Contribution to the geochemistry and tectonic setting of the oligo-miocene a-type granites, South West of the Arabian shield, Yemen Republic

Abstract EN

The Oligo-Miocene A-type granites of Yemen Republic were emplaced in the early stages of rifting and Red Sea floor spreading, as Arabian Plate began to move slowly away toward ENE direction.

These granites intrude the eastern margin of the Red Sea coast, within a nearly north-south trending extensional zone.

Within this zone, alkali magma formed isolated intrusive masses, as well as various volcanic rocks spread all over this part of the Shield.

These Tertiary intrusive bodies are represented essentially by alkali granites and syenites.

The porphyritic texture of the studied granites indicates shallow depths of intrusion (1-2 km).

They consist of perthitic feldspar and quartz, with alkali amphiboles.

Geochemically, these granites belong to the alkaline or per alkaline suite of A-type granite, characterized by high FeOt / MgO and Ga / Al values.

They have high alkalies (8.29–10.29 %), high-field strength elements (HFSE, such as Nb, Ta, Hf, Th, U and Y) and Zn contents, along with low Sr and Ba contents.

They are enriched in REE.

The granites are specially characterized by large amounts of independent Nb-Y-Th minerals which appear in the late stages of continental extension.

The low Nb / Y and high Nb / Y granites, as well as major and trace elements data revealed two geochemical processes ; both assimilation and fractional crystallization origin, with little opportunity of crustal contamination.

The textural features of these granites indicate that they were originated from either water-poor hypersolvus or subsolvus magma, generated from alkali basaltic magma.

They formed in within plate environment under an extensional tectonic setting pertaining to rift related androgenic granites.

This agrees well with the extensional environment accompanying the Red Sea opening.