Petrogenesis and tectonic implications of the Maladob ring complex in the South Eastern Desert, Egypt: new insights from mineral chemistry and whole-rock geochemistry

Abstract

Alkaline ring complexes are widely distributed in the south Eastern Desert (SED) of Egypt, but their petrogenesis and geodynamic settings are a matter of many discussions. In this contribution, mineral chemistry, and whole-rock geochemical data of the Maladob intrusive rocks were used to investigate their petrogenesis. The Maladob ring complex is a small alkaline intrusion in the SED of Egypt, composed of oversaturated syenite, quartz syenites and peralkaline granite. The rocks consist of K-feldspar (Or94–97) and albite (An0-1), alkali amphiboles (arfvedsonite and ferro-katophorite), sodic pyroxene (aegirine), with accessory aenigmatite, zircon, apatite, ilmenite, magnetite and titanite. Geochemically, the rocks are peralkaline, show distinctive geochemical characteristics such as low contents of CaO, MgO, Sr and high contents of alkalis, Rb, Nb, Y, and REE, typical of A-type granites. The rocks are weakly to moderately fractionated with a general enrichment in LREE [(La/Sm)N = 2.96–3.64]. Typically, the Maladob rocks are classified as within plate granites and exhibit A1 subtype characteristics. We suggest that the Maladob rocks were formed from a similar OIB-like mafic magma by fractional crystallization. The fractionation of feldspars and mafic minerals play a significant role during magma evolution. During the Mesozoic intraplate magmatism, the upwelling of asthenosphere causes underplating of lithospheric OIB-like magma which was subjected to prolonged fractional crystallization to produce the Maladob syenites and peralkaline granite.