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Carbonatite lapilli-bearing tuff and a dolomite carbonatite bomb from Murumuli crater, Katwe volcanic field, Uganda

¹ Dipartimento di Scienze della Terra, Università G. d’Annunzio, 66013-Chieti Scalo, Italy
² Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
³ PRIS, University of Reading, Whiteknights, Reading, RG6 6AB, UK
⁴ Department of Environmental, Earth & Atmospheric Sciences, University of Massachusetts, Lowell, MA 01854, USA

^* E-mail: stoppa{at}phobos.unich.it

A group of carbonate-rich tuffs are described from the Murumuli crater, Katwe-Kikorongo volcanic field, SW Uganda which contain abundant carbonatite pelletal lapilli, together with melilitite lapilli and a range of xenocrysts and lithic fragments including clinopyroxenites considered to be of mantle origin. The carbonatite lapilli consist essentially of Sr-bearing calcite and Mg-calcite which form quench-textured laths. The lapilli contain microphenocrysts of Ti-magnetite, perovskite, apatite, clinopyroxene, sanidine and altered prisms of melilite. A 7 cm long dolomite carbonatite bomb is described which displays a form typically assumed by lava clots erupted in a molten state. Chemical analyses of a tuff, the bomb and a range of minerals are presented. Carbonatite clearly played an important role in the Katwe-Kikorongo magmatism and it is suggested that carbonatite magma evolved from carbonate-bearing melilitite.

KEYWORDS: Katwe-Kikorongo, Uganda, carbonatite lapilli, carbonatite bomb, melilitite

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