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131.
Tesfaye Kebede Christian Koeberl Friedrich Koller 《Journal of African Earth Sciences》1999,29(4):1773
Crystalline rocks from the western Ethiopian Precambrian terrain comprise two major rock groups: (1) the often migmatised eastern and western high-grade gneisses; and (2) the central low-grade metavolcanosedimentary rocks. Granitoid bodies of different ages and compositions intrude these rocks. Field observations, petrographic investigations, and geochemical features support a two-fold classification of the granitoid rocks. The volcanic arc granitoids (VAG) are most common and include the Ujjukka granite and granodiorite, and the Dhagaa Booqa and Guttin K-feldspar megacrystic granites. The second and geographically more restricted group represents within-plate or anorogenic (A-type) granitoids, typified by the Tullu Kapii syenite. Geochemically, the Tullu Kapii syenite is characterised by moderate to high contents of SiO2, total alkalis, Y, Nb, Ta, Hf, Zn, Zr, Ga, ΣREE, higher ratios of Fe2O3(total)/MgO,
,
, and lower contents of CaO, MgO, Sr, and Ba, compared to the other granitoids. The VAG group shows chondrite-normalised REE patterns with slightly enriched LREE and flat HREE patterns without significant Eu anomalies. In contrast, the Tullu Kapii A-type granitoid is characterised by a nearly horizontal REE pattern with variable negative Eu anomalies. The Ujjukka granite and granodiorite; and the Dhagaa Booqa and Guttin K-feldspar megacrystic granites originated in a two-step process, which involves batch equilibrium melting of basaltic or andesitic material producing tonalitic magma, followed by fractional crystallisation. The Tullu Kapii syenite was the product of partial melting of source rocks enriched in high field strength elements. 相似文献
132.
The notion of Hill stability is extended from the circular restricted 3-body problem to the general three-body problem; it is even extended to systems of positive energy and the Hill's curves with their corresponding forbidden zones are generalized.Hill stable systems of negative energy present a hierarchy: they have a close binary that can be neither approached nor disrupted by the third body. This phenomenon becomes particularly clear with the distance curves presentation.The three limiting cases, restricted, planetary and lunar are analysed as well as some real stellar cases. 相似文献
133.
Christian Bigler Evastina Grahn Isabelle Larocque Adam Jeziorski Roland Hall 《Journal of Paleolimnology》2003,29(4):509-510
Volume Contents
Volume contents 相似文献134.
Guillaume Favreau Christian Leduc Christelle Marlin Abdou Guéro 《Comptes Rendus Geoscience》2002,334(6):395-401
In southwest Niger, the Continental Terminal water table displays a natural hollow shape about 10 m in depth over an area of 4000 km2. A 10-year survey of this hollow aquifer has shown that current recharge is above . The water table has risen continuously since the 1950–1960s as a result of land clearance. This shows a disequilibrium in the aquifer balance. The long-term recharge rate is estimated by radioisotopes to be around . This figure fits with the only possible origin of the piezometric depression, i.e. evapotranspiration losses in its centre. To cite this article: G. Favreau et al., C. R. Geoscience 334 (2002) 395–401. 相似文献
135.
The configuration of Alpine accumulation areas during the last glacial maximum (LGM) has been reconstructed using glacial–geological mapping. The results indicate that the LGM ice surface consisted of at least three major ice domes, all located south of the principal weather divide of the Alps. This implies that the buildup of the main Alpine ice cover during oxygen isotope stage (OIS) 2 was related to precipitation by dominant southerly atmospheric circulation, in contrast to today's prevalent westerly airflow. Such a reorganization of the atmospheric circulation is consistent with a southward displacement of the Oceanic Polar Front in the North Atlantic and of the associated storm track to the south of the Alps. These results, combined with additional paleoclimate records from western and southern Europe, allow an interpretation of the asynchronous evolution of the different European ice caps during the last glaciation. δ18O stages (OIS) 4 and 3 were characterized by location of the Polar Front north of 46°N (Gulf of Biscay). This affected prevailing westerly circulation and, thus, ice buildup in western Scandinavia, the Pyrénées, Vosges, and northern Alps. At the LGM, however, the Polar Front lay at 44°N, causing dominating southerly circulation and reduced precipitation in central and northern Europe. 相似文献
136.
137.
