An Improved Experimental Calibration of the Olivine-Spinel Geothermometer

The calibration of the olivine-spinel geothermometer by Fabries (1979) is commonly adopted by a number of petrologists. But the temperatures calculated in this way for ultramafic rocks are significantly lower than those obtained by the pyroxene geothermometers. These O1-Sp temperatures are also lower than those measured experimentally in the natural system (four-phase lherzolite) Different rates of cation diffusion cannot fully account for these differences. The temperature deviation is actually related to the inconsistencies between natural and experimental data which support the calibration. A re-evaluation of the calibration is proposed on the basis of a set of new experimental data.