A poorly mixed mantle transition zone and its thermal state inferred from seismic waves

Waszek, Lauren, Tauzin, Benoit, Schmerr, Nicholas, Ballmer, Maxim D., and Afonso, Juan Carlos (2021) A poorly mixed mantle transition zone and its thermal state inferred from seismic waves. Nature Geoscience, 14. pp. 949-955.

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Abstract

The abrupt changes in mineralogical properties across the Earth’s mantle transition zone substantially impact convection and thermochemical fluxes between the upper and lower mantle. While the 410-km discontinuity at the top of the mantle transition zone is detected with all types of seismic waves, the 660-km boundary is mostly invisible to underside P-wave reflections (P660P). The cause for this observation is debated. The dissociation of ringwoodite and garnet into lower-mantle minerals both contribute to the ‘660’ visibility; only the garnet reaction favours material exchanges across the discontinuity. Here, we combine large datasets of SS and PP precursors, mineralogical modelling and data-mining techniques to obtain a global thermal map of the mantle transition zone, and explain the lack of P660P visibility. We find that its prevalent absence requires a chemically unequilibrated mantle, and its visibility in few locations is associated with potential temperatures greater than 1,800 K. Such temperatures occur in approximately 0.6% of Earth, indicating that the 660 is dominated by ringwoodite decomposition, which tends to impede mantle flow. We find broad regions with elevated temperatures beneath the Pacific surrounded by major volcanic hotspots, indicating plume retention and ponding of hot materials in the mantle transition zone.

Item ID: 70895
Item Type: Article (Research - C1)
ISSN: 1752-0908
Copyright Information: © Nature Publishing Group
Funders: Australian Research Council (ARC)
Projects and Grants: ARC DE170100329, ARC LP170100233
Date Deposited: 30 Nov 2021 01:42
FoR Codes: 37 EARTH SCIENCES > 3706 Geophysics > 370604 Geodynamics @ 15%
37 EARTH SCIENCES > 3706 Geophysics > 370609 Seismology and seismic exploration @ 70%
37 EARTH SCIENCES > 3704 Geoinformatics > 370401 Computational modelling and simulation in earth sciences @ 15%
SEO Codes: 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 100%
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