Two-phase data for the join monticellite (CaMgSiO4)-forsterite (Mg2SiO4): Experimental results and numerical analysis

Abstract

Subsolidus equilibria along the CaMgSiO.-Mg,SiOn olivine join are governed by partial immiscibility between the end-member phases. The solvi bounding the two-phase region are determined over the temperature range 800-1300'C at 2, 5, and 10 kbar. Within the limits of experimental error, the two-phase data are symmetric with respect to composition. Nurnerical analysis of the experimental data in terms of a one-constant Margules equation (Thompson, 1967) yields the following relationship for the mixing parameter of the Gibbs Free Energy Function: wc(callmole) : 20,338 + 2355 - 13,560 + 3412 x T(K)/1000 + 3627 + 1228 X (Z/1000X 3s5.4 + 87.5 X P(kbar) + 308.7 +6s.4x P(T/|0[0),S.D. :297.4 Temperature-composition sections of the two-phase region calculated from this equation are in good agreement with the experimental data, The results imply that the maximum amount of CaMgSiOn which may be dissolved in forsteritic olivine is less than 5 mole percent under physico-chemical conditions likely to exist in natural systems.