Basaltic lavas sample recycled crustal materials from their mantle source. Constraining the location and residence time of these recycled materials in the mantle is critical to understand global mantle dynamics. In this study, we present new whole-rock major and trace element abundances, Sr-Nd-Mo-Os isotopes, water contents and He isotopes of volcanic glasses, U-Pb ages of zircons, and compositions of melt inclusions, spinels and olivines from the South China Sea (SCS) seamounts lavas. These new data are compared with literature data from intraplate volcanism of similar age from Southeast (SE) Asia. The isotope data of late Cenozoic lavas from the SCS seamounts and SE Asia can be explained by mixing between enriched mantle 2 (EM2) and depleted mid-ocean ridge basalt mantle components. Our data are consistent with the EM2 signature of late Cenozoic lavas derived from recycled young oceanic crust and sediments. The compositions of olivine phenocrysts indicate an olivine-dominated (peridotitic) mantle source. There is currently no evidence for a high-³He/⁴He mantle plume component beneath the SCS. Our results combined with geophysical data and plate reconstructions suggest that the late Cenozoic magmatism is related to the upwelling of instabilities from the mantle transition zone (MTZ) triggered by a stagnant slab. The SCS seamount lavas sample an enriched MTZ containing young recycled materials, consistent with regional past subduction. Our study provides additional evidence that storage and recycling of crustal materials in or near the MTZ is an important mechanism to develop global mantle heterogeneities sampled by intraplate volcanoes.

中文翻译：

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南海及东南亚晚新生代岩浆作用的成因

玄武岩熔岩从地幔源中提取回收的地壳材料。限制这些回收材料在地幔中的位置和停留时间对于了解全球地幔动力学至关重要。在这项研究中，我们提出了新的全岩主要和微量元素丰度、Sr-Nd-Mo-Os 同位素、火山玻璃的水含量和 He 同位素、锆石的 U-Pb 年龄以及熔体包裹体、尖晶石和橄榄石的成分来自南海 (SCS) 海山熔岩。这些新数据与来自东南亚（SE）亚洲相似年龄的板内火山作用的文献数据进行了比较。来自 SCS 海山和东南亚的晚新生代熔岩的同位素数据可以通过富集地幔 2 (EM2) 和枯竭的大洋中脊玄武岩地幔成分之间的混合来解释。我们的数据与源自再生的年轻洋壳和沉积物的晚新生代熔岩的 EM2 特征一致。橄榄石斑晶的成分表明橄榄石为主（橄榄岩）地幔来源。目前没有证据表明高SCS 下的³ He/ ⁴ He 地幔柱成分。我们的结果结合地球物理数据和板块重建表明，晚新生代岩浆活动与停滞板块引发的地幔过渡带（MTZ）的不稳定性上涌有关。SCS 海山熔岩采样丰富的 MTZ，其中包含年轻的回收材料，与区域过去的俯冲一致。我们的研究提供了额外的证据，表明在 MTZ 内或附近的地壳材料的储存和回收是发展由板内火山采样的全球地幔非均质性的重要机制。