Phase Transitions in the Earth's Mantle: Implications for the Nature of the 410-km and 670-km Discontinuities

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9418945 Fei The proposed research will determine phase relations relevant to the 410-km and 670-km seismic discontinuities by using complementary high-pressure techniques (high- temperature diamond-anvil cell and multi-anvil apparatus). The olivine-modified spinel and the spinel = perovskite + magnesiowustite transitions in the system Mg2SiO4-Fe2SiO4 will be determined by in situ synchrotron x-ray measurements with a high temperature diamond cell. The slopes of the transformations of spinel to perovskite plus magnesiowustite and of ilmentie to perovskite will be precisely determined with the high temperature diamond cell. The compositional effect of the alpha-beta transition pressure and width of the two-phase region will be examined for the first time by using high-resolution and high-efficiency multi-cell sample chamber design in multi-anvil apparatus. The expected results will be used to evaluate the nature of the two discontinuities,whether the sharpness of the 410-km discontinuity is consistent with the width of the two phase region, and whether whole mantle convection can occur based on the slope of the transitions related to the 670-km discontinuity.