マグマ分化作用の物理的考察

概要

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A physical aspect of magmatic differentiation process is quantitatively studied. A relation between physical conditions and variations of crystal composition during the differentiation is our main interests. A continuous reaction series of binary system is studied and the results obtained are applied to olivine and plagioclase. The discussion is reduced to solve a diffusion equation with a moving crystal-melt interface. The moving velocity of interface or the apparent growth rate depends upon a freezing rate, a convection velocity within melts, and a gravitational sinking velocity of crystals. Figures 8〜11 represent variations of crystal composition for various physical conditions. The apparent growth rate is estimated as 10^<-6>〜10^<-4>cm/day for the gabbro intrusion in Skaergaard, Greenland. A convection in a sill-type intrusion is also studied. The natural conditions seem to be unfavourable for the convection. A horizontal temperature gradient in dyke-type intrusion tends the apparent diffusivity of melts to increase and it destroys the convection. The zoning structure of plagioclase is assumed to be due to a rapid change of freezing rate and is quanitatively analyzed.
特定非営利活動法人日本火山学会の論文
1959-02-20