Forsterite Dissolution in Superheated Basaltic, Andesitic and Rhyolitic Melts

C. H. Donaldson
Department of Geology, University of St Andrews, Fife, KY16 ST, Scotland

Abstract: Dissolution 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.

Keywords: forsterite • dissolution rates • melts • basalt • rhyolite • andesite

Mineralogical Magazine; March 1990 v. 54; no. 374; p. 67-74; DOI: 10.1180/minmag.1990.054.374.06
© 1990, The Mineralogical Society
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