A complex magmatic plumbing system beneath the subvolcanic mafic sill intrusions, Gabal Qatrani, Faiyum Depression, NW Desert, Egypt: Evidence from mineral textures, zoning and chemistry

• Petrography and geochemistry of sill intrusions are identifying. • Textural characteristics of minerals-forming sill complexes are clarifying. • Pressure and temperature of these minerals are indicated. • Magma plumbing system underneath sills is discussed. Neogene subvolcanic sills of tholeiitic basalt from Gabal Qatrani, Faiyum Depression, NW Desert, Egypt, represent composite intrusions of monogenetic sequences that are related to Red Sea rifting. The study of diverse textures, zoning patterns and compositions of their crystal cargo is presented for the first time. Phenocrysts sensu stricto and antecrysts are distinguished based on textural and compositional criteria, which are used as the proofs for the testing the open system processes such as magma mixing, replenishment, and magma convection into the magmatic plumbing system. The new mineral-chemical and thermobarometer results of the present study have been shown that five discrete olivine and clinopyroxene populations as well as four plagioclase crystals were recognized, illuminating different magma portions having different origins. The Mg-number [(100*Mg/(Mg + Fe)] displays a distinct variations ranging between 68-40 and 81-56 for olivine and pyroxene, respectively, whereas great compositional array in An content (from An 83 to An 40 ) characterizes plagioclase groups. The latter and pyroxene crystals display strong oscillatory and normal zoning alongside fine and coarse-sieve textures, while olivine and pyroxene crystals reflect normal and reverse zoning as well as significant sector zoning especially for the latter. Their characteristics bear evidences of various petrogenetic processes involving fractional crystallization and accumulation, magma recharge, mingling, and recycling. Qatrani’s plumbing system has been proposed as polybaric fractional crystallization at multi-levels, whereas discrete evolved magma batches crystallized and mixed with early-formed crystals during magma evolution. The P–T array outlines three magma reservoirs namely high-T, deep-seated magma (20-25 km), moderate T, evolved magma situated at moderate depth (10-15 km), and shallow, low-T, fractionated magma reservoir (