Christian Winter 《Sedimentary Geology》2007,202(3):562-571
The application of numerical models for the simulation of coastal hydro-and sediment dynamics requires model verification, calibration and validation with field data. Yet, no commonly accepted rules for the evaluation of sediment transport models exist. This paper discusses the significance of statistical parameters and their limitations considering common time lags in tidal environments. It is shown that the occasionally used discrepancy ratio lacks quantitative and qualitative information on model performance, as the time context information on time series characteristics is lost. As an initial measure of association, the simple linear correlation coefficient r2 is proposed. To account for time lag errors in suspended transport models, a separate cross-correlation analysis for the flood and ebb tidal phase is proposed. For a comparison with other model applications, a concluding rating of model performance can be expressed by a dimensionless error definition which takes into account the quality of field data. 相似文献
138.
Valier Galy Julien Bouchez Christian France-Lanord 《Geostandards and Geoanalytical Research》2007,31(3):199-207
The determination of total organic carbon content and composition in detrital sediments requires careful removal of their carbonate minerals. In detrital sediments containing large amounts of carbonates, including dolomite, this can only be achieved by liquid acid leaching that may solubilise a significant proportion of the organic carbon. For a set of detrital sediments from the Himalayan system and the Amazon River as well as five geological reference materials, we determined the proportion of organic carbon (Corg ) solubilised during acid leaching. This proportion is significant for all analysed sediments and generally tends to increase with the organic carbon content. Compared to other types of sediments analysed, clay fractions extracted from river sediments and bed sediments with very low organic carbon content have high and low proportions of acid soluble Corg respectively. In Himalayan and Amazon river sediments, the proportion of Corg solubilised during acid leaching was relatively constant with average values of 14 and 19 % respectively. Thus, it is possible to correct the Corg content for the dissolved organic carbon content measured after decarbonation. Data presented here show that Corg dissolved during liquid acid leaching must be taken into account. After careful calibration, the method presented here should, therefore, be applied to any carbonate-rich detrital sediment. 相似文献
139.
Matthias Mauder Steven P. Oncley Roland Vogt Tamas Weidinger Luis Ribeiro Christian Bernhofer Thomas Foken Wim Kohsiek Henk A. R. De Bruin Heping Liu 《Boundary-Layer Meteorology》2007,123(1):29-54
The eddy-covariance method is the primary way of measuring turbulent fluxes directly. Many investigators have found that these
flux measurements often do not satisfy a fundamental criterion—closure of the surface energy balance. This study investigates
to what extent the eddy-covariance measurement technology can be made responsible for this deficiency, in particular the effects
of instrumentation or of the post-field data processing. Therefore, current eddy-covariance sensors and several post-field
data processing methods were compared. The differences in methodology resulted in deviations of 10% for the sensible heat
flux and of 15% for the latent heat flux for an averaging time of 30 min. These disparities were mostly due to different sensor
separation corrections and a linear detrending of the data. The impact of different instrumentation on the resulting heat
flux estimates was significantly higher. Large deviations from the reference system of up to 50% were found for some sensor
combinations. However, very good measurement quality was found for a CSAT3 sonic together with a KH20 krypton hygrometer and
also for a UW sonic together with a KH20. If these systems are well calibrated and maintained, an accuracy of better than
5% can be achieved for 30-min values of sensible and latent heat flux measurements. The results from the sonic anemometers
Gill Solent-HS, ATI-K, Metek USA-1, and R.M. Young 81000 showed more or less larger deviations from the reference system.
The LI-COR LI-7500 open-path H2O/CO2 gas analyser in the test was one of the first serial numbers of this sensor type and had technical problems regarding direct
solar radiation sensitivity and signal delay. These problems are known by the manufacturer and improvements of the sensor
have since been made.
The National Center for Atmospheric Research is supported by the National Science Foundation. 相似文献
140.
Gil Michard Christian Fouillac Daniel Grimaud Jérôme Denis 《Geochimica et cosmochimica acta》1981,45(7):1199-1207
A chemical model based on the equilibrium of water with quartz, albite, adularia, calcite, kaolinite or illite, and chlorite can explain the chemical composition of the main groups of hot springs in Massif Central. Temperature is the principal variable for determining this composition. Model temperatures generally agree with those given by classical cation geothermometers (t ? 135–150° C for Vichy. La Bourboule. Evaux and Châteauneuf; t ? 175–180° C for Chaudes Aigues and Saint Nectaire). The model fails to represent the composition of Mont Dore waters: the high temperatures given by classical geothermometers are considered doubtful. 相似文献