Major,trace element and Sr–Nd–Pb–Hf isotopic compositions of Cenozoic basalts in NE China.

We focus on temporal variations in the major element, trace element, and Sr–Nd–Pb–Hf isotopic data of Cenozoic basalts in NE China to better understand deep mantle processes and shed new light on the formation and evolution of the big mantle wedge. The ~52 Ma basalts were derived from partial melting of lithospheric mantle modified by slab-derived fluids and recycled sediments, whereas the ~33 Ma and ~21 Ma basalts were derived from partial melting of asthenospheric mantle. The ~11 Ma basalts were derived from partial melting of residual lithospheric mantle that was the source of the older Cenozoic basalts. However, a larger contribution from asthenospheric mantle is required in the source of ~2 Ma basalts. These findings and published data reveal sustained large-scale upwelling of asthenospheric mantle in NE Asia during the late Eocene to Miocene. The ~33 Ma basalts are interpreted to represent the magmatic response to rollback of the subducting slab and initiation of the big mantle wedge, whereas the ~21 Ma and ~11 Ma basalts record retreat of the trench and opening of the Japan Sea during the final stages of formation of the big mantle wedge. Asthenospheric flow from intracontinental to marginal regions, triggered by rollback of the Pacific slab and retreat of the trench, was the key mechanism that led to opening of the Japan Sea and formation of the big mantle wedge in NE Asia.

本研究聚焦于中国东北部新生代玄武岩中主要元素、微量元素及Sr-Nd-Pb-Hf同位素数据的时序变化，以深化对深部地幔过程的认知，并揭示大地幔楔的形成与演化。约5200万年的玄武岩源于受板块释放流体和再循环沉积物改造的岩石圈地幔的部分熔融，而约3300万年和2100万年的玄武岩则源于地幔软流圈的部分熔融。约1100万年的玄武岩则源于先前新生代玄武岩源岩的残余岩石圈地幔的部分熔融。然而，约20万年的玄武岩源岩中需要更大比例的地幔软流圈贡献。这些发现与已发表的数据揭示了在晚中新世期间，东亚地区地幔软流圈持续的大规模上涌。约3300万年的玄武岩被认为代表了板块俯冲回滚及大地幔楔起始的岩浆响应，而约2100万年和1100万年的玄武岩记录了大地幔楔形成最后阶段的 trench 退缩和日本海的开启。由太平洋板块的回滚和 trench 的退缩引发的岩石圈流从大陆内部至边缘地区的流动，是导致日本海开启及东亚地区大地幔楔形成的关键机制。