The aluminum-in-olivine thermometer for mantle peridotites — experimental versus empirical calibration and potential applications

This study provides an experimental calibration of the empirical Al-in-olivine thermometer for mantle peridotites proposed by De Hoog et al. (2010). We report Al concentrations measured by secondary ion mass spectrometry (SIMS) in olivines produced in the original high-pressure, high-temperature, four-phase lherzolite experiments by Brey et al. (1990). These reversed experiments were used for the calibration of the two-pyroxene thermometer and Al-in-orthopyroxene barometer by Brey and Köhler (1990). The experimental conditions of the runs investigated here range from 28 to 60 kbar and 1000 to 1300 °C. Olivine compositions from this range of experiments have Al concentrations that are consistent, within analytical uncertainties, with those predicted by the empirical calibration of the Al-in-olivine thermometer for mantle peridotites. Fitting the experimental data to a thermometer equation, using the least squares method, results in the expression:

T°C=11245+46.0∗Pkbar/(13.68–lnAlppm–273.

This version of the Al-in-olivine thermometer appears to be applicable to garnet peridotites (lherzolites and harzburgites) well outside the range of experimental conditions investigated here. However, the thermometer is not applicable to spinel-bearing peridotites. We provide new trace element criteria to distinguish between olivine from garnet-, garnet-spinel-, and spinel-facies peridotites. The estimated accuracy of the thermometer is ± 20 °C. Thus, the thermometer could serve as a useful tool in settings where two-pyroxene thermometry cannot be applied, such as garnet harzburgites and single inclusions in diamond.