MELTING AND CRYSTAL-LIQUID PARTITIONING IN THE SYSTEM MG2SIO4-FE2SIO4TO 25 GPA

The melting relation of the Mg2SiO4-Fe2SiO4 system was studied at 8.5 GPa. Olivine and spinel melts incongruently into pyroxene and the liqu id in the Fe2SiO4 rich portion of the system. Olivine melts congruentl y at least in the compositional range from (Mg0.5Fe0.5)(2)SiO4 to (Mg0 .9Fe0.1)(2)SiO4, although the end member of Mg2SiO4 melts incongruentl y into periclase and the liquid at pressures above 8 GPa. The melting relation of (Mg0.9Fe0.1)(2)SiO4 was also studied up to 25 GPa. Olivine and modified spinel of this composition melt incongruently into anhyd rous phase B and liquid, and into magnesiowustite and liquid at higher temperatures in the pressure range from 18 GPa to 23 GPa. Magnesiowus tite is the liquidus phase at higher pressures at least up to 25 GPa i n this composition. The partition coefficients between crystal and liq uid are; D-Mg = 1.19(+/- 0.06), D-Si = 0.88(+/- 0.04), D-V = 0.63(+/- 0.16), D-Cr = 1.04(+/- 0.21), D-Mn = 0.42(+/- 0.08), D-Fe = 0.76(+/- 0 .07), D-Co = 1.24(+/- 0.44), D-Ni = 1.46(+/- 0.81) for modified spinel ; D-Mg = 1.41(+/- 0.06), D-Si = 0.72(+/- 0.03), D-V = 0.44(+/- 0.11), D-Cr = 0.94(+/- 0.12), D-Mn = 0.30(+/- 0.07), D-Fe = 0.56(+/- 0.06), D -Co = 1.19(+/- 0.30), D-Ni = 1.65(+/- 0.87) for anhydrous phase B; D-M g = 2.09(+/- 0.11), D-V = 0.64(+/- 0.06), D-Cr =1.01(+/- 0.05), D-Mn = 0.7(+/- 0.04), D-Fe = 1.45(+/- 0.08), D-Co = 2.73(+/- 0.15), D-Ni = 4 .72(+/- 0.25) for magnesiowustite. The present results of melting rela tions and partitioning are applied for the fractionation in the mantle s of the terrestrial planets, such as Mars and Mercury. (C) 1998 Elsev ier Science B.V. All rights reserved.