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

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

Oct 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pepi...86..165s&link_type=abstract

Physics of the Earth and Planetary Interiors (ISSN 0031-9201), vol. 86, no. 1-3, p. 165-183

Other

32

Convective Flow, Depth, Earth Mantle, Finite Element Method, Geothermal Anomalies, Phase Transformations, Thermal Conductivity, Thermal Expansion, Viscosity, Computerized Simulation, Mathematical Models, Two Dimensional Models

Scientific paper

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 x 10(exp 7) and 10(exp 8) 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.

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