Solubility of TiO<sub>2</sub> in garnet and orthopyroxene: Ti thermometer for ultrahigh-temperature granulites

Abstract

We report the TiO 2 solubility in garnet and orthopyroxene coexisting with rutile calibrated from experimental data at pressures 7-20 kbar and temperatures 850-1300C in two Antarctic granulite systems. The Ti would substitute for the tetrahedral Si, whereas we could not find positive evidence of the coupled substitution of M-Ti (M is Mg or Fe) for Al-Al in octahedral sites as well as the interstitial substitution of -Ti ( is a vacancy) for M-M in triangular-dodecahedral sites of garnet at ultrahigh-temperature (UHT) metamorphic conditions. The TiO 2 content of garnet increases with temperature and decreases with pressure. In orthopyroxene Ti substitutes Opx,IV Si = -11367/T + 3.107, where X is the mole fraction of Ti or Si on the tetrahedral sites and temperature is given in Kelvin.