Corona structures on Venus: Models of origin

Coronae on Venus are circular to elongate structures with maximum widths of 150–1000 km characterized by annuli of concentric ridges surrounding complex interiors. The features have raised topography relative to the surroundings, they are associated with volcanic activity, and most are partially surrounded by a peripheral trough. Variations in morphology between individual coronae are due to differences in their stage of evolution and/or differences in the relative significance of the geologic processes that occur in each stage. We examine models for three processes that may be involved in corona origin and evolution: (1) a hotspot or rising mantle diapir model, (2) a sinking mantle diapir model, and (3) gravitational relaxation of topography. Rising mantle diapirs are caused by heating at depth (e.g., hotspot), while sinking mantle diapirs may result from cooling or a phase change causing increased density and negative buoyancy at the base of the lithosphere. The hotspot model is most consistent with the major characteristics of coronae, with gravitational relaxation occurring as a modificational process. The sinking mantle diapir would produce dominant central compression that has not been observed at coronae; however, higher-resolution image and altimetry data from Magellan can be used to distinguish more fully between the two models. Coronae in various states of formation and degradation can be identified in the Venera 15/16 data, suggesting that the process may be continuing today.