Fluid dynamic processes in basaltic magma chambers

Abstract

Convection in magma chambers is driven by small density differences that originate at the margins of a magma chamber or when a new pulse of magma enters a chamber. Buoyancy anomalies at the margins of magma chambers result from cooling or crystallization at the floor, roof or walls of the intrusion. Cooling produces a thermal boundary layer which is typically between 10 cm and 1 m wide with the temperature drop across the layer between 0.05 and 1°C. Compositional boundary layers, produced by crystallization, are much thinner than thermal boundary layers and are no more than a few millimetres wide. Calculated thermal and compositional flux Rayleigh numbers, assuming convection over the full depth range of the chamber, are typically greater than 1012 and 1019 respectively, well above the critical value of 106 that marks the transition from laminar to turbulent convection. Laminar or cellular convection is only possible in a convecting layer if its depth is less than 10 cm. Show more