Coronae are typically circular features, 100--600 km in diameter, characterized by a deformed annular ring that is often topographically high. The central region may be raised or depressed relative to the ambient elevation. Previous studies have proposed an evolutionary progression beginning with dome-shaped features which have radiating extensional rifts, followed by plateau-shaped features which have both concentric deformation and radial extension, ending with the classic corona as described above. Previous dynamical calculations of a rising and spreading diapir simulated the evolution from dome to plateau-shaped topography, but could not account for the raised rim or depressed central topography of some coronae. We demonstrate that these features can be modeled by a diapir that spreads laterally at a depth of neutral buoyancy. ¿ American Geophysical Union 1996