Natrocarbonatite tephra of Kerimasi volcano, Tanzania

摘要: Carbonatite tephra was discharged in the final eruptive phase of Kerimasi, an extinct nephelinite volcano eastern rift valley northern Tanzania. The dominantly alkali carbonatite composition, thus providing first well-documented example premodern natrocarbonatite volcanism. principal carbonate mineral nyerereite, which is dominant modern lava flows adjacent Oldoinyo Lengai. nyerereite Kerimasi leached its alkalis by meteoric water and now represented calcite pseudomorphs. Natrocarbonatite shows that alkali-rich rocks Lengai are not unique, supporting hypothesis magmas associated with volcanism were originally alkaline subvolcanic calcitic carbonatites a residuum from have been removed, either or fenetizing fluids. A to be tested magma is, worldwide, commonly perhaps composition.