Relations pétrogénétiques entre les basaltes transitionnels et les océanites du Piton de la Fournaise (île de la Réunion, océan Indien) à partir de la composition chimique des inclusions vitreuses des olivines et des spinelles

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Abstract
The phenocrysts of olivine and chrome spinel of recently erupted oceanites (1966 and 1977) from Piton de la Fournaise contain a not insignificant quantity of monophase and polyphase glass inclusions. The inclusions in the spinel contain glass or glass with gas bubbles ; those in the olivine are most frequently glass with gas bubbles and daughter spinel crystals. In a few crystals of olivine have been observed and analysed some crystals of pyroxene and sulfides of Fe, Cu and Ni globules. The sulfides have separated at high temperatures (> 1,200° C) on initial liquid saturated in sulphur. The melt inclusions of the olivines and spinels have a transitional basalt composition. The enriched contents of MgO and Cr2O3 in the melt trapped in spinel show that these minerals began to crystallize before the olivine. The comparison between petrographic and geochemical data of transitional basalt and oceanite shows a cumulative character of the oceanite. This is also suggested by a comparison between chemical composition of melt inclusions on one hand, and melt adhered to the crystals and whole rock on the other hand. The sulphur contents in the melt inclusions (1,800 p. p. m.) are clearly greater than these measured in the whole rocks and they provide a good approximation of the sulphur content of the parental basaltic magma.

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