Interaction of surface water and groundwater in the Nile River basin: isotopic and piezometric evidence     

Kebede  Seifu  Abdalla  Osman  Sefelnasr  Ahmed  Tindimugaya  Callist  Mustafa  Osman 《Hydrogeology Journal》2017,25(3):707-726

Hydrogeology Journal - Past discussions around water-resources management and development in the River Nile basin disregard groundwater resources from the equation. There is an increasing interest...  相似文献   

Chemistry of Zircon in Rare Metal Granitoids and Associated Rocks, Eastern Desert, Egypt     

Hamdy M. Abdalla    Hossam Helba    Hiroharu Matsueda 《Resource Geology》2009,59(1):51-68

Typological study, including paragenic, morphological, textural, and chemical characteristics of zircon from nine rare metal granitic stocks and associated greisens, was carried out in order to identify the metallogenic processes of their host granitoids. The investigated zircon‐bearing granitoids and type occurrences can be categorized into magmatically and metasomatically specialized types. The magmatic type includes: (i) peralkaline, Zr + Nb‐enriched, A₁‐granite (e.g. Um Hibal); (ii) metaluminous, Nb + Zr + Y‐enriched, A₂‐type alkali granite (e.g. Hawashia and Ineigi); and (iii) peraluminous, Ta ≥ Nb + Sn + Be ± W‐enriched, Li‐albite granite (e.g. Nuweibi, Igla and Abu Dabbab). The metasomatized granites are Nb>>Ta + Sn + Zr + Y + U ± Be ± W‐enriched and hydrothermally altered alkali feldspar granite (i.e. apogranite; e.g. Um Ara, Abu Rusheid, and Um Naggat). Zircon of peralkaline granite is characteristically equant with well‐developed pyramidal faces and short prisms (i.e. pseudo‐octahedral form) with length/width ratios in the range of 2:1–1:1. It is of Zr_0.990Hf_0.007SiO₄ composition and is associated with hypersolvus assemblage consisting of alkali feldspar, quartz, aegirine and minor reibeckite. Zircon of metaluminous alkali granites is of Zr_0.99Hf_0.01SiO₄ composition and is associated with sub‐ to transolvus assemblage of K‐feldspar, quartz, plagioclase and annite‐siderophyllite mica. It is prismatic with length/width ratios in the range of 5:1–3:1, doubly terminated with small pyramidal faces. Compositionally, zircon of Li‐albite granite ranges between Zr_0.925Hf_0.075SiO₄ and Zr_0.705Hf_0.295SiO₄. It is idiomorphic with a simple combination of prism and bipyramidal terminations with a length/width ratio of 3:1–2:1. This zircon commonly exhibits a normal zoning with rims consistently higher in Hf than cores. The higher Hf content, of this zircon coupled with its association with topaz, tantalite and lithian micas (e.g. zinnwaldite and Li‐white mica), indicates a higher solubility of Hf‐fluoride complexes and their more stabilized state at lower temperature in Li‐ and F‐rich sodic melts. Zircon of apogranite association ranges in composition between Zr_0.967Hf_0.013SiO₄ in the lower unaltered alkali feldspar granite zone and Zr_0.805Hf_0.064(Y, U, Th, heavy rare‐earth elements) [HREE])_0.125SiO₄ in the apical metasomatized (i.e. microclinized, albitized, and greisenized) apogranite zones. This compositional change appears to reflect a roofward increasing in μ_KF, μ_NaF, and μ_HF of the exsolved fluids. Columbite, xenotime, thorite, cassiterite, beryl and fluorite are common associates of this zircon. This zircon is of bipyramidal to typical octahedral form with complete absence of prism concurrently with conspicuous development of pyramid, thus the zircon crystals have a length/width ratio of 1:1–0.5:1. The neoformed metasomatic zircon commonly exhibits either normal or reverse zoning with rims consistently different in Hf, U, Y, and HREE than cores, reflecting disequilibrium conditions (e.g. sudden change in P, T, salinity, and pH) between the growing crystals and the exsolved fluids.  相似文献   

Groundwater recharge/discharge in semi-arid regions interpreted from isotope and chloride concentrations in north White Nile Rift, Sudan   总被引：1，自引：0，他引：1  

