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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.
Table des matières
Historic and Recent Eruptive Activity of Oldoinyo Lengai.- Field Observations and Measurements of the Physical Properties of Oldoinyo Lengai Alkali Carbonatite Lavas, November 1988.- The Dynamics of Degassing at Oldoinyo Lengai.- Petrology and Geochemistry of Oldoinyo Lengai Lavas Extruded in November 1988: Magma Source, Ascent and Crystallization.- The Trace Element Composition and Petrogenesis of Natrocarbonatites.- Cathodoluminescence Observations of Natrocarbonatites and Related Peralkaline Nephelinites at Oldoinyo Lengai.- Nd and Sr Isotope Systematics of the Active Carbonatite Volcano, Oldoinyo Lengai.- Stable Isotope Characteristics of Recent Natrocarbonatites from Oldoinyo Lengai.- Decay Series Evidence for Transfer and Storage Times of Natrocarbonatite Magma.- An Assessment of the Alleged Role of Evaporites and Saline Brines in the Origin of Natrocarbonatite.- What are the Parental Magmas at Oldoinyo Lengai?.- Peralkaline Nephelinite/Carbonatite Liquid Immiscibility: Comparison of Phase Compositions in Experiments and Natural Lavas from Oldoinyo Lengai.- Experimental Constraints on the Possible Mantle Origin of Natrocarbonatite.
Résumé
Carbonatites are a unique group of volcanic rocks. The book presents the most recent results of investigations carried out at the only existing recent carbonatite volcano (Oldoinyo Lengai, Tanzania, East Africa).
