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排序方式: 共有560条查询结果,搜索用时 31 毫秒
1.
C. Moreno R. Sáez F. González G. Almodóvar M. Toscano G. Playford A. Alansari S. Rziki A. Bajddi 《Mineralium Deposita》2008,43(8):891-911
The Draa Sfar mineralization consists of two main stratabound orebodies, Sidi M’Barek and Tazacourt, located north and south
of the Tensift River (“Oued Tessift”), respectively. Each orebody is comprised by at least two massive sulfide lenses. The
hosting rocks are predominantly black shales, although minor rhyolitic rocks are also present in the footwall to the southern
orebody. Shales, rhyolitic volcanic rocks, and massive sulfides are all included into the Sarhlef Series, which is recognized
as one of the main stratigraphic units of the Moroccan Variscan Meseta. Hydrothermal activity related with an anomalous thermal
gradient, together with a high sedimentation rate in a tectonically driven pull-apart marine basin, favored the accumulation
of organic-rich mud in the deepest parts of the basin and the sedimentary environment suitable for massive sulfide deposition
and preservation. This took place by replacement of the hosting unlithified wet mud below the sediment–water interface. Geochemical
data suggest a sedimentary environment characterized by oxic water column and anoxic sediment pile with the redox boundary
below the sediment–water interface. The low oxygen availability within the sediment pile inhibited oxidation and pyritization
of pyrrhotite. Biostratigraphic analysis, based on the palynological content of the hosting black shales, restricts the age
of the sulfides to the Asbian substage (mid-Mississippian). This age is consistent with earlier geochronological constraints. 相似文献
2.
L. Moreno J. J. Durán M. A. Casermeiro J. R. Quintana Ma A. Fernández 《Environmental Geology》2008,54(3):465-477
Over a period of 4 years and 4 months, the geopurification installations at Dehesas de Guadix (Granada, Spain) were monitored
to determine the impact on soil and groundwater of the controlled discharge of urban wastewater, and also to identify the
best indicators of the entry of the recharged water into the aquifer. The installations are located in an area where the climate
is Mediterranean sub-arid, with an average precipitation of less than 287 mm/year, and a rate of evapotranspiration that is
almost three times greater. The system was controlled by determining the balance of majority nutrients and boron in the soil
and in the groundwater, both at the points affected directly by the wastewater discharge and at others. The quantity of mass
discharged was relatively large (COD 14,656 g/m2, NO3 85 g/m2, NO2 4 g/m2, NH4 2,425 g/m2, PO4 1,143 g/m2, K 1,531 g/m2, B 63 g/m2). It was observed that the elimination of nutrients within the soil (COD 97.5%, PO4 94.4%, K 59.17%, N
total 18.8%, B 12.69%) was very efficient except for the nitrogen, which nevertheless did not reach the groundwater, as it was
eliminated at deep levels of the unsaturated zone. Only 12.69% of the boron was removed, and appreciable, increasing amounts
of this element did reach the groundwater. Unexpectedly, none of the majority nutrients behaved as a reliable indicator of
the impact on groundwater; despite this, the boron and the bicarbonate did clearly reflect the arrival of the recharged water,
and are proposed as the best indicators. 相似文献
3.
