## 抄録

Published experimental data including garnet and clinopyroxene as run products were used to develop a new formulation of the garnet-clinopyroxene geothermometer based on 333 garnet-clinopyroxene pairs. Only experiments with graphite capsules were selected because of difficulty in estimating the Fe^{3+} content of clinopyroxene. For the calibration, a published subregular-solution model was adopted to express the non-ideality of garnet. The magnitude of the Fe-Mg excess interaction parameter for clinopyroxene (W_{FeMg}^{Cpx}), and differences in enthalpy and entropy of the Fe-Mg exchange reaction were regressed from the accumulated experimental data set. As a result, a markedly negative value was obtained for the Fe-Mg excess interaction parameter of clinopyroxene (W_{FeMg}^{Cpx} = -3843 J mol^{-1}). The pressure correction is simply treated as linear, and the difference in volume of the Fe-Mg exchange reaction was calculated from a published thermodynamic data set and fixed to be -120.72 (Jkbar^{-1} mol^{-1}). The regressed and obtained thermometer formulation is as follows: T(°C) = {2784 + 14.52 P + (2601 + 1.44 P) (2X_{grs} X_{prp} - A) + (1183 + 6.98 P) (X_{grs}^{2} - A) - 105(2X_{grs}X_{alm} + B) + (814.6 + 3.61P) (X_{grs}^{2} + B) - (254.6 + 8.42 P) (2X_{prp}X_{alm} - X_{alm}^{2} + C) - 83.6 (X_{prp}^{2} - 2X_{prp}X_{alm} + C) + 1388 X_{sps} 462 (X_{Mg}^{Cpx} - X_{Fe}^{Cpx})}/{InK_{D} + 1.431 +0.695 (2X_{grs}X_{prp} + X_{grs}^{2} - 2A) + 0.203 (X_{grs}^{2} - 2X_{grs}X_{alm}) + 0.922X_{sps}} - 273, where T = temperature, P = pressure (kbar), A = 0.5 X_{grs}(X_{prp} X - X_{alm} - X_{sps}), B = 0.5 X_{grs} (X_{prp} - X_{alm} + X_{sps}), C = 0.5 (X_{grs} + X_{sps}) (X_{prp} - X_{alm}), X_{prp} = Mg/(Fe^{2+} + Mn + Mg + Ca)^{Grt}, X_{alm} = Fe/(Fe^{2+} + Mn + Mg + Ca)^{Grt}, X_{sps} = Mn/ (Fe^{2+} + Mn + Mg + Ca)^{Grt}, X_{grs} = Ca/ (Fe^{2+} + Mn + Mg + Ca)^{Grt}, X Mg^{Cpx} = Mg/ (Al + Fe^{total} + Mg)^{Cpx}, X_{Fe}^{Cpx} = Fe^{2+}/(Al+Fe total + Mg)^{Cpx}, K_{D} =(Fe^{2+}/Mg)^{Grt}/ (Fe^{2+}/Mg)^{Cpx}, Grt = garnet, Cpx = clinopyroxene. A test of this new formulation to the accumulated data gave results that are concordant with the experimental temperatures over the whole range of the experimental temperatures (800-1820°C), with a standard deviation (1 sigma) of 74°C. Previous formulations of the thermometer are inconsistent with the accumulated data set; they underestimate temperatures by about 100°C at >1300°C and overestimate by 100-200°C at <1300°C. In addition, they tend to overestimate temperatures for high-Ca garnet (X_{grs} ≈ 0.30-0.50). This new formulation has been tested against previous formulations of the thermometer by application to natural eclogites. This gave temperatures some 20-100°C lower than previous formulations.

本文言語 | English |
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ページ（範囲） | 495-508 |

ページ数 | 14 |

ジャーナル | Journal of Metamorphic Geology |

巻 | 27 |

号 | 7 |

DOI | |

出版ステータス | Published - 8月 10 2009 |

## ASJC Scopus subject areas

- 地質学
- 地球化学および岩石学