Osman A. E. Abdalla 《Hydrogeology Journal》2009,17(3):679-692

Deuterium, oxygen-18 and chloride were analyzed for 84 samples from deep and shallow wells, precipitation and the river White Nile to investigate groundwater recharge/discharge relations in the semi-arid central Sudan. Spatial and vertical variation in isotopic signature and chloride concentration in the groundwater show similar patterns and indicate local recharge and evaporative discharge. Progressive decrease in isotopic composition along the regional groundwater flow path demonstrates aquifer continuity down the NW–SE recharge-discharge path. Isotope-heavy recharged water progressively mixes with lighter older groundwater formed during cooler and humid conditions in the late Pleistocene. However, evaporative fractionation in the flow path’s final reach in the southeast re-enriches the isotopic composition and suggests evaporative loss of groundwater as the plausible discharge mechanism. Chloride concentration increases down the gradient from the recharge area and reaches its peak in the discharge zones indicating: lack of recharge from direct infiltration down the gradient, evaporation and prolonged rock/water interaction. Head differences and increased isotopic concentration in the vicinity of the White Nile suggest recharge from the river from subsurface flow. Reduced chloride content and relatively heavier isotopic composition in the deep groundwater beneath the wadi of Khor Abu Habil indicate recharge from the streambed into the deep aquifer.  相似文献   

N-body simulations of tidal encounters between stellar systems     

P. Devadas Rao  N. Ramamani  Saleh Mohammed Alladin 《Journal of Astrophysics and Astronomy》1987,8(1):17-31

N-Body simulations have been performed to study the tidal effects of a primary stellar system on a secondary stellar system of density close to the Roche density. Two hyperbolic, one parabolic and one elliptic encounters have been simulated. The changes in energy, angular momentum, mass distribution, and shape of the secondary system have been determined in each case. The inner region containing about 40 per cent of the mass was found to be practically unchanged and the mass exterior to the tidal radius was found to escape. The intermediate region showed tidal distension. The thickness of this region decreased as we went from hyperbolic encounters to the elliptic encounter keeping the distance of closest approach constant. The numerical results for the fractional change in energy have been compared with the predictions of the available analytic formulae and the usefulness and limitations of the formulae have been discussed.  相似文献   

A classification of galactic collisions for galaxies of unequal dimensions     

K. Shankara Sastry  Saleh Mohamed Alladin 《Astrophysics and Space Science》1979,63(1):203-208

The earlier work on classification of galactic collisions for identical galaxies is extended to the situations where the two colliding galaxies differ in mass and dimension. We consider collisions between galaxies of masses 10⁷, 10⁹, 10¹¹ and 10¹³ M and let their radii be 0.1, 1, 10 and 100 kpc, respectively. The density distribution in both galaxies is represented by that of a polytrope of indexn=4. The type of collision is determined for head-on collisions for initial relative velocities 500, 1000, 2000 and 3000 km s^–1. The corresponding final velocities are also indicated.  相似文献   

GEOGRAPHY IN SAUDI ARABIA   总被引：1，自引：1，他引：0  

Nassir A. Saleh 《The Professional geographer》1985,37(2):216-218

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Petrochemical and Tectonogenesis of Granitoids in the Wuyo-Gubrunde Horst,Northeastern Nigeria: Implication for Uranium Enrichment     

Anthony Temidayo Bolarinwa  Saleh Ibrahim Bute 《Natural Resources Research》2016,25(2):197-210

The Wuyo-Gubrunde Horst in the northeastern Nigeria consists of migmatite gneiss, unaltered, altered, and sheared porphyritic granites, pegmatites, aplites, basalts, and sandstone. Uranium has been reported in rhyolite, sheared rocks, and sandstone within the area. The petrogenesis of the granitoids and associated rocks in the area was evaluated in the light of new geochemical data, which showed that the U content of altered porphyritic granite is highest and hydrothermal-related. The granitoids are metaluminous, sub-alkaline, and S-type granite, and have evolved by partial melting of crustal material emplaced at moderate depth of 20–30 km in a syn-to late-collisional within-plate tectonic setting. The negative Eu/Eu* anomaly and high (La/Yb)_N ratio of the granitoids indicate magma fractionation. The low SiO₂ (<53%) and high Fe₂O₃ (10%) of the altered porphyritic granite compared to other similar rock units suggest pervasive alteration. The associated basalts are tholeiitic, emplaced within continental plate tectonic setting, and enriched in Ni, V, Nb, Sr, and light rare earth elements, and they have SiO₂, Fe₂O₃, V, Th, and Co contents that are similar to those of the altered porphyritic granites. The U occurrence in the Wuyo-Gubrunde Horst is believed to be sourced from the adjoining Bima sandstone in the Benue Trough, which locally contains carbonaceous zones with anomalously high concentrations of U. The Fe²⁺/Fe³⁺ redox fronts formed by alteration of the iron-rich basalts provided the requisite geochemical barrier for U-bearing hydrothermal fluid, causing enrichment of U leached and mobilized from the sandstone through fractures in the rocks.  相似文献   

Evaluation of TIGGE Ensemble Forecasts of Precipitation in Distinct Climate Regions in Iran     

