Tectonic features on Venus with characteristic widths and/or spacings can be used to place quantitative constraints on the structure of the mechanical lithosphere through geophysical modeling. We develop theoretical models for both compressional (buckling) and extensional (rifting) deformation based on classical elastic plate models with characteristic spacings determined by the flexural parameter, modified to account for the effects of a realistic rheology. This rheology consists of a relatively weak crust over-lying a more creep-resistant mantle. In both layers the upper portions deform by frictional yielding on preexisting faults with a yield stress that increases linearly with depth, and the lower portions deform by non-Newtonian temperature-dependent creep.

For extensional deformation a graben model is used in which the primary structure of the rift is formed in the strong mantle layer and secondary faulting occurs in the brittle crustal layer. The introduction of a weak zone in the lower crust that acts to decouple these two layers allows the formation of rifts with the large widths and depths observed on Venus. The compressional folding model utilizes an elastic buckling approach in which the nonelastic yielding of the upper and lower portions of the layer modifies the elastic folding wavelength. This approach avoids the unreasonably high stresses that are required for conventional buckling models. The two scales of deformation observed in radar images, 15--25 km and 100--300 km, can be related to the elastic flexural properties of the crust and mantle, respectively, which are separated by an intermediate weak zone in the lower crust. These results imply that for regions in which both scales of deformation are present the crust is 5--15 km thick and the thermal gradient is 10¿--15¿km-1.

In regions such as Ishtar Terra, where only the smaller features are observed, the crust may be considerably thicker. The apparent structure seen in high-resolution images of the Beta Regio rift, with the major faults located at the edges of an extended linear central depression, lends support to the assumption of a graben mechanism of rift formation. ¿ American Geophysical Union 1988