14–20 km.
Calculated compressional seismic velocities (Vp) for the basic granulites are consistent with the range of observed Vp in
the low-velocity region underlying the oceanic crust. Such growth in the thickness of the oceanic crust may be caused by intrusion
of basalts at different levels in the lithosphere and may provide the heat responsible for granulitic metamorphism in the
oceanic setting. This study suggests that basic granulites can account for the observed seismic characteristics of oceanic
plateaux and can be important components of Kerguelen oceanic lithosphere where there has been large-scale magma production.
Moreover we speculate that the Kerguelen islands and perhaps the surrounding plateau represent a continental nucleation process.
Received: 30 September 1997 / Accepted: 17 June 1998 相似文献
133.
Topography and geoid due to lithospheric mass anomalies 总被引:3,自引:0,他引:3
134.
Yves Delage 《Boundary-Layer Meteorology》1988,43(4):365-381
Two formulations of the stable atmospheric boundary layer are proposed for use in weather forecasting or climate models. They feature the log-linear profile near the surface, but are free from the associated critical Richardson number. The diffusion coefficients in the Ekman layer are a natural extension of the surface layer. They are locally determined using wind shear in one case and turbulent kinetic energy in the other. The parameterizations are tested in a one-dimensional model simulating the evolution of the nocturnal boundary layer with and without radiative cooling. Both formulations give very similar results, except near the top of the boundary layer where the transition to the free atmosphere is smoother with the wind shear formulation. A distinctive feature of these schemes is that they retain their simulating skill when resolution is reduced. This is verified for a wide range of situations. In practice, this means that there is no need for a large-scale model to have a level below 50 m or so. 相似文献
135.
Résumé La pegmatite de Covide (Nord-Portugal) fournit un nouvel exemple de litage à quartz-albite-feldspath potassique. Son étude conduit à proposer un modèle de pétrogenèse magmatique faisant intervenir des processus de double diffusion dans un gradient de température. Ces processus provoquent la formation simultanée et périodique de niveaux millimétriques d'albite, en »planchers flottants« horizontaux. Chaque cellule, phénomène-unité du litage compris entre deux niveaux planchers successifs, évolue ensuite en système clos par cristallisation orientée centripète. L'organisation litée est acquise en milieu magmatique liquide.
The Covide pegmatite, (Northern Portugal), exhibit a new example of K-feldspar, Albite, quartz layering. The present study leads to propose a magmatic petrogenetit model, with double diffusive processe in temperature gradient allowing the simultaneous growth of millimetric and horizontal »floating layers« of albite. Each cell, unit-phenomenon between two consecutive boundary layers, evolves in closed system with a centripetal, oriented crystallization. The layered organisation is obtaind in the magmatic liquid medium.
Zusammenfassung Der Pegmetit aus Covide (Nordportugal) stellt ein neues Beispiel für Quarz-Albitfeldspat Wechsellagerung dar. Seine Untersuchung führt zu einem magmatischen Petrogenesemodell, bei dem Prozesse der Doppeldiffusion in einem Temperaturgefälle intervenieren. Diese Prozesse bewirken die gleichzeitige und periodische Bildung von millimeterdicken Albitflächen in horizontalen »schwimmenden Flächen«. Jede Zelle, die ein Phänomen der Einheit der Anlagerungsfläche zwischen zwei aufeinanderfolgenden Flächenlagen ist, entwickelt sich schlie\lich durch zentripetale Kristallisierung zu einem geschlossenen System. Die schichtweise Anordnung erfolgt im flüssigen magmatischen Milieu.
Covide ( ) - . , . . , , -, , .相似文献
136.
