Molybdenum isotopic compositions in volcanic rocks from the Izu arc

Abstract

Mo isotopic composition in volcanic rocks is recognized as a new geochemical tracer to understand the slab dehydration in subduction zones. Previous studies investigated Mo isotope systematics in northern Izu arc volcanoes including Izu Oshima, Niijima, Miyakejima, Hachijojima, and Izu Torishima. In this study, we measured the stable isotopic composition of Mo using TIMS for three basaltic xenoliths from Kozushima as well as basalts from Izu Oshima and Niijima.The samples from the fore-arc volcano (Izu Oshima) were found to possessδ⁹⁸/⁹⁵Mo＝0.13±0.09 ~ -0.11±0.09, whole those from back-arc volcanoes (Niijima and Kozushima) showed δ⁹⁸/⁹⁵Mo＝-0.27±0.09, δ⁹⁸/⁹⁵Mo =-0.15±0.07, which are consistent with previous studies [1]. However, the δ⁹⁸/⁹⁵Mo values is Kozushima samples were higher than those in Niijima, which is inconsistent with the correlation of major and trace element systematics. This suggests that the Kozushima samples may have been affected by factors other than the subduction process, such as secondary alteration.[1] Villalobos-Orchard, Javiera, et al. (2020): 68-82.