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Sound Velocities in FeSi at Lower Mantle Conditions and the Origin of Ultralow‐Velocity Zones
Author(s) -
Mergner V.,
Kupenko I.,
Spiekermann G.,
Petitgirard S.,
Libon L.,
Chariton S.,
Krug M.,
Steinbrügge R.,
Sergueev I.,
SanchezValle C.
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl092257
Subject(s) - mantle (geology) , geology , core–mantle boundary , extrapolation , anharmonicity , geophysics , speed of sound , cosmic microwave background , olivine , mineralogy , physics , thermodynamics , condensed matter physics , optics , anisotropy , mathematics , mathematical analysis
The origin of ultralow‐velocity zones (ULVZs) remains an open question despite recent advances in mineral physics and seismology. Here, we examine the hypothesis that FeSi formed from core‐mantle chemical reactions is a plausible source of ULVZs at the core‐mantle boundary (CMB). The sound velocities of B2‐structured FeSi were measured up to 115(2) GPa and 1600(200) K by nuclear inelastic scattering (NIS) in laser‐heated diamond anvil cells (LH‐DACs). Within uncertainties, the sound velocities of B2‐FeSi display negligible anharmonicity, hence validating the extrapolation of velocity‐density relations (Birch's law) to P ‐ T conditions of the CMB. The sound velocities of B2‐FeSi are significantly lower compared to other candidate phases in a lowermost mantle assemblage, and the Preliminary Reference Earth Model at CMB conditions. Less than 8.4 vol% of FeSi in the aggregate is thus sufficient to explain both the velocity decrements and the high density anomaly observed in a wide range of ULVZs.