During the last 50 Ma, the East Asian continent has been a wide zone of crustal and lithospheric deformation. However, the actual causes of deformation across almost the entire eastern Eurasia are still not clear. Here we present seismic evidence for the presence of eastward asthenospheric beneath the northeastern Tibetan Plateau. The mantle flow from northern Tibet is being blocked by thick Ordos and Sichuan cratonic keels, so that it must rotate around the Ordos and then transform into strong east-west flow beneath the thinner lithosphere that forms the suture between the two cratonic keels. Our results also demonstrate that broad continental deformation in eastern China overlies the region of eastward-channeled asthenospheric flow from Tibet.