Yasuo Ikeda

Effects of recycled materials involved in a mantle source beneath the southwest Japan arc region: evidence from noble gas, Sr, and Nd isotopic systematics

Abstract Isotopic compositions of He, Ar, Kr, Xe, Sr, and Nd and concentrations of noble gases are reported for phenocrysts, megacrysts, and ultramafic xenoliths in Cenozoic basalts from southwest (SW) Japan and compared with those in lavas and tectonic emplaced peridotite from northeast (NE) Japan arc. The mantle source beneath SW Japan arc indicate that the old subducted oceanic crust and sediment (enriched mantle, EM1) is the major source of the mantle. Some mantle source demonstrates mixing of depleted mantle (mid-ocean ridge basalts (MORB) mantle) and recycled materials (EM2). The isotopic data of ultramafic rocks (Tsuyama lherzolite) from SW Japan arc indicate the contribution of a Samoan-like plume component. This suggests that some mantle source beneath the SW Japan arc formed by upwelling of a deep-mantle superplume. The mixing processes among the depleted mantle, recycled materials, and mantle plume may have produced a mantle heterogeneity beneath the SW Japan arc region. On the other hand, ultramafic rocks and olivine phenocrysts in basalt from NE Japan arc have simple binary mixing trends between depleted mantle (MORB mantle) and subducted sediment components (EM2 component).