Corona classification by evolutionary stage

The formation of coronae, abundant volcano-tectonic features on the surface of Venus, has been modeled as the interaction of mantle diapirs with the lithosphere. However, the applicability of this model to features of widely different sizes may not be evident from SAR images due to the lack of a common scale. We use the radius as a scaling parameter for both the distance from the center and relief, obviating this problem, and mapping the effects from coronae of different radii onto a single scale. Normalizing profiles for 394 features, we find many features classified by E. R. Stoffan et al. (1992, J. Geophys. Res. 97, 13,347-13,378) as different types have very similar profiles and relief. Coronae distribute into three shapes (domal, circular, calderic); two shapes not related to coronae (radial and volcanic) remain. Variation between corona shapes is gradational and mirrors the evolution of diapirs from initial domal upwellings to calderas. We test the implied age progression using impact crater populations within three corona radii. Despite the inherent uncertainties of this method, crater statistics for a size-restricted (275-325 km) corona set suggest an age progression from domal through circular to calderic. The calderic coronae have an associated impact crater population very similar to the global mean, though with slightly too few tectonized craters, implying that they approximate the average surface age and are no longer active. The circular coronae have a low impact crater density and a slightly elevated proportion of tectonized craters and thus are currently active. The domal coronae have fewer than the expected number of impact craters, of which more are tectonized than expected, suggesting that surface modification has begun. (C) 1999 Academic Press.