The Process And Influence Of Plate Subduction In The Western Pacific Since Mesozoic

There are extremely complex tectonic environments around East Asia.The eastern edge of East Asia was subducted by the Pacific plate to form an island-arc system with a length of thousands of kilometers,while its southwest was collided and compressed by the Indian plate to form the Qinghai-Tibet Plateau.Those have created the ladder distribution characteristics of today’s East Asian topography,which is high in the west and low in the east.In particular,the eastern margin of the East Asian plate has experienced the long-term subduction of the Izanagi plate and the Pacific plate since the Mesozoic,and the continuous subduction process of oceanic plate has a far-reaching impact on the tectonic environment,igneous rock activity,topographic relief and mineralization in the east of the East Asian plate.Therefore,it is of great significance to study the subduction activities of the western Pacific plate and the corresponding surface response of the East Asian continental plate since the Mesozoic for a deep understanding of the tectonic evolution process in East Asia.From the seismic imaging results,it is found that the North China Craton in East Asia experienced a strong tectonic event in the Mesozoic,which caused the thickness of the lithosphere in the east of the North China Craton thinning from more than 200 km to about 80 km during the Cretaceous.The destruction process of the North China Craton lithosphere is considered to be related to the Paleo-Pacific(Izanagi)Plate subduction process in the Mesozoic.At the same time,seismic tomography revealed that there is a horizontal high-speed anomaly of seismic waves over 1,000 km at the bottom of the mantle transition zone under the East Asian plate,and there is an obvious low-velocity anomaly in the asthenosphere above it.The combination of the horizontal high-speed anomaly zone and its upper mantle is called the big mantle wedge structure.The big mantle wedge structure strongly changes the deep mantle structure and surface tectonic environment in East Asia,resulting in a series of geological responses such as orogeny and igneous rock activity.Therefore,during the subduction of the Pacific plate(Izanagi plate)to East Asia,the morphological evolution of the subducted plate in the mantle transition zone is not only related to the destruction of North China Craton lithosphere during the Mesozoic,but also has a great impact on the distribution of volcanic activities in Northeast Asia during the Cenozoic.We constructed a global mantle convection model constrained by the plate motion velocity boundary condition derived from the plate reconstruction model to study the plate subduction process in the western Pacific region and the morphological evolution of plates in the mantle transition zone since the Mesozoic.The results of our model show that for the Mariana subduction zone and the Izu-Bonin subduction zone,under the constraints of the current plate reconstruction model and only relying on the phase transition of 660km at the bottom of the mantle transition zone and the change of the mantle viscosity structure,the model results can better realize the deflection and extension of the subduction plate in the mantle transition zone to form a horizontal stagnant slab,and weaken the asthenospheric mantle between the horizontal stagnant slab and the overlying plate,forming a big mantle wedge structure.However,for the Honshu subduction zone,our model results show that the subducting plate in this region directly passes through the mantle transition zone and subducts into the lower mantle,which is inconsistent with the seismic tomography results.We believe that other factors are needed to control the subduction plate to form a stagnant slab in the mantle transition zone.At the same time,since the Mesozoic,the Izanagi plate and the Pacific plate have successively subducted under the East Asian plate,which has also had a great impact on the tectonic stress environment of the eastern margin of the East Asian plate.A series of tectonic basins such as the Songliao Basin,Japan sea Basin,Bohai Bay Basin,southern North China basin,Yellow Sea Basin,East China Sea Basin,and Philippine Sea Basin are distributed from north to south in the back-arc area of the eastern margin of the East Asian plate.Moreover,the continuous subduction process of oceanic plates will also change the tectonic environment of existing basins.The change of the basin tectonic environment is one of the important tectonic responses of the surface to the evolution of mantle convection in the earth.We constructed a global mantle convection model with the plate velocity derived from the plate reconstruction model as the surface velocity boundary to study the influence of plate subduction in the Western Pacific on the dynamic topographical fluctuation evolution of East Asia since the Mesozoic.Our model results show that the East Asian region as a whole has been characterized by low dynamic topography since the late Mesozoic.The overall inclination direction of the dynamic topography in East Asia also changed from south to southeast in the early Cenozoic.From 160 Ma to 70 Ma,the dynamic topography of the coastal area of the eastern margin of the East Asian continent experienced successive processes of tectonic subsidence,tectonic uplift,re-tectonic subsidence and re-tectonic uplift.We believe that the inversion of the dynamic topographic uplift and subsidence mode near the subduction trench is related to the advance and retreat of the trench position during the subduction of the Izanagi plate,and there is a temporal and spatial synchronization between them.At the same time,the evolution trend over time of dynamic topography of different basins extracted from Songliao Basin,Ordos Basin and North Yellow Sea Basin.Our model results show that the dynamic topographic uplift and subsidence model in the late Early Cretaceous and early Cenozoic can better match the geological results,and we find that the dynamic topographic curves of the three basins have obvious structural inversion at 120 Ma and 65 Ma,We believe that this may be related to the lithospheric destruction process of the North China Craton and the subduction process of the Izanagi-Pacific mid-ocean ridge in the early Cenozoic,respectively.During the late Cretaceous to the early Cenozoic,the Izanagi-Pacific mid-ocean ridge structure is believed to have subducted under the East Asian plate in the form of parallel to the trench.Similar examples include the Farallon-Pacific mid-ocean ridge subduction process that has continued since the Oligocene.Because the mid-ocean ridge structure has the characteristics of typical high topography and high heat flow,its subduction process will have a strong impact on the geological response such as surface igneous events activity and topographic relief.We constructed a two-dimensional viscoelastic plastic numerical model to study the subduction mode and related control parameters of trench-parallel subduction of the mid-ocean ridge structure.The results of our model show that the subduction modes of trench-parallel subduction of the midocean ridge can be categorized into three types:fast spreading mode,slow spreading mode and extinction mode.The key factor affecting the subduction mode of the midocean ridge is the relative motion between the oceanic plates on both sides of the midocean ridge.Different subduction modes of mid-ocean ridge structures result in different geological and topographical responses of the surface,which can be used to explain geological phenomena related to mid-ocean ridge subduction,such as the of igneous events gap in East Asia during the 55 Ma～45 Ma periodand the igneous events gap in western North America during Miocene.