MR027-01
Velocity and Density Characteristics of Subducted Oceanic Crust and the Origin of Lower-mantle Heterogeneity

Wednesday, 16 December 2020: 16:00
Virtual
Zhongqing Wu1, Wenzhong Wang2, Daoyuan Sun3, Sidao Ni4, Renata Wentzcovitch5 and Yinhan Xu3, (1)University of Science and Technology of China, Laboratory of Seismology and Physics of Earth’s Interior, School of Earth and Space Sciences, Hefei, China, (2)University College London, London, United Kingdom, (3)University of Science and Technology of China, Hefei, China, (4)Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan, Hubei, China, (5)Columbia University in the City of New York, Department of Applied Physics and Applied Mathematics, New York, NY, United States
Recorded Presentation
Abstract:
Seismic heterogeneities detected in the lower mantle was proposed to be related to subducted oceanic crust. However, the velocity and density of subducted oceanic crust at lower-mantle conditions remain unknown. We determined the velocities and density of oceanic crust along different mantle geotherms using the ab initio results on the elastic properties of the related minerals. We find that the subducted oceanic crust shows a large negative shear velocity anomaly at the phase boundary between stishovite and CaCl2-type silica, which is highly consistent with the feature of mid-mantle scatterers. After this phase transition in silica, subducted oceanic crust will be visible as high-velocity heterogeneities as imaged by seismic tomography. This study suggests that the presence of subducted oceanic crust could provide good explanations for some lower-mantle seismic heterogeneities with different length scales except large low shear velocity provinces (LLSVPs).
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