الفهرس 
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Abstract
The present thesis deals with geology, petrography, geochemistry, and mineral chemistry of different study rocks covering the Hadayib and Um Risha ring complexes in the South Eastern Desert of Egypt.
Geologically, Hadayib ring complex is located at the intersection of Latitude 23°8́ N and Longitude 33°33́ E. It measures 4 Km along its N-S axis and about 1.5-3.5 Km width. It includes two superimposed ring structures composed essentially of alkali syenites intruding trachytes masses, which represent remnants of the former original volcanic cone. Um Risha ring complex is located at the intersection of Latitude 23°18́ N and Longitude 33°18́ E. It forms a big ring structure measuring about 5 Km along its N-S axis and about 12 Km in E-W direction. Based on the field observations, it is formed mainly of alkali syenites, but alkali granites form incomplete outer ring surrounding the alkali syenites. Trachytes represent the uplifted parts of the old volcanic cone.
Petrographically, the alkali syenites are composed essentially of potash feldspars, quartz, and plagioclase (An6-12), alkali amphibole and less amounts of biotite. Accessory minerals include zircon, apatite and opaques. Alkali granites are composed essentially of potash feldspars, quartz, alkali amphibole, biotite and minor plagioclase. The accessory minerals include zircon, apatite, sphene and opaques. The trachytes are composed of sanidine phenocrysts, plagioclase feldspar, rock fragment and little amounts of mafic minerals. Trachy-andesites are composed mainly of plagioclase and potash feldspar constituting about 80% of the rock volume. Aegirine and aegirine-augite form the ferromagnesian phenocrysts.
Geochemically, the alkali granites, alkali syenites and trachytes are saturated with silica and have peralkaline character with sodic affinity. Rare earth elements (REEs) patterns for the investigated rocks are characterized by high abundances of REEs (ΣREEs ranges between 359and 573 ppm and averages for Gabal Hadayib and ranges from 407 to 817 ppm for Gabal Um Risha). In general, light rare earth elements (LREEs) enrichment is a characteristic feature of the study alkaline rocks, compared to the heavy rare earth elements (HREEs). (LREEs) increases within Um Risha ring from alkali syenites through trachytes to alkali granites. In contrast to the Um Risha, LREEs of the alkali syenites is slightly higher than that of trachytes in the Hadayib ring complex. The LaN/YbN ratios in both rings range from 9 to 17 indicating a moderate/ high fractionation nature of the rocks forming rings. The difference in the LREE abundances could be explained by
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crystal fractionation of minerals that prefer LREEs. The geotectonic environment of the investigated rocks clears that the alkaline rocks from Hadayib and Um Risha ring complexes exhibit the geochemical signatures of the A1-type granites, which are generally derived from mantle melts in anorogenis within-plate tectonic regime. The correlation of U and Th as well as U and trace and total RRE in the different rock types of the two complexes between indicate that U and Th are preferentially hosted in specific refractory minerals during the crystallization of the magma especially zircon, sphene and iron oxides. U, Th, Nb, Zr and Y as incompatible elements increase with increasing the degree of differentiation of magma, from which the rocks have crystallized.
Amphiboles range from calcic amphibole to sodic amphibole in the alkali syenites and sodic in alkali granites. The overall composition is sodic (Eckermannite, Arfvedsonite to rarely Riebeckite) in alkali granites. In the study alkali syenites calcic amphiboles range from silicic ferro-edenite to ferro edenite-hornblende, while sodic-calcic amphiboles are ferro- richterite. Biotite reflects an alkaline affinity in the alkali syenites and the alkali granites. The plagioclase composition is sodic albite (An1– An10) in the alkali syenites of Hadayib ring complex, sodic albite (An1- An8) in the alkali syenites of Um Risha ring complex. Potash feldspar is Or44-97 in the alkali syenite of Hadayib ring complex, Or45-95 in alkali syenite of Um Risha ring complex, and Or86-98 in the alkali granites of Um Risha ring complex.