HIGH-PRESSURE EXPERIMENTAL STUDIES ON THE ORIGIN OF LAYERED STRUCTURE OF THE EARTH

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In situ X-ray study at high-pressure and high-temperature has been developed using the synchrotron radiation at SPring-8 and a multi-anvil apparatus (MA) equipped with sintered diamond (SD). Pressures to 49 GPa were generated over ca 4 mm^3. Using this systems stability and thermoelastic properties of the cubic SnO_2 (Pa3-) were determined up to 29 GPa and 1500 K.Exploration of 5th polymorph of iron "β-Fe" has been carried out. No evidence of β-Fesofar, but ε-phase is stable up to ca 40 GPa and 1700K.Melting experiments on natural peridotite were carried out up to 35 GPa. It has been found that the first liquidus phase changes from magnesiowustite (Mw) to Mg-perovskite (Mg-Pv) at 31 GPa with increase of pressure. At pressures higher than 33 GPa (deeper than 1000 km in the mantle), Mg-Pv, Mw and Ca-Pv coexist with liquid at temperatures between solidus and liquidus. Mass balance regression analysis suggest that differentiation of 34% Mg-Pv and 3% Ca-Pv from the primitive mantle consistently form the peridotitic material. Fractionation of Mg-Pv and Ca-Pv would have formed an dense and hot region on the bottom of the mantle characterized as an enriched geochemical reservoir. Partioning of Ni and Co between molten iron, and silicate liquid, Mg-Pv and Mw were examined up to 29 GPa The experimental results suggest that core formation in a 1000km-depth magma ocean is consistent with the observed partitioning data of Ni and Co between the mantle and core.