Compositional mantle layering revealed by slab stagnation at ~1,000 km depth
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Ballmer, Maxim D.
Schmerr, Nicholas C.
- Journal Article
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Rights / licenseCreative Commons Attribution 4.0 International
Improved constraints on lower-mantle composition are fundamental to understand the accretion, differentiation, and thermochemical evolution of our planet. Cosmochemical arguments indicate that lower-mantle rocks may be enriched in Si relative to upper-mantle pyrolite, whereas seismic tomography images suggest whole-mantle convection and hence appear to imply efficient mantle mixing. This study reconciles cosmochemical and geophysical constraints using the stagnation of some slab segments at ~1000-km depth as the key observation. Through numerical modeling of subduction, we show that lower-mantle enrichment in intrinsically dense basaltic lithologies can render slabs neutrally buoyant in the uppermost lower mantle. Slab stagnation (at depths of ~660 and ~1000 km) and unimpeded slab sinking to great depths can coexist if the basalt fraction is ~8% higher in the lower mantle than in the upper mantle, equivalent to a lower-mantle Mg/Si of ~1.18. Global-scale geodynamic models demonstrate that such a moderate compositional gradient across the mantle can persist can in the presence of whole-mantle convection Show more
Journal / seriesScience Advances
Pages / Article No.
PublisherAmerican Association of the Advancement Science
SubjectBulk silicate Earth; Mantle convection; Subducted slab; Stagnant slab; Mantle composition
Organisational unit03698 - Tackley, Paul / Tackley, Paul
02506 - Institut für Geophysik / Institute of Geophysics
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