Evidence for two stages of compressive deformation in a buried basin of Mercury

The surface of Mercury shows abundant compressive tectonic landforms, including lobate scarps, wrinkle ridges and high-relief ridges, which are different manifestations of thrust faults, and long-wavelength topography variations, which could be the expression of large scale folding. These landforms probably relate to planetary cooling, although other factors such as mantle convection, tidal despinning or true polar wander could affect the distribution, expression and orientation patterns of compressive features. In this work we show that an area of smooth plains including a buried ∼500-km-diameter impact basin experienced two different stages of deformation. The younger deformation stage is characterized by a set of NW-SE oriented wrinkle ridges affecting the smooth plains and having the same approximate orientation as the wrinkle ridges and lobate scarps deforming the surrounding terrains. The older set of tectonic structures consists of NE-SW oriented, closely spaced, subparallel, quasi-rectilinear and low-relief ridges, partially buried by the smooth plains material and crossed by the wrinkle ridges. Therefore, our results suggest that several events occurred between both deformation stages: at least one stage of basin filling; a change in stress orientation, an increasing in the wavelength and amplitude of deformation, and maybe an increasing of the thickness of the deformed layer. Our observations imply a complex stress history for compressive deformation, maybe influenced by the internal and/or orbital/rotational history of Mercury, and are illustrative of the complexity of tectonic history likely to have affected many or most other regions of the planet.