Zinc isotopic systematics of the Mt. Baekdu and Jeju Island intraplate basalts in Korea, and implications for mantle source lithologies

Abstract

Zinc isotope data for late Cenozoic intraplate basalts from Mt. Baekdu (North Korea) and Jeju Island (South Korea) were determined to characterize their mantle source lithologies. The average δ66Zn values (relative to JMC-Lyon) are 0.34‰ ± 0.08‰ (2SD; N = 13) for the Mt. Baekdu basalts and 0.37‰ ± 0.08‰ (2SD; N = 12) for the Jeju basalts, which are higher than values for refractory peridotites (0.18‰ ± 0.06‰) from the lithospheric mantle beneath the North China Craton. Given that Zn isotopic fractionation is limited during lithospheric processes, such as crustal contamination, magmatic differentiation, degassing, or thermal/chemical diffusion, the elevated δ66Zn values indicate the incorporation of recycled carbonates into the sub-lithospheric mantle source. Plots of Zn/Fe versus δ66Zn or δ26Mg for the Korean basalts can be explained by mixing of at least three source lithologies: (1) carbonated peridotite; (2) recycled siliciclastic sediments; and (3) eclogite. Strontium–Nd–Pb isotopic systematics show that the mantle source follows the DMM-EM1 array for the Mt. Baekdu basalts and a DMM-EM2 array for the Jeju basalts. Both the enriched components have isotopically light Zn and heavy Mg, which are typical of recycled siliciclastic sediments. Combined with the Pb isotope and trace element data, the Zn isotopic compositions suggest that the EM1 component could be ancient K-hollandite-bearing siliciclastic sediments and the EM2 component could be recently recycled clay-rich pelagic sediments.