Determination of the Os isotopic compositions of primary arc magma using chromite and estimation of slab components contribution

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Significant contrast in Os isotopic compositions between mantle and crust allow us to estimate recycled component from subducted slab quantitatively based on the Os isotopic compositions of arc volcanic rocks. However, crustal assimilation during magma ascent possibly masks the original Os isotopic compositions of primary magma. Here we analyze Os in chromites separated from beach sands or whole rocks themselves to determine the Os isotopic compositions of primary magma. Chromite is crystallized in the early stage of magma evolution, and most likely provides information on the chemical compositions of primary magma. We could clearly distinguish the Os from subducted slab and that assimilated during magma ascent. Also, The obtained results showed the oxidation processes of wedge mantle in arc evolution.