[SMP33-P10] Melting experiments in the MgSiO3 – SiO2 system under high pressures
キーワード：エンスタタイトコンドライト、溶融関係、マグマオーシャン、マントル分化、高圧
Melting of silicates played important roles in chemical differentiation in a deep magma ocean in the early Earth. Therefore, melting relations of the MgO–SiO2 system have been extensively studied since a pioneer work by Bowen and Anderson (1914). Furthermore, chemical differentiation in the deep magma ocean has been simulated extensively based on results of high pressure melting experiments (e.g. Kato and Kumazawa, 1985; Ito and Katsura, 1992). However, 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) has been attracted as the bulk earth source material (Javoy et al., 2010) because the isotope systematics of the Earth and Moon are nearly identical to those of E-chondrite over O, N, Mo, Re, Os, and Cr. In E-chondrite, the silicate composition is characterized by SiO2/(SiO2+MgO) = ~0.6, which is substantially higher than that of the peridotitic mantle (~0.4).
In this context, understanding of the melting relations over compositions between MgSiO3 and SiO2 is indispensable to clarify the mantle fractionation. That also relates to investigations of chemical compositions of the crust at early stage of the Earth. Nevertheless, there have been very limited works on the pressure effect on melting in the MgSiO3–SiO2 system. Available information regarding phase relations in the system has been so far limited to 5 GPa (Dalton and Presnall, 1997). In this study, we are determining the melting relations in the MgSiO3–SiO2 system at pressures 5 to 20 GPa. Here we present the results obtained at 10 GPa.
References
Bowen and Anderson (1914) The binary system MgO-SiO2. Am. J. Sci. 4th ser. 37, 487-500.
Dalton and Presnall (1997) No liquid immiscibility in the system MgSiO3-SiO2 at 5.0 GPa. Geochim. Cosmochim. Acta 61, 2367-2373.
Ito and Katsura (1992) Melting of ferromagnesian silicates under the lower mantle conditions. Am. Geophys. Union Monogr. 67, 315-322.
Javoy et al. (2010) The chemical composition of the Earth: Enstatite chondrite models. Earth Planet. Sci. Lett. 293, 259-268.
Kato and Kumazawa (1985) Garnet phase of MgSiO3 filling the pyroxene-ilmenite gap at very high temperature. Nature 316, 803-805.
.
In this context, understanding of the melting relations over compositions between MgSiO3 and SiO2 is indispensable to clarify the mantle fractionation. That also relates to investigations of chemical compositions of the crust at early stage of the Earth. Nevertheless, there have been very limited works on the pressure effect on melting in the MgSiO3–SiO2 system. Available information regarding phase relations in the system has been so far limited to 5 GPa (Dalton and Presnall, 1997). In this study, we are determining the melting relations in the MgSiO3–SiO2 system at pressures 5 to 20 GPa. Here we present the results obtained at 10 GPa.
References
Bowen and Anderson (1914) The binary system MgO-SiO2. Am. J. Sci. 4th ser. 37, 487-500.
Dalton and Presnall (1997) No liquid immiscibility in the system MgSiO3-SiO2 at 5.0 GPa. Geochim. Cosmochim. Acta 61, 2367-2373.
Ito and Katsura (1992) Melting of ferromagnesian silicates under the lower mantle conditions. Am. Geophys. Union Monogr. 67, 315-322.
Javoy et al. (2010) The chemical composition of the Earth: Enstatite chondrite models. Earth Planet. Sci. Lett. 293, 259-268.
Kato and Kumazawa (1985) Garnet phase of MgSiO3 filling the pyroxene-ilmenite gap at very high temperature. Nature 316, 803-805.
.