Mo isotopic compositions in rhyolites and basaltic xenoliths of Kozushima

Abstract

Basaltic xenoliths found in the Membo lava of Kozushima have a composition that was influenced by the slab-derived fluid originating from a deeper slab than the slab beneath Niijima. However, the origin of basaltic xenoliths, as well as the relationship between basaltic xenoliths and rhyolitic magmas remains unclear. In order to investigate the interaction between these two magmas, we have measured the δ98/95Mo values of rhyolites from Kozushima and compared the results with those of the basaltic xenoliths (2021 the geochemically society of Japan, Tamura et al., ). Basaltic xenoliths, pyroclastic materials and three types of rhyolites possess δ98/95Mo values significantly different from one another. Based on the results of previous studies, plagioclase and hornblende fractionation[1,2]played key role in the variation of δ98/95Mo values. In contrast, partially blackened areas in the rhyolite containing captured rocks showed significantly lowδ98/95Mo values compared to those of the host rhyolite, suggesting that the isotopic ratios may have fluctuated due to assimilation with the basaltic magma.