Mineral/Groundmass Partitioning for Chrome Spinel in Boninite

Mineral/magma partition coefficients are important factors for understanding magma genesis. ONUMA et al. [1] have proposed a diagram of partition coefficient (PC) vs. ionic radius (IR) which has a potential ability for elucidating how major and trace elements are distributed between minerals and magma. The PC of an element is under a strong control of the crystal structure, so that each cation position in the crystal structure gives rise to a parobola-shaped peak on the PC-IR diagram [l, 2]. The parabolic dependence is predicted on the basis of simple isotropic balk strain theory [3J or ionic lattice strain theory [4!]. Recently YURIMOTO and SUENO [5] have developed a new method for obtaining a set of coherent data for major and trace elements partitioning from the micro-area in rocks by secondary ion mass spectrometry (SIMS). They found the PC for anions was also under control of the crystal structure for olivine- and plagioclase-groundmass systems. The PC-IR diagrams are well established for major rock forming minerals [e.g. 2]. However, PC’s are least available for spinel which is an important phase in oceanic basalt and boninite.