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31.
Al Yacoubi Latifa Bouchaou Lhoussaine Jaillard Etienne Masrour Moussa Ait Brahim Yassine El Mouden Ahmed Schneider Jana Reichert Barbara 《Arabian Journal of Geosciences》2017,10(7):169
The Agadir-Essaouira area in the occidental High Atlas Mountains of Morocco is characterized by a semi-arid climate. The scarcity and quality of water resources, exacerbated by long drought periods, constitute a major problem for a sustainable development of this region. Groundwater resources of carbonate units within Jurassic and Cretaceous aquifers are requested for drinking and irrigation purposes. In this study, we collected 84 samples from wells, boreholes, springs, and rivers. Hydrochemical and isotopic data were used to examine the mineralization and origin of water, which control groundwater quality. The chemical composition of water seems to be controlled by water-rock interactions, such as dissolution of carbonates (calcite and dolomite), weathering of gypsum, as well as ion exchange processes, which explain the observed variability. Stable isotopes results show that groundwater from the mainly marly Cretaceous aquifer are submitted to an evaporation effect, while samples from the chiefly calcareous Jurassic aquifer indicate a meteoric origin, due to a rapid infiltration of recharge runoff through the karstic outcrops. The low values of δ18O and δ2H suggest a local recharge from areas with elevations ranging from 400 to 1200 m for the Cretaceous aquifer and from 800 to 1500 m for the Jurassic units. 相似文献
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33.
Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix,France) 总被引:1,自引:0,他引:1
Afifé?El KorhEmail author Béatrice?Luais Etienne?Deloule Damien?Cividini 《Contributions to Mineralogy and Petrology》2017,172(6):41
Characterisation of mass transfer during subduction is fundamental to understand the origin of compositional heterogeneities in the upper mantle. Fe isotopes were measured in high-pressure/low-temperature metabasites (blueschists, eclogites and retrograde greenschists) from the Ile de Groix (France), a Variscan high-pressure terrane, to determine if the subducted oceanic crust contributes to mantle Fe isotope heterogeneities. The metabasites have δ56Fe values of +0.16 to +0.33‰, which are heavier than typical values of MORB and OIB, indicating that their basaltic protolith derives from a heavy-Fe mantle source. The δ56Fe correlates well with Y/Nb and (La/Sm)PM ratios, which commonly fractionate during magmatic processes, highlighting variations in the magmatic protolith composition. In addition, the shift of δ56Fe by +0.06 to 0.10‰ compared to basalts may reflect hydrothermal alteration prior to subduction. The δ56Fe decrease from blueschists (+0.19 ± 0.03 to +0.33 ± 0.01‰) to eclogites (+0.16 ± 0.02 to +0.18 ± 0.03‰) reflects small variations in the protolith composition, rather than Fe fractionation during metamorphism: newly-formed Fe-rich minerals allowed preserving bulk rock Fe compositions during metamorphic reactions and hampered any Fe isotope fractionation. Greenschists have δ56Fe values (+0.17 ± 0.01 to +0.27 ± 0.02‰) similar to high-pressure rocks. Hence, metasomatism related to fluids derived from the subducted hydrothermally altered metabasites might only have a limited effect on mantle Fe isotope composition under subsolidus conditions, owing to the large stability of Fe-rich minerals and low mobility of Fe. Subsequent melting of the heavy-Fe metabasites at deeper levels is expected to generate mantle Fe isotope heterogeneities. 相似文献
34.
Nel Etienne Louis 《GeoJournal》1990,22(3):305-313
South African urban areas, because of structural control exercised within them, have developed unique characteristics. One of the more distinctive features of urban apartheid is the creation of Homeland townships lying adjacent to certain of the country's towns and cities. This paper seeks to explore the essential motivation underlying the creation of the ethnically distinct urban centre of Mdantsane in the Ciskei Homeland between 1949 and 1988. The reason for the development of Mdantsane, a dormitory township of East London, are explored, as are the primary issues underlying its emergence. In order to fully investigate Mdantsane's evolution it is essential not to divorce the township from developments, through time, in East London. The impact of apartheid planning on the East London region is assessed. 相似文献
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37.
