Origin and emplacement of a reversely zoned, Pan-African granitoid pluton from the Sinai Massif, Egypt

Abstract

The Iqna granitoid pluton ( ca 580 Ma) is a post-orogenic Pan-African intrusion in the north central sector of the Sinai Massif. Three distinct zones can be recognised on the basis of field relationships and geochemistry. The pluton is reversely zoned from a margin of alkali feldspar granite through an internal zone of syenogranite to a core of monzogranite. The reverse zonation of the Iqna granitoid pluton is interpreted as an emplacement feature of partially fractionated diapirs. Fractional crystallisation modelling suggests that the early formed phases (plagioclase, K-feldspar, biotite and quartz) were produced by the side-wall crystallisation in a deeper magma chamber. The crystallisation of these early fractionates created a less dense residual melt that moved upwards in the magma chambers. Continuous upward accumulation of less dense (more silicic) melt gave rise to a vertically graded magma chamber. The higher-level emplacement of the Iqna Pluton began with the intrusion of the alkali feldspar granite diapir (which became the marginal zone) from the subjacent chamber. This was then followed by the emplacement of the syenogranite diapir mantle zone component that displaced the earlier granite to its margins and finally by the monzogranite portion of the magma chamber into the core of the pluton.