1. Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, Illinois 60637, U.S.A.
2. Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, MRC 119, Washington, D.C. 20013-7012, U.S.A.
3. University of California Santa Cruz, Department of Earth and Planetary Sciences, 1156 High Street, Santa Cruz, California 95064, U.S.A.
4. Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138, U.S.A.
5. † Present address: Department of Earth and Planetary Sciences, University of California Davis, 1 Shields Avenue, Davis, CA 95616, U.S.A.
6. School of Earth Sciences, Ohio State University, 125 S. Oval Mall, Columbus, Ohio 43210, U.S.A.
7. ‡ Present address: Department of Earth, Environmental, and Planetary Sciences, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, U.S.A.
8. Center for Advanced Radiation Sources, University of Chicago, 5640 S. Ellis Avenue, Chicago, Illinois 60637, U.S.A.
9. High Pressure Collaborative Access Team (HPCAT), Geophysical Laboratory, Carnegie Institution of Washington, 9700 S. Cass Avenue, Argonne, Illinois 60439, U.S.A.