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Kilometer-scale structure on the core–mantle boundary near Hawaii

Published version
Peer-reviewed

Type

Article

Change log

Authors

Leng, Kuangdai 
Jenkins, Jennifer 

Abstract

jats:titleAbstract</jats:title> jats:pThe lowermost mantle right above the core-mantle boundary is highly heterogeneous containing multiple poorly understood seismic features visible across a wide range of length scales. The smallest but most extreme heterogeneities yet observed are 'Ultra-Low Velocity Zones' (ULVZ), several of which have recently been linked to the base of mantle plumes. We exploit seismic shear waves that diffract along the core-mantle boundary to provide new insight into these enigmatic structures. We demonstrate that these waves have a strong frequency-dependent sensitivity to structure at different length scales above the core-mantle boundary. We measure a rare core-diffracted signal refracted by a ULVZ at the base of the Hawaiian mantle plume at unprecedentedly high frequencies. This signal shows remarkably longer time delays at higher compared to lower frequencies, indicating extreme internal variability within the Hawaiian ULVZ. Utilizing the latest computational advances in 3D synthetic waveform modeling, we are able to model this high frequency signal and constrain high-resolution structure on the scale of kilometers at the core-mantle boundary, for the first time. Results reveal that the lowermost part of the Hawaiian ULVZ is extremely reduced in shear wave velocity, by up to -40%. This new observation suggests a chemically distinct ULVZ with increasing iron content towards the core-mantle boundary, which has implications for Earth’s early evolutionary history and core-mantle interaction.</jats:p>

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Keywords

Journal Title

Nature Communications

Conference Name

Journal ISSN

2041-1723

Volume Title

Publisher

Nature Research
Sponsorship
European Research Council (804071)