Solidification evolution of a dry Martian magma ocean: Constraints from high pressure-temperature experimental petrology

The Mars is thought to have been covered by a deep magma ocean after its formation. In the past, the solidification of this ocean was modeled by one-step experimental1 and numerical models2 assuming a Fe-rich (~18.7 wt% FeO) mantle composition3. Estimates of the mantle composition and depth of the Martian magma ocean were recently updated by using the latest cosmochemical model (~13.7 wt% FeO)4 and the newest seismic observations from the InSight mission (the depth of the mantle, ~1560 km)5. Here, we present an experimental crystallization study of a nominally dry experimental Martian magma ocean (MMO), simulating up to ~50 percent fractional crystallization of the updated MMO composition and refined core-mantle boundary condition. A ‘two-stage’ model of magma ocean solidification is assumed, which features early efficient crystal suspension up to 50% solidification in magma and corresponding equilibrium crystallization, followed by fractional crystallization of the later residual magma ocean. For the first stage experiments at pressures of 1.5, 5, 10, 13 and 16 GPa and a constant temperature were designed to represent MMO equilibrium crystallization. Results indicate formation of a cumulate pile of olivine, orthopyroxene, clinopyroxene, garnet, spinel, periclase and quartz. Our preliminary result significantly differ from the previous experimental and numerical studies1,2, likely due to the updated mantle composition and interior structure of Mars. Further second-stage experiments will start at the averaged residual magma composition resulting from the first stage, and we will provide more detailed results at the conference. References and Notes 1. Bertka, C. M. & Fei, Y. Mineralogy of the Martian interior up to core-mantle boundary pressures. J. Geophys. Res. Solid Earth 102, 5251–5264 (1997). 2. Elkins-Tanton, L. T., Zaranek, S. E., Parmentier, E. M. & Hess, P. C. Early magnetic field and magmatic activity on Mars from magma ocean cumulate overturn. Earth Planet. Sci. Lett. 236, 1–12 (2005). 3. Dreibus, G. & Wänke, H. Mars, a volatile-rich planet. Meteoritics 20, 367–381(1985). 4. Khan, A., Sossi, P. A., Liebske, C., Rivoldini, A. & Giardini, D. Geophysical and cosmochemical evidence for a volatile-rich Mars. Earth Planet. Sci. Lett. 578, 117330 (2022). 5.  Stähler, S. C. et al. Seismic detection of the martian core. Science 373, 443–448 (2021).