VISCOELASTIC RELAXATION OF TOPOGRAPHIC HIGHS ON VENUS TO PRODUCE CORONAE

Coronae on Venus are believed to result from the gravitationally drive n relaxation of topography that was originally raised by mantle diapir s. We examine this relaxation using a viscoelastic finite element code , and show that an initially plateau shaped load will evolve to the ch aracteristic corona topography of central raised bowl, annular rim, an d surrounding moat. Stresses induced by the relaxation are consistent with the development of concentric extensional fracturing common on th e outer margins of corona moats. However, relaxation is not expected t o produce the concentric faulting often observed on the annular rim. T he relaxation timescale is shorter than the diapir cooling timescale, so loss of thermal support controls the rate at which topography is re duced. The final corona shape is supported by buoyancy and flexural st resses and will persist through geologic time. Development of lower, f latter central bowls and narrower and more pronounced annular rims and moats enhanced by thicker crusts, higher thermal gradients, and crust al thinning over the diapir.