Abstract

Fluid stratification is a common phenomena in magmatic systems. To address this, we conducted a series of analogue experiments and numerical simulations. We present three sets of experiments modelling the behavior of instability that develops between two stably stratified magmas and the degree of mixing that follows. The first set of analogue experiments examines the instability at the interface between two stably stratified fluids of similar composition with a low viscosity ratio wherein the upper fluid is less viscous than the lower fluid. The successive set experiments examine the interface instability between fluids of different compositions with high viscosity ratios wherein the upper fluid is initially more viscous and less dense than the lower fluid. The instability in all three experiments forms through the growth of a chaotic mixing region by the development of Rayleigh-Taylor instabilities through viscous fingering and buoyant ascent of plumes. The three experiments exhibit different degrees of mixing at significantly different timescales which are contingent upon the size of the mixing region relative to the bulk volume of the two fluids. Diffusive processes and small viscosity ratios enhance the growth of the mixing region in the first set of experiments. The growth timescale of the interface instability is characterized by a transient stage and a subsequent rapid stage. Our three-dimensional simulations, based upon the second and third sets of experiments, examine increased viscosity ratios to 3 orders of magnitude above those of our experiments. We discuss the implications for different configurations of stably stratified magma chambers.