Categorization of ring and bulge topographies of infilled craters on Mercury

Mercury boasts a variety of infilled craters, several of which contain central depressions surrounded by unique, bulged, ring-like structures. These rings are comprised of the infill itself, range in size and elevation, and can often exceed the crater rim in which they are contained (e.g. Bryne et al., 2014). Although peak ring crater types are common across Mercury (e.g. Baker et al., 2011; Schon et al., 2011), these bulged infill rings represent an entirely different morphology which represents a process that occurs after the crater and potential peak ring is formed. These bulged rings often present concentric extensional faults on their summits, and in some cases the accompanying central depression contains radial or circular extensional faults (e.g. Cunje & Ghent, 2016; Marchi et al., 2011). The formation process of this topography remains unknown and difficult to constrain, however it has been previously suggested that global contraction could aid their formation (Byrne et al., 2014). However, the weight load of the infill itself has yet to be fully appreciated as a candidate for tectonic processes on Mercury, particularly in the creation of bulged topography (Schmidt & Salvini, 2024). Additionally, lava entry pathways (i.e. lava which exploits circular normal faults within the interior of the craters) may play a role. By analyzing nine craters (four exhibiting the bulged infill topography, four exhibiting peak ring topography, and one seemingly intermediate type of topography) we aim to determine the relationship between bulged rings within infill and their more common peak ring topography counterparts. In so doing, we can determine if this infill topography is merely a lava infill which has conformed to a pre-existing peak ring, or if the weight load of the infill at the center of the crater has the potential to create an elastic response which creates the bulged ring and simultaneously the central depression.

We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2024-18-HH.0

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