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91.
The present study deals with tectonomagmatic evolution of the collision-related leucogranite located near the northwest corner of exposed basement in Sinai, Egypt. The area is composed of: (1) a gabbroic complex; (2) amphibolite; (3) post-orogenic leucogranite; (4) Feiran gneisses. The amphibolite and gabbroic suites, generated in an island arc environment, have a high Fe-tholeiitic affinity and were derived from two independent magmas. On the basis of rare earth element (REE) patterns, the gabbroic melts could have been generated from a garnet- and amphibole-bearing, enriched mantle, and were subsequently modified by fractional crystallization of pyroxene and amphibole with minor plagioclase, whereas the amphibolite melts could be derived from garnet-free depleted mantle.The leucogranite has high Al2O3 content (>13 wt%), alumina saturation index (ASI) mostly >1, and normative corundum, indicating a peraluminous nature. Chondrite-normalized REE patterns for the leucogranite show light REE enrichment (La/SmN=2.7–4.86), general flattening of the heavy REE (Gd/LuN=1.2–2), and negative europium (Eu) anomalies (Eu/Eu*=0.24–0.47). The peraluminous nature and enrichment of the incompatible elements (K, Rb, Ba and Th) in the leucogranite strongly suggest derivation from a crustal source. The most probable source for the leucogranite magmas is represented by the adjacent Feiran gneisses, which could have generated the leucogranite by dehydration melting under water-undersaturated conditions. It appears likely that the restite unmixing model is responsible for the chemical variations within the leucogranite. In accordance with this model, the chemical variation of the leucogranite can be attributed to varying degrees of separation of restitic material from the melt during its emplacement and solidification and fractional crystallization could have played a minor role during magma ascent through the crust. 相似文献
92.
93.
In the last 30 years the climate of the West African Sahel has shown various changes, especially in terms of rainfall, of which inter-annual variabilityis very high. This has significant consequences for the poor-resource farmers, whose incomes depend mainly on rainfed agriculture. The West African Sahel is already known as an area characterized by important interaction between climate variability and key socio-economic sectors such as agriculture and water resources. More than 80% of the 55 million population of West African Sahel is rural, involved in agriculture and stock-farming, the two sectors contributing almost 35% of the countries' GDPs. It is thereforeobvious that climate change seriously affects the economies of these countries. Adding to this situation the high rate of population increase(3%), leading to progressive pressure upon ecosystems, and poorsanitary facilities, one comes to the conclusion that Sahelian countries, Niger amongst them, will be highly vulnerable to climate change.This paper investigates the impact of current climate variability and future climate change on millet production for three major millet-producing regions in Niger. Statistical models have been used to predict the effects of climate change on future production on the basis of thirteen available predictors. Based on the analysis of the past 30-years of rainfall and production data, the most significant predictors of the model are (i) seasurface temperature anomalies, (ii) the amount of rainfall in July, August and September, (iii) the number of rainy days and (iv) the wind erosion factor. In 2025, production of millet is estimated to be about 13% lower as a consequence of climate change, translated into a reduction of the total amount of rainfall for July, August and September, combined with an increase in temperature while maintaining other significant predictors at a constant level. Subsequently,various potential strategies to compensate this loss are evaluated, including those to increase water use efficiency and to cultivate varieties that are adapted to such circumstances. 相似文献
94.
The present study has been undertaken to determine the nature and the factors controlling the distribution of carbonate content in Kuwait Bay sediments. The carbonate content that may be deposited with Kuwait Bay sediments is attributed to the interplay of the deposits fallout from the dust storms over Kuwaiti territory, the deposits carried in suspension by the currents from Shatt Al-Arab area and to the skeletal parts of microorganisms that may be originated in the sediments. The carbonate content increases in the coarse sediments rather than in the fine sediments. The mineral components of the carbonate present are in the form of calcite, aragonite and some dolomite. Therefore, the texture of the sediments, the rate of deposition in addition to the biological interference may exert a considerable control over carbonate distribution. 相似文献
95.
A possible suture between an old craton in West Africa and the Arabian—Nubian shield is marked by a persistent zone of Phanerozoic weakness. This zone extends between the Nile and Niger deltas and passes through the Qattara embayment, along the Bahariya fault, through the Kufra basin, between the Tibesti and Jabal al Uwaynat massifs, through the Bahr el Ghazal and Lake Chad areas, and along the Benoue trough. 相似文献
96.
Thomas Binet Pierre Failler Pablo N. Chavance Mohamed Abidine Mayif 《Global Environmental Change》2013,23(6):1434-1443
This article investigates whether the European Union-Mauritania fisheries agreement, which allocates part of the Europe's financial contribution to the conservation of marine ecosystems located within the Banc d’Arguin National Park, can be regarded as a payment for ecosystem service. A framework for qualification as such payment scheme was established based on an extensive literature review. The criteria identified for the qualification as a payment to ecosystem service pertain to: (1) the definition of the ecosystem service(s) involved; (2) the mechanism involved by the payment; and (3) the nature of the transaction. Interviews with local beneficiaries and subsequent data analysis led to the conclusion that this mechanism could be regarded as a payment to ecosystem service and so, through the European Union-Mauritania Fisheries agreement, the European Union were investing to protect local fish resources that could be exploited by its fishing fleet. This agreement, involving the first International Payment to Ecosystem Service of this kind, marks an important step towards better consideration of marine conservation in international public policy and foreign fishing policy in particular. However, this payment is small when compared to revenues generated through the exploitation of developing countries’ fishing grounds by fishing countries. Nevertheless it opens the door for more detailed applications of payment to ecosystem service schemes to other ecosystems contexts, and can provide a useful alternative source of financing of marine biodiversity conservation. 相似文献
97.
