magma in the Earth's history

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In this project we studied the following three topics ; the nature of the magma ocean in the earliest stage of the terrestrial evolution ; the formation of the crust and evolution of the mantle ; the heterogeneity and material circulation in the earth's interior.We have conducted the melting experiments of the silicate systems such as Mg2SiO4-Fe2SiO4, and MgO-Al2O3-SiO2 systems, and discuss the composition of the magma ocean and the origin of komatiite magmas which were generated in the Archean. We made the high pressure metal-silicate melt partitioning experiments of the siderophile elements such as Co and Ni, and clarified that mantle abundances of these elements can be accounted for by the core-mantle equilibrium in the deep magma ocean with the depth corresponding to the lower mantle.We made detailed geological survey of geological bodies in the Archean in the world such as Isua in Greenland, and Pilvara of Australia. We also conducted the chemical analysis of the various rocks in these areas. On the basis of these data, we could obtain evidence of plate tectonics in the Archean, and discussed the origin of komatiite magmas as a kind of ocean island magmatism. We also obtain evidence for FeO rich upper mantle as a source of Archean MORBs.We determined the density of ultramafic magmas using sink-float test experiment of diamond. Density crossover between diamond and the magma locates at around 15-20 GPa. Our density measurement of the melt implies that the density crossover between magma and olivine does not occur for the most part of the upper mantle, on the contrary to the previous estimation. We synthesized a new hydrous phase, phase G,which is a very important candidate of a carrier of water for circulation into the whole mantle.