Application of new experimental and garnet Margules data to the garnet-biotite geothermometer

Abstract

Garnet-biotite experiments now exist from Ferry and Spear (1978, FS), Perchuk and Lavrent'eva (1983, PL), and Gessmann et al. (1997, GE). Recent garnet Margules parameters exist from Berman and Aranovich (1996, BA), Ganguly et al. (1996, GA), and Mukhopadhyay et al. (1997, MU). A comparison of ∆Gmix plots for garnet binaries shows similarity among models with some significant differences. In all, 20 garnet-biotite geothermometers were retrieved from the various data using a modified form of the approach of Holdaway et al. (1997, HO) such that experimental vs. calculated values of T, in °C, were regressed stepwise to a line with intercept of zero and slope of one, maximizing r2. All tests assumed the GA model for garnet MnMg and the HO Fe3+ correction and ∆WTiBio. The experimental combinations (sets) were: (1) GE + FS with GE values of VIAlBio in FS; (2) PL + FS with GE VIAlBio in FS; (3) PL + FS with GE VIAlBio in FS, increasing WGrMnMg by 5 kJ; (4) PL + FS with no VIAlBio in FS, increasing WGrMnMg by 5 kJ; (5) PL + FS with 0.10 VIAlBio in FS, increasing WGrMnMg by 5 kJ; (6) PL + FS + GE with 0.10 VIAlBio in FS, increasing WGrMnMg by 5 kJ. Models are designated by a number for the experimental set and letters to designate the above garnet model, e.g., 5BA.