排序方式： 共有8条查询结果，搜索用时 15 毫秒
1
1.
Ahmed Touil Abdelmajid El-Boukhari Essaid Bilal Jacques Moutte 《Journal of African Earth Sciences》1999,29(4):81
The Upper Proterozoic granitoids of the western part of the Siroua Massif (central Anti-Atlas, Morocco) are cut by doleritic dykes injected along submeridian and equatorial directions. These dykes were emplaced before deposition of late Neoproterozoic formations (PIII). According to
and incompatible element ratios, these dolerites constitue two discrete chemical groups unrelated to orientation and thickness. They are both enriched in large ion lithophile elements, Zr, Th and light rare earth elements, and correspond to continental tholeiites displaying an alkaline affinity. This alkaline affinity is also confirmed by clinopyroxene and amphibole chemistry. Emplacement of these doleritic dykes occurred under an extensional regime active in the Anti-Atlas range during the Upper Proterozoic. 相似文献
2.
A Hafid J.P Sagon M Julivert M.L Arboleya A Saquaque A El-Boukhari A Saidi J.M.F Soler 《Journal of African Earth Sciences》2001,32(4):2195
Before the Pan-African Orogeny, the Palæoproterozoic basement and its Neoproterozoic cover (limestones and quartzites) of the Zenaga Inlier were cross-cut by a swarm of doleritic dykes. They are more or less altered. The primary mineral assemblage consists of plagioclase, clinopyroxene, very rare orthopyroxene, ilmenite, apatite, micropegmatite and sometimes hornblende and biotite. Mineralogical and geochemical studies indicate that the dolerites are continental tholeiites. Two groups of dykes have been distinguished. Accordingly, rare earth elements, P2O5, Zr, Th, Ba and Sr contents are higher in group I than in group II, which is richer in V. Group I comprises the north-south and northwest-southeast swarms, while group II corresponds to northeast-southwest and east-west swarms, which were emplaced later. These geochemical variations may be explained by a higher degree of melting of the mantle source for the later group II. Doleritic dykes of Zenaga had been emplaced during an extensional episode, prior to Pan-African folding. 相似文献
3.
Abdelmajid Benali 《Comptes Rendus Geoscience》2013,345(1):36-46
When running a groundwater flow model, a recurrent and seemingly subsidiary question arises at the starting step of computations: what value of acceleration parameter do we need to optimize the numerical solver? A method is proposed to provide a practical estimate of the optimal acceleration parameter via a geostatistical analysis of the spatial variability of the logarithm of the transmissivity field Y. The background of the approach is illustrated on the successive over-relaxation method (SOR) used, either as a stand-alone solver, or as a symmetric preconditioner (SSOR) to the gradient conjugate method, or as a smoother in multigrid methods. It shows that this optimum acceleration factor is a function of the standard deviation and the correlation length of Y. This provides an easy-to-use heuristic procedure to estimate the acceleration factors, which could even be incorporated in the software package. A case study illustrates the steps needed to perform this estimation. 相似文献
4.
