| Summary: | A model of three-dimensional shear wave velocity variations in the mantle reveals a tilted low velocity anomaly extending from the core-mantle boundary (CMB) region beneath the southeastern Atlantic Ocean into the upper mantle beneath eastern Africa. This anomaly suggests that Cenozoic flood basalt volcanism in the Afar region and active rifting beneath the East African Rift is linked to an extensive thermal anomaly at the CMB more than 45 degrees away. In contrast, a low velocity anomaly beneath Iceland is confined to the upper mantle. © 1999 American Association for the Advancement of Science. Received 23 August 1999; accepted 9 November 1999. Data were provided by the IRIS and GEOSCOPE data management centers. This research was funded by a grant from the National Science Foundation. We thank D. Anderson, Y. Fialko, and M. Gurnis for helpful discussions. This is contribution number 8687 of the Division of Geological and Planetary Sciences at California Institute of Technology.
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