On the formation of thrust fault-related landforms on Mercury: The key parameters controlling the mechanical structure of the lithosphere

Abstract

There are numerous thrust fault-related landforms widely distributed on the surface of Mercury. Geomorphic interpretations suggest that these landforms are either thin or thick-rooted, reflecting the mechanical structure of Mercury’s lithosphere. In this work, we propose a mechanical model incorporating brittle, semi-brittle, and viscous deformation mechanisms to depict the mechanical and strength profile of Mercury’s lithosphere, where the effective elastic thickness is about 30 km. To investigate which and how parameters control the lithospheric mechanical structure, we apply the random forest algorithm to select features by predicting the deformation mechanism with given sets of randomly generated input parameters, suggesting that the lithospheric viscosity, depth, and rheological model are the most important parameters. On this basis, we discuss how the viscosity and rheological model react to the changes in temperature, strain rates, and creep laws. Our results indicate that lowering the temperature or increasing the strain rate result in an increased strength profile and expanded regions where brittle and semi-brittle deformation occurs in the lithosphere. Qualitative analyses of the importance of Peierls, dislocation, and diffusion creeps in forming the rheological structure are conducted by applying multivariate regression analysis. It shows that Peierls creep dominates and stabilizes the rheological structure in the shallow depth due to its strong stress dependence for low temperatures. Moreover, the rheological model involving Peierls creep results in a reduced strength profile and simpler mechanical structure. Therefore, we emphasize that the Peierls creep is shown to be also critical in determining the strength and mechanical structure of Mercury in addition to temperature and strain rate.