| Reconstruction of plate motion history provides a spatio-temporal context for understanding geological and geophysical data,helps to reveal the driving forces of supercontinent break-up,separation and accretion,helps to establish connections between surface processes and the deep Earth,and helps to understand the mechanisms behind geological processes.We followed a new interpretation of the paleo-Pacific reconstruction and modified the reconstruction of the Izanagi plate based on a previously published global plate reconstruction model.In the modified model,the moving direction of the Izanagi plate was rotated by-20°clockwise after 89 Ma so that the plate moved north-northwestward at around 84 Ma.The average moving speed of the Izanagi plate during 89～77 Ma is～20 cm/yr.After 77 Ma the Izanagi plate subducted beneath northeast Asia and totally fell into the mantle around 55 Ma.The evolution and present state of plates subducted into the mantle have important implications for understanding geodynamic evolution and seismic tomography results.We introduce a tracking technique in numerical models to efficiently track the slab materials during their subduction processes.Numerical simulations show that mantle convection has an important influence on the state of plates entering the mantle.Through numerical simulation and computational analysis of the evolution process of plates,we find that large lithospheric plates,such as Izanagi,Phoenix,and other plates,could be saved for 100～300 Myrs after entering the mantle,but the actual situation is very complicated.If the slab enters the mantle and is located in the subduction area of the subsequent plates,the slab is easily affected,split,or even broken up;if the slab enters the mantle and is shifted away from the subsequent subducting plates by the mantle convection current,it could be saved for 400 Myrs or even longer.Judging from the state of the slabs subducted into the mantle,the use of the remanent slabs and the seismic tomography models can help restore the history of early plate tectonic movements.The slab dynamics of the subducted Izanagi-Pacific plate is still a subject of controversy and its relationship with the tectonic evolution of Eastern Asia remains not well explored.Here,we perform 3-D global convection models to investigate the slab dynamics of the Izanagi-Pacific plate beneath Eastern Asia since the Mesozoic time.We introduce a tracking technique in numerical models to explicitly distinguish the Izanagi slab and the Pacific slab during their subduction processes.We find that all subducted Izanagi slabs have completely fallen into the lower mantle until the late Cenozoic and the stagnant slabs currently observed at the mantle transition zone depth beneath Eastern Asia are entirely from the Pacific plate.We also find that multiple slab stagnation events have occurred during the subduction of the Izanagi plate in the Mesozoic time(～150-120 Ma,90-70 Ma)with a timescale of～20 million years.The stagnation of the subducted slabs facilitates the formation of a big mantle wedge beneath the overriding lithosphere and the time periods of the mantle wedge are consistent with the episodes of magmatic activities in Eastern Asia. |
