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231.
M. Sultan R. D. Tucker Z. El Alfy R. Attia Abdel Ghany Ragab 《International Journal of Earth Sciences》1994,83(3):514-522
The first U-Pb zircon ages are reported for the gneissic bedrock inliers previously interpreted as part of the Nile Craton. The inliers crop out in the Egyptian Western Desert, east of the Uweinat area and west of the Eastern Desert. Multi- and single-grain zircon analyses of granitoid gneiss and migmatite from Gebel Um Shagir, Aswan, and another locality approximately 160 km south-west of Aswan, yield simple discordia with near modern day Pb loss trajectories, and the following Neoproterozoic crystallization ages: 626+4/–3, 634 ± 4 and 741 ± 3 Ma. In contrast, multi- and single-grain U-Pb analyses (zircon and sphene) from an anorthositic gabbro at Gebel Kamil (22°46N 26°21E) and an anorthosite at Gebel El Asr (22°46N 31°10E) yield Archean and Paleoproterozoic emplacement ages. The former yield a crystallization age of > 2.67 Ga and a metamorphic age of 2.0 Ga; the latter a metamorphic age of 0.69 Ga and an inheritance age of 1.9–2.1 Ga. Because high grade gneiss and migmatite of Neoproterozoic, Paleoproterozoic and Archean age crop out west of the Nile, pre-Neoproterozoic crust should no longer be identified by its metamorphic grade. By contrast, mapping the anorthosite and related rocks might provide first-order estimates for the extension of pre-Neoproterozoic crust in north-east Africa. It is suggested that Archean and Paleoproterozoic crust of the Uweinat and Congo Craton are contiguous because these U-Pb (zircon) data show no evidence for a Neoproterozoic thermal overprint in the Gebel Kamil area and there is no pronounced Neoproterozoic magmatic activity south of the Uweinat inlier and north of the Congo Craton. 相似文献
232.
L. Aït Brahim B. Tadili C. Nakhcha I. Mouayn M. Ramdani M. Limouri A. El Qadi F. Sossey Alaoui M. Benhalima 《Pure and Applied Geophysics》2004,161(5-6):1081-1091
— The aim of this study is to conduct a probabilistic seismic hazard analysis for the eastern Rif area in northern Morocco. The source zones were established on the basis of the seismicity database, the fracturing analysis deduced from Landsat7 ETM digital enhancement and marine seismic reflection profiles. By the use of this information together with the selected attenuation relationship, the peak ground acceleration contour maps are produced for specific return periods. The map has been divided into intervals of 0.1 degrees in both latitude and longitude to calculate the values at each grid point and draw the seismic hazard curves. The results of seismic hazard assessment are displayed as iso-acceleration contours expected to be exceeded during typical economic life times of structures. 相似文献
233.
Fixed offshore platforms supported by pile foundations are required to resist dynamic lateral loading due to wave forces. The response of a jacket offshore tower is affected by the flexibility and nonlinear behaviour of the supporting piles. For offshore towers supported by clusters of piles, the response to environmental loads is strongly affected by the pile–soil–pile interaction. In the present study, the response of fixed offshore platforms supported by clusters of piles is investigated. The soil resistance to the pile movement is modelled using dynamic p–y curves and t–z curves to account for soil nonlinearity and energy dissipation through radiation damping. The load transfer curves for a single pile have been modified to account for the group effect. The wave forces on the tower members and the tower response are calculated in the time domain using a finite element package (ASAS). Several parameters affecting the dynamic characteristics of the platform and the platform response have been investigated. 相似文献
234.
235.
近年来在球粒陨石冲击脉体中陆续发现了一些天然高压新矿物和矿物组合,这些发现为地球深部碱性元素的地球化学行为的研究提供了重要依据。在地幔过渡带温度和压力条件下,钠和钙离子优先结合到镁铁-镁铝榴石固溶体和长石高压多形之中,钾离子则选择性地进入到长石高压多形中,副矿物涂氏磷钙石是Na、Ba、Sr和轻稀土等元素的潜在载体相。天然冲击变质球粒陨石为我们提供了探索过渡带和下地幔温度、压力条件下碱性元素载体相特征的重要自然界样品。 相似文献
236.
