Infiltration von Flusswasser in Dünengebieten

Ohne Zusammenfassung     

Spinel lherzolite xenoliths from the Premier kimberlite (Kaapvaal craton, South Africa): Nature and evolution of the shallow upper mantle beneath the Bushveld complex

Coarse-grained, granular spinel lherzolites xenoliths from the Premier kimberlite show evidence of melt extraction and metasomatic enrichment, documenting a complex history for the shallow mantle beneath the Bushveld complex. Compositions of orthopyroxene, clinopyroxene and spinel indicate equilibration within the spinel–peridotite facies of the upper mantle, at depths from 80 to 100 km and temperatures from 720 to 850 °C. Bulk compositions have lower Mg-number [atomic 100 Mg/(Mg + Fe*)] than previously studied spinel peridotites from Premier, and have higher Mg/Si than low-temperature coarse grained garnet lherzolites, suggesting shallower melting conditions or metasomatic enrichment. Clinopyroxene in one sample is highly LREE-depleted indicating very minor modification of a residue of 20% melt extraction, whereas the calculated REE pattern for a melt in equilibrium with a mildly LREE-depleted sample is similar to MORB or late Archean basalt, possibly related to the Bushveld Complex. Bulk and mineral compositions suggest minimal refertilization by silicate melts in four out of six samples, but REE patterns indicate introduction of a LIL-enriched component that may be related to kimberlite.     

Spécificités hydrogéologiques des hautes vallées alpines: Exemple de la Haute-Sarine (Suisse)

The alpine valley of the Haute-Sarine is on several accounts representative of the alluvial aquifers of mountain by its very environment and its hydrogeologic characteristics. The investigations and the analysis carried out within the framework of this study enabled us to improve knowledge on the Quaternary filling of the valley and to highlight the preferential supplies of the aquifer by infiltration of the river and precipitations and also by the underground contributions of evaporitic karsts. We also could note the opulence of groundwater resources of the Haute-Sarine both from the qualitative and the quantitative points of view. The knowledge of these typical characteristics of alluvial aquifers of high altitude allowed finally the development of a concept of management and protection of groundwater resources that falls under a sustainable development policy of the groundwater storage in the alpine areas. Manuscrit re?u le 4 février 2003 Révision acceptée le 30 mars 2005     

Petrogenesis of picrite and associated basalts from the southern Mid-Atlantic Ridge

Basalts dredged from the south wall of a fracture zone transecting the southern Mid-Atlantic Ridge (SMAR) at 54° S are unusual in that they include a suite of highly olivine phyric basalts, sampled along with more normal sparsely plagioclase phyric basalts, and a highly plagioclase phyric basalt. Four basalt types (olivine phyric, sparsely plagioclase phyric, evolved sparsely plagioclase phyric and highly plagioclase phyric) are readily distinguished on the basis of petrography, mineralogy and bulk composition. They range from primitive to evolved, with the olivine phyric basalts having elevated MgO (up to 15.5%) and the plagioclase phyric basalt having elevated Al₂O₃ (19.3%) and CaO (13.1%) contents. Compositional variations are extremely consistant, with the olivine phyric basalts and the sparsely plagioclase phyric basalts defining coherent linear trends. On the basis of the ratios and covariation of the incompatible trace elements Zr, Nb, Y and Ba, distinct parental magmas for each basalt type are required. An investigation of Fe-Mg and Mg-Ni distribution coefficients between olivine and magma indicates that olivines from the olivine phyric basalts are on average too forsteritic and too Ni poor to have crystallized in a magma corresponding to the host bulk rock composition. This implies that these basalts are enriched in xenocrystic olivine. Olivines from the other basalt types are mostly of equilibrium composition, although there are some exceptions. Petrogenetic models for the formation of the different basalt types are quantitatively evaluated in terms of fractional crystallization/crystal accumulation processes. These indicate that (1) the olivine phyric basalts are the products of olivine and minor Cr-spinel accumulation and do not represent analogues of primary magma, or a liquid fractionation trend; (2) that the sparsely plagioclase phyric basalts were formed by polybaric fractional crystallization of olivine, plagioclase and clinopyroxene; and (3) that the evolved sparsely plagioclase phyric basalts are not readily related to one another. The single highly plagioclase phyric basalt is unrelated to the other basalt types and is cumulus enriched in plagioclase.The different basalt types are unrelated to one another and document the presence of at least four distinct magma types erupted in close proximity at this ridge/transform intersection on the southern end of the Mid-Atlantic Ridge.     

