stripes
The central unit of Jebel Tuna is a nepheline syenite with prominent ring-dykes of microsyenite and phonolite. The nepheline syenite comprises perthite, nepheline, sodalite, secondary natrolite, aegirine-augite, calcic-sodic amphibole, biotite and accessories. Surrounding the nepheline syenite is a peralkaline quartz syenite which grades into granite at the outer margin. It contains sodic amphibole and accessory fluorite and zircon. Scattered outcrops at Jebel Kafina to the west are of foid syenite, while Jebel Debkaya, some 5 km to the south, includes peralkaline syenites and granites. Analyses of four specimens of foid syenite are given by Curtis and Lenz (1985).
CURTIS, P. and BRINKMANN, K. 1985. The geology of younger intrusive alkali complexes in the southwestern Nuba Mountains, Sudan. Geologisches Jahrbuch, 63: 3-41.CURTIS, P. and LENZ, H. 1985. Geological and geochronological investigations of selected alkali igneous complexes in the Nuba Mountains, southern Kordofan, Sudan. Geologisches Jahrbuch, 69: 3-24.
