Experimental data on Fe and Mg partitioning between coexisting sapphirine and spinel: an empirical geothermometer and its application

摘要

Specially designed experiments were carried out in the temperature range 950-1100 degrees C at 800 MPa to grow coexisting sapphirine and spinel-bearing metapelitic assemblages in the KFMASH system. Equilibrium phase assemblages contain these two phases with stoichiometric compositions. Compositional data obtained from the two coexisting phases indicate a strong dependence of the Mg-Fe distribution coefficient on temperature. An empirical thermometric expression has been formulated from the experimentally constrained relationship, lnK(D) = -6277/T(degrees K) + 6.4202, where K-D = (X-Mg/X-Fe)(Spr). (X-Fe/X-Mg)(SPl). Application of this thermometer to natural mineral pairs indicate that earlier temperature estimates based on sapphirine-spinel need to be revised upward by 120-160 degrees C.