Mineral chemistry of banded migmatites from Hafafit and Feiran areas, Egypt

The migmatitic rocks exposed in Hafafit and Feiran areas exhibit some migmatitic structures as the banded, agmatic, boudinage and schlieren structures. The dominant type of these structures is the stromatic migmatites. Electron microprobe analyses of plagioclases, biotites and amphiboles from Hafafit and Feiran areas, in the Eastern Desert and Sinai, Egypt, are carried out and the metamorphic conditions are discussed. The present study revealed marked differences in the composition of plagioclases, biotites and amphiboles from Hafafit and Feiran localities. The obtained data indicated that plagioclases of the Feiran migmatites are of andesine and oligoclase composition, and display anorthite content from An₂₀ to An₃₈; whereas the Hafafit migmatites show a wider range of plagioclases from An₁₀ to An₆₀, and therefore plagioclases have labradorite, andesine and oligoclase composition. This may be due to the slow rate of the crystallisation processes. The analyses indicated that biotites of the studied areas are of metamorphic origin showing significant variation in Fe–Mg. It is worth mentioning that biotites from Hafafit migmatites have Mg–biotite composition while that of Feiram migmatites have Fe–biotite composition. High Mg and low Fe contents in biotite suggest higher crystallisation temperature. The composition of amphiboles in Hafafit migmatites is ferro-tschermakitic hornblende, while amphiboles from Feiram migmatites are magnesio-hornblende. High Ti content in the hornblende of Feiran migmatites suggests that they were formed at slightly higher temperatures and lower pressure than the Hafafit migmatites (i.e. Feiram migmatites and Hafafit migmatites were formed at granulite and amphibolite facies, respectively). Discrimination diagrams show that the muscovite is of secondary origin. Moreover, the present study confirmed that these migmatites are mainly formed by metamorphic differentiation via partial melting.     

Geodesics and geodesic deviation in static charged black holes

The radial motion along null geodesics in static charged black hole space–times, in particular, the Reissner–Nordström and stringy charged black holes, are studied. We analyzed the properties of the effective potential. The circular photon orbits in these space–times are investigated. We found that the radius of circular photon orbits in both charged black holes are different and differ from that given in Schwarzschild space–time. We studied the physical effects of the gravitational field between two test particles in stringy charged black hole and compared the results with that given in Schwarzschild and Reissner–Nordström black holes.     

Oblique sand ridges in confined tidal channels due to Coriolis and frictional torques

Ocean Dynamics - The role of the Coriolis effect in the initial formation of bottom patterns in a tidal channel is studied by means of a linear stability analysis. The key finding is that the...     

Radon and thoron content in atmospheric air at Giza,Egypt

Summary The radon and thoron content in atmospheric air at Giza was determined through the period from January (1958 to July 1959) by using the emanometrical technique. The concentration of radon and its decay products was equal to (88±4) 10^–18 Curie/c.c. and that of thoron and its decay products was equal to (51±11) 10^–18 Curie/c.c.     

An application of Markov Chain Model for wet and dry spell probabilities at Juba in Southern Sudan

The theoretical probabilities of wet and dry spells derived from the Markov Chain Model were found to fit very closely the observed probabilities of various sequence lengths at Juba, S Sudan. Monthly variation in the probability values does not seem to follow a secular trend. Anomogram relating observed sequence length frequency of wet and dry spells versus those computed by Markov model is presented.     

U-Pb (zircon) ages for the gneissic terrane west of the Nile,southern Egypt

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.     

A note on estimating urban roof runoff with a forest evaporation model

A model developed for estimating the evaporation of rainfall intercepted by forest canopies is applied to estimate measurements of the average runoff from the roofs of six houses made in a previous study of hydrological processes in an urban environment. The model is applied using values of the mean rates of wet canopy evaporation and rainfall derived previously for forests and an estimate of the roof storage capacity derived from the data collected in the previous study. Although the model prediction is sensitive to the value of storage capacity, close correlation between the modelled and measured runoff indicates that the model captures the essential processes. It is concluded that the process of evaporation from an urban roof is sufficiently similar to that from a forest canopy for forest evaporation models to be used to give a useful estimate of urban roof runoff. Copyright © 2007 John Wiley & Sons, Ltd.     

