5570 20220120124138.0 POSTER-2022-0003 Samuel, Henri Mars seismic structure with a compositional stratification in the deep mantle. 2021 2021-12-15 Deep reflected phases present in the seismic recordings from the InSight mission have recently been identified as core reflected phases, and indicate that the core size of Mars spans the higher end of InSight pre-mission estimates [1]. This large core size together with the current knowledge of Mars composition also suggest by mass balance a substantial amount of light elements in addition to a large fraction of Sulfur in the core. Like many terrestrial planets differentiated into a metallic core and a silicate mantle, Mars probably experienced an early global magma ocean stage. The crystallization of such a magma ocean likely led to the formation of a compositionally distinct layer at the bottom of the mantle [2], heavily enriched in heat-producing elements and in iron, leading to long-term stability with little mixing between the layer and the overlying mantle. The presence of such a layer can strongly affect the evolution of the planet and its present-day state. In particular, it often results in the presence of a molten silicate layer above the core [3] that could act as a deep seismic reflector. We thus considered alternatively deep reflected phases that would correspond to reflections above the core-mantle boundary (CMB), at the interface between the dense molten basal layer and the overlying solid or partially molten silicate mantle. To do so, we conducted Monte Carlo inversions of seismic data, where Mars’ history is part of the forward problem [4]: instead of varying independently seismological parameters along the inversion process we model the thermochemical evolution of Mars' main envelopes: a liquid core, a dense enriched silicate layer above the CMB, overlaid by a less dense and more depleted silicate mantle, convecting under a stagnant lithospheric lid. This approach allows to test the alternative hypothesis of the presence of a basal molten layer at the top of Mars' core, along with the associated consequences on t 3PRODPLANINT/ 3PRODPLANINT/ 3PRODPLANINT NO Drilleau, Melanie Garcia, Raphael F. Rivoldini, Attilio Lognonné, Philippe Henri Staehler, Simon C Khan, Amir Banerdt, William Bruce AGU Fall Meeting 2021, New Orleans, online attilio.rivoldini@observatoire.be CPOSTER