A REVISION OF THE GARNET-CLINOPYROXENE FE2+-MG EXCHANGE GEOTHERMOMETER

A comprehensive experimental dataset was used to analyse the compositional dependence of the garnet-clinopyroxene Fe2+/Mg partition coefficient (K(d)). The Mg no. of garnet was found to have a significant effect on the K(d), in addition to calcium content of garnet. An empirical model was developed to relate these effects with equilibrium temperature and pressure in the form of a conventional geothermometer, T(K) = {-1629[X(Ca)Gt]2 + 3648.55[X(Ca)Gt] -6.59[Mg no. (Gt)] + 1987.98 + 17.66P(kbar)}/(ln K(d) + 1.076). Application of this thermometer produced reasonable temperature estimates for rocks from the lower crust (garnet amphibolites, granulites and eclogites) and the upper mantle (eclogite and lherzolite xenoliths in kimberlites, mineral inclusions in diamonds).