Petrology and Tectonic Setting of the Metagabbros and Granitoids Rocks of Muiswirab Area South Eastern Desert, Egypt

A.M.Mehanna, A.A.Rashwan, M.M.Mogahed and W.M.Saad"


The Precambrian rocks of Muiswirab area in the southeastern desert –Egypt is consisting mainly of gabbroic rocks penetrated by syn-tectonic granitoids. Muiswirab metagabbros occurring as elongated huge mass subparallel with the regional tectonics of the area. These rocks show a partial alteration to one of these constituents’ uralite gabbro, flaser gabbro/ amphibolite and retrograde of amphibolite. The best preserved parts of these metagabbros represent the dominant variety and show ophitic texture with pyroxenes and plagioclase as the major components. Subsequent alteration of these rocks ha s led to formation of uralitized pyroxene and amphibole and sometimes actinolite with plagioclase. Chemically, the present metagabbros always have tholeiitic affinities and show MORB/IAT i.e. transition tectonic setting. Moreover, they exhibit low Ti, Zr and Nb and REE contents this may indicate that, these rocks were generated in the back-arc marginal basin setting. The acidic calc-alkaline intrusive rocks from the studied area have geochemical characteristics of I-type granites with low Nb contents, a feature typical of arc-intrusive and pertaining to G1 granitoids. The most important implication of the geochemical data from the present study is, that the investigated area pertaining to Juvenile Pan-African crust in the Nubian Shield.

Key words

Muiswirab, Area, MORB, IAT, Calc, Alkaline, Backarc, Setting, Juvenile, Crust .