The convective liquidus in a solidifying magma chamber: a fluid dynamic investigation

Abstract

CRYSTALLIZATION at the margins of magma chambers induces strong viscosity variations1, and recent studies2–4 have shown how such crystallization affects the vigour of convection. Here we report an experimental study of the solidification of a layer of paraffin cooled from above. When the fluid is superheated, convection sets in at the beginning of cooling but rapidly decreases in intensity. Once the layer has lost its superheat, convection ceases and further cooling is by conduction. The interior temperature then remains constant until encountered by the upper crust. We define the convective liquidus as the temperature threshold below which convection is very weak or non-existent. In natural basaltic systems, the convective liquidus, although strictly unknown, may be very close to the true liquidus. Rapid convection may therefore not be a dominant process during the crystallization of many magma chambers; instead, convection is part of an overall intimate balance between phase equilibria, crystal growth and heat transfer.