PRELIMINARY UVLAMP DETERMINATIONS OF ARGON PARTITION COEFFICIENTS FOR OLIVINE AND CLINOPYROXENE GROWN FROM SILICATE MELTS

Abstract

An ultra-violet laser ablation microprobe (UVLAMP) has been applied for the first time to investigate argon partition coefficients for olivines and clinopyroxenes grown from silicate melts at 1 bar argon pressure. These preliminary measurements yield crystal/melt partition coefficients ranging from 0.138 (±0.01) to 0.013 (±0.003) for olivine and 0.589 (±0.003) to 0.0016 (±0.0005) for clinopyroxene. The higher values may indicate sub-microscopic melt inclusions, or some other heterogeneous distributions of `non-equilibrium' argon in the crystals. The lower values are probably more representative of true partition coefficients and fall at least an order of magnitude below the previously reported experimental data. The possibility of anomalous, high argon contents for crystals in previous studies is discussed in terms of surface adsorption, `trapped' argon and early partial melting.