Tidal tomography constrains Earth’s deep-mantle buoyancy

Lau, Harriet C. P. and Mitrovica, Jerry X. and Davis, James L. and Tromp, Jeroen and Yang, Hsin-Ying and Al-Attar, David (2017) Tidal tomography constrains Earth’s deep-mantle buoyancy. Nature, 551 (7680). pp. 321-326. ISSN 0028-0836 DOI https://doi.org/10.1038/nature24452

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Earth’s body tide—also known as the solid Earth tide, the displacement of the solid Earth’s surface caused by gravitational forces from the Moon and the Sun—is sensitive to the density of the two Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific. These massive regions extend approximately 1,000 kilometres upward from the base of the mantle and their buoyancy remains actively debated within the geophysical community. Here we use tidal tomography to constrain Earth’s deep-mantle buoyancy derived from Global Positioning System (GPS)-based measurements of semi-diurnal body tide deformation. Using a probabilistic approach, we show that across the bottom two-thirds of the two LLSVPs the mean density is about 0.5 per cent higher than the average mantle density across this depth range (that is, its mean buoyancy is minus 0.5 per cent), although this anomaly may be concentrated towards the very base of the mantle. We conclude that the buoyancy of these structures is dominated by the enrichment of high-density chemical components, probably related to subducted oceanic plates or primordial material associated with Earth’s formation. Because the dynamics of the mantle is driven by density variations, our result has important dynamical implications for the stability of the LLSVPs and the long-term evolution of the Earth system.

Item Type: Article
Uncontrolled Keywords: 2017AREP; IA73
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
Journal or Publication Title: Nature
Volume: 551
Page Range: pp. 321-326
Identification Number: https://doi.org/10.1038/nature24452
Depositing User: Sarah Humbert
Date Deposited: 15 Mar 2018 23:18
Last Modified: 15 Mar 2018 23:18
URI: http://eprints.esc.cam.ac.uk/id/eprint/4129

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