Summary.-The Mediterranean desert of Egypt is distinguished here into «arid» and «hyperarid» provinces on the basis of the ratio between precipitation and potential evapotranspiration, and each is subdivided according to mean temperature of both the coldest and the hottest months. The arid provinces are :(a) the attenuated arid Mediterranean coastal belt, and (b) the accentuated arid inland province. The hyperarid provinces are :(a) with mild winter and very hot summer, (b) with mild winter and hot summer, and (c) with cool winter and hot summer. Spatial and temporal variations in elima tic elements in these provinces are provided.Local vegetational variations in each province are related to the impact of geomorphology and physiography on the local climatic and edaphic characteristics ; and the plant communities associated with these variations are listed.Résumé.-Le désert méditerranéen de l'Egypte est divisé ici entre deux catégories : provinces arides et provinces hyperarides, selon la relation qui existe entre les précipitations et l'éva-potranspiration potentielle ; chaque catégorie est subdivisée en fonction de la température moyenne des mois les plus froids et des mois les plus chauds. Les provinces arides sont :a) la ceinture côtière caractérisée par un climat méditerranéen aride atténué ; b) la province intérieure, avec un climat mé-diterranéen aride accentué. Les provinces hyperarides sont celles qui ont :a) un hiver modéré et un été très chaud ; b) un hiver modéré et un été chaud ; et c) un hiver froid et un été chaud. Les variations des éléments climatiques à travers le temps et l'espace dans ces provinces sont illustrées.Les variations dans le tapis végétal local de chaque province sont reliées à l'impact de la géomorphologie et de la physiographie sur les caractéristiques du climat local et du sol. Les communautés végétales liées à ces variations sont mentionnées.
Gabbro-diorite-tonalite¡granodiorite complexes, derived from subduction-related, calc alkaline magmas represent a distinct unit in the Precambrian basement of Egypt. These intrusive complexes are commonly intruded into ophiolitic mé lange, schistose or gneissic rock assemblages. Well-constrained geological mapping of the Um Eleiga complex, combined with geochemical studies, should enable a better understanding of its genesis, especially its potential as a host for gold mineralisation. This complex represents a composite pluton intruded into the allochthonous, ophiolitic Abu Dahr massif and its associated undifferentiated metavolcanosedimentary mé lange matrix in the southern Eastern Desert of Egypt. Field and petrographic investigations have revealed a compositional continuum from gabbro to granodiorite through diorite and subordinate tonalite. Petrography and bulk rock geochemical data have been used to determine the magma type and tectonic setting of the Um Eleiga complex, whereas the electron microprobe data were valuable for the purpose of determining the pressure-temperature and oxygen fugacity conditions. The compositional continuum, pattern of zonation, shallow magma origin and marked common negative Nb anomalies suggest that a close petrogenetic relationship between the gabbro, diorite, tonalite and granodiorite units of the Um Eleiga complex. Subducted upper mantle wedge is proposed as being the source region for the gabbroic magma, whereas zoning of the complex is attributed to interplay of fractional crystallisation and assimilation. Pressure estimates based on the Al (iv) -in-hornblende geobarometry indicate that the gabbroic and dioritic rocks crystallised under 4-5 kbar, whereas tonalite and granodiorite were formed at 3-4 kbar. The hornblende-plagioclase thermometer indicates a formation temperature range of about 720 to 880uC for the complex. Varied oxidation states are inferred from the mineral assemblages, including magnetite, titanite and ilmenite and checked by Fe/(FezMg) ratios of biotite in the granitoid rocks. The tectonic setting, mineralogical, geochemical characteristics and varied redox state of the Um Eleiga intrusive complex are typical for arc-related intrusives potential for hosting intrusion-related gold in a collisional environment.
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