Back-Arc To Active Continental Margin Pan-African Volcanicitv Along Wadi Fatirah,Central Eastern Desert, Egypt: Petroiogical And Geochemical Investigations

The studied volcanic rocks along Wadi Fatirah cover about 40% of the mapped area and are differentiated into two main groups: a) Metavolcanics, and b) Dokhan volcanics. The metavolcanics are regionally metamorphosed up to the greenschist facies. They are distinguished into:1) Pillowed basic aphyric-phyric metabasalts (typel), and 2) Metavolcanics of aphvric metabasaltic-andesites and andesites together with their equivalent pyroclastics (type 2), which are faulted against the first type. They are commonly characterized by primary sedimentary strictures (Lamination and graded bedding). The Dokhan volcanics occupy an elongate belt and are classified into two main rock suites: a) A lower intermediate volcanics suite, consisting of basaltic andesite, andesite, dacite and their corressponding pyroclastics, and b) An upper acidic volcanic suite comprising rhyodacite. rhyolite and their equivalent pyroclastics. The variation diagrams depict three distinct trends which suggest independent magma source. The metavolcanics (type 1) are tlioleiitic but with a weak calc-alkaline tendency. They straddle the boundaiy between ocean floor basalt (OFB) and island arc tholeiite (IAT) fields, a feature characteristic of back-arc setting. The metabasaltic-andesites-andesites are calcalkaline and were formed in an island arc setting.OFB IAT. The Dokhan volcanics pertain to medium-to high-K calc-alkaline series, formed in an active continental margin. They were formed by interaction a subduction-related magma and the lower crust accompained by low-pressure fractional crystallization en route to the surface