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Thermal structure of crystallizing magma with two-phase Convection

Published online by Cambridge University Press:  01 May 2009

Stearns A. Morse
Stearns A. Morse
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, UK and Department of Geology and Geography, University of Massachusetts, Amherst, MA 01003, USA
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Abstract

Two-phase packets of crystals plus liquid form rapidly at a magma contact having a high thermal contrast with its surroundings. The packets can detach from an upper contact and settle rapidly with respect to crystal settling or turbulent stirring velocities. They carry crystals and supercooling downward and act as heat sinks for crystallization of floor cumulates. Evolution of picritic magma toward neutral buoyancy and overturn into overlying basalt magma proceeds most efficiently with two-phase convection. Sinking of hot bronzite-laden liquid into cooler anorthositic liquid destroys the liquid stratification within a day or so. Two-phase convection rarely yields crystal mush thicknesses suitable for compaction of cumulates, which occurs only for a narrow window of cooling rates. Two-phase convection leads to cool, thin boundary layers above and below hot interior magma and may tend to prevent or control turbulence. The critical timing and scale of two-phase layer detachment need further study.

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Articles
Information
Geological Magazine , Volume 123 , Issue 3 , May 1986 , pp. 205 - 214
Copyright
Copyright © Cambridge University Press 1986

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