Jebel Abu Nahl (Jebel Abu Nahal)

The diameter of 25-30 km makes Abu Nahal one of the largest ring complexes in the Bayuda Desert. It forms a range of hills reaching elevations of 300 m with arcuate ridges up to 80 m developed along ring-dykes cutting basement gneisses. The central part of the complex is a cauldron-like basin filled with extrusive rocks including rhyolitic crystal and pisolitic tuffs and lava flows which are cut by numerous rhyolitic dykes. Along concentric faults amphibole peralkaline granites and some peralkaline syenites were emplaced. In the southwest the large outer ring-dyke passes from medium-grained peralkaline granite into granite porphyry then into rhyolite porphyry with dense felsitic margins. A geologically and morphologically striking feature is the great abundance of the peralkaline rhyolitic, felsitic and microgranitic dykes both within and up to 40 km from the complex. A small stock and two small ring structures about 1.5 km in diameter cut the basement some 7 km northeast of Abu Nahal; they are of syenite, some of it pegmatitic.