Convective crystal dissolution

The effect of free and forced convection on crystal dissolution is examined both theoretically and experimentally. Well-established relationships for heat and mass transfer are applied to obtain approximate expressions for the dissolution velocity and the associated thickness of the compositional boundary layer. These expressions are found to be in good agreement with experimental observations of the dissolution of quartz crystals in basalt and NaCl crystal in water. When applied to light felsic crystals in basaltic magmas, the expressions predict that forced convection will produce a boundary layer thickness of about 100 μm and a dissolution velocity of order 10⁻⁶ cm s⁻¹. These velocities are too slow for xenocrysts to be dissolved significantly during magma ascent in dykes, but are sufficient for cm-size crystals to dissolve in the interior of a convecting magma chamber. Larger crystals are likely to accumulate at the chamber's roof, where free convection is predicted to dissolve them at velocities of order 10⁻⁷ cm s⁻¹. In an Appendix, the dissolution of the chamber's walls is also considered, and a velocity of order 10⁻⁸cm s⁻¹ is predicted. Editorial responsibility: T.L. Grove