2011

Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

A-type Per alkaline granite of Gabal Gharib, Northern Egyptian Shield: Constraints on geochemical characteristics and the origin of intra plate felsic magma

Hussein A. Hegazy

Geology department, Assiut University, Assiut, Egypt

Email: hegazy512000@yahoo.com

Mobile: + 2 0127831604.

Per alkaline A- type granite of Gabal Gharib (476 + 2 Ma), northern part of Egyptian Shield, covers an elongate area of about 60 km2 in NW – trend. This granite represents the last manifestation of igneous activity in this region and surrounds by wide exposure of late – to post – organic I – type granites. The investigated granite is interpreted to have formed in an lithospheric extensional tectonic environment.

The Chemical and Petrological data strongly suggest that there rocks are hypersolvus in nature and mostly originated in intra plate tectonic environment with extensional regime in anorogenic setting. This within plate peralkaline granite consisting essentially of perthite, albite, quartz, alkali amphiboles (from ferroedenite to arfvedsonite) and Fe - rich biotite (titaniferous annite). Zircon, allanite, apatite, titanite, ilmenite and fluorite.are accessories

Geochemically these rocks are enriched in SiO2 , alkalis, Rb, LREE and HFSE (Nb, Zr, Y, Ce), high FeOt / MgO ratio and depleted in Al2O3 , CaO, Sr, Ba and negative Eu anomalies as well as Y/Nb and Ce/Nb ratio . Discrimination diagrams reveal a pure crustal origin for this granite at about 1-5 kbar. It is believed that the most credible mechanism for the origin of this type of granites is the partial melting (anatexis) of late – to post – orogenic I-type crustal granite (at 10-20 km depth), which is in accordance with thickness estimates reported for the Pan- African crust. The results of geochemical modeling suggests that the magma may have formed by a large degree of partial melting (metatexis, F= 0.60) which had been metasomatized possibly by a Na – rich fluid. Metasomatic reactions similar to those  observed in the metasomatized wall rocks are considered to have played an important role just prior to the onset of anetexis and generation of the A-type melt.