Experimental calibration of aluminum partitioning between olivine and spinel as a thermometer




Wan, Zhihuan

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An experimental study of the partitioning of aluminum between olivine and spine] was carried out at 100 kPa over the temperature range 1250-1450°C at an oxygen fugacity 1.8 log units below the quartz-fayalite-magnetite buffer in basaltic starting compositions. The partitioning is temperature sensitive and experimental data can be fitted to the relation: T.al (K) = -10500/ {ln([Al2O3]ol/[Al2O3]SP) - 0.98 *(Cr#-sp-0.5) -- 0.75J where [Al2O3]° and [Al2O3] se are concentrations of Al2O3 in olivine and spinel (wt%), and Cr#-sp is Crl(Cr+A1+Fe3+) in spinel. This thermometer is calibrated for olivine with MgI(Mg+Fe) between 0.87 and 0.93, and spine] with Crl(Cr+Al+Fe3+) between 0.07 and 0.63 and Fe 3+/(Cr+Al+Fe3+) between 0.02 and 0.05. and it reproduces experimental conditions to ±20°C. This thermometer generally yields temperatures lower than the two pyroxene thermometer when applied to natural mantle peridotites. The difference may be caused by inaccuracy in both thermometers or by faster Al diffusion in olivine than Ca diffusion in the pyroxenes. Preliminary investigations of the potential of Cr and Si exchange between olivine and spinel as further geothermobarometers are also presented.



olivine, spinel