- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
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.