摘要
El-Kahfa complex locates at the intersection of Lat. 24°8′18″ N and Long. 34038′55″ E, South Eastern Desert of Egypt. It comprises an outer ring composed of alkaline syenites, ranging from barrento quartz-bearing syenites, an inner ring which varies in composition from leucocratic to melanocratic syenites, and a central stock formed essentially of alkali gabbros. These alkali gabbros are cut by small bodies of alkaline syenites, which occasionally grade into nepheline syenites. The country rocks are represented mainly by metavolcanics and epidiorites. El-Kahfa syenites lack any primary hydrous mafic silicates indicating that their magma was anhydrous. Major and trace elements geochemistry of EI-Kahfa rocks reflects the crystallization of early plagioclase followed by Fe-Ti oxides. Salic members in the complex are co-magmatic and related to crystal liquid fractionation. The REE （rare earth elements）＇s tetrad is obvious on the primitive mantle normalized pattern of El-Kahfa rocks. The M-type tetrads clearly appear in the more evolved rocks. These tetrad effects are either a feature of magma-fluid system before crystallization or inherited from external fluid during or after the emplacement of the magma. Generally, El-Kahfa rocks parental magma was probably derived from Nb-enriched or at least under-plate mantle source within the continental East-Africa rift zone, where it may be subjected to minor contamination through their fractional crystallization.
