Petrogenesis and tectonic implications of the Maladob ring complex in the South Eastern Desert, Egypt: new insights from
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ORIGINAL PAPER
Petrogenesis and tectonic implications of the Maladob ring complex in the South Eastern Desert, Egypt: new insights from mineral chemistry and whole‑rock geochemistry Abdel‑Aal Abdel‑Karim1 · Mokhles Azer2 · Mabrouk Sami3 Received: 3 June 2020 / Accepted: 20 September 2020 © Geologische Vereinigung e.V. (GV) 2020
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. Keywords Alkaline ring complex · Fractional crystallization · Syenite · Peralkaline granite · Nubian Shield · Egypt
Introduction Alkaline to peralkaline magmatic rocks typically occur as small multiphase intrusions with highly variable mineral compositions, within intracontinental extensional settings. They contain an appreciable amount of alkalis and incompatible elements such as Zr, Hf, Nb and Ta. More than 130 Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00531-020-01937-2) contains supplementary material, which is available to authorized users. * Mabrouk Sami [email protected] 1
Geology Department, Faculty of Science, Zagazig University, Zagazig, Egypt
2
Geological Sciences Department, National Research Centre, Cairo, Egypt
3
Geology Department, Faculty of Science, Minia University, El‑Minia 61519, Egypt
alkaline ring complexes are recorded in the NE African province (Egypt, Sudan, and Ethiopia). Their emplacement extends from Neoproterozoic (~ 650 Ma) until Oligocene (~ 25 Ma), and they are closely associated with major structural deep-seated fault zones (Black
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