Research On The Physical Properties Of MgSiO₃ Perovskite Under The Condition Of The Lower Mantle

High pressure and temperature physics is a subject to research the physic properties of matter at high pressure and temperature conditions.At high pressure,matter will show different forces,heat,electricity,light and other properties.The thermodynamic convection of the mantle is closely related to the composition of the mantle and the motion state of the mantle.However,in terms of the current technology,the mantle material cannot be extracted directly.And the material composition of the mantle,especially the lower mantle,can be retrieved by other methods.High temperature and high pressure technology can simulate the temperature and pressure of the earth,and provides an important method and means to explore the deep part of the earth.Based on the research of Geophysics,geochemistry,mineralogy and so on,it is generally accepted that magnesium silicate perovskite,with the chemical composition of(Mg,Fe²⁺,Fe³⁺)?Si,Al?O₃,is the most dominant phase in the Earth's lower mantle,soits P-V-T equation of state?EOS?and thermoelastic parameters are essential to constraining thechemical composition and temperature of the lower mantle,by interpreting the seismological properties.Although magnesium silicate perovskite contains FeO,Fe₂O₃,and Al₂O₃ components,MgSiO₃is the most abundant component,accounting for above 90 mol%of the lower mantle.Thus P-V-T EOS of pureMgSiO₃ perovskite should have great importance as a primary reference for mineralogy of the lower mantle.Its thermal EOS has been extensively studied by shock compression,static compression and theoretical calculations.However,the derived parameters of the thermal EOS of MgSiO₃perovskite are still vary significantly from different studies leading to large uncertainties in mantle models.In this paper we select MgSiO₃ as the research object,and sinter the high pure MgSiO₃ enstatite as the initial sample using large multi-anvils at high pressure and temperature.Using dynamic experimental technique,we measured the equation of state for MgSiO₃ from 80GPa to 140GPa.We proposed a new data processing and analysis method,which makes a self-consistent data for the MgSiO₃ experimental data from the dynamic and static high pressure experiments.The new method proposed not only provides a strong criterion for the high pressure phase transition of MgSiO₃ along Hugoniot,but also provides an important support for the accurate of equation of state for MgSiO₃ under high pressure.According to our experimental data and previous experimental results,we analyze the equation of state and adiabatic bulk modulus for MgSiO₃ perovskite under lower mantle temperature and pressure environment,and compared with the seismic wave data.These results provide an important reference to constrain the content of MgSiO₃ perovskite in the lower mantle.The main innovative points of this paper includes the following three aspects:1?For the first time,with high purity MgO and SiO2 powder as raw materials,high purity artificially synthesized MgSiO₃ was used as experimental material in high pressure experiments and get the experimental data;2?A new methodwasproposed to analyze the equation of state data along Hugoniot,and get the Hugoniot state equation for the initial state of the high-pressure phase.The new Hugoniot parameters obtained by this method are:C₀=7.973,?=1.321,and the thermodynamic parameters K_0Sand K'_0S is very consistent with the static high pressure,which further illustrates that the measurement results of dynamic and static high pressure experiment are self-consistent;3?Based on the measured equation of state along Hugoniot,we calculate equation of state?EOS?and bulk modulus of MgSiO₃ perovskite in the environment of the lower mantle.Compared with PREM data,it is found that the density of pure MgSiO₃ perovskite is smaller than that of the lower mantle.This suggests that the lower mantle should contain elements that are larger than Mg,such as Fe.Whether the Fe is existence as FeO,or?Mg,Fe?SiO₃,or in two ways,we need further theory and experiment to research.