Journal article

A thermodynamic model for Ca-Na clinoamphiboles in Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O-O for petrological calculations

J Dale, R Powell, RW White, FL Elmer, TJB Holland

Journal of Metamorphic Geology | WILEY | Published : 2005

Abstract

A calibration is presented for an activity-composition model for amphiboles in the system Na O-CaO-FeO-MgO-Al O -SiO -H O-O (NCFMASHO), formulated in terms of an independent set of six end-members: tremolite, tschermakite, pargasite, glaucophane, ferroactinolite and ferritschermakite. The model uses mixing-on-sites for the ideal-mixing activities, and for the activity coefficients, a macroscopic multicomponent van Laar model. This formulation involves 15 pairwise interaction energies and six asymmetry parameters. Calibration of the model is based on the geometrical constraints imposed by the size and shape of amphibole solvi inherent in a data set of 71 coexisting amphibole pairs from rocks..

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