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Science 24 November 2006:
Vol. 314. no. 5803, pp. 1272 - 1276
DOI: 10.1126/science.1133280
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Research Articles

A Post-Perovskite Lens and D'' Heat Flux Beneath the Central Pacific

Thorne Lay,1* John Hernlund,2 Edward J. Garnero,3 Michael S. Thorne4

Temperature gradients in a low-shear-velocity province in the lowermost mantle (D'' region) beneath the central Pacific Ocean were inferred from the observation of a rapid S-wave velocity increase overlying a rapid decrease. These paired seismic discontinuities are attributed to a phase change from perovskite to post-perovskite and then back to perovskite as the temperature increases with depth. Iron enrichment could explain the occurrence of post-perovskite several hundred kilometers above the core-mantle boundary in this warm, chemically distinct province. The double phase-boundary crossing directly constrains the lowermost mantle temperature gradients. Assuming a standard but unconstrained choice of thermal conductivity, the regional core-mantle boundary heat flux (~85 ± 25 milliwatts per square meter), comparable to the average at Earth's surface, was estimated, along with a lower bound on global core-mantle boundary heat flow in the range of 13 ± 4 terawatts. Mapped velocity-contrast variations indicate that the lens of post-perovskite minerals thins and vanishes over 1000 kilometers laterally toward the margin of the chemical distinct region as a result of a ~500-kelvin temperature increase.

1 Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA.
2 Institut de Physique du Globe de Paris, 75252 Paris, France.
3 School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287–1404, USA.
4 Arctic Region Super-computing Center, University of Alaska, Fairbanks, AK 99775, USA.

* To whom correspondence should be addressed. E-mail: thorne{at}pmc.ucsc.edu

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