Remote sensing analysis and geodynamic setting of magmatic spessartine-almandine-bearing leucogranites, Um Addebaa area, southeastern Desert, Egypt: Bulk rock and mineral chemistry

This study aims to incorporate optical multispectral remote sensing, petrography, geochemical, and field investigations in producing mapping and surface abundance of garnet mineralization within Um Addebaa area, southeastern Desert of Egypt. Datasets of Landsat-8 OLI/TIRS, ASTER, and Sentinel-2A (S2A) were handled and scaled enhanced to discriminate the units of lithologic rock and garnet mineralization. The spectral mapping techniques of constrained energy minimization (CEM) and matched filtering (MF) are used to detect the garnet-rich zones, which are confined to the leucogranites masses. These granites are spessartine-almandine-rich, certainly along the zone of interaction with the ophiolitic mélange. Notably, they have high total alkalis, SiO₂, and Al₂O₃, Rb, 10⁴Ga/Al, Y, Zr, Pb, Rb/Sr, Al₂O₃/TiO₂, and FeO/MgO, and strong Ti, Sr, and Ba depletion as well as low CaO/Na₂O ratio (<0.3). These geochemical parameters reflect their calc-alkaline nature, and strongly peraluminous S-type magma composition. They are derived by two episodes of partial melting clay-rich metapelite crustal rocks followed by extreme Fe–Ti oxides and feldspar fractionation. These leucogranites formed within an extension tectonic regime during a post-collisional episode, resulting in raising of the asthenosphere and partial melting of the crustal metasedimentary rocks. Garnet occurs as aggregates and/or vein like-shape, subhedral to rounded grains, homogeneous and rarely reveal weak zonation. It's cracked and free of inclusions. It contains appreciatable concentrations of FeO and MnO and minor amounts of CaO and MgO, dominantly spessartine-almandine end-member (Alm_52-59Sps _31-36 Grs _8-12 Prp_0.5-0.8 Adr₀). Garnet chemical compositions reflect its magmatic origin with MnO–FeO-bearing magma that is produced from in situ nucleation from strongly peraluminous magmas in a post-collision geotectonic setting.