Sha-Kaleri

The third largest complex of the Nigerian Younger Granite province, Sha-Kaleri extends over 640 km2. More than 20 units have been distinguished of which two comprise pre-caldera and intra-caldera agglomerates, tuffs and ignimbrites (MacLeod in Buchanan et al., 1971). MacLeod indicates that the complex consists of three structurally and petrologically independent, although overlapping, components. These are Kaleri, which encompasses over 80% of the total complex, consisting of an exceptionally large ring-complex extending nearly 40 km east-west, Manguna, which comprises two concentric granites on the northern margin, and Taf which is on the southern extremity and distinguished by the presence of a large gabbro body, which is intruded by granites. The earliest rocks are rhyolitic pyroclastics associated with the Kaleri centre. These were followed by a succession of arcuate granites and a partial ring-dyke to the east of the complex which follows a polygonal joint system, similar to that of the Ropp complex (No. 122-00-036) to the north. The granites include various biotite-, hornblende- and fayalite-bearing varieties as well as quartz syenite and microgranite. Only the Hotum granite is peralkaline. This forms two arcuate bodies towards the centre of the complex. The rock is equigranular and of quartz, perthite, zoned ferrorichterite/arfvedsonite, fayalite, generally altered and forming cores to the amphibole, and accessories including fluorite and allanite. Along the northern side of the more northerly body of Hotum granite an arfvedsonite-aegirine pegmatite forms an intrusion about 1.5 km in length averaging some 60 m in thickness. Most of the arfvedsonite crystals have cores and marginal intergrowths of aegirine. Analyses of the arfvedsonite and other granites will be found in MacLeod et al. (1971), and for Li and Zr in Bowden (1966a and 1966b). Analyses of arfvedsonite and ferrohastingsite are in Borley (1963).