We have demonstrated that, on one-plate planet with no plate tectonics, large-wavelengths variations in crustal and lithosphere structure can arise during their early growths if a large fraction of the silicate shell is in the form of a slushy mixture which consists in a solid-liquid mixture with a solid-like rheology. During the second period of the ERC project, we will work to place this result in a comparative planetology perspective as we believe that plate tectonics on Earth could have been driven originally by such large-wavelength variations in its plate structure. We expect that, because these lateral variations in the plate structure take time to develop, they require a non-negligible internal heating, and hence, large enough silicate shells to remain partially molten for a long enough time. They are thus likely to develop on bodies such as Mars and the Moon, but are probably unlikely to grow on Mercury which has a large core and a thinner silicate shell. In addition, we want to explore the effect of the planet size on the expected preferred wavelength for these instabilities.
In parallel, and to further test this slushy mixture model, we will work on an opposite model, where planetary crusts form by crystal flotation on top of a totally liquid magma ocean, and explore whether large lateral variations in the crust structure could be sustained and grow.
As regards to dyke ascent in planetary crusts, we will again work further to place our results in a comparative planetology standpoint. In particular, on smaller gravity planets, craters tend to be deeper for a given radius, which favors horizontal dyke deviation. We thus expect dyke deviation and magma storage to be favored below craters on smaller planets at the expense of eruption on crater floors. We also expect to place constraints on the nature and structure of the crust of the Martian Highlands through the study of Martian floor-fractured craters.
