Geology, petrology and age determination of Archaean-Proterozoic basement rocks of western Uganda

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This project aims to assess the relationship of the uplift of the Rwenzori mountains to the generation of volcanism in the Toro Ankole volcanic field by improving our understanding of the generation of the volcanics and of the ultramafic nodules within them. The volcanics comprise an unusual type of potassic alkaline igneous rock known as kamafugite that may be explained by partial melting of mica and clinopyroxene-rich mantle assemblages similar to those found as xenoliths within the volcanics. Isotopes of Sr, Nd and Os will be used to assess the uptake of crust and lithospheric mantle and therefore the possible residence in crustal or mantle magma chambers. Re-Os will shed further light on the nature of the mantle that melted, namely asthenosphere or old lithosphere and the extent of its enrichment. Petrological and mineral chemical characterization of the mica- and clinopyroxenebearing xenoliths will ascertain whether these rocks are xenoliths from the mantle or crustal cumulates from the kamafugites. If mantle xenoliths, the mineral chemistry, including trace elements, will be used to investigate whether they are the result of pervasive metasomatism of peridotite or are restricted to veins. Pervasive metasomatism of the mantle has been proposed in this area to result in a large volume increase in the lithosphere - a possible reason for the uplift of the Rwenzoris.