AN EXPERIMENTAL CALIBRATION OF THE NICKEL IN GARNET GEOTHERMOMETER WITH APPLICATIONS

The partitioning of Ni between olivine and garnet in two multi-component compositions was studied as a function of temperature and pressure in a 6-8 type multi-anvil apparatus. Weighted least squares regression of the experimental results for both compositions give a temperature dependence for Ni partitioning between olivine (Ol) and garnet (Gt) of the form: T = -10210 (+/- 114)/[lnD(Gt/Ol)(Ni) - 3.59 (+/- 67)] . where D-Gt/Ol(Ni) = Ni content of Gt/Ni content of olivine (by weight) and Tis in Kelvin. The pressure effect on Ni exchange between olivine and garnet is estimated to be similar to 0.13 J/bar, and should therefore have a negligible effect on the geothermometer, as is demonstrated in the experiments. The experimentally derived ''Ni in Gt'' geothermometer is in agreement with an extant empirical version between 1100 to 900 degrees C, but the two thermometers produce significantly different results outside of this temperature range.