Ebook: Carbonatite Volcanism: Oldoinyo Lengai and the Petrogenesis of Natrocarbonatites

During the last few years, carbonatites have received a considerable amount of attention. Some of this interest was no doubt kindled by the importance of volatiles in the Earth's mantle, particularly CO , by the fact that carbonatites 2 can be used to monitor the chemical evolution of the sub-continental upper mantle, and by the fact that carbonatites may be effective metasomatizing agents at both mantle and crustal levels. The interest in Oldoinyo Lengai has extended over at least 100 years, but it was not until the eruptions of 1960, when the unique carbonatitic nature of its lavas was recognized, that the volcano took on special significance in volcanology and igneous petrology. The recognition of carbonatitic flows coin­ cided with the first successful laboratory experiments carried out on carbonatitic melts. Since then, Oldoinyo Lengai has formed a cornerstone in all carbonatite discussions. It is probably true to say that the findings from Oldoinyo Lengai have dominated our ideas about carbonatites, in spite of the fact that the alkali­ rich, natrocarbonatitic lavas of Oldoinyo Lengai are markedly different from other carbonatites.

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This volume represents the results of the most recent research on field relationships, volcanology, geochemistry and petrology of Oldoinyo Lengai in Tanzania (East Africa), the only active carbonatite volcano. Peculiarities of carbonatite flows such as the highly sodic composition, their unique mineralogy, their low eruptive temperatures and viscosities, as well as their association with nephelinitic and phonolitic flows are of major interest to igneous petrologists. The wealth of new data, including the role of carbonatitic melts as metasomatizing agents in the earth's mantle are of interest to petrologists and other geoscientists.