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Compositional mantle layering revealed by slab stagnation at ~1000-km depth

Ballmer, MD; Schmerr, NC; Nakagawa, T; Ritsema, J; (2015) Compositional mantle layering revealed by slab stagnation at ~1000-km depth. Science Advances , 1 (11) , Article e1500815. 10.1126/sciadv.1500815. Green open access

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Abstract

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.

Type: Article
Title: Compositional mantle layering revealed by slab stagnation at ~1000-km depth
Open access status: An open access version is available from UCL Discovery
DOI: 10.1126/sciadv.1500815
Publisher version: https://doi.org/10.1126/sciadv.1500815
Language: English
Additional information: Copyright © 2015, The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Keywords: mantle convection, mantle composition, subducted slab, stagnant slab, bulk silicate Earth
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10093536
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