Sr and Nd isotopic data from some young carbonatites from East Africa exhibit an excellent negative correlation on an ϵSr - ϵNd diagram. A simple mixing model involving continental crust was tested and found not to fit the isotope patterns. The mixing of two mantle sources is preferred, one being depleted and the other slightly enriched in the large ion lithophile elements relative to bulk earth. The presence of a depleted source below the Tanzanian Shield is consistent with findings from some Canadian carbonatites.

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