Timing of formation of Beta Regio and its geodynamical implications

Recent evidence suggests that the Beta Regio equatorial highland, generally considered to be a plume-related structure, was emplaced over a relatively short period of time in the recent Venus history (100-400 m.y.). We perform numerical simulations which use this evidence as a new constraint on geodynamic models and find that it is difficult to satisfy simultaneously the constraint on the uplift rate and the constraints on gravity, topography, and rheology. One possible solution is that the effective viscosity contrast between the mantle and the lithosphere does not exceed about 10⁴. If our simple models do capture the basic dynamics of formation of Beta Regio, this value implies that the viscosity of the lithosphere is softer than olivine at subsolidus temperatures and that the Venusian lithosphere may not be much stronger than the terrestrial one.