Thursday, 30 August 2007
4.PS-98
Solubility of TiO2 in Garnet and Orthopyroxene: Ti Thermometer for Ultrahigh-Temperature Granulites
Toshisuke Kawasaki, Earth Sciences, Ehime University, Bunkyo-cho 2-5, Matsuyama, Jordan
We report the TiO2 solubility in garnet and orthopyroxene coexisting with rutile obtained from the experimental data at pressures 7-20 kbar and temperatures 850-1300C. The TiO2 content of garnet should increase with temperature and rather decreases with pressure. In orthopyroxene Ti substitutes for the atoms in the tetrahedral and octahedral sites. The Ti content of orthopyroxene increases with temperature and rather increases with pressure. The Ti solubility in garnet and orthopyroxene is sensitive to temperature change, but insensitive to pressure change. Using the Ti thermometers, we obtain the peak and retrograde metamorphic temperatures of McIntyre granulite as 798 and 1079C, respectively, and the retrograde temperature of Rundvågshetta granulite as 884-921C. These data are consistent with those of our previous estimates. We conclude the Ti-solubility in garnet and orthopyroxene is the useful geothermometer to evaluate the metamorphic temperature of Antarctic granulites with high precision.