Yves T. Prairie 《Aquatic Sciences - Research Across Boundaries》1989,51(3):192-210
The empirical adequacy of four phosphorus mass-balance models is evaluated with respect to how the prediction error variance of the corresponding net sedimentation parameters is propagated in the steadystate equations. Using the criterion of minimum propagation error variance (PEV), different groups of lakes can be distinguished for which different empirical equations are used to predict net phosphorus sedimentation. The classification reduced prediction error significantly and also reflected different patterns of sedimentation. Application of this criterion to time-series of individual lakes shows that it is possible to determine a priori whether net annual sedimentation will be better correlated to the annual loading or to the lake content. The correlations depended also on the load/lake content ratio, suggesting that net sedimentation is best viewed as the sum of the partial sedimentation of the load and of the partial sedimentation of the lake content. On average, 25% of the load and 18% of the lake content are sedimented annually. Viewing net phosphorus sedimentation as a function of both the load and the lake content can also explain and predict the well-known cross-sectional correlation between phosphorus retention and water residence time. 相似文献
137.
Audiomagnetotelluric soundings were carried out on the volcanic island of Mayotte (Comores Archipelago). The field method and data are described and discussed. All the sounding cross sections show coherent curves with a high conductive layer between 100 and 200 m. depth. This layer is considered to be a fluctuating water table zone correlated to yearly climatic changes under tropical weathering processes. Dipping and sudden level variations are linked to tectonic volcanic features and are the visualization of a block faulting system of the primitive basaltic shield, a consequence of a distensive phase possibly connected with the collapse of the western flank of the volcano. Piano-key panels are the typical sub-surface style and the guide-line for any water prospection on the volcano and the activity of the island water transfer system. 相似文献
138.
Denis Vincent Roberto Clocchiatti Yves Langevin 《Earth and Planetary Science Letters》1984,71(2):340-348
We have extended fission-track dating techniques to volcanic pyroclastic rocks, using quartz-bearing uranium-rich glass inclusions. We use both the glass itself and the surrounding quartz as track detectors, the latter having a much higher resetting temperature. We can thus derive the age of the last low-temperature thermal event, as well as that of the most recent deposition of quartz on the walls of the inclusions. This method has been applied to a Sardinian sample and to a Moroccan Precambrian sample. 相似文献
139.
Joseph Canérot Jacques Bauer Michel Bilotte Chantal Bourdillon Jean-Paul Colin Elie-Jean Debroas Françoise Magniez Francis Mediavilla Yves Ternet 《Comptes Rendus Geoscience》2004,336(10):951-958
By us considered as Albo-Aptian in age and generated through halokinetic processes, the Bosmendiette breccias have been recently interpreted as Selandian (Palaeocene) globigerine-bearing sediments deposited in sub-marine canyons within a deep trough crossing the Pyrenees, from the Mediterranean Sea to the Atlantic Ocean. These breccias are really azoic in their lower part and contain a scarce microfauna including radolarians and benthic foraminifera at the top of the formation. They are unconformably covered by the Urgo-Aptian limestones and marls and indicate, under opening marine conditions, Lower Cretaceous collapse movements and northward sliding of the Jurassic slumped cover, related to the growth of the Béloscare–Apoura diapir. To cite this article: J. Canérot et al., C. R. Geoscience 336 (2004). 相似文献
140.
Yves Gallet Agnès GeneveyMaxime Le Goff 《Physics of the Earth and Planetary Interiors》2002,131(1):81-89
Directional secular variation of the geomagnetic field over the last 2000 years has been defined in western Europe from numerous archeomagnetic studies. However, the number of archeomagnetic results for older periods is much more limited. For this reason, we present new data obtained from fired archeological structures found in two French sites (Loupiac and Aspiran) dated within the first millennium b.c. (latest Bronze-earliest Iron Age transition, ∼850-700 b.c. and Iron Age, ∼525-475 b.c., respectively). From a compilation of archeomagnetic results from western Europe (Great Britain, Italy and France) and northern Africa (Tunisia), we propose a directional secular variation curve for western Europe that covers the entire first millennium b.c. This curve exhibits a large clockwise motion with rapid changes during the first half of the millennium, while the last four centuries b.c. are characterized by weak variations. 相似文献