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Thermal and magnetic evolution of a crystallizing basal magma ocean in Earth's mantle

TitleThermal and magnetic evolution of a crystallizing basal magma ocean in Earth's mantle
Publication TypeJournal Article
Year of Publication2020
AuthorsBlanc N.A, Stegman DR, Ziegler L.B
Date Published2020/03
Type of ArticleArticle
ISBN Number0012-821X
Accession NumberWOS:000515198200017
Keywordsbasal magma ocean dynamo; conductivity; core; crossover; early Earth dynamo; Geochemistry & Geophysics; geodynamo; giant impact; high-pressure; Iron; liquids; magnesium precipitation; molten silicates; thermodynamics

We present the thermochemical evolution of a downward crystallizing basal magma ocean (BMO) overlying the liquid outer core and probe its capability to dissipate enough power to generate and sustain an early dynamo. A total of 61 out of 112 scenarios for a BMO with imposed, present-day heat flux, Q(BMO). values of 15, 18, and 21 TW and radiogenic heat, Q(r), values of 4, 8, and 12 TW fully crystallized during the age of the Earth. Most of these models are energetically capable of inducing magnetic activity for the first 1.5 Gyrs, at least, with durations extending to 2.5 Gyrs: with final core-mantle boundary (CMB) temperatures of 4400 +/- 500 K -well within current best estimates for inferred temperatures. None of the models with Q(BMO) = 12 TW achieved a fully crystallized state, which may reflect a lower bound on the present-day heat flux across the CMB. BMO-powered dynamos exhibit strong dependence on the partition coefficient of iron into the liquid layer and its associated melting-point depression for a lower mantle composition at near-CMB conditions -parameters which are poorly constrained to date. Nonetheless, we show that a crystallizing BMO is a plausible mechanism to sustain an early magnetic field. (C) 2020 Elsevier B.V. All rights reserved.

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