Solubility of titanium dioxide in ultrahigh-temperature metamorphic minerals at high pressures and high temperatures to calibrate the geothermobarometer for ultrahigh-temperature granulites

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The solubility of titanium dioxide of garnet and orthopyroxene was investigated at pressures 7-25 kbar and temperatures 850-1300℃. The two granulites: (1) orthopyroxene granulite from McIntyre, Napier Complex; and: (2) the silimanite-cordierite-sapphirine granulite from Rundvagshetta, Lutzow-Holm Complex, were used in the present experiments. A glass starting material was prepared as: the mixture of the powdered McIntyre granulite + 8 wt% SiO_2 + 16 wt% TiO_2 + 8 wt% Al_2O3 was fused at 10 kbar and 1500℃ for 1 minute and quenched (MCTQ). Another stating material was a powdered Rundvagshetta granulite containing 2 wt% of 1102 (RVH). Run durations were 64 to 952 hours. We used the Mo/Pt double capsule or AuPd capsule. The present investigation provided following results: (1) Ti in garnet and orthopyroxene substitutes for the tetrahedral Si and never substitutes for Mg, Fe and AI; (2) the solubility of TiO_2 increases with temperature as In(X^<Grt>_T√X ^<Grt>_<Si>)=-15366/T+5.962 for garn … More et and In(X^<opx>_T√X^<opx>_Ti)=-11367/T+3.107 for orthopyroxene; (3) these thermometer is very useful to estimate the retrograde temperatures where rutile would exsolve; (4)Ti in garnet decreases with pressure although Ti in orthopyroxene increases with pressure. These were published at The 10th International Symposium on Antarctic Earth Science (ISAES2007), Santa Barbara, University of California. From the aid of the descriptive petrology, we proposed the empirical thermometer Ti in quartz as T(℃)=-5895/(InX〓_<TiO2>+1.729)-273. This thermometer is now in press in the Journal of the Geological Society of London, Special Issue. We analyzed the metamorphic processes of the ultrahigh-temperature granulites in detail. During the petrographic analyses we found the Fe^<3+> in quartz increases with temperature. Experiments on the solubility of Fe^<3+> in silica minerals were carried out at temperatures 990-1440℃ in the air. We obtained the found the content of ferric iron in quartz increases with increasing pressure and temperature: InX_<Fe> =(-1092-5.254T +7.75P)IT, where X_<Fe>, T and P are the number of Fe atoms in quartz per formula unit based on a 2-oxygen atom normalization(cationic mole fraction of Fe), temperature in Kelvin and pressure in kbar, respectively. This new geothermometer is applied to the ultrahigh-temperature metamorphosed quartz-magnetite rock from Mt. Riiser-Larsen area, Napier Complex, East Antarctica, resulting that the metamorphic temperatures are estimated as about 994-1095℃ for pressures 5-15 kbar. Less