Nephelinite–melilitite–carbonatite relationships: Evidence from Pleistocene–recent volcanism in northern Tanzania

Abstract The younger ( An integrated model involves carbonated olivine–nephelinite magma generated in the asthenosphere by melting of carbonate-bearing peridotite. Small amounts of the melt migrate rapidly and are extruded as the olivine–nephelinites and –melilitites. Larger amounts of magma pond in the lithosphere with which they react and, during variable periods of stagnation, varying degrees of olivine–pyroxene–spinel fractionation take place before upward migration of now-differing magma batches. Variable residence time within, and reaction with, variably enriched lithosphere accounts for the array between the HIMU and enriched mantle end-members in the isotope mixing model.