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Dr. Mostafa Mohammad Mujahid Ahmed :: Publications:

Title:
Geotectonic significance of the Neoproterozoic ophiolitic metagabbros of Muiswirab area, South Eastern Desert, Egypt: constraints from their mineralogical and geochemical characteristics
Authors: Moustafa M. Mogahed1• Wlaa Mahmoud Saad1
Year: 2020
Keywords: Egypt  Eastern Desert  Muiswirab area  Ophiolitic metagabbros  N-MORB  Arc tholeiites  Forearc tectonic regime  Volcanic-arc setting
Journal: Acta Geochimica
Volume: Not Available
Issue: Not Available
Pages: Not Available
Publisher: Springer
Local/International: International
Paper Link: Not Available
Full paper Mostafa Mohammad Mujahid Ahmed_Mogahed-Saad2020_Article_GeotectonicSignificanceOfTheNe.pdf
Supplementary materials Not Available
Abstract:

Abstract Petrological and geochemical studies of Neoproterozoic metagabbros were carried out in the Muiswirab area, South Eastern Desert of Egypt. The Muiswirab area comprises of ophiolitic metagabbroic rocks (MOM), which are tectonically thrusted over a thick pile of metavolcanic rocks and intruded by syn- and post-tectonic granitoid rocks. The whole-rock geochemical variations coupled with chemical compositions of mineral constituents are used to attain the genesis and tectonic evolution of the studied metagabbros. The geothermobarometric investigation of the analyzed amphiboles from (MOM) revealed that these metagabbros underwent regional metamorphism under lower to upper greenschist facies (biotite zone) conditions (at a temperature of 450 to 500 C and pressure of 1–3 kbar). Geochemically, the metagabbros (MOM) show tholeiitic affinity and exhibiting both arc- and MORB- like characters as evidenced by their clinopyroxene compositions and the Ti/V ratios (11.84–31.65), which considered as prominent features of forearc tectonic regime. The geochemical features suggest a probable fractionation of olivine ± clinopyroxene ± plagioclase as well as insignificant crustal contamination. The parental magma of the investigated MOM rocks seems to be developed in a sub-arc mantle wedge setting due to the enrichments of LILE (e.g., Rb, Ba, Sr, Pb) over HFSE (e.g., Ti, Nb, Y, Zr, Hf, Ta). The studied MOM rocks have lower values of Nb/U relative to MORB and OIB indicating that their geochemical variation produced due to the enrichment of a lithosphere mantle by OIB-like components. The ratios of Zn/Fet, La/Sm, Sm/Yb, Th/Yb and Nb/Yb indicate that the MOM rocks represent a fragment of oceanic crust originated at a supra-subduction zone environment and their parental magma developed by 5–30 % partial melting of a spinel lherzolite mantle rather than pyroxenite in an island arc setting and conformable with most of the Egyptian ophiolitic metagabbros.

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