Mauro Lo Cascio Yan Liang Nobumichi Shimizu Paul C. Hess 《Contributions to Mineralogy and Petrology》2008,156(1):87-102
The grain-scale processes of peridotite melting were examined at 1,340°C and 1.5 GPa using reaction couples formed by juxtaposing
pre-synthesized clinopyroxenite against pre-synthesized orthopyroxenite or harzburgite in graphite and platinum-lined molybdenum
capsules. Reaction between the clinopyroxene and orthopyroxene-rich aggregates produces a melt-enriched, orthopyroxene-free,
olivine + clinopyroxene reactive boundary layer. Major and trace element abundance in clinopyroxene vary systematically across
the reactive boundary layer with compositional trends similar to the published clinopyroxene core-to-rim compositional variations
in the bulk lherzolite partial melting studies conducted at similar P–T conditions. The growth of the reactive boundary layer takes place at the expense of the orthopyroxenite or harzburgite and
is consistent with grain-scale processes that involve dissolution, precipitation, reprecipitation, and diffusive exchange
between the interstitial melt and surrounding crystals. An important consequence of dissolution–reprecipitation during crystal-melt
interaction is the dramatic decrease in diffusive reequilibration time between coexisting minerals and melt. This effect is
especially important for high charged, slow diffusing cations during peridotite melting and melt-rock reaction. Apparent clinopyroxene-melt
partition coefficients for REE, Sr, Y, Ti, and Zr, measured from reprecipitated clinopyroxene and coexisting melt in the reactive
boundary layer, approach their equilibrium values reported in the literature. Disequilibrium melting models based on volume
diffusion in solid limited mechanism are likely to significantly underestimate the rates at which major and trace elements
in residual minerals reequilibrate with their surrounding melt.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
Roberto Danovaro Mauro Fabiano Giancarlo Albertelli Norberto Della Croce 《Marine Ecology》1995,16(2):103-116
Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep-sea sediments. 相似文献
5.
Sixteen mucilages sampled in the Adriatic and Tyrrhenian seas during 1999–2001 were characterised using spectroscopic [Fourier transform infrared spectroscopy (FTIR); colorimetric], chromatographic [thin-layer chromatography (TLC)], and elemental analysis techniques. Most samples contained comparable fractions of organic and inorganic compounds, with the exception of a few samples where the inorganic fraction was greater than the organic fraction. Carbohydrates were important in the samples rich in organic matter, while carbonate and silica (quartz and biogenic silica) were the most important constituents of the inorganic fraction. Carbonate and silica were the only important constituents of the samples with a very low organic content.According to chemical analyses, mucilage aggregates show the typical structure of humin—the insoluble fraction of the humic substance. Classification of mucilage samples as humin-like compounds, together with a reexamination of the factors involved in the formation of organic aggregates in marine environment, has led to the formulation of a reasonable hypothesis for mucilage formation. 相似文献
6.
J. Nicholson I. Broker J. A. Roelvink D. Price J. M. Tanguy L. Moreno 《Coastal Engineering》1997,31(1-4)
Five different coastal area morphodynamic models have been set up to run on the same offshore breakwater layout and an intercomparison carried out on the hydrodynamic and morphodynamic output produced by each scheme. In addition, the predicted morphodynamics was checked against available laboratory and field data.It is concluded that the models are capable of producing realistic estimates for the dominant morphodynamic features associated with offshore breakwaters. Coupling of the wave, current and sediment transport components of each scheme is shown to yield bathymetry which attains a state of equilibrium, unlike models which are based on the initial transport field only. 相似文献
7.
Spectroscopic observations in the spectral region 6000–6600 » of major belts and zones of Jupiter have been carried out at Calar Alto Observatory (Spain) during the 1987 opposition, in support to the International Jupiter Watch Program. More than a hundred long-slit, medium resolution spectra have been taken at the coudé focus of the 1.52 m telescope. The longitudinal and latitudinal distribution of the equivalent widths of the methane and ammonia absorption bands at 6190 » and 6450 » have been investigated. Unlike the CH4-6190 » band, the longitudinal distribution in the NH3-6450 » band shows asymmetries in some of the Jovian regions analyzed, being the absorption greater at West than at East limbs. These results are interpreted in terms of inhomogeneous scattering models by the simultaneous variation of the NH3 cloud optical thickness and its altitude level. The north-south scans show little latitudinal dependence on absorption in both methane and ammonia bands, although some relationship could be established between the absorption and relative continuum reflectivity variation.
