CORONAE ON VENUS AND MARS - IMPLICATIONS FOR SIMILAR STRUCTURES ON EARTH

Complex volcano-tectonic structures, referred to as coronae, had not b een described until the exploration of the surface of Venus. These lar ge, generally circular structures are characterized by an elevated sur face, concentric and radial fracture systems, and extensive volcanism. Thought to be unique to Venus, rare circular features on Mars bear a close resemblance to coronae. The most prominent corona-like feature o n Mars is Alba Patera, a broad, low-relief, plateau-shaped volcano-tec tonic center surrounded by an annulus of concentric fractures similar to 600 km in diameter. A geophysical model for the formation of Venusi an coronae involving uplift due to an ascending mantle diapir followed by gravitationally driven relaxation is applied to Mars. The results indicate that Alba Patera could have formed by such a mechanism. The f ormation of coronae and corona-like features on Venus and Mars from ma ntle diapirs suggests that similar structures may have formed in Earth 's lithosphere.