Seamounts on the drifting oceanic crust are inevitable carried by plate motions and eventually accreted or subducted. However, the geochemical signatures of the subducted seamounts and the significance of seamount subduction are not well constrained. Hundreds of seamounts have subducted beneath the Philippine Sea Plate following the westward subduction of the Pacific Plate since the Eocene (~52 Ma). The subducted oceanic crust and seamount materials can be exhumed from the mantle depth to the seafloor in the Mariana forearc region by serpentinite mud volcanoes, providing exceptional opportunities to directly study the subducted oceanic crust and seamounts. The International Ocean Discovery Program (IODP) expedition 366 has recovered a few metamorphosed mafic clasts exhumed from the Mariana forearc serpentinite mud volcanoes, e.g., the Fantangisña and Asùt Tesoru seamounts. These mafic clasts have tholeiitic to alkaline affinities with distinct trace elements and NdHf isotopes characteristics, suggesting different provenances and mantle sources. The tholeiites from the Fantangisña Seamount have trace element contents typical of mid-ocean ridge basalt. The Pacific-type HfNd isotopic compositions, combined with the greenschist metamorphism of these tholeiites further suggest that they came from the subducted Pacific oceanic crust. The alkali basalts-dolerites from the Fantangisña and Asùt Tesoru seamounts show ocean island basalt (OIB)-like geochemical characteristics. The OIB-like geochemical signatures and the low-grade metamorphism of these alkali basalts-dolerites suggest they came from subducted seamounts that originally formed in an intraplate setting on the Pacific Plate. The Pacific Plate origin of these metabasites suggests they were formed in the Early Cretaceous or earlier.

Two types of OIBs have been recognized from alkali metabasites, one of which is geochemically similar to the HIMU-EMI-type OIBs from the West Pacific Seamount Province, and another is similar to the EMII-type OIBs from the Samoa Island in southern Pacific, with negative Nb-Ta-Ti anomalies and enriched NdHf isotopes. Generally, these alkali metabasites are sourced from the heterogeneous mantle sources that are similar to the present South Pacific Isotopic and Thermal Anomaly. This study provides direct evidence for seamount subduction in the Mariana convergent margins. We suggest seamount subduction is significant to element cycling, mantle heterogeneity, and mantle oxidation in subduction zones.

板块运动不可避免地会在漂流的洋壳上形成海山，并最终增加或俯冲。但是，俯冲海山的地球化学特征和俯冲海山的意义并没有受到很好的限制。自始新世（〜52 Ma）以来，太平洋板块向西俯冲之后，菲律宾海板块俯冲了数百个海山。蛇纹岩泥火山可以将俯冲的洋壳和海山物质从地幔深度挖掘到马里亚纳前臂地区的海底，为直接研究俯冲的洋壳和海山提供了特殊的机会。国际海洋发现计划（IODP）远征366已从马里亚纳前臂蛇纹岩泥火山中挖掘出一些变质的镁铁质碎屑，例如 Fantangisña和AsùtTesoru海山。这些镁铁质岩屑具有与碱性的亲和力，并具有不同的痕量元素和Ndf同位素特征，表明不同的物源和地幔来源。来自Fantangisña海山的菱形岩具有典型的洋中脊玄武岩微量元素含量。太平洋型Hf Nd同位素组成，再加上这些黄水晶的绿变变质，进一步表明它们来自俯冲的太平洋洋壳。来自Fantangisña和AsùtTesoru海山的碱性玄武岩-白云母显示出类似海洋岛玄武岩（OIB）的地球化学特征。这些碱性玄武岩-长石的OIB样地球化学特征和低品位变质表明它们来自俯冲的海山，该海山最初形成于太平洋板块的板内。这些变质岩的太平洋板块起源表明它们形成于早白垩世或更早。

从碱性代谢物中识别出两种类型的OIB，一种在地球化学上类似于西太平洋海山省的HIMU-EMI型OIB，另一种类似于南太平洋萨摩亚岛的EMII型OIB， Nb-Ta-Ti异常为负且Nd Hf同位素富集。通常，这些碱性变质岩均来自与当前南太平洋同位素和热异常相似的非均质地幔源。这项研究为马里亚纳会聚边缘的海山俯冲提供了直接证据。我们认为海山俯冲对俯冲带中的元素循环，地幔非均质性和地幔氧化具有重要意义。