الفهرس 
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Abstract
The Gabal El-Sibai granites are one of the highly fractionated granites outcrops in the CED of Egypt. An integration of field geology, petrography and remote sensing have been conducted to Gabal El-Sibai area. Accordingly, the rock units of Gabel El-Sibai are divided two main lithological units. Alkali feldspar granite (AFG) which constitute the main intrusion rocks. Some AFG deformed verities were recorded in the core of the intrusion. Alkali-amphibole granite (AAG) is recorded at the peripheries of the intrusion. The AFG and AAG are almost identical, with the primary distinguishing feature being the higher abundance of alkali amphiboles in the AAG.
The effectiveness of utilizing Landsat-8 Operational Land Imager (OLI) data in altering images has been assessed to distinguish lithological properties and emphasize areas affected by hydrothermal alteration. These techniques have been examined to enhance and update the geological map of Gabal El-Sibai. Various remote sensing methods, such as FCC, band ratio, PCA), and Corsta or Contrast (FOPC), have been employed on satellite imagery to aid in distinguishing the extensively exposed Neoproterozoic basement rocks in the research region. Consequently, a new revised geological map has been generated for Gabal El-Sibai.
The NW-trending elongation of approximately all topographic features in the Gabel El-Sibai area has drawn our attention of the study. These observations could serve as the starting point for further investigation into the geological and tectonic events that have shaped the area and causing replacement of granitic rocks. The direction of elongation in El-Sibai and Abu El-Tiyur plutons is NW-SE. The analysis of tectonic events affecting Gabal El-Sibai has undergone multiple geological events that have caused deformation to the geological structures. The presence of four distinct phases of deformation at least has occurred at different times and was caused by different geological processes. Early collisional tectonics caused low angle thrusting and ductile type deformations, which included D1 and D2 deformations of structural components running in the NE-SW and ENE-WSW directions, respectively. This was the beginning of the region’s tectonic history. A set of significant, NW-SE trending sinistral strike-slip faults that are subparallel are which make up the third deformation phase (D3). They are related to all features and characteristics of braided fault zones, such as the Arabian Shield’s Najd Shear System (NSS), which has a NW-SE trend. The fourth deformation phase (D4) represented by the Late compressional phase causing refolding of (F1) and folding some dykes.
The granites in the northern segment of Gabal El-Sibai were subjected to detailed mineralogical and geochemical investigation. The AAG phase contain columbite, nioboaeschynite, zircon and thorite as important rare metal bearing minerals host Nb, Y, Ta, Ce, Zr, Th, and U. Geochemically, both of AFG and AAG exhibit a highly evolved nature with a typical peralkaline composition. They are enriched in some LILE (Rb, K, Th) and HFSE (Ta, Pb, Zr, Y), but strongly depleted in Ba, Sr, P and Ti, consistent with an A-type granite geochemical signature. They represent a within-plate anorogenic granites associated with crustal extension and/or rifting. Granites share a common parental magma that underwent magmatic fractionation processes. We argue that these granites are predominantly derived from crustal magmatic sources with a minor contribution from the mantle, which likely provided the necessary heat for crustal melting. Lithospheric delamination is the preferred geotectonic model suggested for the evolution of El-Sibai granites similar to most highly fractionated granites in the Egyptian Nubian Shield. The occurrence of fluorite in the AAG samples clearly indicates the significant role of magmatic volatiles/fluids in the formation of these granites. The substantial presence of fluorine in the magma acts as a complexing agent, increasing the solubility of HFSEs, including Y, Nb, and Ta, leading to their incompatible behavior during magmatic differentiation. Consequently, the generated peralkaline granitic magma becomes enriched with ore metals such as Y, Nb, and Ta through extensive and prolonged fractionation processes. We highly recommend further geological and geochemical exploration in the all grantic phaseses specially the marginal phase of Gabal El-Sibai, which probably could contain economic concentrations of rare metal bearing minerals.