The Earth’s mantle is considered to be geochemically heterogeneous, which is reflected by the diverse compositions of oceanic island basalts (OIB). The mantle enrichment resulting in this is primarily attributed to the influx of recycled crustal materials into the mantle through subduction. Additionally, the sub-continental lithospheric mantle (SCLM) complicates the elucidation of mantle heterogeneity. From this perspective, Northeast Asia, where the Pacific stagnant slab in the mantle transition zone and the SCLM distribution are presented, is the suitable site for examining the upper mantle scale enrichment. Here we report He-Sr-Nd-Pb-O isotope compositions of Cenozoic basalts found around the Korean Peninsula to illustrate the source lithology and components that caused mantle heterogeneity. Our measured helium isotope ratios ranging from 5.7 to 7.3 Ra (3He/4He ratio of air, Ra = 1.39 x 10-6) are mostly within the SCLM range (6.1 ± 0.9 Ra) but lower than the mid-ocean ridge basalt range (MORB; 8 ± 1 Ra). The Sr-Nd-Pb isotope compositions of the basalts generally display a mixture of depleted MORB mantle (DMM), enriched mantle 1 (EM1), and enriched mantle 2 (EM2) components. In addition, the basalts have δ18Oolivine (vs. V-SMOW) values ranging from 4.7 to 5.7 ‰ that deviate from the DMM range (δ18Oolivine = 5.1 ± 0.2 ‰). Our isotopic analysis results highlight the role of a pyroxenite source in the metasomatized SCLM in the genesis of basalts, and the low 3He/4He ratios of the basalts indicates a significant contribution of SCLM. Moreover, the delaminated cratonic SCLM and asthenosphere-lithosphere interaction are scenarios for the low 3He/4He ratios. Therefore, we propose that mixing of DMM (high 3He/4He ratio; 7 to 9 Ra) and the metasomatized SCLM (low 3He/4He ratio; 5 to 7 Ra) allowed enrichment within the upper mantle scale for the Cenozoic intraplate magmatism in Northeast Asia.

中文翻译：

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东北亚新生代板内岩浆作用的上地幔尺度富集：朝鲜半岛周围玄武岩的 He-Sr-Nd-Pb-O 同位素地球化学


地幔被认为在地球化学上是非均质的，这反映在大洋岛屿玄武岩 （OIB） 的多样化成分上。导致这种情况的地幔富集主要归因于回收的地壳物质通过俯冲流入地幔。此外，次大陆岩石圈地幔 （SCLM） 使地幔异质性的阐明变得复杂。从这个角度来看，东北亚展示了地幔过渡带中的太平洋停滞板块和 SCLM 分布，是研究上地幔尺度富集的合适地点。在这里，我们报告了在朝鲜半岛周围发现的新生代玄武岩的 He-Sr-Nd-Pb-O 同位素组成，以说明导致地幔非均质性的源岩性和成分。我们测得的氦同位素比值范围为 5.7 至 7.3 Ra（空气的 3He/4He 比值，Ra = 1.39 x 10-6）大多在 SCLM 范围内（6.1 ± 0.9 Ra），但低于洋中脊玄武岩范围 （MORB;8 ± 1 Ra）。玄武岩的 Sr-Nd-Pb 同位素组成通常显示贫 MORB 地幔 （DMM）、富集地幔 1 （EM1） 和富集地幔 2 （EM2） 成分的混合物。此外，玄武岩的 δ18Oolivine（相对于 V-SMOW）值范围为 4.7 至 5.7 ‰，偏离 DMM 范围（δ18Oolivine = 5.1 ± 0.2 ‰）。我们的同位素分析结果强调了辉石矿源在交代化 SCLM 中对玄武岩成因中的作用，玄武岩的低 3He/4He 比率表明 SCLM 的显着贡献。此外，分层的克拉通 SCLM 和软流圈-岩石圈相互作用是低 3He/4He 比值的情况。 因此，我们提出 DMM （高 3He/4He 比率;7 至 9 Ra） 和交代化 SCLM （低 3He/4He 比率;5 至 7 Ra）的混合允许在东北亚新生代板内岩浆作用的上地幔尺度内富集。