Ni partitioning between olivine and highly alkaline melts: An experimental study
A. N. Koshlyakova, А. В. Соболев, Stepan Petrovich Krasheninnikov, Valentina Batanova, А. А. Борисов
Abstract
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 °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:lnDNimolar=–lnXMgOliqXMgSi0.5O2ol–2.308±0.111+3551±175/T+1.421±0.193·XSi0.5O–1.368±0.402·XNa2O–4.806±0.540·XK2O–1.465±0.265·XCaO–3.074±1.124·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.