2016年6月
Ti-in-garnet thermometer for ultrahigh-temperature granulites
JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES
- ,
- 巻
- 111
- 号
- 3
- 開始ページ
- 226
- 終了ページ
- 240
- 記述言語
- 英語
- 掲載種別
- 研究論文(学術雑誌)
- DOI
- 10.2465/jmps.150709
- 出版者・発行元
- JAPAN ASSOC MINERALOGICAL SCIENCES
We propose a Ti-in-garnet thermometer for ultrahigh-temperature granulites calibrated from experimentally reversed data of the TiO2 solubility in garnet coexisting with orthopyroxene, rutile and quartz at pressures 7-23 kbar and temperatures 850-1300 degrees C. We confirm that the combined substitution (TiAlIV)-Al-VI reversible arrow (AlSiIV)-Si-VI, quasi-chemically equivalent to Ti reversible arrow Si, is predominant rather than the coupled substitution (MTiVI)-Ti-VI reversible arrow (AlAlVI)-Al-VI (M: Ca, Mg, Fe). The chemical formula of Ca-and Ti-poor garnet under ultrahigh-temperature metamorphic conditions can be expressed as M3Al2Si3-xTixO12, which indicates that the relation N-Si + N-Ti = 3 is not an evidence of Ti-IV reversible arrow Si-IV.
The TiO2 content of garnet increases with temperature and pressure, though the pressure dependence is small, as is given by the following equation:
17777 + 0.964T + 139.5P = T ln N-Ti(2) /NAlNSi ,
where N is the number of cation per formula unit based on a 12-oxygen atom normalisation. Temperature T and pressure P are given in Kelvin and kbar, respectively.
The present thermometer is useful to estimate metamorphic conditions. This new thermometer is applied to natural garnet in geologically and petrologically well-characterised Antarctic ultrahigh-temperature granulites. The resultant pressure and temperature estimates are consistent with those reported from granulites of these areas.
The TiO2 content of garnet increases with temperature and pressure, though the pressure dependence is small, as is given by the following equation:
17777 + 0.964T + 139.5P = T ln N-Ti(2) /NAlNSi ,
where N is the number of cation per formula unit based on a 12-oxygen atom normalisation. Temperature T and pressure P are given in Kelvin and kbar, respectively.
The present thermometer is useful to estimate metamorphic conditions. This new thermometer is applied to natural garnet in geologically and petrologically well-characterised Antarctic ultrahigh-temperature granulites. The resultant pressure and temperature estimates are consistent with those reported from granulites of these areas.
- リンク情報
- ID情報
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- DOI : 10.2465/jmps.150709
- ISSN : 1345-6296
- eISSN : 1349-3825
- Web of Science ID : WOS:000385267300007