The area of Gabal Zeiatit, South Eastern Desert, Egypt represents one of a series of ophiolitic-island arc complexes
found within the Arabian–Nubian Shield (ANS). The present study introduces new major, trace, and rare
earth element analyses and mineral composition data of gabbroic rocks encountered in this area with the goal of
constraining their geotectonic setting. The investigated area consists of two types of gabbroic rocks. The Zeiatit
ophiolitic metagabbros (ZMG) are always associated with serpentinites of ophiolitic affinity and were subjected
to metamorphism of greenschist to lower amphibolite facies and exhibit tholeiitic affinity and MORB-like
characters. Serpentinites and metagabbros are tectonically thrusted over a thick pile of metavolcanic rocks. The
Zeiatit intrusive gabbros (ZIG) are related to Egyptian Alaskan-type mafic-ultramafic complexes and intrude the
studied ophiolitic rocks and island arc rocks. Geochemical data reveal that both studied gabbroic types originated
in sub-arc setting. Mineral chemistry data for the two types of the studied gabbroic rocks indicate that they
possess different characteristics. The NiO (< 0.15 wt%) and Fo (< 83mol.%) contents of olivine from the investigated
ZIG are lower than those of the Egyptian ophiolites. The clinopyroxene composition of the ZIG show
arc related cumulate. Geochemically, the ZMG exhibit MORB-like and arc-like signatures as they display Ti/V
ratios ranging from 14.52 to 21.09. Such phenomenon of hybrid mixture between island arc tholeiite (IAT) and
MORB is generally acknowledged being unique to forearc tectonic regime. Moreover, depleted LREE and HFSE
and relatively high CaO in the studied ZMG suggest derivation from Cpx-rich mantle at forearc tectonic setting.
The ZIG have Nb/Yb (0.28–1.04) and Th/Yb (0.1–0.42) which are typical for oceanic island arcs. The ZIG are
highly depleted in Nb, Ta, and Zr, but enriched in Ba, Pb, Sr, U and Th suggest their derivation from a metasomatized
lithospheric mantle source that modified by hydrous fluids derived from the subducting slab in a
subduction zone. ZIG have Th/Ta (0.69–2.05) and Ta/Hf (0.16–0.28) indicating that they were mainly derived
from partial melting of a depleted mantle source, being mixed with crustal material. The present geochemical
and mineralogical studies revealed that, the investigated ZMG are fragment of oceanic lithosphere probably
developed in a supra-subduction zone environment and originated by 10–30% partial melting of a spinel
lherzolite mantle in a sub-arc (forearc) setting at shallow depth which consistent with the most recent conclusions
of the Egyptian ophiolitic metagabbros. However, the investigated ZIG are akin to the Alaskan-type rocks. |