Energy distribution of a stringy charged black hole

The energy distribution associated with a stringy charged black hole is studied using Møller’s energy-momentum complex. Our result is reasonable and it differs from that known in literature using Einstein’s energy-momentum complex.     

Interannual variability of Mediterranean evaporation and its relation to regional climate

Gridded monthly evaporation data for 1958–2006 from the Woods Hole Oceanographic Institution data set are used to investigate interannual variability of Mediterranean evaporation during cold and hot seasons and its relation to regional atmospheric dynamics, sea surface temperature and atmospheric elements of the hydrological cycle. The first EOF mode of Mediterranean evaporation, explaining more than 50% of its total variance, is characterized by the monopole pattern both in winter and summer. However, despite structural similarity, the EOF-1 of Mediterranean evaporation is affected by different climate signals in cold and hot seasons. During winter the EOF-1 is associated with the East Atlantic teleconnection pattern. In summer, there is indication of tropical influence on the EOF-1 of Mediterranean evaporation (presumably from Asian monsoon). Both in winter and summer, principal components of EOF-1 demonstrate clear interdecadal signals (with a stronger signature in summer) associated with large sea surface temperature anomalies. The results of a sensitivity analysis suggest that in winter both the meridional wind and the vertical gradient of saturation specific humidity (GSSH) near the sea surface contribute to the interdecadal evaporation signal. In summer, however, it is likely that the signal is more related to GSSH. Our analysis did not reveal significant links between the Mediterranean evaporation and the North Atlantic Oscillation in any season. The EOF-2 of evaporation accounts for 20% (11%) of its total variance in winter (in summer). Both in winter and summer the EOF-2 is characterized by a zonal dipole with opposite variations of evaporation in western and eastern parts of the Mediterranean Sea. This mode is associated presumably with smaller scale (i.e., local) effects of atmospheric dynamics. Seasonality of the leading modes of the Mediterranean evaporation is also clearly seen in the character of their links to atmospheric elements of the regional hydrological cycle. In particular, significant links to precipitation in some regions have been found in winter, but not in summer.     

Recharge and contamination sources of shallow and deep groundwater of pleistocene aquifer in El-Sadat industrial city: isotope and hydrochemical approaches

Hydrochemical and isotopic researches were conducted in El-Sadat City groundwater system to identify groundwater alteration, recharge, residence time and extent of pollution. The groundwater salinity gradually increases as the groundwater moves from northeastern to southwestern parts of the city. Groundwater generally shows mineralization decreasing with depth, indicating that the possibility of recent water penetration far below the surface is limited. Shallow groundwater has an elevated level of nitrate, which is attributed to anthropogenic sources due to intensive agricultural activity. The limit of high nitrate water may mark the maximum penetration of groundwater from the surface, which is found in depths <100 m. The northeastern and southwestern industrial areas are highly contaminated by some heavy metals, which may originate from some local industrial effluents. The sewage oxidation ponds seem to show no effect on groundwater; hence, these ponds are not a point source for these heavy metals. Dissolved ions depict five different hydrochemical facies, and stable isotopes define the recharge mechanisms, the origin of groundwater and the hydraulic confinement of deep groundwater. The deep groundwater is untritiated and has long residence times (in the order of thousands of years). Three different hydrochemical groups have been recognized and mapped in El-Sadat City, based on the chemical and isotopic information of the groundwater. These groups have different levels of contamination. The deep groundwater samples are significantly less impacted by surface activities and it appears that these important water resources have very low recharge rates and would, therefore, be severely impacted by overabstraction. The extensive exploitation of groundwater for drinking water supply would shortly be reflected by a gradual decline of the groundwater table in El-Sadat City. Amelioration of groundwater quality requires further management strategies and efforts in the forthcoming years.