Layered convection and crystal layers in multicomponent systems

Abstract

Laboratory experiments^1–5 in aqueous solutions have been used to model some of the physical and dynamical processes occurring during crystallization in magma chambers. In particular, it has been demonstrated^2,3,5 that crystallization at the side walls can lead to density stratification and layering in an initially homogeneous container, and also to the formation of vertical compositional gradients (that is, to ‘differentiation’) when more than one solute is present. Density gradients and compositional layers can alternatively be set up by replenishing a container from below with fluid of different temperature and composition^4,6,7. Underlying all this work has been the concept that some aspects of the regularity and large horizontal extent of layering in well-documented igneous intrusions^8,9 might be explained in terms of ‘double-diffusive’ effects in the fluid state, with the growth of crystals subsequently being affected by these pre-existing layers. In the latest experiments reported here, we have explicitly addressed the problems of horizontal layering produced in the crystals themselves, when a compositionally-stratified tank of fluid containing several solutes has been cooled from either below or above. The relationship between the scales of the layers in the fluid and in the crystals has also been examined.