Optimization of the garnet-biotite geothermometer: Part II. Calibration equations and accuracy of the estimation

Calibrations of the garnet-biotite geothermometer are considered with allowance for the effect of the nonideality of the coexisting garnet and biotite upon K _D . The calibrations based on the model of an asymmetric subregular Prp-Alm-Grs-Sps solid solution with W _i−j ^Grt (after Ganguly et al. (1996) and Holdaway (2000) and taking into account the experimental data published by Perchuk et al. (1983)) are the most accurate. The same may be said about the equations additionally taking into consideration the model of the symmetric regular Phl-Ann-Ms-(Ti-Bt) solution with W _i−j ^Bt after Holdaway et al., (1997), Kaneko and Miano (2004), and the data published by Ferry and Spear (1978) and Perchuk et al. (1983). These equations well reproduce the temperature at which the Prp + Ann = Alm + Phl equilibrium is reached in experiments, and they are the least sensitive to the variation of the Ca and Mn contents in garnet and Al^VI and Ti in biotite. The uncertainty of the temperature interval is 30–46°C (2σ).