Ni partitioning between olivine and highly alkaline melts: An experimental study

Here, we present the results of 55 one atmosphere experiments conducted to determine the effects of Na2O and K2O on Ni-Mg partitioning between olivine and highly alkaline melts. The experiments were performed in the temperature range of 1250-1450 degrees C at Ni/NiO buffer conditions using a crucible-supported loop technique, which allowed the alkali content to be kept constant in melts containing up to 12 wt% K2O and up to 8 wt% Na2O. Based on the obtained experimental data combined with 169 olivine-melt pairs from the literature, and using the Ni-Mg olivine-melt exchange reaction, we calibrated an equation to predict the Ni partitioning coefficient: ln(D-Ni(molar)) = -ln (XMgoXMgsi0.5O2ol)-X-liq/ -2.2.308(+/- 0.111) + 3551(+/- 175)/T + 1.421(+/- 0.193)center dot XSi0.5O-1.368(+/- 0.402)center dot XNa2O-4.806(+/- 0.540)center dot XK2O-1.465(+/- 0.265)center dot XCaO-3.074(+/- 1.124)center dot XTiO2 The effects of Na2O and K2O on the Ni-Mg partitioning were found to be significant. Both K and Na along with Ti and Ca decrease the exchange equilibrium constant value, whereas Si increases it. The effect of K is more significant, than the effect of Na.