Non-ideal Mg-Fe binary mixing in cordierite: Constraints from experimental data on Mg-Fe partitioning in garnet and cordierite and a reformulation of garnet-cordierite geothermometer

Abstract

The non-ideal regular Mg-Fe binary in cordierite has been derived through multivariate linear regression of the expression RT ln KD +(P -1)ΔK1.2980 along with up-dated subregular mixing parameter of almandine-pyrope solution (Hackler and Wood 1989; Herman 1990). The data base used for multivariate analyses consists of published experimental data (n=177) on Mg-Fe partitioning between garnet and cordierite in the P-T range 650-1050°C and 4-12 K. bar. The non-ideality can be approximated by temperature-dependent Margules parameters. The retrieved values of ΔH〈T〉0 and ΔS〈T〉0 of exchange reaction between garnet and cordierite and enthalpy and entropy of mixing of Mg-Fe cordierite were combined with recent quaternary (Fe-Mg-Ca-Mn) mixing data in garnet to obtain the geothermometric expressions to determine temperature (T Kelvin): T(HW) = 6832 + 0031(P-l)-{166(XMgGt)2-506(XFeGt)2 + 680XFeGtXMgGt + 336(XCa + XMn). © Printed in India.