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181.
182.
Ahmed H. Ahmed Shoji Arai Yaser M. Abdel-Aziz Moha Ikenne Abdellatif Rahimi 《Journal of African Earth Sciences》2009,55(1-2):92
The distribution of platinum-group elements (PGEs), together with spinel composition, of podiform chromitites and serpentinized peridotites were examined to elucidate the nature of the upper mantle of the Neoproterozoic Bou Azzer ophiolite, Anti-Atlas, Morocco. The mantle section is dominated by harzburgite with less abundant dunite. Chromitite pods are also found as small lenses not exceeding a few meters in size. Almost all primary silicates have been altered, and chromian spinel is the only primary mineral that survived alteration. Chromian spinel of chromitites is less affected by hydrothermal alteration than that of mantle peridotites. All chromitite samples of the Bou Azzer ophiolite display a steep negative slope of PGE spidergrams, being enriched in Os, Ir and Ru, and extremely depleted in Pt and Pd. Harzburgites and dunites usually have intermediate to low PGE contents showing more or less unfractionated PGE patterns with conspicuous positive anomalies of Ru and Rh. Two types of magnetite veins in serpentinized peridotite, type I (fibrous) and type II (octahedral), have relatively low PGE contents, displaying a generally positive slope from Os to Pd in the former type, and positive slope from Os to Rh then negative from Rh to Pd in the latter type. These magnetite patterns demonstrate their early and late hydrothermal origin, respectively. Chromian spinel composition of chromitites, dunites and harzburgites reflects their highly depleted nature with little variations; the Cr# is, on average, 0.71, 0.68 and 0.71, respectively. The TiO2 content is extremely low in chromian spinels, <0.10, of all rock types. The strong PGE fractionation of podiform chromitites and the high-Cr, low-Ti character of spinel of all rock types imply that the chromitites of the Bou Azzer ophiolite were formed either from a high-degree partial melting of primitive mantle, or from melting of already depleted mantle peridotites. This kind of melting is most easily accomplished in the supra-subduction zone environment, indicating a genetic link with supra-subduction zone magma, such as high-Mg andesite or arc tholeiite. This is a general feature in the Neoproterozoic upper mantle. 相似文献
183.
AbstractThe multi-layered Jeffara de Gabes aquifer system is greatly influenced by tectonics. This system is limited at the base and laterally by evaporite layers and has lateral contacts with the sebkhas (salt flats). The groundwater in this aquifer is characterized by high salinity (3–10 g L-1). Multivariate statistical analysis and a geochemical approach were applied to determine the influence of the evaporite layers and sebkhas on the hydrochemical quality of the Jeffara de Gabes aquifer, and to understand the processes governing its salinity. According to these methods, and based in part on the Sr2+/Ca2+ ratio, it is demonstrated that the strong salinity of the groundwater is due to interactions between water and the evaporite layers that act as a substratum of this aquifer, as well as saltwater intrusion from the sebkhas. Moreover, the medium- to poor-quality groundwaters are characterized by geochemical interactions: cationic exchange and the precipitation/dissolution process of minerals in the aquifer formations.Editeur Z.W. KundzewiczCitation Ben Alaya, M., Zemni, T., Mamou, A. et Zargouni, F., 2014. Acquisition de salinité et qualité des eaux d’une nappe profonde, Tunisie: approche statistique et géochimique. Hydrological Sciences Journal, 59 (2), 395–419. 相似文献
184.
Ahmed Mahmood 《国际地球制图》2013,28(2):91-101
In the case of a major disaster, information derived from satellite observation is not only highly useful, it may at times be indispensable because of the damage caused by the disaster to ground infrastructure. The International Charter ‘Space and Major Disasters’ (‘the Charter’) has been one of the primary sources of satellite data for the past 11 years to cover events like floods, fires, tsunamis, ocean storms, earthquakes, volcanic eruptions and oil spills. With the growing membership of the Charter, an increasingly large number of sensors are now available, which can be planned with the required temporal frequency and spectral range to cover a disaster event. Some of the type Charter activation cases are reported in this article to demonstrate the innovative use of multi-satellite imagery for disaster response. 相似文献
185.
Theoretical and Applied Climatology - Gridded precipitation products are becoming good alternative data sources for regions with limited weather gauging stations. In this study, four climate... 相似文献
186.
Mahdi S. Sheraz Dhekale B. S. Jan Rukhsana Bhat M. Anwar Hussain Ashaq Jehangir Intikhab Aalum Sofi Najeebul Rehman Ahmed Latief Qureshi Asif M. Iqbal Aezum Aziz Mujtaba Bangroo Shabir A. Wani Owais Ali Bahar F. A. Mishra S. K. 《Theoretical and Applied Climatology》2022,149(1-2):727-741
Theoretical and Applied Climatology - Analysis of climatic variables is important for the detection and attribution of climate change trends and has received considerable attention from researchers... 相似文献
187.