Also at Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, Campus Universitario Fuentenueva, Granada, Spain. 相似文献
Resumen Se presentan los resultados obtenidos de las observaciones espectroscópicas de las principales zonas y cinturones de Júpiter realizadas durante la oposición de 1987 como una contribución al International Jupiter Watch Program. Las observaciones fueron llevadas a cabo haciendo uso del foco coudé del telescopio de 1.52 m del observatorio hispanoalemán de Calar Alto (España), habiéndose obtenido algo más de cien espectros, de resolución media, en la región espectral de 6000–6600 ». Se exponen los resultados de las anchuras equivalentes de las bandas de absorción del metano en 6190 » y del amoniaco en 6450 », estudiándose, al mismo tiempo, la distribución tanto longitudinal como latitudinal de las mismas. Mientras que los resultados para la banda del metano presentan un comportamiento simétrico en todas las regiones analizadas, las anchuras equivalentes para la banda NH3-6450 » presentan un comportamiento asimétrico en algunas regiones del planeta, con una mayor absorción hacia el limbo del oeste que hacia el del este. Los resultados son interpretados en base a un modelo de scattering no homogéneo, variando, simultáneamente, el espesor óptico y la altitud de la nube de amoniaco. Los espectros tomados en la dirección norte-sur, aunque presentan una dependencia latitudinal pequeña en la absorción de las bandas mencionadas, sugieren una relación entre la absorción y las variaciones de reflectividad en el continuo.
Also at Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, Campus Universitario Fuentenueva, Granada, Spain. 相似文献
8.
Mauro Cacace Ulf Bayer Anna Maria Marotta 《International Journal of Earth Sciences》2008,97(5):899-913
The large-scale crustal deformations observed in the Central European Basin System (CEBS) are the result of the interplay
between several controlling factors, among which lateral rheological heterogeneities play a key role. We present a finite-element
integral thin sheet model of stress and strain distribution within the CEBS. Unlike many previous models, this study is based
on thermo-mechanical data to quantify the impact of lateral contrasts on the tectonic deformation. Elasto-plastic material
behaviour is used for both the mantle and the crust, and the effects of the sedimentary fill are also investigated. The consistency
of model results is ensured through comparisons with observed data. The results resemble the present-day dynamics and kinematics
when: (1) a weak granite-like lower crust below the Elbe Fault System is modelled in contrast to a stronger lower crust in
the area extending north of the Elbe Line throughout the Baltic region; and (2) a transition domain in the upper mantle is
considered between the shallow mantle of the Variscan domain and the deep mantle beneath the East European Craton (EEC), extending
from the Elbe Line in the south till the Tornquist Zone. The strain localizations observed along these structural contrasts
strongly enhance the dominant role played by large structural domains in stiffening the propagation of tectonic deformation
and in controlling the basin formation and the evolution in the CEBS. 相似文献
9.
Isotope geochemistry of caliche developed on basalt 总被引:1,自引:0,他引:1
Enormous variations in oxygen and carbon isotopes occur in caliche developed on < 3 Ma basalts in 3 volcanic fields in Arizona, significantly extending the range of δ18O and δ13C observed in terrestrial caliche. Within each volcanic field, δ18O is broadly co-variant with δ13C and increases as δ13C increases. The most 18O and 13C enriched samples are for subaerial calcite developed on pinnacles, knobs, and flow lobes that protrude above tephra and soil. The most 18O and 13C depleted samples are for pedogenic carbonate developed in soil atmospheres. The pedogenic caliche has δ18O fixed by normal precipitation in local meteoric waters at ambient temperatures and has low δ13C characteristic of microbial soil CO2. Subaerial caliche has formed from 18O-rich evapoconcentrated meteoric waters that dried out on surfaces after local rains. The associated 13C enrichment is due either to removal of 12C by photosynthesizers in the evaporating drops or to kinetic isotope effects associated with evaporation. Caliche on basalt lava flows thus initially forms with the isotopic signature of evaporation and is subsequently over-layered during burial by calcite carrying the isotopic signature of the soil environment. The large change in carbon isotope composition in subsequent soil calcite defines an isotopic biosignature that should have developed in martian examples if Mars had a “warm, wet” early period and photosynthesizing microbes were present in the early soils. The approach can be similarly applied to terrestrial Precambrian paleocaliche in the search for the earliest record of life on land. Large variations reported for δ18O of carbonate in Martian meteorite ALH84001 do not necessarily require high temperatures, playa lakes, or flood runoff if the carbonate is an example of altered martian caliche. 相似文献
10.