Convection-driven subsolidus crustal thickening on Venus

We analyze the phenomenon of subsolidus crustal flow in response to mantle convection and test the hypothesis that Venusian crustal plateaus such as Ovda Regio formed over mantle downwellings. We investigate this process using results from the parameterized convection models of Solomatov and Moresi [1996] to calculate stress boundary conditions for the finite element code TECTON. The effects of a brittle crust are simulated by constraining the minimum crustal strain rates in the models with a diabase strength envelope. A series of models that could correspond to Venus ~1 Gyr ago were created by varying such parameters as the crustal and mantle flow laws, plastic behavior of the upper crust, crustal thermal conductivity, and the temperature at the planet's surface (possibly higher due to increased interior outgassing). As expected, crustal thickening was found to be negligible in a stagnant lid regime, regardless of crustal rheology. In a small viscosity contrast regime, plateaus greater than 1 km in elevation are possible within the lifetime of a mantle downwelling only for a weak crustal flow law. Therefore it is unlikely that Venusian crustal plateaus such as Ovda Regio formed as a result of subsolidus crustal thickening over downwelling unless the crust had considerably less strength than indicated by the dry diabase measurements of Mackwell et al. [1995, 1996].