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.