期刊
GEOPHYSICAL RESEARCH LETTERS
卷 48, 期 14, 页码 -出版社
AMER GEOPHYSICAL UNION
DOI: 10.1029/2020GL092257
关键词
B2-FeSi; sound velocities; ultralow-velocity zones; core-mantle reactions; nuclear inelastic scattering
资金
- German Research Foundation (DFG) [AOBJ:662965 GZ.:KU 3832/2-1]
- WWU Munster
- Projekt DEAL
Studies suggest that FeSi formed from core-mantle chemical reactions may be a plausible source of ultralow-velocity zones (ULVZs) at the core-mantle boundary (CMB). The low sound velocities of FeSi compared to other candidate phases in a lowermost mantle assemblage could explain the velocity decrements and high density anomalies observed in a wide range of ULVZs with less than 8.4 vol% of FeSi in the aggregate.
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.
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