RECENT ERUPTIVE EPISODES OF THE RUNGWE VOLCANIC FIELD (TANZANIA) RECORDED IN LACUSTRINE SEDIMENTS OF THE NORTHERN MALAWI RIFT

Discrete ash horizons in Holocene sediments from northern Lake Malawi provide evidence of six eruptive episodes within the nearby Rungwe Vol canic Field between c.9000-360 BP. Rare earth element (REE) analyses s how the ash layers to be strongly enriched in La, Ce, Pr, Nd, Sm, Th, Dy, Er, Tm, Yb and Lu, with low Eu/Eu and high La(N)/Sm(N) values, re lative to the surrounding muds. Mixing calculations suggest possible a ffinities between the Rungwe ash emissions and silicic volcanics from other important Quaternary centres (e.g. Naivasha) with respect to HRE E geochemistry. The LREE spectra are less comparable and may indicate a less fractionated ash assemblage for Rungwe Field. In the absence of clear in situ evidence regarding the timing and frequency of Holocene eruptions at Rungwe, the Lake Malawi sediments may prove a valuable r econstructive tool. However, the direction and extent of ash dispersal is strongly controlled by wind/climatic factors and the retention of a complete record at any single location is unlikely.