Effects of depth-dependent properties on the thermal anomalies produced in flush instabilities from phase transitions

Volker Steinbach, David A. Yuen

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The effects of depth-dependent thermal expansivity, viscosity and thermal conductivity on mantle convection with phase transitions have been examined with two-dimensional finite-element simulations in an aspect-ratio four box. The model includes a core-mantle thermal coupling boundary condition which takes into play the secular cooling of the core by the overlying mantle flow. Initial surface Rayleigh numbers between 2 × 107 and 108 have been considered. With time the surface Rayleigh number decreases to a value upon which a transition takes place from layered to single-cell convection. This tumultuous period is marked by large-scale coherent breakthrough of cold material, trapped in the transition zone, all the way to the base of the mantle and a violent reaction of hot plume in the upper mantle. Both hot and cold anomalies have large magnitudes. Cold anomalies with temperatures exceeding 1000 K are found at the base of the mantle. The magnitude of the cold anomalies is largest with all three depth-dependent properties. The timescales of this catastrophic event are between 20 and 50 Myr, with the longest being produced by the model with depth-dependent expansivity and viscosity. Results from these simple two-dimensional cartesian models represent a lower bound to the larger cold thermal anomalies, potentially capable of being generated in spherical-shell convection models.

Original languageEnglish (US)
Pages (from-to)165-183
Number of pages19
JournalPhysics of the Earth and Planetary Interiors
Issue number1-3
StatePublished - Oct 1994

Bibliographical note

Funding Information:
We thank Ulli Hansen for discussions and encouragement, and L.M. Weyer for technical assistance. We also thank an anonymous reviewer for his stimulating comments. This research has been supported by the Geochemistry program at NSF, NASA, the Von Humboldt Stiftung of Germany and the Deutsche Forschungsgemeinschaft.


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