Dynamics of equatorial highlands on Venus

Recent constraints on the age of Venusian equatorial highlands, generally considered to be plume-related structures, suggests that the Beta Regio equatorial highland was emplaced over a relatively short period of time in the recent Venus history (100 400 m.y.). The emplacement of Laufey, Western and Central Eistla regions took place at the time close to the average age of Venusian surface (300 750 m.y.), and Atla Regio was active relatively recently (30 70 m.y.). We perform numerical simulations which use this evidence as a new constraint on geodynamic models. Two-dimensional models require the strength of the Venusian lithosphere to be similar to that of the Earth to satisfy simultaneously the constraint on the uplift rate and the constraints on gravity, topography and rheology. This is difficult to reconcile with the differences in the abundance of water for the Earth and Venus (Venus is essentially dry). Three-dimensional models can resolve this contradiction. Three-dimensional plumes exert a more concentrated force on the lithosphere and accelerate the uplift by a factor of 2. This seems to be sufficient to satisfy the constraints on the uplift rate, geoid, topography, and the rheology of a dry olivine.