Compressional and shear wave velocities of Fe-bearing silicate post-perovskite in Earth’s lowermost mantle  

作　　者：Jing Yang Suyu Fu Jin Liu Jung-Fu Lin 

机构地区：[1]Department of Earth and Planetary Sciences,Jackson School of Geosciences,University of Texas at Austin,Austin,TX 78712,USA [2]Earth and Planet Laboratory,Carnegie Science,Washington,DC 20015,USA [3]Department of Earth and Planetary Science,The University of Tokyo,Bunkyo,Tokyo 113-0033,Japan [4]School of Environmental and Chemical Engineering,Yanshan University,Qinhuangdao 066004,PR China

出　　处：《Geoscience Frontiers》2025年第1期303-311,共9页地学前缘(英文版)

基　　金：the U.S.National Science Foundation Geophysics Program(EAR-2001381);the resources of the Advanced Photon Source,a U.S.Department of Energy(DOE)Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No.DE-AC02-06CH11357.

摘　　要：The bridgmanite(Bgm)to silicate post-perovskite(PPv)phase transition is believed to be the main cause for the distinct seismic features observed in the D''layer,the lowermost region of the Earth’s mantle.However,the transition depth and elasticity of the PPv phase have been highly debated,as the chemical complexity within the D''layer can largely affect the Bgm-PPv transition pressure and the associated velocity contrast.Experimental measurements of sound velocities for PPv with different chemical compositions under relevant lowermost-mantle conditions are essential but remain limited.In this study,we have reliably measured both compressional wave velocity(VP),shear wave velocity(V_(S)),and density,for two Fe-bearing PPv compositions[(Mg_(0.85)Fe_(0.15))SiO_(3)and(Mg0.75Fe0.25)SiO_(3)]at lowermost mantle pressures using Impulsive Stimulated Light Scattering(ISS),Brillouin Light Scattering(BLS),and X-ray Diffraction(XRD)in diamond anvil cells.Our results indicate that the velocities of Fe-bearing PPv at 120 GPa can be described by the following relationships:V_(S)(km/s)=7.65-2.8XFe and VP(km/s)=14.11-3.8XFe,where XFe represents mole fraction of the Fe content.The variations in the Fe content of PPv may provide one of the explanations for the seismic lateral variations observed at the Earth’s core mantle boundary.By comparing our results with the high-pressure velocities of Bgm,our velocity model suggests significant discontinuities across the Bgm-PPv transition,characterized by a reduction in both VP and VΦ,and an increase in V_(S).These findings highlight the importance of considering the influence of chemical composition,particularly Fe content which could vary significantly at the D''region,on the seismic properties of the PPv phase.The observed velocity contrasts across the Bgm-PPv transition may contribute to the complex seismic signatures observed in the D''layer,underscoring the potential role of this phase transition in interpreting the seismic features of the lowermost mantle region.

关 键 词：Fe-bearing post-perovskite D"layer Sound velocities 

分 类 号：P31[天文地球—固体地球物理学]