POLYGONAL IMPACT CRATERS ON MERCURY’S LOBATE SCARPS: IMPLICATIONS FOR CONTRACTIONAL TECTONISM THROUGHOUT THE SOLAR SYSTEM

Polygonal impact craters (PICs) identified on planetary bodies across the solar system reflect pre-existing extensional and strike-slip faults and fractures in the target material. PIC straight rim segments, aligned with sub-resolution and/or sub-regolith fracture systems, therefore provide crucial information for deciphering the tectonic histories of planetary bodies. However, the relationship between PICs and contractional features, such as thrust faults, has not been previously investigated on any planetary body. Mercury’s lobate scarps are widely accepted to be the surface expressions of thrust faults, and therefore represent an ideal testbed to investigate how these features affect crater geometries. The results of this work have important implications for planetary bodies throughout the solar system since interpretations of PICs are limited by the lack of knowledge regarding the relationship between craters and thrust faults.

In this work, we used MESSENGER Mercury Dual Imaging System (MDIS) images to analyze 163 impact craters of 20 km or greater in diameter that overprint lobate scarps on Mercury. By applying Pearson’s Chi-Squared tests to the azimuth distributions of each crater’s rim, our results show that many of these craters are PICs, while in other cases craters are circular impact craters (CICs). In addition, our preliminary results indicate that the orientations of PIC straight rim segments are sub-parallel to the orientations of the underlying lobate scarps. We are investigating the relationship between the distance from the PIC rims and lobate scarps (a measure of how close the crater center is to the overprinted lobate scarp). Prior studies demonstrated that PICs reflecting extensional structures on other bodies are in some cases constrained to specific crater sizes. We are investigating if PICs on Mercury’s lobate scarps are similarly constrained to a specific range of diameters. In future work, we will analyze smaller impact craters (5 to 20 km diameters) overprinting lobate scarps to further investigate the relationship between PICs and contractional features.