Sabaloka And Wadi Abu Tuleih

The Sabaloka complex is bisected by the River Nile which has incised a deep gorge through it; Wadi Abu Tuleih is a much smaller complex lying 2 km to the northeast. Sabaloka is sharply defined by an outer ring-dyke and fracture zone which in places forms a graben feature. It comprises mica granites, ignimbrites, rhyolitic and some basic lavas. These rocks are not generally peralkaline but Almond (1977) is of the opinion that some facies, notably some of the ignimbrites and some minor intrusions which contain fayalite and clinopyroxene, are similar to some of the Nigerian peralkaline granites and may originally have been peralkaline but that the diagnostic peralkaline minerals have been altered. The Tuleih complex consists of a quartz syenite and a granite. The former comprises perthite, oligoclase-andesine, ferrohastingsite, pale-green clinopyroxene, quartz and occasional biotite. The mafic minerals of the granite are pseudomorphed by iron oxides and quartz but are considered to have been aegirine. Over 200 dykes are concentrated in the area of the Tuleih complex; they are mostly of syenitic compositions including felsite, quartz porphyry, trachyte and rhyolite. The youngest dykes are generally peralkaline and include microgranites and microsyenites with arfvedsonite and aegirine, while astrophyllite and aenigmatite also occur. One rhyolite dyke contains phenocrysts of quartz, microcline and clinopyroxene, the last surrounded by fringes of blue amphibole and needles of aegirine; aegirine and zircon are abundant in the matrix. A detailed account of the structure of the complexes and a full range of rock analyses are in Almond (1977), and Harris et al. (1983b) give major and trace element, including RE, and Rb-Sr isotopic data. Sadig et al. (1974) report a gravity study of the complex and Cavanagh (1979) palaeomagnetic data.