Caroline Marie Clémence Tramier Pierre Genthon Quentin Réginald Camille Paul Delvienne Nicolas Luc Sauvan Jean-Jérôme Olivier Cassan Etienne Ebrard Pascal Sébastien Dumas Yann Queffélean 《水文研究》2021,35(3):e14071
In New Caledonia wildfires and invasive mammals (deer and wild pigs) constitute the major agents of land surface degradation. Our study reveals the linkage between land cover and water balance on the northeast coast of New Caledonia (2400 mm annual rainfall) located on a micaschist basement. The hydrological regime of characteristic and representative land surfaces is assessed using a 1-year record from three 100 m2 plots each, located in a forest area degraded by an invasive fauna, in a woody savannah which is regularly burned, and in a healthy forest area. The three plots present highly contrasting hydrological regimes, with annual and maximum runoff/rain ratios during a rain event of, respectively, 0.82, 0.16, 0.03, and 2.7, 0.7, 0.2, for the degraded forest, the savannah and the healthy forest. Such results suggest that subsurface flow originating from the contributing area above the degraded forest plot should exfiltrate inside the plot. A conceptual model for the degraded forest plot shows that water exfiltrating inside the plot represents 61% of the observed runoff. In savannahs, water should mainly be transferred downstream by subsurface flow within a thick organic soil layer limited by an impervious clay layer at a 20–30 cm depth. Savannahs are generally located above forests and generate the transfer of rainwater to downslope forests. Exfiltration into the forests can be the result of this transfer and depends on the thickness and permeability of the forest topsoils and on topographic gradients. Water exfiltration in forest areas highly degraded by pigs and deer enhances erosion and increases further degradation. It probably also limits percolation in the areas located downstream by increasing the amount of superficial runoff concentrated in gullies. 相似文献
38.
B. Christophe P. H. Andersen J. D. Anderson S. Asmar Ph. Bério O. Bertolami R. Bingham F. Bondu Ph. Bouyer S. Bremer J.-M. Courty H. Dittus B. Foulon P. Gil U. Johann J. F. Jordan B. Kent C. Lämmerzahl A. Lévy G. Métris O. Olsen J. Pàramos J. D. Prestage S. V. Progrebenko E. Rasel A. Rathke S. Reynaud B. Rievers E. Samain T. J. Sumner S. Theil P. Touboul S. Turyshev P. Vrancken P. Wolf N. Yu 《Experimental Astronomy》2009,23(2):529-547
The Solar System Odyssey mission uses modern-day high-precision experimental techniques to test the laws of fundamental physics
which determine dynamics in the solar system. It could lead to major discoveries by using demonstrated technologies and could
be flown within the Cosmic Vision time frame. The mission proposes to perform a set of precision gravitation experiments from
the vicinity of Earth to the outer Solar System. Its scientific objectives can be summarized as follows: (1) test of the gravity
force law in the Solar System up to and beyond the orbit of Saturn; (2) precise investigation of navigation anomalies at the
fly-bys; (3) measurement of Eddington’s parameter at occultations; (4) mapping of gravity field in the outer solar system
and study of the Kuiper belt. To this aim, the Odyssey mission is built up on a main spacecraft, designed to fly up to 13
AU, with the following components: (a) a high-precision accelerometer, with bias-rejection system, measuring the deviation
of the trajectory from the geodesics, that is also giving gravitational forces; (b) Ka-band transponders, as for Cassini,
for a precise range and Doppler measurement up to 13 AU, with additional VLBI equipment; (c) optional laser equipment, which
would allow one to improve the range and Doppler measurement, resulting in particular in an improved measurement (with respect
to Cassini) of the Eddington’s parameter. In this baseline concept, the main spacecraft is designed to operate beyond the
Saturn orbit, up to 13 AU. It experiences multiple planetary fly-bys at Earth, Mars or Venus, and Jupiter. The cruise and
fly-by phases allow the mission to achieve its baseline scientific objectives [(1) to (3) in the above list]. In addition
to this baseline concept, the Odyssey mission proposes the release of the Enigma radio-beacon at Saturn, allowing one to extend
the deep space gravity test up to at least 50 AU, while achieving the scientific objective of a mapping of gravity field in
the outer Solar System [(4) in the above list].
相似文献
39.
Lobes in deep-sea turbidite systems: State of the art 总被引:1,自引:0,他引:1
40.
Marc Blanchard Guillaume Morin Michele Lazzeri Etienne Balan 《Geochimica et cosmochimica acta》2010,74(14):3948-14056
A series of hematite structures containing various amounts of aluminum and hydroxyl groups was modeled using first-principles methods based on the density functional theory. Evolution of the lattice parameters was quantified as a function of Al and H concentrations. The a and c lattice parameters decrease with the aluminum content and increase with the water content. This allows explaining experimental data reported for synthetic hematites, in particular the observed deviation from the Vegard’s rule. Investigation of several hydroxyl configurations associated with cationic vacancies suggests that the speciation of water also significantly affects the hematite structure. The 57Fe and 18O reduced partition functions (β-factor) were determined. Results show a linear dependence of the iron and oxygen β-factors on the aluminum content. An incorporation of 18 mole % Al2O3 in hematite would increase the iron β-factor of about 0.6‰ and the oxygen β-factor of about 5.5‰ at 0 °C. This effect is sufficiently large to be measurable and to affect the interpretation of natural isotopic compositions. On the other hand, the effect of water is found to be negligible for the hydroxyl configuration investigated. 相似文献