Saleh AMINYAVARI  Bahram SAGHAFIAN  Majid DELAVAR 《大气科学进展》2018,35(4):457-468

The application of numerical weather prediction(NWP) products is increasing dramatically. Existing reports indicate that ensemble predictions have better skill than deterministic forecasts. In this study, numerical ensemble precipitation forecasts in the TIGGE database were evaluated using deterministic, dichotomous(yes/no), and probabilistic techniques over Iran for the period 2008–16. Thirteen rain gauges spread over eight homogeneous precipitation regimes were selected for evaluation.The Inverse Distance Weighting and Kriging methods were adopted for interpolation of the prediction values, downscaled to the stations at lead times of one to three days. To enhance the forecast quality, NWP values were post-processed via Bayesian Model Averaging. The results showed that ECMWF had better scores than other products. However, products of all centers underestimated precipitation in high precipitation regions while overestimating precipitation in other regions. This points to a systematic bias in forecasts and demands application of bias correction techniques. Based on dichotomous evaluation,NCEP did better at most stations, although all centers overpredicted the number of precipitation events. Compared to those of ECMWF and NCEP, UKMO yielded higher scores in mountainous regions, but performed poorly at other selected stations.Furthermore, the evaluations showed that all centers had better skill in wet than in dry seasons. The quality of post-processed predictions was better than those of the raw predictions. In conclusion, the accuracy of the NWP predictions made by the selected centers could be classified as medium over Iran, while post-processing of predictions is recommended to improve the quality.  相似文献   

Utilisation of Fast Fourier Transform and Least-squares Modification of Stokes formula to compile a gravimetric geoid model over Khartoum State: Sudan     

Ahmed Abdalla  Chris Green 《Arabian Journal of Geosciences》2016,9(3):236

We use Fast Fourier Transform (FFT) and least-squares modification (LSM) of Stokes formula to compute the geoid over Khartoum State in Sudan. The two methods (FFT and LSM) have been utilised to test their efficiency with respect to EGM08 and the local GPS-levelling data. The FFT method has many advantages, it is fast and it reduces the computational complexity. The modification of Stokes formula is widely used in geoid modelling; however, its implementation based on point-wise summation requires a considerable amount of time. In FFT, we combine the terrestrial gravity data and the global geopotential model (GGM) by means of a remove-compute-restore procedure and we successfully apply the modification of the Stokes formula in the least-squares sense. FFT and LSM geoid solutions are evaluated against EGM2008 and the GPS-levelling data. The analysis of the undulation differences shows that the LSM solution is more compatible with EGM08 and GPS-levelling data. The discrepancies of the differences are removed using a 4-parameter model, the standard deviation (STD) of the undulation differences of LSM decreased from 0.41 to 0.37 m and from 0.48 to 0.39 m for FFT solution. There is no significant impact to the LSM geoid when adding the additive corrections, while the FFT geoid solution is slightly improved when terrain correction is applied.  相似文献   

Development of calcrete of the Late Cretaceous carbonate platform,northern Jordan,and its tectonic implications     

Abdulkader M. Abed  Saja Abu Taha  Tasneem H. Hiasat  Abdalla Abu Hamad 《Arabian Journal of Geosciences》2016,9(11):587

A calcrete horizon, 3–10 m thick, is found exposed in northern Jordan in three localities, Rumman, Marsa’, and Wasfi At Tal forest (WTF). It is situated at the base of the dominantly limestone, Late Cenomanian Hummar Formation, separating it from the underlying marly Fuheis Formation. The calcrete horizon exhibits all the diagnostic features characteristic of calcrete, such as diagenetic pisoids; a mottled or clotted texture; circumgranular cracks around grains in a nodular texture; pendant or microstalactitic cement; meniscus cement; plant roots or rhizogenic structures, both longitudinal and transverse; exfoliation on boulder and cobbles; alagally laminated hard pans; and abundant dissolution of cracks and vugs. Consequently, it represents a subaerial erosional unconformity and type 1 sequence boundary (SB) that was not previously noticed. The Hummar Formation is considered as a third-order sequence with the SB at the base of the calcrete horizon, while the calcrete horizon itself forms the lowstand system tracts (LST). The transgressive systems tracts (TST) involve the lower two third of the Hummar Formation ending with peloidal grainstone representing the maximum flooding surface (MFSs). The rest of the formation is the falling highstand systems tracts (HST). The next SB is not seen due to a thick soil-covered gap. The calcrete horizon formed due to the formation of a paleohigh, in the study area, associated with the compression produced by the initial subduction of the Afro-Arabian Plate under the Eurasian Plate during the Late Cenomanian, slightly earlier than the previously known Turonian subduction and compression.  相似文献