Petrogenesis of Maktali fractionated calc-alkaline younger granitoids, Central Eastern Desert, Egypt

Abstract

The Egyptian calc-alkaline younger granitoids represent part of broadly distributed late collisional high-K calc-alkaline granitoids in the northern Arabian-Nubian Shield. In the Eastern Desert of Egypt, these granitoids have a significant economic value that they are commonly associated with rare metal-bearing granites. Maktali granitoids are located in Central Eastern Desert and they constitute a two-phase pluton, which consists of leucogranites and monzogranites. They intrude the country metavolcanics with sharp contacts. These granitoids are slightly peraluminous and moderately to highly fractionated high-K calc-alkaline granitoids. Leucogranites and monzogranites were emplaced at temperatures 699.8-8.28.8°C and 757.2–909.6°C and under pressure 1.22–4.8 and 2.36–2.98 kbars respectively. Leucogranites and monzogranites were emplaced at depths 3.28–22.96 km and 6.36–8.5 km and they were crystallized under log Oxygen fugacity between − 13.2 to − 16.1 and − 11.6 to − 14.7 respectively. They are magnetite-series granitoids and their crystallization was controlled by NNO fugacity buffer. Leucogranites and monzogranites share the same magmatic source and they were emplaced during late-collisional stage by melting of crustal source rocks may occur as a consequence of decompression following delamination of the lithospheric root and slab breakoff. Maktali leucogranites could be generated by partial melting and subsequent fractional crystallization of mafic lower crust with addition of melts from the mantle. Maktali monzogranites show distinctive characteristics of rare metal-bearing granites that they contain Fe-columbite and transitional micas. Field and textural evidences together with chemistry of columbite, micas, and trace element behavior suggest the magmatic origin of monzogranites. Moreover, REEs in monzogranites show a pronounced Eu anomaly and a well-visible tetrad effect, supporting their generation by fractional crystallization and fluid-rock interaction during the late stage of granite crystallization.