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We have reconstructed the compositional evolution of the silicate and carbonate melt, and various crystalline phases in the subvolcanic reservoir of Kerimasi Volcano in the East African Rift. Trace element concentrations of silicate and carbonate melt inclusions trapped in nepheline, apatite and magnetite from plutonic afrikandite (clinopyroxene–nepheline–perovskite–magnetite–melilite rock) and calciocarbonatite (calcite–apatite–magnetite–perovskite–monticellite–phlogopite rock) show that liquid immiscibility occurred during the generation of carbonatite magmas from a CO₂-rich melilite–nephelinite magma formed at relatively high temperatures (1,100 °C). This carbonatite magma is notably more calcic and less alkaline than that occurring at Oldoinyo Lengai. The CaO-rich (32–41 wt%) nature and alkali-“poor” (at least 7–10 wt% Na₂O + K₂O) nature of these high-temperature (>1,000 °C) carbonate …