Abstract
WE present here evidence that apatite crystals formed in alkaline magmas during the early stages of both the ijolitic (pyroxenite→ijolite→urtite) and carbonatitic (sövite→alvikite) differentiation series1 have similar chemical compositions, but that with subsequent crystal differentiation in both series, the compositions of the apatites can change progressively along two separate paths. The evidence of a bifurcating pattern of apatite compositions from the various rock types studied is not in accord with the theory2,3 that carbonatites are the ultimate product of fractional crystallisation of the ijolitic series. The evidence suggests that ijolite and sövite are the crystalline products of conjugate immiscible liquids.
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LE BAS, M., HANDLEY, C. Variation in apatite composition in ijolitic and carbonatitic igneous rocks. Nature 279, 54–56 (1979). https://doi.org/10.1038/279054a0
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DOI: https://doi.org/10.1038/279054a0
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