Petrogenesis of Gabal El kahfa Ring Complex, Eastern Desert of Egypt.

Gabal El kahfa Ring Complex occurs in the southern Eastern Desert, Egypt, at the intersection of lat. 24o 8/ 18// N and long 34o 38/ 55// E on the northern side of Wadi El Khrit. The ring complex exhibits incomplete type forming a horse-shoe ridge opened to the south, where the central stock (~1 km in diameter) is located near the southern opening.
Petrographically the diorite and porphyrites (Metavolcanic) represent the country rocks of the area. The ring complex is represented by alkali syenites and quartz syenites in the outer ring and the melanocratic synenites. Also, the central stocks are mainly represented by essexite gabbros and different dykes. The studied syenitic rocks are characterized by the presence of perthitic feldspar and plagioclase feldspar which mean that they are subsolvus.
The geochemical features revealed that the syenitic rocks of Gabal El kahfa Ring Complex originated from metaluminous alkaline magmas that developed in within plate tectonic setting being generated at depth of about 9-21 km equivalent to 3-6 kb and temperature more than 840^οc with multi-processes of both assimilation and fractional crystallization involving plagioclases, hornblende and Fe-Ti oxides from a partial melted lithospheric magma.
The total rare earth elements (REE) concentrations show an increase from the outer ring to the inner ring and have positive correlation with silica content which indicates that there are separate magmatic pulses. The chondrite-normalized REE patterns of the studied samples of the inner and outer ring complex show strong light rare-earth elements (LREE) enrichment over the heavy rare-earth elements (HREE) displaying pronounced fractionation and the negative Eu anomaly and consistent with plagioclase fractionation. The REE composition of the outer ring structure was achieved at 49%fractional crystallization whereas that the inner ring structure was achieved at 53% crystal fractionation.
The relations between U and Th elements reflect enrichment with magmatic differentiation. Also, the behavior of U and Th respect to Rb show there is thus a close link between Rb, Th and U in the evolution of magmatic series whether this evolution follows magmatic processes. It is clear that the U and Th contents are controlled by the presence of some accessory minerals (zircon, allanite, apatite and iron oxides) whereas iron oxide and hydroxides have the ability of adsorbing uranium from circulating solutions.