Geochemistry and petrogenesis of some gabbroic intrusions invaded the basement rocks from Al-Maqatirah and Al-Ahkum areas, SE Taiz, Republic of Yemen

الملخص

The Al-Maqatirah and Al-Ahkum areas are located in SE of Taiz within the southwestern outcrops of the basement rocks of Yemen, which represent the southern extension of the Arabian Nubian Shield (ANS). This paper focuses on the study of gabbroic intrusions that have invaded these basement rocks in these areas. These gabbroic intrusions were unmetamorphosed, variably altered, and sometimes affected by Na-rich fluid fluxes. They exhibit many types of textures and structures, and according to the abundance and appearance of major mineral constituents, these gabbroic rocks are classified into several types. Chemically, these gabbroic intrusions are classified as low-Ti intrusions generated from low-Ti magma, which is characteristic of an intra oceanic island arc setting and formed in a subduction zone setting by partial melting and re-melting of a depleted peridotite mantle source. However, some samples show indications of subsurface mixing of contemporaneous magma batches with low Ti and high Ti compositions. The major element compositions of these gabbroic rocks reflect their derivation from primitive magma subjected to significant degrees of fractional crystallization. These gabbroic intrusions have an ocean island basalt (OIB) signature and transitional character of magma from alkaline to sub-alkaline (tholeiitic) magma series, which indicate their derivation by variable degrees of partial melting of the mantle source at various depths during the change from arc to intraplate setting. The OIB signature of these mafic intrusions suggests lithospheric attenuation and significant upwelling of the asthenosphere caused by continental rifting, which mostly occurs during the formation of the Arabian lithosphere. Finally, the studied gabbroic intrusions can be compared with similar gabbroic intrusions in the Arabian-Nubian shield from Saudi Arabia, which are emplaced post-collision at the end of the Pan-African Orogeny and generated from mafic magma derived from a peridotite mantle source.