Mercury’s Lobate Scarps Reveal That Polygonal Impact Craters Form on Contractional Structures

Analysis of polygonal impact craters (PICs) can be used to investigate the presence and orientations of subtle and/or buried faults and fractures across the solar system that may otherwise be unobservable in spacecraft images. Although this technique has been vetted for the analysis of extensional structures, no previous work has investigated if PICs also form on contractional thrust faults. This determination, which we investigated in this work, is critical for accurate tectonic setting interpretations from PICs. Mercury shows an abundance of thrust-fault-related landforms, making it an ideal laboratory to perform this investigation. In this work, we found that Mercury’s thrust faults, and their overlying folds and fractures, cause some complex craters ∼20 km or larger to form PICs. However, in most cases, craters form as circular impact craters on these structures. When PIC straight rim segments do form, they parallel the lobate scarp thrust faults and fold hinges. Some PICs likely formed as a result of an impact’s interaction with the thrust fault itself, while others may have interacted with fold hinge joints. The parallel relationship between PICs and shortening structures is consistent with the well-established relationship between PICs and extensional structures. Therefore, in addition to extensional fractures, contractional features should also be taken into consideration when utilizing PICs to interpret tectonic settings on bodies across the solar system.