Earth science: The slippery base of a tectonic plate

Rychert, Catherine A. (2015) Earth science: The slippery base of a tectonic plate. Nature, 518 (7537), 39-40. (doi:10.1038/518039a).

Record type: Article

Abstract

In the theory of plate tectonics, the outer shell of the Earth, known as the lithosphere, consists of several rigid plates, which move relative to each other over the weaker, flowing asthenosphere. The bottom of the lithosphere, the lithosphere–asthenosphere boundary (LAB), is fundamental to our understanding of how plate tectonics works, although an exact understanding of the mechanism that gives the plates their rigidity and defines their thickness remains elusive and widely debated. On page 85 of this issue, Stern et al.1 describe how they have used reflected seismic waves generated by explosive sources in steel-cased boreholes to image the Pacific plate as it descends beneath New Zealand. They find a LAB that is less than 1 kilometre thick at the top of a 10-km-thick channel, in which slow seismic velocities may require the presence of water or melt (Fig. 1). The authors suggest that the thin channel decouples the lithosphere from the asthenosphere and allows plate tectonics to take place. The existence of such a localized channel probably has implications for the driving forces of plate tectonics and mantle dynamics.

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