THERMOBAROMETERS BASED ON REE PARTITIONING BETWEEN MANTLE MINERALS
For well-equilibrated peridotites and eclogites, the temperatures derived from the REE-based thermobarometers agree very well with those derived from the major element-based thermometers, which independently justifies our REE-based thermobarometers. However, systematic differences between the REE-derived and major element-derived temperatures appear in mafic and ultramafic rocks that experienced fast cooling or significant metasomatic processes: for abyssal peridotites and mafic cumulates that experienced fast cooling processes, the REE-derived temperatures are systematically higher than the major element-derived values; for garnet peridotites and mantle eclogites from metasomatized lithospheric mantle, the REE-derived temperatures are systematically lower than the major element-derived values. Because REE diffuse slower than divalent cations in these mantle minerals, the REE-based thermometer may record early thermal events, whereas the major element-based thermometers may record more recent thermal perturbations. Independently calibrated REE-in-two-mineral thermobarometers may offer new insights into the thermal history of mafic and ultramafic rocks.