The influence of magma ocean crystallization on mantle dynamics
investigating the Martian and lunar magma oceans
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Maxime Maurice Olivier, Technische Universität Berlin, Nicola Tosi
2020
Abstract
The early stages of terrestrial planets evolution play a crucial role in determining their long-term development. In particular, the differentiation between an iron core and a silicate mantle is likely followed by the crystallization of a primordial magma ocean, controlling the initial conditions for solid-mantle thermal and dynamical evolution. Because it was thought that magma ocean crystallization was much faster than the onset of solid-mantle dynamics, the interplay between these two processes has not been considered so far. However, the outgassing of a thick opaque atmosphere from a crystallizing magma ocean, or the formation of a solid flotation lid at the surface can strongly slow down the solidifiation of the mantle. In this case, solid-state dynamics can set in before the end of the magma ocean's lifetime, nducing peculiar regimes of mantle mixing and thermal feedback mechanisms. In this thesis, we use mantle convection tools to study the effects of the early onset of solid-state dynamics in a solidifying mantle. A general model of simultaneous magma ocean solidification and mantle convection is introduced for a case based on the Martian magma ocean. We show that for realistic parameters, it is likely that Mars underwent mantle convection and mixing before the complete solidification of its magma ocean. This new paradigm sheds new light on the possibility for the Martian mantle to sustain long-term mantle activity, as suggested by traces of late volcanism. We then apply this model to the case of the Moon, where the existence of a primordial magma ocean, solidifying below an insulating flotation crust, is best documented. We show that the thermal feedbacks resulting from simultaneous magma ocean solidification and mantle convection lead to a solidification of the lunar mantle extending over up to 200 millions of years, in agreement with geochronological estimates for the lunar crust age span. By coupling our thermal evolution simulations with a trace-element fractionation and radio-isotopes decay model, w [...]
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