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

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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.