Ulleungdo, a volcanic island located in the back-arc basin (East Sea/Sea of Japan) of the Japanese arc, is one of the Cenozoic intraplate volcanoes in Northeast (NE) Asia. Due to the distinctive geotectonic properties of transitioning from a past back-arc environment to a current intraplate tectonic setting, the elucidation of the magma origin of this volcano allows us to evaluate the possible influence of diverse upper mantle components on intraplate magmatism. Here we report the results of water and dissolved gas geochemistry sampled from 13 springs in Ulleungdo. The springs can be categorized into high CO₂ concentration (HC) and low CO₂ concentration (LC) types, each exhibiting a different evolutionary pathway. The HC springs show high ³He/⁴He ratios (1.04 to 5.87 Ra) and δ¹³C-CO₂ values (–7.3 to –5.1 ‰), indicating the release of mantle-derived helium and CO₂. Although some of the LC springs also show mantle-derived helium (0.98 to 4.51 Ra), their lower δ¹³C-CO₂ values (–22.3 to –17.3 ‰) and CO₂/³He ratios (3.79 x 10⁸ to 1.39 x 10¹⁰) reflect calcite precipitation during fluid ascent. The consistency in the ³He/⁴He ratios between the springs and the previously reported Ulleungdo volcanic rocks suggests the preservation of the helium isotope ratio in the Ulleungdo magma from at least 1.37 Ma to the present. Collectively, helium and carbon isotope data from Ulleungdo, Mt. Baekdu, and Wudalianchi in NE Asia could be determined by regional variations in continental lithosphere thickness. Thus, it may be explained by contributions from the sub-continental lithospheric mantle and/or interaction with the continental crust during fluid ascent, rather than from the introduction of subducted slab materials into the magma sources. Our findings highlight that the interaction between the magma derived from the upwelling asthenospheric mantle and the overlying continental lithosphere can be a crucial factor in the volatile geochemistry of the NE Asian Cenozoic intraplate volcanic regions.

more >> https://doi.org/10.1016/j.jhydrol.2024.132286