Synthetic olivine capsules for use in experiments

Abstract

We have developed a method for the manufacture of polycrystalline olivine capsules, suitable as containers for olivine-saturated melts in near-liquidus experiments. The aim was to avoid some of the problems found in 1-atm gas-mixing experiments, notably iron loss from silicate melts to Pt wire loops and reaction between noble metal loops and sulfide liquids. Use of olivine capsules of fixed Mg/Fe enables the Mg# of the coexisting melt to be controlled and doping of the capsule with minor elements of interest enables partition coefficients to be determined at measureable concentrations. Capsules with olivine compositions ranging from Fo.70 to Fo.90 have been manufactured and found to remain impermeable to basaltic melts for extended periods. In the case of magnesian compositions (∼Fo90), we found that several cycles of heating and cooling from (1250 to 1550 °C) were needed to enhance grain growth and reduce permeability to an acceptable level. In contrast, our iron-rich composition (Fo70) functioned well after a single cycle of heating from 800 to 1350 °C.