PRELIMINARY UVLAMP DETERMINATIONS OF ARGON PARTITION-COEFFICIENTS FOROLIVINE AND CLINOPYROXENE GROWN FROM SILICATE MELTS

An ultra-violet laser ablation microprobe (UVLAMP) has been applied fo r the first time to investigate argon partition coefficients for olivi nes and clinopyroxenes grown from silicate melts at 1 bar argon pressu re. These preliminary measurements yield crystal/melt partition coeffi cients ranging from 0.138 (10.01) to 0.013 (+/- 0.003) for olivine and 0.589 (+/- 0.003) to 0.0016 (+/- 0.0005) for clinopyroxene. The highe r values may indicate sub-microscopic melt inclusions, or some other h eterogeneous distributions of 'non-equilibrium' argon in the crystals. The lower values are probably more representative of true partition c oefficients and fall at least an order of magnitude below the previous ly reported experimental data. The possibility of anomalous, high argo n contents for crystals in previous studies is discussed in terms of s urface adsorption, 'trapped' argon and early partial melting. (C) 1998 Elsevier Science B.V. All rights reserved.