Constraints on the Venusian crustal thickness variations in the isostatic stagnant lid approximation

The isostatic stagnant lid (ISL) approximation is applied to the long-wavelength Venusian topography and geoid to place constraints on the thickness of the crust and lithosphere. Previous studies showed that a purely thermal isostasy model of the lithosphere (the "stagnant lid") accounts for a significant portion of the topography and geoid anomalies. Here we assume that the remaining discrepancy between the observed and model geoid is due to crustal thickness variations and that the crust, the lithosphere and the mantle are in a state of double isostatic equilibrium: the lithosphere is isostatically floating on top of the mantle and the crust is isostatically floating on top of the lithosphere. The addition of another variable, the crustal thickness, allows an exact fit to the observed topography and geoid. This also makes the solution non-unique: an exact fit to topography and geoid can be achieved in a broad range of average lithospheric and crustal thicknesses. Additional constraints such as the gabbro-eclogite phase transition and the existence of relatively young volcanism limit this range to some extent. The inferred variations in the crustal thickness are less sensitive to model assumptions and generally agree with the results obtained in previous studies.