Geodynamic Simulation Study Of Lithospheric Thinning Mechanism In North China Craton

As an ancient tectonic unit in China,the North China Craton(NCC)has been floating on the asthenosphere and has maintained its stable properties for a long time due to its low density and hardness.However,a large number of studies show that the North China Craton has been destroyed,and a certain amount of thinning has occurred at the bottom of the craton’s lithosphere.The geodynamic mechanisms of the craton thinning include delamination,thermal erosion,mechanical stretching,hydration,etc.The direct subduction of the paleo-Pacific plate to North China is the primary factor for the thinning and destruction of the North China Craton.At present,there are few subduction models of the paleo-Pacific plate,and the geodynamic mechanism of the North China Craton remains unclear,and further study is needed.In this paper,a modern numerical simulation code(ASPECT)is used to simulate the destruction process of the North China Craton by the paleo-Pacific plate subduction during the Yanshan period and to analyze the specific dynamic destruction mechanism of the North China Craton.This paper first establishes several two-dimensional ocean-continent subduction dynamics models to explore the impact of the following factors on the subduction process,including the yield stress and viscosity of the marine lithospheric mantle,the initial subduction angle of the oceanic plate,the back arc area,and the two-side subduction.The study found that(1)increasing the yield stress and viscosity accumulation increases the strength of the rock.(2)the subduction angle affects the erosion range of the overlying plate and the subduction shape of the plate.(3)the existence of the fragile mantle accelerated the rate of plate destruction.(4)The two-side subduction mode could induce subduction of the overlying continental plate.Based on the existing geological data,this study established a subduction model of the paleo-Pacific plate,and analyzed the thinning mechanism of the North China Craton.During the Pacific plate subduction,the water was carried into the asthenosphere by the subducting paleo-Pacific plate,causing the melt of the asthenosphere.Metasomatism and hydration reactions occurred at the bottom of the continental lithosphere,and significantly changed the properties of the overlying lithospheric mantle.At the same time,the downward subduction of the cold plate broke the original temperature balance and produced mantle convection,causing thermal-mechanical erosion.The Pacific plate changed from downward subduction to flat subduction close to the continental lithospheric mantle if a light thick ocean plateau existed in the subducting Pacific plate.This flat subduction process remarkably thinned the lithospheric root of the North China Craton.It can be seen that the thinning of the North China Craton is a very complex process,which is the result of the interaction of multiple destructions and thinning mechanisms as a result of the subduction of the paleo-Pacific plate.