Experimental study of Fe–Mg partitioning and zoning during rapid growth of olivine in Hawaiian tholeiites

The partitioning behavior of Fe and Mg between olivine and basalt melt is of key importance to the study of terrestrial and extraterrestrial basalts. Olivine-melt partitioning studies generally focus on near-equilibrium crystallization conditions. Recent works highlight the tendency for both experimental and natural olivine to grow rapidly, possibly under non-equilibrium conditions. To better understand whether kinetic effects (e.g. boundary layer formation) can influence Fe–Mg partitioning and the development of zoning during rapid crystal growth, we use series of rapid cooling experiments involving a natural Hawaiian tholeiite as starting composition. Experimental charges were held at superliquidus conditions and cooled rapidly to final temperatures corresponding to undercoolings of 10–100 ºC. Overall, we find that within the parameter space of our experiments, rapid growth has largely negligible effects on both Fe–Mg partitioning and zoning patterns. These results are most applicable to relatively crystal-poor natural magmas undergoing a sudden thermal or chemical perturbation. We combine all experiments performed on natural Hawaiian tholeiites to propose a revised MgO-in-glass thermometer applicable to the temperature range T = 1060–1500 ºC: T (ºC) = 21.2 × MgO (wt.