Jeju Island, South Korea, is a Cenozoic intraplate volcano located in East Asia. The Jeju basalts display ocean island basalt (OIB)-like trace element patterns and enriched mantle type 2 (EM2) radiogenic isotope compositions, but the source that enriched the mantle remains unclear. Here we report new geochemical compositions of basalts and xenoliths, including the first helium isotope and element analysis of olivine phenocrysts to constrain the source of basalt. Olivines in the Jeju basalts have ³He/⁴He ratios of 3.5 to 7.3 R_a while olivines in the mantle xenoliths are 2.9 to 6.3 R_a. They provide no evidence of a lower mantle plume but overlap the range of the regional subcontinental lithospheric mantle (SCLM) and OIBs with low ³He/⁴He values. Olivine phenocrysts included in the basalts show variations in Mn, Ni, and Ca concentrations with forsterite (Fo) contents, similar to the trend for olivines crystallized from the pyroxenite-derived melts. Elemental ratios of Ca-Fe-Ni-Mg-Mn for the olivines also indicate the pyroxenite contribution. Considering our results, it is suggested that the main source of the Jeju basalts is the SCLM containing pyroxenite. In addition, the tomography image shows the low-velocity zone extending to the asthenosphere mantle beneath the central Jeju Island. This implies that the localized asthenospheric upwelling is caused by edge-driven convection, and the high-velocity zones exist around Jeju island indicating a thick cratonic lithosphere. Therefore, we propose that the interaction between the SCLM component containing pyroxenite and the rising asthenosphere is the main mechanism to generate enriched basaltic magmas for the Cenozoic intraplate volcanism in East Asia, including Jeju Island.

韩国济州岛是位于东亚的新生代板内火山。济州玄武岩显示出海洋岛屿玄武岩（OIB）样的痕量元素模式和2型富集地幔（EM2）的放射性同位素组成，但富集地幔的来源尚不清楚。在这里，我们报告了玄武岩和异岩的新地球化学成分，包括第一个氦同位素和橄榄石表晶的元素分析，以限制玄武岩的来源。济州玄武岩中的橄榄石的³ He / ⁴ He比为3.5至7.3 R _a，而地幔异岩中的橄榄石为2.9至6.3 R _a。它们没有提供下地幔柱的证据，但是与区域性陆下岩石圈地幔（SCLM）和OIB的范围重叠，但覆盖率较低。³他/ ⁴他很重视。玄武岩中的橄榄石类隐晶石显示镁，镍和钙的浓度随镁橄榄石（Fo）含量的变化而变化，这与从辉石矿衍生的熔体中结晶出来的橄榄石趋势相似。橄榄石中Ca-Fe-Ni-Mg-Mn的元素比也表明了辉石的贡献。考虑到我们的结果，建议济州玄武岩的主要来源是含有辉石的SCLM。另外，断层图像显示低速区域延伸到济州岛中部下方的软流圈地幔。这意味着局部的软流圈上升是由边缘驱动的对流引起的，济州岛周围存在高速带，表明克拉通岩石圈较厚。所以，