Optimization with the Gradual Deformation Method

Building reservoir models consistent with production data and prior geological knowledge is usually carried out through the minimization of an objective function. Such optimization problems are nonlinear and may be difficult to solve because they tend to be ill-posed and to involve many parameters. The gradual deformation technique was introduced recently to simplify these problems. Its main feature is the preservation of the spatial structure: perturbed realizations exhibit the same spatial variability as the starting ones. It is shown that optimizations based on gradual deformation converge exponentially to the global minimum, at least for linear problems. In addition, it appears that combining the gradual deformation parameterization with optimizations may remove step by step the structure preservation capability of the gradual deformation method. This bias is negligible when deformation is restricted to a few realization chains, but grows increasingly when the chain number tends to infinity. As in practice, optimization of reservoir models is limited to a small number of iterations with respect to the number of gridblocks, the spatial variability is preserved. Last, the optimization processes are implemented on the basis of the Levenberg–Marquardt method. Although the objective functions, written in terms of Gaussian white noises, are reduced to the data mismatch term, the conditional realization space can be properly sampled.     

Trace element geochemistry of phlogopite-rich mafic mantle xenoliths: their classification and their relationship to phlogopite-bearing peridotites and kimberlites revisited

Kimberlite magmas from the Kimberley area of South Africa have sampled two main types of phlogopite-rich mafic xenoliths which represent deep mantle segregations from highly alkaline melts. The first group corresponds to the MARID rocks characterised by the mineral association mica (phlogopite)-amphibole (K-richterite)-rutile-ilmenite-clinopyroxene and the second group consists of the PIC rocks characterised by the mineral association mica (phlogopite)-ilmenite-clinopyroxene-minor rutile. The two groups are clearly distinguished from one another by their mineral paragenesis, by the major element composition of their phlogopite and ilmenite, by the trace element content of their clinopyroxene and by their clinopyroxene and whole rock Sr and Nd isotope ratios. The combined major and trace element variations are interpreted to indicate a genetic relationship between the PIC rocks and group I kimberlite magma, and between the MARID rocks and group II kimberlite magma. The two types of parental melts percolated through, and metasomatised, the upper mantle beneath the Kimberley area as indicated by the trace element characteristics of the clinopyroxenes of the studied phlogopite-bearing peridotites.     

Water organisation at the solid–aqueous solution interfaceOrganisation de l'eau à l'interface solide–solution aqueuse

The aim of this review is to examine the present knowledge about water structure close to an interface or confined in porous spaces. First, the structure of liquid water is briefly described. Though its understanding remains incomplete, it appears that it is largely dominated by the hydrogen bond network and its dynamical evolution. The presence of any ‘foreign’ substance in water perturbs such a structure by changing at least locally the hydrogen bond network. For this reason, the presence of a solid interface significantly modifies the structure of the first adsorbed layers. Whatever the support, it is now clearly evidenced that structural perturbations are limited to distances lower than 10–15 Å from the interface. The nature, energetic heterogeneity and hydrophilicility/hydrophobicity of the solid surface influence the arrangement of water molecules. This surface organisation must definitely be considered when studying adsorption phenomena at the solid–aqueous solution interface. The relevance of such problems to geosciences is illustrated by a few situations in which water structure plays a prominent role. To cite this article: L.J. Michot et al., C. R. Geoscience 334 (2002) 611–631.     

Directional wave spectra at the regional scale with the KuROS airborne radar: comparisons with models

Ocean Dynamics - In situ observations, satellite observations, and regional observations from airborne remote sensing are very useful to characterize sea state evolution and related physical...     

Flexibility, technology, and the daily life practices of distance students living beyond the digital mainstream

In this paper it is argued that even though communication technologies release distance students considerably from their dependency on a campus, students are still very much connected to places in their daily lives. These connections are constituted through the “placing” of technology, the students’ relations to people in their daily lives and the students’ relations to the education institution. Communication technology not only releases students from the spatial dimensions; it also attaches them to specific places. It is argued that the use of technology in distance education can reduce the students’ flexibility even if they do not have to attend campus regularly. The empirical analysis presented in this paper is based on a case study of a Master’s degree programme in Public Management offered by Open University Indonesia (Universitas Terbuka).     

Late Holocene Mediterranean coastal change along the Tiber Delta and Roman occupation of the Laurentine shore, central Italy

A line of Roman villas once dominated the Mediterranean coastline to the south of the Tiber river mouth near Ostia in central Italy. The Roman remains, which were constructed within a series of dune ridges, now lie up to 900 m from the current shoreline as a result of the continued evolution of the Tiber delta in response to postglacial sea level rise, sediment inputs from the Tiber river catchment and tectonic uplift. Infrared stimulated luminescence (IRSL) ages of potassium-rich feldspars extracted from dune sands are in good agreement with the independent age control provided by the Roman structures and allow us to hypothesise an increase in aggradation rates of five times since the end of the period of Roman occupation compared with the earlier Holocene.