Abstract
Globules of quenched Fe-oxide melt (63–75 wt% FeO tot , 5–13 wt% SiO 2 ) are found in syenite xenoliths ejected during phreatomagmatic eruptions near Pincina in southern Slovakia. The xenoliths represent flotation cumulates formed during fractionation of alkali basaltic magma in the deep crust. Micro-XANES spectra reveal only ferric iron in the Fe oxide globules and dominantly ferrous iron in the associated trachytic glass (6–10% FeO tot , 62–66 % SiO 2 ,), thus indicating almost complete disproportionation of Fe 2+ and Fe 3+ during the immiscible separation of the two melt phases. If taking place at an earlier stage of the magmatic differentiation, segregation of the Fe oxide phase could lead to significant change of the oxidation potential of the residual silicic melt.
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