Geotectonic significance of the Neoproterozoic ophiolitic metagabbros of Muiswirab area, South Eastern Desert, Egypt: co
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ORIGINAL ARTICLE
Geotectonic significance of the Neoproterozoic ophiolitic metagabbros of Muiswirab area, South Eastern Desert, Egypt: constraints from their mineralogical and geochemical characteristics Moustafa M. Mogahed1
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Wlaa Mahmoud Saad1
Received: 14 September 2019 / Revised: 3 January 2020 / Accepted: 29 January 2020 Ó Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
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
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11631-020-00404-8) contains supplementary material, which is available to authorized users. & Moustafa M. Mogahed [email protected] 1
Geology Department, Faculty of Science, Benha UniversityEgypt, P.O. Box 13518, Benha, Egypt
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. Keywords Egypt Eastern Desert Muiswirab area Ophiolitic metagabbros N-MORB Arc tholeiites Forearc tectonic regime Volcanic-arc setting
1 Introduction The characteristics and origin of oceanic island arcs rocks attract considerable attention. Most studies have focused on volcanic rocks, as volcanic ro
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