Granitoids and trachytes of Um Shager-Hamadat area, Central Eastern Desert, Egypt: Remote sensing characterization and petrology

Abstract

The late Neoproterozoic granitoids of Gebel Um Shager and Gebel Hamadat, Central Eastern Desert of Egypt, in addition to Paleozoic trachytes of both areas were discriminated using Landsat-8, and Sentinel-2 dataset. Band rationing and Principal Component Analysis techniques were applied. The studied granitoids represent the extreme end-members of the subduction-related I-type calc-alkaline granitic magmas (primitive to more evolved varieties) that developed over a long period of time. These granites were extruded by Paleozoic intra-plate trachytes. Petrography and petrogenesis of these rocks were dealt with and discussed. The Um Shager Older Granitoids (calcic tonalite to quartz monzodiorite) represent poorly differentiated metaluminous magma characterized by very low Rb/Sr ratio ∼0.07. Evolutionary, they follow the calc-alkaline subtype trend and most probably were originated from parent gabbroic magma by fractional crystallization in a volcanic arc setting. On contrary, the Hamadat Younger Granites represent alkali calcic magma which was developed in post-collision setting. They comprise evolved subsolvus metaluminous syenogranite and alkali feldspar granite. Evolutionary, they follow the subalkaline subtype trend. Crystallization courses of both syenogranite and alkali feldspar granite were started by alkali feldspar, followed by cotectic crystallization of alkali feldspar and quartz and ended by eutectic crystallization of all quartzofeldspathic minerals. The trachytes represent intra-plate continental alkaline magmatism. The Um Shager trachytes were developed at local extension zones, while the Hamadat trachytes were originated during global continental rifting system. Syenogranite, alkali feldspar granite and trachytes are important sources of alkali feldspar, which has wide spectrum applications in industry and agriculture.

Keywords

• Granitoids
• Trachytes
• Gebel Um Shager-Gebel Hamadat
• Remote sensing analyses