Petrology of pelitic schists in the oligoclase-biotite zone of the Sanbagawa metamorphic terrain,Japan : Phase equilibria in high-grade zone of an intermediate high-pressure metamorphism 三波川変成帯の灰曹長石-黒雲母帯における泥質片岩の岩石学的研究 : とくに高圧中間群変成作用の高温部における相平衡の解析

博士論文

The oligoclase-biotite zone of the Bessi area, central Shikoku is characterized by sodic plagioclase-bearing assemblages in pelitickl schists, and resents the highest-grade zone of the Sanbagawa metamorphic terrain. Mineral assemblages of pelitic schists in this zone, all with quartz, sodic plagioclase, muscovite and clinozoisite (or zoisite), are garnet + biotite + chlorite + paragonite, garnet + biotite + hornblende +chlorite, and partial assemblages of the above types. Correlations between mineral compositions, mineral assemblages and mineral stability date assuming suggest that metamorphic conditions of this zone are about 610 ± 25°C and 10 ±1Kb. Based upon the comparative study of mineralogy and chemistry of pelitic schists in the oligoclase-biotite zone with those in New Caledonia omphacite zone as a typical high-pressure type and with those in upper staurolite zone as medium-pressure type, progressive as semblages within these zones can be related by such reactions as: omphacite zone garnet + glaucophane + omphacite + muscovite = oligoclase-biotite zone biotite + hornblende + plagioclase + quartz + H2O oligoclase-biotite zone garnet + hornblende + paragonite + muscovite = upper staurolite zone staurolite + biotite + plagioclase + quartz +H2O dP/dT values of these equations calculated using natural compositions are 3-6 and 16-19, respectivel, and their gradients are gentle. This implies that the contrasts of mineral parageneses in pelitic schists related by the aboveequations result mainly from the difference in pressure during progressive metamorphism. A combination of mineral assemblages observed in the Sanbagawa oligoclase-biotite zone represents a characteristic mineral paragenesis of pelitic schists in the high-grade part of an intermediate high-pressure metamorphism.

名古屋大学博士学位論文 学位の種類:理学博士 (課程) 学位授与年月日:昭和58年11月4日