Late precambrian metavolcanics of um anab north eastern desert, egypt, geochemistry and tectonic environment studies

The volcanic history of the Neoproterozoic belt in the Eastern Desert of Egypt encompasses two major magmatic episodes. An earlier episode (950-750 Ma) produced the Shadli metavolcanic assemblages, and younger episodes (680-550 Ma) produce the Dokhan volcanic series. Um Anab metavolcanics (UAV), represent one of the significant metavolcanic suites in the northern part of the Nubian Shield. They mainly comprise amphibolites, meta-andesites, metafelsites to metarhyolites, with the meta-andesites being the most abundantly represented of the group. The grade of metamorphism is low to medium i.e.greenschist and amphibolite facies conditions. Geochemically, the Um Anab metavolcanics have a transitional character from tholeiite to calc alkaline. The absence of a compositional SiO2 gap and the general systematic variation for some major and trace elements could be interpreted as evidence of fractional crystallization through one magma source. The metavolcanics are enriched in LILE and depleted in HFSE, with a pronounced negative Nb anomaly. Thus the UAV were most probably derived from a mantle source, and erupted in an island arc environment at a active continental plate margin. Fractional crystallization processes have played a vital role during evolution of Wadi Um Anab metavolcanics.