Title Empirical thermometer of TiO2 in quartz for ultrahigh-temperature granulites of East Antarctica
Author Kawasaki, T.; Osanai, Y.
Author Affil Kawasaki, T., Ehime University, Department of Earth Sciences, Ehime, Japan. Other: National Institute of Polar Research, Japan; Kyushu University, Japan; Chiba University, Japan; Kyuschu University, Japan
Source Geodynamic evolution of East Antarctica; a key to the east-west Gondwana connection, edited by M. Satish-Kumar, Y. Motoyoshi, Y. Osanai, Y. Hiroi and K. Shiraishi. Geological Society Special Publications, Vol.308, p.419-430, . Publisher: Geological Society of London, London, United Kingdom. ISSN: 0305-8719. ISBN: 978-1-86239-268-7
Publication Date 2008
Notes In English. 31 refs. Ant. Acc. No: 85832
Index Terms Antarctica--East Antarctica; Antarctica--Enderby Land; annealing; Antarctica; Archean; chemical composition; cristobalite; East Antarctica; Enderby Land; experimental studies; framework silicates; geologic thermometry; granulites; heating; International Polar Year 2007-08; IPY 2007-08 Research Publications; laboratory studies; metamorphic rocks; metamorphism; Napier Complex; oxides; Precambrian; quartz; rutile; silica minerals; silicates; solubility; temperature; ultrahigh temperature
Abstract Two preliminary experiments, heating of rutilated quartz grains with 0.082 wt% TiO2 on average from Bunt Island, Napier Complex, East Antarctica and a synthetic TiO2- SiO2 (rutile-cristobalite) system in air at 1300C for 39 days, showed increasing solubility of TiO2 in silica minerals with temperature. Bunt quartz was converted to cristobalite and traversed by many transparent seams with the disappearence of needles and spots of rutile. Unreacted host grains retained many fine needles of rutile. The seams are homogeneous and slightly enriched in TiO2 up to 0.149 wt% on average, which is about one-fifth lower than that of the synthesized TiO2-SiO2 cristobalite (0.767 wt% on average). Area analyses with an electron beam in the raster mode at a magnification of 5000 gave 0.308 wt% TiO2 for the bulk composition of the Bunt quartz. This indicates that needles of rutile exsolved from the TiO2-saturated quartz at the cooling stage, or during retrograde metamorphism. Natural examples of quartz in geologically and petrologically well- characterized metamorphic rocks were chemically analysed to examine the temperature controls on the Ti saturation level in quartz. The TiO2 content of quartz in equilibrium with rutile increases sensitively with the metamorphic temperature, which can be expressed as T(C) = -5895/(ln XQtzTiO2+1.729)-273 where XQtzTiO2 is the mole fraction of TiO2, or the number of Ti atoms per formula unit based on a two-oxygen atom normalization. This empirical equation is very useful to evaluate the metamorphic temperatures for ultrahigh-temperature granulites. The temperatures calculated by the existing Ti-in-quartz thermometer are about 200C higher than those estimated by the present thermometer, potentially because of underestimates of Ti solubility in quartz in the previous calibration.
URL http://hdl.handle.net/10.1144/SP308.21
Publication Type journal article
Record ID 290775