The existence of historical flat slabs remains debated. We evaluate past
subduction since 200 Ma using global models with data assimilation. By
reproducing major Mesozoic slabs whose dip angles satisfy geological
constraints, the model suggests a previously unrecognized
continental-scale flat slab during the Late Cretaceous beneath East
Asia, a result independent of plate reconstructions, continental
lithospheric thickness, convergence rate, and seafloor age. Tests show
that the pre-Cretaceous subduction history, both along the western
Pacific and Tethyan trenches, is the most important reason for the
formation of this prominent flat Izanagi slab. Physically, continuing
subduction increases the gravitational torque, which, through balancing
the suction torque, progressively reduces dynamic pressure above the
slab and decreases the slab dip angle. The flat Izanagi slab explains
the observed East Asian lithospheric thinning that led to the formation
of the North-South Gravity Lineament, tectonic inversion of sedimentary
basins, uplift of the Greater Xing'an-Taihang-Xuefeng mountains and the
abrupt termination of intraplate volcanism during the Late Cretaceous.