Mars' first stratified layers and their preservation: Global thermochemical convection models
Abstract
The Martian crustal dichotomy and Tharsis volcanic province are believed to have an ancient and linked origin. While recent efforts explain these first order features by possible giant impact scenarios, the pertinent formation of a degree 1 convection could also be demonstrated, at least to some extent, with an endothermic mechanism. Therefore, primordial heterogeneities within the mantle, arisen at the end of the magma ocean stage, may also be important in forming such features.
Previous studies suggest that towards the end of Mars' planetary magma ocean stage, overturn of an iron enriched top layer may have occurred and leads to mantle stratification with a dense layer at the core-mantle boundary underlying the rest of the Martian mantle. Settlement to such a stable configuration can occur as soon as the first 10s Myr since magma ocean crystallization. The formation of such a layer may delay or suppress the onset of thermal convection and influence the distribution of heat producing elements. On the other hand, presence of primordial crust in Mars' early geological history already at ≈4.547 Ga is also suggested, and may as well affect the geodynamics and thermal history of the planet. We use the thermochemical convection code StagYY in 2D spherical annulus geometry to model the long-term geodynamical evolution of Mars following its magma ocean stage. Assuming a fractional crystallization scenario, a dense 'primordial' layer is imposed at the base of Mars' mantle at the beginning of the simulation to represent the end result of a magma ocean overturn. Primordial crust is imposed on top of the mantle. We systematically explore parameters such as initial crustal thickness, the amount of heat producing elements partitioned into the primordial crust, and density contrast between the basal layer the rest of the mantle. The resulting topography, mantle temperature and the geometry of mantle upwellings are used to test model predictions with observations on Mars.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V43D0111C
- Keywords:
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- 1009 Geochemical modeling;
- GEOCHEMISTRY;
- 1025 Composition of the mantle;
- GEOCHEMISTRY;
- 1028 Composition of meteorites;
- GEOCHEMISTRY;
- 1060 Planetary geochemistry;
- GEOCHEMISTRY