Two suites of spinel peridotites of the Westeifel/West Germany were found to have equilibrated in a narrow temperature interval each. Temperatures calculated from the CaO-solubility in orthopyroxene using experimental data of Lindsley and Dixon (1976) are 945~ to 980~ for the amphibole bearing Ia-suite and 1,150~ to 1,165~ for the Ib-suite. From the study of phase equilibria in both series it appears that Al-solubility in orthopyroxene is controlled by the composition of the coexisting spinel. Temperatures calculated from Al-solubility in orthopyroxene using an equation of Fujii (1976) derived from the univariant reaction en+sp+--,fo+Al-en in the MgO-A1203-SiO 2 system show a clear dependence on the FeCr204 component in the spinel phase, although ideal solution correction allowing for additional components was made. Temperatures obtained for the most chromite rich spinel orthopyroxene pairs are 1,370 ~ C and 1,240 ~ C, respectively. These temperatures are by 220 ~ C higher than those from Cr-poor pairs and those obtained from Ca solution in orthopyroxene.
For practical purposes of geothermometry in spinel peridorites, an empirical equation 4.59 +ln K-1.552 Y~P 7(oc) = 0.0025 allowing for the mole fraction of FeCr204 in spinel has been derived by a linear least squares fit to the orthopyroxene spinel compositional data and temperatures calculated from the CaO-solubility of orthopyroxene in the present paper 9