Petrological and geochemical studies of highly fractionated I-type granites at Abu Marwa–Abu Harba area, Northern Eastern Desert, Egypt

The granite rocks at the Abu Marwa-Abu Harba area, located at the North Eastern Desert, are classified into trondhjemite, syenogranite, and alkali feldspar granite. They are formed through the Neoproterozoic late to post-orogenic period (~ 600 Ma). The common fault trends in the area based on their number and length proportions are NE-SW, ENE-WSW, WNW-ESE, E-W, N-S, NNE-SSW, NNW-SSE, and NW–SE. The study area is characterized by the abundance of joint systems and was divided into shear and tension joints based on their tectonic origin. Mineralogicaly, the trondjhmite consists of plagioclase, quartz, k-feldspar, biotite, and hornblende. On the other hand, the syenogranite and alkali feldspar granite are mineralogicaly similar and composed of plagioclase, quartz, k-feldspar, biotite, and hornblende but the k-feldspar and quartz in the alkali feldspar granites are more abundant relative to the syenogranite. The Abu Marwa-Abu Harba granite rock types are classified as peraluminous, Fe-rich granites with calc-alkaline and highly fractionated I-type affinity. The trondhjemite has a significantly lower content of TiO₂, CaO, K₂O, Ba, Rb, Sr, Zr, and ƩREE than the syenogranite and the alkali feldspar granite. The trondhjemite displays a gullwing-shaped REE pattern with deeper negative Eu anomaly while the syenogranite and the alkali feldspar granite are rather smooth and subparallel with negative Eu anomaly. The late orogenic trondjhmite was suggested to be generated by partial melting of the mantle source followed by fractional crystallization of k-feldspar, plagioclase, and apatite phases. On the other hand, the post-orogenic syenogranite and alkali feldspar granite were generated by partial melting of the upper crust at different depths followed by fractional crystallization. The fractionated phases were plagioclase, k-feldspar, biotite, hornblende, apatite, and titanite. In addition, the hydrothermal volatile-rich fluids played a role in the formation and generating of the studied post-orogenic syenogranite and alkali feldspar granite.