Phase equilibria and melting in the Martian mantle and the formation of shergottites

Shergottites are a group of meteorites that are thought to originate from the surface of Mars. They are primitive rocks that represent close to mantle-derived melts, presumably produced in upwelling thermal plumes. Martian meteorites have a range of crystallisation ages, and shergottites are comparatively young at < 600 Ma, and as such, understanding their formation in the Martian mantle can provide valuable constraints on the more recent thermal and magmatic history of the planet. This study presents a phase equilibrium approach to understanding the Martian mantle. Thermodynamic modelling, performed in THERMOCALC and using the most recent iteration (1) of the model of Holland et al. (2018) (2) is presented. Phase relations in the Martian mantle are investigated, including melting behaviour (parameterisations of solidus, liquidus and melt productivity) and melt compositions, to understand i) if the newly-published Martian mantle composition of Yoshizaki and McDonough (3) can reasonably produce shergottite-like compositions, and ii) the extents and depths of melting required, which places constraints on the lithospheric thickness and mantle temperatures in the Martian interior. E. L. Tomlinson, T. J. B. Holland, J. Petrol. 62 (2021), doi:10.1093/petrology/egab012. T. J. B. Holland, E. C. R. Green, R. Powell, J. Petrol. 59, 881900 (2018). T. Yoshizaki, W. F. McDonough, Geochim. Cosmochim. Acta. 273, 137162 (2020).