Mustapha El Ghorfi Thomas Oberthür Frank Melcher Volker Lüders Abdelmajid El Boukhari Lhou Maacha Rachid Ziadi Hssain Baoutoul 《Mineralium Deposita》2006,41(6):549-564
The structurally controlled Au–Pd mineralization at Bleïda Far West occurs in a volcano-sedimentary rock sequence in altered amphibolites and chlorite schists of the Neoproterozoic Bou Azzer–El Graara inlier. The Au–Pd mineralization is virtually sulfide-free; instead, gold is associated with hematite, barite, quartz, and calcite. The gold grains are silver- and palladium-bearing (up to 19 wt% Ag and 6.3 wt% Pd) and are intergrown with a distinct suite of mainly Pd-dominated platinum group minerals, namely mertieite-I/isomertieite, merenskyite, keithconnite, kotulskite, palladseite, and sperrylite, defining a Au–Pd–As–Sb–Se–Te chemical signature. Stable isotope and fluid inclusion studies indicate a wide range of fluid compositions with a prominent saline component. In conjunction with the mineral association, oxidizing fluids are indicated, and Au and PGE transport and deposition likely took place by chloride complexes in the epithermal range, at elevated f O2 and/or low pH. It is still speculative whether the mineralization is late Pan-African (～600–550 Ma) in age, or connected with the Variscan orogeny (～330–300 Ma), or related to some other hydrothermal event. Common to all Au–Pd mineralizations worldwide (Brazil, Australia, UK), including Bleïda Far West, is their formation in the epithermal (<300°C) range; deposition mainly in brittle structures; sulfide-poor mineral assemblages comprising hematite, sulfate minerals, and selenides; and metal transport by, and deposition from, oxidized, chloride-rich fluids. These deposits are further characterized by noble metal abundances in the order Au>Pd>Pt and the chemical signature Au–Pd–Se–Te (±As, Sb, Bi). As such, the Au–Pd association represents a discrete style of gold mineralization distinct from other classes of gold deposits. 相似文献
5.
T. El-Khanchaoui M. Lahmam A. El-Boukhari H. El-Beraaouz 《Journal of African Earth Sciences》2001,32(4):265
Petrological study and zircon typology provide important information that is related to the classification and genesis of Neoproterozoic granitoids in the Khzama area (northeast Siroua). The Pan-African granitoids show a transition from island-arc magmatism to alkaline magmatism. A space and time zonation of magmatism from the north to the south is evident. Early Pan-African granitoids were generated from various magma sources through different petrogenetic mechanisms. The first association corresponds to the low-K calc-alkaline plutons of Ait Nebdas, the second one correponds to high-K calc-alkaline post-collisional granites (Tamassirte-Tiferatine and Ifouachguel). Finally, shoshonitic magmatism (Irhiri) ends the magmatic evolution of the region. Thus, the late Pan-African granitic plutonism began with calc-alkaline associations and ended with K-alkaline magmatism in a transtensional setting, heralding the onset of the Moroccan Palæozoic cycle. 相似文献
6.
Youssef Hach Abdelouahed Abahamid Mohammed Sabil Abdelmajid Benhida Zouhair Benkhaldoun Abdelfatah Habib Youssef Elazhari 《Experimental Astronomy》2010,28(2-3):87-99
Over the past years, several differential image motion monitors (DIMM) have been built almost everywhere. The DIMM instrument is made up of simple material such as telescope, mask, camera ..., and it is widely used in seeing measurement campaigns. In order to carry out a prospecting campaign, for the European Extremely Large Telescope (ELT) project, in the Moroccan High Atlas, we have built a new DIMM instrument in our laboratory. To characterize this instrument, we have carried out a cross-calibration between DIMM monitors using different configurations. In this paper we will present the results of those various experiments respectively at Oukaimden site and at the “École Normal Supérieure” (ENS) in the city of Marrakech. 相似文献
7.
8.
M El-Baghdadi A El-Boukhari S Nadem A Benyoucef A Jouider 《Journal of African Earth Sciences》2001,32(4):635
The Precambrian inlier at Sidi Flah-Bouskour is cut by several successive intrusions of Neoproterozoic granitoids, whose zircon crystal morphology allows precise definition of granite types (Pupin, 1976, 1980, 1988) and, by inference, an assessment of tectonic settings. The first intrusion consists of gabbro, quartz-diorite and amphibole-granodiorite, belonging to the Pan-African B1 phase related to a pre-collision domain. It shows a calc-alkaline granodioritic composition. The second intrusion includes the Bouskour biotite-granite, which belongs to the high-K calc-alkaline suite emplaced at the time of the second Pan-African B2 phase in the context of syn-collision. These units are intruded by a Late Proterozoic pink granite followed by injection of submeridian sigmoidal cracks of rhyolitic dykes that represent the last Precambrian magmatic event in this area. 相似文献
1