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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L12S01, doi:10.1029/2006GL025691, 2006

Unsolved problems in the lowermost mantle

Kei Hirose

Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan


Shun-ichiro Karato

Department of Geology and Geophysics, Yale University, New Haven, Connecticut, USA


Vernon F. Cormier

Physics Department, University of Connecticut, Storrs, Connecticut, USA


John P. Brodholt

Department of Earth Sciences, University College London, London, UK


David A. Yuen

Department of Geology and Geophysics and Minnesota Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota, USA


Abstract

Many characteristics of D″ layer may be attributed to the recently discovered MgSiO3 post-perovskite phase without chemical heterogeneities. They include a sharp discontinuity at the top of D″, regional variation in seismic anisotropy, and a steep Clapeyron slope. However, some features remain unexplained. The seismically inferred velocity jump is too large in comparison to first principles calculations, and the sharpness of the discontinuity may require a chemical boundary. Chemical heterogeneity may play an important role in addition to the phase transformation from perovskite to post-perovskite. Phase transformation and chemical heterogeneity and the attendant changes in physical properties, such as rheology and thermal conductivity, are likely to play competing roles in defining the dynamical stability of the D″ layer. Revealing the relative roles between phase transition and chemical anomalies is an outstanding challenge in the study of the role of D″ in thermal-chemical evolution of the Earth.

Received 6 January 2006; accepted 24 February 2006; published 31 March 2006.

Index Terms: 1212 Geodesy and Gravity: Earth's interior: composition and state (7207, 7208, 8105, 8124); 1213 Geodesy and Gravity: Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120); 3924 Mineral Physics: High-pressure behavior; 7208 Seismology: Mantle (1212, 1213, 8124); 8121 Tectonophysics: Dynamics: convection currents, and mantle plumes.

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Citation: Hirose, K., S. Karato, V. F. Cormier, J. P. Brodholt, and D. A. Yuen (2006), Unsolved problems in the lowermost mantle, Geophys. Res. Lett., 33, L12S01, doi:10.1029/2006GL025691.