Carbonatite volcanism. Oldoinyo Lengai and the petrogenesis of natrocarbonatites / Карбонатитовый вулканизм. Олдоиньо Ленгаи и петрогенезис натрокарбонатитов

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 CO2 , by the fact that carbonatites 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 coincided 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 alkalirich, natrocarbonatitic lavas of Oldoinyo Lengai are markedly different from other carbonatites. 

Oldoinyo Lengai lies in the East African rift in northern Tanzania near the Kenya-Tanzania border, south of Lake Natron, and was considered for many years to be fairly inaccessible. It was therefore surprising that in one year, 1988, two expeditions visited Oldoinyo Lengai - the Krafft-Keller expedition in June and the Dawson expedition in November. Findings from these two expeditions stimulated renewed interest in Oldoinyo Lengai, particularly the findings that the temperatures and viscosities of erupting natrocarbonatite flows were among the lowest measured in terrestrial materials. Also, detailed petrographic and geochemical analyses, long awaited on fresh samples, became available. <...>