Nadia Mzoughi Fayçal Hellal Mohamed Dachraoui Jean-Pierre Villeneuve Chantal Cattini Stephen J de Mora Amor El Abed 《Comptes Rendus Geoscience》2002,334(12):893-901
The marine environment is very complex, with several important chemical, biological, and sedimentological interactions. Sediments constitute a reservoir for numerous pollutants, including polycyclic aromatic hydrocarbons (PAHs). PAHs are known by their mutagenic and/or carcinogenic effect. This study evaluates contamination levels in Bizerte Lagoon with respect to PAHs. The extraction efficiency of PAHs from sediment has been evaluated using Soxhlet or ultrasonic procedures, based on the recovery of an internal standard (9,10-dihydroanthracene). Several PAHs were found, including sixteen that are reported in the priority list of pollutants of the US Environmental Protection Agency (EPA). PAHs analysis was carried out by GC–FID and GC–MS for 16 samples sampled in two seasons: summer and winter. Results permit an assessment of PAHs pollution in the Bizerte Lagoon. To cite this article: N. Mzoughi et al., C. R. Geoscience 334 (2002) 893–901. 相似文献
237.
Fluid Inclusions in the Gold—Bearing Quartz Veins at Um Rus Area,Eastern Desert,Egypt 总被引:2,自引:0,他引:2
MOHAMEDELTOKHI ABDALLAELMUSLEM 《中国地球化学学报》2002,21(2):131-139
Fluid inclusions in the gold-bearing quartz veins at the Um Rus area are of three types: H2O, H2O−CO2 and CO2 inclusions. H2O inclusions are the most abundant, they include two phases which exhibit low and high homogenization temperatures ranging
from 150 to 200°C and 175 to 250°C, respectively. The salinity of aqueous inclusions, based on ice melting, varies between
6.1 and 8 equiv. wt% NaCl. On the other hand, H2O−CO2 fluid inclusions include three phases. Their total homogenization temperatures range from 270 to 325°C, and their salinity,
based on clathrate melting, ranges between 0.8 and 3.8 equiv. wt% NaCl. CO2 fluid inclusions homogenize to a liquid phase and exhibit a low density range from 0.52 to 0.66 g/cm3. The partial mixing of H2O−CO2 and salt H2O−NaCl fluid inclusions is the main source of fluids from which the other types of inclusions were derived. The gold-bearing
quartz veins are believed to be of medium temperature hydrothermal convective origin. 相似文献
238.
Hmidou El Ouardi 《Comptes Rendus Geoscience》2002,334(2):141-146
In the Mejez El Bab–Testour area (northern Tunisia), the Early Eocene extension induced block tilting and salt tectonics of the Triassic evaporites. Tectonic events and halokinesis have determined the organization of Ypresian sediments. Diapiric structures have been generated during Cretaceous along the east–west, north–south and NE–SW major faults and emphasised during Lower Eocene. In this region, the Ypresian deposits constitute a filling sequence and show several thickness and facies variations. They correspond to a Nummulitic and Globigerina mixed facies characterizing a platform-basin transition zone. To cite this article: H. El Ouardi, C. R. Geoscience 334 (2002) 141–146. 相似文献
239.
Abdeen Mamdouh M. Ramadan Fatma S. Nabawy Bassem S. El Saadawy Omnia 《Natural Resources Research》2021,30(5):3575-3603
Natural Resources Research - Sedimentary basins in south Egypt, in particular Komombo and Nuqra basins, have been paid more attention during the last few decades, due to their hydrocarbon... 相似文献
240.
O. V. Serebrennikova I. V. Russkikh E. B. Strel’nikova E. A. El’chaninova P. B. Kadychagov 《Water Resources》2017,44(5):774-783
New data on the distribution of organic compounds at different horizons (0–10, 30–40, and 70–80 cm) of bottom sediments of the fresh Fyrkal Lake (Republic of Khakaßsia) and the salt Lake Mormyshanskoe (Altai Territory) have been collected. The compositions of organic compounds in the sediments in the examined lakes has been found to differ considerably, though some parameters in their composition show changes in the same direction. The concentrations of triterpenoids of the groups of lupane, oleanane, and hopane in the sediments decrease with depth. An increase in the share of saturated compounds in the composition of steroids is accompanied by a decrease in the ratio of their isomers (5β/5α). Terrestrial vegetation dominates among organic matter sources, while, in Lake Fyrkal, the contributions of terrestrial plants and macrophytes are similar. The presence of thermally transformed steroids and triterpenoids throughout the vertical profile of sediments in Lake Mormyshanskoe may be an indication to a slight oil pollution of the water body. 相似文献