Geochemistry of the Wadi Hawashia Granite Complex, northern Egyptian Shield

Abstract

The Hawashia Complex is comprised of calc-alkaline granitic rocks of peraluminous character. The bulk of the complex is composed of biotite granite, while the other intrusive phases, namely the “leucocratic-and alkali feldspar” granites, only constitute a minor proportion of the exposed surface area of the complex. Fractional crystallization is the dominant mechanism, which is necessary to explain the chemical attributes within the complex. Geochemical modelling reveals that an early stage of crystallization, which was controlled by plagioclase and amphibole separation, is necessary to generate the biotite granite. Later stages are dominated by K-feldspar crystallization, which evolves into the alkali feldspar granite. In contrast with the leucocratic granite, the alkali feldspar granite displays a significant enrichment in HFS elements (Nb, Y, Th, Zr) and a strong depletion in Ba and Sr. The small volume and the restriction of the alkali feldspar granite to the roof of the pluton, together with the specialized chemical signature, all substantiate the role of the volatile enhancement in the upper portion of the magma chamber. This volatile fraction was efficient in removing highly charged cations from the leucocratic granite and re-enriching them in the alkali feldspar granite.