Empirical thermometer of TiO2 in quartz for ultrahigh-temperature granulites of East Antarctica

Toshisuke Kawasaki, Yasuhito Osanai

Research output: Contribution to journalArticle

16 Citations (Scopus)

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 1300 °C 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 where XQtz TiO2 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 200 °C higher than those estimated by the present thermometer, potentially because of underestimates of Ti solubility in quartz in the previous calibration.

Original languageEnglish
Pages (from-to)419-430
Number of pages12
JournalGeological Society Special Publication
Volume308
DOIs
Publication statusPublished - Dec 1 2008

Fingerprint

Thermometers
Quartz
quartz
rutile
cristobalite
temperature
Needles
Temperature
solubility
Solubility
silica mineral
Metamorphic rocks
Antarctica
retrograde metamorphism
Atoms
raster
Temperature control
metamorphic rock
Electron beams
Minerals

All Science Journal Classification (ASJC) codes

  • Ocean Engineering
  • Water Science and Technology
  • Geology

Cite this

Empirical thermometer of TiO2 in quartz for ultrahigh-temperature granulites of East Antarctica. / Kawasaki, Toshisuke; Osanai, Yasuhito.

In: Geological Society Special Publication, Vol. 308, 01.12.2008, p. 419-430.

Research output: Contribution to journalArticle

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