Li isotopic disequilibrium of the Cenozoic subcontinental lithospheric mantle in East Asia

Abstract

Mantle-derived spinel peridotite xenoliths, enclosed in alkali basalt and dating between 18.9 Ma and <1.2 Ma occur in southwestern Japan (On-yama and Arato-yama), South Korea (Baegryeong Island, Man and Pyeongtaeg, Boeun, Jeju Island, and Goseong), and eastern China (Qixia and Nushan). Sample locations were specifically selected to evaluate spatial differences in lithium (Li) isotopes in the spinel peridotite xenoliths, which have undergone both enrichment and depletion processes under mantle conditions. Li concentrations and isotopic compositions of coexisting olivine, orthopyroxene, and clinopyroxene in the spinel peridotite xenoliths from these units reveal both elemental and isotopic disequilibrium. The observed Li isotopic disequilibrium between xenolith minerals may reflect fractional infiltration of Li isotopic compositions from the host magma by later metasomatism during transport from the mantle to the surface.