GEOCHEMICAL EFFECTS OF SMALL PACKET CRYSTALLIZATION IN LARGE MAGMA CHAMBERS - FURTHER RESOLUTION OF THE HIGHLY COMPATIBLE ELEMENT PARADOX

This is a study of the effect of solidifying a magma body by partial c rystallization of a series of small packets of liquid, mixing the resi dual liquid into the main body of liquid before repeating the process. It confirms the major conclusions of earlier workers and demonstrates that the dominant geochemical effect of the small packet process is t o sustain the relative concentrations of the compatible elements in th e residual liquids from partial crystallization. Formal introduction o f integrated partial crystallization within the small packets of liqui d enhances these effects. Incorporation of such a crystallization mode l into a refilled, tapped and fractionated magma body enhances the eff ects still more. The process affords a way to explain the 'anomalously ' high compatible element concentrations in erupted liquids which have nevertheless been subject to substantial low pressure crystallization . It may also have a bearing on the ratios of extremely compatible ele ments whose concentrations in the upper mantle are high and relatively undifferentiated relative to chondrites.