Abstract

The upper Tertiary volcanic rocks of northern Tanganyika comprise an older and a younger group of extrusives. The former are olivine basalts, trachytes, and phonolites that formed lava plateaus. The younger group, erupted following a period of faulting of the earlier lavas in lower? Pleistocene time, are predominantly pyroclastics ejected from smaller central volcanoes. The lavas are ultrabasic with associated carbonatite. Several carbonate-rich pyroclastic cones are described. The tuffs have a calcite-rich matrix; the volcanic origin of the carbonate is verified by trace element analyses. Nodules of ultrabasic rocks (lherzolite, harzburgite, and others) ejected at Lashaine show a great similarity to kimberlite and substantiate previous suggestions of a link between kimberlites and surface carbonatitic eruptions.

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