On the formation of thrust fault-related landforms in Mercury’s Northern Smooth Plains: A new mechanical model of the lithosphere

There are numerous tectonic shortening structures distributed across the planet, Mercury. As Mercury’s largest single volcanic deposit, the northern smooth plains (NSP) is dominated by thrust fault-related landforms, showing particularity in their tectonic patterns compared with their counterparts in other geological terrains on Mercury. Geomorphic interpretations of these landforms assume an internal layering lithosphere to account for the deformation accommodating superficial units, implying the deformation in the NSP is thin-rooted dominated. However, the commonly used lithospheric mechanical model is an oversimplification that only allows for the sharp transition from brittle to ductile deformation, failing to explain the thin-rooted deformation well. In this work, we propose a new mechanical model incorporating the semi-brittle deformation in the lithosphere to account for an equivalent weak layer at shallow depth, filling the gap between brittle and ductile deformation. In addition, we implement 2-D numerical simulations to simulate the formation of thrust fault-related landforms in the NSP of 3.8 billion years ago. As a result, we obtain surface topographies roughly consistent with lobate scarps. Our results also support that most thrust fault-related landforms were likely formed over a period with a gradually decreased background compressive strain rate, and these landforms can retain their basic geomorphic features on this planet with little to no erosion. Although the physical properties of semi-brittle deformation are not fully understood, considering such a deformation model in planetary science is still promising, especially when studying the thermodynamic processes of a planet.