Fractional Crystallisation and Magma Mixing

It has been noted in the previous sections that the most evolved rocks from the Roman volcanoes can be derived from mafic parents by evolution processes, including fractional crystallisation and mixing. These have affected most if not all the Roman volcanics including the most mafic ones, as demonstrated by the scarcity or absence of rocks showing mantle- 

Fractional crystallisation has been dominated by separation of various proportions of clinopyroxene and olivine in the mafic magmas, and of cli-nopyroxene and feldspars in the felsic melts. These generated decrease in ferromagnesian elements (FeO, MgO, Ni, Co, Cr, etc.) and increase in incompatible elements (e.g. Th, Ta, Nb, REE), with ongoing evolution. In contrast, ratios of incompatible trace elements were not affected by fractionation processes, and can be used to infer compositions of mantle-equilibrated melts. 

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