Coupled core-mantle thermal evolution after a giant impact

Details Coupled core-mantle thermal evolution after a giant impact Coupled core-mantle thermal evolution after a giant impact

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.u21d..01s&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #U21D-01

Mathematics

Logic

5455 Origin And Evolution, 8115 Core Processes (1213, 1507), 8124 Earth'S Interior: Composition And State (1212, 7207, 7208, 8105), 8125 Evolution Of The Earth (0325), 8130 Heat Generation And Transport

Scientific paper

Various arguments suggest that the Earth's mantle was partially or completely molten at the end of planetary accretion (the magma ocean hypothesis). The early Earth's core was likely to be even hotter than the mantle, perhaps by thousands of degrees Kelvin. Here we address the following questions: What role did the core play in the evolution of the magma ocean and how hot was the core upon crystallization of the magma ocean? We model the coupled evolution of the core-mantle system immediately after the last giant impact. In the early stages of evolution, the core was cooling very fast. This generated a high heat flow at the base of the mantle and may have even caused additional melting of the mantle. When the average temperature of the lower mantle dropped below solidus, the heat flow from the core decreased but was still very high due to the remaining molten layer at the base of the mantle and the narrow melt channels formed throughout the mantle. The heat from the core could have also been removed by plumes produced by the instability of the thermal boundary layer at the base of the mantle. The presence of the initially hot core does not affect much the time it takes the lower mantle to crystallize and it does not affect the previously suggested conclusion that the lower mantle crystallized without any significant chemical differentiation. When the core-mantle boundary temperature decreased below the critical temperature for the rheological transition (about 60 percent crystal fraction), the heat loss rate of the core dropped by several orders of magnitude. The subsequent core cooling was relatively slow and the temperature at the core-mantle boundary may have never decreased below mantle solidus. This model is consistent with the estimates of the present-day temperature at the core-mantle boundary and with the estimates of the core temperature change during planetary evolution. A partially molten base of the present-day mantle is consistent with the existence of the ultra-low velocity zone at the base of the mantle.

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