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. |
