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Chromian spinel in volcanic rocks is a potential discriminant for magma chemistry. The TiO2 content of spinel, compared at similar Fe3+/(Cr + A1 + Fe 3+) ratios, can distinguish island arc basalts from intraplate basalts. MORB spinels are low in this ratio and are intermediate for the TiOe level at comparable Fe 3+ ratios. Spinels from back-arc basin basalts, although similar in TiO2/Fe 3+ ratio, are more enriched in Fe 3+ than the MORB spinels. Spinels in the oceanic plateau basalts are distinctly lower in TiO2 than other intraplate basalt spinels and even slightly lower in TiOa than the MORB spinels. The data were successfully applied to estimate the kind of the magma from which spinelbearing cumulates, especially dunites, were formed. Original magma chemistry of altered or metamorphosed volcanics in which spinels survive can also be estimated by the chemistry of relict spinel alone. It is possible to estimate the magma type of source volcanics for detrital spinel particles of volcanic derivation.K E Yw o RI~ s : chromian spinel, TiO2 content, MORB, island-arc basalt and andesite, intraplate basalt, magma chemistry.

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