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431.
Robert Temdjim Pierre Boivin Gilles Chazot Claude Robin Émilie Rouleau 《Comptes Rendus Geoscience》2004,336(14):1239-1244
Volcanic deposits from the lake Nyos (Cameroon) contain ultrabasic xenoliths: lherzolites, harzburgites and websterites, sometimes containing amphibole. Major and trace element compositions of clinopyroxene and amphibole allow the recognition of an old depletion event followed by two episodes of incompatible-element enrichment. One is high in light rare-earth elements, while the other one is low in these elements, but high in U and Th. Their relative chronology is not yet established. To cite this article: R. Temdjim et al., C. R. Geoscience 336 (2004). 相似文献
432.
In two limno-corrals loaded with heavy metals the density of tubificid worms and chironomid larvae was higher than in the
control. The better oxygen conditions observed in the heavy metal loaded corrals might explain this discrepancy. The higher
oxygen concentration at the sediment-water interface was due to lower organic sedimentation, consequence of the primary production
reduced by heavy metals. In all limno-corrals, the tubificid populations consisted ofTubifex tubifex. The size structure of tubificid populations in the heavy metal loaded corrals indicated a delayed reproduction compared
to the control. 相似文献
433.
434.
Currently understood liquidus phase relations in the anhydrous mafic-ultramafic system at high pressures favour polybaric
rather than isobaric crystallization models for the origin of the websterites and pyroxenites associated with spinel-lherzolites
from Freychinède in the French Pyrénées. Such models call for a thermally perturbed upper mantle which was dynamic rather
than static in character. A vertical transport distance of some 60 km in the mantle was recorded by the subsolidus mineral
chemistry of garnet-websterite 70–385 and its single-phase subcalcic clinopyroxenite precursor (Kornprobst, 1976; Herzberg,
1978a). 相似文献
435.
Claude T. Herzberg 《Geochimica et cosmochimica acta》1979,43(8):1241-1251
A simple ionic model which describes the solution of the forsterite component of olivine in silicate liquids is reported. The melting relation is represented: (Mg2SiO4)ol = 2(Mg2+)L + (SiO44?L and is extended to all silicate liquids by normalizing their compositions to 4 oxygens. At 1 bar, the temperature at which olivine is in equilibrium with any alkali-depleted basaltic composition can be calculated to within ±30°C. This error is increased considerably when applied to terrestrial basalts which contain several weight percent alkalis. Alkalis interfere with the equilibrium by generating strongly repulsive interionic forces which can be crudely modelled in a manner consistent with constraints imposed by regular solution theory.The model quantifies the reduced activity of SiO44? monomers due to increasing SiO2 concentrations in the melt. This is a consequence of polymerization which does not appear to operate gradually over the entire spectrum of mafic and ultramafic compositions. The coordination of alumina in melts which precipitate olivine only appears to be dominantly octahedral. Titanium acts as a polymerizing agent by interconnecting previously isolated SiO44? monomers. Calcium associated with normative diopside tends to exhibit small but perceptible repulsive forces involving Mg2+. 相似文献
436.
Claude J. Allègre Michel Treuil Jean-François Minster Bernard Minster Francis Albarède 《Contributions to Mineralogy and Petrology》1977,60(1):57-75
This paper describes an extended application of the Rayleigh distillation law to trace element behavior in a fractional crystallization sequence. Using a trace element with a very low bulk partition coefficient as a reference (as suggested by Anderson and Greenland, 1969, and extended by Treuil and Varet, 1973), we can derive bulk partition coefficients for other elements and, in turn, the mineralogical composition of the cumulates. Trace elements with large D, such as Ni and Cr, further constrain the system, and we can deduce the initial composition of the magma. An example of this technique is shown for Terceira Island in the Azores.Contribution IPGNS no 229Now at Dept. of Geological Sciences, California Institute of Technology, Pasadena, California, USA 相似文献
437.
Claude F. Noiseux 《Dynamics of Atmospheres and Oceans》1985,9(1):39-48
The deep ocean waveform that results from a seismic event localized near a coastline is investigated using a simple model for the near-shore topography and the ground motion. It is found that the variable depth underlying the ground upthrust substantially enhances the distortion of the emerging Tsunami. An appropriate initial-value problem is solved numerically, from which an empirical formula is inferred that provides an approximate assessment of the deep ocean waveshape. 相似文献
438.
A PbSrNd isotope study of South West and East Indian Ridges confirms that the Indian Ocean belongs to a specific regional isotopic domain, as previously suggested by the results from islands of this ocean. The isotopic domain defined by the Indian MORB is indeed different from that of the North Atlantic and East Pacific Oceans. This demonstrates that the convective circulation of the upper mantle does not allow a rapid homogenization from one region to the other.The isotopic data of the Indian ridges can be interpreted by a contamination model, in which the depleted upper mantle (identical to that under the North Atlantic) is contaminated by two different types of contaminant, one corresponding to the source of the “central Indian Ocean” islands (Amsterdam, St. Paul, Marion, Prince Edward, Réunion, Rodriguez, Mauritius), and the other to a source similar to that of Walvis or Ninety East aseismic ridges. These two contaminants would have contributed to the ridge volcanism in different proportions over time. 相似文献
439.
440.
We assess the ability of multivariate statistical analyses applied to event hydrographs parameters, to characterize a catchment hydrological behaviour. Motivation for such an approach lies in the fact that streamflow records have yet to be exploited to their full potential towards hydrological interpretation and can be used to infer a catchment state of connectivity from a qualitative standpoint. We have therefore processed 96 event hydrographs from a small headwater temperate humid forested catchment using principal component analysis, variation partitioning and classification tree analysis. These techniques prove to be promising in discriminating contrasted types of hydrologic responses (e.g. low‐ vs high‐magnitude events, slow vs quick timing events), identifying the main hydro‐meteorological variables that control these responses and determining thresholds values of the hydro‐meteorological variables leading to a switch between catchment response types. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献