stripes
Rising some 1000 m above the plain Kwahera Mountain is composed dominantly of coarse-bedded nephelinitic tuff and agglomerate that overlie domed Usagaran metamorphic rocks. The agglomerates contain numerous blocks of Usagaran quartzite and gneiss, often fenitized, together with nephelinite fragments. There are probably some nephelinite lava flows in the summit area. Nearly 100 explosion craters occur within a 14 km radius of Kwahera summit. They vary in diameter from a few hundred metres to nearly 2 km. Ringing the craters are bedded agglomerates and crystal and lapilli tuffs with Usagaran gneiss sometimes exposed in the lower part of the crater walls. Fragments of augite, aegirine-augite, olivine, amphibole and mica occur in the crystal tuffs set in a matrix which is often calcitic. Among the craters are a few hills of melilite and olivine basalt. An approximately circular sovite plug 1 km in diameter is located in the breached crater of Kwahera (M.S. Garson, pers. comm., 1988). This apparently filled the original crater and a lava flow issued from it and extended 8 km to the southeast. Remnants of the flow are underlain by calcareous and micaceous lahars and tuffs and overlain by nephelinite. The flow varies from 1-2 m in thickness and consists of calcite, stratiform magnetite, pyrochlore, vermiculite, apatite and sodic amphibole. Locally it contains abundent xenoliths of sovite, fenitized quartzite, gneiss and marble. The sovite intrusion has a similar mineralogy.
BAGDASARYAN, G.P., GERASIMOVSKIY, V.I., POLYAKOV, A.I., GUKASYAN, R.K. and VERNADSKIY, V.I. 1973. Age of volcanic rocks in the rift zones of East Africa. Geochermistry International, 10: 66-71.M.S. Garson, pers. comm., 1988. MUDD, G.C. and ORRIDGE, G.R. 1966. Babati. Mineral Resources Division, Tanzania, Quarter Degree Sheet, 85.
