Melt contribution to partitioning of trace element between plagioclase and basaltic magma of Fuji volcano, Japan

Abstract

Ion microprobe analyses of trace elements in plagioclase crystals apply to partitioning between plagioclase phenocrysts and basaltic magma of Fuji volcano. The partitioning of trace elements of plagioclase is governed not only by the site preference of ions in the crystal as it is widely accepted, but also by the components of melt. The observed logarithmic count ratios of the ion microprobe analyses between trace and host elements in plagioclase, is linear with X An (anorthite composition of plagioclase), in the range of X An (0.55–0.85). The observed ratio is proportional with K′-value (apparent exchange partition coefficient) because of nearly constant composition of the basalt. We separate the K′-value into two terms: plagioclase component controlled term and non-plagioclase component controlled term. The second term mainly characterizes the pattern of the Onuma PC-IR-diagram in a magmatic system.