Interaction of Plate, Mantle, core and the magmatism in the earth's history

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We made a fieldwork at Acasta granitic complex in Canada, which is the oldest igneous body in the world formed at 4 Ga. We revealed the sequence and timing of formation of igneous complex on the basis of zircon dating and geological evidences. We made a fieldwork also at Pilbara craton in Australia, which is one of the oldest granite-greenstone terrain formed at 2.8-3. 5 Ga. We investigated igneous activities both at mid-oceanic ridges and convergent margins at that age. Results indicate that Archean seawater included large amounts of carbon-dioxide, and it formed significant proportions of carbonate minerals in oceanic crust through hydrothermal activities. Such carbonated crust subducted at convergent margins carrying large amount of carbon into the deep interior. In addition, melt inclusion studies of 3.5 Ga komatiites from Zimbabwe revealed that plume mantle included lots of water at that time. We also performed high P-T experiments using Kawai-type apparatus in order to investigate the melting processes in the lower mantle. Melting phase relations both of pyrolite and basalt compositions were determined, and trace element partitioning were investigated. These experimental results suggest that CaSiO_3-perovskite plays predominant roles in the partitioning of trace elements in the lower mantle including melting process at the core-mantle boundary. The characteristic pattern of trace elements expected to be formed by melting at the bottom of the mantle is found in the xenolith clinopylroxenes in the plume mantle at Hawaii and south Pacific, suggesting that they originated from that region. We further performed ultra-high P-T experiments using laser-heated diamond anvil cell. We revealed that silica phase undergoes phase transition twice in the lower mantle, and α-PbO_2-type phase is stable at the lowermost mantle conditions.