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A new olivine-melt thermometer based on the partitioning of Ni (D   Ni    Ol/liq$D_{\text{Ni}}^{\text{Ol/liq}}$), with a form similar to the  Beattie (1993)D   Mg    Ol/liq$D_{\text{Mg}}^{\text{Ol/liq}}$thermometer, is presented in this study. It is calibrated on a data set of 123 olivine-melt equilibrium experiments from 16 studies in the literature that pass the following five filters:  (1)  1 bar only,  (2)  analyzed totals between 99.0–101.0 wt% for olivine and 98.5–101.0 wt% for quenched glasses,  (3)  olivine is the only silicate phase in equilibrium with the melt,  (4)  the NiO concentration is  ≥ 0.1 wt% in olivine and  ≥ 0.01 wt% in quenched glass, and  (5)  no metallic phase is present other than the capsule. The final data set spans a wide range of temperatures (1170–1650 °C), liquid compositions (37–66 wt% SiO 2 ; 4–40 wt% MgO; 107–11 087 ppm Ni), and olivine compositions (Fo 36-100 ; 0.10–15.7 wt% NiO). The Ni-thermometer recovers the 123 experimental temperatures within ±29 °C (1σ), with an average residual of 0 °C. A re-fitted version of the Mg-thermometer of  Beattie (1993) , calibrated on the same 123 experiments as for the Ni-thermometer, results in an average residual of 1 ± 26 °C (1σ). When both thermometers are applied to the same 123 experiments, the average Δ T  ( T  Mg  –  T  Ni ) is 1 ± 29 °C (1σ), which confirms that the Mg- and Ni-thermometers perform equally well over a wide range of anhydrous melt composition and temperature at 1 bar. The pressure dependence of the Ni-thermometer under crustal conditions ( ≤ 1 GPa) is shown to be negligible through comparison with experimental results from  Matzen et al. (2013) , whereas the pressure dependence of the Mg-thermometer is up to 52 °C at  ≤ 1 GPa ( Herzberg and O’Hara 2002 ). Therefore, neglecting the effect of pressure when applying both thermometers to basalts that crystallized olivine at crustal depths ( ≤ 1 GPa) is expected to lead to negative Δ T  ( T  Mg  –  T  Ni ) values ( ≤  –52 °C). Application of the two thermometers to nine mid-ocean ridge basalts results in an average Δ T  of –3°, consistent with shallow crystallization of olivine under nearly anhydrous conditions. In contrast, application of the two thermometers to 18 subduction-zone basalts leads to an average Δ T  of +112°; this large positive Δ T  value cannot be explained by the effect of pressure, temperature or anhydrous melt composition. It is well documented in the literature thatD   Mg    Ol/liq$D_{\text{Mg}}^{\text{Ol/liq}}$is affected by dissolved water in the melt and that Mg-thermometers overestimate the temperature of hydrous basalts if an H 2 O correction is not applied (e.g.,  Putirka et al. 2007 ). Therefore, the reason why hydrous arc basalts have higher Δ T  ( T  Mg  –  T  Ni ) values than MORBs may be becauseD   Ni    Ol/liq$D_{\text{Ni}}^{\text{Ol/liq}}$is less sensitivite to water in the melt, which is supported by new Ni-partitioning results on three olivine-melt equilibrium experiments on a basaltic andesite with up to 5 wt% H 2 O. More hydrous experiments are needed to confirm that the Ni-thermometer can be applied to hydrous melts without a correction for H 2 O in the melt.

american mineralogist

A comparison of olivine-melt thermometers based on  D  Mg  and  D  Ni : The effects of melt composition, temperature, and pressure with applications to MORBs and hydrous arc basalts