REASSESSMENT OF THE GARNET-CLINOPYROXENE FE-MG EXCHANGE THERMOMETER: II. THERMODYNAMIC ANALYSIS

Abstract

The garnet (Grt)-clinopyroxene (Cpx) Fe−Mg exchange thermometer has been re-evaluated through analysis of phase equilibrium experiments defining the Fe−Mg exchange between Grt and Cpx, Grt and Ol (Ol=Olivine), and Cpx and Ol, together with thermophysical and other phase equilibrium constraints on solid solution and individual end-member properties. Results show that all data are mutually compatible if the heterogeneity range of Grt and Cpx in run products previously obtained by Pattison and Newton (PN) are accounted for in assessing equilibrium Grt-Cpx compositions. Derived mixing properties are in good agreement with results from numerous recent phase equilibrium studies. Application of the newly calibrated thermometer to a number of amphibolite to granulite facies terrains indicates temperatures between 70 and 200 °C above PN's thermometer, and general compatibility with independent temperature estimates.