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A big mantle wedge (BMW) is an important deep Earth structure that has implications for our understanding of geodynamic processes. The eastern and northeastern Asian BMWs have been extensively studied in the past two decades. This paper reviews evidence for the age, formation, spatial extent, and geodynamic effects of BMWs, with the aim of distinguishing between two BMWs. The eastern Asian BMW initially formed in the late Early Cretaceous and was active from 110 to 55 Ma due to rollback of the subducted Paleo-Pacific Plate and eastward-directed deep mantle flow. This BMW affected the entire eastern Asian continental margin and controlled the late Mesozoic–early Paleogene tectonic evolution of the margin, including destruction of the North China Craton and reworking of continental crust in South China. The northeastern Asian BMW has been active from 20 Ma to the present-day due to rollback of the subducted Pacific Plate and eastward mantle flow. It has mainly affected northeast Asia and resulted in different types of Cenozoic intraplate volcanism and occurrence of earthquakes with deep epicenters. • Eastern (E) and northeastern (NE) Asian big mantle wedges (BMW) are identified. • E Asian BMW formed in late K1 and controlled late Mesozoic-early Cenozoic evolution. • NE Asian BMW formed at ca.20 Ma and controlled intraplate volcanism and earthquakes. [ABSTRACT FROM AUTHOR]

The timing and mantle processes of the Cenozoic transition from an active continental margin to a trench–arc–basin system in northeast Asia remain controversial. Here we present major and trace element, and Sr–Nd–Pb–Hf isotope data for Cenozoic basaltic rocks from the Russian Far East, which provide new constraints on the deep mantle processes during the transition. The basaltic rocks formed mainly in four stages. The results show that middle Eocene basaltic rocks have arc-like geochemical features, such as depletions in high-field-strength elements, indicating an origin by partial melting of a mantle wedge that had been modified by slab-derived fluids and recycled sediments. Early and middle Miocene basaltic rocks also have arc-like geochemical features, and have relatively low contents of fluid-mobile elements and high contents of fluid-immobile elements, as compared with the middle Eocene basaltic rocks. This suggests that these magmas were derived by the melting of previously melted lithospheric mantle that had been modified by slab-derived fluids. In contrast, late Miocene basalts have ocean island basalt-like geochemical features, such as enrichments in high-field-strength elements, indicating their derivation by partial melting of the asthenospheric mantle. The temporal variations in the mantle sources of the Cenozoic basaltic rocks in the Russian Far East, along with an abrupt change in Sr Nd isotopic compositions at ca. 20 Ma, demonstrate that the transition from an active continental margin to a trench–arc–basin system in northeast Asia occurred at ca. 20 Ma. • The basalts in the Russian Far East formed mainly at ca. 45, 20, 13, and 7 Ma. • The temporal variations in the sources of the Cenozoic basalts were determined. • Transition from active continental margin to trench-arc-basin occurred at 20 Ma. • The rollback of Pacific Plate and trench retreat control the tectonic transition. [ABSTRACT FROM AUTHOR]