Constraints on corona formation from an analysis of topographic rims and fracture annuli

Venusian coronae are circular to oblong features which are defined by their circumferential fracture annuli. Most coronae have a circumferential rim, which may or may not correlate spatially with the fracture annulus. Corona topographies are thought to evolve depending on their specific formation mechanisms, which broadly include initiation due to a rising plume or due to plume-induced subduction or delamination. Further, the observed topographies may represent particular stages of formation of coronae. As such, models for corona formation have sought to reproduce topographies observed at coronae. Concentric fractures at coronae are proposed to form when the topographic rim has some threshold high curvature, and so fracture patterns should record high curvature at rims. Models generally suggest that rims migrate outward, and so we expect that fracture should largely appear interior to and/or overlapping to the topographic rims. In this work, we aim to assess models of corona formation though a comparison of fracture location to topographic rims and their dimensions. We analyze topography and fracture annuli patterns in 94 coronae. We find that most coronae have fracture overlapping topographic rims, supporting little rim migration inward or outward. We also find that topographic rim dimensions are not remarkably different in profiles with or without fractures, leaving us to conclude that fracture formation may be largely controlled by another parameter, such as strain rate or stress field, or that the topographic rims have relaxed since fracture formation.