Experiments were conducted to test the hypothesis that interaction of a carbonatitic magma with quartz-rich rocks plays a key role in shaping carbonatite complexes. The host rocks were represented by quartz, and the magma was represented by synthetic mixtures of CaCO3, MgCO3, and Na2CO3. With increasing distance from the quartz, the reaction between the carbonate liquid and quartz produced a domain of Na(Ca)-rich silicate glass, a domain of metasomatic wollastonite, diopside, and forsterite, and a carbonate-rich domain. This zonation reproduces that observed in many carbonatite complexes, e.g., Kovdor, Russia. The experiments provide strong evidence that carbonatitic magma/host-rock interaction controls the evolution of carbonatite complexes and explains how Mg-Ca-carbonatitic magmas from the mantle can evolve to produce the natrocarbonatites and associated alkaline silicate rocks observed at Oldoinyo Lengai, Tanzania.

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