Title: Electron probe study of Ti-rich hydroandradites in the Sanbagawa metamorphic rocks.
Abstract: Ti-rich hydroandradites have been found in metamorphosed ultramafics and associated gabbroic rocks, typically coexisting with chlorite or rarely serpentine, and recrystallized clinopyroxene. These garnets, though they commonly exhibit intensely zoned structure, have been studied mainly by means of EPMA. They contain about 33-35 wt. % of CaO. The Fe content tends to decrease from 30 to 12 wt. % as Fe2O3 with increasing Ti up to 18.2 wt. % as TiO2. Assuming that all Fe and Ti hold oxidized states, Ca exceeds 3.0 cations in all their calculated formula units on the anhydrous basis of 12 oxygens, suggesting their hydrous nature. TGA-DTA curves and IR spectra on the two garnets separated from host rocks support the idea that they have some hydrogarnet components. Based upon the examination of EPMA results, it appears possibly that some of these garnets contain not only Fe2+ but also Ti3+ as reduced cations.