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Science 24 April 2009:
Vol. 324. no. 5926, pp. 495 - 498
DOI: 10.1126/science.1169754
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Reports

A Global View of the Lithosphere-Asthenosphere Boundary

Catherine A. Rychert* and Peter M. Shearer

The lithosphere-asthenosphere boundary divides the rigid lid from the weaker mantle and is fundamental in plate tectonics. However, its depth and defining mechanism are not well known. We analyzed 15 years of global seismic data using P-to-S (Ps) converted phases and imaged an interface that correlates with tectonic environment, varying from 95 ± 4 kilometers beneath Precambrian shields and platforms to 81 ± 2 kilometers beneath tectonically altered regions and 70 ± 4 kilometers at oceanic island stations. High-frequency Ps observations require a sharp discontinuity; therefore, this interface likely represents a boundary in composition, melting, or anisotropy, not temperature alone. It likely represents the lithosphere-asthenosphere boundary under oceans and tectonically altered regions, but it may constitute another boundary in cratonic regions where the lithosphere-asthenosphere boundary is thought to be much deeper.

Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, M/C 0225, La Jolla, CA 92093, USA.

* To whom correspondence should be addressed. E-mail: crychert{at}ucsd.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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The Thickness of Tectonic Plates.
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Science. ISSN 0036-8075 (print), 1095-9203 (online)