Stabilizing inverse ringwoodite with defects,and a possible origin for the 560-km seismic discontinuity  

作　　者：Xuwei Zhao Joshua M.R.Muir Mingda Lv Zhigang Zhang Xinjian Bao Xi Liu 

机构地区：[1]School of Earth and Space Sciences,Peking University,Beijing 100871,China [2]Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education of China,Beijing 100871,China [3]State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China [4]Department of Earth and Environmental Sciences,Michigan State University,East Lansing,MI 48824,USA [5]Key Laboratory of Earth and Planetary Physics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China

出　　处：《Geoscience Frontiers》2025年第1期287-302,共16页地学前缘(英文版)

基　　金：supported by the Strategic Priority Research Program(B)of Chinese Academy of Sciences(Grant No.XDB42000000);the Natural Science Foundation of China(Grant No.42373034).

摘　　要：Ringwoodite is an important mineral in the mantle transition zone,and its cationic disorder can profoundly affect its physicochemical properties,but there is currently much controversy about this disorder.In this study,we investigate the cation disorder states of pure Mg2SiO4-ringwoodite and defective ringwoodite under mantle transition zone conditions through DFT calculations and thermodynamic models.Two stable endmembers are seen,one with normal ringwoodite structure and the other with inverted structure(its Si atoms and half of its Mg atoms have swapped sites).Our results indicate that pure ringwoodite does not invert(swap Mg and Si cations)under normal mantle temperatures but the introduction of a Si-excess,Mg-deficient defect induces a swap at normal mantle temperatures and this swap is likely induced by a wide range of defects including water.Thus,in the presence of such a defect or similar defects the olivine phase transition sequence may then go from olivine to wadsleyite to inverse ringwoodite,and then normal ringwoodite.We calculate the seismic properties of normal and inverse ringwoodite and find significantly slower wave speeds in inverted ringwoodite.Due to this difference the presence of inverse ringwoodite may provide a potential explanation for the discontinuous interface of seismic waves at the depth of∼560 km.

关 键 词：Normal ringwoodite Inverse ringwoodite Cation disorder DEFECTS 560-km seismic discontinuity 

分 类 号：P31[天文地球—固体地球物理学]