[S-MP44] [JJ] Physics and Chemistry of Minerals

[SMP44-P01] Melting relations in the system of MgSiO₃ – SiO₂ at high pressures

*Takuya Moriguti¹, Akira Yoneda¹, Eiji Ito¹ (1.Institute for Planetary Materials, Okayama University)

Keywords:enstatite chondrite, melting relation, magma ocean, mantle differentiation, high pressure

Melting relations in the MgO–SiO₂ system at high pressures have been extensively studied to simulate chemical differentiation in a deep magma ocean formed in the early stage of the Earth (e.g. Kato and Kumazawa, 1985; Ito and Katsura, 1992). Almost all of these works have been carried out on the compositions ranging from MgO to MgSiO₃, assuming that the bulk mantle composition is peridotitic or close to that derived from CI chondrite. Recently enstatite chondrite (E-chondrite) was proposed as the bulk earth source material (Javoy et al., 2010) because the isotope systematics over O, N, Mo, Re, Os, and Cr for the Earth and Moon are almost identical to that of E-chondrite. In E-chondrite, the silicate composition is characterized by MgO/SiO₂ = 0.5 (in weight ratio) which is substantially lower than that of the peridotitic mantle (~0.85).
In this context, melting relations on compositions more SiO₂ enriched than MgSiO₃ are indispensable to clarify the mantle fraction. However, available information regarding phase relations in the system MgSiO₃–SiO₂ is so far limited to 1 GPa. In the present study, therefore, we would determine the melting relations at pressures 5 to 20 GPa, focusing on the compositions of MgO-xSiO₂ (x = 0.8 to 1.2). We expect to present some new results.