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The Earth's mantle

Nature volume 412, pages 501–507 (2001)Cite this article

Abstract

Seismological images of the Earth's mantle reveal three distinct changes in velocity structure, at depths of 410, 660 and 2,700 km. The first two are best explained by mineral phase transformations, whereas the third—the D″ layer—probably reflects a change in chemical composition and thermal structure. Tomographic images of cold slabs in the lower mantle, the displacements of the 410-km and 660-km discontinuities around subduction zones, and the occurrence of small-scale heterogeneities in the lower mantle all indicate that subducted material penetrates the deep mantle, implying whole-mantle convection. In contrast, geochemical analyses of the basaltic products of mantle melting are frequently used to infer that mantle convection is layered, with the deeper mantle largely isolated from the upper mantle. We show that geochemical, seismological and heat-flow data are all consistent with whole-mantle convection provided that the observed heterogeneities are remnants of recycled oceanic and continental crust that make up about 16 and 0.3 per cent, respectively, of mantle volume.

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Figure 1: Speeds of seismic waves in the Earth, showing the major discontinuities at 410 and 660 km depth, and the D″ layer at the base of the mantle.
Figure 2: Schematic phase diagram of Mg2SiO4 olivine in mantle peridotite.
Figure 3: Angular correlation function of a shear-wave tomographic model30 as a function of depth.
Figure 4: Approximate mass balance for a bulk silicate Earth made up of continental crust, ‘sterile’ mantle, recycled oceanic crust, old recycled oceanic crust, and recycled continental material.
Figure 5: Visibility of mantle heterogeneity by seismic scattering.
Figure 6: Sketch of proposed model of a chemically unstratified mantle.

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  1. Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-Ku, Tokyo, 152-8551, Japan

    George R. Helffrich

  2. Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK

    George R. Helffrich & Bernard J. Wood

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Helffrich, G., Wood, B. The Earth's mantle. Nature 412, 501–507 (2001). https://doi.org/10.1038/35087500

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