title: A post-perovskite lens and D'' heat flux beneath the central Pacific.
abstract: 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 (approximately 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 approximately 500-kelvin temperature increase.
authors.affiliation: Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064, USA. thorne@pmc.ucsc.edu
authors.forename: Thorne
authors.initials: T
authors.lastname: Lay
authors.forename: John
authors.initials: J
authors.lastname: Hernlund
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Garnero
authors.forename: Michael S
authors.initials: MS
authors.lastname: Thorne