Forsterite dissolution in superheated basaltic, andesitic and rhyolitic melts

Abstract

AbstractDissolution rates of small forsterite spheres in superheated melts of basalt, andesite and rhyolite composition have been measured at 1300°C, atmospheric pressure. The rate is constant (83 µm hr−1) in the basalt, regardless of run duration. In the andesite the initial dissolution rate is 200µm hr−1, followed by a decrease to a constant value of 16µmhr−1 in 2–3 hours. Dissolution rate in the rhyolite decreases from an initial value of 1.7 to <0.1 µmhr−1 over 280 hours and never reaches a constant rate. Once the rate of dissolution has become constant, the film of contaminated melt that forms in melt about a crystal does not thicken with time, indicating attainment of a steady-state condition. Steady state is attributed to natural convection arising from the difference in density between the film of contaminated melt surrounding a crystal and that beyond. The density difference is approximately 2% of the density of the rock melt.