|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1990 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1989 : ¥1,500,000 (Direct Cost : ¥1,500,000)
The Sambagawa metamorphic terrain of Kanto Mountains is classified into three zones on the basis of mineral assemblages of pelitic and psammitic schists. The zones are, from lower to higher grade, Zone 1, Zone 2 and Zone 3. The zonal boundaries are highly complicated and often difficult to trace precisely. The graphitizing degree measured on pelitic and psammitic rocks is a function of metamorphic temperature, and a good positive correlation is observed between the degree and the Mg-Fe partition coefficient in garnet-chlorite pair of the same rock. Therefore, the basis of zonal classification has been established as follows. Zone 1 ; chlorite, G. D. <27, Zone 2 ; chlorite+garnet, G. D. 28-35, and Zone 3 ; chlorite+garnet+biotite and chlorite+biotite, G. D. >36. A few thin lenticular masses of Zone 2 are interlayered in the Zone 1 area, those of Zone 1 and Zone 3 rocks in Zone 2, and those of Zone 2 in Zone 3. The zonal structure of the area is interpreted to be stacks of a number of lenses, each of which has a particular assemblage and G. D. Furthermore, in a Zone 2 lens contiguous to Zone 3, G. D. does not increases towards their boundary but decreases. Therefore, that boundary is not a thermal isograd of metamorphic crystallization.
As compared with the petrological data obtained in the central Shikoku Sambagawa terrain, remarkable differences have been found. 1) The appearance temperature of garnet in pelitic schists are roughly the same in both areas (G. D. about 28), 2) on the other hand, the temperature of biotite formation is distinctly lower (G. D. about 36) in Kanto Mountains than in Shikoku (G. D. about 50), and 3) the temperature width of the garnet zone is narrower in Kanto than in Shikoku. It is suggested that the metamorphic pressure also is lower in the former than in the latter areas.