THE PARTITIONING OF LITHIUM BETWEEN MAFIC MINERALS AND TERRESTRIAL AND MARTIAN BASALTS

The abundance of lithium (Li), a light-lithophilic element, in Earth materials can provide evidence of planetary evolution. Although Li is thought to be moderately incompatible in mafic minerals, its behavior during crystallization and melting events is still unclear. New experimental measurements of Li compatibility in mafic systems are required to quantitatively use Li abundances as tracers of processes like magma differentiation or degassing. We quantified the partitioning of Li between basaltic minerals (clinopyroxene, orthopyroxene and plagioclase) and melt by running piston-cylinder experiments at varying temperatures (1025-1275˚C) and pressures (0.8-1.5GPa) using terrestrial and martian basaltic bulk compositions. All experiments were temperature cycled to enhance the growth of large mineral phases. Completed experiments were polished and analyzed using laser ablation ICP-MS to quantify the abundances of Li in all phases. Calculated mineral-melt partition coefficients indicate that Li is incompatible in all phases. In experiments where more than one mineral phase is present, Li is most compatible in clinopyroxene, followed by orthopyroxene then plagioclase. Our preliminary results show Li is more strongly partitioned into clinopyroxene at elevated temperatures and pressure in both terrestrial and martian compositions. This trend may provide an alternative explanation for the core-to-rim decrease in Li abundances observed in clinopyroxenes in martian meteorites (e.g., McSween et al. 2001).

McSween, H.Y. et al. (2001) Nature 409, 487-490.