GIS and multi-criteria analysis to select potential sites of agro-industrial complex 总被引:1,自引:1,他引:0
Houda Sahnoun Mohamed Moncef Serbaji Boubaker Karray Khaled Medhioub 《Environmental Earth Sciences》2012,66(8):2477-2489
The selection of the potential sites to the creation of an agro-industrial complex requires a large amount of spatial information. Geographical information systems are capable of managing this information, providing the ability to integrate multiple layers of information and deriving new ones. This study incorporates environmental, social, economic, geological and infrastructural data. A multi-criteria analysis is performed to select the potential sites to the creation of an agro-industrial complex in the city of Sfax (the southern coast of Tunisia). The comparison by pair method adopted in this paper, based on a linear combination pondered after having assigned to every factor of decision a coefficient of level-headedness, creates many scenarios among which we selected the sustainable development one. This scenario assigned the highest weight to the economical, environmental and social factors (0.3 for each factor), which shows the presence of nine suitable sectors for the creation of an agro-industrial complex. The ELECTRE method enabled us to make a site ordering for the identification of the most three appropriate sites. 相似文献
98.
Forecasting solar and geomagnetic levels of activity is essential to help plan missions and to design satellites that will
survive for their useful lifetimes. Therefore, amplitudes of the upcoming solar cycles and the geomagnetic activity were forecasted
using the neuro-fuzzy approach. Results of this work allow us to draw the following conclusions: Two moderate cycles are estimated
to approach their maximum sunspot numbers, 110 and 116 in 2011 and 2021, respectively. However, the predicted geomagnetic
activity shown to be in phase with the peak of the 24th sunspot cycle will reach its minimum three years earlier, then it
will rise sharply to reach the 25th maximum a year earlier (i.e., 2020). Our analysis of the three-century long sunspot number data-set suggests that the quasi-periodic variation of the
long-term evolution of solar activity could explain the irregularity of the short-term cycles seen during the past decades. 相似文献
99.
Martin Menzies Dan Bosence Hamed A. El-Nakha Salah Al-Khirbash Mohamed A. Al-Kadasi Abdulkarim Al Subbary 《地学学报》1990,2(4):340-350
This paper analyses new field and radiometric age data on the timing of extension, sedimentation and magmatism related to the opening of the Red Sea. The first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine Tawilah Formation of Cretaceous to early Tertiary age. The first indication of magmatism is the eruption of alkaline basalts (43.5–21.2 Ma) on to marine and non-marine sandstones of lower to middle Tertiary age. The lack of an angular unconformity at the sediment-basalt contact, over a period of 25 Myr, corroborates a diachronous relationship between the Tawilah sandstones and the Yemen Volcanics. These data also indicate that the onset of volcanism in Yemen was in the Eocene, as is the case in Ethiopia and Saudi Arabia. A passive rifting model is supported by early extension and sedimentation followed by syn- and post-tectonic magmatism. 相似文献
100.
Alaa I. Ibrahim Hisham Anwer Mohamed H. Soliman Nicholas Mackie-Jones Kalvir S. Dhuga William C. Parke Jean H. Swank Tilan Ukwatta M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):535-539
A 6.4 keV emission line was discovered in an unusual burst from the soft gamma repeater SGR 1900+14 with the Rossi X-ray Timing
Explorer (RXTE). The line was detected in part of a complex multipeak precursor that preceded the unusual burst of 1998 August
29, i.e. two days after the giant flare of August 27 from the source. The origin of the line was not firmly identified and
two possible interpretations were equally plausible including (a) Kα fluorescence from a small iron rich material that was ejected to the magnetosphere during the August 27 flare, and (b) proton
or α-particle cyclotron resonance. If the iron scenario was correct, we expect to find evidence for the line during the intervening
interval between the flare and the August 29 burst, i.e. on August 28. Here we present the results of the August 28 burst
observation, taken with RXTE. We detect a total of seven bursts whose individual and joint spectra do not show evidence for
spectral lines. We also investigated a sample of nine bursts before and after the August 29 burst (from 1998 June to December)
that do not reveal evidence for a spectral line near 6.4 keV or elsewhere. These results disfavor the iron scenario and make
the proton/α-particle cyclotron resonance interpretation more plausible. The appearance of the emission line in part of a complex burst
and its absence from the studied sample indicate that the line is likely due to a transient phenomenon that may depend on
the burst morphology, energetics and the properties of the emission region.
相似文献