Iqbal Zafar Shahid Shamsuddin Ahmed Kamal Wang Xiaojun Ismail Tarmizi Gabriel Hamza Farooq 《Theoretical and Applied Climatology》2022,148(3-4):1429-1446
Theoretical and Applied Climatology - Satellite-based precipitation (SBP) is emerging as a reliable source for high-resolution rainfall estimates over the globe. However, uncertainty in SBP is... 相似文献
188.
Probabilistic seismic hazard of Pakistan, Azad-Jammu and Kashmir 总被引:2,自引:2,他引:0
The seismic hazard study for Pakistan and Azad Jammu and Kashmir has been conducted by using probabilistic approach in terms
of peak ground acceleration (PGA) in m/s2 and also seismic hazard response spectra for different cities. A new version of Ambraseys et al. (Bull Earthq Eng 3:1–53,
2005) ground acceleration model is used, and parameterization is based on most recent updated earthquake catalogs that consisted
of 14,000 events. The threshold magnitude was fixed at M
w 4.8, but seismic zones like northern Pakistan–Tajikistan, Hindukush and northern Afghanistan–Tajikistan border had M
w 5.2. The average normalized ‘a’ and ‘b’ values for all zones are 6.15 and 0.95, respectively. Seismicity of study area was modeled, and ground motion was computed
for eight frequencies (0.025, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 s) for different annual exceedance rates of 0.02, 0.01, 0.005,
0.002 and 0.001 (return periods 50, 100, 200, 500 and 1,000 years) for stiff rocks at the gridding of 0.1° × 0.1°. Seismic
hazard maps based on computed PGA for 0.02, 0.01 and 0.002 annual exceedance are prepared. These maps indicate the earthquake
hazard of Pakistan and surrounding areas in the form of acceleration contour lines, which are in agreement with geological
and seismotectonic characteristics of the study area. The maximum seismic hazard values are found at Muzaffarabad, Gilgit
and Quetta areas. 相似文献
189.
Experimental Study of Undrained Shear Strength of Silty Sand: Effect of Fines and Gradation 总被引:2,自引:1,他引:1
Mostefa Belkhatir Ahmed Arab Noureddine Della Tom Schanz 《Geotechnical and Geological Engineering》2012,30(5):1103-1118
Two strong earthquakes occurred in the region of Chlef (north western part of Algeria) during the last century. From the geological context, there were several great masses of sandy soil ejections on to the ground surface level and severe damages to civil and hydraulic structures. These damages were due to the soil liquefaction phenomenon. The objective of this laboratory investigation is to study the effect of low plastic fines and gradation characteristics on the undrained shear strength (liquefaction resistance) response of sand-silt mixture samples. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with different fines content ranging from 0 to 50?% at two initial relative densities (Dr?=?20 and 91?%). The initial confining pressure was kept at 100?kPa. The evaluation of the data indicates that the undrained shear strength at the peak (qpeak) can be correlated to the undrained residual strength (Sus), the excess pore pressure (Δu), the fines content (Fc) and the intergranular void ratio (es). The test results indicate also that the undrained shear strength at the peak decreases with the increment of the coefficient of uniformity and fines content as well as with the decrement of the mean grain size in the range of 0–50?% fines content for both relative densities (Dr?=?20 and 91?%). 相似文献
190.
Major, trace, and REE data for three localities of calc?Calkaline older granitoid rocks exposed in the north Eastern Desert of Egypt are presented. These rocks were selected to cover wide compositional spectrum of the Egyptian older granitoid varieties. They are petrographically represented by granodiorite, tonalite, quartz?Cdiorite, and quartz?Cmonzodiorite. The rocks are comparable with the peraluminous, unfractionated calc?Calkaline suites and fall within the volcanic arc and I-type granite fields. So, they can be regarded as belonging to the volcanic arc collision stage (665?C614?Ma). The granitoids are geochemically similar to other rocks recorded from continental margin arc-systems being exhibit light-REE enriched patterns with variable but chiefly positive Eu anomaly. The latter has reverse relationship with the ??REE, which was attributed to the fractionation of hornblende during partial melting. These patterns are comparable with models involving partial melting of amphibolitic source. This source must represent basalts, gabbros, or volcanics of an island arc system that were transformed to the level of the island arc crust during continental growth where the P?CT conditions are suitable for partial melting. Thus, it is plausible that the studied rocks were derived by partial melting of LREE-enriched, garnet-free, and amphibole-bearing (i.e., hydrated) mafic source. Wadi Milaha granitoids are consistent with the derivation by a high degree of partial melting (30?C40%) of amphibolite protolith in the deep crust. However, the two other localities (Wadi Umm Anab and West Gharib) are matching with 20?C30% partial melting. Within each locality, variation in rock types from granodiorite to tonalite is said to be dominated by variable degree of restite separation during magma ascent. The high water and volatile contents in Wadi Milaha granitoids allowed higher degree of partial melting (30?C40%). Moreover, the lower volatile contents in the other two localities (Wadi Umm Anab and West Gharib) gave lower degrees of partial melting (20?C30%). These processes may resemble important geodynamic features of the Arabo-Nubian Shield evolution in the north Eastern Desert of Egypt. 相似文献