Journal of Petrology
M.J. O'Hara, N. Fry
Abstract
This is a study of the effect of solidifying a magma body by partial crystallisation
of a series of small packets of liquid, mixing the residual 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 effects of
the small packet process is to sustain the relative concentrations of the compatible
elements in the residual liquids from partial crystallisation. Formal introduction
of integrated partial crystallisation within the small packets of liquid enhances
these effects. Incorporation of such a crystallisation model into a refilled,
tapped and fractionated magma body enhances the effects 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
crystallisation. It may also have a bearing on the ratios of extremely compatible
elements whose concentrations in the upper mantle are high and relatively undifferentiated
relative to chondrites.
Keywords
nickel;platinum group elements;in situ crystallisation;boundary layer;integrated
crystallisation
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