Heavy nitrogen in carbonatites of the Kola Peninsula: A possible signatureof the deep mantle

Nitrogen and argon isotopes were measured in carbonatites and associated ro cks from the Kola Peninsula in Russia. The Kola mantle source, which is tho ught to be Located in the deep mantle, is enriched in heavy nitrogen (+3 pe r mil relative to air) as compared to Earth's surface (atmosphere and crust , +2 per mit) and the shallow mantle (-4 per mil). Recycling of oceanic cru st (+6 per mil) or metal-silicate partitioning may account for the nitrogen isotopic composition of the deep mantle.