K-Ar dates and chemical compositions of lavas in Sikhote Alin, Far East Russia, demonstrate marked secular variation in lava chemistry and suggest a linkage between magmatism and the major tectonic opening of the Japan Sea backarc basin. Lavas having typical arc magma chemistry were produced at 40--25 Ma in the eastern part of Sikhote Alin. A conspicuous volcanic hiatus is revealed in the region at 25--20 Ma, which is contemporaneous with the period of the major rifting of the backarc basin. Subduction-related magmatism may have been switched off by an oceanward retreat of the arc-trench system. In contrast, intraplate-type lavas with typical hotspot magma compositions have dominated magmatism in both the eastern and western Sikhote Alin since 20 Ma, and occupy the eastern margin of the Cenozoic intraplate magmatism in the NE Asian continent. ¿ 2000 American Geophysical Union