A SPATIAL DOMAIN STOKES-FLOW MODEL FOR THE GRAVITY AND TOPOGRAPHY OF THE MIDDLE LATITUDES OF VENUS

A new modeling strategy is developed and applied to the long-wavelength gravity, topography, and internal density structure of Venus. Geodynamic modeling of planetary scale phenomena is usually carried out in the wavenumber transform domain (spherical harmonics or Fourier transforms). However, because of limitations associated with the gravity and topography data available for Venus, a spatial domain approach is preferable. Smoothed representations of the gravity and topography of Venus are developed in terms of quadratic B splines on 10-degrees centers in latitude and longitude. over the latitude interval from 45-degrees-S to 45-degrees-N. These models reproduce 83.6% and 98.3% of their respective data variances. A similarly constructed model is then presented for the dynamic support of gravity and topography on Venus. Internal mass anomalies are specified at two discrete depths (50 and 500 km), with lateral variations determined by two constraints: (1) that the slow viscous flow induced by the anomalies will distort the free surface into a form matching the observed topography and (2) that the sum of the gravitational effects of the internal anomalies plus that due to the surface distortion they cause will match the observed gravity. There are four major features evident in the gravity and topography data sets: Atla, Beta, Ovda, and Thetis regiones. All four have compensating mass patterns consistent with a mantle plume origin. The surficial flow pattern associated with this model does not resemble terrestrial plate tectonic patterns.