MELTING OF IRON-MAGNESIUM-SILICATE PEROVSKITE

Iron-magnesium-silicate perovskite was melted in a laser-heated diamond anvil cell and monitored by thermal analysis. Two signals were identified at each pressure: a lower temperature signal and a higher temperature signal. The lower signal may correspond to the temperature where iron diffuses rapidly. The higher signal would then correspond to melting of magnesium-enriched silicate perovskite. Alternatively, the lower signal may be the solidus where (Fe.14Mg.86)SiO3 undergoes incongruent melting to an iron-magnesium-enriched solid plus a silica-enriched liquid. Then, the higher signal would be the liquidus. The slope for the melting curve (the higher signal) between 30GPa and 94GPa is slightly negative. Fitting to a straight line gives a value for the slope of -2.5 +/- 0.6K/Gpa. At 30GPa, the lower signal is almost-equal-to 300K below the melting curve. They converge slightly at higher pressures and differ by almost-equal-to 140K at 94GPa. Our melting curve is several hundred degrees (K) below previous estimates.