Constrains on mantle recycling procedures at continental margins by Pb-Nd-Sr isotopic compositions

来自欧亚板块边缘东部(日本西南部、日本海和中国东北部)的火山岩显示出富集型(EMI)成分特征。日本海裕廊岛和狗岛火山岩具有典型的DUPAL异常特征，具有极高的208204Pb值(高达143)和高的Ndsr同位素组成(END=-3~5，87sr/86sr=-0.705)。208/204Pb值与南半球DUPAL异常(高达140)的值相似。由于日本海玄武岩的电磁干扰特征比西南部玄武岩和内陆中国玄武岩的电磁干扰特征更为极端，我们认为旧地幔岩石圈在早期(元古代以前)与俯冲相关的流体(不存在俯冲系统)交代，使其略有不相容元素的富集，并长期具有高的Th/U。这一研究结果支持了古老的次大陆地幔岩石圈是大洋玄武岩电磁干扰的来源，电磁干扰不需要长期储存在核/地幔边界层的观点。日本海大和盆地海脊的疏浚样品和小圆丘显示出与滨海弧玄武岩相似的同位素特征，支持大和盆地是扩张中心的观点，导致日本东北部弧与欧亚大陆的分离。

Volcanic rocks from the eastern Eurasian plate margin (southwestern Japan, the Sea of Japan, and northeastern China) show enriched (EMI) component signatures. Volcanic rocks from the Ulreung and Dog Islands in the Sea of Japan show typical DUPAL anomaly characteristics wit extremely high delta 208/204 Pb (up to 143) and enriched Nd and Sr isotopic compositions (eNd = -3 to 5, 87Sr/86Sr = -0.705). The delta 208/204 Pb values are similar to those associated with the DUPAL anomaly (up to 140) in the southern hemisphere. Because the EMI characteristics of basalts from the Sea of Japan are more extreme than those of southwestern Japan and inland China basalts, we propose that old mantle lithosphere was metasomatized early (prior to the Proterozoic) with subduction-related fluids (not present subduction system) so that it has been slightly enriched in incompatible elements and has had a high Th/U for a long time. The result of this study support the idea that the old subcontinental mantle lithosphere is the source for EMI of oceanic basalts, and that EMI does not need to be stored at the core/mantle boundary layer for a long time. Dredged samples form seamounts and knolls form the Yamato Basin Ridge in the Sea of Japan show similar isotopic characteristics to basalts from the Marina arc, supporting the ida that the Yamato Basin Ridge is a spreading center causing separation of the northeast Japan Arc form Eurasia.