Effects of lithospheric properties on the formation of Type 2 coronae on Venus

Abstract

Over 500 coronae occur on Venus. A recent survey defined Type 2 coronae as those with <50% complete fracture annuli. This paper synthesizes the results from a statistical study of the size, topographic morphology and geologic setting of the entire corona population and a study of the gravity and topography of the 32 Type 2 coronae resolved in the gravity data. Using the estimated lithospheric properties, loading signature, and geologic characteristics, we examine the factors controlling corona morphology, size and fracture completeness (Type 1 versus Type 2). We find no difference between lithospheric properties in the plains and fractures belts. Nearly half of the Type 2 coronae studied are isostatically compensated, and probably inactive. This implies that the final stage of a corona may have a wide range of topographic morphologies. Elastic thickness has no correlation with diameter and therefore does not limit corona size. The ratio of crustal thickness to plume diameter does not control morphology as a function of size, as predicted by a spreading drop model. However, rim‐only coronae, which are predicted to form via isostatic rebound of crust thickened by delamination, are supported by a density interface. Isostasy and delamination of the lower lithosphere are likely to have a greater effect on corona formation, and possibly in understanding the evolution of the Venusian lithosphere, than variations in elastic thickness. The role of isostasy in the formation of Type 2 coronae suggests that surface fractures may be reduced due to low strain rates.