Melting of iron‐magnesium‐silicate perovskite

Abstract

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 ≈300K below the melting curve. They converge slightly at higher pressures and differ by ≈140K at 94GPa. Our melting curve is several hundred degrees (K) below previous estimates.

The melting curve and premelting of MgO

“…Measuring melting curves to extreme pressures is very difficult, and there have been significant discrepancies among laboratories on melting curves of the important geophysical materials Fe [Anderson and Ahrens, 1996;Boehler, 1996] and MgSiO 3 perovskite [Heinz et al, 1994;27;Sweeney and Heinz, 1993;Zerr and Boehler, 1993]. It is also very difficult to calculate melting curves theoretically in spite of many attempts to develop predictive models for melting.…”

Influence of Potential Parameters on the Melting Temperature of MgSiO3 Perovskite

“…However, a long-standing disagreement exists concerning the melting of MgSiO 3 perovskite. The melting temperatures simulated on a perfect lattice system [4] appear to be rather high compared to the melting temperature observed in experiments (ZB [5], HJ [6], KJ [7] and SH [8]). The experimental melting temperatures are significantly lower than the values calculated by Chaplot using a system with 1 % vacancies [4], and lower than the values reported in the Refs.…”

“…The melting temperatures are close to simulation [10] (open squares). Comparison is made with the experimental data [5] up to 62.5 GPa and its extrapolations (L,S,KK) to higher pressures using different melting relations as reported in ZB and also with earlier laser heating experiment(HJ [6],KJ [7], SH [8], (SH indicates a lower bound only)). The present MD simulation is closer to the experimental data by ZB.…”

Inelastic Neutron Scattering, Lattice Dynamics, Computer Simulation and Thermodynamic Properties

“…The physical and thermodynamic properties of this mineral are of importance for interpreting the physics of the Earths interior. In view of its geophysical importance, extensive experimental studies of its crystal structure [91], elastic constants, phonon frequencies [92,93], equation of state [94,95], specific heat [96], thermal expansion, melting [97][98][99][100] and so on have been reported. The phase transitions of MgSiO 3 silicate perovskite have involved several controversies [54,[101][102][103][104] and are of interest, as they may contribute to observed seismic discontinuities in the Earths mantle [54,105].…”