[S-IT20] Deep Earth Sciences

[SIT20-P15] Effect of Water on Martian Magma Ocean Evolution: Experimental Insights into dense silicate layer at the CMB

*Dilan Harsha Fernando Diyalanthonige¹, Takashi Yoshino¹ (1.Institute for Planetary Materials, Okayama University)

Keywords:Mars, Martian Magma Ocean, Basal mantle layer (BML), Hydrous dense melts

Recent Insight seismic surveys of Mars have suggested a partial molten layer just above the Martian core, but the commonly proposed composition of the Martian mantle [1] makes it difficult to create such a molten zone at the base of the mantle [2,3,4]. The existence of such a melt zone throughout Mars' history would require the presence of dense, low-melting-point material that escaped convection. This study examines whether iron-rich hydrous melt could sink to the core-mantle boundary (CMB) and form a melt zone during differentiation of the early Martian magma ocean based on the melting relation of the Martian mantle with 2 wt.% H₂O at varying pressure and temperature by high-pressure and high-temperature experiments conducted in a Kawai-type multi-anvil apparatus. The results of these experiments reveal that at temperature above solidus the melt starts very enriched in Fe and high density as the temperature increases the Mg# of the melt increases by reducing the density of the melt. The effect of water in the system allow to decrease the temperature of the solidus readily move to the melt at higher temperatures. These experiments are to consider the validity of the formation of a hydrous melt layer, the melt density was calculated using the partial melt composition and compared with the density of the solid phase above the solidus both determined in this study. Below 15 GPa, the density of the hydrous melt does not exceed that of the solid phase. At 20 GPa, melt with a water content of at least 2.0 wt% can sink to the core-mantle boundary. The calculated melt density to exceed 4.0 g/cm³, which is consistent with that predicted from the latest InSight studies for a heterogeneous Martian mantle [2]. These findings provide strong evidence for the presence of a basal mantle layer (BML) [2,3] in the early Martian magma ocean, with water content being a key factor in its formation. Future research should focus on extending experimental conditions to deeper mantle regions, conducting more detailed quantitative analyses of Fe partitioning, and exploring comparative studies across different planetary bodies to enhance our understanding of planetary differentiation processes.

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[2]A. Khan, D. Huang, C. Durán, P. A. Sossi, D. Giardini, and M. Murakami (2023), Nature, vol. 622, no. 7984, pp. 718–723.
[3]H. Samuel et al.,(2023), Nature, vol. 622, no. 7984, pp. 712–717.
[4]M. S. Duncan, N. C. Schmerr, C. M. Bertka, and Y. Fei (2018), Geophys. Res. Lett., vol. 45, no. 19.