A magmatic loading model for coronae on Venus

Models for the formation of coronae, quasi‐circular, volcanotectonic features on Venus, must explain four critical characteristics: coronae display (1) a wide range of diameters, (2) complex, varied topography, (3) fracture annuli, and (4) sometimes extensive volcanism. Previous models have difficulty simultaneously satisfying all four constraints. On the basis of observations and interpretations of features on Venus and Earth and experiments in geophysical fluid dynamics, we propose that coronae form in response to magmatic loading of the crust over zones of partial melting at the tops of thermally buoyant heads of transient mantle plumes that impinge on the base of the thermal lithosphere. By tying corona formation to a melt zone and not directly to an impinging upwelling, our conceptual model can account for the wide range in corona diameters. Lateral crustal flow, facilitated by magmatic heating, may lead to central depressions characteristic of many coronae. A thermomechanical, finite element simulation with a dissipating thermal anomaly leads to crustal thinning and predicts an elevation profile consistent with one of the more populous topographic classes of coronae. Deformation concentrated at the transition from thicker to thinner lithosphere above the thermal anomaly yields a narrow annulus of enhanced differential stress, consistent with formation of fracture annuli. Estimates of excess heat in an upwelling exceed the thermal energy in the melt that comprises the corona. Band‐pass‐filtered maps of the topography and gravity fields in the Beta‐Atla‐Themis region are consistent with upwellings now impinging on the lithosphere beneath seven coronae previously inferred to be active.