Physics and chemistry of melt transportation in the melt-rock reaction system of the upper mantle

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The importance of fluid influx and melt segregation in a melting region in the upper mantle, which may govern abundance and chemical composition of magmas, has been pointed out for many years. In this study, we have transported silicate melt through a partially molten material at high temperature and pressure conditions in laboratory and analyzed physical processes during the melt transportation. We used a few millimeter-sized forsterite-jadeite melt system as an analogue material of natural partially molten mantle peridotites. A jadeite glass-forsterite chip, which had been annealed for a long time at the same P-T conditions to attain textural equilibrium, was put in a graphite capsule with diamond aggregate in one end. The size of diamond is 〜1μm and the thickness is 〜500μm. After the experiments, we examined abundance of melt segregated into the diamond aggregate and texture of melt-segregated region. We focused on the effects of melt fraction (10 vs. 5 %), size of forsterite grain (〜50μm vs.10μm), size distribution of forsterite (untreated vs.sieved to obtain homogeneous size). The results shows that the permeability estimated from the grain size and melt fraction predict too large effect to explain the amount of melt segregated into the diamond aggregate. The size distribution of forsterite is considered to have played an important role to quickly seal the path of melt segregation into the diamond. The examination of forsterite texture by an SEM-EBSD system shows that the sample with wide size distribution shows marked shape and lattice preferred orientation compared to that with narrow size variation. This is consistent with the inference that effective rotation and dislocation creep of is the major mechanism to suppress melt segregation in the partially molten system.