Pseudosection analysis for the Sanbagawa pelitic schist and its implication to the thermal structure of high-pressure intermediate type of metamorphism

Abstract

Phase equilibrium relationships for the pelitic schists were examined by "pseudosection" method using the bulk rock composition of Sanbagawa pelitic schist in the garnet zone of central Shikoku, Japan. The obtained P-T pseudosections reproduce the observed sequence of mineral zones in the Sanbagawa pelitic schist: the chlorite, garnet and biotite zones with an increasing order of metamorphic grade. The effect of MnO content on the stability of garnet was examined on P-T pseudosections by changing the MnO content of the bulk rock composition from 0.0 to 0.2 wt%. It follows that the characteristic sequence of the mineral zones observed in the Sanbagawa pelitic schist owes to the higher pressure of metamorphism along with the MnO content.