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Raman spectroscopic analysis at low (−100 • C) or high (100-200 • C) temperature is shown to be effective for detecting small amounts of H 2 O in CO 2 -rich fluid inclusions from the deep lithosphere, which have previously been thought to be water-free.

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The evolution of a carbonated nephelinitic magma can be followed by the study of a statistically significant number of melt inclusions, entrapped in coprecipitated perovskite, nepheline and magnetite in a clinopyroxene-and nepheline-rich rock (afrikandite) from Kerimasi volcano (Tanzania). Temperatures are estimated to be 1,100°C for the early stage of the melt evolution of the magma, which formed the rock. During evolution, the magma became enriched in CaO, depleted in SiO 2 and Al 2 O 3 , resulting in immiscibility at *1,050°C and crustal pressures (0.5-1 GPa) with the formation of three fluidsaturated melts: an alkali-and MgO-bearing, CaO-and FeO-rich silicate melt; an alkali-and F-bearing, CaO-and P 2 O 5 -rich carbonate melt; and a Cu-Fe sulfide melt. The sulfide and the carbonate melt could be physically separated from their silicate parent and form a Cu-Fe-S ore and a carbonatite rock. The separated carbonate melt could initially crystallize calciocarbonatite and ultimately become alkali rich in composition and similar to natrocarbonatite, demonstrating an evolution from nephelinite to natrocarbonatite through Ca-rich carbonatite magma. The distribution of major elements between perovskite-hosted coexisting immiscible silicate and carbonate melts shows strong partitioning of Ca, P and F relative to Fe T , Si, Al, Mn, Ti and Mg in the carbonate melt, suggesting that immiscibility occurred at crustal pressures and plays a significant role in explaining the dominance of calciocarbonatites (sövites) relative to dolomitic or sideritic carbonatites. Our data suggest that Cu-Fe-S compositions are characteristic of immiscible sulfide melts originating from the parental silicate melts of alkaline silicate-carbonatite complexes.

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